Smithian (Olenekian, Early Triassic) Conodonts from Ammonoid-Bearing Limestone Blocks at Crittenden Springs, Elko County, Nevada, USA
Smithian (Olenekian, Early Triassic) Conodonts from Ammonoid-Bearing Limestone Blocks at Crittenden Springs, Elko County, Nevada, USA
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DOI：
10.2517/2020pr022
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发表时间：
2021-07
影响因子：
0.9
通讯作者：
T. Maekawa;J. Jenks
中科院分区：
文献类型：
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作者：
T. Maekawa;J. Jenks
抽象的。在经典的克里滕登泉菊石遗址的含菊石石灰岩块属于下三叠统Thaynes群的下部。这些0.5-1.2米厚的岩块主要由生物碎屑浮岩和岩石组成，含有丰富的宏微观化石，如菊石、腹足类、双壳类和舟足类贝壳，以及牙形石元素、鱼类和海胆遗骸。从三个区块获得的菊石和牙形石组合用于生物地层学分析。12个非正式的Smithian菊石生物地层间隔从以前的研究被浓缩成四个菊石床，根据年龄诊断类群的范围，按升序排列：Meekoceras millardense-M。aff. olivieri层、Owenites koeneni层、Anasibirites multiformis层和Condensoceras koeni层。三个区块共发现牙形刺15属30种，其中包括一个新描述的分类单元，Guangxidella minuta Maekawa和詹克斯新种Guangxidella minuta Maekawa，Jenks sp. nov. Novispathodus ex gr. waageni间隔带和Nv.根据其首次出现的表生类群，将其划分为平顶山山虎斑蝶属（Pingdingshanensis）间隔带。此外，四个牙形石分布区，即，根据这4个指标种的分布区，可划分为Paulllameki分布区、Guangxidellabransoni分布区、Scythogondolellamilleri分布区和Borinellabuurensis分布区。这些间隔和范围带内的牙形刺的年龄从中史密斯到最后史密斯不等。关于史密斯-斯帕蒂安界线（SS B）的关键菊石和牙形石类群的存在，如AW（Anasibirites和Wasatchites）和GXP（Glyptophiceras，Xenoceltites和Pseudosageceras）菊石组合和牙形石B。布伦西斯，内华达州。平顶山亚种和平顶山亚种。milleri的研究表明，该研究区是一个重要的参考网站的SSB在东泛海拉萨地区。
Abstract. The ammonoid-bearing limestone blocks at the classic Crittenden Springs ammonoid site belong to the lower part of the Lower Triassic Thaynes Group. These 0.5–1.2 m thick blocks, consisting mainly of bioclastic floatstone and rudstone, contain abundant macro- and micro-fossils such as ammonoids, gastropods, bivalves and scaphopod shells, as well as conodont elements, fish and echinoid remains. Ammonoid and conodont assemblages obtained from three blocks are utilized for biostratigraphical analysis. Twelve informal Smithian ammonoid biostratigraphic intervals from a previous study are condensed into four ammonoid beds, based on the range of age-diagnostic taxa, in ascending order: Meekoceras millardense-M. aff. olivieri beds, Owenites koeneni beds, Anasibirites multiformis bed, and Condensoceras youngi bed. Conodonts recovered from the three blocks consist of 30 species distributed among 15 genera, including one newly described taxon, i.e., Guangxidella minuta Maekawa and Jenks sp. nov. The blocks are divided into two conodont interval zones, i.e., the Novispathodus ex gr. waageni Interval Zone and Nv. pingdingshanensis Interval Zone, based on the first occurrences of their eponymous taxa. Additionally, four conodont range zones, i.e., the Paullella meeki Range Zone, Guangxidella bransoni Range Zone, Scythogondolella milleri Range Zone, and Borinella buurensis Range Zone are recognized, based on the ranges of these four index species. Conodonts within these interval and range zones vary in age from middle Smithian to latest Smithian. The presence of key ammonoid and conodont taxa regarding the Smithian-Spathian boundary (SSB) such as the AW (Anasibirites and Wasatchites) and GXP (Glyptophiceras, Xenoceltites and Pseudosageceras) ammonoid assemblages and the conodonts B. buurensis, Nv. pingdingshanensis and S. milleri demonstrate that the study area is an important reference site for the SSB in the eastern Panthalassa area.