二叠纪末期海洋缺氧:来自黄铁矿形态的证据

晚二叠世是古生代环境和生物演化的重要时期,也是重要的"冰室气候"时期,但其中仍然含有大量的富有机质沉积,并发育成为我国南方扬子板块重要的烃源岩层位.为恢复这一时期古海洋氧化还原状态,我们对湖北恩施赵家坝剖面大隆组硅质岩和四川广元上寺长江沟剖面大隆组碳酸盐岩中草莓状黄铁矿的粒径大小和分布进行了测量、统计和研究.统计结果显...

Oceanic anoxia during the Late Permian: Evidence from pyrite morphology

Late Permian is an important stage marked by vast environmental and biological changes in the Paleozoic.Although an “Ice House climate” predominated over the period，organic rich sediments，which are served as important source rocks，were deposited extensively in intra platform basins on Yangtze block，South China.In order to reconstruct the paleoredox conditions of the Yangtze sea during this period，we measured framboid size of pyrite in cherts and siliceous carbonates of Dalong Formation at Zhaojiaba section，Hubei province，and Changjianggou section，Sichuan province，respectively.Our data indicate that pyrite framboids in the cherts and carbonates are mostly of primary origin，although minor idiotopic crystals showing post depositional transformation are observed.Pyrite framboids generally vary in a very narrow range in size，mostly smaller than 5 μm，and over 80％ of which are smaller than 77 μm.These suggest that，during the Late Permian，the organic rich sediments were deposited from the extremely anoxic(even sulfidic)water columns within the intra shelf basins(or depressions).The subsequent Permian Triassic mass extinction could have been triggered by this extreme anoxia from the late Changxingian stage.