Paleogeography Of The Cretaceous Bearing Footprints And Bonebeds In Jiaolai Basin

Jiaolai basin is located in the east of the North China Craton,Shandong Province,which is a typical downfaulted basin in late Mesozoic.There is a set of sedimentary rocks and volcanic rocks and which is composed of some groups,that is,Laiyang Group?Qingshan Group(Dasheng Group)and Wangshi Group from the bottom up.Laiyang Group belongs to Lower Cretaceous and Wangshi Group belongs to Upper Cretaceous.The analysis of the age data of the volcanics in Jiaolai basin and its neighbouring area shows that the age of Dasheng Group is younger than Qingshan Group.So its unreasonable for predecessors to compare Dasheng Group with Qingshan Group.This paper suggests putting the Dasheng group up the Qingshan Guoup,and compare it with Linjiazhuang formation and Xingezhuang formation,which belongs to Wangshi Group.There are abundant footprints and dinosaur bone fossils in Jiaolai basin.The main formations where footprints saved in are the upper Yangjiazhuang Formation in Zhucheng area and Longwangzhuang in Laiyang area,which are deposited during the same period.Both of them belong to Laiyang Group in Lower Cretaceous.There also are some footprints in Dasheng Group,which are saved in Tianjialou Formation in Junan area.The formation bearing bonebeds is mainly Wangshi Group,which is Hongtuya Formation in Zhucheng area and Jingangkou Formation.There also are some dinosaur bone fossils in Qingshan Group in Laiyang area.The outcrop data reveals most of the Yangjiazhuang Formation(Longwangzhuang formation and Shuinan formation)consists of finestone,siltstone and mudstone where the mud crack,ripple marks and cross stratification developed well.,It's typical lake or delt facies,which is also proved by the well log information.Tianjialou formation in Junan area is mainly composed of fuchsia mudstone,finestone,and siltstone with mud crack,ripple marks and cross stratification,which is also derived from lake sedimentary environment.According to the palaeosedimentary environment of the dinosaur footprints,the area between lake and river environment is the best place to form and reserve dinosaur footprints.The Hongtuya Formation in Jiaolai basin is composed of conglomerate,sandy conglomerate,sandstone and mudstone.The coarse clastic rocks occupied a large proportion,while the gravel is often seen in siltstone and mudstone.It is rich in calcium and the cailchenodule is very common.There is large mixed melange with developed erosion surface,which belongs to alluvial fan environment.The dinosaur fossils were buried in fan root and middle fan,The main sedimentary micro-facies are debris flow,diluvial plain and braided river channel.The geochemistry analysis of the dinosaur fossil and.its surrounding rocks in Zhucheng suggest that it might formed in active continental margin.Accoding to the research of sedimentary paleogeography,buring facies and taphonomy,the dinosaur fossils in Kugou and Longgujian went through gregarious,losing of soft tissue,weathering,debris flow transporting in a short distance,rapid burial,staining,compaction and structural damage during the death to the formation of fossil.The fossil reservoirs is in the north of Kugou and Longgujian.The mother rocks of the sedimentary rocks are the volcanic rocks from Qinshan Group in the north.