Late Mesozoic Environment And Ecology Evolution Based On Palynological Records From Central East Asia

The most big environmental, climatic, and biotic events occurred in the late Mesozoic with typical character of green-house climate profoundly impact the evolyion of life and development process of the earth. However, the geo-science community still lack a full understanding of this environment change and ecological evolution during the green-house period. Especially, currently study on the climate and early angiosperm in inner continent is almost empty. This research based on the Late Jurassic to latest Early Cretaceous deposits respectively from Gongpoquan Basin,Jiuquan Basin, Yin-E Basin and Liupanshan Basin, by the palynological method lastly to reconstruct the palaeoclimatic and palaeoecological process in the background of green-house environment. We try to understand the relation between climatic changes occurred in the inner land of East Asia with global environmental changes, and driving factor of climate to the early angiosperm evolution.Firstly, the spore-pollen assemblages from these basins respectively are, 1) the Gongpoquan Basin, the first Cyathidites ? Classopollis assemblage from the lower Shazaohe Formation, upper strata produced by high contents of Classopollis; 2) the Jiuquan Basin, the first assemblage was named by Trilete spores- Perinopollenites-Bisaccate pollen from upper Chijinbao Formation. The lower Xiagou Formation yielded the assemblage of Perinopollenites- Bisaccate pollen. The assemblage turned into Bisaccate pollen - Perinopollenites at the upper Xiagou Formation. 3) the Yin-E Basin in the western inner Mongolia, the Bisaccate pollen - Jiaohepollis from middle and lower Bayingebi Formation, to the upper Bayingebi Formation and lower Suhongto Formation yielded Classopollis - Trilete spores, the upper Suhongtu Formation yielded Classopollis - Bisaccate pollen - Jiaohepollis. 4) the Liupanshan Basin, the assemblage from upper Liwaxia to Naijiahe formations was characterized by high Classopollis. In the these spore-pollen assemblages include many age-diagnostic taxa , and consider the other categories of fossils with stratigraphical significance, radioactive age data and magnetostratigraphic ages which further accurately check the strata age. In the Gongpoquan Basin, the Shazaohe Formation of was dated as Late Jurassic and the Lower Laoshuwo Grounp was dated as earliest Cretaceous (potentially in Berriasian to Valanginian age); The Chijinbao and Xiagou formations exposed in the Hongliuxia Section of Jiuquan Basin are more likely gave an age of middle Early Cretaceous (likely Berriasian to Valanginian). In the Yin-E Basin, the Bayingebi and lower Suhongtu formations were gave an age of late Barremian to Aptian. Lastly, the upper Liwaxia to Naijiahe formations were likely dated as late Aptian to Albian.Based on the palynological records, and consider the sedimentary features and other fossils, the environmental changes during Late Jurassic to latest Early Cretaceous can been summarized by the following stages. In early Late Jurassic, the flora was dominated by hygrophilous and thermophlic ferns and thermophlic-dry Cheirolepidiaceae plants. The deposited sequence was characterized by reddish and calcareous sedimentary rocks. These characters were indicated a humid and hot climate. To the middle to late Late Jurassic, just thermophlic-dry Cheirolepidiaceae were dominate the flora and the sedimentary rocks with character of grey green calcareous mud which all indicate an hot and dry environments with character of severe habitat. The diversified and abundant flora such as ferns, conifers and Taxodiaceae were flourishing in the earliest Early Cretaceous, and coal-bearing and black shale were widely distributed. Apparently, a suitable environment with enough moisture was indicated in this period. To middle Early Cretaceous, the vegetation was slightly monotonous dominated by hygrophilous and cold-tolerant conifers and Taxodiaceae. Grey green to green mudstone characterized the sedimentary sequence.These evidence indicate an humid and cold climate. Cheirolepidiaceae plants again increased at the Aptian age, and the ferns slightly increased, the calcium ingredient in deposits obviously increased all of which indicate an climate turned to dry and hot environment. It is potentially that inner continent was begin suffered by Mid-Cretaceous Green-house. Into Albian, the contents of Cheirolepidiaceae plants still increased indicate that the Green-house intensified. Above climate changes occurred in the inner land were almost consistent with global changes from marine records, despite few difference existed.Abundant early angiosperm pollen were discovered from several deposits which can be divided into three stages and three secondary stages based on the emerged time and quantity in different assemblages. The first stage is blank stage at earliest Cretaceous to early Barremian; the second stage is Monocolpate pollen stage at late Barremian to Aptian, which can be divided into few Clavatipollenites stage, few Asteropollis stage and abundant monocolpate pollen stage; Third stage is Tricolpate pollen stage at Albian. From these stages, there two distinct leap stages are abundant monocolpate pollen stage and Tricolpate pollen stage which all corresponding to temperature rise. This first interesting discovery probably has significant implications for early evolution of early angiosperm.