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1
Savage, B., B. M. Covellone, and Y. Shen. "Wave speed structure of the eastern North American margin." Earth and Planetary Science Letters 459 (February 2017): 394–405. http://dx.doi.org/10.1016/j.epsl.2016.11.028.
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Servali, Andrea, Maureen D. Long, Jeffrey Park, Margaret H. Benoit, and John C. Aragon. "Love-to-Rayleigh scattering across the eastern North American passive margin." Tectonophysics 776 (February 2020): 228321. http://dx.doi.org/10.1016/j.tecto.2020.228321.
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Lynner, Colton, Harm J. A. Van Avendonk, Anne Bécel, Gail L. Christeson, Brandon Dugan, James B. Gaherty, Steven Harder, et al. "The Eastern North American Margin Community Seismic Experiment: An Amphibious Active‐ and Passive‐Source Dataset." Seismological Research Letters 91, no. 1 (October 30, 2019): 533–40. http://dx.doi.org/10.1785/0220190142.
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Abstract The eastern North American margin community seismic experiment (ENAM‐CSE) was conceived to target the ENAM Geodynamic Processes at Rifting and Subducting Margins (GeoPRISMS) primary site with a suite of both active‐ and passive‐source seismic data that would shed light on the processes associated with rift initiation and evolution. To fully understand the ENAM, it was necessary to acquire a seismic dataset that was both amphibious, spanning the passive margin from the continental interior onto the oceanic portion of the North American plate, and multiresolution, enabling imaging of the sediments, crust, and mantle lithosphere. The ENAM‐CSE datasets were collected on‐ and offshore of North Carolina and Virginia over a series of cruises and land‐based deployments between April 2014 and June 2015. The passive‐source component of the ENAM‐CSE included 30 broadband ocean‐bottom seismometers (OBSs) and 3 onshore broadband instruments. The broadband stations were deployed contemporaneously with those of the easternmost EarthScope Transportable Array creating a trans‐margin amphibious seismic dataset. The active‐source portion of the ENAM‐CSE included several components: (1) two onshore wide‐angle seismic profiles where explosive shots were recorded on closely spaced geophones; (2) four major offshore wide‐angle seismic profiles acquired with an airgun source and short‐period OBSs (SPOBSs), two of which were extended onland by deployments of short‐period seismometers; (3) marine multichannel seismic (MCS) data acquired along the four lines of SPOBSs and a series of other profiles along and across the margin. During the cruises, magnetic, gravity, and bathymetric data were also collected along all MCS profiles. All of the ENAM‐CSE products were made publicly available shortly after acquisition, ensuring unfettered community access to this unique dataset.
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Mazza, Sarah E., Esteban Gazel, Elizabeth A. Johnson, Michael Bizimis, Ryan McAleer, and C. Berk Biryol. "Post-rift magmatic evolution of the eastern North American “passive-aggressive” margin." Geochemistry, Geophysics, Geosystems 18, no. 1 (January 2017): 3–22. http://dx.doi.org/10.1002/2016gc006646.
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Lynner, Colton, and Robert W. Porritt. "Crustal structure across the eastern North American margin from ambient noise tomography." Geophysical Research Letters 44, no. 13 (July 3, 2017): 6651–57. http://dx.doi.org/10.1002/2017gl073500.
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Lynner, Colton, and Miles Bodmer. "Mantle flow along the eastern North American margin inferred from shear wave splitting." Geology 45, no. 10 (August 4, 2017): 867–70. http://dx.doi.org/10.1130/g38980.1.
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Attias, Eric, Rob L. Evans, Samer Naif, Jimmy Elsenbeck, and Kerry Key. "Conductivity structure of the lithosphere-asthenosphere boundary beneath the eastern North American margin." Geochemistry, Geophysics, Geosystems 18, no. 2 (February 2017): 676–96. http://dx.doi.org/10.1002/2016gc006667.
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Long, Maureen D., Margaret H. Benoit, Rob L. Evans, John C. Aragon, and James Elsenbeck. "The MAGIC Experiment: A Combined Seismic and Magnetotelluric Deployment to Investigate the Structure, Dynamics, and Evolution of the Central Appalachians." Seismological Research Letters 91, no. 5 (July 1, 2020): 2960–75. http://dx.doi.org/10.1785/0220200150.
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Abstract The eastern margin of North America has undergone multiple episodes of orogenesis and rifting, yielding the surface geology and topography visible today. It is poorly known how the crust and mantle lithosphere have responded to these tectonic forces, and how geologic units preserved at the surface related to deeper structures. The eastern North American margin has undergone significant postrift evolution since the breakup of Pangea, as evidenced by the presence of young (Eocene) volcanic rocks in western Virginia and eastern West Virginia and by the apparently recent rejuvenation of Appalachian topography. The drivers of this postrift evolution, and the precise mechanisms through which relatively recent processes have modified the structure of the margin, remain poorly understood. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment, part of the EarthScope USArray Flexible Array, consisted of collocated, dense, linear arrays of broadband seismic and magnetotelluric (MT) stations (25–28 instruments of each type) across the central Appalachian Mountains, through the U.S. states of Virginia, West Virginia, and Ohio. The goals of the MAGIC deployment were to characterize the seismic and electrical conductivity structure of the crust and upper mantle beneath the central Appalachians using natural-source seismic and MT imaging methods. The MAGIC stations operated between 2013 and 2016, and the data are publicly available via the Incorporated Research Institutions for Seismology Data Management Center.
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SHEARD, John W., Alexander K. EZHKIN, Irina A. GALANINA, Dmitry HIMELBRANT, Ekaterina KUZNETSOVA, Akira SHIMIZU, Irina STEPANCHIKOVA, et al. "The lichen genusRinodina(Physciaceae,Caliciales) in north-eastern Asia." Lichenologist 49, no. 6 (November 2017): 617–72. http://dx.doi.org/10.1017/s0024282917000536.
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AbstractRinodinais a widespread, polyphyletic genus of crustosePhysciaceaewithc. 300 species worldwide. A major missing link in understanding its global biogeography has been eastern Asia where the genus has never been systematically revised. Here we review specimen and literature records forRinodinafor north-eastern Asia (Russian Far East, Japan and the Korean Peninsula) and recognize 43 species. We describe two species,R. hypobadiaandR. orientalis, as new to science.Rinodina hypobadiais distinguished by its pigmented hypothecium,Dirinaria-type ascospores and pannarin in both thallus and epihymenium.Rinodina orientalisis characterized by its erumpent apothecia that remain broadly attached, with discs sometimes becoming convex and excluding the thalline margins, ascospores belonging to thePhyscia-type and secondary metabolites absent. Nine other species are reported from the region for the first time. These includeR. dolichospora,R. freyi,R. metaboliza,R. sicula,R. subminutaandR. willeyi. Of particular biogeographical interest are three additional new records that have western North American–eastern Asian distributions: the corticolous speciesR. endospora,R. macrosporaandR. megistospora. Six species have the better known eastern North American–eastern Asian distributions:R. ascociscana(syn.R. akagiensis,R. melancholica),R. buckii,R. chrysidiata,R. subminuta,R. tenuis(syn.R. adirondackii) andR. willeyi, and two have eastern North American–eastern Asian–European distributions:R. excrescensandR. moziana(syn.R. destituta,R. vezdae). Our study begins to close one of the largest gaps in our knowledge of circumboreal species distributions inRinodinaand, together with previous studies in North America and Europe, provides new insights into circumboreal crustose lichen biogeography.Rinodina cinereovirens(syn.R. turfaceavar. cinereovirens) is also reported as new to North America.
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Falkowski, P. G., P. E. Biscaye, and C. Sancetta. "The lateral flux of biogenic particles from the eastern North American continental margin to the North Atlantic Ocean." Deep Sea Research Part II: Topical Studies in Oceanography 41, no. 2-3 (January 1994): 583–601. http://dx.doi.org/10.1016/0967-0645(94)90036-1.
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Redhead, S. A. "Notes on the genus Xeromphalina (Agaricales, Xerulaceae) in Canada: biogeography, nomenclature, taxonomy." Canadian Journal of Botany 66, no. 3 (March 1, 1988): 479–507. http://dx.doi.org/10.1139/b88-073.
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Eleven of the 13 North American species of Xeromphalina are reported from Canada. A key to 14 North American and northern Eurasian species is given. Type specimens for 9 names were examined. In Canada, subgenus Heimiomyces is represented by two species: X. tenuipes (Schw.) Smith (sect. Heimiomyces) and X. fulvipes (Murr.) Smith (sect. Fulvipes). Subgenus Xeromphalina is represented by sections Xeromphalina and Mutabiles. Xeromphalina brunneola Miller and X. campanella (Batsch: Fr.) Kuhner & Maire are circumboreal species documented from across Canada. Xeromphalina kauffmanii Smith occurs in southern Quebec, Nova Scotia, Costa Rica, the eastern United States, and in Japan. Section Mutabiles stat.nov. is completely revised based on pigmentation of the pileipellis, on the distribution and types of pileocystidia, and on the pigmentation of the stipe, in addition to characters used previously in the genus. The term "circumcystidia" is coined for pileocystidia largely confined to a band around the pileus margin. In North America, the name X. cauticinalis (Fr.) Kühner & Maire frequently has been misapplied to X. cornui (Quél.) Favre, a common, widespread species in Canada. Xeromphalina fraxinophila Smith is reported from across Canada and the United States and in Eurasia. The name Marasmius cauticinalis is neotypified. In North America X. cauticinalis ssp. cauticinalis occurs in western areas. Xeromphalina cauticinalis ssp. pubescentipes (Peck) comb. et stat. nov. occurs in eastern areas in North America, in Japan, and together with ssp. cauticinalis in Europe. Xeromphalina parvibulbosa (Kauff. & Smith) comb.nov. occurs across North America. Xeromphalina cirris sp.nov. from montane or boreal coniferous forests floors in British Columbia, Ontario, Colorado, Idaho, New Mexico, Oregon, Utah, Washington, and Wyoming and X. campanelloides sp.nov. from coastal British Columbia and Washington, and eastern montane New York and Quebec, on coniferous logs, are described. Rhizomorphs are formed by all Canadian species except X. tenuipes.
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McKerrow, W. S., and N. J. Soper. "The Iapetus suture in the British Isles." Geological Magazine 126, no. 1 (January 1989): 1–8. http://dx.doi.org/10.1017/s0016756800006099.
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AbstractThe position of the Iapetus Ocean suture can be traced between Ordovician fossil localities in the Southern Uplands and the Lake District which contain, respectively, distinct North American and European faunas. The Southern Uplands contains North American Caradoc faunas in the Northern Belt, and is considered to have been accreted onto the Laurentian (North American) margin between the Llandeilo and the end of the Wenlock. Deep seismic reflection profiling shows that a surface, probably parallel to the suture zone, dips down to the northwest from the Solway Line. In eastern Ireland, the surface trace of the suture coincides with the Navan Fault, which separates the Longford-Down massif from Ordovician sediments containing European faunas. The Navan–Silvermines Fault may represent the surface expression of the suture, but it is masked by Wenlock turbidites, which appear to have crossed over the plate boundary. Northward subduction of continental crust below the margin of Laurentia during the late Silurian may explain the influx of turbidite fans from the north or north west onto depressed crust to the south of the suture. Termination of subduction coincides with the widespread Acadian Orogeny in the Emsian (at 395±5 Ma).
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PE-PIPER, GEORGIA, and LUBOMIR F. JANSA. "Geochemistry of late Middle Jurassic–Early Cretaceous igneous rocks on the eastern North American margin." Geological Society of America Bulletin 99, no. 6 (1987): 803. http://dx.doi.org/10.1130/0016-7606(1987)99<803:golmjc>2.0.co;2.
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Carrera, Marcelo G., and Colin D. Sumrall. "Ordovician sponges from the Lenoir Limestone, Tennessee: new evidence for a differential sponge distribution along the margins of Laurentia." Journal of Paleontology 94, no. 1 (September 13, 2019): 34–44. http://dx.doi.org/10.1017/jpa.2019.67.
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AbstractFive genera of anthaspidellid and streptosollenid demosponges are described from the Ordovician Lenoir Limestone near Lenoir City, Loudon County, Tennessee, USA including: Rhopalocoelia regularis Raymond and Okulitch, Rugocoelia loudonensis n. sp., Psarodictyum sp. (Anthaspidellidae), Allosacus pedunculatus n. sp., and Zitelella varians Raymond and Okulitch (Streptosolenidae). These findings confirm the major paleobiogeographic picture for Laurentian sponges (i.e., the differential distribution of sponge faunas along both North American margins), because none of these eastern margin species has been reported from western margin faunas. Only one genus typical of the Great Basin fauna, Rugocoelia Johns, 1994, is reported from Tennessee, but as a new species. Possible explanations are discussed for this differential distribution, mainly related to climatic constraints or sedimentary differences, preventing the free distribution of sponge species between Laurentian continental margins.UUID: http://zoobank.org/2b990a4c-7bc8-4eb6-b8a9-fe4ecf7bdbf9
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Gehrels, George E., William C. McClelland, Scott D. Samson, and P. Jonathan Patchett. "U–Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska." Canadian Journal of Earth Sciences 28, no. 8 (August 1, 1991): 1285–300. http://dx.doi.org/10.1139/e91-114.
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Metamorphic rocks within and west of the northern Coast Mountains in southeastern Alaska consist of an Upper Proterozoic(?) to upper Paleozoic continental margin assemblage that we interpret to belong to the Yukon-Tanana terrane. U–Pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of ~495 Ma, ~750 Ma, 1.05–1.40 Ga, 1.75–2.00 Ga, ~2.3 Ga, 2.5–2.7 Ga, and ~3.0 Ga. Multigrain fractions from two samples yield upper intercepts between 2.0 and 2.3 Ga, but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of < 2.0 and > 2.3 Ga grains. Zircons in these rocks generally overlap in age with (i) detrital zircons in metasedimentary rocks of the Yukon–Tanana terrane in eastern Alaska and Yukon, (ii) detrital zircons in strata of the Cordilleran miogeocline, and (iii) plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata. In addition, the pre-1.7 Ga grains overlap in age with dated crystalline rocks of the western Canadian Shield. These similarities raise the possibility that metaclastic rocks in the northern Coast Mountains accumulated in proximity to western North America. The younger zircon populations were likely shed from mid-Proterozoic to early Paleozoic igneous rocks that now occur locally (but may have been widespread) along the Cordilleran margin. Recognition of a continental margin assemblage of possible North American affinity in the Coast Mountains raises the possibility that some arc-type and oceanic terranes inboard of the Coast Mountains may be large klippen that have been thrust over the North American margin.
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Beranek, Luke P., James K. Mortensen, Michael J. Orchard, and Thomas Ullrich. "Provenance of North American Triassic strata from west-central and southeastern Yukon: correlations with coeval strata in the Western Canada Sedimentary Basin and Canadian Arctic Islands." Canadian Journal of Earth Sciences 47, no. 1 (January 2010): 53–73. http://dx.doi.org/10.1139/e09-065.
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New detrital mineral age and whole-rock geochemical data provide the first constraints on the composition and source of North American Triassic strata in the northern Canadian Cordillera. Conodont-bearing Triassic strata collected from five locations across west-central to southeastern Yukon contain trace-element ratios ((La/Yb)N = ∼8; Eu/Eu* = ∼0.66), εNd(248 Ma) values (–9 to –10), and detrital zircon ages (400–680, 980–1200, 1500–1650, 1800–2000 Ma) that correspond with those of coeval rocks in the Canadian Arctic Islands and the Western Canada Sedimentary Basin of British Columbia and Alberta. The majority of detrital zircons were cannibalized from Ellesmerian clastic wedge and western Laurentian margin strata and recycled into Triassic rocks. Conspicuous early Paleozoic and Neoproterozoic detrital zircons may have been ultimately derived from allochthonous rocks of Caledonian–Baltican affinity in northern North America, such as the Pearya and Arctic Alaska – Chukotka terranes. One Early Triassic unit in eastern Yukon contains ca. 360 Ma detrital muscovite, and samples from several localities include single-grain occurrences of Mississippian detrital zircon. Mississippian detrital mineral ages likely record a partial source from mid-Paleozoic rocks of the allochthonous Slide Mountain and Yukon–Tanana terranes following their Late Permian – Early Triassic emplacement onto the Cordilleran margin. More substantial evidence of terrane-derived sediment deposited along the North American margin may be further identified within Triassic strata that are exposed to the west (outboard) of our sample sites, immediately adjacent to the Slide Mountain and Yukon–Tanana terranes.
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O’Connor, Darragh, Ricardo L. Silva, and Grant Wach. "Earliest sedimentological evidence for marine ingressions in the eastern North American rift system, Central Atlantic Margin." Lithosphere 10, no. 6 (October 11, 2018): 783–91. http://dx.doi.org/10.1130/l713.1.
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Chang, Alice S., Thomas F. Pedersen, and Ingrid L. Hendy. "Late Quaternary paleoproductivity history on the Vancouver Island margin, western Canada: a multiproxy geochemical studyThis article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network." Canadian Journal of Earth Sciences 45, no. 11 (November 2008): 1283–97. http://dx.doi.org/10.1139/e08-038.
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Multiproxy analysis of a 38 m long sediment core recovered from the Vancouver Island margin (48.97°N, 127.04°W, water depth 1243 m) has yielded a millennial-scale history of upwelling and export production over the last ∼50 ka. Higher concentrations of marine organic carbon, opal, and trace Mo suggest that production was higher, and sedimentary pore waters more anoxic, during the warm Holocene, Bølling–Allerød, and interstadial events between 31 and 44 ka BP. Relatively lower production and higher inputs of terrigenous organic matter occurred during the last glacial (14.7–31 ka BP; Cordilleran ice sheet proximal to coring site at ∼19.5 ka BP) and from 44–50.4 ka BP. Enrichments in sedimentary δ15N during interstadial events are interpreted to reflect episodic delivery and upwelling of isotopically heavy nitrate to the surface waters and subsequent vectoring to the seafloor via settling planktonic detritus. Similar patterns are seen in southern California and other areas along the western margin of North America, implying that heavier nitrate generated by denitrification in the Eastern Tropical North Pacific has in the past been carried northward in the California Undercurrent at least as far as central Vancouver Island. This inference is consistent with modern hydrographic observations in the region. Comparison of the coherent Vancouver Island, Oregon, California, and northwest Mexico margin records with late Pleistocene climate history in Greenland reinforces the conclusion that a tight physical and biogeochemical coupling has existed for at least 50 ka between the North Atlantic and North American margin waters, including those off Vancouver Island.
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Andres, Heather J., and Lev Tarasov. "Towards understanding potential atmospheric contributions to abrupt climate changes: characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation." Climate of the Past 15, no. 4 (August 22, 2019): 1621–46. http://dx.doi.org/10.5194/cp-15-1621-2019.
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Abstract. Abrupt climate shifts of large amplitudes were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately 20 000 years ago, but their causes are not yet established. Midlatitude atmospheric dynamics may have played an important role in these climate variations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterizes deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations using the PlaSim Earth system model (run at T42 resolution) and the TraCE-21ka (T31) simulation. Though driven with yearly updates in surface elevation, we detect multiple instances of NAtl jet transitions in the PlaSim simulations that occur within 10 simulation years and a sensitivity of the jet to background climate conditions. Thus, we suggest that changes to the NAtl jet may play an important role in abrupt glacial climate changes. We identify two types of simulated wind changes over the last deglaciation. Firstly, the latitude of the NAtl eddy-driven jet shifts northward over the deglaciation in a sequence of distinct steps. Secondly, the variability in the NAtl jet gradually shifts from a Last Glacial Maximum (LGM) state with a strongly preferred jet latitude and a restricted latitudinal range to one with no single preferred latitude and a range that is at least 11∘ broader. These changes can significantly affect ocean circulation. Changes to the position of the NAtl jet alter the location of the wind forcing driving oceanic surface gyres and the limits of sea ice extent, whereas a shift to a more variable jet reduces the effectiveness of the wind forcing at driving surface ocean transports. The processes controlling these two types of changes differ on the upstream and downstream ends of the NAtl eddy-driven jet. On the upstream side over eastern North America, the elevated ice sheet margin acts as a barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability in the jet at LGM, so the jet shifts in sync with ice sheet margin changes. In contrast, the downstream side over the eastern NAtl is more sensitive to the thermal state of the background climate. Our results suggest that the presence of an elevated ice sheet margin in the south-eastern sector of the North American ice complex strongly constrains the deglacial position of the jet over eastern North America and the western North Atlantic as well as its variability.
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Routson, Cody C., Darrell S. Kaufman, Nicholas P. McKay, Michael P. Erb, Stéphanie H. Arcusa, Kendrick J. Brown, Matthew E. Kirby, et al. "A multiproxy database of western North American Holocene paleoclimate records." Earth System Science Data 13, no. 4 (April 19, 2021): 1613–32. http://dx.doi.org/10.5194/essd-13-1613-2021.
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Abstract. Holocene climate reconstructions are useful for understanding the diverse features and spatial heterogeneity of past and future climate change. Here we present a database of western North American Holocene paleoclimate records. The database gathers paleoclimate time series from 184 terrestrial and marine sites, including 381 individual proxy records. The records span at least 4000 of the last 12 000 years (median duration of 10 725 years) and have been screened for resolution, chronologic control, and climate sensitivity. Records were included that reflect temperature, hydroclimate, or circulation features. The database is shared in the machine readable Linked Paleo Data (LiPD) format and includes geochronologic data for generating site-level time-uncertain ensembles. This publicly accessible and curated collection of proxy paleoclimate records will have wide research applications, including, for example, investigations of the primary features of ocean–atmospheric circulation along the eastern margin of the North Pacific and the latitudinal response of climate to orbital changes. The database is available for download at https://doi.org/10.6084/m9.figshare.12863843.v1 (Routson and McKay, 2020).
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Thomas, William A. "Tectonic inheritance at multiple scales during more than two complete Wilson cycles recorded in eastern North America." Geological Society, London, Special Publications 470, no. 1 (February 9, 2018): 337–52. http://dx.doi.org/10.1144/sp470.4.
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AbstractEastern North America holds clear records of two Wilson cycles and hints of two earlier cycles, through which tectonic inheritance is evident at multiple scales. Large-scale transform offsets of rifted margins indicate inheritance through multiple cycles; transform-parallel intracratonic fault systems suggest a transform-parallel fabric in the lithosphere. Rift segments of the continental margins did not inherit the locations of earlier rifts; synrift intracratonic fault systems follow earlier contractional fabrics of supercontinent assembly. Large-scale curves of the Appalachian–Ouachita orogenic belt (closing of the Iapetus Ocean) mimic the shape of the Iapetan rifted margin of Laurentia. Basins along the Iapetan rifted margin reflect inheritance from transform faults in the greater magnitudes of early post-rift thermal subsidence and later synorogenic tectonic loading and flexural subsidence. Older synrift basement faults buttressed the frontal ramps of Appalachian–Ouachita thin-skinned thrust faults. Basement fault blocks and associated synrift stratigraphic variations in the weak layers that host the regional décollement localized transverse alignments of lateral ramps, as well as tectonic thickening of a mud-dominated graben-fill succession in a ductile duplex (mushwad). The many examples of tectonic inheritance attest to the linkages between processes of successive opening and closing of oceans, as well as the break-up and assembly of supercontinents, through successive Wilson cycles.
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Symons, David T. A., and Kazuo Kawasaki. "Eocene rotation of the Coast Plutonic Complex and Intermontane Belt: paleomagnetism of Eocene plutons along the Klondike Highway." Canadian Journal of Earth Sciences 48, no. 3 (March 2011): 645–60. http://dx.doi.org/10.1139/e10-093.
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Paleomagnetic results are reported for the ∼59 Ma Skagway, ∼54 Ma Fraser, ∼53 Ma Summit Lake, and ∼48 Ma Clifton felsic plutons of the eastern Coast Plutonic Complex (CPC) that outcrop along the south Klondike Highway in Alaska and British Columbia. Thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization (ChRM) directions for all 29 sites of normal, reversed, and mixed polarity. The ChRM resides in single or pseudosingle domain magnetite and (or) pyrrhotite that is shown to be primary by contact tests with the ∼47 Ma vertical White Pass mafic dikes. Paleopoles from six 56 to 50 Ma (mean 52 ± 2 Ma) Intermontane Belt – Yukon–Tanana terrane (IMB–YTT) units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 Ma (mean 52 ± 4 Ma) eastern CPC paleopoles. Both paleopole populations show nonsignificant poleward (northward) translation relative to North America (IMB–YTT, 3.7° ± 5.3°N; CPC, 4.3° ± 6.4°S; overall, 1.2° ± 4.9°S), indicating that northward translation of the accreted terranes ended by ∼58 Ma. Conversely, both populations show clockwise (CW) rotation that is either highly significant or substantial (IMB–YTT, 19.3° ± 10.5 °CW; CPC, 7.1° ± 16.1 °CW; overall 12.8° ± 10.9 °CW). The results are best explained by tectonic rotation from ∼50 to ∼45 Ma of the IMB–YTT as a thin-skin on top of North America during emplacement and co-incident rotation of the massive Eocene plutons of the eastern CPC along the North American margin.
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GLON, MAEL G., ROGER F. THOMA, MARYMEGAN DALY, and JOHN V. FREUDENSTEIN. "Lacunicambarus chimera: a new species of burrowing crayfish (Decapoda: Cambaridae) from Illinois, Indiana, Kentucky, and Tennessee." Zootaxa 4544, no. 4 (January 14, 2019): 451. http://dx.doi.org/10.11646/zootaxa.4544.4.1.
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Lacunicambarus diogenes (Girard 1852) was, until recently, considered to be one of the most widely distributed North American crayfish species, occurring in 31 U.S. States and one Canadian province east of the North American Rocky Mountains. Glon et al. (2018) investigated this claim and found that L. diogenes sensu lato was actually a species complex. The authors redescribed L. diogenes and restricted its range to the Atlantic Coastal Plain and Piedmont ecoregions of eastern North America. In doing so, they also revealed the existence of several probable undescribed species of Lacunicambarus that were previously considered to be L. diogenes. Here, we use morphological and molecular techniques to distinguish and describe one of these species: Lacunicambarus chimera sp. nov., a large primary burrowing crayfish found in parts of the Lower Mississippi, Ohio, Tennessee and Upper Mississippi River Basins. Lacunicambarus chimera is morphologically similar to L. diogenes, from which it can be distinguished by the greater number of spines on the ventrolateral margin of its merus, its wider antennal scale terminating in a short spine, and the presence of a single longitudinal stripe on the dorsal side of its abdomen. We also provide an updated key to Lacunicambarus.
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Hanger, Rex Alan. "Paleobiogeographic and paleogeographic significance of Permian brachiopod faunas of the Bilk Creek Limestone, Nevada, and the McCloud Limestone, California." Paleontological Society Special Publications 6 (1992): 119. http://dx.doi.org/10.1017/s2475262200006791.
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The Bilk Creek Limestone of the Black Rock Terrane in northwestern Nevada and the McCloud Limestone of the Eastern Klamath Terrane in northern California contain a diverse and abundant Permian brachiopod fauna currently under study. The composite rock record of both limestones spans the Wolfcampian and Leonardian stages of the Permian, during which both terranes were part of a volcanic arc separated from the North American continent by a marginal basin of unknown dimension. Brachiopods of this volcanic arc provide important evidence bearing on current hypotheses of Permian paleobiogeography and paleogeography.The Bilk Creek/ McCloud brachiopods are best characterized as an endemic fauna of a unique province and not as a mixed, “Tethyan” and North American fauna. The central problem of these arc faunas is not how similar they are to faunas of the Tethyan basin but why they are so dissimilar from North American faunas. Overlying rock units in both terranes contain Guadalupian brachiopod faunas that are North American in character. The paleobiogeographic pattern is one of decreasing levels of endemism throughout the Wolfcampian and Leonardian, to ultimate deprovincialization during the Guadalupian. This is not consistent with a pantropic dispersal hypothesis.The temporal pattern is consistent with a paleogeographic hypothesis of initial, long-distance separation of arc and continent with convergence of the arc toward the North American continental margin. The dissimilarity of the arc brachiopod faunas to coeval, same-environment faunas of North America suggests that the marginal basin that separated the two must have been several thousand kilometers wide during the Early Permian, producing the endemic fauna. A Japan-style model, with arc and continent in close proximity is not supported.
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Cook, Frederick A. "Lithospheric processes and products in the southern Canadian Cordillera: a Lithoprobe perspective." Canadian Journal of Earth Sciences 32, no. 10 (October 1, 1995): 1803–24. http://dx.doi.org/10.1139/e95-139.
Full textAbstract:
Analyses of Lithoprobe and other data from southwestern Canada provide new insights on how this portion of the Cordillera formed during plate convergence along the western margin of North America. Crustal rocks are detached from their mantle lithosphere, which must have been consumed during subduction. Detachment occurred at or near the base of the crust beneath the Intermontane and (or) Omineca belts, probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool, mechanically rigid, North American craton. During the Late Cretaceous and early Tertiary, rotation of detached rocks caught between the North American craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western Cordillera, and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern Cordillera during the same time interval. Transpression associated with rotation in the Foreland and Omineca belts ceased by the early Tertiary because detached allochthonous rocks of the crust became mechanically attached to, and thus physically part of, North America. Continued plate convergence led to regional transtensional shearing and associated crustal extension in the southern Canadian Cordillera, and perhaps as far inboard as northern Montana, where coeval magmatism was probably associated with new, or reactivation of ancient, lithosphere-penetrating fracture systems.
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COCKS, L. R. M., W. S. MCKERROW, and C. R. VAN STAAL. "The margins of Avalonia." Geological Magazine 134, no. 5 (September 1997): 627–36. http://dx.doi.org/10.1017/s0016756897007425.
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During Cambrian and earliest Ordovician times, Avalonia was an area forming an integral part of the huge Gondwanan continent, probably along the northern margin of Amazonia, until in early Ordovician (late Arenig or Llanvirn) time it split off from Gondwana, leaving a widening Rheic Ocean to its south. Today, its southern margin with Gondwana extends northeast from east of Cape Cod, Massachusetts, through Nova Scotia north of the Meguma terrane, and thence below sea level to the south of Newfoundland. On the eastern side of the present Atlantic, the southern margin may separate southwest Portugal from the rest of the Iberian Peninsula; it can be traced eastwards with more certainty from the south Cornwall nappes to a line separating the Northern Phyllite Belt (on the southern margin of the Rhenohercynian terrane) and the Mid-German Crystalline High. There is no certain evidence of Avalonian crust to the northeast of the Elbe Line. The northern margin of Avalonia extends westwards from south of Denmark to the British Isles, where it merges with the Iapetus Ocean suture between Scotland and England. Traced westwards, it crosses Ireland and reappears in northern Newfoundland to the east of New World Island, where it may follow the trace of the Dog Bay Line and the Cape Ray Fault. Recent work suggests that the northern margin of Avalonia may clip the northern tip of Cape Breton Island in Nova Scotia, and then enter the North American mainland at the Bay of Chaleur; it may then be traced from north and west of the Popelogan and Bronson Hill arcs to Long Island Sound near Newhaven, Connecticut. The Cambrian to Devonian faunas reflect the history of Avalonia: initially they were purely Gondwanan but, as Ordovician time proceeded, more genera crossed firstly the Tornquist Ocean as it narrowed between Avalonia and Baltica to close in latest Ordovician and early Silurian times, and secondly the Iapetus Ocean, so that by the early Silurian most of the benthic shelly faunas, apart from the ostracods, were the same round the adjacent margins of all three palaeocontinents.
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Stockmal, G. S., S. P. Colman-Sadd, C. E. Keen, S. J. O'Brien, and G. Quinlan. "Collision along an irregular margin: a regional plate tectonic interpretation of the Canadian Appalachians." Canadian Journal of Earth Sciences 24, no. 6 (June 1, 1987): 1098–107. http://dx.doi.org/10.1139/e87-107.
Full textAbstract:
An idealized plate tectonic model for the pre-Carboniferous development of the Canadian Appalachians explains the 400 km dextral offset of tectonostratigraphic zones from Quebec and northern New Brunswick to Newfoundland and the up to 600 km offset of oppositely verging belts of Acadian deformation from the Gaspé Peninsula to eastern Newfoundland. It is proposed that these offsets, which occur at the St. Lawrence promontory, result from the collision of an irregular North American passive continental margin with island arc and continental crust to the east, along an east-dipping subduction zone. The line of subduction is assumed to have been linear and the subducting slab to have maintained its mechanical integrity during collision. A "jigsaw fit" of the opposite sides of the Iapetus Ocean is made unnecessary by invoking lithospheric delamination and tectonic wedging during the Acadian orogeny in Newfoundland. The model is consistent with surface geology and recent deep seismic reflection observations from north of Newfoundland.
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Halls, H. C., and E. G. Shaw. "Paleomagnetism and orientation of Precambrian dykes, eastern Lake Superior region, and their use in estimates of crustal tilting." Canadian Journal of Earth Sciences 25, no. 5 (May 1, 1988): 732–43. http://dx.doi.org/10.1139/e88-069.
Full textAbstract:
Archean rocks form the eastern margin of the 1.1 Ga old Central North American rift along the eastern shore of Lake Superior and have been tilted westwards in response to rifting. Paleomagnetic and structural data from 2.6 Ga old Matachewan dykes suggest a westward crustal tilt of about 60°, which agrees well with dips recorded in nearby Keweenawan volcanics that rest directly on basement rocks. The Matachewan dyke swarm occurs throughout the east shore region of Lake Superior, whereas Keweenawan supracrustal sequences, which give a more precise estimate of tilt, are restricted to a few isolated shoreline patches. Estimates of crustal tilt can be obtained from the dykes on a regional basis, thus generating a more complete picture of basement deformation adjacent to a major intracratonic rift.
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Wheeler, Russell L., and Arch C. Johnston. "Geologic Implications of Earthquake Source Parameters in Central and Eastern North America." Seismological Research Letters 63, no. 4 (October 1, 1992): 491–514. http://dx.doi.org/10.1785/gssrl.63.4.491.
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Abstract The relations between geology and earthquakes remain mostly enigmatic in North America east of the Rocky Mountains. Hypocentral depths and the dips of rupture zones (preferred nodal planes) are among the seismological variables most likely associated with geologic structure in the stable continental region (SCR) of central and eastern North America (CENA). We compiled well-constrained depths and dips for 20 SCR shocks in CENA with magnitudes (M) between 4.9 and 6.8. The appendix lists the values we chose, our reasons for selecting specific values, and the uncertainties associated with each value. The median depth is 10 km, but an aseismic interval from about 15 to 25 km depth separates three midcrustal hypocenters from the others. The median dip of preferred nodal planes is 54°, and the larger earthquakes tend to rupture along shallower dips. These results combined with geologic evidence lead to four inferences about SCR earthquakes with M≥ 4.9 in CENA. (1) If rupture generally progresses updip, then the tendency for large earthquakes to rupture more shallowly-dipping surfaces than small earthquakes can explain the scarcity of surface ruptures in CENA. (2) The few midcrustal earthquakes might be evidence that mafic or granulite facies rocks are present. (3) CENA seismicity is concentrated in Late Proterozoic and Phanerozoic orogens and extended terranes that rim an older, stable, central craton. Unusually shallow large CENA earthquakes have been observed only in the central craton, where they might cause severe but localized shaking. (4) Earthquakes in the Appalachian orogen tend to be shallower than those of comparable size in the Late Proterozoic rifted continental margin that underlies and borders the northwest side of the orogen. As a result, some Appalachian earthquakes could cause more localized shaking than comparable shocks in the rifted margin.
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Gray, Keith D., V. Isakson, D. Schwartz, and Jeffrey D. Vervoort. "Orogenic link ∼41°N–46°N: Collisional mountain building and basin closure in the Cordillera of western North America." Geosphere 16, no. 1 (December 5, 2019): 136–81. http://dx.doi.org/10.1130/ges02074.1.
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Abstract Polyphase structural mapping and mineral age dating across the Salmon River suture zone in west-central Idaho (Riggins region; ∼45°30′N, ∼117°W–116°W) support a late Mesozoic history of penetrative deformation, dynamothermal metamorphism, and intermittent magmatism in response to right-oblique oceanic-continental plate convergence (Farallon–North America). High-strain linear-planar tectonite fabrics are recorded along an unbroken ∼48 km west-to-east transect extending from the Snake River (Wallowa intra-oceanic arc terrane; eastern Blue Mountains Province) over the northern Seven Devils Mountains into the lower Salmon River Canyon (ancestral North America; western Laurentia). Given the temporally overlapping nature (ca. 145–90 Ma) of east-west contraction in the Sevier fold-and-thrust belt (northern Utah–southeast Idaho–southwest Montana segment), we propose that long-term terrane accretion and margin-parallel northward translation in the Cordilleran hinterland (∼41°N–46°N latitude; modern coordinates) drove mid- to upper-crustal shortening >250 km eastward into the foreland region (∼115°W–113°W). During accretion and translation, the progressive transfer of arc assemblages from subducting (Farallon) to structurally overriding (North American) plates was accommodated by displacement along a shallow westward-dipping basal décollement system underlying the Cordilleran orogen. In this context, large-magnitude horizontal shortening of passive continental margin strata was balanced by the addition of buoyant oceanic crust—late Paleozoic to Mesozoic Blue Mountains Province—to the leading edge of western Laurentia. Consistent with orogenic float modeling (mass conservation, balance, and displacement compatibility), diffuse dextral-transpressional deformation across the accretionary boundary (Salmon River suture: Cordilleran hinterland) was kinematically linked to eastward-propagating structures on the continental interior (Sevier thrust belt; Cordilleran foreland). As an alternative to noncollisional convergent margin orogenesis, we propose a collision-related tectonic origin and contractional evolution for central portions of the Sevier belt. Our timing of terrane accretion supports correlation of the Wallowa terrane with Wrangellia (composite arc/plateau assemblage) and implies diachronous south-to-north suturing and basin closure between Idaho and Alaska.
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Kear, Benjamin P., Thomas H. Rich, Mohammed A. Ali, Yahya A. Al-Mufarrih, Adel H. Matiri, Abdu M. Al-Masary, and Mohammed A. Halawani. "First Triassic lungfish from the Arabian Peninsula." Journal of Paleontology 84, no. 1 (January 2010): 137–40. http://dx.doi.org/10.1666/09-098.1.
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Triassic lungfish (Dipnoi) have been extensively documented from the Gondwanan continental and marine shelf deposits of Africa and Madagascar (Teixeira, 1949; Lehman et al., 1959; Beltan, 1968; Martin, 1979, 1981; Kemp 1996), Australia (Kemp, 1993, 1994, 1997a, 1998), India (Jain et al, 1964; Jain, 1968), and Antarctica (Dziewa, 1980). Numerous records also exist from Laurasian landmasses including Europe (Agassiz, 1838; Schultze, 1981), North America (Case, 1921) and central and eastern Asia (Liu and Yeh, 1957; Vorobyeva, 1967; Martin and Ingavat, 1982). By comparison, nothing is known of contemporary lungfish fossils from the Middle East. Thus, the recent recovery of a single tooth plate representing a new geographic occurrence of the genus Ceratodus Agassiz, 1838 from paralic marine deposits of the Jilh Formation, a latest Anisian to lower Carnian unit that crops out along the eastern margin of the Proterozoic Arabian Shield in central Saudi Arabia (Fig. 1), is significant because it provides the stratigraphically oldest record of dipnoans from the Arabian Peninsula.
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Greene, John A., Masako Tominaga, Nathaniel C. Miller, Deborah R. Hutchinson, and Matthew R. Karl. "Refining the Formation and Early Evolution of the Eastern North American Margin: New Insights From Multiscale Magnetic Anomaly Analyses." Journal of Geophysical Research: Solid Earth 122, no. 11 (November 2017): 8724–48. http://dx.doi.org/10.1002/2017jb014308.
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Tamay, José, Jesús Galindo-Zaldivar, John Soto, and Antonio J. Gil. "GNSS Constraints to Active Tectonic Deformations of the South American Continental Margin in Ecuador." Sensors 21, no. 12 (June 10, 2021): 4003. http://dx.doi.org/10.3390/s21124003.
Full textAbstract:
GNSS observations constitute the main tool to reveal Earth’s crustal deformations in order to improve the identification of geological hazards. The Ecuadorian Andes were formed by Nazca Plate subduction below the Pacific margin of the South American Plate. Active tectonic-related deformation continues to present, and it is constrained by 135 GPS stations of the RENAGE and REGME deployed by the IGM in Ecuador (1995.4–2011.0). They show a regional ENE displacement, increasing towards the N, of the deformed North Andean Sliver in respect to the South American Plate and Inca Sliver relatively stable areas. The heterogeneous displacements towards the NNE of the North Andean Sliver are interpreted as consequences of the coupling of the Carnegie Ridge in the subduction zone. The Dolores–Guayaquil megashear constitutes its southeastern boundary and includes the dextral to normal transfer Pallatanga fault, that develops the Guayaquil Gulf. This fault extends northeastward along the central part of the Cordillera Real, in relay with the reverse dextral Cosanga–Chingual fault and finally followed by the reverse dextral Sub-Andean fault zone. While the Ecuadorian margin and Andes is affected by ENE–WSW shortening, the easternmost Manabí Basin located in between the Cordillera Costanera and the Cordillera Occidental of the Andes, underwent moderate ENE–WSW extension and constitutes an active fore-arc basin of the Nazca plate subduction. The integration of the GPS and seismic data evidences that highest rates of deformation and the highest tectonic hazards in Ecuador are linked: to the subduction zone located in the coastal area; to the Pallatanga transfer fault; and to the Eastern Andes Sub-Andean faults.
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MOUMBLOW, R. M., G. A. ARCURI, A. P. DICKIN, and C. F. GOWER. "Nd and Pb isotope mapping of crustal domains within the Makkovik Province, Labrador." Geological Magazine 156, no. 5 (April 3, 2018): 833–48. http://dx.doi.org/10.1017/s0016756818000195.
Full textAbstract:
AbstractThe Makkovik Province of eastern Labrador represents part of an accretionary orogen active during an early stage in the development of the Palaeoproterozoic southern Laurentian continental margin. New Nd isotope data for the eastern Makkovik Province suggest that accreted juvenile Makkovik crust was generated in the Cape Harrison domain during a single crust-forming event at c. 2.0 Ga. Pb isotope data support this model, and show a strong similarity to radiogenic crustal signatures in the juvenile Palaeoproterozoic crust of the Ketilidian mobile belt of southern Greenland. As previously proposed, an arc accretion event at c. 1.9 Ga triggered subduction-zone reversal and the development of an ensialic arc on the composite margin. After the subduction flip, a temporary release of compressive stress at c. 1.87 Ga led to the development of a retro-arc foreland basin on the downloaded Archean continental edge, forming the Aillik Group. Unlike previous models, a second arc is not envisaged. Instead, a compressive regime at c. 1.82 Ga is attributed to continued ensialic arc plutonism on the existing margin. The tectonic model for the Makkovikian orogeny proposed here is similar to that for the Ketilidian orogeny. Major- and trace-element analyses suggest that much of the magmatism in the Makkovik orogen results from post-accretionary ensialic arc activity, and that few vestiges remain of the original accreted volcanic arc. This pattern of arc accretion and intense post-accretion reworking is common to many accretionary orogens, such as the South American Andes and North American Cordillera.
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de Castro, D. L., and F. H. R. Bezerra. "Fault evolution in the Potiguar rift termination, equatorial margin of Brazil." Solid Earth 6, no. 1 (February 12, 2015): 185–96. http://dx.doi.org/10.5194/se-6-185-2015.
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Abstract. The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify architecture of fault systems and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The basin is located along the NNE margin of South America that faces the main transform zone that separates the North and the South Atlantic. The Potiguar rift is a Neocomian structure located at the intersection of the equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide, and ~ 40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en echelon system of NW–SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by postrift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the rift termination but also as isolated structures away from the main rift. This study indicates that the strike-slip shearing between two plates propagated to the interior of one of these plates, where faults with similar orientation, kinematics, geometry, and timing of the major transform are observed. These faults also influence rift geometry.
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Narkiewicz, Katarzyna, and Pierre Bultynck. "Taxonomy and biostratigraphic significance of Icriodus orri Klapper and Barrick and related Middle Devonian conodont species." Journal of Paleontology 90, no. 6 (October 11, 2016): 1181–96. http://dx.doi.org/10.1017/jpa.2016.41.
Full textAbstract:
AbstractThe present study of the Eifelian icriodid conodonts is based on collections from Belarus and the Michigan Basin (USA). It is here proposed that forms originally included in Icriodus orri Klapper and Barrick, 1983 can be attributed to I. retrodepressus Bultynck, 1970, Icriodus orri sensu stricto, and Icriodus michiganus new species, each displaying a distinct morphology, stratigraphical range, and geographic distribution. Icriodus retrodepressus, characterized by a triangular spindle, deep depression in its posterior part, and a well-pronounced spur and antispur, appeared in the lower partitus Zone of the lowermost Eifelian and disappeared in the upper Eifelian kockelianus Zone. Icriodus michiganus n. sp., distinguished by a lachrymiform spindle with a shallow posterior depression, ranges from the lower costatus Zone to the upper kockelianus Zone. Icriodus orri differs from the other two species by the occurrence of transverse denticle rows with lateral denticles displaying sharp edges. It ranges from the upper kockelianus Zone to the ensensis Zone of the uppermost Eifelian. Icriodus retrodepressus first occurred in the European part of the Euramerican continent and later migrated into the North American area. Icriodus michiganus n. sp. has been found in the interior part of the North American Craton and near the eastern Euramerican margin. Icriodus orri occurs in the North American interior, in British Columbia (Canada), and in the eastern part of Euramerica (Belarus). The introduction of I. retrodepressus can be related to the transgressive Choteč Event, whereas that of I. orri to a transgressive stage of the Ie eustatic cycle.
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Markina, M. Y., J. H. P. Studholme, and S. K. Gulev. "Ocean Wind Wave Climate Responses to Wintertime North Atlantic Atmospheric Transient Eddies and Low-Frequency Flow." Journal of Climate 32, no. 17 (August 6, 2019): 5619–38. http://dx.doi.org/10.1175/jcli-d-18-0595.1.
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Abstract Atmospheric transient eddies and low-frequency flow contributions to the ocean surface wave climate in the North Atlantic during boreal winter are investigated (1980–2016). We conduct a set of numerical simulations with a spectral wave model (WAVEWATCH III) forced by decomposed wind fields derived from the ERA-Interim reanalysis (0.7° horizontal resolution). Synoptic-scale processes (2–10-day bandpassed winds) are found to have the largest impact on the formation of wind waves in the western midlatitudes of the North Atlantic along the North American and western Greenland coasts. The eastern North Atlantic is found to be influenced by the combination of low-frequency forcing (>10-day bandpassed winds) and synoptic processes, contributing up to 60% and 30% of the mean wave heights, respectively. Midlatitude storm track variability is found to have a direct relationship with wave height variability along the eastern and western margins of the North Atlantic, implying an association between cyclogenesis over the North American eastern seaboard and wave height anomalies in the eastern North Atlantic. A change in wave height regimes defined using canonical correlation analysis is reflected in changes to their wave height distribution shapes. The results highlight the important role of transient eddies for the ocean surface wave climatology in the midlatitudes of the eastern North Atlantic both locally and through association with cyclone formation in the western part of the basin. These conclusions are presented and discussed particularly within the context of long-term storm track shifts projected as a possible response to climate warming over the coming century.
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Kuiper, Yvette D., Margaret D. Thompson, Sandra M. Barr, Chris E. White, J. Christopher Hepburn, and James L. Crowley. "Detrital zircon evidence for Paleoproterozoic West African crust along the eastern North American continental margin, Georges Bank, offshore Massachusetts, USA." Geology 45, no. 9 (July 10, 2017): 811–14. http://dx.doi.org/10.1130/g39203.1.
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Pe-Piper, Georgia, and David JW Piper. "Were Jurassic tholeiitic lavas originally widespread in southeastern Canada?: a test of the broad terrane hypothesis." Canadian Journal of Earth Sciences 36, no. 9 (September 1, 1999): 1509–16. http://dx.doi.org/10.1139/e99-059.
Full textAbstract:
Two competing models have been proposed for Early Jurassic magmatism on the eastern North American margin. The "broad terrane" hypothesis argues that tholeiitic lavas were extruded over a large area and later eroded. Alternatively, the lavas were extruded only in the basins in which they now outcrop. We compare the stratigraphy and geochemistry of the tholeiitic lavas and dykes from Atlantic Canada with those of the type section of the Newark basin and use this correlation to test these two models. The earliest high-Ti quartz tholeiites in the type section are represented by lavas in the Fundy basin (North Mountain Basalt), Scotian basin, and eastern Grand Banks and by the Shelburne and Ministers Island dykes. Spatial and temporal geochemical variations in the North Mountain Basalt are mirrored by the Shelburne dyke, strengthening the case that the two were geochemically related. Basalts in Grand Manan Island, on the footwall of the Grand Manan fault that bounds the Fundy basin, are geochemically similar to the lowest North Mountain Basalt flow. These observations suggest that the earliest basalt flows were originally more extensive and have become restricted by later uplift and erosion. However, younger magmas in the Newark basin are represented only by the Caraquet, Anticosti, and Avalon dykes in Atlantic Canada, and corresponding lavas were never deposited in the Fundy basin or eastern Grand Banks. Thus, Jurassic tholeiitic lava distribution lies in between the predictions of the "broad terrane" and the "restricted basin" models.
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Welford, J. Kim, Ron M. Clowes, Robert M. Ellis, George D. Spence, Isa Asudeh, and Zoltan Hajnal. "Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia." Canadian Journal of Earth Sciences 38, no. 8 (August 1, 2001): 1169–89. http://dx.doi.org/10.1139/e01-020.
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The lithospheric structure of the transition from the craton to the Cordillera in northeastern British Columbia is interpreted from inversion of seismic refraction wide-angle reflection data along a 460-km profile, and from 3-d (3-dimensional) inversion and 2.5-d forward modelling of Bouguer gravity data. The seismic profile extends westward from the sediment-covered edge of cratonic North America across the Foreland and Omineca morphogeological belts to the eastern boundary of accreted terranes, beyond the Tintina Fault. Across the ancient cratonic margin, the resultant models reveal a westward-thickening package of low upper crustal velocities (6.2 km/s and less) and low densities to almost 20 km depth below the Western Canada Sedimentary Basin, overlying a west-facing ramp of higher velocities and densities in the middle and lower crust. These features are inferred to represent passive-margin sediments deposited on the ancient rifted margin during the mid-to-late Proterozoic and early Paleozoic. A wedge-shaped high-velocity (7.3 km/s) crustal layer at the base of the crust beneath the edge of cratonic North America is interpreted to be the result of magmatic underplating during rifting. In the Cordilleran Foreland Belt, high velocities (6.4 km/s) in the upper 5 km of the crust indicate rocks upthrust from the middle crust. A narrow trench of low velocities in the near-surface, which is imaged ~20 km to the west of the inferred location of the Tintina Fault, is interpreted to represent the actual location of the fault or a major splay. From east to west, the Moho decreases in depth from ~40 km to ~34 km below the rifted margin of ancestral North America, then defines a small root at ~38 km depth below the high topography and upper crustal velocities of the eastern Foreland Belt, and gradually shallows to ~34 km beneath the Omineca belt. An enigmatic laterally heterogeneous upper mantle has anomalously high velocities (up to 8.3 km/s) beneath the Foreland Belt, flanked by regions of low velocities (7.77.8 km/s). Results indicate that the location of the Cordilleran deformation front west of the ramped cratonic margin directly affected the tectonic evolution of the region.
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Withjack, Martha, MaryAnn Malinconico, and Michael Durcanin. "The “Passive” Margin of Eastern North America: Rifting and the Influence of Prerift Orogenic Activity on Postrift Development." Lithosphere 2020, no. 1 (August 24, 2020): 1–29. http://dx.doi.org/10.2113/2020/8876280.
Full textAbstract:
Abstract We have analyzed and synthesized geologic and geophysical data from the onshore Newark rift basin and adjacent onshore and offshore basins to better understand the Mesozoic development of the eastern North American rift system and passive margin. Our work indicates that rifting had three phases: (1) an initial, prolonged phase of extension and subsidence; (2) a short-lived phase with higher rates of extension and subsidence, intrabasin faulting, and intense magmatism; and (3) a final phase with limited subsidence and deposition. Additionally, our work shows that anomalous uplift and erosion, associated with crustal-scale arching/warping subparallel to the prerift and syn-rift crustal fabric not the continent-ocean boundary, affected a region landward of the basement hinge zone. Uplift and erosion began during the final rifting phase and continued into early drifting with erosion locally exceeding 6 km. Subsequent subsidence was minimal. We propose that denudation unloading related to relic, prerift orogenic crustal thickness and elevated topography triggered the anomalous uplift and erosion. After the Paleozoic orogenies, postorogenic denudation unloading (cyclic erosion and isostatic rebound/uplift) significantly thinned the thickened crust and reduced topographic elevation. During rifting, extension stretched and tectonically thinned the crust, promoting widespread subsidence and deposition that dampened the postorogenic cycle of erosion and isostatic rebound/uplift. During the rift-drift transition, with extension focused near the breakup site, denudation unloading resumed landward of the basement hinge zone, producing significant erosion and uplift (related to isostatic rebound), crustal thinning, and topographic decay that left behind only eroded remnants of the once massive rift basins.
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Cowan, Hugh, Graeme Beattie, Katherine Hill, Noel Evans, Craig McGhie, Gary Gibson, Graeme Lawrance, et al. "The M8.8 Chile earthquake, 27 February 2010." Bulletin of the New Zealand Society for Earthquake Engineering 44, no. 3 (September 30, 2011): 123–66. http://dx.doi.org/10.5459/bnzsee.44.3.123-166.
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The largest earthquake of 2010 by magnitude (MW8.8), and the subject of this article, struck south-central Chile in the early hours of 27 February 2010. The earthquake was a “mega-thrust” event, involving the rupture of a section of the Nazca-South American plate boundary, where the Nazca plate dips at a shallow angle beneath the Pacific margin of South America.
Understanding this event and its effects, including tsunami is of particular significance to urban centres that share close proximity to “subduction zones”. These include Seattle, Vancouver, Tokyo and Wellington, together with smaller New Zealand towns of the eastern North Island and upper South Island. The tectonic setting of south-central Chile has similarities to the East Coast of the North Island, and the modern built environment of Chile shares attributes with New Zealand. However, New Zealand has not experienced a large subduction earthquake in the North Island region in at least 200 years, so an understanding of the Chile event and its impact is important for bench-marking of local practices and building resilience.
This report summarises the observations of the NZSEE/EQC teams, supplemented by media updates on the Chilean reconstruction experience one year after the earthquake.
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Greig, Charles J. "Jurassic and Cretaceous plutonic and structural styles of the Eagle Plutonic Complex, southwestern British Columbia, and their regional significance." Canadian Journal of Earth Sciences 29, no. 4 (April 1, 1992): 793–811. http://dx.doi.org/10.1139/e92-067.
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The Eagle Plutonic Complex is an elongate north-northwest-trending body of deformed Middle to Late Jurassic and middle Cretaceous rocks which underlies the southwestern margin of the Intermontane terrane. New mapping of the complex and its country rocks, in concert with geochronometry, has defined episodes of contractional, ductile deformation in the Middle to Late Jurassic and middle Cretaceous, as well as brittle deformation in Tertiary time. Synkinematic Middle to Late Jurassic Eagle tonalite at the eastern margin of the Eagle Complex intrudes mylonitic Nicola Group rocks and structurally overlies them along a southwest-dipping belt of high strain (Eagle shear zone) with a structural thickness of > 1 km and a strike length of > 100 km. In the central and western Eagle Complex, Eagle tonalite grades into tonalite orthogneiss (Eagle gneiss), and both are crosscut by mid-Cretaceous, muscovite-bearing plutons of the Fallslake Plutonic Suite. Fallslake Suite rocks are themselves ductilely deformed along the Pasayten fault, which bounds the Eagle Complex on the west and was active mainly in the mid-Cretaceous (ductile deformation with sinistral, east-side-up, reverse displacement). The Jurassic and Cretaceous episodes of deformation may reflect the respective initial and final stages of the accretion of the Insular terrane to the North American margin. West of the Pasayten fault, Middle to Late Jurassic and older(?) rocks of the Zoa Complex are structurally overlain, in part, by deformed Middle Eocene and middle Cretaceous sedimentary rocks. In the north, the Middle Eocene rocks are intruded on their west side by the Middle Eocene Needle Peak pluton.
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Umhoefer, Paul J., C. Plattner, and R. Malservisi. "Quantifying rates of “rifting while drifting” in the southern Gulf of California: The role of the southern Baja California microplate and its eastern boundary zone." Lithosphere 12, no. 1 (February 1, 2020): 122–32. http://dx.doi.org/10.1130/l1132.1.
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Abstract The southern Baja California (Mexico) microplate has been rapidly moving away from the North America plate since ca. 12 Ma. This relative motion toward the northwest developed an oblique-divergent plate boundary that formed the Gulf of California. The rift-drift hypothesis postulates that when a continent ruptures and seafloor spreading commences, rifting on the plate margins ceases, and the margins start to drift, subside, and accumulate postrift sediments, eventually becoming a passive margin. In contrast to this hypothesis, the southern part of the Baja California microplate (BCM), and in particular its actively deforming eastern boundary zone, has continued significant rifting for millions of years after seafloor spreading initiated within the southern Gulf of California at 6–2.5 Ma. This is a process we call “rifting-while-drifting.” Global positioning system (GPS)–based data collected from 1998 to 2011 show relative motion across the eastern boundary zone up to ∼2–3.2 mm/yr with respect to a stable BCM. Furthermore, the velocity directions are compatible with normal faulting across the eastern boundary zone nearly perpendicular to the trend of the plate boundary at the latitude of La Paz and therefore a highly strain partitioned domain. North of 25°N latitude up to the Loreto area, there is a domain with no strain partitioning, and northwest-directed transtensional deformation dominates. From long-term geologic and paleoseismology studies, late Quaternary faulting rates are equal to or less than the GPS-derived rates, while geologic rates older than 1–2 Ma are commonly much higher. We suggest that the “rifting-while-drifting” process may be caused by the large topographic relief across the BCM margin, which created a significant gradient in gravitational potential energy that helps in driving continued relatively slow faulting. The relief was inherited from the much faster faulting of the BCM eastern boundary zone before plate motions largely localized along the modern transform–spreading centers in the axis of the Gulf of California. The low sediment flux from the small drainages and arid climate on the southern Baja California Peninsula result in the maintenance of underfilled to starved basins, and the relatively slow late Quaternary active faulting promotes continued topographic relief over millions of years.
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Stone, Philip. "Geology reviewed for the Falkland Islands and their offshore sedimentary basins, South Atlantic Ocean." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 106, no. 2 (June 2015): 115–43. http://dx.doi.org/10.1017/s1755691016000049.
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ABSTRACTThe position of the Falkland Islands adjacent to the South American continental margin belies the close association of their geology with that of South Africa. A Mesoproterozoic basement is unconformably overlain by a Silurian to Devonian succession of fluvial to neritic and shallow marine, siliciclastic strata. This is disconformably succeeded by a largely Permian succession that, near its base, includes a glacigenic diamictite and, thence, passes upwards into a succession of deltaic and lacustrine strata. The lithological succession and the character of its deformation bear striking similarities to the Cape Fold Belt and Karoo retroarc foreland basin. Swarms of Early Jurassic dykes were coeval with the Karoo magmatism and the initial break-up of Gondwana; Early Cretaceous dykes were intruded during the opening of the South Atlantic Ocean. Offshore sedimentary basins surrounding the archipelago contain Late Jurassic to Palaeogene successions and are currently the focus of hydrocarbon exploration. Best known is the North Falkland Basin, a classic failed rift. To the SE, the passive margin, Falkland Plateau Basin may also be rift-controlled, whilst the South Falkland Basin is a foreland basin created at the boundary of the South American and Scotia plates. The role of the Falkland Islands during the breakup of Gondwana remains controversial. Compelling evidence from the onshore geology favours rotation of an independent microplate from an original position adjacent to the Eastern Cape, South Africa. Alternative interpretations, justified largely from offshore geology, favour extension of the Falkland Plateau as a fixed promontory from the South American margin.
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Greenwood, David R., S. Bruce Archibald, Rolf W. Mathewes, and Patrick T. Moss. "Fossil biotas from the Okanagan Highlands, southern British Columbia and northeastern Washington State: climates and ecosystems across an Eocene landscape." Canadian Journal of Earth Sciences 42, no. 2 (February 1, 2005): 167–85. http://dx.doi.org/10.1139/e04-100.
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The late Early to early Middle Eocene Okanagan Highlands fossil sites, spanning ~1000 km northsouth (northeastern Washington State, southern British Columbia) provide an opportunity to reconstruct biotic communities across a broad upland landscape during the warmest part of the Cenozoic. Plant taxa from these fossil sites are characteristic of the modern eastern North American deciduous forest zone, principally the mixed mesophytic forest, but also include extinct taxa, taxa known only from eastern Asian mesothermal forests, and a small number of taxa restricted to the present-day North American west coast coniferous biome. In this preliminary report, paleoclimates and forest types are reconstructed using collections from Republic in Washington State, USA., and Princeton, Quilchena, Falkland, McAbee, Hat Creek, Horsefly, and Driftwood Canyon in British Columbia, Canada. Both leaf margin analysis (LMA) and quantitative bioclimatic analysis of identified nearest living relatives of megaflora indicated upper microthermal to lower mesothermal moist environments (MAT ~1015 °C, CMMT > 0 °C, MAP > 100 cm/year). Some taxa common to most sites suggest cool conditions (e.g., Abies, other Pinaceae; Alnus, other Betulaceae). However, all floras contain a substantive broadleaf deciduous element (e.g., Fagaceae, Juglandaceae) and conifers (e.g., Metasequoia) with the bioclimatic analysis yielding slightly higher MAT than LMA. Thermophilic (principally mesothermal) taxa include various insects, the aquatic fern Azolla, palms, the banana relative Ensete, taxodiaceous conifers, Eucommia and Gordonia, taxa which may have occurred near their climatic limits. The mixture of thermophilic and temperate insect and plant taxa indicates low-temperature seasonality (i.e., highly equable climate).
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Lowey, Grant W. "Very low-grade metamorphism of the Dezadeash Formation (Jura-Cretaceous): Constraints on the tectonometamorphic history of the Dezadeash flysch basin and implications regarding the tectonic evolution of the Northern Cordillera of Alaska and Yukon." AIMS Geosciences 7, no. 3 (2021): 355–89. http://dx.doi.org/10.3934/geosci.2021022.
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<abstract> <p>Mesozoic convergence of the Wrangellia composite terrane with the western margin of North America resulted in the collapse of intervening flysch basins. One of these basins, the Jurassic-Cretaceous Gravina-Nuzotin belt, comprises from south to north, the Gravina sequence and Gravina belt in southeastern Alaska, the Dezadeash Formation in Yukon, and the Nutzotin Mountains sequence in eastern Alaska. Previous work shows that the Gravina sequence and Gravina belt were underthrust > 20 km beneath the margin of North America in mid-Cretaceous time, culminating in amphibolite facies metamorphism. This tectonometamorphic scenario was subsequently applied to the entire Gravina-Nutzotin belt, despite any detailed studies pertaining to the tectonometamorphic evolution of the Dezadeash Formation. The present analysis of the Dezadeash Formation reveals that metamorphic mineral assemblages in sandstone and tuff document subgreenschist, high temperature zeolite facies metamorphism; Kübler indices of illite and Árkai indices of chlorite in mudstone record diagenetic to high anchizone metapelitic conditions; and the color of organic matter (i.e., the Thermal Alteration Index of palynomorphs and the Conodont Alteration Index) and pyrolysis of organic matter in mudstone and hemipelagite beds document thermal maturation at catagenesis to mesogenesis stages. Collectively, the mineralogic and organic thermal indicators in the Dezadeash Formation suggest that strata experienced maximum pressure-temperature conditions of 2.5 ± 0.5 kbar and 250 ± 25 ℃ in the Early Cretaceous. The inferred tectonometamorphic evolution of the Dezadeash Formation does not support the northern part of the Gravina-Nutzotin belt being underthrust > 20 km beneath the western margin of North America in mid-Cretaceous time, thus contrasting sharply with the Gravina sequence and Gravina belt in the southern part of the Gravina-Nutzotin belt. The diverse tectonometamorphic histories recorded by the southern and northern parts of the Gravina-Nutzotin belt may be a manifestation of oblique collision and diachronous south-to-north accretion of the Wrangellia composite terrane to North America.</p> </abstract>
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Shorten, Chilisa M., and Paul G. Fitzgerald. "Episodic exhumation of the Appalachian orogen in the Catskill Mountains (New York State, USA)." Geology 49, no. 5 (January 26, 2021): 571–75. http://dx.doi.org/10.1130/g48011.1.
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Abstract Increasing evidence indicates the eastern North American passive margin has not remained tectonically quiescent since Jurassic continental breakup. The identification, timing, resolution, and significance of post-orogenic exhumation, notably an enigmatic Miocene event, are debated. We add insight by constraining the episodic cooling and exhumation history of the Catskill Mountains (New York, USA) utilizing apatite fission-track thermochronology and apatite (U-Th)/He data from a ∼1 km vertical profile. Multi-kinetic inverse thermal modeling constrains three phases of cooling: Early Jurassic to Early Cretaceous (1–3 °C/m.y.), Early Cretaceous to early Miocene (∼0.5 °C/m.y.), and since Miocene times (1–2 °C/m.y.). Previous thermochronologic studies were unable to verify late-stage cooling and/or exhumation (typically post-Miocene and younger) because late-stage cooling was commonly a spurious artifact of earlier mono-kinetic annealing algorithms. Episodic cooling phases are correlative with rifting, passive-margin development, and drainage reorganization causing landscape rejuvenation. Geomorphologic documentation of increased offshore mid-Atlantic sedimentation rates and onshore erosion support the documented accelerated Miocene cooling and exhumation.
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Timmermans, Ann C., Brian L. Cousens, and Christopher D. Henry. "Geochemical study of Cenozoic mafic volcanism in the west-central Great Basin, western Nevada, and the Ancestral Cascades Arc, California." Geosphere 16, no. 5 (July 10, 2020): 1179–207. http://dx.doi.org/10.1130/ges01535.1.
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Abstract Processes linked to shallow subduction, slab rollback, and extension are recorded in the whole-rock major-, trace-element, and Sr, Nd, and Pb isotopic compositions of mafic magmatic rocks in both time and space over southwestern United States. Eocene to Mio-Pliocene volcanic rocks were sampled along a transect across the west-central Great Basin (GB) in Nevada to the Ancestral Cascade Arc (ACA) in the northern Sierra Nevada, California (∼39°–40° latitude), which are interpreted to represent a critical segment of a magmatic sweep that occurred as a result of subduction from east-northeast convergence between the Farallon and North American plates and extension related to the change from a convergent to a transform margin along the western edge of North America. Mafic volcanic rocks from the study area can be spatially divided into three broad regions: GB (5–35 Ma), eastern ACA, and western ACA (2.5–16 Ma). The volcanic products are dominantly calc-alkalic but transition to alkalic toward the east. Great Basin lavas erupted far inland from the continental margin and have higher K, P, Ti, and La/Sm as well as lower (Sr/P)pmn, Th/Rb, and Ba/Nb compared to ACA lavas. Higher Pb isotopic values, combined with lower Ce/Ce* and high Th/Nb ratios in some ACA lavas, are interpreted to come from slab sediment. Mafic lavas from the GB and ACA have overlapping 87Sr/86Sr and 143Nd/144Nd values that are consistent with mantle wedge melts mixing with a subduction-modified lithospheric mantle source. Eastern and western ACA lavas largely overlap in age and elemental and isotopic composition, with the exception of a small subset of lavas from the westernmost ACA region; these lavas show lower 87Sr/86Sr at a given 143Nd/144Nd. Results show that although extension contributes to melting in some regions (e.g., selected lavas in the GB and Pyramid Lake), chemical signatures for most mafic melts are dominated by subduction-related mantle wedge and a lithospheric mantle component.
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Hyndman, Roy D., Paul Flück, Stephane Mazzotti, Trevor J. Lewis, John Ristau, and Lucinda Leonard. "Current tectonics of the northern Canadian Cordillera." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1117–36. http://dx.doi.org/10.1139/e05-023.
Full textAbstract:
The northern Canadian Cordillera is remarkably tectonically and seismically active, extending from a terrane collision zone on the continental margin to an active fold and thrust belt at the eastern mountain front. The source and distribution of the deformation are constrained by (i) precision global positioning system (GPS) measurements; (ii) the seismicity distribution, mechanisms, and rates; (iii) the thermal regime; (iv) estimates of lithosphere thickness and strength; and (v) topography and gravity. The ongoing oblique collision of the Yakutat block in the northeast corner of the Gulf of Alaska has produced large deformation and uplift in the adjacent Saint Elias and Chugach mountains and appears to be responsible for the current deformation 800 km to the northeast. Northern Cordillera GPS velocities are ∼5 mm/year northeast relative to the North American Craton. Deformation rates across the eastern mountain front from earthquake statistics are similar, i.e., ∼4 mm/year of thrust shortening across the Mackenzie Mountains and right-lateral strike-slip in the Richardson Mountains. This large-scale motion is explained by a quasi-rigid displacement of the upper crust over a lower crust detachment. The detachment zone is a consequence of the high temperature of the northern Cordillera lithosphere and a weak eastern Cordillera deformation front. Regional Moho temperatures of 800950 °C are indicated by very high heat flow and other indicators of deep temperature and by the thin lithosphere effective thickness (Te). The northern Cordillera model may have application in other areas, such as the earlier thrusting in the southern Canadian Rocky Mountains driven by terrane collision along the Pacific margin.