车镇凹陷古近系层序地层格架及发育模式

Sequence stratigraphic framework and model for the Palaeogene strata in the Chezhen depression

关键词:  层序地层|格架|层序模式|构造演化|车镇凹陷

Key words:  sequence stratigraphy|framework|sequence stratigraphic model|structural evolution|Chezhen depression

摘要:

本文将车镇凹陷古近系划分为1个一级层序(构造层序组),3个二级层序(构造层序)和9个三级层序,从而建立起该区层序地层格架。整个古近系跨时约40Ma,构成1个一级层序,可分为4个二级层序,孔店组不发育而只剩下3个,对应时间跨度度分别约7.5Ma,4Ma和13.4Ma,进一步可识别出9个三级层序,时间跨度差别较大,以层序3~5最小,约1.0~1.5Ma,层序6最大,约5.2Ma。从构造演化上,在车镇凹陷可划分为孔店一沙四期伸展半地堑充填的初期断陷阶段、沙三一沙二下期断块强烈活动的强烈断陷阶段和沙二上—东营期断块活动复杂化的断陷萎缩阶段。根据构造演化及沉积充填特征,可将古近系层序划分出初陷期干旱蒸发构造坡折型、深陷期深水沉积坡折型和萎缩期浅水斜坡型3种模式,各种层序模式中体系域构成、沉积充填和砂体发育存在较大差异,这对油气勘探目标的选择具有重要指导意义。

Abstract:

The Palaeogene strata in the Chezhen depression may be divided,on the basis of classical theory of sequence stratigraphy,into one first-order sequence(structural sequence set),three second-order sequences(structural sequence) and nine third-order sequences.The second-order sequences vary in time duration about 7.5 Ma,4.0 Ma and 13.4 Ma,respectively.As for the third-order sequences,the sequences 3 to 5 range in time duration from 1.0 to 1.5 Ma while the sequence 6 has a maximum time duration of about 5.2 Ma.Structurally,the Chezhen depression has gone through the early rifting stage represented by the extensional half-graben filling during the Sha-4 deposition,the intensely rifting stage represented by the intense faulting during the Sha-3 to the early Sha-2 deposition,and the rifting decline stage during the late Sha-2 to the Dongyingian deposition.Three models are presented for the Palaeogene sequences including the structural break type in the dry and evaporatic conditions during the early rifting stage,deep-water depositional break type during the intensely rifting stage,and shallow-water slope type during the rifting decline stage.The systems tracts,sediment filling and sandstone development vary greatly in individual sequence stratigraphic models.The results of research in this study are significant to the selection of petroleum exploration targets.