南鄱阳盆地二甲村凹陷乐平组官山段古地理环境特征

Paleogeographic environment characteristics of the Guanshan Member of the Leping Formation in Erjiacun Depression, Southern Poyang Basin

曾广平,王峻,张春光,赵晴,吴双

ZENG Guangping, WANG Jun, ZHANG Chunguang, ZHAO Qing, WU Shuang

成都理工大学沉积地质研究院，四川 成都 610059

Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China

上二叠统乐平组官山段是南鄱阳盆地二甲村凹陷页岩气勘探重要目的层系，其快速变迁的古地理环境制约了有利烃源岩分布。综合利用钻井、露头、薄片、古生物和地球化学等资料，对古地理环境演化、沉积体系特征及平面展布进行分析，建立了官山段障壁海岸相至冲积平原相的沉积模式——在“南东高、北西低”的古地貌背景下，物源自南东向北西推进，近物源处形成冲积平原、三角洲前缘沉积，海岸线至障壁岛间发育潮坪、潟湖、沼泽沉积。受频繁升降的海平面影响，障壁岛与冲积平原相砂岩及潮坪相泥页岩在垂向上相互叠置，利于形成岩性圈闭。官山段泥页岩呈南西—北东向带状展布，具备良好的页岩气成藏条件，有利烃源岩发育的优势相带为潮坪、潟湖相。

 The Guanshan Member of the Upper Permian Leping Formation is crucial target strata for shale gas exploration in the Erjiacun Depression, Southern Poyang Basin. The rapidly changing paleogeographic environment of the Guanshan Member restricts the distribution of effective source rocks. Using drilling, outcrop, thin section, paleontological and geochemical data, the evolution of the paleogeographic environment, characteristics of sedimentary systems and plane distribution are analyzed, and the sedimentary pattern from barrier coastal phase to alluvial plain phase in the Guanshan Member is established: under the paleogeomorphic background of high in the southeast and low in the northwest, the source is advanced from southeast to northwest, and the sedimentation of alluvial plain to delta front is formed near the source, and the sedimentation of tidal flat to lagoon and marsh is developed between the coastline and the barrier island. Under the influence of the frequently fluctuating sea level, the sandstones of the barrier island to the alluvial plain phase and the mud shale of the tidal flat phase are superimposed on each other in the vertical direction, which is conducive to the formation of a lithological trap. The mud shale of the Guanshan Member is distributed in a southwest to northeast trending belt, which has good accumulation conditions for shale gas, and the dominant phase zone for source rock development is the tidal flat and lagoon phase.

10.6056/dkyqt202202010