Integrated δ13Ccarb, conodont, and graptolite biochemostratigraphy of the Silurian from the Illinois Basin and stratigraphic revision of the Bainbridge Group
Integrated δ13Ccarb, conodont, and graptolite biochemostratigraphy of the Silurian from the Illinois Basin and stratigraphic revision of the Bainbridge Group
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DOI：
10.1130/b32033.1
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发表时间：
2019-01-01
影响因子：
4.9
通讯作者：
Day, James E.
中科院分区：
文献类型：
--
作者：
McAdams, Neo E. B.;Cramer, Bradley D.;Day, James E.
伊利诺伊州西南部和密苏里州东南部的伊利诺伊盆地包含北美最广泛的志留纪记录之一，是全球海平面和古气候/古海洋学研究的潜在关键区域。不幸的是，志留系地层学在区域上仍未得到充分研究，往往只能在层序层面上进行全球对比。伊利诺伊州西南部和密苏里州东南部的志留纪地层目前被划分为Sexton Creek石灰岩、76页岩、St.Clair石灰岩和MocCasin Springs组。后三个单元被不同地认为是班布里奇组的成员或班布里奇组内的组。我们主张将Bainbridge一词在其整个使用范围内在集团一级正规化，包括(按升序)76组(在此按等级提升并在地理上扩展)、St.Clair组(在本文中按地层学扩展)和MocCasin Springs组，有四个成员：Greens Ferry、Seppard Point、Lithium(在此建议)和Randol成员。贝恩桥群不整合地被志留系Sexton Creek组覆盖，并被Pridoli-泥盆系Bailey组整合地覆盖。伊利诺伊州西南部和密苏里州东南部三个地区的综合碳同位素(增量C-13)、牙形刺和笔石生物化学地层学表明，在贝恩布里奇群中存在早期谢因伍德式的“Ireviken”、Hmer式的“Mulde”和Ludfordian的“Lau”正碳同位素漂移(首次发表于北美)。这项研究中提出的地层修正为班布里奇群在整个区域范围内提供了一个一致且广泛适用的岩石地层命名法。这项研究还首次提供了来自这个重要的劳伦斯盆地的所有三个主要文洛克-路德福迪亚三角洲C-13漂移的详细综合生物化学地层学记录，并首次将班布里奇群与全球志留纪年代地层方案进行了精确对比。
The Illinois Basin of southwestern Illinois and southeastern Missouri contains one of the most extensive Silurian records in North America and is a potentially critical area for global sea-level and paleoclimatic/paleoceanographic studies. Unfortunately, the Silurian stratigraphy regionally remains understudied and often can only be correlated globally at series level. Silurian strata from southwestern Illinois and southeastern Missouri are currently assigned to the Sexton Creek Limestone, Seventy-Six Shale, St. Clair Limestone, and Moccasin Springs Formation. The latter three units are variously considered members of the Bainbridge Formation or formations within the Bainbridge Group. We advocate the formalization of the term Bainbridge at the group level throughout its area of use, composed of (in ascending order) the Seventy-Six Formation (raised in rank and geographically expanded herein), the St. Clair Formation (stratigraphically expanded herein), and the Moccasin Springs Formation with four members: the Greens Ferry, Sheppard Point, Lithium (proposed herein), and Randol members. The Bain-bridge Group is unconformably underlain by the Silurian Sexton Creek Formation and conformably overlain by the ?Pridoli-Devonian Bailey Formation. Herein, additional nomenclatural changes are presented to the Cason Formation of Arkansas as well.Integrated carbon isotope (delta C-13), conodont, and graptolite biochemostratigraphy of three localities in the southwestern Illinois and southeastern Missouri area indicate the presence of the early Sheinwoodian "Ireviken," Homerian "Mulde," and Ludfordian "Lau" positive carbon isotope excursions in the Bain-bridge Group (the first published consecutive occurrence from North America). The stratigraphic revisions presented in this study provide a consistent and widely applicable lithostratigraphic nomenclature for the Bainbridge Group throughout its areal extent. This study also provides the first detailed integrated biochemostratigraphic record of all three major Wenlock-Ludfordian delta C-13 excursions from this important Laurentian basin, and it enables the first precise correlation of the Bainbridge Group into the global Silurian chronostratigraphic scheme.