鄂尔多斯盆地西南缘奥陶系深水牵引流沉积

ORDOVICIAN DEEP-WATER TRACTION CURRENT DEPOSITS ON THE SOUTHWESTERN MARGIN OF ORDOS BASIN

深水牵引流沉积是沉积学中的一个重要研究领域,包括内潮汐、内波沉积和等深流沉积两大类,主要发育于海洋深水区。深水牵引流沉积的研究起步较晚,目前主要集中于现代深海沉积和野外露头研究,对深埋地下的古代深水牵引流沉积发现较少,其所具有的油气潜能还不被人们所认识。本文论述了鄂尔多斯盆地西南缘奥陶系内潮汐沉积、等深流沉积的特征和沉积类型。内潮汐沉积是在研究区首次发现,以灰色中-细砂岩为主,部分为粗粉砂岩,单层厚十余厘米至数十厘米,砂岩以普遍发育双向交错纹理为特征。等深岩丘主要由3种碳酸盐等深岩组成,即砂屑等深岩、粉屑等深岩和灰泥等深岩,共发育有4种层序样式。最后,阐明了其油气勘探意义,并分析了其潜在的油气勘探价值。

Deep-water traction current deposits are an important domain of sedimentology. It includes internal-tide and internal-wave deposits and contourite, mainly developing in deep water of ocean. The study about deep-water traction current deposits started late in China. At present, such study concentrates on modern marine sediment and field outcrop. But archaic deep-water traction current deposits have been rarely found. People have little knowledge of its potential of oil and gas. The authors discuss the characters and sedimentary styles of Ordovician internal-tide deposits and contourite on the southwestern margin of Ordos basin. The interal-tide deposits are identified for the first time in the study area and dominated by gray medium-fine sandstone.Coarse farinaceous sandstone is little. The layer thickness is from about 10 cm to tens of centimeters. Sandstone has abundant bidirectional cross-beds. The contour drift is composed of three kinds of carbonate contourites, that is, calcarenitic contourite, calcisiltitic contourite and calcilutitic contourite. There are four sequence styles. Such deposits are of significance for oil and gas exploration.