藏北羌塘地区早中侏罗世过渡期缺氧事件沉积与碳同位素异常研究

在西藏北部羌塘地区，沿侏罗纪班公-怒江洋大陆边缘分布有侏罗系中下统连续沉积的地层剖面，根据菊石化石控制的定年资料，这一地区土阿辛阶曲色组顶部为一套泥晶灰岩与钙质泥岩沉积，叠覆其上的阿林阶-巴柔阶色哇组则是黑色页岩地层，它在尼玛-安多一带广泛分布。根据我们在色哇地区建组剖面采集样品的初步研究，在曲色组与色哇组界线可观察到碳同位素曲线的明显波动，可分辨多级次的碳同位素正向和负向异常，这是侏罗纪早中期全球海洋碳循环与平衡发生偏移的标志。通过区域对比，发现这一地区黑色页岩沉积要比欧洲、美洲和澳洲报道的Toarcian期缺氧事件发生的时间晚、层位高，它可能是侏罗纪古海洋研究中漏失的一个环节。本项申请拟选择双湖县色哇地区菊石化石丰富的典型地层剖面，同步开展无机碳和有机碳同位素分析，研究J2/J1界线岩相过渡转换期碳同位素变化曲线的异常信号和驱动机制，为我们参与全球古海洋、古气候变化研究提供一个切入点。

The continuous stratigraphic sections of Lower-Middle Jurassic occur along northern continental margin of Bangong-Nujian paleoocean in the Qiangtang area of northern Xizang Plateau. According to ammonite biochronology, the top strata of the Quse Formation consists of micritic limestone and calcareous shale, overlying Aalenian-Bajocia black shale sedimention, which has extensive distributions in Nima-Anduo area. The carbon isotope curves of collected samples from standard stratigraphic sections, preliminary demonstrate obvious fluctuations across the Quse Formation and Sewa Formation boundary, The multiple positive and negative anomaly are distinguished, and indicate carbon cycle changes during Early-Middle Jurassic paleoocean. Based on regional and global correlation, it present stratigraphic horizon of the boundary in this area is higher than Toarcian oceanic anoxic event in European, America and Australia. We propose it is missed events in Jurassic paleoocean evolution history. This application will select typical sections with abundant ammonite fossils and collect rock samples, synchronously measure carbon isotope signatures from carbonate and organic matter across the Lower and Middle Jurassic lithofacies transform boundary, check and calibrate carbon isotopic signals. It will highlight unique features in Asian-Tethyan realm and provide us an entry point to participate in global paleoocean and paleoclimate changes.