北康盆地新生代沉积特征

CENOZOIC SEDIMENTATION OF BEIKANG BASIN

北康盆地为南沙中部海域一重要的含油气盆地。盆地内主要发育了中始新统一第四系地层,最大沉积厚度11000 m。本文通过区域地质背景分析,认为北康盆地位于南沙地块,主体奠基于火成岩带上,盆地基底主要为火成岩及前新生代变质岩。晚始新世以前,南沙地块与华南陆块相连,北康盆地位于古南海西北缘,为一张性拉张盆地,盆地西北大部为陆相环境,东南部为滨浅海环境。晚始新世至早渐新世早期,南沙地块从华南陆块裂离向南漂移,北康盆地成为裂离陆块上的断坳盆地并具走滑特征。随古南海洋壳的被动消减和新南海的扩张,盆地水体加深,除西北尚有陆相沉积外,盆地大部为海相环境。早渐新世以后,南沙地块与婆罗洲地块拼贴,北康盆地整体位于海相环境。本文在详细地震相分析的基础上,对盆地新生界地层划分出三个超层序,7个层序,对上新统以下的5个层序进行了沉积相分析,并编制了平面相图。

Beikang Basin is one of the most important basins which bearing hydrocarbon potential. It is lo- cated at the central part of Nansha Islands ocean areas where the middle Eocene to Quatermary strata are developed well and the thickest stratum arrived to 11000 meters. In this paper, based on regional geological background analysis, it is believed that Beikang Basin belong to Nansha block, and its main body lay on a foundation of igneous rock zone. Before the Eocene, Nansha block connected with south China block, Beikang basin was a extensional basin that located at the north-western margin of the palieo-south China sea. During this time, a large part of the north-western part of the basin was land environments, the south-eastern part of it was shore-shallow marine environments. From late Eocene to early part of early Oligocene, Nansha block separated from south China block and drifted away to south direction, Beikang basin was become a rift-depression basin with the characters of strike-slip basin which located at a separted continental block. Accompanied the subduction of the palieo-south China sea ocean crust, water depth of the basin more and more higher, excepted a small part of the north- western part of the basin were continental environments, the other parts were marine environments. Af- ter early Oligocene Nansha block with kaliamantan block collided together, the main body of Beikang basin became marine environments. Relied on detail seismic facies analysis, three super sequences, seven sequences were divided, and the sedimentary facies of the five sequences among them were ana- lyzed, and their plane sedimentary facies maps were drawn too.