Marine and terrestrial records of Toarcian (Early Jurassic) climate and environmental change - Phase 2: Evolution of Early Jurassic Environment in NE-Germany

在本项目的第一阶段，我们调查了普连斯巴契期/托阿尔西期和托阿尔西期环境危机期间的环境扰动，提出了三个待验证的假说，所有这些假说都是可以证明的。1)托阿尔西亚气候变暖与大陆冰冻圈的消亡有关。冰川融化影响了特提斯陆架水的18O值，掩盖了生物钙化体中储存的氧同位素温度信号。独立的证据是通过使用Tex-86代理建立基于冰体积独立的分子古温度测量的古温度记录来实现的。2)通过对海洋和陆源光合作用产物的同位素特征的研究，我们推测普连斯巴契期和托阿尔西亚早期的气候事件对陆地和海洋环境的影响是一样的。3)海洋初级生产者群落直接受到海水温度上升和大气CO2浓度上升导致的海洋酸化的影响。我们利用卢森堡Toarcian沉积物的三萜类生物标志物组成，识别出6个反映早期Toarcian初级生产者组合(红色与绿色分支)变化的生物事件。我们现在的目标是通过在空间和时间域上扩展研究目标来扩展对早侏罗世古环境演化的研究。研究Pliensbchian/Toarcian环境变化优先在具有“沥青相”的缺氧/正辛期盆地中进行。在这些基础上，严重的氧气枯竭影响了碳循环，并将一阶全球驱动因素与二阶区域驱动因素分开。在碳酸盐台地上发育的非沥青剖面，特别是北冈瓦那边缘和伊比利亚的剖面，缺乏连续的沉积，由于有氧环境中有机物的不稳定沉积/侵蚀和降解，很难详细记录有机物质的分子和同位素组成的环境变化。我们建议研究东北-德国盆地早侏罗世的环境变化，那里的沉积物沉积在托阿尔西亚陆架连续的、地层约束良好的边缘盆地中，不受严重缺氧和沥青相发育的影响。利用分子生物标志物和同位素地球化学方法，可以确定二氧化碳和碳同位素的一级全球驱动因素。托阿尔西期的古环境演化发生在约200 Ma前营地火山作用引发的冈瓦那裂解之后。我们将利用东北-德国盆地中两个以前未被研究过的岩芯，跟踪Rhaetian到Aalenian的整个古环境变化，并将建立一个化学地层学和生物地层学框架，以解释30 Ma以来早侏罗世的古环境变化，最终导致托尔西亚海洋缺氧事件。

In the first phase of this project, we investigated environmental perturbations during the Pliensbachian/Toarcian and Toarcian environmental crisis formulating three hypothesis to be tested, all of which could be proven. 1) Toarcian warming was associated with a demise of a continental cryosphere. Ice melting impacted on 18O values of Tethyan shelf water and obscured the oxygen isotope temperature signal stored in biocalcifiers. Independent proof was achieved by establishment of a paleotemperature record based on ice volume-independent molecular paleothermometry using the TEX-86 proxy. 2) We postulated that Pliensbachian and early Toarcian climate events equally affected terrestrial as well as marine environments, proven by investigation of isotopic signatures in marine and terrigenous photosynthate. 3) Marine primary producer communities directly suffered from rising seawater temperatures and ocean acidification via rising atmospheric CO2 concentration. We identified six biotic events reflecting changes in primary producer associations (red versus green clades) in the Early Toarcian using triterpenoidal biomarker compositions of Toarcian sediments from Luxembourg.We now aim to extend the research on early Jurassic paleoenvironment evolution by extending the study objectives in both the spatial and temporal domain. Investigations addressing Pliensbachian/Toarcian environmental change were preferentially conducted in anoxic/euxinic basins with “bituminous facies”. Severe oxygen depletion affected carbon cycling in those basis and affords a separation of first-order global drivers from second-order regional drivers. Non-bituminous sections, particularly from the north Gondwana margin and Ibera that developed on carbonate platforms lack continuous sedimentation and a detailed record of environment change in the molecular and isotopic composition of organic material is difficult to achieve, due to erratic sedimentation/erosion and degradation of organics in oxygenated environments. We propose to study early Jurassic environmental change in the NE-German Basin, where sediments were deposited in a continuous and stratigraphically well-constrained marginal basin of the Toarcian shelf not subject to severe anoxia and development of bituminous facies. First order global drivers on pCO2 and carbon isotopes can thus be identified by means of molecular biomarker and isotope geochemistry.The Toarcian paleoenvironmental evolution occurred in the wake of the Gondwana break-up initiated by CAMP volcanism some 200 Ma ago. We will follow the entire succession of Rhaetian to Aalenian paleoenvironmental change employing two cores available in the NE-German Basin that have not been studied previously and will establish a chemostratigraphic and biostratigraphic framework for interpretation of early Jurassic paleoenvironmental change over a period of 30 Ma culminating in the Toarcian oceanic anoxic event.