华南晚泥盆世F-F之交海水古温度变化及其生物多样性响应

The F-F event that occurred at the Late Devonian Frasnian-Famennian (F-F) transition is one of the most interesting topics attracting global geologists. However, the process and genetic mechanism of this event is far from clear. Through intensive collecting, processing and identifying conodont samples from two stratigraphic sections that represent two different sedimentary facies, i.e. the carbonate platform slope facies and basinal faices, high-resolution conodont biostratigraphic framework across facies during the F-F transition of the Late Devonian can be established in South China. In order to reconstruct the paleotemperature history of the F-F transition in South China, oxygen isotope composition of conodont phosphate was measured by high temperature conversion elemental analyzer (TC-EA) coupled isotope mass spectrometer. Linking the changes in abundances and diversities of different types of organisms compiled from the literature and our own data, with background sedimentological and sedimentary geochemical features by means of paleotemperature of seawater, this proposal aims to shed light on the impact of paleotemperature on biodiversities. The implement of this proposal will provide new materials and insights to understand the enigmatic cause of the F-F event.

晚泥盆世弗拉期-法门期(F-F)之交的F-F事件是国内外地质学领域的研究热点之一，但是该事件的发生过程、成因机制至今悬而未决。本研究通过对碳酸盐台地斜坡相、盆地相剖面进行系统采集、处理、鉴定牙形石样品，以构建华南晚泥盆世F-F之交跨相区高分辨率牙形石生物地层格架；根据高温还原同位素质谱法测试(TC-EA)的牙形石磷酸根氧同位素值，恢复华南晚泥盆世F-F之交海水古温度的变化过程；以海水古温度为纽带，综合文献和实际材料中多门类生物的丰度和分异度的变化特征以及沉积学、沉积地球化学数据，试图深入剖析F-F之交古温度变化对生物多样性的影响，为研究F-F事件的成因之谜提供新的资料和认识。

晚泥盆世弗拉期-法门期（F-F）之交是显生宙生物演化与环境变迁的关键时期，其间发生的显生宙五大生物灭绝事件之一的F-F事件（或称Kellwasser事件）是国内外地学领域研究的热点。大量证据表明，气候变化是联系生物演化和环境变迁的重要纽带。因此，查明F-F之交气候变化对于揭示F-F事件的成因机制具有重要意义。项目通过对华南杨堤和南峒剖面F-F之交地层的实测，牙形石化石样品的系统采集、处理和分析，获得完整牙形石标本15377枚（P1分子），鉴定出牙形石6属48种。基于系统古生物学工作，建立了华南晚泥盆世F-F之交跨相区高分辨率牙形石生物地层格架，为F-F事件研究提供了高精度的地层时间框架。根据高温还原同位素质谱法测试的牙形石磷酸根氧同位素（δ18OPO4）比值重建的定量古温度曲线显示，华南晚泥盆世F-F之交表层海水古温度范围为27~36℃，在下、上Kellwasser事件层中分别出现了幅度为~ 3℃和~ 6℃的降温，时间上分别对应于F-F事件第一幕（~ 0.7 Myr）的珊瑚-层孔礁的锐减和F-F事件第二幕（主幕，~ 0.2 Myr）的底栖和浮游生物的灭绝。F-F之交碳酸盐岩碳同位素正偏、δ18OPO4正偏以及生物灭绝在时间上的耦合，揭示了大量有机碳埋葬引起大气CO2分压降低、气候快速变冷，最终造成F-F生物灭绝。上述研究成果不仅为揭示F-F生物灭绝事件的成因机制提供了重要线索，而且为诠释当今气候、生物与环境之间的协同演化关系提供了长时间尺度的地史借鉴。