Establishing a new method for Cr isotopes to understand redox change of seawater in the geological pasts

在两年的时间里，我建立了一种新的方法，从沉积在地质历史的沉积岩中分离铬，测量铬同位素，这可能是一个新的指标，在深部的海水缺氧缺氧条件。我测量了主，微量和稀土元素的浓度以及铬同位素组成的下白垩统沉积物中太平洋山脉的碳酸盐岩。在分辨率盖奥特上，我比较了DSDP 463站深海白垩和ODP 866站浅水石灰岩之间碳酸盐的化学成分。我的数据跟踪地层间隔代表海洋缺氧事件（OAE）-1a早期阿普梯时间，其特征是几乎同步的全球沉积的有机碳丰富的黑色页岩。这些数据表明，在OAE-1a之前的几十万年，海水化学已经发生了变化。

During the two years, I have established a new method to separate Cr from sedimentary rocks deposited in the geological past to measure Cr isotopes which could be a new indicator of oxic-anoxic condition of seawater in the deep time. I measured major, trace and rare earth element concentrations as well as Cr isotopic compositions of carbonate rocks of Lower Cretaceous sediments from Mid-Pacific Mountains. I compared chemical compositions of carbonate between deep pelagic chalk from DSDP Site 463, and shallow water limestone from ODP Site 866 on Resolution Guyot. My data track a stratigraphic interval representing Oceanic Anoxic Event (OAE)-1a of early Aptian time, characterised by an almost synchronous global deposition of organic carbon-rich black shale. The data suggest that seawater chemistry have changed a few hundred of thousand years before OAE-1a.