Inter-annual Paleoclimates In The Cretaceous Songliao Basin And Its Adjcent Areas

High-resolution palaeoclimatic research has become a hot and difficult point in the current study of global climate change.Tree rings,corals,ice cores,stalagmites and varves provide the possibility for high-resolution palaeoclimatic research.Compared with a variety of high-resolution geological records,the annual laminations/varves are widely distributed,long lasting and carry a large amount of paleoclimatic information,so they can reflect regional biology,geochemistry,and sedimentology to a seasonal or annual resolution.Besides,they can also provide accurate dating reflecting the sedimentary environment and climate change,making varves a special and significant position in reconstructing the global paleoclimatic evolution.Rresearch on the lacustrine varves can not only provide a high-precision and continuous chronological time scale,the thickness and components of the annual laminations can also provide a large amount of seasonal paleoclimatic and paleoenvironmental information.This paper aims to investigate the El Ni(?)o-Southern Oscillation(ENSO)and solar activity during the Cretaceous period through the study of annual laminations in Cretaceous Northeastern China.El Ni(?)o and La Ni(?)a are collectively referred to as ENSO.They are the main climatic factors that cause extreme climate changes on earth,affect the global ecosystem and the growth of crops.However,the scientific problem,how ENSO will evolve under green house climate,has attracted extensive attention of the academic community.Some researchers think that as the global warming,a "permanent El Ni(?)o" state may emerge.However,due to a lack of evidences from seasonal or inter-annual geological evidences,this hypothesis is still controversial.Fortunately,we have collected annual laminations from the Yixian Formation of the Early Cretaceous Sihetun Bird Fossil Museum section in Western Liaoning Province,the Yixian Formation of the Early Cretaceous Xiushui Basin in Northern Liaoning,and the Nenjiang Formation of the Late Cretaceous Songliao Basin.The annual laminations of the Early Cretaceous Yixian Formation in the Western Liaoning and the Late Cretaceous Songliao Basin are mainly clastic varves,which are closely related to seasonal precipitation;while the annual laminations of the Early Cretaceous Yixian Formation in the Xiushui Basin are mainly biogenic varves,which are affected by seasonal growth of the microbial mats.The statistical analysis of these lacustrine varves show obvious cycles of 2-7 years,and these cycles are very similar to the modern ENSO cycle,but show higher(without cycles more than 5 years)and stronger frequencies and variabilities than that of the current ENSO.Therefore,this paper provides robust geological evidences of probably stronger ENSO cycles under the early Cretaceous greenhouse climate,and does not support the "permanent El Ni(?)o" hypothesis.In addition,as one of the main extraterrestrial factors that regulate the Earth's climate system,the solar cycles are also worth exploring for its changes in geological historical periods.Based on statistical analysis of annual laminations in this paper,especially the annual laminations in the early Cretaceous Xiushui Basin,which originate from microbial mats,and show strong and multiple solar cycles,such as the ?11-year Schwabe sunspot cycles,?22-year of solar Hale cycles,and 30?45-year of Bruckner solar cycles.More importantly,by compiling the varve records of the deep-time/pre-Quaternary solar cycles,we found that the ?11-year Schwabe sunspot cycles and the ?22-year Hale cycles change little since the Paleoproterozoic era,indicating that the sun has relatively stable influences on the Earth's climate system since the Proterozoic.