断-坳转换期物源体系分析:以霸县凹陷东三段为例

Provenance System Characters of Fault-Depressed Transforming Period:Insights from the Third Member of Dongying Formation in Baxian Sag

以霸县凹陷东三段古物源体系为例,对其进行了不同角度与不同层次的精细研究,进而探讨了霸县凹陷断-坳转换期的物源体系特征及其控制因素。结果表明,霸县凹陷断-坳转换期物源特征主要受古构造与古气候的控制,表现为:一方面,受继承性裂陷末期断陷样式的影响,凹陷快速地构造沉降,使得隆凹格局明显,易于形成近源堆积;另一方面,受古气候频繁变化的影响,气候干燥时,整体处于暴露环境,加速了剥蚀速度,气候潮湿时,沉积范围扩大,加速了凹陷填平补齐,准平原化。在古构造和古气候双重因素控制下,形成了霸县凹陷断-坳转换期独特的物源特征,表现为以凹陷边缘凸起为主的近物源慢速堆积特征。综合多种物源分析方法,得出研究区物源来自东部的大城凸起和西部的牛驼镇凸起,具体包括东部的长丰镇物源;史各庄物源和苏桥物源;西部的鄚州物源和岔河集物源;南部的饶阳物源和北部的南孟物源。在物源体系、构造组合特征及气候的控制下,东三段主要发育扇三角洲和浅水三角洲沉积体系。

This research,taking the provenance system of the third Member of Dongying Formation in Baxian Sag as a typical example,aims to study the provenance system characters and control factors during fault-depression transforming period from different perspectives.The result shows the provenance characteristics during fault-depression transforming period are affected by both tectonics and paleoclimate.Because of the inherited fault styles at the end of rifting stage,Baxian Sag underwent rapidly structural subsidence,which led to the obvious relief between the sag and its adjacent uplift and thus,the formation of proximal provenance.Meanwhile,dominated by the frequent changes of paleoclimate,the provenance system was marked by different features.When the climate became arid,the sag overall was exposed,accelerating erosion.When the climate became humid,the deposition range expanded,leading to rapid filling up and peneplain.Under the joint control of the tectonics and paleoclimate,the main source during the fault-depression transforming period was the uplift area at the margin of the Sag.Specifically,the sediments mainly derived from both the Dacheng uplift in the east and the Niutuozheng uplift in the west,according to multiple provenance analysis.These two source areas can be further subdivided into seven sources,including Changfengzhen source,Shigezhuang source,and Suqiao source from east part,Maozhou source and Chaheji source from west,southern Raoyang source,and northern Nanmeng source.The provenance systems,the structure patterns and paleoclimate worked together to have gnerated fandelta and shallow-water delta as the dominant depositional systems in Baxian Sag.