摘要
本文运用沉积学和地球化学、地球物理学及数理统计学方法,对研究区上侏罗——下白垩统的沉积特征.依地面与井下资料作了综合研究,划分出7种沉积相类型,探讨了相组合分布、相序演化规律及构造运动、古气候、古地形等诸多控制因素,建立了石北箕状同生凹陷沉积模式,并总结出各类沉积相的元素指标及伴随相演化、锶/钡、钒/镍、镁/钙等多项元素比值变化的规律.
This paper deals with the information of sedimentary rocks , primary sedimentary structures, stratigraphic sequence, grain size, fossils, heavy minerals, clay minerals, trace elements and well logging, which have been obtained from Upper Jurassic to Lower Cretaceous in Shibei district is analyzed by synthetical methods including the sedimentologic analysis, geochemical analysis, geophysical and mathematical statistics etc. Seven sedimentary facies types in this area have been identified.They are diluvium fan, fluvial facies, deltaic, shore and shallow lacustrine, deeper and deep梬ater lacustrine, subaqueous fan and deep-water turbidity fan facies.These formed in different and closely related sedimentary environments.
Based on these data, it can be seen that due to the characteristics, especially in hydrodynamic condition of Shibei District, norrow facies belt formed and facies change rapidly, even in series of facies belts lack of some one facies. Each of the facies has its own distinctive feature-all of these are evidently different from that of the same kind of sedimentary facies forming in giant basins and vast alluvial plain areas.The fluvial facies in studied area, with fans of braided stream and diluvial characteristics. Most of the deltaic facies in the area are 'constructional delta' .Subaqueous fan are characterized by proximal, relatively coarser grains in shallow- water environment, and have characters both of alluvial and turbidity deposits. Deep-water environment and turbidity developed in intermittent all of which may be characteristics of facies of turbidity fan.In addition, the shapes of grain-size distribution curve of each facies are quite different.lt can be summarized as eight types which can be used as one of the basis of identifying sedimentary facies types.
The results show that Northeast trend Bainan Contemporaneous Faults No.2 & No.3 and Shibei Asymmetric Depression is controlled by these faults and the facies association may depend
on which-during the active period diluvial and subaqueous fan developed in the steep bank
zone of the depression whereas the fluvial (point bar) and deltaic facies association developed in the gentle slope belt; During the more active stage, subaqueous fan and trubidity fan, deep-water mudstone and shale facies are developed in a belt of steep bank whereas fluvial, deltaic, shore and shallow lacustrine facies may be developed in a gentle slope belt.On the other hand, deep lacustrine facies mainly developed in the central region of the lake.The succession of sedimentary facies has certain regularities. The facies association and succession are controlled strictly by many factors such as tectonism, paleoclimate, paleogeographic, condition of depositional medium.
The author also studies the abundance of trace elements and characteristics of paired ratios, in which the different terrestrial environments being recognize.In the summary, the values of V/ Ni, Sr/ Ba, Rb/ K ratio increasing synchronously, however, the values of Ni/ Co, Fe/ Mn, K / Na, Na/ Ca, Sr/ Ca, Mg/ Ca ratio decreasing gradually with the evolution of facies from diluvial to fluvial, delta, shore and shallow lacustrine, deeper and deep lacustrine facies.These provide reference evidences for identifying sedimentary facies.
出处
《沉积学报》
CAS
CSCD
北大核心
1989年第4期105-111,共7页
Acta Sedimentologica Sinica
