AUTHOR=Yi Xuefei , Ji Xia , Huang Yunfei , Liu Zuosong , Meng Jianghui 

TITLE=Black Shale Paleo-Environmental Reconstructions: A Geochemical Case Study of Two Ordovician–Silurian Boundary Sections in Middle Yangtze Area, China

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2022.842752

DOI=10.3389/feart.2022.842752

ISSN=2296-6463

ABSTRACT=Under the promotion of exploration and development for shale oil & gas, marine shale has become a hot spot of fine-grained sedimentary studies in China. Paleo-environment reconstruction has always been an important aim, especially for black shale. Based on a large number of samples collected from Wufeng and Longmaxi Formations of two field sections in western Hubei and eastern Chongqing, this paper compares the vertical variations of total organic carbon content, quartz /clay minerals value and trace elements compositions of these two profiles to reflect the paleo-environment changes from latest Ordovician to earliest Silurian. The results show that during the later Ordovician period, when Wufeng Formation deposited, the study area experienced a water depth change from from relative deep facies to shallow marine, and paleo-redox changed from oxygen rich to anoxic, and even euxinic, followed by the content of oxygen increase. When the Guanyinqiao Bed deposited, the basin suddenly became shallower, and the deposition environment changed to be oxygen enriched for high water energy, circulating oxygen enriched. In the earliest stage Silurian, when the Longmaxi Formation formed, and the paleo-water also suffered several changes of sea level, and the paleo-environment also changed from anoxic to oxic. These changes can correspond to the third-forth order sequences well.