准噶尔盆地南缘中二叠统芦草沟组富砂型湖泊深水扇沉积特征及其相模式

Sedimentary characteristics and facies model of deep-water fan in sand-rich lake of the Middle Permian Lucaogou Formation in southern Junggar Basin

以准噶尔盆地南缘韭菜园子沟剖面中二叠统芦草沟组野外露头为研究对象,结合该地区芦草沟组沉积时期坳陷湖盆的沉积特征和大套灰黑色油页岩的发育背景,对芦草沟组上部砂体进行了观察描述和沉积分析。在露头剖面上,芦草沟组以灰黑色油页岩为主,但笔者首次在该组上部发现了厚约60 m的砂岩,其与上覆红雁池组灰黑色油页岩呈整合接触,具有明显的深水沉积背景。通过对该套砂体的岩石类型划分与沉积现象解析,共识别出2大类10种砂泥岩类型,明确了牵引流和浊流共同发育的特征。该套砂体中可识别出深水扇的3种沉积亚相和相应沉积微相,由3期富砂型湖泊深水扇叠置形成。结合此次露头观察与特征描述,分析了研究区由厚层砂岩到泥砂岩互层的演化过程,并建立了芦草沟组富砂型湖泊深水扇沉积模式。这个典型露头的沉积解剖,是对准噶尔盆地南缘芦草沟组深水沉积体系研究的有益补充。

The Jiucaiyuanzigou section at the southern Junggar Basin which exposes the Lucaogou Formation in the Middle Permian is the objective of this study.Based on sedimentary characteristics of the Lucaogou Formation in the depression lake basin and development background of the thick dark-grey oil shale,sedimentary characteristics of the sand bodies in the Upper Lucaogou Formation have been described and analyzed.The Lucaogou Formation mainly consists of dark-grey oil shale.A set of sandbodies with thickness of 60m was initially discovered at outcrop section,which presents conformable contact with the overlaid oil shale of the Hongyanchi Formation,indicating sedimentary background of deep-water.By using lithology subdivision and analysis of sedimentary characteristics,the sand and mudstone were classified into 10 kinds and 2groups,and the thick sandbody was developed by traction and turbidity flows.Three kinds of sub-facies and their microfacies were subdivided by using identification of sandbody microfacies.The sand body was comprised of three stacked,sand-rich deep-water fans in lacustrine.On the basis of understanding deep-water reservoir origin and architectures,evolution from the thick sandstone to interbedded sandstone and mudstone were analyzed mainly based on outcrop observation and description.The sand-rich,deep-water fan in lacustrine basin of the Lucaogou Formation has been established,which provides implications for study of deep-water systems in the Lucaogou Formation at southern Juggar Basin.