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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Early Hettangian ammonites and radiolarians from the Queen Charlotte Islands, British Columbia and their bearing on the definition of the Triassic-Jurassic boundary
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Early Hettangian ammonites and radiolarians from the Queen Charlotte Islands, British Columbia and their bearing on the definition of the Triassic-Jurassic boundary

机译：来自不列颠哥伦比亚省夏洛特皇后群岛的早期Hettangian炸药和放射虫及其对三叠纪-侏罗纪边界的定义的影响

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摘要

The Triassic-Jurassic boundary (T-J boundary) interval is one of the most important but poorly understood intervals in the Phanerozoic. Here we fully document the ammonite and radiolarian successions at several sites in the Queen Charlotte Islands (QCI), British Columbia. Eleven ammonite taxa are described and eighteen radiolarian taxa are discussed with the radiolarian genus Tipperella described as new (type species T kennecottensis n. sp.). There are two continuous T-J boundary sections in the QCI, one is located at Kennecott Point on Graham Island (section I), the other on the southeastern shore of Kunga Island (section III). A second section at Kennecott Point contains fossils of early Hettangian age only (section II). Radiolarian faunas include taxa, from the upper Rhaetian Globolaxtorum tozeri Zone in the two continuous sections and the lower Hettangian Canoptum merum Zone in all three sections. In each section, the lowest Hettangian fossils are radiolarians and a few collections contain rare Rhaetian holdovers. These mixed faunas may equate with the lowest Hettangian ammonite zone, the Spelae Zone of the North American succession. The upper portion of section I contains a sparse ammonite fauna which indicates an early Hettangian age. This section has also provided carbon isotope data with a negative excursion spanning the T-J boundary. Section II contains a more diverse early Hettangian ammonite assemblage that permits correlation of the upper portion of this section with the lower Hettangian Minutus Zone. Section III has been previously proposed as a potential basal Hettangian Global Stratotype Section and Point (GSSP). In addition to an outstanding radiolarian fauna, the section contains moderately diverse early Hettangian ammonites that permit correlation of the lower portion of the section with the Minutus and Pacificum zones and the upper portion with the lower Hettangian Polymorphum Zone. This section has previously provided a U-Pb date of 199.6 +/- 0.3 Ma from 3.6 m below the T-J boundary. Currently, there are four candidates and no ideal GSSP for the basal Hettangian. A section in New York Canyon, Nevada has also been proposed as a potential GSSP. This section is easily accessible and provides a virtually complete ammonoid succession but lacks geochronology and microfossils. The section on Kunga Island in the QCI provides geochronologic data and excellent radiolarian constraints. In essence, the sections at Kunga Island in the QCI and New York Canyon in Nevada are complementary. Close correlations between the two sections are possible using ammonite faunas. We suggest the section from Nevada be designated as holostratotype for the basal Hettangian and the QCI. section be designated as a parastratotype to improve recognition of this interval. (c) 2006 Elsevier B.V. All rights reserved.
机译：三叠纪-侏罗纪边界（T-J边界）间隔是古生代中最重要但认识不到的间隔之一。在这里，我们完整记录了不列颠哥伦比亚省夏洛特皇后群岛（QCI）多个地点的菊石和放射l虫的演替。描述了11个am虫类群，讨论了18个放射虫类群，其中放射虫属蒂珀雷拉属被描述为新的（类型为T肯尼科特种n.sp.）。 QCI中有两个连续的T-J边界区域，一个位于格雷厄姆岛的肯尼科特角（第一部分），另一位于昆加岛的东南海岸（第三部分）。肯尼科特角的第二部分仅包含Hettangian早期的化石（第二部分）。放射虫动物群包括来自两个连续部分的上部Rhaetian Globolaxtorum tozeri区和所有三个部分的Hettangian Canoptum merum区类群。在每个部分中，最低的Hettangian化石是放射虫，少数集合包含稀有的Rhaetian残留物。这些混杂的动物区系可能相当于最低的Hettangian炸药区，即北美演替的Spelae区。第一节的上部包含稀疏的mon虫类动物，这表明它属于早唐人时代。本节还提供了跨T-J边界的负偏移的碳同位素数据。第二部分包含更多样化的早期Hettangian am石组合，使该部分的上部与下部Hettangian Minutus区相关联。先前已提议将第三节作为潜在的基础Hettangian全球分层定型和定点（GSSP）。除了出色的放射虫动物区系外，该区域还包含中等程度多样的早期Hettangian铵盐，这些区域允许该区域的下部与Minutus和Pacificum区相关，而上部与下部Hettangian Polymorphum区相关。本节以前在T-J边界以下3.6 m处提供了199.6 +/- 0.3 Ma的U-Pb数据。目前，有四个候选对象，而基础Hettangian没有理想的GSSP。内华达州纽约峡谷的一部分也被提议作为潜在的GSSP。该部分易于取用，并提供了几乎完整的氨仿性演替，但缺少年代学和微化石。 QCI中关于Kunga岛的部分提供了年代学数据和出色的放射虫约束。本质上，QCI的坤加岛和内华达州的纽约峡谷的部分是互补的。使用亚mon族动物群，可以在两个部分之间建立紧密的联系。我们建议将内华达州的断面指定为基础Hettangian和QCI的整型。部分被指定为拟原模板以改善对该间隔的识别。 （c）2006 Elsevier B.V.保留所有权利。

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