华南中泥盆世珍尼赛欧(Geneseo)事件及其地质意义

The Devonian is a vital turning period of the biosphere in Earth history (such as faunal and floral invasions of land and F/F mass extinctions), which is the time interval our proposed project concerns. As agreed in the international Devonian scientific community, pelagic-neritic correlation, correlation with the GSSP levels and substage boundaries, and refinements of event stratigraphy are a few research aspects that particularly need to focus on in various regions. In this connection, our proposed project focuses on the South China region. It features a comprehensive research of paleontological, sedimentological, and geochemical aspects of the Devonian Geneseo Event intervals selected on the basis of our study in the past, with an emphasis on stratigraphic correlation between deeper and shallow water facies. To achieve such a goal, conodont samples will be processed from some well-known neritic sections that still lack sufficient conodont data so far. Efforts will be made to clarify detailed stratigraphic distribution of some major fossil groups (such as brachiopods and some pelagic forms) in order to clarify their successions and possible turnovers, and to find out extents and distribution pattern of the event (including depositional and geochemical). The objective of such studies is to investigate the nature of this event, to discuss finer (substage level) stratigraphic divisions and correlation and to provide valuable data for understanding the possible coupling between the biosphere and its environments in this critical time interval.

泥盆纪是地史中生物界的一个重大转折时期（动植物登陆、F/F大绝灭等），本课题就是针对这个时间段提出的。在泥盆纪古生物地层研究中，浮游相与浅水相对比、亚阶界线、事件地层等内容是学界近年来的几项工作重点。有鉴于此，本课题以华南为主要工作区，在过去多年工作积累中，针对泥盆纪珍尼赛欧(Geneseo)事件层段，开展古生物、沉积及地球化学等方面综合研究，采取多种手段加强浅水相区与较深水相区之间的地层对比；搞清主要化石类群(如腕足类、珊瑚等)的详细地层分布，以期获得这些生物可能的演替情况；了解该地质事件(包括沉积的、地化的等)的规模及其分布情况，探讨其性质及较精细的（亚阶级别）地层划分与对比，为认识该时间段内生物与环境可能存在的耦合关系等人们关心的问题提供重要参考资料。

在泥盆纪古生物地层研究中，浮游相与浅水相对比、亚阶界线、事件地层等内容是学界近年来的几项工作重点。有鉴于此，本课题以华南为主要工作区，其主要研究内容有两个方面：1）华南珍尼赛欧(Geneseo)事件层段的生物地层研究：一是涉及浮游生物，适宜作为地层对比的标志并建立较为准确的生物带格架；二是底栖生物，包括腕足动物及珊瑚等; 2）华南珍尼赛欧事件层段的沉积环境特征：通过综合沉积学、地球化学分析等，并结合古生物资料，恢复该事件层段的沉积环境演变，探讨与之相关的生物群演变。. 本课题取得的主要成果及科学意义：1）首先确认了所测大山剖面是一个比较完美的中-上泥盆统浮游相地层剖面，识别出了连续的牙形石生物带，据此划分出了14个牙形石生物带，对识别中-上泥盆统及各阶/亚阶界线提供扎实依据；2）确认了珍尼赛欧事件位于牙形石S. hermanni - Po. cristatus带之底，该层位代表了吉维阶上亚阶的底部。该层位发生了一次区域性的海平面上升，有关的底栖生物群也经历了重要演替，因此，这些标志可用于地层划分与对比；3）地球化学特征也经历了明显变化，包括有机碳同位素的震荡式降低及上升、几种主要微量元素则在事件层之上出现一个明显的峰值，反映的是古海洋化学的均一性及差异性；4）详细对比研究了中-上泥盆统的石燕贝类腕足动物化石，搞清了渥纽尔贝科模式属种的内部构造,这对认识渥纽尔贝科的准确特征及其超科归属提供了依据。