The Heinrich Event Recognized In The Second Member Of Nenjiang Formation In Songliao Basin And Its Mechanism

Ice-rafted debris?IRD event?,recorded in North Atlantic during the last glacial represents a highly-frequent climate variability which occurred every⁷kyr and last for500±200yr,and often refers to Heinrich events characterized by abrupt increase in temperature.The increasing evidence unveiled by various proxies recorded over the word,such as East Asia,North America,Africa,and during several Periods,including Carboniferous and Permian shows that the Heinrich may belong to a global event and is not exclusive to the ice age,while,the mechanism for this view is still an arguable topic.Nearly the entire Cretaceous terrestrial sediments were deposited in the Songliao Basin,Northeastern China,which preserved favorable paleoclimate records of the greenhouse.The successively-recovered cores for Cretaceous strata implemented by Continental Scientific Drilling Project of Cretaceous Songliao Basin?SK₂e?in Songliao basin provide us precious materials for studying millennial cycle events.In this text,the 2nd Member of Nenjiang Formation?K₂n₂?deposited during Campanian of Late Cretaceous was selected as the research object,and the high-resolution XRF scanning data was employed to carry out the identification and mechanism research of the millennial events.The MTM and REDFIT spectrum results for paleoclimate proxies,K/Al,Zr/Rb,Sr/Ca,Rb/Sr,all shows that the Late Cretaceous terrestrial strata well document the Milankovitch and the millennial signals.The raw ratio data of elements was decomposed into several Intrinsic Mode Functions?IMFs?with different characteristic periods by Complementary Ensemble Empirical Mode Decomposition?CEEMD?method,and the well-coupled paleoclimate correlation of orbital-scale IMFs reveals that the Milankovitch signals recognized by spectrum estimation are true,and with the constraint of absolute ages,the proposed sedimentary rate⁷cm/kyr is reasonable.Under this rate,the period of millennial signal equals to⁷kyr,which can be compared with North Atlantic Heinrich events.The main periods of envelopes,gained by the Hilbert transformation of the IMFs with periods of⁷kyr,are highly consistent with the orbital precession and obliquity,which reveals that the precession and obliquity signal modulate the Heinrich event.The spectrum estimations of REDFIT and Evolution Harmonic Analysis?EHA?show that the obliquity dominates.The comparison of our Heinrich signals to the counterparts revealed in the contemporary marine strata evidents that the Heinrich events are actually the non-linear response to the orbital signal,and it is mainly modulated by the precession signal in the middle-low latitudes,while by the obliquity in the middle-high latitudes.The East Asia Monsoon is characteristic with evident Heinrich event,the paleoclimate proxies and simulations of East Asian climate testify that the Songliao basin may be affected by the East Asia Monsoon even during Late Cretaceous,thus,we think the correlation between orbital forcing and Heinrich is connected by Monsoon,but the specific modulation process of orbital signal to Heinrich event is still ambiguous,more evidence and numerical modelling are needed to disentangle this enigma.