152 / 2022-02-27 14:55:50

晚三叠世卡尼期湿润幕事件诱发粗菊石科的辐射演化？

菊石辐射演化，卡尼期湿润幕事件，三叠纪，华南

摘要：菊石类是中生代头足类的一个最主要分支，它出现于泥盆纪，灭绝于K-Pg事件。 它们在古代生态系统中有着重要的地位，既是捕食者，也是小鱼、鲨鱼甚至一些海生爬行动物的重要猎物。根据化石记录，菊石类的生活环境广泛，从陆表海的表层海域到深水区均有发现，并且分布广泛，在南半球和北半球都有发现的报道。它们的物种多样性变化与环境变化密切相关，通常菊石的灭绝事件均伴随着气候变化。  

作为上三叠纪最重要的气候变化事件之一，卡尼阶湿润幕事件(CPE)标志着海洋和陆地上生命的深刻变化。该事件开始于Julian 2底部，结束于Tuvanlian 2，其沉积现象是降雨增加而导致大量陆源沉积物进入沉积盆地以及碳酸盐沉积向黑色页岩沉积转换。前人研究表明，菊石类曾在Julian - Tuvanlian 界线附近出现了一次较为明显的灭绝现象。 然而，在Julian 1- Julian 2界线附近，暨CPE的开始阶段，对菊石多样性的研究较少。

本文在云南省泸西县晚三叠世卡尼期Julian 1- Julian 2界线附近的地层中发现一菊石组合，并在该地采集菊石200余枚。通过鉴定共识别菊石9属13种，其中Yakutosirenites和Anasirenites为华南首次发现。基于本文以及来自Paleobiology Database(PBDB)的数据,本文认为：在Julian 2 时期Trachyceratidae迎来了一次大辐射事件,如Anasirenites Sirinites, Neosirenites, Seimkanites, Pamphagosirenites, Striatosirenites, Austrotrachyceras和Neoprotrachyceras均在该时期得以蓬勃发展。Trachyceratidae大辐射的原因可能是卡尼洪湿润幕事件所致。卡尼洪湿润幕事件期间，强降雨将大量陆源碎屑带进沉积盆地，这使海底变平，并使陆缘海海域变得更为宽广。这为Trachyceratidae的生存和繁殖提供了适宜的环境。其次，大量陆源碎屑的输入势必也会给沉积盆地带来不同的营养物质。这可能会进一步增加Trachyceratidae所需的关键营养元素。第三，卡尼阶湿润幕事件重塑了整个海洋生态系统，这为Trachyceratidae创造了更多新的生态位。  

Abstract: Ammonoids (order Ammonoidea), one dominate taxon of cephalopods during Mesozoic, which appeared in the Devonian and went extinct in Cretaceous−Paleogene event. They had an important position in ancient ecosystems, both as predators and important prey for small fish, sharks even some marine reptiles. Based on their fossil records, Ammonoids inhabited surface to deep waters of epicontinental sea, and were present cosmopolitan, both in the southern and northern hemisphere extend subtropical to polar areas. Their diversity shifts are closely correlated to environmental changes, including extinction events and climate variations.

As one of the most important climate shifts during upper Triassic, Carnian Pluvial Episode (CPE) marks a time of profound changes to life, in the ocean and on land. CPE started at the base of Julian 2 and end in Tuvanlian 2 and the sedimentological phenomenon is an increase in rainfall that caused input of terrigenous sediments and black shales deposition into sedimentary basins and the carbonate production meet crises. Previous studies believed some clades of ammonoidea met crisis during the Julian-Tuvalian boundary interval. However, there were few ammonoid diversity research during the Julian 1- Julian 2 boundary interval, which marked the beginning of CPE.

In this study, we described an ammonoid assemble from Julian 1- Julian 2 boundary interval of Luxi county, Yunnan province, south-west China. A total of more than 200 ammonoids were collected, and 13 species of 9 genera were recognized, among which Yakutosirenites and Anasirenites were the first discovered in south-west China. Basing on our research and data from Paleobiology Database (PBDB) we find that at the genus level, the Trachyceratidae experienced an explosive radiation in Julian 2, such as Anasirenites, Sirinites, Neosirenites, Seimkanites, Pamphagosirenites, Striatosirenites, Austrotrachyceras and Neoprotrachyceras were flourished during this time. The reason of Trachyceratidae explosive radiation may caused by CPE. To be more specific, during CPE, the heavy rainfall carried a lot of terrigenous clastics into the sedimentary basins. It caused the seafloor became flattened and broaden the epicontinental sea field. It provided a suitable environment to Trachyceratidae living and reproduction. Secondly, an amount of terrigenous clastics input the marine would also bring different nutrients into sedimentary basin. It may increase the key elements which Trachyceratidae needed. Thirdly,  major climate change reformed the whole marine ecosystem. It may create some new ecological niches that can be occupied by Trachyceratidae. 



References

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