Effects of astronomical orbital cycle and volcanic activity on organic carbon accumulation during Late Ordovician–Early Silurian in the Upper Yangtze area, South China  

作　　者：ZHANG Xi ZHANG Tingshan ZHAO Xiaoming ZHU Haihua MIHAI Emilian Popa CHEN Lei YONG Jinjie XIAO Qiang LI Hongjiao 

机构地区：[1]School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China [2]Faculty of Geology and Geophysics,University of Bucharest,Bucharest 010041,Romania

出　　处：《Petroleum Exploration and Development》2021年第4期850-863,共14页石油勘探与开发（英文版）

基　　金：Supported by the China National Science and Technology Major Project(2017ZX05063002-009);National Natural Science Foundation of China(4177021173,41972120);CNPC-Southwest Petroleum University Innovation Consortium Science and Technology Cooperation Project(2020CX020000)。

摘　　要：Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied using cyclostratigraphic and geochemical methods.d13 C and chemical index of alteration(CIA)were used to filter the astronomical orbit parameters recorded in sediments.It is found that the climate change driven by orbital cycle controls the fluctuations of sea level at different scales,obliquity forcing climate changes drive thermohaline circulation(THC)of the ocean,and THC-induced bottom currents transport nutrient-laden water from high latitude regions to the surface water of low-latitude area.Hence,THC is the main dynamic mechanism of organic-carbon supply.The marine productivity indexes of Ba/Al and Ni/Al indicate that volcanic activities had limited effect on marine productivity but had great influences on organic carbon preservation efficiency in late Hirnantian(E4).Paleo-ocean redox environmental indicators Th/U,V/Cr and V/(V+Ni)show that there is a significant correlation between volcanism and oxygen content in Paleo-ocean,so it is inferred that volcanisms controlled the organic carbon preservation efficiency by regulating oxygen content in Paleo-ocean,and the difference in volcanism intensity in different areas is an important factor for the differential preservation efficiency of organic carbon.The organic carbon input driven by orbital cycle and the preservation efficiency affected by volcanisms worked together to control the enrichment of organic carbon in the Middle–Upper Yangtze region.

关 键 词：CYCLOSTRATIGRAPHY organic carbon accumulation geochemical weathering index thermohaline circulation volcanic activity Upper Ordovician Wufeng Formation Lower Silurian Longmaxi Formation 

分 类 号：P618.13[天文地球—矿床学]