Northern Jiangsu Xinghua Source Tracer Study Two Holes Since The Late Miocene Heavy Mineral Matter

Subei Basin experienced the breaking and depression stage and finally developed into a shallow dish basin,in which duration deposited extremely thick sediments. These sediments record the provenance change and the adjust information of water systems of Subei Basin.Because of the abrasion performanceand stability,heavy mineral retained the major characteristics of its parent rock.So it occupies an important position in the provenance analysis. It mainly used to distinguish the type of the parent rock and the tectonic setting of the source area,infer the transport distance of the sediment and determine the direction of provenance. We commonly used methods as fllows:the analysis of single mineral,the combination of heavy mineral and the characteristic exponent of heavy mineral etc.We select two drilling as the study object in this paper. We collected66samples from XH2,length of750m and time span of7.75Ma. And we collected20samples from JH,length of490m as the contrast drilling. We collect15samples from the Huaihe River and the Yangtze River Basin.We conduct the comparative analysis under the base of clearing the heavy mineral composition,content and combined variation and the existing research results of Predecessors,to reveal the water system adjustments and provenance changes in the Subei Basin since8Ma.We identified26kinds of heavy minerals in the XH2,19kinds in JH, and21kinds in river sediments.It can be divided into five different heavy mineral assemblages according to the change of the type and content of heavy minerals in different layers. After the contrasting,we find the heavy mineral assemblages were corresponding between Ⅰ、Ⅱ layers in XH2(745.14m-414m,7.75Ma-4.31Ma)andⅡ、Ⅲlayers(440m-180m)in JH,indicate both basin were affected by the same provenance at this time.Both the drilling of the heavy mineral index were synchronization changes. With the shallow of the depth,heavy mineral index, the deposition area from the source area is getting closer,the sediments accumulated rapidly,lead to poorly sorted. According to heavy mineral types and index analysis,we speculated the I of JH may correspond to deeper layer of XH2,the source area is far at this time. The heavy mineral assemblage of111(4.31Ma-2.81Ma)in XH2was difference withⅠ、 Ⅱ but it’s similar to main stream combination of the Yangtze River,and there is no corresponding interval wih JH. The characteristics mineral in this phase is garnet The index of heavy mineral analysis showed the stage hydrodynamic is strong,the maturity of heavy minerals is high. We can speculate that Subei basin is influenced mianly by the Yangtze at this river at this stage.The heavy mineral assemblage in Ⅳ、Ⅴ layers(2.8Ma-0.68Ma)of both drilling were basically the same,and it is consistent with the ruins of Shunshan set and the bottom of Xuyi,which indicates Subei Basin is mainly controlled by the Huai River this phase.The combination of heavy mineral in Ⅴ layers of both drilling are similarly. Though the provenance change can be reflected by tremendous heavy mineral change,it also affected heavily by climate in this stage.