柴达木盆地油砂山湖盆网状河三角洲沉积模式

柴达木盆地油砂山地区上新统底部湖盆网状河三角洲沉积,主要受盆地长轴控制,砂砾岩占近30%,成分和结构成熟度均较低。垂向层序表现为不规则的正旋回、反旋回的频繁交替,与湖盆半干旱气候下间歇性涨缩密切相关。三角洲平原亚相最为发育,由网状河道砂体、河道间洪泛及天然堤、决口扇组成。河道砂体呈低弯度窄条带状相互网结,以砂砾比例高、砂体规模和宽厚比小为特点。三角洲前缘亚相规模不大,水下分流河道向湖延伸不远,河口坝砂体规模较小,前缘席状砂则在湖水作用下分布较广,可建立枯水期、洪水初期、洪水中晚期及最大湖涨期4种沉积模式。

SEDIMENTARY MODELS OF ANASTOMOSED DELTA AT YOUSHASHAN,CHAIDAM BASIN

The anastomosed deltaic deposits at the bottom of the Pliocene in Youshashan,Chaidam Basin are controlled mainly by the macro axis of a lake basin.The contents of sandstone and conglomerate is about 30%.The lower maturity of composition and texture of the sandstone and conglomerate reflect quick deposition and near provenance.The vertical sequences of irregularly alternate normal and reversal cycles are related to intermittent expanding and shrinking of the lake water level.The anastomosed deltaic plain subfacies developed well,consisting of braided channel sandbodies,interchannel proluvials,dams and splays.Deltaic front subfacies is not big,river mouth bars are small,deltaic front sheet sands distribute widely.According to the above mentioned characters,four sedimentary models such as low water,the early stage and the mid late stage of flood and flush sedimentary models could be established.