层序地层学在河流相地层研究中的应用

河流相地层沉积环境特殊,经典层序地层学的适用性存在一定的挑战.对河流相地层中基准面旋回受控因素和层序界面进行分析讨论,结果表明:河流沉积环境中,基准面旋回主要受气候和构造沉降的控制,但是不同地区的河流,海(湖)平面升降对其影响程度有较大的差异,远离海(湖)盆的内陆河流,可容空间完全不受海(湖)平面升降的影响,但是靠海(湖)的河流仍然不同程度地受海(湖)平面升降的影响.在基准面旋回变化的不同阶段,由于可容空间增加速率与沉积物供给量比值的不同,发育不同类型的河流.在河流相地层中,层序界面通常为一较强的侵蚀冲刷面,此界面表现为低自然伽马、高钍/钾和高氧化铁含量,而与海相地层中的密集段相对应的为一套海(湖)侵泥岩、炭质泥岩、煤层及低能沉积环境下的暗色泥岩等.基准面旋回受控因素不同的河流,层序地层学的适用性存在差别,应慎重对待.

Application of sequence stratigraphy in the research of fluvial strata

The applicability of typical sequence stratigraphy to fluvial strata should be discussed because of the particularity of the fluvial strata.The control factors of base-level cycles and the sequence interfaces in fluvial strata are analyzed.The results show that the base-level cycles are controlled mainly by climate and basin subsidence,but in different area,the change of sea (lake) level has the different influence on the base-level cycles in the fluvial deposition.The change of sea (lake) level has no influence on the containable space of the fluvial deposition far away from sea (lake),but it has some influence on the containable space of the fluvial deposition near to sea (lake).In the different stages of the variation of the base-level cycles,different types of fluvial facies will develop because of different ratio of A to S.In fluvial strata,a sequence interface is usually a strongly erosional surface,and the surface is characterized by low natural gamma,high ratio of thorium to potassium and high content of iron oxide.While in marine strata,the condensed sections are invaded transgressive mudstome,carbon mudstone,coal bed and some dark mudstone formed in low energy environment.The applicability of sequence stratigraphy to the fluvial strata in which the control factors of base-level cycles are different is different.