塔里木中部地区东河砂岩段沉积特征和沉积环境演变

塔里木盆地东河砂岩段是中国首例获高产工业性油气流的海相滨岸沉积,它是石炭纪初期海侵阶段的沉积产物,包括底部砾岩、中部块状砂岩和上部含砾砂岩沉积。东河砂岩段主体岩性为中细石英质砾岩和岩屑质细砂岩,具有中等偏高的成份和结构成熟度、酸性岩浆岩的重矿物组合、海相沉积物的微量元素特征,发育不同类型的交错层理、平行层理、冲洗层理以及生物扰动构造,垂向上构成河口湾(河流)和滨岸沉积序列。底部砾岩形成于受古地形控制的砾质河流沉积环境;中部块状砂岩和上部含砾砂岩形成于河口湾和前滨、临滨沉积环境。平面上,塔中10井和塔中14井以西地区以前滨和临滨沉积为特征,以东地区以河口湾沉积为特征,整体表现出自西向东的海侵特征。

SEDIMENTARY FACIES AND ENVIRONMENTAL CHANGES OF THE DONGHE SANDSTONE IN CENTRAL TARIM

The Donghe Sandstone was the first littoral sediments producing a commercial oil gas in China, which formed in early stage of Carboniferous transgression. It was divided into three members: the lower conglomerate, middle massive sandstone and upper pebbly sandstone. The major lithology of the Donghe Sandstone was middle fine quartzitic conglomerate and fine grained lithic sandstone. These conglomerate and sandstone were deposited in estuary and littoral environments, with the characteristics of middle high composition and texture maturities, heavy mineral combination of acidic rocks, trace element of marine environment, developed different types of cross beddings, parallel bedding, swash bedding and bioturbate structure. The lower conglomerate developed in fluvial environment which originated from incised valley, obviously controlled by paleogeography. The middle massive sandstone and upper pebbly sandstone formed in an estuary, foreshore and nearshore environments. The sediments in the west part of the wells TZ10 and TZ14 were characterized by foreshore and nearshore environments, while in the east part by estuary, which indicated the early stage transgression during Carboniferous from west to east in the Tarim basin.