塔北古生界滨岸相混控碎屑岩体系沉积学和沉积模式

Sedimentology and depositional model of a mixed fluvial,wave-and tide-influenced Paleozoic clastic coastal system in the northern Tarim basin

滨岸相混控碎屑岩沉积体系是指发育在滨岸带,受河流、波浪和潮汐混合水动力作用产生的复合碎屑岩沉积体系。受区域构造、物源、古地貌、海平面变化和滨岸水动力控制,塔里木盆地沙雅隆起区在志留纪—泥盆纪—石炭纪时期发育了辫状河三角洲、潮汐和波浪作用相互交替的滨岸相碎屑岩复合沉积体系。本文基于野外露头、钻井和测井等资料,开展了沙雅隆起区志留系—石炭系沉积层序、沉积相和沉积模式的综合研究,建立复合沉积体系的沉积学模式,包括:(1)志留系—泥盆系的浪控-潮控海湾沉积体系;(2)下石炭统巴楚组的台地-蒸发潟湖-潮坪沉积体系;(3)下石炭统卡拉沙依组的河控-浪控-潮控三角洲沉积体系。下志留统柯坪塔格组滨岸滩坝和潮坪砂体、上泥盆统东河塘组冲积平原、海湾滩坝砂体和下石炭统卡拉沙依组辫状河三角洲砂体在塔北地区大面积分布,其冲积平原、三角洲前缘、水下分流河道砂体被后期潮汐和波浪作用改造后,形成潮汐水道砂体、河口坝砂体和滨岸滩坝砂体,物性条件明显改善,有利于形成优质储层区带。目前,滨岸混合水动力碎屑岩沉积体系已获得重大油气勘探突破,其沉积学模式可为塔北地区古生界碎屑岩油气勘探提供理论基础。

A mixed-controlled clastic shoreline system is a composite clasolite sedimentary system developed in the clastic shoreline zone and controlled by hybrid hydrodynamics, which in turn is affected by river, wave and tidal action. During Silurian, Devonian and Carboniferous periods, under the control of regional tectonics, provenance, paleogeomorphology, sea level change and coastal mixed hydrodynamic conditions, there developed an onshore composite clasolite sedimentary system controlled by braided river, tidal and wave interaction in the Shaya uplift area of the Tarim basin. Based on outcrop, drilling and logging data, a systematic study has been carried out in the Shaya uplift area, including Silurian-Devonian-Carboniferous sedimentary sequence, sedimentary facies and sedimentary model. The sedimentology models of the composite sedimentary system are established indicate that:(1) the bay system controlled by wave-tidal developed during Silurian-Devonian;(2) a platform-evaporative lagoon-tidal flat system developed in the Early Carboniferous Bachu Formation;(3) a fluvial-wave-tidal influenced delta depositional system developed during the period of the Early Carboniferous Kalashayi Formation. The shoreland sand bodies of the Lower Silurian Kalpintage Formation, the Upper Devonian Donghetang Formation, and the braided river delta sand-bodies of the Lower Carboniferous Kalashayi Formation, which are widely distributed in a large area in northern Tarim basin, were all reformed by tidal and wave action in different degrees. The sand bodies of the high sinuosity braided river alluvial plain developed in the early stage, of which braided river delta front, and subaqueous distributary channel etc., were all inherited, superimposed and reformed by tidal and wave action. The reformed sand bodies of tidal channel, mouth bar, and onshore beach bar, which improved significantly in physical properties, have become favorable zones for the development of the high quality reservoirs. Significant breakthrough has been made in oil and gas exploration, in a favorable target area and strategic replacement area for oil and gas exploration in the future. The depositional models in study area will become theoretical basis for oil and gas exploration of Paleozoic clastic rock reservoirs in the northern Tarim basin.