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-猫眼课题宝

DOI：

10.5194/sd-32-1-2023

发表时间：

2023-10

期刊：

Scientific Drilling

影响因子：

1.2

通讯作者：

中科院分区：

文献类型：

作者：

S. Hesselbo;A. Al-Suwaidi;Sarah J. Baker;Giorgia Ballabio;C. Belcher;Andrew Bond;Ian Boomer;Remco Bos;C. Bjerrum;Kara Bogus;Richard Boyle;J. Browning;Alan R. Butcher;Daniel J. Condon;P. Copestake;S. Daines;Christopher Dalby;M. Damaschke;S. Damborenea;J. Deconinck;A. Dickson;I. Fendley;C. Fox;Ángela Fraguas;J. Frieling;Thomas A. Gibson;Tianchen He;Kat Hickey;L. Hinnov;T. P. Hollaar;Chunju Huang;A. J. Hudson;H. Jenkyns;E. Idiz;Mengjie Jiang;W. Krijgsman;Christoph Korte;Melanie J. Leng;T. Lenton;Katharina Leu;C. Little;C. MacNiocaill;M. Manceñido;T. Mather;E. Mattioli;Kenneth G. Miller;Robert J. Newton;Kevin N. Page;J. Pálfy;Gregory Pieńkowski;Richard J. Porter;S. Poulton;Alberto C. Riccardi;J. Riding;Ailsa Roper;M. Ruhl;Ricardo L. Silva;M. Storm;G. Suan;D. Szȕcs;Nicolas Thibault;Alfred Uchman;James N. Stanley;C. Ullmann;B. van de Schootbrugge;Madeleine L. Vickers;S. Wadas;Jessica H. Whiteside;P. Wignall;T. Wonik;Weimu Xu;C. Zeeden;Ke Zhao

抽象。国际大陆科学钻探计划（ICDP）早侏罗世地球系统和时标项目（JET）的钻探工作于2020年10月至2021年1月进行。钻井现场位于一个小型的同形盆地，形成于柴郡盆地的主要二叠纪-三叠纪半地堑系统之上，形成于三叠纪末至侏罗纪早期。该钻孔的位置是为了恢复一个扩大的和完整的继承，以补充遗留的核心从兰贝德尔（莫赫拉斯农场）钻孔钻通过1967-1969年的边缘开衫湾盆地，北威尔士。该项目的总体目标是为早侏罗世构建一个天文校准的综合时间尺度，并提供对早侏罗世地球系统运行的见解。第四纪覆盖层和早侏罗世泥岩的岩芯取自两个浅的部分取芯的岩土钻孔（Prees 2A至地表以下32.2 m（m b.s.）和Prees 2B至37.0 m b.s.）以及主孔Prees 2C的早侏罗世和晚三叠世泥岩，取芯深度为32.92 - 651.32 m（校正后的岩心深度标度）。Prees 2C岩心采收率为99.7%。恢复的地层年龄范围从晚三叠世（可能是雷期）到早侏罗世，早Pliensbachian（Ibex Ammonoid Chronozone）。已钻遇的早侏罗世地层已全部识别出菊石年代带。完整的岩性序列包括Mercia泥岩群的Branscombe泥岩和蓝色主播地层、Penarth群的韦斯特伯里和Lilstock地层以及Lias群的Redcar泥岩地层。在Redcar泥岩组的晚Sinemurian内识别出一个明显的粉砂岩段，并建议将其命名为“Prees粉砂岩段”。沉积环境从晚三叠世的干盐湖到早侏罗世的远岸海相。从岩心中编译的初始数据集包括射线照相、自然伽马射线、密度、磁化率和X射线荧光（XRF）。还进行了全套井下测井。有机碳富集的时间间隔发生在Rhaetian（晚三叠世）韦斯特伯里组和Redcar泥岩组的最早Hettangian和最早Pliensbachian地层中，其中记录了高达4%的总有机碳（TOC）。该系列的其他部分通常是有机贫乏的，含有低于1%的TOC。还确定了来自散装有机质的碳同位素值，最初的分辨率为1.01米，这些为Prees 2序列与相邻钻孔和全球层型剖面和点（GSSP）露头之间的详细对比提供了基础。目前正在进行多项补充研究，初步结果有望为Prees和Mochras相结合的继承以及对背景过程和主要古环境变化动态的见解提供天文校准的生物地层学，磁性地层学和化学地层学。

Abstract. 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 32.2 m below surface (m b.s.) and Prees 2B to 37.0 m b.s.) together with Early Jurassic and Late Triassic mudstone from the principal hole, Prees 2C, which was cored from 32.92 to 651.32 m (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 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 4 % total organic carbon (TOC) is recorded. 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 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.

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

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