12 research outputs found
The toarcian oceanic anoxic event (Early Jurassic) in the Neuquén Basin, Argentina: A reassessment of age and carbon isotope stratigraphy
The Toarcian oceanic anoxic event (T-OAE) is recorded by the presence of globally distributed marine organic carbonâ rich black shales and a negative carbon isotope shift, with ÎŽ13Corg values as low as -33â°, interrupting an overarching positive excursion. Here we present new biostratigraphic data and high-resolution ÎŽ13Corg data from two Southern Hemisphere localities: Arroyo Serrucho in the north and Arroyo Lapa in the south of the NeuquĂ©n Basin, Argentina. Previous studies at these localities aimed to provide an accurate numerical age for the T-OAE and characterization of its carbon isotope stratigraphy. The new carbon isotope data and ammonite biostratigraphy presented here from Arroyo Serrucho show the T-OAE to be recorded lower in the section than supposed by previous authors, thus calling into question the published age of the T-OAE in this section. A newly investigated exposure at Arroyo Lapa North shows a complex carbon isotope record with at least three high-amplitude fluctuations in the hoelderi zone (equivalent to the serpentinum zone in northwestern Europe), with ÎŽ13Corg values of <-28â°, and two intervening positive isotope excursions, with ÎŽ13Corg values around -24â°. At Arroyo Lapa South, the characteristic major stepped negative carbon isotope excursion is recorded, with ÎŽ13Corg values of <-30â° and total organic-carbon contents increasing to 11%; above this level an erosional surface of a submarine channel truncates the section. These new data are globally correlative and unambiguously illustrate the global reach of the T-OAE.Fil: Al Suwaidi, Aisha H.. Petroleum Institute University; Emiratos Ărabes UnidosFil: Hesselbo, Stephen P.. University of Exeter; Reino UnidoFil: Damborenea, Susana Ester. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. DivisiĂłn PaleozoologĂa Invertebrados; ArgentinaFil: Manceñido, Miguel Oscar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. DivisiĂłn PaleozoologĂa Invertebrados; ArgentinaFil: Jenkyns, Hugh C.. University of Oxford; Reino UnidoFil: Riccardi, Alberto Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata; ArgentinaFil: Angelozzi, Gladys NoemĂ. YPF - TecnologĂa; ArgentinaFil: Baudin, François. UniversitĂ© Pierre et Marie Curie; Franci
New age constraints on the Lower Jurassic PliensbachianâToarcian Boundary at Chacay Melehue (NeuquĂ©n Basin, Argentina)
The PliensbachianâToarcian boundary interval is characterized by aâ~â3â° negative carbon-isotope excursion (CIE) in organic and inorganic marine and terrestrial archives from sections in Europe, such as Peniche (Portugal) and Hawsker Bottoms, Yorkshire (UK). A new high-resolution organic-carbon isotope record, illustrating the same chemostratigraphic feature, is presented from the Southern Hemisphere Arroyo Chacay Melehue section, Chos Malal, Argentina, corroborating the global significance of this disturbance to the carbon cycle. The negative carbon-isotope excursion, mercury and organic-matter enrichment are accompanied by high-resolution ammonite and nannofossil biostratigraphy together with UâPb CA-ID-TIMS geochronology derived from intercalated volcanic ash beds. A new age ofâ~â183.73â+â0.35/ââ0.50 Ma for the PliensbachianâToarcian boundary, and 182.77â+â0.11/ââ0.15 for the tenuicostatumâserpentinum zonal boundary, is assigned based on high-precision UâPb zircon geochronology and a Bayesian Markov chain Monte Carlo (MCMC) stratigraphic age model
Initial results of coring at Prees, Cheshire Basin, UK (ICDP JET project): Towards an integrated stratigraphy, timescale, and Earth system understanding for the Early Jurassic
Drilling for the International Continental Scientific Drilling Program (ICDP) Early Jurassic Earth System and Timescale project (JET) was undertaken between October 2020 and January 2021. The drill site is situated in a small-scale synformal basin of the latest Triassic to Early Jurassic age that formed above the major Permian-Triassic half-graben system of the Cheshire Basin. The borehole is located to recover an expanded and complete succession to complement the legacy core from the Llanbedr (Mochras Farm) borehole drilled through 1967-1969 on the edge of the Cardigan Bay Basin, North Wales. The overall aim of the project is to construct an astronomically calibrated integrated timescale for the Early Jurassic and to provide insights into the operation of the Early Jurassic Earth system. Core of Quaternary age cover and Early Jurassic mudstone was obtained from two shallow partially cored geotechnical holes (Prees 2A to 32.2gÂŻm below surface (mgÂŻb.s.) and Prees 2B to 37.0gÂŻmgÂŻb.s.) together with Early Jurassic and Late Triassic mudstone from the principal hole, Prees 2C, which was cored from 32.92 to 651.32gÂŻm (corrected core depth scale). Core recovery was 99.7gÂŻ% for Prees 2C. The ages of the recovered stratigraphy range from the Late Triassic (probably Rhaetian) to the Early Jurassic, Early Pliensbachian (Ibex Ammonoid Chronozone). All ammonoid chronozones have been identified for the drilled Early Jurassic strata. The full lithological succession comprises the Branscombe Mudstone and Blue Anchor formations of the Mercia Mudstone Group, the Westbury and Lilstock formations of the Penarth Group, and the Redcar Mudstone Formation of the Lias Group. A distinct interval of siltstone is recognized within the Late Sinemurian of the Redcar Mudstone Formation, and the name "Prees Siltstone Member"is proposed. Depositional environments range from playa lake in the Late Triassic to distal offshore marine in the Early Jurassic. Initial datasets compiled from the core include radiography, natural gamma ray, density, magnetic susceptibility, and X-ray fluorescence (XRF). A full suite of downhole logs was also run. Intervals of organic carbon enrichment occur in the Rhaetian (Late Triassic) Westbury Formation and in the earliest Hettangian and earliest Pliensbachian strata of the Redcar Mudstone Formation, where up to 4gÂŻ% total organic carbon (TOC) is recorded. Other parts of the succession are generally organic-lean, containing less than 1gÂŻ% TOC. Carbon-isotope values from bulk organic matter have also been determined, initially at a resolution of g1/4gÂŻ1gÂŻm, and these provide the basis for detailed correlation between the Prees 2 succession and adjacent boreholes and Global Stratotype Section and Point (GSSP) outcrops. Multiple complementary studies are currently underway and preliminary results promise an astronomically calibrated biostratigraphy, magnetostratigraphy, and chemostratigraphy for the combined Prees and Mochras successions as well as insights into the dynamics of background processes and major palaeo-environmental changes
A pedâs story: Weathering out climatic change during the mid-Cretaceous
Thesis (M.S.)--University of Kansas, Geology, 2007.The upper Ruby Ranch Member and basal Mussentuchit Member of the Cedar Mountain Formation in the vicinity of the Price River II Quarry (CEU-PR2) in the Price River area, East Central Utah, consists of fluvially derived sediments in a floodplain environment with a seasonal xeric regime. Bulk organic matter carbon isotope chemostratigraphic profiles ÎŽ 13Corg for measured sections in the CEU-PR2 area are constrained by detrital zircon ages ranging from 109 to 116 Ma (Burton et al., 2006). These ÎŽ13Corg profiles show prominent excursions and structure that have been correlated with global ÎŽ13C org chemostratigraphy of Bralower et al. (1999) and show carbon excursion events C10-C13. This correlation suggesting that the Aptian-Albian boundary is captured by the Ruby Ranch Member and makes the upper most Ruby Ranch Member and Mussentuchit Member strictly Albian in age
A southern hemisphere record of the Toarcian Oceanic Anoxic Event from the Neuquén Basin, Argentina
The Toarcian, Early Jurassic, Oceanic Anoxic Event (T-OAE: ~183 Ma) was characterized by globally synchronous deposition of sediments rich in organic carbon (black shales), and is associated with an abrupt negative carbon isotope excursion, disrupting a positive carbon-isotope excursion during the tenuicostatumâserpentinum ammonite Zone boundary. The T-OAE has been extensively studied in northern and southern Europe, but evidence from the southern hemisphere is limited. New geochemical data from the tenuicostatumâhoelderi (~serpentinum) Andean ammonite Zone, from the NeuquĂ©n Basin, Argentina provides evidence for the global imprint of the event. The event is recorded in bulk-sediment from Arroyo Lapa (North and South) and Arroyo Serrucho with ÎŽ13Corg values of -30â° â -32.5â° and ÎŽ13C values from fossil wood fall to -30.7 â°, isotopic ratios that are comparable to those identified in Europe for the T-OAE. Hydrogen Index (HI) data for the T-OAE in Argentina give values ranging from 12 to 425 mg HC/ g TOC, indicating a mixture of terrestrial and marine organic components. Pristane/Phytane ratios and pyrite framboid distribution data indicative of anoxic conditions occur at some levels, and new ÎŽ98/95Mo data, with values ranging from ~ -0.2 to 0.78 â°, which contrast with previously published molybdenum-isotope values from T-OAE black shales of northern Europe. Sedimentological data also reveals a marine transgression during the tenuicostatumâhoelderi Andean ammonite zone
A southern hemisphere record of the Toarcian Oceanic Anoxic Event from the Neuquén Basin, Argentina
The Toarcian, Early Jurassic, Oceanic Anoxic Event (T-OAE: ~183 Ma) was characterized by globally synchronous deposition of sediments rich in organic carbon (black shales), and is associated with an abrupt negative carbon isotope excursion, disrupting a positive carbon-isotope excursion during the tenuicostatumâserpentinum ammonite Zone boundary. The T-OAE has been extensively studied in northern and southern Europe, but evidence from the southern hemisphere is limited. New geochemical data from the tenuicostatumâhoelderi (~serpentinum) Andean ammonite Zone, from the NeuquĂ©n Basin, Argentina provides evidence for the global imprint of the event. The event is recorded in bulk-sediment from Arroyo Lapa (North and South) and Arroyo Serrucho with ÎŽ13Corg values of -30â° â -32.5â° and ÎŽ13C values from fossil wood fall to -30.7 â°, isotopic ratios that are comparable to those identified in Europe for the T-OAE. Hydrogen Index (HI) data for the T-OAE in Argentina give values ranging from 12 to 425 mg HC/ g TOC, indicating a mixture of terrestrial and marine organic components. Pristane/Phytane ratios and pyrite framboid distribution data indicative of anoxic conditions occur at some levels, and new ÎŽ98/95Mo data, with values ranging from ~ -0.2 to 0.78 â°, which contrast with previously published molybdenum-isotope values from T-OAE black shales of northern Europe. Sedimentological data also reveals a marine transgression during the tenuicostatumâhoelderi Andean ammonite zone.This thesis is not currently available via ORA
The TriassicâJurassic boundary event from an equatorial carbonate platform (Ghalilah Formation, United Arab Emirates)
ÎŽ13C<sub>carb</sub> data from bulk roc
New Geochronological Age Constraint and Chemostratigraphy for Aptian Lacustrine Strata, Cedar Mountain Formation, Utah
Abstract The Early Cretaceous is an important time of transition in Earth history, marked by a succession of oceanic anoxic events and carbon cycle perturbations that drove changes on land and in the ocean. The need for more precise geochronologic constraints in terrestrial sediments of Early Cretaceous age that record faunal and floral transitions is especially critical. The Cedar Mountain Formation (CMF) is a continental lithostratigraphic unit that hosts a trove of paleoclimate archives and important dinosaurian fossil localities. Determining the timing of deposition of CMF strata has been an ongoing effort for many years. Here, we present new lithostratigraphic and carbon isotope chemostratigraphic data along with highâprecision radiometric ages to further constrain the Ruby Ranch Member of the CMF at a unique locality referred to as âLake Carpenter,â where a thick section of dominantly lacustrine strata overlies fluvialâoverbank to palustrine strata more typical of other Ruby Ranch Member outcrops. A bentonite bed near the base of the section provides one of the most precise ages yet determined within the Ruby Ranch Member of 115.92 ± 0.14 Ma via CAâIDâTIMS UâPb analysis of zircons. The age and the trends in the carbon isotope record indicate that the Lake Carpenter sediments were deposited entirely within the late Aptian Stage. These unique new data provide an important step toward improving our understanding of the timing of Early Cretaceous evolutionary and paleoclimate events