关键词: 浊积岩, 沙河街组三段, 渐新世, 沉积速率, 湖盆, 泥岩层, 介形虫, 碎屑岩层, 储盖组合, 化石

Abstract: 53.2 m of cores from C-well in Kenli District, being a suite of coarse clastics intercalated with thin beds of mudstone, are identified to be non-marine lacustrine turbidites of the 3rd member of the Shahejie Formation in Oligocene. The sedim eats include 4 cycles and, at least, 19 rhythmic successions grading from coarse to finer sandstones and mudstones. From their composition, granularity, structure, fossils, grain morphology and rate of deposition etc., characteristic of lacustrine turbidites, they can be geologically reconstructed as follows: The basin is believed to be surrounded by an area rich in source materials,with a steep floor dipping at about 5-10. Under these conditions, triggered by the powerful and pulsatory hydrodynamic agents as mountain torrents, the turbidity currents containing large amounts of epicontinental elastics in suspension slipped along the subaqueous slope towards the deep-water region where the C-Well is located. A turbidite mass was thus deposited, characterized with the occurrence of coarse elastics containing little fossils and fine elastics with reworked neritic organisims alternating with mudstone containing deep-water fossils. Judging from the facies sequence, it is presumed that this section is a thick intermediate layer lying between two distal series, favourable for the formation of oil and gas pools.