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

• Autores: Hesselbo, Stephen P.; Al Suwaidi, Aisha; Baker, Sarah J.; Ballabio, Giorgia; Belcher, Claire M.; Bond, Andrew; Boomer, Ian; Bos, Remco; Bjerrum, Christian J.; Bogus, Kara; Boyle, Richard; Browning, James V.; Butcher, Alan R.; Condon, Daniel J.; Copestake, Philip; Daines, Stuart; Dalby, Christopher; Damaschke, Magret; Damborenea, Susana Ester; Deconinck, Jean Francois; Dickson, Alexander J.; Fendley, Isabel M.; Fox, Calum P.; Manceñido, Miguel Oscar; Whiteside, Jessica H.; Wignall, Paul B.; Wonik, Thomas; Xu, Weimu; Zeeden, Christian; Zhao, Ke
• Año de publicación: 2023
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: ICDP JET project; Cheshire Basin; Hettangian; Sinemurian; Pliensbachian
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

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 32.2m below surface (m b.s.) and Prees 2B to 37.0mb.s.) together with Early Jurassic and Late Triassic mudstone from the principal hole, Prees 2C, which was cored from 32.92 to 651.32m (corrected core depth scale). Core recovery was 99.7% 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 theEarly 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 organiccarbon enrichment occur in the Rhaetian (Late Triassic) Westbury Formation and in the earliest Hettangian andearliest Pliensbachian strata of the Redcar Mudstone Formation, where up to 4% total organic carbon (TOC) isrecorded. Other parts of the succession are generally organic-lean, containing less than 1%TOC. Carbon-isotope values from bulk organic matter have also been determined, initially at a resolution of 1 m, 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 preliminaryresults 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.
Fil: Hesselbo, Stephen P.. University of Exeter; Reino Unido
Fil: Al Suwaidi, Aisha. Khalifa University of Science and Technology; Emiratos Arabes Unidos
Fil: Baker, Sarah J.. University of Exeter; Reino Unido
Fil: Ballabio, Giorgia. University of Exeter; Reino Unido
Fil: Belcher, Claire M.. University of Exeter; Reino Unido
Fil: Bond, Andrew. University of Exeter; Reino Unido
Fil: Boomer, Ian. University of Exeter; Reino Unido
Fil: Bos, Remco. University of Exeter; Reino Unido
Fil: Bjerrum, Christian J.. University of Exeter; Reino Unido
Fil: Bogus, Kara. University of Exeter; Reino Unido
Fil: Boyle, Richard. University of Exeter; Reino Unido
Fil: Browning, James V.. University of Exeter; Reino Unido
Fil: Butcher, Alan R.. University of Exeter; Reino Unido
Fil: Condon, Daniel J.. University of Exeter; Reino Unido
Fil: Copestake, Philip. University of Exeter; Reino Unido
Fil: Daines, Stuart. University of Exeter; Reino Unido
Fil: Dalby, Christopher. University of Exeter; Reino Unido
Fil: Damaschke, Magret. University of Exeter; Reino Unido
Fil: Damborenea, Susana Ester. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina
Fil: Deconinck, Jean Francois. University of Exeter; Reino Unido
Fil: Dickson, Alexander J.. University of Exeter; Reino Unido
Fil: Fendley, Isabel M.. University of Exeter; Reino Unido
Fil: Fox, Calum P.. University of Exeter; Reino Unido
Fil: Manceñido, Miguel Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina
Fil: Whiteside, Jessica H.. University of Exeter; Reino Unido
Fil: Wignall, Paul B.. University of Exeter; Reino Unido
Fil: Wonik, Thomas. University of Exeter; Reino Unido
Fil: Xu, Weimu. University of Exeter; Reino Unido
Fil: Zeeden, Christian. University of Exeter; Reino Unido
Fil: Zhao, Ke. University of Exeter; Reino Unido