鄂尔多斯盆地旬邑地区延长组砂质碎屑流沉积特征及其风暴成因探讨

Sedimentary characteristics and storm origin of the sandy debris flow deposits from the Yanchang Formation in the Xunyi region,Ordos Basin:An approach

鄂尔多斯盆地南部延长组长8-长6油层组沉积相为曲流河三角洲-半深湖、深湖,重力流沉积发育。以前认为这些重力流沉积物是浊流沉积。本文通过对旬邑地区延长组岩心、测井资料的研究,认为研究区长8-长6油层组发育砂质碎屑流沉积。岩心中常见大段块状砂岩、面状碎屑组构、顶底突变接触、漂砾、底部剪切带及滑塌变形构造等,相应测井曲线特征以箱型为主。砂质碎屑流为风暴诱因,可见丰富的风暴沉积特征,如侵蚀构造、底模、浪成沙纹层理、波痕、生物逃逸迹等。研究区理想的风暴沉积单元由下向上可概括为:块状层理段(A);滞留沉积段(B);平行层理段(C);丘状交错层理或浪成沙纹层理段(D);泥页岩段(E)。根据岩心风暴沉积特征总结出风暴岩的3个垂向沉积序列组合。砂质碎屑流及风暴作用的研究对于研究区油气勘探及古地理、古气候研究具有重要意义。

The Chang-8 to Chang-6 oil reservoirs from the Yanchang Formation in the southern part of the Ordos Basin belong to the meandering delta-bathyal to abyssal lake deposits with developed gravity flow deposits.These gravity flow deposits were once reported as the turbidity current deposits and sandy debris flow deposits.The latter are supported by the authors on the basis of cores and well logs for the Yanchang Formation in the Xunyi region.These sandy debris flow deposits are originated from the storm processes,and characterized by the storm deposits such as erossional structures,sole casts,wave ripple laminations,wave marks and biological escape traces.The idealized depositional units of storm deposits in the study area consist of the intervals of massive beddings（A）,lag deposits（B）,parallel beddings（ C）,hummochy cross-beddings and /or wave ripple laminations（ D）,and argillutite（E）,which are involved into three vertical depositional sequences.The approach to the sandy debris flow deposits and storm processes herein is significant to the study of palaeogeography and palaeoclimates and petroleum exploration in the study area.