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1
Gannaway Dalton, C. Evelyn, Katherine A. Giles, Mark G. Rowan, Richard P. Langford, Thomas E. Hearon, and J. Carl Fiduk. "Sedimentologic, stratigraphic, and structural evolution of minibasins and a megaflap formed during passive salt diapirism: The Neoproterozoic Witchelina diapir, Willouran Ranges, South Australia." Journal of Sedimentary Research 90, no. 2 (February 20, 2020): 165–99. http://dx.doi.org/10.2110/jsr.2020.9.
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ABSTRACT This study documents the growth of a megaflap along the flank of a passive salt diapir as a result of the long-lived interaction between sedimentation and halokinetic deformation. Megaflaps are nearly vertical to overturned, deep minibasin stratal panels that extend multiple kilometers up steep flanks of salt diapirs or equivalent welds. Recent interest has been sparked by well penetrations of unidentified megaflaps that typically result in economic failure, but their formation is also fundamental to understanding the early history of salt basins. This study represents one of the first systematic characterizations of an exposed megaflap with regards to sub-seismic sedimentologic, stratigraphic, and structural details. The Witchelina diapir is an exposed Neoproterozoic primary passive salt diapir in the eastern Willouran Ranges of South Australia. Flanking minibasin strata of the Top Mount Sandstone, Willawalpa Formation, and Witchelina Quartzite, exposed as an oblique cross section, record the early history of passive diapirism in the Willouran Trough, including a halokinetically drape-folded megaflap. Witchelina diapir offers a unique opportunity to investigate sedimentologic responses to the initiation and evolution of passive salt movement. Using field mapping, stratigraphic sections, petrographic analyses, correlation diagrams, and a quantitative restoration, we document depositional facies, thickness trends, and stratal geometries to interpret depositional environments, sequence stratigraphy, and halokinetic evolution of the Witchelina diapir and flanking minibasins. Top Mount, Willawalpa, and Witchelina strata were deposited in barrier-bar-complex to tidal-flat environments, but temporal and spatial variations in sedimentation and stratigraphic patterns were strongly influenced from the earliest stages by the passively rising Witchelina diapir on both regional (basinwide) and local minibasin scales. The salt-margin geometry was depositionally modified by an early erosional sequence boundary that exposed the Witchelina diapir and formed a salt shoulder, above which strata that eventually became the megaflap were subsequently deposited. This shift in the diapir margin and progressive migration of the depocenter began halokinetic rotation of flanking minibasin strata into a megaflap geometry, documenting a new concept in the understanding of deposition and deformation during passive diapirism in salt basins.
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Mel’nikov, N. V. "The Vendian–Cambrian Cyclometric Stratigraphic Scale for the Southern and Central Siberian Platform." Russian Geology and Geophysics 62, no. 08 (August 1, 2021): 904–13. http://dx.doi.org/10.2113/rgg20214339.
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Abstract —The general Vendian stratigraphic scale of Siberia, with the uncertain age of the Vendian base ranging from 600 to 630– 640 Ma in most of recent publications, remains worse constrained than the Cambrian scale, in which the boundaries of epochs and stages have been well defined. However, the imperfect classical stratigraphic division has been compensated by data on the cyclicity of the Vendian–Cambrian sedimentary section. The Vendian stratigraphy of the Siberian Platform and the related deposition history with cycles of sedimentation and gaps, as well as the hierarchy of sedimentation processes, can be inferred from the succession of alternating clastic, carbonate, and salt units. The cyclicity of geologic processes and their recurrence are attributed to periodic oscillatory motions of the crust. The ranks of these motions correlate with the cyclicity of sedimentary strata, including regocyclites, nexocyclites, and halcyclites separated by gaps. Each Vendian long-period oscillatory motion begins with a regocyclite and ends with a regional-scale gap. The Cambrian section includes one pre-Mayan regional gap at the end of the early Cambrian long-period cycle. Cambrian regocyclites are composed of carbonate subformations and formations in the lower part and alternating salt and carbonate beds in the upper part.
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Corfu, Fernando, and Shoufa Lin. "Geology and U-Pb geochronology of the Island Lake greenstone belt, northwestern Superior Province, Manitoba." Canadian Journal of Earth Sciences 37, no. 9 (September 1, 2000): 1275–86. http://dx.doi.org/10.1139/e00-043.
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Mapping and U-Pb geochronology have been used to examine the tectonic and depositional history of the Archean Island Lake greenstone belt in the northwestern Superior Province. The Island Lake greenstone belt comprises two main supracrustal successions, the older Hayes River Group and the younger Island Lake Group. Zircon data for two volcanic units from the Hayes River Group provide identical ages of 2852 ± 1.5 Ma, whereas a turbidite of this group contains a detrital zircon population with ages between 2858 and 2847 Ma. Younger intrusive events include the emplacement of tonalite in the southern batholith at 2825 ± 2 Ma and the Whiteway Island gabbro at 2807 ± 1 Ma. A wacke at the base of the Island Lake Group is dominated by detrital zircon grains yielding ages between 2830 and 2821 Ma, the latter defining a maximum age of sedimentation. A relatively early time of deposition of the lower stratigraphic sections of the Island Lake Group is also supported by an age of 2744 ± 2 Ma obtained for a crosscutting tonalite. By contrast, two turbidite horizons from higher stratigraphic levels of the Island Lake Group contain detrital zircon populations with ages mostly younger than 2730 Ma, the youngest zircon grains providing maximum ages of sedimentation at 2722 and 2712 Ma, respectively. Our results confirm the protracted evolution of the greenstone belt and show in particular that major sedimentary processes were active throughout the main stages of volcanism of the belt. This pattern of protracted sedimentation is comparable to that observed in other greenstone belts of the northwestern Superior Province, all of which developed on pre-Kenoran crust.
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Gong, Chenglin, Dongwei Li, Kun Qi, and Hongxiang Xu. "Flow processes and sedimentation in a straight submarine channel on the Qiongdongnan margin, northwestern South China Sea." Journal of Sedimentary Research 90, no. 10 (October 1, 2020): 1372–88. http://dx.doi.org/10.2110/jsr.2020.68.
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ABSTRACT Straight channels are ubiquitous in deep-water settings, yet flow dynamics and sedimentation in them are far from being well understood. Stratigraphy and flow dynamics of a middle to late Miocene straight channel in Qiongdongnan Basin were quantified, in terms of angle of channel-complex-growth trajectories (Tc), stratigraphic mobility number (M), Froude number (Fr), layer-averaged flow velocity (U), flow thickness (h), and water entrainment coefficient (Ew). The documented channels are composed of three channel complexes (CC1 to CC3) all of which are all characterized by symmetrical channel cross sections without levees and by organized vertical channel-stacking patterns (represented by high mean value of Tc = 37.4° and low mean value of M = 0.038). Turbidity currents in them were estimated to have U of 1.6 to 2.0 m/s (averaging 1.8 m/s), h of 63 to 89 m (averaging 78), Fr of 0.849 to 0.999 (averaging 0.912), and Ew of 0.0003 to 0.0005. They were, in most case, subcritical over most of the channel length, and had a low degree of water entrainment and low flow height scaled to the channel depth (i.e., 0.786 to 0.81 of the channel depth), most likely inhibiting the gradual loss of sediment to form levees. With reference to modeling results of secondary flow velocity vectors of numerical straight channels with the same sinuosity, two parallel gullies seen on both sides of the interpreted channel beds are interpreted to be induced by high-velocity downward backflows produced by the negative buoyancy. Such symmetrical secondary flow structures most likely promoted symmetrical intrachannel deposition (i.e., less deposition along both channel margins but more deposition near the channel center), and thus forced individual channel complexes to progressively aggrade in a synchronous manner, forming straight-channel complexes with symmetrical channel cross sections and organized vertical channel-stacking patterns.
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Walley, C. D. "Depositional history of southern Tunisia and northwestern Libya in Mid and Late Jurassic time." Geological Magazine 122, no. 3 (May 1985): 233–47. http://dx.doi.org/10.1017/s0016756800031447.
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AbstractThe good exposures of virtually undeformed Callovian and Oxfordian strata along the Djeffara escarpment of southern Tunisia and northwestern Libya have allowed analysis of regional depositional history during this time.A number of lithostratigraphic problems are considered. In Tunisia, the Foum Tatahouine Formation is subdivided into members and in Libya some of the stratigraphic issues are clarified. A correlation between the two sequences is proposed. The widely claimed aeolian origin for the Libyan Chameau Mort Sandstone is rejected.The depositional patterns of the Callovian and Oxfordian strata are described in the context of Mid and Late Jurassic sedimentation in the eastern Ghadames basin of the African craton. After a regressive Bathonian sequence, transgressive conditions commenced in Early Callovian time. In a series of continental–marine cycles, this transgressive sequence culminated in widespread shallow, restricted-marine micritic deposition. A regression in Late Callovian time resulted in emergence marked by a thin but widespread calcrete horizon. In Mid? Oxfordian time a renewed transgression brought in open marine, high-energy, shallow-water carbonates. Later, regressive conditions returned, leading to increasing restriction, and latest Jurassic time saw the first signs of the fluvio-deltaic deposition that was to dominate the region in Early Cretaceous time.
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Strogen, Dominic P., Karen E. Higgs, Angela G. Griffin, and Hugh E. G. Morgans. "Late Eocene – Early Miocene facies and stratigraphic development, Taranaki Basin, New Zealand: the transition to plate boundary tectonics during regional transgression." Geological Magazine 156, no. 10 (March 11, 2019): 1751–70. http://dx.doi.org/10.1017/s0016756818000997.
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AbstractEight latest Eocene to earliest Miocene stratigraphic surfaces have been identified in petroleum well data from the Taranaki Basin, New Zealand. These surfaces define seven regional sedimentary packages, of variable thickness and lithofacies, forming a mixed siliciclastic–carbonate system. The evolving tectonic setting, particularly the initial development of the Australian–Pacific convergent margin, controlled geographic, stratigraphic and facies variability. This tectonic signal overprinted a regional transgressive trend that culminated in latest Oligocene times. The earliest influence of active compressional tectonics is reflected in the preservation of latest Eocene – Early Oligocene deepwater sediments in the northern Taranaki Basin. Thickness patterns for all mid Oligocene units onwards show a shift in sedimentation to the eastern Taranaki Basin, controlled by reverse movement on the Taranaki Fault System. This resulted in the deposition of a thick sedimentary wedge, initially of coarse clastic sediments, later carbonate dominated, in the foredeep close to the fault. In contrast, Oligocene active normal faulting in a small sub-basin in the south may represent the most northerly evidence for rifting in southern Zealandia, related to Emerald Basin formation. The Early Miocene period saw a return to clastic-dominated deposition, the onset of regional regression and the southward propagation of compressional tectonics.
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Mitchell, Ross N., Uwe Kirscher, Marcus Kunzmann, Yebo Liu, and Grant M. Cox. "Gulf of Nuna: Astrochronologic correlation of a Mesoproterozoic oceanic euxinic event." Geology 49, no. 1 (August 25, 2020): 25–29. http://dx.doi.org/10.1130/g47587.1.
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Abstract The ca. 1.4 Ga Velkerri and Xiamaling Formations, in Australia and the north China craton, respectively, are both carbonaceous shale deposits that record a prominent euxinic interval and were intruded by ca. 1.3 Ga dolerite sills. These similarities raise the possibility that these two units correlate, which would suggest the occurrence of widespread euxinia, organic carbon burial, and source rock deposition. Paleomagnetic data are consistent with Australia and the north China craton being neighbors in the supercontinent Nuna and thus permit deposition in a single large basin, and the putative stratigraphic correlation. However, lack of geochronological data has precluded definitive testing. The Xiamaling Formation has been shown to exhibit depositional control by orbital cycles. Here, we tested the putative correlation with the Velkerri Formation by cyclostratigraphic analysis. The Velkerri Formation exhibits sedimentological cycles that can be interpreted to represent the entire hierarchy of orbital cycles, according to a sedimentation rate that is consistent with Re-Os ages. Comparison of the inferred durations of the euxinic intervals preserved in both the Xiamaling and Velkerri Formations reveals a nearly identical ∼10-m.y.-long oceanic euxinic event. This permits the interpretation that the two hydrocarbon-rich units were deposited and matured in the same basin of Nuna, similar to the Gulf of Mexico during the breakup of Pangea.
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de Wet, Carol B., Andrew P. de Wet, Linda Godfrey, Elizabeth Driscoll, Samuel Patzkowsky, Chi Xu, Sophia Gigliotti, and Melina Feitl. "Pliocene short-term climate changes preserved in continental shallow lacustrine-palustrine carbonates: Western Opache Formation, Atacama Desert, Chile." GSA Bulletin 132, no. 9-10 (December 23, 2019): 1795–816. http://dx.doi.org/10.1130/b35227.1.
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Abstract Multiple climate proxies indicate episodic changes in moisture levels within an ∼1 Ma duration (early–mid Pliocene) interval. Limestones within the Opache Formation, Calama Basin, Atacama Desert region, Chile, contain evidence for wetter and drier periods on short time scales. Proxies include carbonate lithological changes, paleontology (stromatolites, oncolites, gastropods, ostracods and diatoms), O and C stable isotopes, geochemistry, and mineralogical changes (aragonite, calcite, Mg-calcite, dolomite and gypsum) throughout a 30 m stratigraphic section. Stromatolite fossil cyanobacteria dark and light laminations and mesohaline to hypersaline diatom species suggest Pliocene annual seasonality. Short-term changes between wetter and drier conditions indicate that at least this part of the Atacama region was experiencing relatively rapid early–mid Pliocene climate instability. The predominance of limestone in the Opache Formation, in contrast to the 1500 m of Oligocene-Miocene siliciclastic conglomerates and sandstones, interpreted as arid climate alluvium, that underlie it, indicates a shift from arid or hyperarid climate to a semi-arid climate. Semi-arid conditions promoted limestone deposition in a shallow lacustrine-palustrine environment. In this setting, events such as storms with associated surface water flow, erosion, siliciclastic sand, gravel, and intraclast deposition, coupled with significant biological activity, represent sedimentation during more humid periods in a shallow lacustrine depositional environment. In contrast, limestone characterized by mudcracks, Navicula diatoms, and vadose syndepositional cementation, reflect periods of enhanced evaporation, water shallowing, and episodic desiccation, characteristic of a palustrine depositional system. These facies shifts, in conjunction with geochemical and isotopic proxy evidence, yield a sedimentary record of wetter and drier climate shifts.
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John-Joe, Traynor. "Arenig sedimentation and basin tectonics in the Harlech Dome area (Dolgellau Basin), North Wales." Geological Magazine 127, no. 1 (January 1990): 13–30. http://dx.doi.org/10.1017/s0016756800014138.
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AbstractArenig (Ordovician) clastic sediments crop out in the Harlech Dome region (North Wales), and are placed in a single stratigraphic unit: the Allt Lwyd Formation. This unit records a marine transgression onto an erosion surface produced during late Tremadoc arc volcanicity. Four discrete petrofacies are denned, and reflect differing proportions of detritus derived from Tremadoc-type basic-intermediate igneous rocks, and the local sedimentary basement. Initial shallow marine siliciclastic sandstones and conglomerates are overlain by extensive deep water mud-rich units. These generally shallow up into a complex arc-apron deposit, with sediments derived from the eroding Tremadoc arc, as well as from similar, synchronous volcanics. Predominantly epiclastic sandstones and conglomerates were deposited in deltaic and tidal environments in an arc-apron complex, and capped by condensed mudstones and an ironstone, deposited as sea level rose across these systems. Sediments were ponded in north–south orientated troughs and derived from uplifted blocks. Facies and petrofacies distribution were controlled by syn-sedimentary north-south and northeast–southwest faults. The Allt Lwyd Formation was ponded in a fault-controlled basin (the Dolgellau Basin), one of a series of interconnected sub-basins flooded by the Arenig transgression. The sediments preserved reflect deposition during the transgression of a volcanic arc, prior to the extrusion of marginal basin-type volcanics.
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Riggs, N. R., T. B. Sanchez, and S. J. Reynolds. "Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA." Geosphere 16, no. 4 (June 30, 2020): 1042–57. http://dx.doi.org/10.1130/ges02193.1.
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Abstract A shift in the depositional systems and tectonic regime along the western margin of Laurentia marked the end of the Paleozoic Era. The record of this transition and the inception and tectonic development of the Permo-Triassic Cordilleran magmatic arc is preserved in plutonic rocks in southwestern North America, in successions in the distal back-arc region on the Colorado Plateau, and in the more proximal back-arc region in the rocks of the Buckskin Formation of southeastern California and west-central Arizona (southwestern North America). The Buckskin Formation is correlated to the Lower–Middle Triassic Moenkopi and Upper Triassic Chinle Formations of the Colorado Plateau based on stratigraphic facies and position and new detrital zircon data. Calcareous, fine- to medium-grained and locally gypsiferous quartzites (quartz siltstone) of the lower and quartzite members of the Buckskin Formation were deposited in a marginal-marine environment between ca. 250 and 245 Ma, based on detrital zircon U-Pb data analysis, matching a detrital-zircon maximum depositional age of 250 Ma from the Holbrook Member of the Moenkopi Formation. An unconformity that separates the quartzite and phyllite members is inferred to be the Tr-3 unconformity that is documented across the Colorado Plateau, and marks a transition in depositional environments. Rocks of the phyllite and upper members were deposited in wholly continental depositional environments beginning at ca. 220 Ma. Lenticular bodies of pebble to cobble (meta) conglomerate and medium- to coarse-grained phyllite (subfeldspathic or quartz wacke) in the phyllite member indicate deposition in fluvial systems, whereas the fine- to medium-grained beds of quartzite (quartz arenite) in the upper member indicate deposition in fluvial and shallow-lacustrine environments. The lower and phyllite members show very strong age and Th/U overlap with grains derived from Cordilleran arc plutons. A normalized-distribution plot of Triassic ages across southwestern North America shows peak magmatism at ca. 260–250 Ma and 230–210 Ma, with relatively less activity at ca. 240 Ma, when a land bridge between the arc and the continent was established. Ages and facies of the Buckskin Formation provide insight into the tectono-magmatic evolution of early Mesozoic southwestern North America. During deposition of the lower and quartzite members, the Cordilleran arc was offshore and likely dominantly marine. Sedimentation patterns were most strongly influenced by the Sonoma orogeny in northern Nevada and Utah (USA). The Tr-3 unconformity corresponds to both a lull in magmatism and the “shoaling” of the arc. The phyllite and upper members were deposited in a sedimentary system that was still influenced by a strong contribution of detritus from headwaters far to the southeast, but more locally by a developing arc that had a far stronger effect on sedimentation than the initial phases of magmatism during deposition of the basal members.
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Rigueti, Ariely L., Patrick Führ Dal' Bó, Leonardo Borghi, and Marcelo Mendes. "Bioclastic accumulation in a lake rift basin: The Early Cretaceous coquinas of the Sergipe–Alagoas Basin, Brazil." Journal of Sedimentary Research 90, no. 2 (February 27, 2020): 228–49. http://dx.doi.org/10.2110/jsr.2020.11.
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ABSTRACT Coquinas constitute widespread deposits in lacustrine, estuarine, and shallow marine settings, where they are a valuable source of information on environmental conditions. Thick coquina successions were deposited in a series of lacustrine rift basins that formed along the Brazilian Continental Margin during the early stages of the opening of the South Atlantic Ocean, in the Early Cretaceous. In the Sergipe–Alagoas Basin, the coquina sequence, equivalent to the Morro do Chaves Formation, crops out in the Atol Quarry, and is considered a relevant analog for the economically important hydrocarbon reservoirs in the Pre-salt strata (Barremian to Aptian) of the Campos Basin (Pampo, Badejo, and Linguado oil fields), which occur only in the subsurface. The aim of this study is to generate a depositional and stratigraphic model through facies and stratigraphic analyses of a well core. These analyses allowed the geological characterization of the Morro do Chaves Formation and of its transition to the adjacent stratigraphic units, the Coqueiro Seco Formation above and the Penedo Formation below, contributing to the growing knowledge of sedimentation in rift basins and exploratory models in hydrocarbon-producing reservoirs. Facies analysis consists of sedimentological, taphonomic, and stratigraphic features of the rocks. Fourteen depositional facies were recognized, stacked into low-frequency and high-frequency, deepening-upward and shallowing-upward cycles driven by the interaction between climate and tectonism. A depositional model is presented, based on the correlation between well-core and outcrop data described in previous studies, providing insights into the spatial distribution of facies. The detailed analysis of facies and stacking patterns sheds light on depositional processes, paleoenvironmental conditions, and the evolution of the system through time, so we may better understand analogous deposits in the geological record.
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Soto-Kerans, Graham M., Daniel F. Stockli, Xavier Janson, Timothy F. Lawton, and Jacob A. Covault. "Orogen proximal sedimentation in the Permian foreland basin." Geosphere 16, no. 2 (January 6, 2020): 567–93. http://dx.doi.org/10.1130/ges02108.1.
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Abstract The sedimentary fill of peripheral foreland basins has the potential to preserve a record of the processes of ocean closure and continental collision, as well as the long-term (i.e., 107–108 yr) sediment-routing evolution associated with these processes; however, the detrital record of these deep-time tectonic processes and the sedimentary response have rarely been documented during the final stages of supercontinent assembly. The stratigraphy within the southern margin of the Delaware Basin and Marathon fold and thrust belt preserves a record of the Carboniferous–Permian Pangean continental assembly, culminating in the formation of the Delaware and Midland foreland basins of North America. Here, we use 1721 new detrital zircon (DZ) U-Pb ages from 13 stratigraphic samples within the Marathon fold and thrust belt and Glass Mountains of West Texas in order to evaluate the provenance and sediment-routing evolution of the southern, orogen-proximal region of this foreland basin system. Among these new DZ data, 85 core-rim age relationships record multi-stage crystallization related to magmatic or metamorphic events in sediment source areas, further constraining source terranes and sediment routing. Within samples, a lack of Neoproterozoic–Cambrian zircon grains in the pre-orogenic Mississippian Tesnus Formation and subsequent appearance of this zircon age group in the syn-orogenic Pennsylvanian Haymond Formation point toward initial basin inversion and the uplift and exhumation of volcanic units related to Rodinian rifting. Moreover, an upsection decrease in Grenvillian (ca. 1300–920 Ma) and an increase in Paleozoic zircons denote a progressive provenance shift from that of dominantly orogenic highland sources to that of sediment sources deeper in the Gondwanan hinterland during tectonic stabilization. Detrital zircon core-rim age relationships of ca. 1770 Ma cores with ca. 600–300 Ma rims indicate Amazonian cores with peri-Gondwanan or Pan-African rims, Grenvillian cores with ca. 580 Ma rims are correlative with Pan-African volcanism or the ca. 780–560 Ma volcanics along the rifted Laurentian margin, and Paleozoic core-rim age relationships are likely indicative of volcanic arc activity within peri-Gondwana, Coahuila, or Oaxaquia. Our results suggest dominant sediment delivery to the Marathon region from the nearby southern orogenic highland; less sediment was delivered from the axial portion of the Ouachita or Appalachian regions suggesting that this area of the basin was not affected by a transcontinental drainage. The provenance evolution of sediment provides insights into how continental collision directs the dispersal and deposition of sediment in the Permian Basin and analogous foreland basins.
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Fetrow, Anne C., Kathryn E. Snell, Russell V. Di Fiori, Sean P. Long, and Joshua W. Bonde. "Early Sevier orogenic deformation exerted principal control on changes in depositional environment recorded by the Cretaceous Newark Canyon Formation." Journal of Sedimentary Research 90, no. 9 (September 1, 2020): 1175–97. http://dx.doi.org/10.2110/jsr.2020.52.
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ABSTRACT Terrestrial sedimentary archives record critical information about environment and climate of the past, as well as provide insights into the style, timing, and magnitude of structural deformation in a region. The Cretaceous Newark Canyon Formation, located in central Nevada, USA, was deposited in the hinterland of the Sevier fold–thrust belt during the North American Cordilleran orogeny. While previous research has focused on the coarser-grained, fluvial components of the Newark Canyon Formation, the carbonate and finer-grained facies of this formation remain comparatively understudied. A more complete understanding of the Newark Canyon Formation provides insights into Cretaceous syndeformational deposition in the Central Nevada thrust belt, serves as a useful case study for deconvolving the influence of tectonic and climatic forces on sedimentation in both the North American Cordillera and other contractional orogens, and will provide a critical foundation upon which to build future paleoclimate and paleoaltimetry studies. We combine facies descriptions, stratigraphic measurements, and optical and cathodoluminescence petrography to develop a comprehensive depositional model for the Newark Canyon Formation. We identify six distinct facies that show that the Newark Canyon Formation evolved through four stages of deposition: 1) an anastomosing river system with palustrine interchannel areas, 2) a braided river system, 3) a balance-filled, carbonate-bearing lacustrine system, and 4) a second braided river system. Although climate undoubtedly played a role, we suggest that the deposition and coeval deformation of the synorogenic Newark Canyon Formation was in direct response to the construction of east-vergent contractional structures proximal to the type section. Comparison to other contemporary terrestrial sedimentary basins deposited in a variety of tectonic settings provides helpful insights into the influences of regional tectonics, regional and global climate, catchment characteristics, underlying lithologies, and subcrop geology in the preserved sedimentary record.
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Lyon, Eva C., Michael M. McGlue, Edward W. Woolery, Sora L. Kim, Jeffery R. Stone, and Susan R. H. Zimmerman. "Sublacustrine geomorphology and modern sedimentation in a glacial scour basin, June Lake, eastern Sierra Nevada, U.S.A." Journal of Sedimentary Research 89, no. 10 (October 21, 2019): 919–34. http://dx.doi.org/10.2110/jsr.2019.52.
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ABSTRACT Small sub-alpine glacial lakes are often targeted as Holocene paleoclimate archives, but their evolution as landforms and depositional basins is understudied. At June Lake in the eastern Sierra Nevada of California (USA), bathymetry, surface sediment composition, and seismic stratigraphy are studied to assess the modern sedimentary system and gain insight into the basin's origins. A basin-wide seismic survey reveals sublacustrine morphological features that attest to the role of ice in scouring the June Lake basin, including a prominent abraded bedrock shoal and an adjacent overdeepened depression. The seismic survey reveals four acoustically distinct stratigraphic units that reflect the history of sedimentation following glacial scouring. The youngest of these is represented in the recovered lacustrine core records as hemipelagically deposited, organic-rich, laminated diatomaceous oozes alternating with coarse tephra beds. The organic-rich oozes are characterized by low carbon and nitrogen stable-isotope values and occur in profundal areas of the modern lake floor. These sediments suggest an algae-dominated productivity regime and preservation of organic matter at depth. With no perennial streams entering June Lake, surface-sediment grain-size distribution and geochemistry are controlled by water depth and basin morphology. Additional modern facies types include poorly sorted coarse detrital landslide deposits below steep basin walls and volcaniclastic sandy gravel in windward littoral areas. These data provide a modern facies model for sedimentation in ice-scoured, hydrologically closed sub-alpine lakes and a baseline for future paleoclimate studies using June Lake sediment cores.
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Lukeneder, Alexander, Eva Halásová, Andreas Kroh, Susanne Mayrhofer, Petr Pruner, Daniela Reháková, Petr Schnabl, Mario Sprovieri, and Michael Wagreich. "High resolution stratigraphy of the Jurassic-Cretaceous boundary interval in the Gresten Klippenbelt (Austria)." Geologica Carpathica 61, no. 5 (October 1, 2010): 365–81. http://dx.doi.org/10.2478/v10096-010-0022-3.
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High resolution stratigraphy of the Jurassic-Cretaceous boundary interval in the Gresten Klippenbelt (Austria)The key objective of investigation of hemipelagic sediments from the Gresten Klippenbelt (Blassenstein Formation, Ultrahelvetic paleogeographic realm) was to shed light on environmental changes around the Jurassic-Cretaceous (J/K) boundary on the northern margin of the Penninic Ocean. This boundary is well exposed in a newly discovered site at Nutzhof. Around the critical interval including the boundary, this new outcrop bears a rich microplanktonic assemblage characterized by typical J/K (Tithonian/Berriasian) boundary faunas. The Nutzhof section is located in the Gresten Klippenbelt (Lower Austria) tectonically wedged into the deep-water sediments of the Rhenodanubian Flysch Zone. In Late Jurassic-Early Cretaceous time the Penninic Ocean was a side tract of the proto-North Atlantic Oceanic System, intercalated between the European and the Austroalpine plates. Its opening started during the Early Jurassic, induced by sea floor spreading, followed by Jurassic-Early Cretaceous deepening of the depositional area of the Gresten Klippenbelt. These tectonically induced paleogeographic changes are mirrored in the lithology and microfauna that record a deepening of the depositional environment from Tithonian to Berriasian sediments of the Blassenstein Formation at Nutzhof. The main lithological change is observed in the Upper TithonianCrassicollariaZone, in Chron M20N, whereas the J/K boundary can be precisely fixed at theCrassicollaria-Calpionellaboundary, within Chron M19n.2n. The lithological turnover of the deposition from more siliciclastic pelagic marl-limestone cycles into deep-water pelagic limestones is correlated with the deepening of the southern edge of the European continent at this time. Within the Gresten Klippenbelt Unit, this transition is reflected by the lithostratigraphic boundary between siliciclastic-bearing marl-limestone sedimentation in the uppermost Jurassic and lowermost Cretaceous limestone formation, both within the Blassenstein Formation. The cephalopod fauna (ammonites, belemnites, aptychi) and crinoids from the Blassenstein Formation, correlated with calcareous microfossil and nannofossil data combined with isotope and paleomagnetic data, indicate the Tithonian to middle Berriasian (Hybonoticeras hybonotumZone up to theSubthurmannia occitanicaZone; M17r-M21r). The succession of the Nutzhof section thus represents deposition of a duration of approximately 7 Myr (ca. 150-143 Ma). The deposition of the limestone, marly limestone and marls in this interval occurred during tectonically unstable conditions reflected by common allodapic material. Along with the integrated biostratigraphic, geochemical and isotopic analysis, the susceptibility and gamma-ray measurements were powerful stratigraphic tools and important for the interpretation of the paleogeographic setting. Two reverse magneto-subzones, Kysuca and Brodno, were detected within magnetozones M20n and M19n, respectively.
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Cumberpatch, Zoë A., Ian A. Kane, Euan L. Soutter, David M. Hodgson, Christopher A.-L. Jackson, Ben A. Kilhams, and Yohann Poprawski. "Interactions between deep-water gravity flows and active salt tectonics." Journal of Sedimentary Research 91, no. 1 (January 31, 2021): 34–65. http://dx.doi.org/10.2110/jsr.2020.047.
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ABSTRACTBehavior of sediment gravity flows can be influenced by seafloor topography associated with salt structures; this can modify the depositional architecture of deep-water sedimentary systems. Typically, salt-influenced deep-water successions are poorly imaged in seismic reflection data, and exhumed systems are rare, hence the detailed sedimentology and stratigraphic architecture of these systems remains poorly understood.The exhumed Triassic (Keuper) Bakio and Guernica salt bodies in the Basque–Cantabrian Basin, Spain, were active during deep-water sedimentation. The salt diapirs grew reactively, then passively, during the Aptian–Albian, and are flanked by deep-water carbonate (Aptian–earliest Albian Urgonian Group) and siliciclastic (middle Albian–Cenomanian Black Flysch Group) successions. The study compares the depositional systems in two salt-influenced minibasins, confined (Sollube basin) and partially confined (Jata basin) by actively growing salt diapirs, comparable to salt-influenced minibasins in the subsurface. The presence of a well-exposed halokinetic sequence, with progressive rotation of bedding, beds that pinch out towards topography, soft-sediment deformation, variable paleocurrents, and intercalated debrites indicate that salt grew during deposition. Overall, the Black Flysch Group coarsens and thickens upwards in response to regional axial progradation, which is modulated by laterally derived debrites from halokinetic slopes. The variation in type and number of debrites in the Sollube and Jata basins indicates that the basins had different tectonostratigraphic histories despite their proximity. In the Sollube basin, the routing systems were confined between the two salt structures, eventually depositing amalgamated sandstones in the basin axis. Different facies and architectures are observed in the Jata basin due to partial confinement.Exposed minibasins are individualized, and facies vary both spatially and temporally in agreement with observations from subsurface salt-influenced basins. Salt-related, active topography and the degree of confinement are shown to be important modifiers of depositional systems, resulting in facies variability, remobilization of deposits, and channelization of flows. The findings are directly applicable to the exploration and development of subsurface energy reservoirs in salt basins globally, enabling better prediction of depositional architecture in areas where seismic imaging is challenging.
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Álvaro, J. Javier, and Marie-Madeleine Blanc-Valleron. "Stratigraphic and structural framework of the Neoproterozoic Paracuellos Group, Iberian Chains, NE Spain." Bulletin de la Société Géologique de France 173, no. 3 (May 1, 2002): 219–27. http://dx.doi.org/10.2113/173.3.219.
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Abstract The Neoproterozoic Paracuellos Group of the Iberian Chains constitutes the core of two disconnected faulted blocks, named the Paracuellos and Codos antiforms. Precise lithostratigraphic correlations between both areas are not possible due to the structural complexity and because marker beds do not persist laterally. This paper presents a crustal cross-section of the Neoproterozoic axial core (the Paracuellos antiform) based on surface geology, boreholes and seismic reflection profiles. Seismic reflection data reveal that the basement was directly involved by a major Hercynian structure, named here the Paracuellos fault, which splits longitudinally the Paracuellos axial core. In seismic profiles this fault occurs as a northeasterly-dipping reflector (60–70° steep), evidencing a bivergent geometry of the lateral crustal elements. The sedimentary evolution of the Neoproterozoic Iberian platform ranges from transgressive, non-cyclic, offshore to hemipelagic, black and green shales (Sestrica Formation) to progradational trends recording shoaling during episodes of rapid sediment influx (Saviñán Formation), presumably in response to a low standing sea-level. The siliciclastic succession is punctuated in the inner platform by deposition of phosphatic limestones (Codos Bed), representing a major shoaling event and demarcating a sharp regional change of sedimentation separating two similar siliciclastic tendencies. A diagenetically induced bedded chert (Frasno Bed) occurs in the outer platform, and is interpreted as being the product of at least two silicification episodes. Both the Codos and Frasno Beds are overlain by the Aluenda Formation, which exhibits nearshore to offshore features. An important sedimentary discontinuity appears across the Neoproterozoic-Cambrian transition. The Cambrian(?) Bámbola Formation is paraconformable with the Paracuellos Group displaying a gradual transition in inner platform areas, whereas an erosive unconformity occurs in outer areas. The horizon of the Neoproterozoic-Cambrian boundary is not identified in the Iberian Chains, where neither Cadomian deformation nor discordances are recognisable.
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Jones, Matthew M., Bradley B. Sageman, Rosie L. Oakes, Amanda L. Parker, R. Mark Leckie, Timothy J. Bralower, Julio Sepúlveda, and Victoria Fortiz. "Astronomical pacing of relative sea level during Oceanic Anoxic Event 2: Preliminary studies of the expanded SH#1 Core, Utah, USA." GSA Bulletin 131, no. 9-10 (March 1, 2019): 1702–22. http://dx.doi.org/10.1130/b32057.1.
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AbstractProximal marine strata of the North American Western Interior Basin (WIB) preserve a rich record of biotic turnover during Oceanic Anoxic Event 2 (OAE2; ca. 94 Ma), a pronounced Late Cretaceous carbon cycle perturbation interpreted to reflect global warming, widespread hypoxia, and possible ocean acidification. To develop a more robust synthesis of paleobiologic and geochemical data sets spanning this Earth-life transition, we drilled the 131 m Smoky Hollow #1 Core (SH#1), on the Kaiparowits Plateau of southern Utah, USA, recovering the Cenomanian–Turonian Boundary (CTB) interval in the Tropic Shale Formation. A 17.5 m positive excursion in high-resolution bulk carbon isotope chemostratigraphy (δ13Corg) of SH#1 characterizes the most expanded OAE2 record recovered from the mid-latitudes of the WIB.Depleted values in a paired carbonate carbon isotope (δ13Ccarb) chemostratigraphy cyclically punctuate the OAE2 excursion. These depletions correspond to intervals in the core with a higher degree of carbonate diagenesis and correlate well to an existing sequence stratigraphic framework of flooding surfaces in the shoreface facies of the Markagunt Plateau (∼100 km west). We detect statistically significant evidence for astronomical cycles in the δ13Ccarb data set, imparted by diagenesis at flooding surfaces, and develop a floating astronomical time scale (ATS) for the study interval. Stable eccentricity cycles (405 k.y.) align with stratigraphic sequences and associated trends in sedimentation rate, and short eccentricity cycles (∼100 k.y.) pace nested parasequences. These results confirm an astronomical signal and, therefore, climatic forcing of relative sea level during OAE2 in the WIB. Furthermore, cross-basin correlation of the ATS and expanded δ13C chemostratigraphy of SH#1 suggests that these transgressive-regressive parasequences modulated siliciclastic sediment delivery in the seaway and contributed to deposition of prominent rhythmically bedded CTB units across the WIB, including the Bridge Creek Limestone. The presented approach to analysis of these proximal offshore siliciclastic facies links early diagenetic influences on chemostratigraphy to astronomically modulated sequence stratigraphic horizons, and helps to resolve rates of paleobiologic and paleoenvironmental change during a significant Mesozoic carbon cycle perturbation.
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Ali, Syed Haroon, Osman M. Abdullatif, Lamidi O. Babalola, Fawwaz M. Alkhaldi, Yasir Bashir, S. M. Talha Qadri, and Ali Wahid. "Sedimentary facies, depositional environments and conceptual outcrop analogue (Dam Formation, early Miocene) Eastern Arabian Platform, Saudi Arabia: a new high-resolution approach." Journal of Petroleum Exploration and Production Technology 11, no. 6 (May 15, 2021): 2497–518. http://dx.doi.org/10.1007/s13202-021-01181-7.
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AbstractThis paper presents the facies and depositional environment of the early Miocene Dam Formation, Eastern Arabian platform, Saudi Arabia. Deposition of Dam Formation (Fm.) was considered as a restricted shallow marine deposition. Few studies suggest the role of sea-level change in its deposition but were without decisive substantiation. Here, we describe the facies and high-resolution model of Dam Fm. under varying depositional conditions. The depositional conditions were subjected to changing relative sea level and tectonics. High-resolution outcrop photographs, sedimentological logs, and thin sections present that the mixed carbonate–siliciclastic sequence was affected by a regional tectonics. The lower part of Dam Fm. presents the development of carbonate ramp conditions that are represented by limestones and marl. The depositional conditions fluctuated with the fall of sea level, and uplift in the region pushed the siliciclastic down-dip and covered the whole platform. The subsequent rise in sea level was not as pronounced and thus allowed the deposition of microbial laminites and stromatolitic facies. The southeast outcrops, down-dip, are more carbonate prone as compared to the northwest outcrop, which allowed the deposition of siliciclastic-prone sedimentation up-dip. All facies, architecture, heterogeneity, and deposition were controlled by tectonic events including uplift, subsidence, tilting, and syn-sedimentary faulting, consequently affecting relative sea level. The resulting conceptual outcrop model would help to improve our understanding of mixed carbonate–siliciclastic systems and serve as an analogue for other stratigraphic units in the Arabian plate and region. Our results show that Dam Fm. can be a good target for exploration in the Northern Arabian Gulf.
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Larena, Z., C. Arenas, J. I. Baceta, X. Murelaga, and O. Suarez-Hernando. "Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum." Geologica Acta 18 (May 20, 2020): 1–26. http://dx.doi.org/10.1344/geologicaacta2020.18.7.
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Stratigraphic and sedimentological study of distal alluvial and lacustrine deposits in the Plana de la Negra-Sancho Abarca area (western-central Ebro Basin, NE Iberia) within the early and middle Miocene allows five main lithofacies to be characterized and mapped within two tectosedimentary units, construction of a sedimentary facies model and discussion on allogenic controls on sedimentation. In this area, the boundary between tectosedimentary units T5 and T6 appears to be conformable and is marked by the change from dominant clastics to carbonates. Correlation of the studied outcrops with nearby sections that already had magnetostratigraphic and biostratigraphic data allows the studied succession to be dated from C5Dr to C5Cn (Burdigalian-Langhian), placing the boundary T5/T6 at ca. 16.1-16.05Ma. Seven vertical facies sequences document deposition of distal alluvial clastics and palustrine and lacustrine carbonates. Sandstones and mudstones represent low-sinuosity channels and lateral and terminal splays by unconfined flows runnig across the alluvial plain, associated to the Pyrenean-derived Luna fluvial system. The carbonates contain charophytes, ostracods, bivalves and gastropods, indicating deposition in 2-4m deep lakes. Laminated carbonate facies record reworking of shore carbonates and the influx fine-siliciclastic sediment offshore. Abundant bioturbation and desiccation features indicate episodic submergence and subaerial exposure. Four main episodes of alluvial and associated palustrine/lacustrine facies belt shifts are identified. Alluvial deposition in the studied T5 unit is related to low lake level conditions, rather than to a Pyrenean uplift. The maximum extent of the freshwater carbonates occur at the base of unit T6. This is consistent with conditions of increasing humidity of the Middle Miocene Climatic Optimum.
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Mozherovsky, Anatoly V. "Practical Application of the Mineralogical Mapping Method for Stratigraphy of the Cretaceous Deposits of Southern Primorye (Russian Far East)." Minerals 11, no. 8 (August 4, 2021): 840. http://dx.doi.org/10.3390/min11080840.
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Highly ordered mixed-layer formations of chlorite–smectite (corrensite) and mica–smectite (rectorite) were found in the volcanogenic–sedimentary rocks of Southern Primorye. They have shown a rather narrow “living” time interval (Cretaceous–Paleogene). The associations of corrensite and rectorite with chlorite, mica, kaolinite, and laumontite have great value in labeling. Their study would determine the time and thickness parameters of sedimentation conditions, the nature of the transformation stages, the physicochemical and climatic parameters of the accumulation of the depositional material, and the geological history and stratigraphic construction of Mesozoic–Cenozoic volcanogenic–sedimentary rocks of the Primorye Region.
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Myrow, P. M., N. C. Hughes, and N. R. McKenzie. "Reconstructing the Himalayan margin prior to collision with Asia: Proterozoic and lower Paleozoic geology and its implications for Cenozoic tectonics." Geological Society, London, Special Publications 483, no. 1 (November 21, 2018): 39–64. http://dx.doi.org/10.1144/sp483.10.
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AbstractReconstructing the stratigraphic architecture of deposits prior to Cenozoic Himalayan uplift is critical for unravelling the structural, metamorphic, depositional and erosional history of the orogen. The nature and distribution of Proterozoic and lower Paleozoic strata have helped elucidate the relationship between lithotectonic zones, as well as the geometries of major bounding faults. Stratigraphic and geochronological work has revealed a uniform and widespread pattern of Paleoproterozoic strata >1.6 Ga that are unconformably overlain by <1.1 Ga rocks. The overlying Neoproterozoic strata record marine sedimentation, including a Cryogenian diamictite, a well-developed carbonate platform succession and condensed fossiliferous Precambrian–Cambrian boundary strata. Palaeontological study of Cambrian units permits correlation from the Indian craton through three Himalayan lithotectonic zones to a precision of within a few million years. Detailed sedimentological and stratigraphic analysis shows the differentiation of a proximal realm of relatively condensed, nearshore, evaporite-rich units to the south and a distal realm of thick, deltaic deposits to the north. Thus, Neoproterozoic and Cambrian strata blanketed the northern Indian craton with an extensive, northward-deepening, succession. Today, these rocks are absent from parts of the inner Lesser Himalaya, and the uplift and erosion of these proximal facies explains a marked change in global seawater isotopic chemistry at 16 Ma.
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Salles, Lise, Mary Ford, Philippe Joseph, Christian Le Carlier De Veslud, and Antoine Le Solleuz. "Migration of a synclinal depocentre from turbidite growth strata: the Annot syncline, SE France." Bulletin de la Société Géologique de France 182, no. 3 (May 1, 2011): 199–220. http://dx.doi.org/10.2113/gssgfbull.182.3.199.
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AbstractThe Annot Sandstone turbidites of the Alpine foreland basin in SE France (Eocene-Oligocene: 40-32 Ma), provide an excellent case-study of tectono-sedimentary relations in a deepwater compressional system. The Annot outlier is a synclinal remnant previously interpreted as a static depocentre. A multi-disciplinary approach including geometrical and kinematic analyses and modelling demonstrates instead that this was a tectonically active turbidite depocentre where gentle thrust related folding controlled turbidite architecture.Stratigraphic and new structural field data are integrated with previous sedimentological studies to build a 3D geometric model of the Annot depocentre. Derived thickness maps associated with paleocurrent measurements clearly illustrate three main phases in the evolution of depocentre topography. (1) Early turbidite flows were mainly trapped by oblique intrabasinal inherited structures. (2) Once these structures were buried, the NNW-SSE active syncline constituted the main topographic control. (3) Decreasing activity of this syncline is recorded by filling and flow bypass. The progressive stages of the accepted depositional model (flow ponding, flow stripping and flow bypass), for the Annot depocentre, may therefore have a tectonic origin.The kinematic evolution of the synclinal depocentre was defined at different scales. Stratigraphic architecture records a decrease in bedding dips up through the turbidite succession on the western synclinal limb. Comparison with idealized case studies of the interaction of sedimentation with an active syncline indicates that this geometrical pattern corresponds to progressive westward migration of the synclinal hinge and depocentre. This tends to promote lateral rather than vertical stacking of sand bodies during turbidite sedimentation. Trishear kinematic modelling was used to simulate (in 2D) the rolling synclinal hinge. Stratigraphic surface geometries and turbidite depocentre migration define thrust and fold geometries at depth. The synclinal depocentre developed between two alternating or coeval fault propagation anticlines that exploited two detachment levels (Triassic evaporites and Cenomanian marls) in the underlying succession.
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Thompson Jobe, Jessica Ann, Katherine A. Giles, Thomas E. Hearon, Mark G. Rowan, Bruce Trudgill, C. Evelyn Gannaway Dalton, and Zane R. Jobe. "Controls on the structural and stratigraphic evolution of the megaflap-bearing Sinbad Valley salt wall, NE Paradox Basin, SW Colorado." Geosphere 16, no. 1 (November 21, 2019): 297–328. http://dx.doi.org/10.1130/ges02089.1.
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Abstract The interplay between sedimentation and salt rise around a diapir results in distinct geometries that can be used to determine the structural and stratigraphic history within a basin. Using new geologic mapping, measured stratigraphic sections, and subsurface interpretations of seismic and well logs, we describe circum-diapir stratal geometries and deformation at the Sinbad Valley salt wall in the proximal, northeastern Paradox Basin, southwest Colorado (USA). We interpret these geometries in the context of newly recognized halokinetic features and salt-associated deformation (megaflaps, counterregional faults, intrasalt inclusions), present a revised stratigraphic and salt tectonic history of Sinbad Valley diapir, and compare these proximal features to those at the distal Gypsum Valley diapir and infer local versus regional controls on their formation. The deposition of conglomerates within the Paradox Formation, now preserved as intrasalt inclusions in the center of Sinbad Valley, record early elevation of the Uncompahgre Uplift. Subsequent differential sedimentary loading resulted in initiation of passive diapirism during the late Pennsylvanian through the latest Triassic/Early Jurassic, facilitated by movement on a NE-dipping, listric, counterregional fault that extends for >22 km southeast of the diapir. Exposures of a steeply dipping stratal panel of late Pennsylvanian-aged Honaker Trail Formation along the southwestern flank of Sinbad Valley are interpreted as a megaflap, a preserved remnant of the diapir roof that was folded into a vertical position by drape-folding during passive salt rise. Significant lateral changes in the surface geometry and depositional facies of the megaflap define four structural domains that may result from a combination of radial faulting and varying degrees of folding via limb rotation or limb rotation with minor hinge migration. Using key differences between Sinbad Valley and Gypsum Valley salt walls in regard to the megaflap facies, timing of megaflap formation, and the presence of a Paradox Formation conglomeratic intrasalt inclusion, we conclude that salt wall position (i.e., proximal versus distal) within a basin influences the characteristics of some of these features, whereas the timing of other features (e.g., megaflap formation) appears to be similar throughout the basin suggesting a more regional control.
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Wang, Jian-Gang, Xiumian Hu, Eduardo Garzanti, Marcelle K. BouDagher-Fadel, Zhi-Chao Liu, Juan Li, and Fu-Yuan Wu. "From extension to tectonic inversion: Mid-Cretaceous onset of Andean-type orogeny in the Lhasa block and early topographic growth of Tibet." GSA Bulletin 132, no. 11-12 (April 8, 2020): 2432–54. http://dx.doi.org/10.1130/b35314.1.
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Abstract Recent studies have indicated that an Andean-type orogen (Lhasaplano) developed on the Lhasa block in the Cretaceous during northward subduction of Neo-Tethyan oceanic lithosphere. When and how uplift of the Lhasaplano began, however, has remained controversial. This article integrates stratigraphic, sedimentological, tectonic, and provenance data from the latest marine to nonmarine strata in the Linzhou Basin to pinpoint the early topographic growth in southern Tibet. The Takena Formation mainly consists of lagoonal carbonates and mudstones yielding foraminiferal assemblages of Early Aptian age (ca. 123–119.5 Ma). The conformably overlying lower member of the Shexing Formation, mainly deposited in fluvial environments, was fed by volcanic and sedimentary rock fragments from the north Lhasa terrane. Clasts of the Gangdese arc to the south firstly appeared in the middle member and became dominant in the upper member of the Shexing Formation. By contrast, coarse grained, braided river facies occur in the uppermost part of the Shexing Formation, where detritus was mostly recycled from Paleozoic strata of north Lhasa, with minor volcaniclastic contribution from the Gangdese arc. Basin analysis indicates accelerating subsidence and sedimentation rates during deposition of Takena to middle Shexing strata (ca. 125–108 Ma), followed by steady subsidence during deposition of upper Shexing strata (ca. 108–96 Ma). Given this regional tectonic and sedimentary evidence, such an evolution is interpreted to reflect tectonic extension followed by thermal subsidence. Basin inversion and regional compression initiated during deposition of the uppermost Shexing strata (ca. 96 Ma), as indicated by active thrust faults and widespread accumulation of syntectonic conglomerates in the western part of the Lhasa block. This event marked the beginning of the Andean-type orogeny in southern Tibet. Such a paleotectonic evolution, from extension to tectonic inversion, is also documented in the Andes mountain range. It may be typical of the early stage growth of Andean-type active continental margins.
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Myrow, Paul M., Michael C. Pope, John W. Goodge, Woodward Fischer, and Alison R. Palmer. "Depositional history of pre-Devonian strata and timing of Ross orogenic tectonism in the central Transantarctic Mountains, Antarctica." GSA Bulletin 114, no. 9 (September 1, 2002): 1070–88. http://dx.doi.org/10.1130/0016-7606(2002)114<1070:dhopds>2.0.co;2.
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Abstract A combination of field mapping, detailed sedimentology, carbon isotope chemostratigraphy, and new paleontological finds provides a significantly improved understanding of the depositional and tectonic history of uppermost Neoproterozoic and lower Paleozoic strata of the central Trans ant arc tic Mountains. On the basis of these data, we suggest revision of the existing stratigraphy, including introduction of new formations, as follows. The oldest rocks appear to record late Neoproterozoic deposition across a narrow marine margin underlain by Precambrian basement. Siliciclastic deposits of the Neoproterozoic Beardmore Group—here restricted to the Cobham Formation and those rocks of the Goldie Formation that contain no detrital components younger than ca. 600 Ma—occupied an inboard zone to the west. They consist of shallow-marine deposits of an uncertain tectonic setting, although it was likely a rift to passive margin. Most rocks previously mapped as Goldie Formation are in fact Cambrian in age or younger, and we reassign them to the Starshot Formation of the Byrd Group; this change reduces the exposed area of the Goldie Formation to a small fraction of its previous extent. The basal unit of the Byrd Group—the predominantly carbonate ramp deposits of the Shackleton Limestone—rest with presumed unconformity on the restricted Goldie Formation. Paleontological data and carbon isotope stratigraphy indicate that the Lower Cambrian Shackleton Limestone ranges from lower Atdabanian through upper Botomian. This study presents the first description of a depositional contact between the Shackleton Limestone and overlying clastic units of the upper Byrd Group. This carbonate-to-clastic transition is of critical importance because it records a profound shift in the tectonic and depositional history of the region, namely from relatively passive sedimentation to active uplift and erosion associated with the Ross orogeny. The uppermost Shackleton Limestone is capped by a set of archaeocyathan bioherms with up to 40 m of relief above the seafloor. A widespread phosphatic crust on the bio herms records the onset of orogenesis and drowning of the carbonate ramp. A newly defined transitional unit, the Holyoake Formation, rests above this surface. It consists of black shale followed by mixed nodular carbonate and shale that fill in between, and just barely above, the tallest of the bioherms. This formation grades upward into trilobite- and hyolithid-bearing calcareous siltstone of the Starshot Formation and alluvial-fan deposits of the Douglas Conglomerate. Trilobite fauna from the lowermost siltstone deposits of the Starshot Formation date the onset of this transition as being late Botomian. The abrupt transition from the Shackleton Limestone to a large-scale, upward-coarsening siliciclastic succession records deepening of the outer platform and then deposition of an eastward-prograding molassic wedge. The various formations of the upper Byrd Group show general stratigraphic and age equivalence, such that coarse-grained alluvial-fan deposits of the Douglas Conglomerate are proximal equivalents of the marginal-marine to shelf deposits of the Starshot Formation. Paleocurrents and facies distributions from these units indicate consistent west (or southwest) to east (or northeast) transport of sediment. Although the exact structural geometry is unknown, development of imbricate thrust sheets in the west likely caused depression of the inner margin and rapid drowning of the Shackleton Formation carbonate ramp. This tectonic activity also caused uplift of the inboard units and their underlying basement, unroofing, and widespread deposition of a thick, coarse clastic wedge. Continued deformation in the Early Ordovician (younger than 480 Ma) in turn affected these synorogenic deposits, causing folding and thrust repetition of all pre- Devonian units.
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Gadd, M. G., J. M. Peter, D. Hnatyshin, R. Creaser, S. Gouwy, and T. Fraser. "A Middle Devonian basin-scale precious metal enrichment event across northern Yukon (Canada)." Geology 48, no. 3 (January 3, 2020): 242–46. http://dx.doi.org/10.1130/g46874.1.
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Abstract Hyper-enriched black shale (HEBS) Ni-Mo-Zn-Pt-Pd-Au-Re mineralization is geographically widespread across the Richardson trough in northern Yukon (Canada), where it discontinuously outcrops at the regional contact between the Road River Group and overlying Canol Formation. Stratigraphic relationships indicate that the contact is Middle Devonian, but there are no precise age constraints for the HEBS. We apply Re-Os geochronology to HEBS mineralization from two localities that are 130 km apart, the Nick prospect and the Peel River showing, to date directly the age of sulfide mineralization. The Nick prospect yields an isochron age of 390.7 ± 5.1 (2σ) Ma, whereas the Peel River showing yields an isochron age of 387.5 ± 4.4 (2σ) Ma. Within error, these ages are identical and overlap with the biostratigraphically constrained age of the sedimentary host rocks, indicating that mineralization and sedimentation were coeval. Significantly, the ages of the HEBS overlap those of Middle Devonian Kačák, pumilio, and Taghanic global-scale biotic events which are characterized by eustatic sea-level rise and black shale deposition. Linkage of the Yukon HEBS to one (or more) of these bio-events indicates that sea-level rise may have been requisite to formation of basin-scale HEBS mineralization in northwestern Canada during latest Eifelian and Givetian time.
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Dam, Gregers. "Mantle plumes and sequence stratigraphy; Late Maastrichtian- Early Paleocene of West Greenland." Bulletin of the Geological Society of Denmark 48 (December 31, 2001): 189–207. http://dx.doi.org/10.37570/bgsd-2001-48-11.
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The sedimentary history of the upper Maastrichtian–Paleocene succession underneath the extensive Paleocene flood basalts in central West Greenland supports models for the generation of flood basalt provinces in response to rising, hot mantle plumes. The rise of the North Atlantic mantle plume was associated with deposition of at least three sedimentary sequences; each associated with incision of submarine canyons and valleys. Relative sea-level changes were caused by plumerelated tectonics and generation of sequence boundaries was in general associated with catastrophic sedimentation and very rapid development of sequences. As such the late Maastrichtian–early Paleocene sequences record a spectacular and significant but rare geological event.
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Trop, Jeffrey M., Jeffrey A. Benowitz, Donald Q. Koepp, David Sunderlin, Matthew E. Brueseke, Paul W. Layer, and Paul G. Fitzgerald. "Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault." Geosphere 16, no. 1 (November 21, 2019): 82–110. http://dx.doi.org/10.1130/ges02127.1.
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Abstract The Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone. These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska.
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McArthur, Adam D., Julien Bailleul, Geoffroy Mahieux, Barbara Claussmann, Alex Wunderlich, and William D. McCaffrey. "Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand." Journal of Sedimentary Research 91, no. 4 (April 9, 2021): 362–89. http://dx.doi.org/10.2110/jsr.2020.013.
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ABSTRACT Concepts of the interaction between autogenic (e.g., flow process) and allogenic (e.g., tectonics) controls on sedimentation have advanced to a state that allows the controlling forces to be distinguished. Here we examine outcropping and subsurface Neogene deep-marine clastic systems that traversed the Hikurangi subduction margin via thrust-bounded trench-slope basins, providing an opportunity to examine the interplay of structural deformation and deep-marine sedimentation. Sedimentary logging and mapping of Miocene outcrops from the exhumed portion of the subduction wedge record heavily amalgamated, sand-rich lobe complexes, up to 200 m thick, which accumulated behind NE–SW-oriented growth structures. There was no significant deposition from low-density parts of the gravity flows in the basin center, although lateral fringes demonstrate fining and thinning indicative of deposits from low-density flows. Seismic data from the offshore portion of the margin show analogous lobate reflector geometries. These deposits accumulate into complexes up to 5 km wide, 8 km long, and 300 m thick, comparable in scale with the outcropping lobes on this margin. Mapping reveals lobe complexes that are vertically stacked behind thrusts. These results illustrate repeated trapping of the sandier parts of turbidity currents to form aggradational lobe complexes, with the finer-grained suspended load bypassing to areas downstream. However, the repeated development of lobes characterized by partial bypass implies that a feedback mechanism operates to perpetuate a partial confinement condition, via rejuvenation of accommodation. The mechanism proposed is a coupling of sediment loading and deformation rate, such that load-driven subsidence focuses stress on basin-bounding faults and perpetuates generation of accommodation in the basin, hence modulating tectonic forcing. Recognition of such a mechanism has implications for understanding the tectono-stratigraphic evolution of deep-marine fold and thrust belts and the distribution of resources within them.
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GEYER, G. "The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic–Cambrian boundary problem revisited." Geological Magazine 142, no. 5 (September 2005): 465–98. http://dx.doi.org/10.1017/s0016756805000956.
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The Fish River Subgroup of the Nama Group, southern Namibia, is restudied in terms of lithostratigraphy and depositional environment. The study is based on partly fine-scaled sections, particularly of the Nababis and Gross Aub Formation. The results are generally in accordance with earlier studies. However, braided river deposits appear to be less widely distributed in the studied area, and a considerable part of the formations of the middle and upper subgroup apparently were deposited under shallowest marine conditions including upper shore-face. Evidence comes partly from sedimentary features and facies distribution, and partly from trace fossils, particularly Skolithos and the characteristic Trichophycus pedum. Environmental conditions represented by layers with T. pedum suggest that the producer favoured shallow marine habitats and transgressive regimes. The successions represent two deepening-upward sequences, both starting as fluvial (braided river) systems and ending as shallow marine tidally dominated environments. The first sequence includes the traditional Stockdale, Breckhorn and lower Nababis formations (Zamnarib Member). The second sequence includes the upper Nababis (Haribes Member) and Gross Aub formations. As a result, the Nababis and Gross Aub formations require emendation: a new formation including the Haribes and Rosenhof and possibly also the Deurstamp members. In addition, four distinct sequence stratigraphic units are deter-minable for the Fish River Subgroup in the southern part of the basin. The Proterozoic–Cambrian transition in southern Namibia is most probably located as low as the middle Schwarzrand Subgroup. The environmentally controlled occurrence of Trichophycus pedum undermines the local stratigraphic significance of this trace fossil which is eponymous with the lowest Cambrian and Phanerozoic trace fossil assemblage on a global scale. However, occurrences of such trace fossils have to be regarded as positive evidence for Phanerozoic age regardless of co-occurring body fossils. Other suggestions strongly dispute the concept of the formal Proterozoic–Cambrian and Precambrian–Phanerozoic boundary. Carbon isotope excursions and radiometric datings for the Nama Group do not help to calibrate precisely the temporal extent of the Fish River Subgroup. Fossil content, sequence stratigraphy and inferred depositional developments suggest that this subgroup represents only a short period of late orogenic molasse sedimentation during the early sub-trilobitic Early Cambrian.
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Moore, Shawn A., Lauren P. Birgenheier, Matthias D. Greb, Daniel Minisini, Maísa Tunik, and Julieta Omarini. "Facies heterogeneity and source potential of carbonate-mudstone-dominated distal ramp deposits, Agrio Formation, Neuquén Basin, Argentina." Journal of Sedimentary Research 90, no. 5 (May 7, 2020): 533–70. http://dx.doi.org/10.2110/jsr.2020.25.
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ABSTRACT The carbonate-mudstone-dominated Lower Cretaceous Agrio Formation is the youngest marine source rock of the hydrocarbon-prolific Neuquén Basin in Argentina, yet its facies variability and unconventional hydrocarbon potential remains relatively understudied. Detailed studies of mudstone facies variability in thick, carbonate mudstone successions deposited largely below storm wave base (i.e., chalk–marl, black shale, limestone), like the Agrio Formation, are rare and instead commonly focus on biostratigraphy or organic geochemistry alone. A continuous northern section of the Agrio Formation and a southern composite section of the lower Pilmatué and middle Avilé members, totaling ∼ 1,200 m of outcrop, were measured. From these measured sections, programmed pyrolysis (n = 339 samples), X-ray diffraction (XRD; n = 69), and thin sections (n = 69) were used to develop a high-resolution integrated macrofacies and microfacies scheme. The four most volumetrically abundant facies include detrital-quartz-silt-bearing fine mudstone (facies 1), radiolarian-bearing calcareous fine mudstone (facies 2), detrital-quartz-silt- and shell-bearing calcareous fine mudstone (facies 3), and calcareous wackestone (facies 4). All four facies are volumetrically dominated by carbonate mud matrix (i.e., micrite) that represents either 1) original pelagic coccolithophore deposition modified by diagenesis, 2) transported carbonate mud (i.e., bottom currents like contour currents or sediment gravity flows), or 3) a combination of both. Outcrop observations, XRD mineralogic trends, and petrographic variations in grain composition between detrital quartz silt, radiolarian and microfossil to macrofossil content (mainly benthic foraminifera and bivalves) distinguish the four mudstone facies. The facies scheme indicates distinctly more heterogeneous and current-influenced sedimentation in the downdip sub-storm wave base than previously described in the Agrio and in carbonate-dominated basinal settings in general. A depositional model is proposed for further testing that may prove valuable towards re-evaluating basinal carbonate mudstone successions worldwide. Utilizing TOC, S2, and HI value cutoffs, this study defines five discrete stratigraphic packages in the Agrio Formation that have the highest source potential, collectively totaling ∼ 140 m thick. The novel integration of macrofacies and microfacies analysis, stratigraphy, and a geochemical analysis allow both depositional insights and the assessment of a potential source rock. The study adds to a growing body of literature on 1) carbonate ramp (or slope) to basinal processes and 2) facies models for organic-rich, carbonate-dominated mudstone successions that are unconventional hydrocarbon systems.
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Cherchi, Antonietta, Nicoletta Mancin, Lucien Montadert, Marco Murru, Maria Teresa Putzu, Francesco Schiavinotto, and Vladimiro Verrubbi. "The stratigraphic response to the Oligo-Miocene extension in the western Mediterranean from observations on the Sardinia graben system (Italy)." Bulletin de la Société Géologique de France 179, no. 3 (May 1, 2008): 267–87. http://dx.doi.org/10.2113/gssgfbull.179.3.267.
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Abstract The Sardinian Cainozoic rifted basin is a useful model for studying the stratigraphic response to the Oligo-Miocene structural extension in the western Mediterranean because it allows precise observations on the relationship between sedimentation and normal faulting based on outcrops and seismic reflection data. The purpose of this paper, essentially of stratigraphic nature is to propose a chronology as precise as possible of the tectonic events and of the sedimentary formations. Indeed the tectono-sedimentary framework is complex, characterized by an extreme facies variability, from continental to marginal transitional and to marine environments (shallow-water, hemipelagic). Rifting, active calc-alkaline volcanism and sea-level changes caused rapid physiographical evolution, which controlled progressive marine ingression. New chronobiostratigraphical data presented in this paper allow correlating the sequences, defining their environment and depth of deposition and specifying precisely the timing of pre-, syn-, and post-rift stages in the Oligo-Miocene graben system. In southwestern Sardinia during the middle-late Eocene, after the Pyrenean phase, a continental graben (Cixerri), W-E oriented, preceded the Oligo-Miocene extension, which reactivated inherited Eocene and Palaeozoic faults. The calc-alkaline volcanic activity ranging from 32 to 13 Ma, provides a good estimate for the time span of the west-dipping Apenninic subduction responsible for the continental extension and the oceanic accretion in the western Mediterranean. In Sardinia the Oligo-Miocene extensional tectonics started in a continental environment, preceding the earliest calc-alkaline volcanic products (32 Ma). The marine ingression is dated to the late Chattian-Aquitanian interval and corresponds to a rapid deepening of the Oligo-Miocene graben system of tectonic origin. The end of the rifting i.e. the end of normal faulting activity is pre-middle Burdigalian in age. When Sardinia was in the post-rift stage, extension continued until late Burdigalian – Langhian in the Algero-Provençal basin with oceanic accretion and rotation of the Corsica-Sardinia block (CSB).
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DARABI, M. H., and J. D. A. PIPER. "Palaeomagnetism of the (Late Mesoproterozoic) Stoer Group, northwest Scotland: implications for diagenesis, age and relationship to the Grenville Orogeny." Geological Magazine 141, no. 1 (January 2004): 15–39. http://dx.doi.org/10.1017/s0016756803008148.
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The Stoer is the lowest of three groups comprising the Torridonian Supergroup, a clastic succession deposited late in Mesoproterozoic times on the (Lewisian) metamorphic foreland to the Caledonian Orogen in northwest Scotland. This study reports a palaeomagnetic, rock magnetic and magnetic fabric investigation through the full stratigraphic thickness of the succession. A primary magnetic fabric of sedimentary origin defines current flow from a westerly veering to northwesterly source. Rock magnetic studies identify the presence of both magnetite and hematite in these sediments. Magnetite is apparently of primary detrital origin whilst the hematite probably results mostly from early diagenesis in an environment of restricted chemical weathering. Palaeomagnetic study of sedimentary slumps shows that magnetic remanence post-dates deposition but was probably fixed by early dewatering and lithification because slumped blocks of Stoer in basal Torridon Group sediments preserve a primary remanence. Tilt adjustment, although inconclusive, also implies that magnetic remanence is older than pre-Torridian Group tectonic deformation. The lower part of the Stoer succession shows a progressive increase of magnetic inclination with shallower components resident in magnetite and steeper components in hematite. The succession above the Stac Fada Member has the steepest magnetic inclination and shows no significant difference between magnetite and hematite component directions. The inferred time sequence of palaeopoles coincides with the Gardar palaeomagnetic track (∼ 1250–1130 Ma) at 1180 Ma, conforming to a Pb–Pb determination of 1199±70 Ma. The Stoer Group was fully lithified and deformed before deposition of the Torridon Group at ∼ 1030 Ma because it contains no vestige of the range of Caledonian and later overprints found extensively in the latter. Sedimentation and lithification of the Stoer Group are therefore linked with a phase of extensional tectonism at 1200–1150 Ma and deformation is attributed to a culminating phase of deformation in the nearby Grenville Belt at ∼ 1100 Ma.
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CORDANI, UMBERTO G., ANA M. MIZUSAKI, KOJI KAWASHITA, and ANTONIO THOMAZ-FILHO. "Rb–Sr systematics of Holocene pelitic sediments and their bearing on whole-rock dating." Geological Magazine 141, no. 2 (March 2004): 233–44. http://dx.doi.org/10.1017/s0016756803008616.
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In many cases, when dealing with argillaceous fine-grained sedimentary rocks, the isotopic ages obtained from Rb–Sr whole-rock isochron calculations are of geological significance, despite the fact that the initial conditions of Sr isotopic homogenization are not fulfilled. To explain this, a mechanical mixing during deposition has been suggested, leading to an aggregate of mixed material with fairly uniform 87Sr/86Sr values, whatever Rb/Sr ratio is found in the analysed samples. This investigation of the behaviour of Rb and Sr during sedimentation and early diagenesis, involves study of more than 60 samples of fine-grained recent sediments from selected coastal localities of Brazil. The results indicate that pelitic samples from some recent to present-day transitional or shallow marine environments, such as the Jacarepaguá tidal flat and the Amazonas River mouth, where halmirolysis could have occurred, may produce nearly horizontal best-fit lines in a Rb–Sr isochron diagram. Moreover, the initial isotopic 87Sr/86Sr ratios appear to be well above 0.710. In open marine environments, such as the Campos Basin, where sampling was spread over more than 100 metres, exchanges between the argillaceous sediments and seawater potentially happen at low temperature, inducing a reduction of the 87Sr/86Sr isotopic composition of the sediments to nearly 0.710. An almost horizontal best-fit line is produced for the entire stratigraphic section, independent of the sedimentation age. We believe that in similar environments such ‘zero age isochrons’ are maintained for some time, testifying to exchanges between the sediment and the interstitial fluids, before the onset of burial diagenesis. The above described studies on fine-grained and recent argillaceous sediments seem to confirm the production of horizontal best-fit lines in isochron diagrams, justifying the application of the Rb–Sr whole-rock method to pelitic sedimentary rocks. The nature of the material is critical. The pelitic sediments to be analysed should contain only very limited amounts of coarse clastic material (especially feldspars and mica fragments) and consist mainly of fine clay minerals in which smectites, illite and mixed layers illite–smectite largely predominate.
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Ślączka, Andrzej, M. Gasiñski, Marta Bąk, and Godfrid Wessely. "The clasts of Cretaceous marls in the conglomerates of the Konradsheim Formation (Pöchlau quarry, Gresten Klippen Zone, Austria)." Geologica Carpathica 60, no. 2 (April 1, 2009): 151–64. http://dx.doi.org/10.2478/v10096-009-0010-7.
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The clasts of Cretaceous marls in the conglomerates of the Konradsheim Formation (Pöchlau quarry, Gresten Klippen Zone, Austria)Investigations were carried out on foraminiferids and radiolaria from redeposited clasts within the conglomerates of the Konradsheim Formation (Gresten Klippen Zone) in the area of the Pöchlau hill, east of Maria Neustift. These shales and marls are of Middle to Late Jurassic and Early Cretaceous age. In the latter clasts, foraminiferal assemblages withTritaxiaex gr.gaultinaas well as radiolaria speciesAngulobracchia portmanniBaumgartner,Dictyomitra communis(Squinabol),Hiscocapsa asseni(Tan),Pseudodictyomitra lodogaensisPessagno,Pseudoeucyrtis hanni(Tan),Rhopalosyringium fossile(Squinabol) were found. In one block from the uppermost part of the sequence there is an assemblage withCaudammina(H)gigantea, Rotalipora appenninicaandGlobotruncana bulloides.However, the brecciated character of this block and occurrence near a fault suggest that it was probably wedged into the conglomerates of the Konradsheim Formation during tectonic movements. In pelitic siliceous limestones below the Konradsheim Limestone radiolarian assemblages of Middle Callovian to Early Tithonian age were found. They enable correlation with the Scheibbsbach Formation. In a marly sequence, above the conglomeratic limestone, the foraminiferal assemblages contain taxa from mid-Cretaceous up to Paleocene. The present biostratigraphic investigation confirmed the previous stratigraphic assignments and imply clearly that the sedimentation of deposits similar to the Konradsheim Formation also occurred at the end of the Early Cretaceous and deposition of conglomeratic limestones within the Gresten Klippen Zone, and especially within the Konradsheim Formation, was repeated several times during the Late Jurassic and Early Cretaceous.
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Dechesne, Marieke, Ellen D. Currano, Regan E. Dunn, Pennilyn Higgins, Joseph H. Hartman, Kevin R. Chamberlain, and Christopher S. Holm-Denoma. "A new stratigraphic framework and constraints for the position of the Paleocene–Eocene boundary in the rapidly subsiding Hanna Basin, Wyoming." Geosphere 16, no. 2 (January 16, 2020): 594–618. http://dx.doi.org/10.1130/ges02118.1.
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Abstract The Paleocene–Eocene strata of the rapidly subsiding Hanna Basin give insights in sedimentation patterns and regional paleogeography during the Laramide orogeny and across the climatic event at the Paleocene–Eocene Thermal Maximum (PETM). Abundant coalbeds and carbonaceous shales of the fluvial, paludal, and lacustrine strata of the Hanna Formation offer a different depositional setting than PETM sections described in the nearby Piceance and Bighorn Basins, and the uniquely high sediment accumulation rates give an expanded and near-complete record across this interval. Stratigraphic sections were measured for an ∼1250 m interval spanning the Paleocene–Eocene boundary across the northeastern syncline of the basin, documenting depositional changes between axial fluvial sandstones, basin margin, paludal, floodplain, and lacustrine deposits. Leaf macrofossils, palynology, mollusks, δ13C isotopes of bulk organic matter, and zircon sample locations were integrated within the stratigraphic framework and refined the position of the PETM. As observed in other basins of the same age, an interval of coarse, amalgamated sandstones occurs as a response to the PETM. Although this pulse of relatively coarser sediment appears related to climate change at the PETM, it must be noted that several very similar sandstone bodies occur with the Hanna Formation. These sandstones occur in regular intervals and have an apparent cyclic pattern; however, age control is not sufficient yet to address the origin of the cyclicity. Signs of increased ponding and lake expansion upward in the section appear to be a response to basin isolation by emerging Laramide uplifts.
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Jelsma, H. A., R. W. Nesbitt, and C. M. Fanning. "Exploring our current understanding of the geological evolution and mineral endowment of the Zimbabwe Craton." South African Journal of Geology 124, no. 1 (March 1, 2021): 279–310. http://dx.doi.org/10.25131/sajg.124.0020.
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Abstract A.M. Macgregor (1888-1961) is remembered for his enormous contribution to geology. His maps changed the course of geological thinking in southern Africa. Following in his footsteps we examine aspects of our current understanding of the geological evolution of the Zimbabwe Craton and, using new SHRIMP U-Pb ages of zircons from felsic volcanic and plutonic rocks from northern Zimbabwe and unpublished data related to the seminal paper by Wilson et al. (1995), a synthesis is proposed for the formation of the Neoarchaean greenstones. The data suggest marked differences (lithostratigraphy, geochemistry and isotope data, mineral endowment and deformational history), between Eastern and Western Successions, which indicate fundamentally different geodynamic environments of formation. The Eastern Succession within the southcentral part of the craton, largely unchanged in terms of stratigraphy, is reminiscent of a rift-type setting with the Manjeri Formation sediments and overlying ca. 2 745 Ma Reliance Formation komatiite magmatism being important time markers. In contrast, the Western Succession is reminiscent of a convergent margin subduction-accretion system with bimodal mafic-felsic volcanism and accompanying sedimentation constrained to between 2 715 and 2 683 Ma. At ca. 2 670 Ma, a tectonic switch likely marks the onset of deposition of Shamvaian felsic volcanism and sedimentation. The Shamvaian resembles pull-apart basin successions and is dominated by deposition of a coarse clastic sedimentary succession, with deposition likely constrained to between 2 672 and 2 647 Ma. The late tectonic emplacement of small, juvenile multiphase stocks, ranging in composition from gabbroic to granodioritic was associated with gold ± molybdenum mineralisation. Their emplacement at 2 647 Ma provides an upper age limit to the timespan of Shamvaian deposition. Amongst the youngest granites are the extensive, largely tabular late- to post-tectonic ca. 2 620 to 2 600 Ma Chilimanzi Suite granites. These granites are characterised by evolved isotopic systems and have been related to crustal relaxation and anatexis following deformation events. After their emplacement, the Zimbabwe Craton cooled and stabilised, with further deformation partitioned into lower-grade, strike-slip shear zones, and at ca. 2 575 Ma the craton was cut by the Great Dyke, its satellite dykes and related fractures.
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Dey, Sumit, Prabir Dasgupta, Kaushik Das, and Abdul Matin. "Neoproterozoic Blaini Formation of Lesser Himalaya, India: Fiction and Fact." GSA Bulletin 132, no. 11-12 (March 16, 2020): 2267–81. http://dx.doi.org/10.1130/b35483.1.
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Abstract The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueous debris flows is indicated by the associated deposits of entrained turbidity currents. The limestone also bears the signature of claciturbidites. The appearance of diamictite bodies and associated limestone in two distinct levels is not a stratigraphic disposition; on the contrary, the deposits were dislocated and repeated by two successive regional thrust faults. The Chemical Index of Alteration (CIA) values of the light brown shale and the matrix of the diamictites indicate that these sediments formed through prolonged subaerial weathering. The events leading up to development of the rift system and evidence of prolonged weathering within the basin-fill sediments are consistent with supercontinental break up, the prologue of Snowball Earth.
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Moynihan, David P., Justin V. Strauss, Lyle L. Nelson, and Colin D. Padget. "Upper Windermere Supergroup and the transition from rifting to continent-margin sedimentation, Nadaleen River area, northern Canadian Cordillera." GSA Bulletin 131, no. 9-10 (March 8, 2019): 1673–701. http://dx.doi.org/10.1130/b32039.1.
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AbstractNeoproterozoic–Cambrian rocks of the Windermere Supergroup and overlying units record the breakup of Rodinia and formation of the northwestern Laurentian ancestral continental margin. Understanding the nature and timing of this transition has been hampered by difficulty correlating poorly dated sedimentary successions from contrasting depositional settings across Mesozoic structures. Here we present new litho- and chemo-stratigraphic data from a Cryogenian–lower Cambrian succession in east-central Yukon (Canada), establish correlations between proximal and distal parts of the upper Windermere Supergroup and related strata in the northern Canadian Cordillera, and consider implications for the formation of the northwestern Laurentian margin. The newly defined Nadaleen Formation hosts the first appearance of Ediacaran macrofossils, while the overlying Gametrail Formation features a large negative carbon isotope anomaly with δ13Ccarb values as low as –13‰ that correlates with the globally developed Shuram-Wonoka anomaly. We also define the Rackla Group, which includes the youngest (Ediacaran) portions of the Windermere Supergroup in the northern Cordillera. The top of the Windermere Supergroup is marked by an unconformity above the Risky Formation that passes into a correlative conformity in the Nadaleen River area. This surface has been interpreted to mark the top of the rift-related succession, but we draw attention to evidence for tectonic instability through the early-middle Cambrian and argue that the transition from rifting to post-rift thermal subsidence is marked by a widespread unconformity that underlies upper Cambrian carbonate rocks. This is younger than the interpreted age of the rift to post-rift transition elsewhere along the ancestral western Laurentian continental margin.
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RYAN, PAUL D., and N. JACK SOPER. "Modelling anatexis in intra-cratonic rift basins: an example from the Neoproterozoic rocks of the Scottish Highlands." Geological Magazine 138, no. 5 (September 2001): 577–88. http://dx.doi.org/10.1017/s0016756801005696.
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The Neoproterozoic metasediments of northwestern Scotland were deformed during the 470 Ma Grampian orogeny. Their pre-Ordovician history has proved difficult to elucidate, due to conflicting evidence. While the stratigraphic record indicates deposition in intracontinental rift basins associated with the break-up of Rodinia, isotopic dates in the range 870–780 Ma from granite gneiss, early pegmatites and metamorphic garnets have been attributed to a Neoproterozoic ‘Knoydartian’ orogeny. Stratigraphic evidence for this orogeny is lacking, and it is not represented elsewhere on the Laurentian margin. An alternative interpretation is that much of the Knoydartian history can be related to extensional, not collisional processes. Specifically, it has been proposed that the 870 Ma West Highland granite gneiss that is intruded into the Moine rocks of northwestern Scotland is not the product of synorogenic anatexis but represents a suite of granite sheets that were generated during extensional rifting and were subsequently deformed and gneissified during the Grampian orogeny. This contribution presents numerical models of extension-related anatexis to test this hypothesis.We first develop a methodology to estimate stretch values and the duration of extension and thermal subsidence for the Moine rift basins. A thermal model is then constructed for these basins using transient finite element techniques. This model shows that lithospheric extension sufficient to produce major rift basins, even if they are filled with feldspathic sediment with Neoproterozoic heat production characteristics, will not lead to crustal anatexis. However, a regional suite of mafic dykes in the more easterly (Loch Eil) Moine suggests that stretching led to decompression melting of the mantle. We model the effect of advecting heat into the extending lithosphere by the introduction of a modest volume of basaltic magma, and show that substantial granitic melt can be generated in the basement beneath the basin. The amount of anatexis varies with the locus of basalt intrusion. Some 30% more granite is generated by dykes emplaced along basin-bounding faults than by either dykes emplaced beneath the centre of the basin, or by underplating sills. The spatial distributions of the West Highland gneiss and of the mafic suite are compatible with this finding. There is clear field evidence that the protolith of the West Highland gneiss consisted of a suite of pre-tectonic granite sheets, and our modelling demonstrates that they could have been generated during the later stages of extensional rifting and Moine sedimentation.
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Penn-Clarke, Cameron R., Bruce S. Rubidge, and Zubair A. Jinnah. "Eifelian–Givetian (Middle Devonian) high-paleolatitude storm- and wave-dominated shallow-marine depositional systems from the Bidouw Subgroup (Bokkeveld Group) of South Africa." Journal of Sedimentary Research 89, no. 11 (November 27, 2019): 1140–70. http://dx.doi.org/10.2110/jsr.2019.61.
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ABSTRACT The sedimentology of the Eifelian–Givetian (Middle Devonian) Bidouw Subgroup in the Clanwilliam Sub-basin of South Africa has been reassessed. Four distinct lithofacies associations are recognized (A–D) and are representative of the deposits of offshore (Os), offshore transition zone to distal lower shoreface (OTZ-dLSF), proximal lower shoreface (pLSF), and upper shoreface–beach (USF-Beach) paleoenvironments. These paleoenvironments are arranged as several T-R-controlled storm- and wave-dominated shallow-marine depositional systems. The presence of storm- and wave-dominated shallow-marine depositional systems in the Bidouw Subgroup, as well as the preceding Emsian–Eifelian (Early–Middle Devonian) Ceres Subgroup provides an alternative explanation to storm- and wave-dominated delta and mixed wave- and-tide-dominated delta models that have previously been proposed for the Bokkeveld Group. Sequence-stratigraphic analysis of the Bidouw Subgroup suggests that although sedimentation occurred during two large-scale second-order transgressive events, the succession was predominantly regressive. Third-order and fourth-order transgressive–regressive (T-R) sequences are more numerous with respect to the preceding Ceres Subgroup, suggesting that the driver for T-R cyclicity and relative sea-level change was more active during the Eifelian–Givetian than in the Emsian–Eifelian of South Africa. These data are important since relative sea-level change and its effects on paleoenvironmental change at high paleolatitudes during the Devonian Period are poorly known.
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Stratton, Laurel E., and Gordon E. Grant. "Autopsy of a reservoir: Facies architecture in a multidam system, Elwha River, Washington, USA." GSA Bulletin 131, no. 11-12 (April 2, 2019): 1794–822. http://dx.doi.org/10.1130/b31959.1.
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AbstractThe 2011–2014 removal of two large dams on the Elwha River, Washington State, the largest dam removal yet completed globally, created extensive cutbank exposures of reservoir sediments, allowing the first characterization of the facies architecture of sediments through direct observation in reservoirs worldwide and providing an unparalleled opportunity to assess the relationship between environmental influences, such as changes in sediment supply, and their expression in the stratigraphic record. Using a combination of facies description from observation of 49 measured sections and >100 exposures and analysis of digital elevation models and historic aerial photographs, we delineated the characteristic depositional zones of each reservoir and mapped the evolution of the subaerial delta over the life span of the reservoir. Former Lake Mills, the younger, upstream reservoir, was characterized by a tripartite, subaerial Gilbert-style delta that prograded >1 km into the main reservoir from 1927 to 2011. Sediments were composed of coarse-grained topset beds, steeply dipping foreset beds, and a fine-grained, gently dipping prodelta. While individual event horizons were discernible in fine-grained sediments of former Lake Mills, their number and spacing did not correspond to known drawdown or flood events. Former Lake Aldwell, impounded from 1913 to 2011, was initially defined by the rapid progradation of a Gilbert-style, subaerial delta prior to the upstream completion of Glines Canyon Dam. However, the 1927 closure of Glines Canyon Dam upstream caused the delta to evolve to a fine-grained, mouth-bar–type delta indicative of low, finer-grained sediment. This evolution, combined with a previously unrecognized landslide deposit into the upper delta plain, suggests that understanding the exogenic influences on reservoir sedimentation is critical to interpretation and prediction of the sedimentation within individual systems.
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Fambrini, Gelson Luís, Diego da Cunha Silvestre, José Acioli Bezerra de Menezes-Filho, Ian Cavalcanti da Costa, and Virgínio Henrique de Miranda Lopes Neumann. "Architectural and facies characterization of the Aptian fluvial Barbalha Formation, Araripe Basin, NE Brazil." Geological Society, London, Special Publications 488, no. 1 (2019): 119–50. http://dx.doi.org/10.1144/sp488-2017-275.
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AbstractThe Aptian Barbalha Formation records the beginning of the post-rift stage of the Araripe Basin. It consists predominantly of sandstones and mudstones interbedded with thin layers of bituminous black shales and conglomerates. The depositional and architectural features of the alluvial succession of the Barbalha Formation were characterized by detailed study and descriptions of the selected outcrops and analysis of well core data. In this study, two main depositional sequences were identified. The lower depositional sequence is more than 100 m thick and comprises a vertical facies succession composed of amalgamated, multistorey, braided fluvial channel sandstone bodies overlain by a widespread lacustrine black shale up to 10 m thick. The lacustrine black shales–carbonate mixed interval is known as the Batateira Beds and constitutes a regionally important stratigraphic correlation marker in the basin. This interval records the establishment of a large lake that experienced severe water-level fluctuations and anoxic events. The upper depositional sequence is 60–95 m thick, and mainly consists of thin, yellowish, medium- to fine-grained sandstones and variegated shales. The upper sequence rests unconformably on the lacustrine black shales of the Batateira Beds. Thin and discontinuous conglomerate beds at the base of the upper sequence laterally grade into coarse-grained sandstones. These coarse-grained sandstones are overlain by interbedded sandstones and mudstones organized in fluvial cycles. The upper and lower sequences of the Barbalha Formation are separated by an erosive unconformity, traceable throughout the study area, formed during a period of stratigraphic base-level lowering. This surface marks a change in the lower sequence from a dominantly fluvial depositional style, with amalgamated multistorey braided fluvial channel sand bodies, to a lacustrine system in the top to an eminently fluvial sedimentation, which in the basal section comprises amalgamated, multistorey, braided fluvial channel sand bodies, and in the superior section the amalgamated fluvial channels are overlain by floodplain and overbank sandstone bodies with fixed fluvial channel deposits, interpreted as a suspended-load-dominated fluvial system in the upper sequence. This change in the depositional style is accompanied by a reduction in grain size and a change in the fluvial regime, suggesting that the drainage system was restructured due to tectonic movements in the basin and climatic variations. In addition to the restructuring of the drainage basin, the characteristics of the discharge of the river system have changed, probably because of the more humid climatic conditions that dominated during the deposition of the upper sequence. The fluvial deposition in the lower sequence is associated with more ephemeral river systems, while the facies architecture of the upper sequence is associated with perennial systems and is suggestive of a suspended-load-dominated fluvial system. This fluvial system is capped by lacustrine deposits of the Crato Formation. The upper sequence grades upwards into the Crato Formation. The boundary between these two units is delineated by the presence of greenish calciferous shales that are covered by lacustrine laminated limestones and shales of Neoaptian age. Palaeocurrent readings from the fluvial deposits of both sequences display a consistent palaeoflow to the SE. Sedimentological and palaeontological evidence indicates a tectonic control on sedimentation and humid to subhumid climate conditions.
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Hager, H., K. Rescher, A. Verstraelen, S. Leroi, M. van den Bosch, A. Abraham, E. Nickel, and R. J. W. van Leeuwen. "The geometry of the Rupelian and Chattian depositional bodies in the Lower Rhine district and its border area: implications for Oligocene lithostratigraphy." Bulletin of the Geological Society of Denmark 45 (September 25, 1998): 53–62. http://dx.doi.org/10.37570/bgsd-1998-45-06.
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Three profiles are constructed through the Oligocene succession of the borderland between Belgium, Germany and the Netherlands. The profiles illustrate the geometric relationships between Rupelian and Chattian successions and the lateral and vertical variations within the Rupelian and Chattian deposits. The end-Rupelian profile between Central Belgium and the Achterhoek area in the Netherlands shows a rather uniform thickness distribution. This is in sharp contrast to the fault controlled sedimentation during the Chattian as represented on an end-Chattian profile between the same areas. Within the Chattian succession several lithostratigraphic units can be identified and correlated using a dense net of geophysical well logs. Remarkably similar subdivisions are found in the different tectonic blocks, suggesting eustatic sea-level fluctuations. In the central part of the subsiding area the Chattian deposits are largely continental to deltaic. Laterally,these deposits developed into marine glauconitic sediments. The end-Chattian profile between Bonn and Asten in the Netherlands runs approximately parallel with the subsidence axis. The cyclicity expressed by facies alternations due to a periodically shifting coastline can be correlated over the different blocks again suggesting the involvement of eustatic controls. On this last profile, an anomalous geometry is due to SE-NW stress-induced movements along the Variscan Aachen overthrust.The three lithological profiles are meant to represent a frame for formal stratigraphic subdivisions and nomenclature.
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Dobbs, Stephen C., Nancy R. Riggs, Kathleen M. Marsaglia, Carlos M. González-León, M. Robinson Cecil, and M. Elliot Smith. "The Permian Monos Formation: Stratigraphic and detrital zircon evidence for Permian Cordilleran arc development along the southwestern margin of Laurentia (northwestern Sonora, Mexico)." Geosphere 17, no. 2 (February 25, 2021): 520–37. http://dx.doi.org/10.1130/ges02320.1.
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Abstract The southwestern margin of Laurentia transitioned from a left-lateral transform margin to a convergent margin by middle Permian time, which initiated the development of a subduction zone and subsequent Cordilleran arc along western Laurentia. The displaced Caborca block was translated several hundred kilometers from southern California, USA, to modern Sonora, Mexico, beginning in Pennsylvanian time (ca. 305 Ma). The Monos Formation, a ∼600-m-thick assemblage of mixed bioclastic and volcaniclastic units exposed in northwestern Sonora, provides lithostratigraphic, petrographic, and geochronologic evidence for magmatic arc development associated with subduction by middle Permian time (ca. 275 Ma). The Monos Formation was deposited in a forearc basin adjacent to a magmatic arc forming along the southwestern Laurentian margin. Detrital zircon U-Pb geochronology suggests that Permian volcanic centers were the primary source for the Monos Formation. These grains mixed with far-traveled zircons from both Laurentia and Gondwana. Zircon age spectra in the Monos Formation are dominated by a ca. 274 Ma population that makes up 65% of all analyzed grains. The remaining 35% of grains range from 3.3 Ga to 0.3 Ma, similar to age spectra from Permian strata deposited in the Paleozoic sequences in the western continental interior. An abundance of Paleozoic through early Neoproterozoic ages suggests that marginal Gondwanan sources from Mexico and Central America also supplied material to the basin. The Monos Formation was deposited within tropical to subtropical latitudes, yet faunal assemblages are biosiliceous and heterotrophic. The lack of photozoan assemblages suggests that cold-water coastal upwelling combined with sedimentation from the Cordilleran arc and Laurentian continent promoted conditions more suitable for fauna resilient to biogeochemically stressed environments. We propose that transform faulting and displacement of the Caborca block ceased by middle Permian time and a subduction zone developed along the southwestern margin of Laurentia as early as early Permian time. The Monos basin developed along the leading edge of the continent as a magmatic arc developed, and facies indicate a consistent shoaling trend over the span of deposition.
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WENDT, JOBST, BERND KAUFMANN, ZDZISLAW BELKA, CHRISTIAN KLUG, and STEFAN LUBESEDER. "Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara)." Geological Magazine 143, no. 3 (March 30, 2006): 269–99. http://dx.doi.org/10.1017/s0016756806001737.
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The Ahnet and Mouydir regions of southern Algeria are part of one of the world's largest, almost undeformed exposures of Palaeozoic rocks which exemplify a hitherto poorly known early Variscan development of a Devonian basin and ridge system. This area includes a series of intracratonic basins along the northern margin of the West African Craton which consists (from W to E) of the Reggane Basin, Azel Matti Ridge, Ahnet Basin, Foum Belrem Ridge and Mouydir Basin. The depositional and palaeogeographic interpretation is based on 71 sections in this region, which for the first time were biostratigraphically calibrated by means of conodonts, goniatites and brachiopods. The structural evolution during Devonian times was probably controlled by reactivation of ancient N–S- to NW–SE-running faults in the Precambrian basement, which caused differential subsidence and uplift of a previously largely unstructured siliciclastic shelf. A hiatus during Emsian times indicates widespread emergence during this interval. The entire area was flooded during the earliest Eifelian, when the first vestiges of the Azel Matti Ridge become evident by stratigraphic condensation. The palaeogeographic differentiation is most apparent during the Givetian, when a shoal with reduced carbonate sedimentation was established on the Azel Matti Ridge passing towards the west and east into basinal environments of the Reggane and Ahnet basins, respectively. The Foum Belrem Ridge is distinguished by increased subsidence during the early Givetian and by revived uplift during the late Givetian. In the Mouydir Basin further east, up to 1000 m of shales were deposited during the Givetian. The early Frasnian is marked by the ubiquitous sedimentation of black shales and bituminous styliolinites. These lithologies occur repeatedly already during the Middle Devonian and document intermittent anoxic conditions. The basin and ridge topography is levelled by the shallowing-up sequence of up to 1400 m thick upper Frasnian and Famennian shales which grade into a deltaic sequence of uppermost Famennian/Tournaisian sandstones. The up to now only vaguely discriminated lithostratigraphic formations of the Devonian have been biostratigraphically defined in suitable type sections.
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Gibson, Timothy M., Sarah Wörndle, Peter W. Crockford, T. Hao Bui, Robert A. Creaser, and Galen P. Halverson. "Radiogenic isotope chemostratigraphy reveals marine and nonmarine depositional environments in the late Mesoproterozoic Borden Basin, Arctic Canada." GSA Bulletin 131, no. 11-12 (April 24, 2019): 1965–78. http://dx.doi.org/10.1130/b35060.1.
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Abstract The ca. 1050 Ma Bylot Supergroup in Arctic Canada is one of the best-preserved archives of late Mesoproterozoic geochemistry and biology and offers evidence that this period of Earth history may have been more biogeochemically dynamic than previously appreciated. The Bylot Supergroup was deposited in the Borden Basin and is the most thoroughly studied stratigraphic succession from a series of broadly contemporaneous late Mesoproterozoic intracratonic basins known as the Bylot basins. This ∼6-km-thick mixed carbonate-siliciclastic succession has undergone minimal postdepositional deformation and is now exposed on Baffin and Bylot Islands, Nunavut, Canada. Deep-water and tidally influenced carbonate facies, traditionally interpreted as marine, have yielded important insights into the evolution of Proterozoic seawater chemistry; however, more recent studies indicate that the Borden Basin was restricted marine or lacustrine for portions of its depositional history. Here, we present new multiproxy radiogenic isotope chemostratigraphic data spanning the Bylot Supergroup. A comparison of stratigraphic trends in radiogenic isotope data from hydrogenous (black shale 187Os/188Os and limestone 87Sr/86Sr) and detrital (whole-rock mudstone 143Nd/144Nd) sedimentary phases elucidates the complex hydrologic history of the Borden Basin and reconciles these disparate interpretations. Episodic coupling and decoupling between the composition of basin waters (from Os and Sr isotopes) and the local weathering input to the basin (from Nd isotopes) indicate that depositional environments within the Borden Basin fluctuated between marine and nonmarine (i.e., lacustrine). Variations in basin hydrology controlled secular sedimentation patterns through changes in basin water chemistry. These interpretations help to characterize the environment in which the early red algal fossil Bangiomorpha pubescens evolved. Episodically restricted epeiric seaways, such as within the Borden Basin, were relatively widespread within Rodinia and may have exerted unique selective pressures on eukaryotic evolution in the Mesoproterozoic Era. Hydrogenous and detrital radiogenic isotope chemostratigraphy, as implemented in this study, may provide a useful paleoenvironmental framework for future paleontological studies aimed at testing the role of freshwater environments in eukaryotic evolution. In addition, 87Sr/86Sr compositions from 81 new middle Bylot Supergroup marine limestone samples, calibrated by recent Re-Os geochronology, contribute to the terminal Mesoproterozoic marine 87Sr/86Sr curve. These data display a rise from ∼0.705 to 0.706 that reflects weathering of the active Grenville orogenic belt and demonstrates a global increase in chemical weathering during the amalgamation of Rodinia.
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Pratt, Brian R., and Juan J. Ponce. "Sedimentation, earthquakes, and tsunamis in a shallow, muddy epeiric sea: Grinnell Formation (Belt Supergroup, ca. 1.45 Ga), western North America." GSA Bulletin 131, no. 9-10 (February 15, 2019): 1411–39. http://dx.doi.org/10.1130/b35012.1.
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AbstractInterpreting the deposits of ancient epeiric seas presents unique challenges because of the lack of direct modern analogs. Whereas many such seas were tectonically relatively quiescent, and successions are comparatively thin and punctuated by numerous sedimentary breaks, the Mesoproterozoic Belt Basin of western North America was structurally active and experienced dramatic and continuous subsidence and sediment accumulation. The Grinnell Formation (ca. 1.45 Ga) in the lower part of the Belt Supergroup affords an opportunity to explore the interplay between sedimentation and syndepositional tectonics in a low-energy, lake-like setting. The formation is a thick, vivid, red- to maroon-colored mudstone-dominated unit that crops out in northwestern Montana and adjacent southwestern Alberta, Canada. The mudstone, or argillite, consists of laminated siltstone and claystone, with normal grading, local low-amplitude, short-wavelength symmetrical ripples, and intercalations of thin tabular intraclasts. These intraclasts suggest that the muds acquired a degree of stiffness on the seafloor. Halite crystal molds and casts are present sporadically on bedding surfaces. Beds are pervasively cut by mudcracks exhibiting a wide variety of patterns in plan view, ranging from polygonal to linear to spindle-shaped. These vertical to subvertical cracks are filled with upward-injected mud and small claystone intraclasts. Variably interbedded are individual, bundled, or amalgamated, thin to medium beds of white, cross-laminated, medium- to coarse-grained sandstone, or quartzite. These are composed of rounded quartz grains, typically with subangular to rounded mudstone intraclasts. Either or both the bottoms and tops of sandstone beds commonly show sandstone dikes indicative of downward and upward injection. Both the mudcracks and the sandstone dikes are seismites, the result of mud shrinkage and sediment injection during earthquakes. An origin via passive desiccation or syneresis is not supported, and there is no evidence that the sediments were deposited on alluvial plains, tidal flats, or playas, as has been universally assumed. Rather, deposition occurred in relatively low-energy conditions at the limit of ambient storm wave base. The halite is not from in situ evaporation but precipitated from hypersaline brines that were concentrated in nearshore areas and flowed into the basin causing temporary density stratification. Sandstone beds are not fluvial. Instead, they consist of allochthonous sediment and record a combination of unidirectional and oscillatory currents. The rounded nature of the sand and irregular stratigraphic distribution of the sandstone intervals are explained not by deltaic influx or as tempestites but as coastal sands delivered from the eastern side of the basin by off-surge from episodic tsunamis generated by normal faulting mainly in the basin center. The sands were commonly reworked by subsequent tsunami onrush, off-surge, seiching, and weak storm-induced wave action. Although the Grinnell Formation might appear superficially to have the typical hallmarks of a subaerial mudflat deposit, its attributes in detail reveal that sedimentation and deformation took place in an entirely submerged setting. This is relevant for the deposits of other ancient epeiric seas as well as continental shelves, and it should invite reconsideration of comparable successions.
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Wolfe, Brent, and James T. Teller. "Sedimentation in Ice-Damned Glacial Lake Assiniboine, Saskatchewan, and Catastrophic Drainage Down the Assiniboine Valley." Géographie physique et Quaternaire 49, no. 2 (November 30, 2007): 251–63. http://dx.doi.org/10.7202/033040ar.
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ABSTRACTIce-dammed glacial Lake Assiniboine covered approximately 1500 km2in eastern Saskatchewan at about 11,000 BP. Lithofacies in two cores from the lake basin were identified, correlated, and linked to paleolake strandlines and inflow and outflow channels discerned from aerial photos and surface mapping. Deeper lake stages are reflected by silt and clay varve deposition in the deepest part of the basin, whereas shallower stages are represented by fluctuating grain size and current-generated sedimentary structures in sediments nearer to where influxes of melt-water occurred. The stratigraphie record revealed six lake phases, beginning with a shallow period when water collected in the interlobate area between ice on the Duck Mountain Upland to the east and the Assiniboine Ice Lobe to the west. A rise in lake level to about 495 m occurred as the southern outlet was dammed by ice. After about 85 varve years, waters from the Porcupine Hills Upland to the north flooded into glacial Lake Assiniboine, perhaps as a result of the drainage of an ice marginal lake, causing erosion at the lake's southern outlet and a drop in lake level. A second major influx of water from the Porcupine Hills area, at least 20 varve years later, led to downcutting of the outlet and draining of Lake Assiniboine. Shallow and deep channels, streamlined hills, and scattered boulders adjacent to the now-entrenched Assiniboine valley at the former outlet of glacial Lake Assiniboine suggest that the lake drained catastrophically. Similar geomorphic features at sites downstream along the Assiniboine valley are also indicative of catastrophic flow, although only those areas north of the Qu'Appelle River spillway junction are predominantly attributed to outbursts from glacial Lake Assiniboine.