The Mesozoic And Cenozoic Stratigraphic Sequence And Evolution History Of Wulaga Fault-depression Basin Of Jiayin, Heilongjiang Province

There has been a large disagreement on the division and correlation of Mesozoic and Cenozoic stratigraphic succession in Wulaga fault depression basin, which as South-eastern branch fault of Sunwu-Jiayin basin,Whether there exists Jiayin group of upper Cretaceous, there has not been reported about it at the outcrop stratigraphy before.Jiayin group can't be found in Wulaga fault at 1:200000 geological survey (1979),only a suite of black shale were discovered in the vicinity of beacon towers,owing to no information of fossil, they correlated this sets of stratigraphic for Wuyun group Paleogene (Tertiary old) at that time,at 1991 when the Wulaga town residents excavated sand,they excavated dinosaur fossils accidentally,which identified as a typical fossil assemblage of Yuliangzi Formation,late Cretaceous at Jiayin region,Heilongjiang province,in the view of above,ZhouHaibin et (2006)determined the Sunwu formation extensive within fault of Neogene which originally delineated by 1:200000 to Yuliangzi formation of upper Cretaceous,however,as a result of failure to identify the micro-angle unconformity between Yuliangzi formation and Sunwu formation, this led to the surface spatial distribution of Yuliangzi formation expanding in Wulaga fault.The basement of Wulaga fault basin are Paleozoic metamorphic rocks and Hercynian,Indosinian granites, sedimentary cover mainly are Mesozoic and Cenozoic Sequence,the filled strata sequence from bottom to up are lower Cretaceous,which include Ningyuancun Formation,Taoqihe Formation,Fuminhe Formation,Upper Cretaceous Jiayin Group(Yongancun Formation,Taipinglinchang Formation,Yuliangzi Formation) and Sunwu Formation of Oligocene to Pliocene.Based on a solid work of geological survey of the field, Jiayin group was paid to special attention in this paper.We collected a large number of Estheria fossils in black shale,oil shale at abandoned mining pit of the original gold brick field, south mountain of Wulaga,identified them as chain fossil of China northern Estheria (Halysestheria qinggangensis band)at late Cretaceous. In view of above, it was confirmed that Jiayin group is developing and distrubuting widely in Wulaga fault depression,the formation angularly unconformited above the lower Cretaceous series.This has important significance to establishing the strata framework of Crataceous at research area and studying on the law of basin evolution.Preliminary achievements of this paper are as following:1.By studying and determining the rock association of every formation unit,fossils and depositional environment systematically, I study on comparing it to other fault depressions of Sunwu-Jiayin and Songliao basin,then establish the sequence framework of Cretaceous in fault basin.2.Through comprehensive studying on biostratigraphy,estheria,sporopollen assemblages, we determine the age of Taipinglinchang Formation and the direct evidence of its development in Wulaga Fault Basin, descripte the estherias as 3 genus 5species,this lays basis for establishing regional stratigraphic framework.3.Through field measuring of volcanic rocks,then identify the evolution of volcano-magmatic incident of the early Cretaceous, the volcanic eruption event in region at early of early Cretaceous,it was multi-phase and multi-cycle eruption, combined with isotopic age data, we determined the period and characterister of volcanic activity;4.Through field geological survey in detail,we found that after hypabyssal porphyry intrusion events,a strong uplift denudation event occurred in the region,caused the contact angular unconformity between Taipinglinchang Formation of upper Cretaceous and Taoqihe,Ningyuanchun Formation,granite porphyry of lower Cretaceous and Heilongjiang Group;Identify the strata deformation characteristics of early Cretaceous, Accordingly to this,there exist a southeast-northwest structure extruded event at late of early Cretaceous in the region;5.Based on systematically summarizes regional stratigraphy,geotectonic and magmatic petrology, through researching on stratigraphic sequence of Mesozoic and Cenozoic, contactions between stratigraphy and tectonic deformation,We can identify 2 angle unconformity interfaces at Wulaga fault depression basin,there respectively are:â‘ Jiayin group of lower Crataceous series unconformable contact with Upper Crataceous seriesâ‘¡Jiayin group of lower Crataceous series unconformable contact with Neogene series.So there were 3 stages superposition evolution character of basin,then analayzed tectonic evolution history of Meso-Cenozoic of Wulaga Basin,then divided into 3 periods, respectively for:â‘ Continental rift fault basin evolution stage of early Crataceousâ‘¡Large inland depression basin evolution stage of late Crataceousâ‘¢Inland intermontane basin evolution stage of Neogene.