南京地区早三叠世碳酸盐沉积动力过程初探  

Preliminary Study on Sediment Dynamic Processes of Early Triassic Carbonate Deposits in Nanjing Area,Eastern China

作　　者：高抒[1] GAO Shu(School of Geography and Ocean Science,Nanjing University,Nanjing 210023,China)

机构地区：[1]南京大学地理与海洋科学学院,南京210023

出　　处：《沉积学报》2023年第6期1673-1680,共8页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41530962)。

摘　　要：【目的】早三叠世碳酸盐沉积揭示了二叠纪末生物大灭绝之后的沉积环境剧变,如何用沉积动力学方法获取沉积环境信息,其主要困难是现场观测不可实施、初始和边界条件未知、沉积物来源和去向未知。新的思路之一是根据复杂系统理论重构控制方程,以达到正确计算或模拟的目的。【方法】针对南京地区早三叠世和龙山组24个周期的泥质—碳酸盐沉积,构建沉积环境参数计算方法,提取沉积记录信息。【结果】各周期性沉积的垂向尺度为10^(0)~10^(2)cm,碳酸盐层与泥质层交替出现,沉积构造以纹层为特征,在24个周期中碳酸盐沉积厚度占74%,沉积构造以纹层为特征;根据泥质层的沉积速率推算每个周期的时间尺度为5~40ka,虽然泥质层厚度只占总厚度的26%,但却占总时长的73%;泥质和碳酸盐物质沉积速率、沉降通量、水层悬沙浓度、碳酸盐物质产出、生物生产等各项环境参数与现今深海碳酸盐沉积环境相当。【结论】该沉积记录反映研究区域古海洋环境和气候变化特征,但计算方法的进一步改进有赖于碳酸盐沉积的杂质含量、纹层厚度和保存潜力、沉积物和有机质来源等约束条件的确定。[Objective]Early Triassic carbonate deposits indicate the dramatic change of sedimentary environment after the Permian mass extinction.However,the main difficulties in obtaining sedimentary environment information by sediment dynamics lie in the difficulties in field observation,unknown initial and boundary conditions,and un-known source and transport direction of sediments.One of the new approaches is to reconstruct the governing equa-tions according to the complex system theory to achieve the goal of reliable simulation.[Methods]Here a method for calculating sedimentary environment parameters is established to analyze the sedimentary record of the Early Triassic(Helongshan Formation)carbonate deposits in the Nanjing area,which contain 24 mud-carbonate cycles.[Results and Discussions]The preliminary results show that the cyclic deposition has a vertical scale of 10^(0)-10^(2) cm,the car-bonate and the muddy layers appear alternately,the sedimentary structure is characterized by laminae,and the thick-ness of the carbonate deposit accounts for 74%in the 24 cycles.The time scale of each cycle is 5-40 ka,as calculated according to the deposition rate of the mud layers.Although the thickness of the mud layers only accounts for 26%of the total thickness,it accounts for 73%of the total temporal duration.The environmental parameters,such as deposi-tion rate,vertical settling flux,suspended sediment concentration,carbonate and biological production,are similar to those of the present deep-sea carbonate sedimentary environment.[Conclusions]Cyclic sedimentation reflects the characteristics of paleo-marine environment and climate change in this region,but the further improvement of the cal-culation method depends on the definition of the constraining conditions associated with the impurity content of car-bonate,the thickness and preservation potential of laminae,and the production of sediment and organic matter with-in the water column.

关 键 词：碳酸盐沉积 早三叠世 动力过程 周期性 沉积速率 南京地区 

分 类 号：P534.51[天文地球—古生物学与地层学]