Paleoenvironment Evolution Of The Late Cretaceous Dinosaur Egg-Bearing Hongtuya Formation,Jiaolai Basin

Since the Industrial Revolution,the content of greenhouse gases such as CO₂ and CH₄ in the atmosphere has continued to increase,and the global temperature has continued to rise,and the future earth system is likely to slide into the abyss of the"hot chamber earth".How to scientifically predict future climate change?"Ancient to modern"is an important method of geological research,the Cretaceous period is a relatively recent greenhouse climate period,in-depth study of the Cretaceous climate evolution process,may be able to provide reference and guidance for us to better understand and cope with future climate change.At present,the paleoenvironment research of the terrestrial Cretaceous has received more and more attention,and the continental Cretaceous system in the Jiaolai Basin is fully developed,which is an ideal area to study the climate evolution of the Cretaceous.At the same time,A large number of nesting dinosaur egg fossils exist in Hongtuya Formation.Reconstruction of the paleoenvironment of this stratum can enrich the paleoecological environment data of dinosaur survival in the basin,and may provide a basis for the cause of dinosaur extinction.In this paper,sedimentology（lithology,color,structure,etc.）and geochemistry(elemental,TOC content,δ¹³C andδ¹⁸O of carbonate,carbonate content)were carried out on the late Cretaceous fossilized Hongtuya Formation in Zhangying area of Jiaozhou City,Jiaolai Basin,and the sedimentary environment and climatic environment of the Hongtuya Formation were reconstructed.The following understandings have been achieved:（1）During the deposition of the Hongtuya Formation,the material source did not change greatly,the sediment maturity was low,and the sediment transport distance was short,mainly the volcanic rocks of Qingshan Group and the sedimentary rocks of Laiyang Group in the southern margin of the basin.The sedimentary environment analysis showed that the Hongtuya Formation in Zhangying area of Jiaozhou City were Alluvial fan-fluvial facies sedimentation,mainly composed of river channel microfacies and floodplain microfacies,and lacustrine sedimentation existed in some periods.Climate change and tectonic activities jointly controlled the sedimentary facies of the Hongtuya Formation.（2）Through the study of the geochemical characteristics of sedimentary facies and sedimentary rocks of the Hongtuya Formation,the four-stage climate evolution sequence of the Hongtuya Formation was established,namely"hot humidity-warm dry-high temperature and rainy-warm dry",and from the early to the late stage,there was a trend of decreasing temperature and increasing drought.Among them,the hot and humid climate of stage I can be divided into three secondary cycles:I-1 is a hot and dry climate,I-2 is high temperature and rainy,and I-3 is a relatively warm and humid climate.In general,the PM401 profile Hongtuya Formation stage II,stage III and stage IV have the same climatic evolution trend as the Hongtuya Formation in the northern Laixi area of the basin,reflecting the consistency of climate change in the southern and northern parts of the basin during this period.（3）Comprehensive analysis of climate change and global climate record of the Late Cretaceous Hongtuya Formation in the Jiolai Basin showed that the climate change of the Late Cretaceous in the Jiolai Basin was consistent with global climate change.The climate of"hot humidity-warm dry-high temperature and rainy-warm dry"in the Jiolai Basin may respond to the relatively humid and hot climate of the global Cenomanian-late Campanian period（about 100.5～72Ma）,the global cooling near the Campanian-Maastrichtian boundary（about 72～69.5 Ma）,and the middle Maastrichtian period（about 69.5～）.68.5 Ma and the global temperature decline in the middle and late Maastrichtian（about 68.5～66.5 Ma）.（4）In Zhangying area of Jiaozhou City,Jiaolai Basin,the fossilized dinosaur eggs of the Hongtuya Formation were preserved in the sediments of the floodplain with a relatively warm and dry climate,and the decrease in temperature and humidity caused the dinosaur eggs buried in the sandy soil to not hatch normally,which may be one of the reasons for the large distribution of dinosaur egg fossils in the Hongtaya Formation.