Recognition of Milankovitch cycles in XRF core-scanning records of the Late Cretaceous Nenjiang Formation from the Songliao Basin (northeastern China) and their paleoclimate implications

• Published in: Journal of Asian earth sciences 2020-06, Vol.194, p.104183, Article 104183
• Main Authors: Yang, Hanfei, Huang, Yongjian, Ma, Chao, Zhang, Zhifeng, Wang, Chengshan
• Format: Article
• Language: English
• Subjects: Late cretaceous; Milankovitch cycles; Paleoclimate; SK-2e borehole; Songliao Basin; XRF scanning
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2019.104183

[Display omitted] •Milankovitch cycles were recorded in Rb/Sr series from Member 1 (K2n1) and Member 2 (K2n2) of the Nenjiang Formation.•K2n1 experienced a longer humid period and more pronounced climatic fluctuation than K2n2.•The mean sedimentation rates of 6.577 and 8.369 cm/ka for K2n1 and K2n2 were provided by ASM method.•The collectively regulation of obliquity and precession amplified the paleomonsoon effect during humid periods in K2n1 and K2n2. Cretaceous terrestrial sedimentary records are crucial for our understanding of geological systems’ responses to past climate change under greenhouse condition. Numerous publications have documented that Milankovitch cycles were a dominant climate driver over multi-millennial timescales. However, most of these orbital signals were derived from marine records obtained during the Cenozoic geological period, whereas knowledge of Milankovitch cycles preserved in lacustrine sediments prior to the Cenozoic is limited due to the lack of a precise chronological framework, poor preservation rate of terrestrial sediments, limited records, and fewer experts in this research area. This paper reports high-resolution X-ray fluorescence (XRF) elemental records of K, Ti, Rb, Sr, Zr, Zr/Rb, Rb/Sr, and K/Ti from Member 1 (k2n1) and Member 2 (k2n2) of the Nenjiang Formation, which were obtained from a near-continuous SK-2 East (SK-2e) borehole drilled in the Songliao Basin (SB) of northeastern (NE) China. Variations of the elemental records reveal a humid-arid-humid-semiarid climatic evolution throughout the deposition of k2n1 and a humid-arid-humid-arid climatic variation throughout the deposition of k2n2. In this context, K2n1 experienced a relatively longer humid period and more pronounced climatic fluctuation than K2n2. A method of average spectral misfit (ASM) was adopted to successfully identify two optimal sedimentation rates of 6.577 and 8.369 cm/ka for K2n1 and K2n2, respectively. Based on these two sedimentation rates, nearly all significant Milankovitch cycles preserved in the Rb/Sr record were recognized. It is suggested that westerly wind was the main climatic driving factor of climate evolution in the SB under the forcing of Milankovitch cycles. The collectively regulation of obliquity and precession increased the seasonal contrasts during humid periods in the Nenjiang Formation and thereby amplified the paleomonsoon effect, thus bringing more moisture towards the SB and lead to enhanced rainfall.