恩施剖面栖霞组下部贫氧-缺氧环境成因模式

我国华南地区二叠系栖霞组沉积了多套富有机碳的暗色岩系，是华南地区油气勘探的潜在烃源岩。其形成主要与水体的氧化还原以及古特提斯海洋洋流系统有关。然而，栖霞期水体的缺氧-贫氧的成因模式还需要更多的地质证据。本文选择湖北省恩施剖面栖霞组下部臭灰岩段钙质页岩及碳酸盐岩夹层为研究对象，开展稀土元素REE、微量元素Th/U比值以及碳酸盐矿物晶格内微量硫酸盐硫同位素组成分析。研究结果表明，栖霞组下部臭灰岩段的下部沉积水体主要为缺氧至贫氧条件，而臭灰岩段上部主要为贫氧至氧化条件。这些缺氧至贫氧沉积主要是由洋流的上涌造成。洋流的上涌将深水环境中缺氧、贫氧的底部水体涌至陆棚斜坡地带，造成斜坡浅水地带形成一个近似倒三角的缺氧-贫氧水体带，从而沉积了栖霞组暗色薄层石灰岩或钙质页岩。

Formation model of anoxic-dysoxic environments in the Lower Chihsia Formation in the Enshi section

In South China，the Permian Chihsia Formation contains several organic-rich dark rock series，which are the potential source rocks of hydrocarbon. Their formations is mainly related with the redox conditions and the ocean current system of paleo-Tethys Ocean. However，the formation model of this anoxic-dysoxic environment during the Chihsian stage is still needed more geological evidences. We carried on the REE，trace element Th/U raio and the carbonate-associated sulfate sulfur isotopic composition in the calcareous shale interbedded with carbonate rock in the stinkstone member of the Chihsia Formation in the Enshi section，West Hubei Province. Our results show that the lower part of the stinkstone member was anoxic-dysoxic environments while the upper part reflects oxic-dysoxic environments. This anoxic-dysoxic environment resulted from the upwelling. This upwelling brought the oxygen-depleted bottom water in the deep-water environment to the shallow water of the slope environment，resulting in an interted triangle-shape oxygen-depleted water zone and depositing the dark-gray thin-bedded limestones or calcareous shale of the Chihsia Formation.