Study On Paleoclimate Of The Late Cretaceous Based On Continental Special Deposits In China

The Cretaceous has been thought to be a period of"greenhouse".By systemically summarizing geological data,we have identified the following types of continental special deposits that may indicate the climate characteristics,namely,the calcareous deposit,flammable organic rock,evaporite,desert sedimentary system,lateritic weathering crust,ferruginous deposit,copper-bearing deposit,volcanic deposit,limestone,dolostone,and bentonite. By incorporating all types of continental special deposit that may indicate the climate characteristics into six different times of the late Cretaceous,create table of stratigraphic units in same area and compare with other areas.On the basis of distribution maps of 6 periods of the late Cretaceous,we are able to discuss the temporal and spatial distribution characteristics of different special deposit.Combined with climate significance of continental special deposits , we summarized the climate indexes as follows:the flammable organic rock,the pyrite and siderite associated with black shale,and the bentonite reflect warm and humid climate;the lateritic weathering crust and ferric deposit reflect humid and hot-hot climate;the gypsum and limestone reflect warm and dry climate;the rock salt,glauberite,desert sedimentary system and dolostone reflect hot and dry climate;the volcanic deposit reflect high temperature climate;the calcareous deposit and copper-bearing deposit reflect arid-semiarid climate.Onthe basis of distribution and assembly characteristics of special deposit,seven climate types can be classified:(1)warm and humid-warm and dry climate;(2)warm and dry climate;(3)hot and dry climate;(4)dry-arid and hot climate;(5)hot and humid climate;(6)hot and dry-semiarid climate;(7)hot and humid-hot and dryclimate。Hot and dry climate zone and dry-arid and hot climate zone were dominant in the Cenomanian and the Turonian.From Coniacian to Maastrichtian,the scope of warm and humid-warm and dry climate had reduced,the scope of hot and dry-semiarid climate zone had enlarged,the types of climate area had decreased.The East-West hot and dry climate zone was appeared after the Santonian.Compare with the early Cretaceous,the climate of the late Cretaceous was drier and hotter.The climate was driest in the Cenomanian and Turonian.The climate was hotter from Coniacian to Maastrichtian.