Reconstruction of the silicate weathering feedback in the mid-Cretaceous high-CO2 world

构造与气候过程的相互作用和长期关系是理解全球碳循环变率的关键问题。白垩纪中期（130-90 Ma），大陆裂谷和海洋地壳的产生速度加快，导致大气中二氧化碳含量增加，温室气候条件明显。反过来，大气CO2的减少是通过有机物埋藏、硅酸盐风化强度的变化或两者的结合来实现的。海相碳酸盐岩的锂同位素组成是硅酸盐风化反馈强度的代用指标，记录了海水δ 7 Li的长期变化。海水δ 7 Li反映了粘土形成过程中，由于同位素分馏作用，陆源硅酸盐和大洋硅酸盐的风化变化所控制的源汇平衡。通过这个项目，我们的目标是生成一个新的白垩纪中期海水锂同位素曲线之间的间隔130-90 Ma前，以评估硅酸盐风化反馈，类似于现有的记录新生代。我们将使用大量的碳酸盐和原始保存的骨骼方解石（腕足动物，箭石和双壳类的外壳）的档案，其中有一个很好的日期收集的标本存在。新记录包括两个海洋缺氧事件OAE 1a和OAE 2以及Aptian晚期/Albian早期和Cenomanian的间歇性冷阶段，并将为极端温室气候条件下的风化提供参考。该项目的主要预期成果是：1）对白垩纪中期海水δ 7 Li值长期演化的进一步认识，2）关于白垩纪中期背景δ 7 Li值的信息，以评估其相对于OAE、海水锶同位素记录和玄武岩风化量的长期变化，3）关于白垩纪中期海水δ 7 Li值的一致性的新信息，（强度）的风化相对于间歇性冷阶段，和4）估计的潜在不确定性δ 7 Li相对于不同程度的骨骼方解石保存和分类特定的重要影响的锂同位素分馏不同的钙化。

The interaction and secular relationship between tectonic and climatic processes are key issues for our understanding of global carbon cycle variability. The mid-Cretaceous period (130-90 Ma) witnessed elevated rates of continental rifting and oceanic crust production, resulting in increased atmospheric CO2 and pronounced greenhouse climate conditions. Atmospheric CO2 reduction, in turn, is achieved either by organic matter burial, by changes in the intensity of silicate weathering or a combination of both. The lithium isotopic composition of marine carbonates is a proxy for the intensity of the silicate weathering feedback and records secular changes in seawater δ7Li. The seawater δ7Li reflects the balance of sources and sinks controlled by variations in the weathering of continental and oceanic silicates due to the isotopic fractionation during the formation of clays. With this project we target the generation of a new mid-Cretaceous seawater lithium isotope curve for the interval between 130-90 Ma ago to assess the silicate weathering feedback, analogue to the already existing record for the Cenozoic. We will use the archives of bulk carbonate and pristine preserved skeletal calcites (shells of brachiopods, belemnites and bivalves) for which a well-dated collection of specimens exists. The new record includes the two oceanic anoxic events OAE1a and OAE2 as well as intermittent cold phases in the late Aptian/early Albian and Cenomanian and will serve a reference for weathering during extreme greenhouse climate conditions. The main expected deliveries of this project will be 1) an improved knowledge about the secular evolution of mid-Cretaceous seawater δ7Li values, 2) information about mid-Cretaceous background δ7Li values to assess its long-term variability relative to OAEs, the seawater strontium isotope record, and the amount of basalt weathering, 3) new information about the congruency (intensity) of weathering relative to intermittent cold phases, and 4) estimates about potential uncertainties in δ7Li relative to different degrees of skeletal calcite preservation and taxon-specific vital effects of lithium isotope fractionation among different calcifiers.