The First Results of U–Pb Isotope Dating of Detrital Zircons from the Upper Mesoproterozoic Gulliksenfellet Quartzite (Southern Part of Wedel Jarlsberg Land, Southwest Spitsbergen)
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Chronostratigraphic sequences of wide areal extent beneath the United States Atlantic margin north of Cape Hatteras have been delineated by: (1) examination of four COST (Continental Offshore Stratigraphic Test) wells, 1 exploratory well (Shell, Blk. 272, No. 1, OCS A 0096), 14 shallow AMCOR (Atlanctic Margin Coring) core holes, and eight ASP (Atlantic Slope Project) core holes; (2) analysis of multichannel seismic reflection profiles collected along several thousand kilometers of track lines; and (3) comparison of these interpretations to the Canadian offshore chronostratigraphy. In the Baltimore Canyon Trough and Georges Bank basin, seismically identified regional unconformities are associated with Lower Jurassic, Middle Jurassic, Upper Jurassic-Lower Cretaceous, upper auterivian, Cenomanian, Turonian-Coniacian, Upper Cretaceous-lower Paleocene, Oligocene, and upper Miocene-Pliocene rocks. The Tertiary unconformities are identified best in the Baltimore Canyon Trough where the thickness of Tertiary rocks exceeds 1,400 m. There, seismic profiles near the COST B-3 well reveal several probable unconformities of Miocene to Pliocene age that are not documented in the wells. Across the Georges Bank basin, subtle Jurassic unconformities appear to be present on seismic records within a thick, poorly dated section of interbedded limestone, dolomite, and anhydrite. Microfossil records from the deep wells and shallow core holes reveal seven unconformities of regional extent, forming chronostratigraphic gaps in the early to middle Cenomanian, late Turonian-early Coniacian, late Maestrichtian-early Paleocene, late Eocene-early Oligocene, early Miocene, late Miocene-early Pliocene, and late Pliocene-early Pleistocene. These gaps in the fossil record are comparable with the gaps found in wells in the Scotian basin, and correspond to unconformities inferred from the seismic profiles. The chronostratigraphic sequences bounded by these unconformities help to better define the curve of coastal onlap during the Cretaceous and to support the major trends in sea level change during the late Mesozoic and Cenozoic noted by Vail, Pitman, and others. End_of_Article - Last_Page 973------------
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In central Nevada, stratigraphic successions of Whiterockian-Llandoverian lithofacies, transitional with autochthonous platform/shelf carbonates to the east, occur in isolated windows in outer slope to basinal lithotopes of the Roberts Mountains allochthon. Petrologic, chronostratigraphic and lithostratigraphic, and paleontologic comparison of those successions with platform/shelf facies to the east is integral for reconstruction of Ordovician-Silurian platform margin paleogeography and pre-Antler genesis of the western North American continental margin. Numerous facies changes and/or stratigraphic omissions in central Nevada can be related to sea level fluctuation and aggradation/progradation of the carbonate platform to the east, and not to a postulated, offshore geanticline (i.e., the Toiyabe Ridge). Stratigraphic omission of the Eureka Quartzite above Pogonip equivalents in transitional successions of the Toquima Range and the presence of correlative quartzite in outer slope/basinal parautochthonous facies of the Toiyabe Range suggest development of a possible bypass-margin during the Middle Ordovician. Deposition of Late Ordovician platform margin dolostones (Ely Springs Dolostone) and upper ramp limestones (Hanson Creek Formation and Martin Ridge strata) followed Late Ordovician transgression that drowned the margin and reestablished the carbonate factory. Glacioeustatic drawdown of Late Ordovician-earliest Silurian seas due to the Gondwanan glacial fluctuation can be recognized in strata along the platform margin andmore » upper ramp. Rapid, Early Silurian transgression produced dark-gray carbonates and may have induced marginal flexure and regional, massive slope failure in central Nevada, generating stratigraphic hiatuses west of the platform margin.« less
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The ancient Laurentian margin rifted in the latest Neoproterozoic to early Cambrian but appears not to have developed as a simple passive margin through a long, post-rift, drift phase. Stratigraphic and conodont biostratigraphic information from four platform-to-basin transects across the margin has advanced our knowledge of the early Paleozoic evolution of the margin. In northeastern British Columbia, two northern transects span the Macdonald Platform to Kechika Trough and Ospika Embayment, and a third transect spans the parautochthonous Cassiar Terrane. In the southern Rocky Mountains, new conodont biostratigraphic data for the Ordovician succession of the Bow Platform is correlated to coeval basinal facies of the White River Trough. In total, from 26 stratigraphic sections, over 25 km of strata were measured and > 1200 conodont samples were collected that yielded over 100 000 conodont elements. Key zonal species were used for regional correlation of uppermost Cambrian to Middle Devonian strata along the Cordillera. The biostratigraphy temporally constrains at least two periods of renewed extension along the margin, in the latest Cambrian and late Early Ordovician. Alkalic volcanics associated with abrupt facies changes across the ancient shelf break, intervals of slope debris breccia deposits, and distal turbidite flows suggest the margin was characterized by intervals of volcanism, basin foundering, and platform flooding. Siliciclastics in the succession were sourced by a reactivation of tectonic highs, such as the Peace River Arch. Prominent hiatuses punctuate the succession, including unconformities of early Late Ordovician, sub-Llandovery, possibly Early to Middle Silurian and Early Devonian ages.
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Research Article| February 01, 1941 Jurassic stratigraphy of Central Oregon R. L. LUPHER R. L. LUPHER Search for other works by this author on: GSW Google Scholar GSA Bulletin (1941) 52 (2): 219–270. https://doi.org/10.1130/GSAB-52-219 Article history received: 03 Jun 1940 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation R. L. LUPHER; Jurassic stratigraphy of Central Oregon. GSA Bulletin 1941;; 52 (2): 219–270. doi: https://doi.org/10.1130/GSAB-52-219 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Ten formations are recognized in the Jurassic marine sequence of central Oregon. Angular unconformities separate these formations from the Paleozoic and Upper Triassic formations below and the Upper Cretaceous above. No marked diastrophism is indicated within the Jurassic sequence, though long intervals of nondeposition are present.A chronologic arrangement of the formations shows four formations in and near the Middle Lias, four in the early Middle Jurassic, one in the early Upper Jurassic, and one in the Upper Jurassic or Cretaceous. A marked threefold lithologic grouping of the sequence is evident but does not correspond to the chronologic arrangement. The oldest lithologic division consists of late Lower Lias shales and sandstones, over 2000 feet thick, at the isolated Donovan Ranch locality in the Silvies River Canyon near Burns. The second lithologic division contains three Lias formations and two early Middle Jurassic formations at the base of the section in the main Jurassic area. It is characterized by thin calcareous formations abounding in well-preserved fossils. The third division includes the remaining part of the Jurassic sequence consisting of two formations of the early Middle Jurassic and one of the early Upper Jurassic, as well as the uppermost formation of uncertain age. It is characterized by thick, noncalcareous formations of sandstone and shale in which fossils are less abundant and not well preserved. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.
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During the last 10 m.y., the Nanga Parbat Haramosh Massif in the northwestern Himalaya has been intruded by granitic magmas, has undergone high‐grade metamorphism and anatexis, and has been rapidly uplifted and denuded. As part of an ongoing project to understand the relationship between tectonism and petrologic processes, we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism. Our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m.y. We suggest that the rapid uplift of the massif created a dual hydrothermal system, consisting of a near‐surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic/metamorphic volatiles. Meteoric fluids derived from glaciers near the summit of Nanga Parbat were driven deep into the massif along the transpressional faults causing δ 18 O and δD depletions in the gneisses and marked oxygen isotopic disequilibrium between mineral pairs from the fault zones. The discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif. At deeper levels within the massif, infiltration of low δ 18 O magmatic fluids caused δ 18 O depletions in the gneisses within the migmatite zone. These low δ 18 O fluids were derived from the young (<4 Ma), relatively low δ 18 O granites (∼8‰c) that are found within the core of the massif. Geochronological evidence in the form of fission track and 40 Ar/ 39 Ar cooling ages and U/Pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined. Fluid infiltration in the migmatite zone rocks located along the Tato traverse was coeval with metamorphism, granite emplacement, and rapid denudation, in the interval 0.8–3.3 Ma. Finally, we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the Nanga Parbat‐Haramosh Massif.
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