Sedimentary Environment And Source Region Characteristics Of The Lower Cambrian Zhushadong Formation In Southwest Henan Province

The long uplift and denudation of the North China Platform through the Neoproterozoic,the Paleo-landform pattern is North High South Low,West High East Low,beginning to accept the transgression in the early Cambrian subsidence,and the late Ordovician uplift to the land,which constitutes a complete sedimentary cycle.In the late Cambrian period,most of the North China platform was covered by seawater,and the Xinji Formation was deposited with the phosphate clastic rocks and the Zhushadong Formation containing gypsum carbonate rocks.The secondary sedimentary cycles of the Xinji Formation-Zhushadong Formation were formed.This study studied the Zhushadong Formation of gypsum rock series in Lushan area,by studying the field work and the measured section of Zhushadong Formation in Lushan area.The results show that the main lithology of Zhushadong Formation in Lushan area is a set of carbonate rocks and evaporation rocks.It can be divided into three parts.In the low part,leopard porphyry limestone and muddy limestone are developed,and dolomite limestone is the main occurrence layer of gypsum.In the middle part,main development of bright grain limestone,including wave-like algae layer,particles have powder powder grains,sand crumbs.In the upper part,the muddy limestone and the clastic limestone are developed.Through microscopic observation,XRD,electron probe and other methods,this paper studies the mineralogical of the gypsum-containing rock series,and concludes that the main minerals are quartz,dolomite,calcite,gypsum and anhydrite,Gypsum rock contains CaSO₄ maximum of 10.08%.Through Elemental geochemistry studies,we discuss the trace elements and ratios of Sr,Ba,Th,U,Ree and so on.This paper discusses the sedimentary environment characteristics of Zhushadong Formation,the results showed that the early deposition of Zhushadong Formation inherited the trend of the Xinji Formation,and the normal seawater and hot water deposition under the environment of the continental margin of anoxic environment.The Zhushadong Formation was shallow depthof sea water,and the sedimentary environment turbulence belonged to the typical tidal salt flat deposition.In this paper,the material sources of the gypsum-containing rock series in Zhushadong Formation were preliminarily discussed by the high stability trace elements?La,Zr,Th,Sc and Co?in the Zhushadong Formation sandstone and the clastic zircon dating?Zircon U-pb dating?.It is inferred that the provenance region of the Zhushadong Formation is the source region of the Felsic based source area of the North China Craton.In addition to the tectonic-thermal events of the 2600Ma and1800Ma,the Zhushadong Formation in the southern margin of the North China landmass recorded the tectonic activity of the 1200Ma,and the tectonic setting was in the continental island arc and the Ocean island arc.