深水等深积岩丘及其含油气潜能

等深积岩丘大量存在干现代海洋调查和古代地层记录的深水沉积中,其规模可与深海大型浊积扇相比拟。岩性一般由泥级、粉砂级、砂级及细砾级等深漉沉积构成,成分上可以是陆源碎屑的或是碳酸盐的,其中粉砂级和砂级等深流沉积的单层厚度在数厘米至数十厘米,厚者可达2m 左右。颗粒的分选性一般中等一较好,局部很好,原生孔隙发育,并与深水原地沉积的页岩、泥岩互层沉积,具有良好的生储盖组合特性。对比了大西洋东缘现代沉积的 Faro 等深积岩丘和中国古代奥陶纪沉积的湘北九溪等深积岩丘、甘肃平凉等深积岩丘的层序特征,提出了等深积岩丘的形成分为萌生、成型和衰退三个阶段的沉积模式。认为等深积岩丘具有潜在的油气勘探前景。

Deep-water Contourite Drifts and Their Hydrocarbon Potential

The modern oceanographic investigations and the studies of contour deposits in the ancient stratigraphic record indicate that contourite drifts are well-developed in the deep-water de- posits and are comparable to large-scaled submarine fans in extent.Contourite drifts are usually composed of mud-sized, silt-sized,sand-sized and even gravel-sized contourite de- posits in lithology and terrigenous clastics or carbonates in constituent.For the silt-sized and sand-sized contourites,the thickness of a single bed is usually a few to tens centimeters, sometimes about 2 meters,and the sorting is usually moderate to good and locally even very good.The primary porosities of the contourites are well developed.The silt-sized and sand- sized contourite drifts are interbedded with autochthonously depposited deep-water shale and mudstone so that good source reek-reservoir-cover combinations may be formed. Comparing the characteristics of vertical succession in Faro Drift developed in the eastern margin of North Atlantic Ocean with that of the ancient drifts in China including the Ordovician Jiuxi Drift in northern Hunan and Pingliang Drift in Gansu,the author has proposed a sedimentation model of contourite drifts from rudimentary and mature stages to declining stage.It is suggested that contourite drifts have potential hydrocarbon prospect.