High-resolution Organic Geochemical Records In The Late-Cretaceous Qingshankou Formation From The Songliao Basin And Paleoclimate Implications

The Late Cretaceous is a prototypical example of a past greenhouse period,and therefore terrestrial paleoclimatic and paleoenvironmental studies of this period provide valuable constraints on future climate predictions.The SK-1 Continental Scientific Drilling Project in the Songliao Basin obtains a nearly continuous terrestrial record of the Late Cretaceous,which provides an excellent material foundation for the study of the terrestrial climate change.In this study,we used the high-resolution geochemistry data(TOC and?¹³C_org)of the Qingshankou Formation in the SK-1 core to study the orbital time scale climate change.These two proxies both recorded the Milankovitch cycle signals,but mainly in the short eccentricity and obliquity cycle.Meanwhile,we used the high-frequency TOC data to carry out the cyclostratigraphy analysis and established the Qingshankou Formation?F.m?age framework.Furthermore,we also discussed the intrinsic relationship between the organic carbon content and the orbital cycle and we found that the maximum value of the short eccentricity was corresponding to the maximum of the TOC content and finally we have figured out the driving effect of the Earth orbital cycle on the organic carbon burial in the Qingshankou F.m.On the other hand,we found the organic carbon isotope positive excursion in the upper of the member2+3,according to the high-precision chronological constraint,we considered this positive excursion event has a relationship with the OAE3,the last oceanic anoxic event of the Late Cretaceous.The special OAEs is discussed from the angle of orbital parameter variation,we not only found the ultra-long orbital period of 1.2Ma and2.4Ma in organic carbon isotope data,but also the long period transition of eccentricity between the Earth and Mars which caused by the chaotic resonance of the solar system in the late Cretaceous,i.e.?s4-s3?—?g4-g3?to?s4-s3?—2?g4-g3??from2.4Ma to 1.2Ma?.It is believed that the changes in the configuration of the orbital parameters have an impact on the Earth's surface climate system,leading to the climate change during the OAE3 in the Late Cretaceous.