塔西南坳陷早白垩世物源体系和沉积古地理分析

摘要

Located between the west Kunlun Mountain and south Tianshan Mountain,there deposited huge thickness of coarse clastic Kezilesu Group in Lower Cretaceous southwest depression of Tarim Basin,which is one of the major reservoirs for oil/gas exploration.Based on lots of outcrops observation and well contrast,three 3 rd sequences have been classified,and sedimentary system have been recognized furthermore under the se-quence-stratigraphy framework,such as alluvial fan,braided river-braided delta and fluvial delta.Provenance analysis according to the heavy mineral of sandstone samples came from both outcrop and drill cores has revealed very complex source rock types,including magmatogenic,metamorphogenetic and recycled-orogenic source. Hematite,magnetite and leucoxene dominated.It's characteristic with high grade metamorphism in the south Tianshan Mountain,low grade metamorphism and basic igneous rock in north and south of the west Kunlun Mountain,respectively.Provenance analysis provided useful information for the paleogeography restore.There mainly deposited alluvial fan and fan delta along the south Tianshan Mountain,and fluvial dominated early in the north of the west Kunlun Mountain,and evolved an alluvial fan later,while fluvial and fluvial delta domina-ted the south of the west Kunlun Mountain.Fan-braided delta front distributary channel,delta front distributary channel and mouth bar sandstones are favor of good reservoir.Source system and paleogeography distribution have significance to favorable reservoir prediction.%塔西南坳陷位于西昆仑和南天山山前，早白垩世克孜勒苏群充填巨厚的粗碎屑沉积，是塔西南坳陷油气勘探的主要目标层段之一。通过大量的野外露头和盆内钻井对比，在克孜勒苏群内划分出3个三级层序，识别出冲积扇、辫状河、辫状河三角洲和曲流河-河流三角洲等沉积类型。重矿物物源体系分析表明，塔西南坳陷山前带和盆内钻井样品物质来源较复杂，既有岩浆成因，也有变质成因和再造沉积物，重矿物含量以赤铁矿、磁铁矿和白钛矿占绝对优势。重矿物组合类型反映出本区母岩性质主要为变质成因和岩浆成因，根据所处的地理位置进一步区分出南天山白垩纪高级变质岩母源区、西昆仑北带低级变质岩母源区和西昆仑南带基性火成岩3种不同的母源区。物源分析为沉积古地理恢复提供了重要依据，南天山西段山前以冲积扇-扇三角洲沉积为主，西昆仑北带早期以河流沉积为主，后期逐渐演化为冲积扇，西昆仑南带主要沉积河流-河流三角洲。扇/辫状河三角洲前缘水下分流河道、三角洲前缘水下分流河道和河口坝是形成优质储层的有利区。物源体系和沉积古地理分析对区内有利储集相带分布预测具有重要意义。