江苏高邮凹陷古近系戴南组一段物源体系和沉积相

Provenance system and sedimentary facies of the Member 1 of Paleogene Dainan Formation in Gaoyou Sag,Jiangsu Province

对碎屑组分和重矿物的分析结果表明,高邮凹陷戴南组一段沉积时期,北部斜坡带的花庄、富民北部和永安地区沉积物来自柘垛低凸起方向,联盟庄和马家嘴地区沉积物来自菱塘桥低凸起方向;南部陡坡带沉积物来自通扬隆起,周庄地区沉积物来自东部物源区。戴一段沉积物母岩岩性以中—低级变质岩为主,中酸性火山岩的分布较基性火山岩要广,深成岩较少或没有。根据岩心观察、录测井资料分析,及研究区物源体系特征,认为高邮凹陷戴南组一段沉积时期,发育扇三角洲、三角洲、近岸水下扇和湖泊沉积。凹陷北部斜坡带地形坡度较缓,来自柘垛低凸起和菱塘桥低凸起方向的沉积物呈点物源形式沿水下河道在缓坡带形成三角洲沉积,物源供给量的差异导致三角洲朵体大小不同;凹陷南部陡坡带地形高差较大,在湖岸临近高地发育多条水下河道,沉积物被剥蚀后呈多物源形式就近入湖沉积,加之母岩类型差异,在湖盆陡坡带形成近岸水下扇、扇三角洲沉积体;凹陷西南部因汉留断层的存在造成三角洲前缘与前三角洲的高差,使原沉积的三角洲前缘沉积物发生滑塌,并以线状物源形式在较深水处形成滑塌浊积扇;凹陷中部和砂岩及砂砾岩沉积体的侧翼和远端受构造活动影响较小,物源供给不充分,发育湖泊相沉积。

Clastic component and heavy mineral analyses show that sediments of Huazhuang,northern Fumin and Yong＇an areas in the northern slope were all from Zheduo low convex,while those of Lianmengzhuang and Majiazui areas came from the Lingtangqiao low convex,those of the southern steep slope were from Tongyang Uplift,and those of Zhouzhuang area came from eastern provenance during the depositional period of the Member 1 of Paleogene Dainan Formation in the Gaoyou Sag.Mother rocks of the Member 1 of Dainan Formation are mainly medium-low grade metamorphic rocks,while neutral and acid igneous rocks are distributed widely than basic igneous rocks,with little or none plutonite.Cores observation,data of logs and well logging,combined with characteristics of provenance systems in the study area indicate that mainly fan delta,delta,neritic subaqueous fan and lacustrine facies are developed.The northern slope of the sag has a low gradient and sediments from the Zheduo and Lingtangqiao low convexes are deposited on the gentle slope along the subaqueous channels by spotted source type,which formed deltaic facies,and the difference of sediment supply controlled the scale of delta.In the southern steep slope of the sag,with a steep gradient,due to the development of many subaqueous channels near the bank,the sediments derive from multiple sources and different types of mother rocks are deposited in lake after erosion,leading to the formation of subaqueous fan near banks and fan delta deposition on different tectonic positions.In the southwest area of the sag,sediments of the former delta front collapsed and formed collapsing turbidite fan in deeper water in the form of linear type for the altitude difference between delta front and prodelta,resulted from the existence of the Hanliu Fault.In the middle part of the sag or flanks and distal end of sandstone and sand conglomerate deposits,due to the slight effect of tectonic movement and inadequate supply of source rocks,lacustrine facies are developed.