TY - JOUR

T1 - Initial results of coring at Prees, Cheshire Basin, UK (ICDP JET project)

T2 - Towards an integrated stratigraphy, timescale, and Earth system understanding for the Early Jurassic

AU - Hesselbo, Stephen P.

AU - Al-Suwaidi, Aisha

AU - Baker, Sarah J.

AU - Ballabio, Giorgia

AU - Belcher, Claire M.

AU - Bond, Andrew

AU - Boomer, Ian

AU - Bos, Remco

AU - Bjerrum, Christian J.

AU - Bogus, Kara

AU - Boyle, Richard

AU - Browning, James V.

AU - Butcher, Alan R.

AU - Condon, Daniel J.

AU - Copestake, Philip

AU - Daines, Stuart

AU - Dalby, Christopher

AU - Damaschke, Magret

AU - Damborenea, Susana E.

AU - Deconinck, Jean Francois

AU - Dickson, Alexander J.

AU - Fendley, Isabel M.

AU - Fox, Calum P.

AU - Fraguas, Angela

AU - Frieling, Joost

AU - Gibson, Thomas A.

AU - He, Tianchen

AU - Hickey, Kat

AU - Hinnov, Linda A.

AU - Hollaar, Teuntje P.

AU - Huang, Chunju

AU - Hudson, Alexander J. L.

AU - Jenkyns, Hugh C.

AU - Idiz, Erdem

AU - Jiang, Mengjie

AU - Krijgsman, Wout

AU - Korte, Christoph

AU - Leng, Melanie J.

AU - Lenton, Timothy M.

AU - Leu, Katharina

AU - Little, Crispin T.S.

AU - Macniocaill, Conall

AU - Manceñido, Miguel O.

AU - Mather, Tamsin A.

AU - Mattioli, Emanuela

AU - Miller, Kenneth G.

AU - Newton, Robert J.

AU - Page, Kevin N.

AU - Pálfy, József

AU - Pieńkowski, Gregory

AU - Porter, Richard J.

AU - Poulton, Simon W.

AU - Riccardi, Alberto C.

AU - Riding, James B.

AU - Roper, Ailsa

AU - Ruhl, Micha

AU - Silva, Ricardo L.

AU - Storm, Marisa S.

AU - Suan, Guillaume

AU - Szúcs, Dominika

AU - Thibault, Nicolas

AU - Uchman, Alfred

AU - Stanley, James N.

AU - Ullmann, Clemens V.

AU - Van De Schootbrugge, Bas

AU - Vickers, Madeleine L.

AU - Wadas, Sonja

AU - Whiteside, Jessica H.

AU - Wignall, Paul B.

AU - Wonik, Thomas

AU - Xu, Weimu

AU - Zeeden, Christian

AU - Zhao, Ke

N1 - Publisher Copyright: © Copyright:

PY - 2023

Y1 - 2023

N2 - 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 32.2g¯m below surface (mg¯b.s.) and Prees 2B to 37.0g¯mg¯b.s.) together with Early Jurassic and Late Triassic mudstone from the principal hole, Prees 2C, which was cored from 32.92 to 651.32g¯m (corrected core depth scale). Core recovery was 99.7g¯% 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 4g¯% total organic carbon (TOC) is recorded. Other parts of the succession are generally organic-lean, containing less than 1g¯% TOC. Carbon-isotope values from bulk organic matter have also been determined, initially at a resolution of g1/4g¯1g¯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 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.

AB - 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 32.2g¯m below surface (mg¯b.s.) and Prees 2B to 37.0g¯mg¯b.s.) together with Early Jurassic and Late Triassic mudstone from the principal hole, Prees 2C, which was cored from 32.92 to 651.32g¯m (corrected core depth scale). Core recovery was 99.7g¯% 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 4g¯% total organic carbon (TOC) is recorded. Other parts of the succession are generally organic-lean, containing less than 1g¯% TOC. Carbon-isotope values from bulk organic matter have also been determined, initially at a resolution of g1/4g¯1g¯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 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.

U2 - 10.5194/sd-32-1-2023

DO - 10.5194/sd-32-1-2023

M3 - Journal article

AN - SCOPUS:85178667339

VL - 32

SP - 1

EP - 25

JO - Scientific Drilling

JF - Scientific Drilling

SN - 1816-8957

ER -