Journal articles: 'Sandstone Geology, Stratigraphic Sedimentation and deposition'

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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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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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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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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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Branagan, David. "The Desert Sandstone of Australia A Late Nineteenth-Century Enigma of Deposition, Fossils, and Weathering." Earth Sciences History 23, no. 2 (January 1, 2004): 208–56. http://dx.doi.org/10.17704/eshi.23.2.gj680520775h7m27.

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The term "Desert Sandstone" was featured on geological maps and in the literature of Australian geology for more than eighty years from 1872. The name was suggested by Richard Daintree (1832-1878) (1868) for what were later described as "a promiscuous lot of sediments that form a dissected tableland in some of the drier portions of the continent" (Howchin, 1918). The name became current, particularly in Queensland, but there were many problems in mapping the unit, which was at first thought to be of Tertiary age, but then became largely accepted as Late Cretaceous.While some geologists thought the unit was of marine origin, others believed it was aeolian, even partly made of volcanic dust, but most geologists thought it was largely lacustrine. In many areas the rock appeared to be highly silicified, and opinions differed as to the source of silicification—a former covering of basalt, or siliceous hot waters from below?Complications arose when Glossopteris, regarded as a Late Palaeozoic fossil, was found in the "Desert Sandstone," and arguments arose about the possibility of this plant having persisted in Australia until the late Mesozoic.The stratigraphic/palaeontological problems were eventually sorted out by detailed mapping, which showed that there were in fact a number of sandstones of similar appearance but quite different ages. It took longer to realise that the apparent uniformity of sedimentary rocks of different ages was largely the result of weathering, which produced the silicified "duricrust" in many parts of inland Australia.The "Desert Sandstone" played an important part in the unravelling of three important lines of earth history in Australia (and there were even repercussions abroad). These were: (a) sedimentation during the Mesozoic and Cainozoic; (b) the clarification of the temporal range (and lateral extent) of the Glossopteris flora; and (c) the weathering processes that produced some of the characteristic scenery of inland Australia.

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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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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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Mertzanides, Y., E. Kargiotis, and A. Mitropoulos. "GEOLOGICAL AND GEOPHYSICAL DATA OF “EPSILON” FIELD IN PRINOS OIL BASIN." Bulletin of the Geological Society of Greece 43, no. 5 (July 31, 2017): 2257. http://dx.doi.org/10.12681/bgsg.11425.

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The Epsilon field, is located at the centre of Prinos oil basin (N. Aegean, Greece), 11 km NW of the island of Thassos and 4 km NW of the Prinos field, the first productive oil field in the Aegean Sea. The taphrogenetic basin of Prinos has been widely studied, due to its hydrocarbon reservoirs. Extensive geophysical survey, started at early 1970 ‘s, led to a number of drilling jobs, which confirmed the existence of hydrocarbons in the area. The combined geological information, derived from the analysis of lithological, stratigraphic and geochemical data of the basin, suggested a structural and depositional model, strongly related to the Miocene tectonics and sedimentation. The new geophysical and drilling data from Epsilon oil field, are correlated to that already known, completing the model of the basin. Pay zone is found to be below an evaporitic sequence, consisting predominantly of salt, with anhydrite, clay and sandstone intercalations. These upper Miocene aged evaporites extend, varying in thickness, throughout Prinos basin. Reservoir consists mainly of sandstone with intercalations of claystone and trace of siltstone. The geology of the structure and the initial productivity, were positive for further drilling operations in Epsilon field.

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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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Buatois, Luis A., and Francisco J. Medina. "Stratigraphy and depositional setting of the Lagrelius Point Formation from the Lower Cretaceous of James Ross Island, Antarctica." Antarctic Science 5, no. 4 (December 1993): 379–88. http://dx.doi.org/10.1017/s0954102093000513.

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The Lagrelius Point Formation (?Barremian–Aptian) is the basal unit of the Gustav Group and crops out on the north-west coast of James Ross Island. It consists of about 250 m of coarse-grained siliciclastic rocks. The type section of the Lagrelius Point Formation is defined here from just south of Lagrelius Point. The measured section comprises the uppermost 80 m of the unit and mainly consists of clast-supported, boulder, cobble to pebble conglomerates; very coarse to medium-grained sandstones occur rarely. Four sedimentary facies are recognized. A disorganized conglomerate facies (1) is interpreted as having been deposited from non-cohesive debris flows and high density gravelly turbidity currents. Inversely graded conglomerate facies (2) and normally graded to graded stratified conglomerate and pebbly sandstone facies (3) reflect sedimentation from high density gravelly turbidity currents. Massive and parallel stratified sandstone facies (4) is thought to record deposition from high density sandy turbidity currents. Two types of facies assemblages have been recognized. A major channel assemblage, represented by the lower part of the measured section and the minor channel assemblage forming the upper part of the section. The total succession is thought to represent the aggradation of a major submarine braided channel followed by the establishment and subsequent infill of a series of minor channels in a marginal terrace.

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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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Cuitiño, José I., Sergio F. Vizcaíno, M. Susana Bargo, and Inés Aramendía. "Sedimentology and fossil vertebrates of the Santa Cruz Formation (early Miocene) in Lago Posadas, southwestern Patagonia, Argentina." Andean Geology 46, no. 2 (May 31, 2019): 383. http://dx.doi.org/10.5027/andgeov46n2-3128.

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Lago Posadas is located at the foot of the Southern Patagonian Andes, in southwestern Argentina, where the early Miocene Santa Cruz Formation (SCF) shows thick and laterally continuous exposures. This region has been scarcely explored for fossil vertebrates since the first efforts by J.B. Hatcher in 1898-99. In this contribution, we performed sedimentologic and paleontological studies in order to reconstruct depositional environments and the associated fossil vertebrate fauna. Sedimentologic data suggest that the sedimentary record begins with restricted marine-estuarine deposits grading upward to fluvial floodplains and fluvial channels. Extensive floodplains, occasionally interrupted by low-sinuosity, sand-dominated channels, show dominant reddish coloration, moderate to low paleosol development, abundant crevasse splay sandstones and lack of vegetal remains, suggesting deposition in a low gradient, oxygenated setting under elevated sedimentation rates. Vertical stratigraphic trends are subtle, suggesting little paleoenvironmental changes during deposition of the whole SCF in this region. Paleocurrent directions, sandstone composition and paleogeographic reconstructions all indicate that deposition of the SCF was strongly associated to the contemporaneous uplift of the Andes. Fossil vertebrates analyzed are the result of our collecting effort and revision of museum collections. The faunal assemblage includes 31 taxa: 28 mammals and three birds. Mammals belong to the main groups recorded in other areas of the SCF (metatherians, xenarthrans, notoungulates, litopterns, astrapotheres and rodents). The assemblage allows a Santacrucian Age sensu lato assignment for the fauna at Lago Posadas. Taxonomic revisions of several taxa are necessary to further adjust the biostratigraphic significance of this association. The combined record of arboreal, browser and frugivores, on one side, and grazer mammals and rheas, on the other, suggest the presence of both trees and open environments. Frugivores, among primary consumers, and the secondary consumers guild are under-represented due to sample and fossil remain size biases. The sedimentologic and paleontological record of the SCF in Lago Posadas suggests that the uplift of the Southern Patagonian Andes acted as a primary control on basin subsidence and sediment supply, providing a special signature for sub-andean localities. However, previously registered climatic changes are poorly recorded in this study.

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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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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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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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16

Liu, Li, and Daniel F. Stockli. "U-Pb ages of detrital zircons in lower Permian sandstone and siltstone of the Permian Basin, west Texas, USA: Evidence of dominant Gondwanan and peri-Gondwanan sediment input to Laurentia." GSA Bulletin 132, no. 1-2 (May 23, 2019): 245–62. http://dx.doi.org/10.1130/b35119.1.

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Abstract The Permian Basin of west Texas, one of the most economically significant hydrocarbon basins in the United States, formed along the southwest margin of Laurentia in the foreland of the Ouachita-Marathon orogen during the late Paleozoic. While its stratigraphic record temporally coincides with syn- and post-orogenic Ouachita-Marathon sedimentation, sediment provenance, sediment routing and dispersal, and paleo-drainage evolution have remained controversial. This study presents more than 2000 new detrital zircon U-Pb ages from 16 samples across the Permian Basin to elucidate early Permian sediment provenance and basin-fill evolution. The data show that Wolfcampian sandstones are dominated by 950–1070 Ma and 500–700 Ma detrital zircon U-Pb ages, whereas Leonardian sandstones and siltstones are dominated by 500–700 Ma and 280–480 Ma detrital zircon U-Pb ages. Most of these age clusters are not typical Laurentian basement ages, but rather indicative of a southern Gondwanan and peri-Gondwanan sources of Mexico and Central America. This interpretation is corroborated by zircons with peri-Gondwanan and Gondwanan rim-core relationships, as well as major age components of euhedral zircons, matching Maya block basement ages. Regional comparison of these new detrital zircon results with published data from Carboniferous and Permian sedimentary rocks in various terranes of Mexico and Central America, Appalachian foreland basins, Ouachita orogenic belt, midcontinent of United States, and Fort Worth Basin (Texas), indicates that most sediment influx to the Permian Basin during the early Permian (Wolfcampian and Leonardian) was derived from basement or recycled upper Paleozoic strata associated with Gondwanan and peri-Gondwanan terranes in modern Mexico and Central America. North American basements such as the Appalachian Grenville (950–1300 Ma), Granite-Rhyolite (1300–1500 Ma), and Yavapai-Mazatzal (1600–1800 Ma) provinces, appear to have provided only minor amounts of sediment. In light of depositional age constraints, the timing of Marathon-Ouachita collision, and careful detrital zircon U-Pb age spectra comparison, the sediment provenance shift from Wolfcampian to Leonardian points to a diachronous, oblique continent-continent collision between Gondwana/peri-Gondwanan terranes and Laurentia.

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17

Escuder-Viruete, J., Á. Suárez-Rodríguez, J. Gabites, and A. Pérez-Estaún. "The Imbert Formation of northern Hispaniola: a tectono-sedimentary record of arc–continent collision and ophiolite emplacement in the northern Caribbean subduction–accretionary prism." Solid Earth 7, no. 1 (January 15, 2016): 11–36. http://dx.doi.org/10.5194/se-7-11-2016.

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Abstract. In northern Hispaniola, the Imbert Formation (Fm) has been interpreted as an orogenic “mélange” originally deposited as trench-fill sediments, an accretionary (subduction) complex formed above a SW-dipping subduction zone, or the sedimentary result of the early oblique collision of the Caribbean plate with the Bahama Platform in the middle Eocene. However, new stratigraphical, structural, geochemical and geochronological data from northern Hispaniola indicate that the Imbert Fm constitutes a coarsening-upward stratigraphic sequence that records the transition of the sedimentation from a pre-collisional forearc to a syn-collisional basin. This basin was transported on top of the Puerto Plata ophiolitic complex slab and structurally underlying accreted units of the Rio San Juan complex, as it was emplaced onto the North America continental margin units.The Imbert Fm unconformably overlies different structural levels of the Caribbean subduction-accretionary prism, including a supra-subduction zone ophiolite, and consists of three laterally discontinuous units that record the exhumation of the underlying basement. The distal turbiditic lower unit includes the latest volcanic activity of the Caribbean island arc; the more proximal turbiditic intermediate unit is moderately affected by syn-sedimentary faulting; and the upper unit is a (chaotic) olistostromic unit, composed of serpentinite-rich polymictic breccias, conglomerates and sandstones, strongly deformed by syn-sedimentary faulting, slumping and sliding processes. The Imbert Fm is followed by subsidence and turbiditic deposition of the overlying El Mamey Group.The 40Ar ∕ 39Ar plagioclase plateau ages obtained in gabbroic rocks from the Puerto Plata ophiolitic complex indicate its exhumation at ∼ 45–40 Ma (lower-to-middle Eocene), contemporaneously to the sedimentation of the overlying Imbert Fm. These cooling ages imply the uplift to the surface and submarine erosion of the complex to be the source of the ophiolitic fragments in the Imbert Fm, during or shortly after the emplacement of the intra-oceanic Caribbean island arc onto the continental margin.

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18

Devlin, William J. "Stratigraphy and sedimentology of the Hamill Group in the northern Selkirk Mountains, British Columbia: evidence for latest Proterozoic – Early Cambrian extensional tectonism." Canadian Journal of Earth Sciences 26, no. 3 (March 1, 1989): 515–33. http://dx.doi.org/10.1139/e89-044.

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Three informal stratigraphic divisions are recognized in the uppermost Proterozoic – Lower Cambrian Hamill Group in the northern Selkirk Mountains of British Columbia. These informal divisions include a lower sandstone unit, a greenstone–graded-sandstone unit, and an upper sandstone unit. Both the lower and upper sandstone units display sedimentary characteristics that are uniform along strike and indicate a shallow-marine environment of deposition. As is typical of other exposures of the Hamil Group in southeastern British Columbia, the lower sandstone unit is coarser grained and more poorly sorted than the mature quartz arenites of the upper sandstone unit.The greenstone–graded-sandstone unit is a complex assemblage of mafic metavolcanic rocks and associated sandstone facies. This unit is highly variable along strike but essentially consists of a thick succession of subaqueous extrusive rocks overlain by a variety of sediment gravity-flow deposits. These latter deposits include resedimented conglomerates, debris-flow deposits, and trubidites (deposited from both high- and low-density turbidity currents). Stratigraphic sections of this unit are described in detail from three different localities and are examined in terms of their transport and depositional mechanisms.The stratigraphic succession of the Hamill Group indicates that deposition of the shallow-marine sands of the lower sandstone unit was abruptly interrupted by a period of volcanism, the creation of a paleoslope, and the deposition of a large volume of sediment gravity-flow deposits of the greenstone–graded-sandstone unit. These relations are attributed to an episode of syndepositional normal faulting. The inferred fault(s) could have served as the conduit for the extrusion of the volcanics. Offset along the fault(s), the tilting of fault blocks, and the consequent formation of an unstable slope adjacent to a fault scarp created an environment favorable for deposition of the sediment gravity flows. In general, deposition of proximal, base-of-slope deposits was followed by an aggradational basin-fill phase of sedimentation. With the waning of tectonic activity and the filling of the fault-bounded basin, depositon of shallow-marine sands resumed (the upper sandstone unit). The stratigraphic relations of the Hamill Group in the northern Selkirk Mountains are considered direct evidence for an episode of latest Proterozoic – Early Cambrian extensional tectonism. The evidence for an episode of rift-related tectonism in the northern Selkirk Mountains supports inferences concerning the timing of this event as derived from tectonic subsidence analyses of post-rift strata of the Cordilleran miogeocline.

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19

Azmi, Azyan Syahira, Mohd Suhaili Ismail, Jasmi Ab Talib, and Nur Marina Samsudin. "Environment Of Deposition Of The Jurassic-Cretaceous Continental Deposit In Central Pahang (Peninsular Malaysia) By Sedimentary Facies Analysis." Bulletin Of The Geological Society Of Malaysia 70, no. 1 (November 30, 2020): 153–62. http://dx.doi.org/10.7186/bgsm70202013.

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Spatial lithofacies and lithofacies association serves as one of the reliable methods in assessing the depositional process of sediments and interpreting its depositional environment. The method of facies analysis is adapted in this study where four newly exposed stratigraphic sections along the Jerantut-Maran road in Jerantut, Central Pahang of Peninsular Malaysia were studied. Previous studies showed that the environment of deposition of these continental deposits is broadly of braided-meandering river. Sedimentological data from the newly exposed stratigraphic sections had given a better understanding on the sedimentation processes involved in these deposits where interpretation on the environment of deposition is construed up to its sub-environment. The main lithofacies recognized include conglomerate, sandstone, and fine-grained facies. The facies associations identified include (i) massive to laminated silt/mudstone, (ii) massive sandstone, (iii) thin to thick ripple to parallel laminated sandstone, (iv) conglomeratic sandstone, (v) graded channelized sandstone, (vi) coarsening upwards medium bedded sandstone and (vii) heterolithic sandstone. The different facies associations are grouped to four (4) facies assemblages showing characteristics of certain environment: (1) floodplain, (2) channel bar complex, (3) point bar and (4) crevasse splay. Floodplain facies assemblage is marked by fine-grained facies, mainly siltstone/mudstone and fine-grained sands with lower flow regime structures. Channel bar complex is identified by high energy deposits of coarse-to-medium grained sandstones often with scoured bottom and lenticular geometry. Point bar is recognized by the lateral accretion surfaces often consisting of normal graded sandstone with sharp top and bottom contact, sometimes capped with thin mudstones. Crevasse splay facies assemblage is characterized by heterolithic sandstone, dominated by flaser-wavy bedding and coarsening upwards medium bedded sandstone that is overlain by fine-grained facies of the floodplain assemblage. The overall facies based on an outcrop scale suggests general features of fluvial facies with fluctuations in flow energy. The environment of deposition is thus interpreted to be of braided river with floodplains and isolated point bar.

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20

Hubbard, Stephen M., Zane R. Jobe, Brian W. Romans, Jacob A. Covault, Zoltan Sylvester, and Andrea Fildani. "The stratigraphic evolution of a submarine channel: linking seafloor dynamics to depositional products." Journal of Sedimentary Research 90, no. 7 (July 15, 2020): 673–86. http://dx.doi.org/10.2110/jsr.2020.36.

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ABSTRACT We investigate the relationship between the cross-sectional geomorphic expression of a submarine channel as observed on the seafloor and the stratigraphic product of long-lived erosion, bypass, and sediment deposition. Specifically, by reconstructing the time–space evolution of an individual channel fill (i.e., channel element) exposed in outcrop, we establish a genetic link between thick-bedded channel-element-axis sandstone to thinly interbedded channel-element-margin deposits. Although the bounding surface between axis sandstone and margin thin beds is sharply defined, it is composed of a series of geomorphic surface segments of various ages; as such, the composite stratigraphic surface (∼ 17 m relief) was formed from numerous incision events that repeatedly sculpted the conduit. By demonstrating the origin of the stratigraphic surface, we conclude that geomorphic surfaces with 2–7 m of erosional relief were largely responsible for the observed intra-channel-element architecture (and ultimately, the composite 17-m-thick element). The widely documented channel element axis-to-margin architecture is a product of submarine-channel thalweg dynamics, primarily recording interactions between the seafloor and the basal high-concentration layers of channelized turbidity currents.

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21

WENT, DAVID J. "Alluvial fan, braided river and shallow-marine turbidity current deposits in the Port Lazo and Roche Jagu formations, Northern Brittany: relationships to andesite emplacements and implications for age of the Plourivo-Plouézec Group." Geological Magazine 154, no. 5 (August 3, 2016): 1037–60. http://dx.doi.org/10.1017/s0016756816000686.

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AbstractFacies and stratigraphic analysis of the Port Lazo and Roche Jagu formations, together the lower part of the Plourivo-Plouézec Group, suggests deposition in three distinct depositional systems. The lower part of the Port Lazo Formation comprises red conglomerate, sandstone and shale of alluvial fan to alluvial plain origin. A conformable interval of grey sandstone and shale succeeds the lower Port Lazo red beds and records a period of subtidal sedimentation dominated by river-fed, shallow-water turbidity currents (hyperpycnites). The succeeding Roche Jagu Formation comprises red sandstones and shales of braided fluvial origin. It is intercalated with, and succeeded by, andesites. The andesites succeeding the fluvial strata overlie a prominent erosion surface and are lava flows, whereas those intercalated with the fluvial strata are intrusions. Rb–Sr radiometric dating of the andesites at 472+/−5 Ma is commonly used as evidence for the whole Plourivo-Plouézec Group being Early Ordovician in age. However, the stratigraphic relationships and patterns of sedimentation in the Port Lazo and Roche Jagu formations, together with the localized presence of Arumberia, suggest they are most likely of early Cambrian age and related to a phase of post-Cadomian rifting. The facies deposited show both similarities to and differences from neighbouring strata of equivalent age, and highlight the control exerted by sediment load on alluvial and nearshore processes on early Palaeozoic environments.

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22

Gaetani, Maurizio, Eduardo Garzanti, Riccardo Polino, Yuri Kiricko, Serghiei Korsakhov, Simonetta Cirilli, Alda Nicora, Roberto Rettori, Cristiano Larghi, and Raffaella Bucefalo Palliani. "Stratigraphic evidence for Cimmerian events in NW Caucasus (Russia)." Bulletin de la Société Géologique de France 176, no. 3 (May 1, 2005): 283–99. http://dx.doi.org/10.2113/176.3.283.

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Abstract The Upper Permian and Triassic sequences of the NW Caucasus present a good record of the Cimmerian events, rather undisturbed by the subsequent Alpine deformations. Original field work with new fossil identifications, microfacies analysis, and sandstone petrography were carried out. During the late Permian, active strike-slip basins were filled by continental clastics successions. Marine ingressions during the latest Permian, led to the formation of sponge reefs and skeletal carbonate ramps. During the Triassic, several siliciclastic wedges were intercalated within the marine carbonate succession. Most important is a conglomerate body made up of serpentinite pebbles of Spathian age (early Triassic), recording the exhumation and erosion of schistose antigorite serpentinites. By the late Anisian a severe deformation affected the Peredovoy (= Fore) Range of the NW Caucasus. Lower Triassic to Anisian sediments deformed also in chevron folds were overlaid with angular unconformity by a siliciclastic, and also volcaniclastic, conglomeratic and arenitic body, up to several hundred meters thick. By the late Ladinian-earliest Carnian, marine sedimentation resumed locally, forming a carbonate ramp during part of the Norian. Towards the end of the Norian, the entire area emerged and was again mildly tilted. The subsequent post-Cimmerian transgression occurred largely during the Middle Jurassic. Consequently, the most important Cimmerian deformations appear to be of early and middle Triassic age.

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23

Hersi, Osman Salad, and George R. Dix. "Hog's Back Formation: a new (Middle Ordovician) stratigraphic unit, Ottawa Embayment, eastern Ontario, Canada." Canadian Journal of Earth Sciences 34, no. 5 (May 1, 1997): 588–97. http://dx.doi.org/10.1139/e17-047.

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The Hog's Back Formation, exposed in Ottawa, Ontario, is a new stratigraphic unit that disconformably overlies the Rockcliffe Formation and underlies, with apparent conformity, the Pamelia Formation of the Ottawa Group. The Hog's Back Formation is 14.3 m thick at its type section (Prince of Wales Falls, Ottawa) and thickens eastward to 27 m in Russell County, about 40 km southeast of Ottawa. It consists of lower, dark green shales with thin lime-mudstone and sandstone interbeds, and upper thin to thick beds of fine crystalline greenish grey sandy and calcareous dolostones with thin to medium (10–30 cm) pinkish grey, bioclastic packstone and grainstone interbeds. The latter thicken eastward and correlate with the "St. Martin calcarenites" of the Beaconsfield Member, Laval Formation, in the Montréal area. Together, these beds correlate with the Valcour Formation, Chazy Group, in the Lake Champlain area of New York. Conodonts and macrofossils indicate a Chazyan (Llandeilian) age for the Hog's Back Formation. The lower sandstone–shale–carbonate assemblage of the formation indicates sedimentation in peritidal environments, and documents initial regional flooding of nearshore sandy facies of the Rockcliffe Formation. The overlying carbonate facies represent sabkha environments punctuated by storm deposition. The gross shallowing-upward succession of the formation was terminated by renewed flooding associated with another regional transgressive event heralding deposition of the Ottawa Group.

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24

Hagen, F., J. G. Gluyas, and G. Goffey. "The Acorn and Beechnut fields, Blocks 29/8a(S), 29/8b, 29/9a(S) and 29/9b, UK North Sea." Geological Society, London, Memoirs 52, no. 1 (2020): 349–59. http://dx.doi.org/10.1144/m52-2018-31.

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AbstractUnocal discovered the Acorn South Field with wells 29/8b-2 and 29/8b-2s in 1983. The well and its side-track found a small accumulation of oil in Upper Jurassic, Fulmar Formation sandstones in an inter-pod setting. Well 29/8b-3 drilled two years later on what was thought to be the same structure found Acorn North, a larger accumulation of oil in a Triassic Skagerrak Formation reservoir on the crest of a Triassic pod. Premier discovered the Beechnut Field two years later, well 29/9b-2 finding oil in the Fulmar and Skagerrak formations in a faulted, inter-pod setting. Both Acorn and Beechnut are deep, high-pressure and high-temperature fields with complex reservoir stratigraphy due to halokinesis during sedimentation and post-depositional structuration. The Skagerrak Formation reservoir in Acorn North is appreciably poorer than similar-age reservoirs further north whilst the Fulmar Formation in Beechnut is relatively poorly developed.Acorn's mid-case oil in place is 90 MMbbl in the Skagerrak Formation and 13 MMbbl in the Fulmar Formation and, for Beechnut, is 15 MMbbl in the Fulmar Formation. Neither field has been developed. Limiting factors include the resource size, variable reservoir development (Beechnut), modest reservoir quality (Acorn North), compartmentalization concerns and development costs.

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25

Box, Stephen E., Susan M. Karl, James V. Jones, Dwight C. Bradley, Peter J. Haeussler, and Paul B. O’Sullivan. "Detrital zircon geochronology along a structural transect across the Kahiltna assemblage in the western Alaska Range: Implications for emplacement of the Alexander-Wrangellia-Peninsular terrane against North America." Geosphere 15, no. 6 (October 16, 2019): 1774–808. http://dx.doi.org/10.1130/ges02060.1.

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Abstract The Kahiltna assemblage in the western Alaska Range consists of deformed Upper Jurassic and Cretaceous clastic strata that lie between the Alexander-Wrangellia-Peninsular terrane to the south and the Farewell and other pericratonic terranes to the north. Differences in detrital zircon populations and sandstone petrography allow geographic separation of the strata into two different successions, each consisting of multiple units, or petrofacies, with distinct provenance and lithologic characteristics. The northwestern succession was largely derived from older, inboard pericratonic terranes and correlates along strike to the southwest with the Kuskokwim Group. The southeastern succession is characterized by volcanic and plutonic rock detritus derived from Late Jurassic igneous rocks of the Alexander-Wrangellia-Peninsular terrane and mid- to Late Cretaceous arc-related igneous rocks and is part of a longer belt to the southwest and northeast, here named the Koksetna-Clearwater belt. The two successions remained separate depositional systems until the Late Cretaceous, when the northwestern succession overlapped the southeastern succession at ca. 81 Ma. They were deformed together ca. 80 Ma by southeast-verging fold-and-thrust–style deformation interpreted to represent final accretion of the Alexander-Wrangellia-Peninsular terrane along the southern Alaska margin. We interpret the tectonic evolution of the Kahiltna successions as a progression from forearc sedimentation and accretion in a south-facing continental magmatic arc to arrival and partial underthrusting of the back-arc flank of an active, south-facing island-arc system (Alexander-Wrangellia-Peninsular terrane). A modern analogue is the ongoing collision and partial underthrusting of the Izu-Bonin-Marianas island arc beneath the Japan Trench–Nankai Trough on the east side of central Japan.

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26

Van Yperen, Anna E., John M. Holbrook, Miquel Poyatos-Moré, and Ivar Midtkandal. "Coalesced Delta-front Sheet-like Sandstone Bodies from Highly Avulsive Distributary Channels: The Low-accommodation Mesa Rica Sandstone (Dakota Group, New Mexico, U.S.A.)." Journal of Sedimentary Research 89, no. 7 (July 25, 2019): 654–78. http://dx.doi.org/10.2110/jsr.2019.27.

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Abstract Low-accommodation deltaic systems are often challenging to interpret due to their condensed, low-gradient nature, which often results in extensive, sheet-like sandstone bodies. As a result, detailed studies of such systems are scarce, and their internal depositional architecture is still poorly understood. We analyze one such system, the Cenomanian deltaic Mesa Rica Sandstone (Dakota Group), which was deposited in the Western Interior Seaway, in east-central New Mexico, USA. A > 20-km-long escarpment, subparallel to the main delta progradation direction, allows a detailed analysis of facies distribution, depositional architecture, and the spatial extent of stratigraphic surfaces. Results reveal an arrangement of laterally variable shallowing-upward facies successions with three depositional cycles preserved. The first cycle is characterized by deltaic sheet-like sandstone bodies that are consistently overlain by sand-filled amalgamated distributary-channel deposits. The two successive cycles record a progressive reduction of sediment supply into the basin. Vertical and lateral relationships between facies associations and architectural geometries allow the recognition of regional key stratal surfaces, incised-valley fills, and the presence of lagoonal deposits at a sub-regional scale. The Mesa Rica deltaic system represents a river-dominated delta with multiple distributary channels. The sheet-like delta-front sandstone bodies are interpreted as the result of the combined effect of high sandy-sediment supply and low accommodation. The latter acted as an accelerator for autogenic depositional mechanisms such as mouth-bar deposition and abandonment, and for the highly avulsive character of distributary channels. After deposition, minor wave reworking facilitated lateral sand redistribution and favored bioturbation. This study demonstrates that sheet-like delta-front sandstone geometries from low-accommodation systems can be formed without the dominance of wave redistribution processes. This cautions against interpretations of amalgamated shoreline systems based solely on apparent sandstone geometries, without taking into account the preservation potential and postdepositional modification of primary deltaic characteristics.

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27

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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28

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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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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Letourmy, Yohan, Steven G. Driese, and Justin R. Sims. "Absence of evidence of climate-driven cycles in Carboniferous deposits of Joggins, Nova Scotia, Canada: influence of salt withdrawal tectonics on deposition and pedogenesis." Journal of Sedimentary Research 91, no. 2 (February 28, 2021): 167–85. http://dx.doi.org/10.2110/jsr.2020.78.

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ABSTRACT During the Late Paleozoic Ice Age, the fault-bounded equatorial Cumberland Basin of Nova Scotia experienced rapid subsidence, accumulating kilometer-thick fluvial sedimentary units derived from two highlands to the northwest and southeast. Major variations are recorded in the paleosols exposed at the Joggins Fossil Cliffs, ranging from oxidized and well-drained paleosols with recognizable vertic features to highly reduced organic-rich paleosols. These different soil lithologies suggest alternating conditions between well-drained floodplain environments and water saturation associated with overall poor soil development. Although halokinetic subsidence of the Cumberland Basin is known to have been operative during deposition of these units, previous research favored glacio-eustatic processes as the primary forcing mechanism of sedimentation. A total of 474 fluvial aggradational cycles were identified within a kilometer-thick interval and show a fluctuating accommodation history with a very abrupt nature. The series of fluvial aggradational cycles was used to develop threshold autoregressive models based on 1) their thickness, 2) their paleosol thickness, 3) their sandstone content, and 4) their paleosol-to-sandstone ratio. For each model, results suggest no evidence of statistically significant cyclicity, contradicting the hypothesis that fluvial sedimentation was mainly driven by glacio-eustatic cyclothems. Additionally, a total of 7 lithologies were recognized through 1,655 beds. Evaluation of 8 spherical semivariograms suggests no evidence for cyclicity in the frequency, order, or distribution of the data based on lithologies, although some covariance was found at distances between 550 and 750 m suggesting similar processes controlling sedimentation in the lower and upper Joggins Formation. The Cumberland Basin is known to have been rapidly subsiding, mainly because of ductile deformation of salt deposits in the deeper basinal units. Our results suggest that Joggins records tectonically induced ponding of a part of the sedimentary basin, allowing more extensive preservation of abundant coal and organic-rich units, as well as still-standing fossil forests exposed along the cliffs. These new results suggest that tectonic subsidence of the Cumberland Basin during the Late Paleozoic Ice Age was a more important driver of fluvial sedimentation than previously thought. This novel application of the TAR methodology provides a mathematical description of the sediment accumulation history of terrestrial basins when applied to conformable sedimentary successions, along with the means of linking paleosol development to climatic processes.

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Spalletti, Luis, and Ferrán Colombo. "Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina." Andean Geology 46, no. 3 (September 30, 2019): 471. http://dx.doi.org/10.5027/andgeov46n3-3170.

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The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic conglomerates with the predominance of basalt- dominated clasts, coarse- medium-grained conglomeratic sandstones and medium- to coarse-grained sandstones. These deposits occur as stacked or single bodies, display both sheet and channelized geometries, and contain a range of internal sedimentary structures, such as planar, low angle stratification and cross-bedding. This facies association is interpreted as the deposit of a multichannel fluvial system characterized by high bed load, steep gradient and non-cohesive bank materials. Facies and architecture of the fluvial deposits are the result of high bank full discharge related to rapid deglaciation of the Andean Last Glacial Maximum. The pyroclastic facies association is characterized by lapilli and ash tuffs deposited from air fall, pyroclastic density current, and density stratified surge mechanisms. In the Huarenchenque Formation the fluvial and the pyroclastic facies associations show a clear physical separation, suggesting that sedimentation occurred in two distinct (intereruptive and syneruptive) phases. During the long-lived intereruptive phases the sedimentary record corresponds mainly to the deposits of the gravelly braided fluvial system, whereas during syneruptive phases the fluvial valley was almost entirely occupied by primary pyroclastic deposits related to high-explosive episodes of the neighbor Andean strato-volcanoes. Although most of the cross-bedded sandstones and conglomerate sandstones are rich in basaltic fragments, some strata are composed almost entirely of pumiceous fragments, while in others there is a marked alternation between “basalt” and “pumiceous” foresets. These attributes reflect the preservation of intrabasinal pyroclastic fragments and allow suggest that: i. explosive volcanic events could be more frequent than reflected by the pyroclastic deposits themselves; ii. syneruptive pyroclastic materials could be eroded (even eliminated) by the fluvial system; iii. contributions of primary pyroclastic material persisted during intereruptive (fluvial-dominated) phases.

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Hickey, Leo, and Richard Yuretich. "The Paleocene Chance Member of the Fort Union Formation, northern Bighorn Basin, Montana and Wyoming: aperiodic cyclothems in a tectonically dominated lake basin." Mountain Geologist 53, no. 4 (October 2016): 259–81. http://dx.doi.org/10.31582/rmag.mg.53.4.259.

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A 400 m-thick sequence characterized by prominent tabular sandstone beds and a significant amount of marl and limestone occurs in Paleocene strata of the northern part of the Bighorn Basin (Clarks Fork Basin) of Wyoming and Montana. These strata, currently designated as the Belfry Member of the Fort Union Formation, actually consist of two separate but related lithogenetic units. The lower unit, which includes the Belfry Member stratotype, shows a gradual upward increase in tabular sandstone and marl or limestone and is inferred to have been deposited on a drowning flood plain under paralacustrine conditions. The upper unit, here proposed as the Chance Member, is characterized by the presence of six asymmetrical, basin-wide cyclothems. Each cycle begins abruptly with a transgressive surface overlain by laterally extensive tabular sandstone, followed by a micrite-dominated interval that together represent the lacustrine phase of the cycle. These are succeeded by lenticular interbeds of mudstone and sandstone inferred to have been deposited as a prograding fluvio-deltaic and flood plain sequence. The cyclothems are of variable thickness, ranging from ∼30m in the lowest cycle to ∼10 m in the uppermost cycles. Detailed stratigraphic mapping and correlation with the paleomagnetic and vertebrate biostratigraphic framework for the Bighorn Basin places the entire Chance Member within a portion of one vertebrate zone, Ti4, of the middle Tiffanian Provincial Age (59.2 to 58.5 Ma). The variable thickness of the cycles points toward deposition during unequal time intervals and suggests a tectonic origin most likely related to episodic movement of faults bounding the Bighorn Basin.

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ANDREWS, S. D., and N. H. TREWIN. "Palaeoenvironmental significance of lacustrine stromatolite forms from the Middle Old Red Sandstone of the Orcadian Basin." Geological Magazine 151, no. 3 (July 19, 2013): 414–29. http://dx.doi.org/10.1017/s0016756813000290.

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AbstractThe form of microbialite accumulations is largely the product of environmental processes and microbial activity. Recent work has largely concentrated on the identification and classification of microbialites with little attention being paid to their environmental significance. This study describes the environmental distribution of the varied stromatolite forms recorded from the Middle Old Red Sandstone sequences of the Orcadian Basin. Comparisons are made with Triassic examples from East Greenland and modern microbialite accumulations. The Middle Old Red Sandstone of Northern Scotland was deposited in a predominantly lacustrine setting. Stromatolites are recorded from both steep basin margin coincident settings and lower gradient settings where the lake margin was distant from the basin margin. In the latter case stromatolite development is largely restricted to transgressive lacustrine sequences, during the deposition of which reduced rates of sedimentation resulted from the migration of sediment input points towards the basin margin. Stromatolite sheets, domal mounds, aligned mounds (and associated runnels), sand-cored stromatolite mounds and reefal stromatolite accumulations have been identified representing the transition from more sheltered to more exposed environments. In basin margin coincident settings stromatolite accumulation is restricted to areas of low sedimentation where microbialites coat boulders and pebbles. A model for the palaeoenvironmental distribution of the stromatolite forms described is proposed and is shown to be applicable to similar examples from the Triassic of East Greenland. It is suggested that this model may be more widely applicable to stromatolitic accumulations in similar lacustrine settings through large portions of the Phanerozoic.

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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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Syzdek, Joseph, David Malone, and John Craddock. "Detrital Zircon U-Pb Geochronology and Provenance of the Sundance Formation, Western Powder River Basin, Wyoming." Mountain Geologist 56, no. 3 (August 1, 2019): 295–317. http://dx.doi.org/10.31582/rmag.mg.56.3.295.

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This study uses detrital zircon U-Pb geochronology to investigate the provenance of the Jurassic Sundance Formation in the western Powder River Basin, Wyoming. Understanding the provenance of the Sundance Formation is critical as it was deposited during the transition from cratonic to synorogenic sedimentation derived from the Sevier-Laramide foreland. The Sundance in the western Powder River Basin consists of an oolitic limestone and green glauconitic sandstone at the base, green shales in the middle, and a yellow quartz arenite with coquina “oyster” beds at the top. U-Pb analyses of detrital zircons using LA-ICP-MS were conducted on two samples collected in the Bud Love Wildlife Habitat Management Area, 20 km northwest of Buffalo, WY. The two samples were taken from the upper and lower sandstone members of the Sundance Formation (n=289 concordant U-Pb zircon ages). The samples show a distinct difference in detrital zircon age spectra. The lower sandstone age spectrum ranges from 260-3172 Ma with 23% of the ages being Paleozoic, 71% being Proterozoic, and 6% being Archean. This lower stratum has detrital zircon age peaks at 343, 432, 686, 1039, 1431, 1662, 1748, 1941, 2433, and 3179 Ma. The lower sandstone shows an easterly Appalachian-Ouachita provenance, which persisted in the region beginning in the Carboniferous. In comparison to the upper strata, ages range from 157-2949 Ma and age peaks at 170, 243, 440, 545, 1082, 1467, 1681, and 1985 Ma. The maximum deposition age for the upper member is 160 Ma. Mesozoic aged grains make up 15.6% of the zircons, 14.7% were Paleozoic, 65.7% were Proterozoic, and 4% were Archean in age. The appearance of Mesozoic zircons in the upper sandstone marks the first significant appearance of westerly sourced zircons, and perhaps reflects the earliest uplift of the Sevier fold and thrust belt. Previous research has found this same signature in the Sundance but not in the underlying Triassic Chugwater Formation, resulting in a broad boundary of the change in sediment dispersal and the onset of the Sevier Orogeny between the Triassic and Jurassic. This study was conducted for a higher resolution to the provenance of the Sundance Formation and to further narrow the boundary of differing sedimentation from an eastern recycled to western synorogenic source.

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36

Fielding, Christopher R., W. John Nelson, and Scott D. Elrick. "Sequence stratigraphy of the late Desmoinesian to early Missourian (Pennsylvanian) succession of southern Illinois: Insights into controls on stratal architecture in an icehouse period of Earth history." Journal of Sedimentary Research 90, no. 2 (February 26, 2020): 200–227. http://dx.doi.org/10.2110/jsr.2020.10.

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ABSTRACT Uncertainty persists over whether repetitive stratal rhythms in the Pennsylvanian of Euramerica (so-called “cyclothems”) were externally forced, in all likelihood by waxing and waning of glacial ice centers on Gondwana, or were controlled by autogenic processes. A key to resolving this dispute is the lateral extent of the individual cyclothems, with broad regional extent (beyond the plausible breadth and length of individual depositional systems such as deltas) arguing in favor of an external forcing control. This study provides a sedimentological and sequence stratigraphic analysis of the middle Pennsylvanian (Desmoinesian to early Missourian in North American stratigraphic terminology, Moscovian to early Kasimovian in the terms of the global stratigraphic nomenclature) succession of the southern Illinois Basin in Illinois, Indiana, and Kentucky, eastern USA. An array of eleven lithofacies is recognized, recording deposition of clastic, humic organic, and bioclastic carbonate sediments on a broad, low-gradient, low-paleolatitude shelf and coastal plain that were undersupplied by sediment. These facies are arranged into thirteen repetitive vertical cycles (sequences), each of which can be traced across the entire basin west to east (perpendicular to the paleoslope direction) across a distance of 250 km. Sequences are bounded by erosion surfaces that define 1–4 km-wide, deeply incised valley-fills (IVFs) that are mostly elongate towards the south-southwest, the dominant direction of paleoflow. In the west–east direction, valley erosion surfaces pass laterally into well-developed paleosols, incised locally by smaller channels. Each of these surfaces is laterally persistent across the basin. IVFs comprise multi-story bodies of conglomerate–breccia and sandstone, passing upward into heterolithic sandstone–mudrock associations, recording fluvial and later estuarine environments. Coal bodies typically occur at the tops of IVFs and are interbedded with heterolithic facies recording tidal influence, indicative of initial flooding by the sea. They are in turn overlain by estuarine and marine mudrocks and bioclastic carbonates, recording the maximum extent of marine flooding in a cycle. Each sequence is completed by heterolithic to sandstone-dominated facies of deltaic aspect that are typically truncated by the next erosion surface (sequence boundary). Plausible modern analogs suggest that sea-level excursions were of the order of 20–40 m. The great lateral persistence of not only the thirteen sequences, but also many of their component beds, argues strongly for an external control on sediment accumulation. Eccentricity-paced glacial cycles in Gondwana are invoked as the most likely cause of the cyclicity. The low-accommodation context of the Illinois Basin (average accumulation rate 6 cm/ky) contributed to the incomplete, condensed, and strongly top-truncated nature of preserved sequences.

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Haque, Md Masidul, and Mrinal Kanti Roy. "Geology and sedimentary environment of the Surma Group of rocks, Bandarban anticline, Bandarban, Bangladesh." Journal of Nepal Geological Society 62 (September 14, 2021): 88–106. http://dx.doi.org/10.3126/jngs.v62i0.38697.

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The study illustrates the effect of tectonics, climate, and relative sea-level change on the depositional process of the Miocene Bhuban and Boka Bil Formation of Bengal Basin. Outcrop sediments of five transverse sections exposed along the axial zone of Bandarban anticline were studied. Twelve lithofacies such as Gm, Gms, Sm, ST, Sp, Sr, Sl, Sf, Sll, Fw, Fl and Fm have been identified within the successions and grouped into (i) turbidite generated, (ii) outer fan distal lobe basin plain and (iii) tide-influenced facies association. The analyses reveal that the Bhuban Formation was turbidite- generated that deposited below the continental shelf-slope environment. The Lower Bhuban Member consists of gray to brownish-gray calcareous sandstone with shale deposited under the channelized lobe of submarine fan. The Middle Bhuban Member dominated by black shale-siltstone deposited in distal turbidite lobe due to change the flow regime. The Upper Bhuban Member consists of yellow to yellowish gray, coarse to medium-grained sandstone-siltstone with black shale that deposited under channelized to nonchannelized lobes of submarine fan. The increasing sedimentation during the formation of the Upper Bhuban Member can be caused by increased the intensity of the Asian Monsoon that carried huge sediment from the Himalaya. The Boka Bil Formation was deposited under estuary to tidal flat environment. The area was uplifted during and/or after subduction of the Indian Plate beneath the Burmese Plate. The monsoonal intensity enhances sedimentation that moved prograding delta towards the south. These processes shifted depositional environment from continental shelf-slope to marginal shallow marine during deposition of the Boka Bil Formation. The continental slope aligned east-west direction and sediments likely derived from the Himalaya and Trans-Himalaya in the present geographical setup during deposition of the sediments.

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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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Al-Mufti, Omar N., and R. William C. Arnott. "The origin and significance of convolute lamination and pseudonodules in an ancient deep-marine turbidite system: From deposition to diagenesis." Journal of Sedimentary Research 90, no. 5 (May 7, 2020): 480–93. http://dx.doi.org/10.2110/jsr.2020.29.

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ABSTRACT Soft-sediment deformation structures, like convolute lamination and pseudonodules, are common in deep-marine turbidites, but details of their origin and timing of formation remain a source of debate. Deep-marine basin-floor deposits of the Neoproterozoic Upper Kaza Group (Windermere Supergroup) crop out superbly in the Castle Creek study area and provide an ideal laboratory to investigate these aspects in convolute-laminated pseudonodules, and also how that deformation influenced later diagenesis. Pseudonodules consist of well-sorted, matrix-poor, upper medium- to coarse-grained, planar-stratified or cross-stratified sandstone that are underlain and overlain by comparatively more poorly sorted, matrix-rich, graded sandstone of similar grain size. Deposition of the stratified pseudonodules is interpreted to have occurred during the same event that deposited the graded sandstone, albeit during a period of general transport bypass, whereby isolated, shallow, seafloor depressions became filled with well-sorted, stratified sand. As stratified sand accumulated the depressions slowly subsided until a critical thickness had built up and exceeded the load-bearing capacity of the substrate composed of graded sand. This destabilized the surface separating the two layers and resulted in the stratified unit foundering, and in some cases becoming completely enveloped by, the upward-displaced lower-density substrate. Surprisingly, despite the deformed macroscopic character of the stratified sediment, primary grain fabric, including intergranular porosity up to 40%, was preserved and influenced early diagenesis, which, owing to dispersed phosphate cement and depleted carbon isotope composition of the pervasive carbonate cement, would have begun very near the sediment–water interface. Importantly also, pseudonodules are common in basin-floor deposits but comparatively rare in continental-slope strata. Expanding flow conditions over the basin floor would have promoted grain settling, and in turn development of a more stably (density) stratified flow structure. Ultimately this resulted in higher local rates of sedimentation on the basin floor and the accumulation of a substrate more prone to later liquidization.

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Schieber, J. "The origin of the Neihart Quartzite, a basal deposit of the Mid-Proterozoic Belt Supergroup, Montana, U.S.A." Geological Magazine 126, no. 3 (May 1989): 271–81. http://dx.doi.org/10.1017/s0016756800022366.

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AbstractThe Neihart Quartzite is the basal quartz arenite unit (≍270m thick) of the Mid-Proterozoic Belt Supergroup of western North America. Petrographic studies indicate a source area with plutonic granitic, metamorphic and felsic volcanic rocks. Extreme textural maturity and bimodality indicate an episode of aeolian transport for the detrital quartz grains. The lower 80% of the Neihart Quartzite were probably deposited by braided streams, whereas the upper 20% were deposited in shoreline environments. Residual material that was ‘stored up’ on the pre-Beltian cratonic surface and underwent aeolian reworking was the likely source material for most of the Neihart Quartzite. Less mature sediments in the top portion of the Neihart Quartzite indicate uplift and erosion of new source material during Neihart deposition. Other known cratonic quartz arenites, such as the St. Peter Sandstone (Ordovician), Lamotte Sandstone (Cambrian) and Flathead Quartzite (Cambrian), are thin (tens of metres thickness) and exhibit sheet-like geometry. In contrast, the Neihart Quartzite and its probable lateral equivalents are considerably thicker and increase in thickness towards the central portions of the basin. It thus appears that Belt sedimentation began with accumulation of a basal quartz arenite unit, and that sand for that unit was transported by braided streams from the surrounding craton to a gradually subsiding Belt basin.

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Reesink, Arnold Jan H., Jim Best, Jared T. Freiburg, Nathan D. Webb, Charles C. Monson, and Robert W. Ritzi. "Interpreting pre-vegetation landscape dynamics: The Cambrian Lower Mount Simon Sandstone, Illinois, U.S.A." Journal of Sedimentary Research 90, no. 11 (November 30, 2020): 1614–41. http://dx.doi.org/10.2110/jsr.2020.71.

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ABSTRACT The Cambrian Mount Simon Sandstone has been the subject of extensive study and multiple industrial-scale carbon storage demonstrations at Decatur, Illinois, USA. The development of a reliable paleoenvironmental model is critical to successful large-scale carbon dioxide (CO2) storage, but is complicated by the need to interpret pre-vegetation sedimentation processes. The present study presents a paleoenvironmental model of the Lower Mount Simon Sandstone, based on analysis of primary sedimentary structures in two cores and four complete high-resolution resistivity logs (FMI). The Lower Mount Simon Sandstone represents a vertical “drying-up” sequence composed of three associated depositional units: a north–south oriented coastal system at the base, an eastward-directed fluvial unit in the middle, and a westward-directed eolian system at the top that recycled medium- and fine-grained sand in the basin. Quantitative analysis of fluvial cross-strata indicates that the perennial river system was shallow (c. 1 m deep) with relatively narrow channel belts (c. 1 km). Adjacent sandy eolian-floodplain deposits contain abundant thin, crinkly planar laminae that are enriched in fines and are interpreted as cementation surfaces, likely of biological origin. Deflation lags and wind-ripple strata are commonly interbedded with the crinkly strata, suggesting that the recurrence of erosion and deposition that controlled sedimentary preservation on the floodplain were dominated by eolian transport, re-wetting, and (bio-) cementation. Such a prominent role of exposure to the wind, basin-scale sediment recycling, and eolian removal of fine-grained sediment would have ceased to exist for most climates after the development of vegetation on land, yet, may well be key to understanding the environmental context for early life on Earth.

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Nelson, Walter W., and Stephen A. Sonnenberg. "Sequence stratigraphy and regional context of the Mancos-Niobrara in the northern San Juan Basin." Mountain Geologist 58, no. 2 (April 1, 2021): 105–57. http://dx.doi.org/10.31582/rmag.mg.58.2.105.

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In the northern San Juan Basin, the Niobrara Formation is represented by the upper half of the Mancos Shale (the Smoky Hill Member and Cortez Member). This section is generally equivalent to the Niobrara Formation along the Colorado Front Range. Although the Fort Hays Limestone is absent west of Pagosa Springs, the C Chalk and B Chalk are well-expressed as two resistant bench-forming calcareous units in the northern San Juan Basin. These two calcareous units have also been established as prospective hydrocarbon targets by operators in the area. Calcareous facies equivalent to the A Chalk were not deposited in the northern San Juan Basin due to siliciclastic dilution during the regressive latter half of the Niobrara marine cycle. The overall third-order Niobrara marine cycle includes these members of the Mancos Shale: the Juana Lopez, Montezuma Valley, Smoky Hill, and Cortez members. The Smoky Hill Member sits just above the basal Niobrara unconformity in most of the study area, and the entire section also has greater thickness and siliciclastic content than its equivalent farther east along the Front Range. Several extensive outcrop locations (in and around Pagosa Springs, Piedra, and Durango, CO) along with three new cores along the CO-NM border form the foundation for sequence stratigraphic interpretation of the Niobrara marine cycle in this study. All these locations and cores were tied back to the Mancos reference section at Mesa Verde National Park established by Leckie et al. (1997) which provides detailed description and biostratigraphy for the entire Mancos Shale. Establishing and applying a sequence stratigraphic framework to any section creates consistent reference standards for communication, research, and further correlation. Comparisons of chemostratigraphic data from equivalent strata between the northern San Juan Basin and Denver-Julesburg (DJ) Basin reveal significant differences in the timing and style of source-rock deposition (and associated low-oxygen conditions). The sequence stratigraphic framework also emphasizes tremendous lateral facies changes in the basal Niobrara section (i.e., Fort Hays Limestone to Tocito Sandstone). Once refined and applied, this stratigraphic framework can be used for predicting the distribution of reservoir properties, in addition to enhancing understanding of the Niobrara marine cycle and the Western Interior Seaway.

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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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Dam, Mai Hoang, Vu Thi Tuyen, Nguyen Tan Trieu, and Nguyen Thi Tham. "Biostratigraphic and petrological characteristics of Cretaceous–Paleogene sediments in the eastern Cuu Long delta." Journal of Petroleum Exploration and Production Technology 11, no. 5 (April 12, 2021): 2055–73. http://dx.doi.org/10.1007/s13202-021-01156-8.

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AbstractThe basic structure of reservoir models is strongly affected by the stratigraphic interpretation and the properties of reservoir rock. The estimation of the volume of hydrocarbon accumulation will depend on the accuracy of predicting and distributing reservoir quality. Biostratigraphic and sedimentary petrologic results provide geological information to clarify the stratigraphy and properties of sedimentary rocks on the eastern margin of the Cuu Long delta plain trough. On the basis of stratigraphic correlation of the wells and studying the structures of the area, the deposition, thickness of sediments and the ability to correlate with prospect rocks on the southeastern Vietnam continental shelf were determined. The results have identified the basement rock of wells TC-1 and TC-2, which are Cretaceous metasandstones and were deposited in freshwater fluvial environments with high-energy conditions. The upper Paleogene sediments were overlaid directly on the Cretaceous basement rock in the TC-2 well but were completely absent in the TC-1 well. The lithologic composition is mainly feldspathic litharenite sandstone, which is formed in freshwater fluvial and freshwater lacustrine environments. This study provides new data on stratigraphic column of the eastern Cuu Long delta plain. The data show that the age of the sedimentary basement rock is Cretaceous which has not been determined in previous studies. The findings of this study can help for better understanding of the geological development history and the completely stratigraphic column of the Cuu Long delta to correlate with objects that are hydrocarbon accumulation in Cuu Long sedimentary basin in order to improve efficiency in petroleum exploration activities.

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Lupin, Janifar H., and Gary J. Hampson. "Sediment-routing controls on sandstone bulk petrographic composition and texture across an ancient shelf: Example from Cretaceous Western Interior Basin, Utah and Colorado, U.S.A." Journal of Sedimentary Research 90, no. 10 (October 1, 2020): 1389–409. http://dx.doi.org/10.2110/jsr.2020.044.

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ABSTRACT Sediment-routing controls on sandstone texture and bulk petrography have been evaluated in linked alluvial–coastal–shelfal deposits of the Upper Cretaceous Castlegate Sandstone, Blackhawk Formation, Star Point Sandstone, and Mancos Shale (Western Interior Basin, Utah and Colorado, USA) using thin-section analysis of representative outcrop samples in the context of a high-resolution sequence stratigraphic and paleogeographic framework. The studied strata record deposition from two styles of sediment-routing system within an overfilled foredeep and contiguous intra-continental seaway. First, multiple transverse drainages supplied sand to fluvial, shoreline, and shelf segments of sediment-routing systems characterized by down-dip transport distances of 150–450 km and significant strike-oriented sediment transport along the shoreline. Second, the distal shoreline–shelf segment of an axially supplied sediment-routing system was characterized by sand transport for a distance of c. 300 km. Bulk petrographic composition indicates that transverse sediment-routing systems were sourced from catchments that supplied quartz-rich sand with a subordinate lithic component, while the large axial sediment-routing system was sourced from a catchment(s) supplying slightly more feldspathic sand. Thin-section measurements of mean grain size, sorting, skewness, and ratio of minimum-to-maximum diameter (a proxy for sphericity) are similar for sandstones deposited in fluvial, shoreline, and shelf segments of the transverse sediment-routing systems and in the shoreline–shelf segment of the axial sediment-routing systems, although hydrodynamic sorting is important in locally segregating grain-size populations within each segment. Further, textural analysis of detrital quartz, feldspar, and lithic sand-grain populations shows little evidence of relative change in mean grain size or apparent grain sphericity with downsystem distance, implying that sand-grain populations of different petrographic composition did not undergo significant differential mechanical breakdown during transport. Instead, the textural characteristics of these sand-grain populations are inferred to have been controlled mainly by bedrock lithology and recycling in source catchments. The textural signal of sediment-source areas then propagated downsystem in the sand fraction of detrital sediment supply. This inference is supported by the fine- to medium-grained, well- to very well-sorted character of all sandstone samples, consistent with recycling of sandstones and quartzites from the Sevier fold-and-thrust belt.

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Hicks, N., D. J. C. Gold, M. Ncume, and L. Hoyer. "A new lithostratigraphic framework for portions of the Pongola Supergroup within the Nkandla sub-basin, southern Kaapvaal Craton, South Africa; insights into Mozaan Group stratigraphy." South African Journal of Geology 124, no. 3 (September 1, 2021): 717–34. http://dx.doi.org/10.25131/sajg.124.0039.

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Abstract A revised lithostratigraphic framework for Mozaan Group-equivalent strata within the Nkandla sub-basin is presented based on new field data, remote sensing and genetic sequence stratigraphic interpretations. Although previous literature has suggested that no Mozaan Group lithologies were deposited within the sub-basin, reinterpretations presented here indicate that 90% of the lithostratigraphy developed within the main basin occurs within the Nkandla and Mhlatuze inliers. Mozaan Group units previously defined as the Vutshini and Ekombe formations are correlated with stratigraphy from the lowermost Sinqeni Formation to the Gabela Formation. Although thinner than units within the type area in the main basin, thicknesses of the Sinqeni Formation are comparable to those observed within the White Mfolozi Inlier. A ~1 000 m composite reference profile is measured within the Mdlelanga Syncline of the Nkandla Inlier. Further profiles were measured for sequences in the Gem-Vuleka Syncline of the Nkandla Inlier, as well as within the Mhlatuze Inlier. These latter profiles, however, host only lower Mozaan Group strata. In all sections the basal portion of the sequence comprises two quartz arenite units, separated by a ferruginous shale, which hosts minor iron formation interbeds. This predominantly coarse-grained lower sequence is overlain by a shale-dominated succession with multiple sandstone interbeds. A prominent coarse-grained quartz arenite unit forms a distinct marker in the middle portion of the sequence. This is overlain by a sequence of shales and sandstones with two prominent igneous units present. Genetic sequence stratigraphic interpretations indicate cyclical deposition of dominantly shallow marine sediments with condensed sections, marked by iron formations or ferruginous shales, denoting periods of marine highstand along the southeastern margin of the Kaapvaal Craton. The evidence of Mozaan Group stratigraphy within the Nkandla sub-basin supports a passive margin tectonic model whereby deposition occurred in an arcuate shallow continental margin which opened to the southeast. The extension of Mozaan Group strata into the Nkandla sub-basin suggests that the Mozaan Basin likely formed a single depository rather than separate sub-basins as previously proposed.

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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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Tye, Robert S., Donald R. Lowe, and J. J. Hickey. "Ediacaran (Vendian)-period alluvial and coastal geomorphology applied to development of Verkhnechonskoye and Yaraktinskoye fields, East Siberia, Russian Federation." Journal of Sedimentary Research 90, no. 1 (January 22, 2020): 67–101. http://dx.doi.org/10.2110/jsr.2020.8.

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ABSTRACT Ediacaran-age (635–542 Ma) oil-bearing strata in the Yarakta Horizon at the Verkhnechonskoye and Yaraktinskoye fields, East Siberia, consist of conglomerate, sandstone, dolomitic sandstone, and mudstone overlying and onlapping igneous to metasedimentary highlands of the East Siberia craton. Initial drainage networks formed within structurally defined valleys, and early deposition occurred in localized alluvial to shallow-marine depositional systems. Base-level-controlled depositional cycles aggraded the valleys; thus, as valleys aggraded, they buried interfluves and coalesced forming broad alluvial and coastal plains. Three to seven bedsets of variable net-to-gross content constitute a genetic cycle. Depositional cycles varied locally, as nine and eight cycles separated by decimeter- to multi-meter-thick mudstones are defined at Verknechonskoye and Yaraktinskoye, respectively. Within one genetic cycle, facies associations grade basinward from alluvial (channel-bar, channel-fill, floodplain, playa, and crevasse-splay) to shallow marine (sabkha, tidal-flat, estuarine-channel, and poorly developed shoreface). Coarse-grained lithofacies are typically arranged in decimeter- to meter-scale bedsets with sharp to scoured bases. Bedsets commonly, but not always, show an upward decrease in grain size, bed thickness, and scale of sedimentary structure. Typically, medium-grained sandstones exhibit low-angle cross bedding and are gradationally overlain by fine-grained sandstones exhibiting scour-and-fill, cuspate-ripple lamination, climbing-ripple lamination, and parallel lamination. Clay clasts and small pebbles are accessories. Interbedded mudstones, siltstones, and sandstones show ripple cross bedding, wavy to lenticular bedding, abundant soft-sediment deformation (e.g., shear, fluid-escape, slump features), and slickensides. Thin-bedded sandstones are micaceous and contain granule-size mud chips. Some mudstones exhibit crinkled to parallel laminae indicative of algal growth. Sandstone fills mudcracks. Interbedded green and black mudstones, plus pyrite and siderite cements, indicate alternating redox conditions. Alluvial facies have patchy quartz, anhydrite, and carbonate cements. Marine-influenced facies show early and well-developed quartz cement as well as abundant halite. Gypsum and halite dissolution formed secondary pores. Calculated estimates of fluvial-channel dimensions and sinuosities indicate that despite the lack of vegetation, fluvial channels in the Yarakta Horizon were shallow and relatively narrow, moderately sinuous, and exhibited varying degrees of mud-prone overbank deposition. Recognition and correlation of flooding surfaces and channel diastems bounding genetically related strata identified multiple stratigraphic compartments in each field. Porosity loss at chronostratigraphic boundaries accounts for complex water, oil, and gas contacts. Economic field development is hampered by locally varying reservoir quality and sandstone continuity caused by its channelized and onlapping stratigraphy and diagenesis. Reservoir simulation of varying geostatistical models demonstrate that differing porosity-distribution methods had little effect on estimates of in-place hydrocarbon volumes. Model differences in porosity and permeability distribution and lithofacies connectivity show large variations in recovery factor and productivity/injectivity.

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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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Angus, Lynsey, Gary J. Hampson, Francesco Palci, and Alastair J. Fraser. "Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern U.K. and northern France." Journal of Sedimentary Research 90, no. 3 (March 27, 2020): 313–35. http://dx.doi.org/10.2110/jsr.2020.19.

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ABSTRACT The influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces. Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression. Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.

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Journal articles on the topic 'Sandstone Geology, Stratigraphic Sedimentation and deposition'

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