琼东南盆地东部低位体系域的时空组合特征及油气勘探意义

Characteristics of time-space combination of lowstand system tracts and their exploration significance in eastern Qiongdongnan basin

琼东南盆地经历了裂陷期和坳陷期 ,可进一步划分为 5个演化阶段。与构造演化对应 ,层序上可划分为上、下两个巨层序、5个超层序和 19个层序。低位体系域在盆地的不同演化阶段均发育 ,具有多期性、多样性特点。构成低位体系域的沉积体系主要有盆底扇、斜坡扇、前积楔、三角洲、扇三角洲、冲积扇、海底峡谷和下切谷等。这些沉积体系的时空组合特征可归纳为孤立式、断控悬挂式和相互依存式。裂陷期呈孤立式、断控悬挂式 ;坳陷期以相互依存式为主。这些低位沉积体与上下岩层构成了有利的生储盖组合 ,可以形成岩性圈闭、地层 -岩性及构造 -岩性等复合型圈闭 。

Qiongdongnan basin has experienced chasmic and depression stages, which can be further divided into 5 substages. Correspondingly, there can be 2 mega sequences (TA, TB), 5 super sequences and 19 sequences. Lowstand system tracts have been developed in every evolutionary stage and are characterized by their multistage and multiplicity. The sedimentary systems of lowstand system tracts include basin floor fan, slope fan, progradational wedge, delta, fan delta, alluvial fan, submarine valley and incised valley. These sedimentary systems are characterized by their time space combination, and can be categorized into isolated type, fault controlled suspension type and coexisting type. Sedimentary systems during chasmic stage are mainly of isolated type, fault controlled suspension type; while those during depression stage are mainly of coexisting type. These lowstand sediments are favorable for the development of source reservoir cap rock combinations, hence there can be various composite traps, such as lithologic, stratigraphic lithologic and structural lithologic traps, which would have large exploration and development potentials.