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A continuous terrestrial succession was recovered from the Songke‐2 (SK‐2) borehole in the Songliao Basin, Northeastern China. This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period, following a series of achievements of the Songke‐1 (SK‐1) core. In this study, thorium (Th) logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis. The Th series varies quasi‐periodically; power spectra and evolutionary fast Fourier transformation (FFT) analysis reveal significant cycles in the Quantou (K2q), Qingshankou (K2qn), Yaojia (Ky and Nenjiang (K2n) formations. The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1, corresponding to long orbital eccentricity (405 kyr), short orbital eccentricity (100 kyr), obliquity (37 kyr), and precession cycles (22.5 kyr and 18.4 kyr). The durations of the K2n, K2y, K2qn and K2q are estimated as 6.97, 1.83, 5.30 and 4.52 Myr, respectively, based on the constructed ∼18.62 Myr "floating" astronomical time scale (ATS). Comparison of the durations between the SK‐1 s and SK‐2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2qn and K2y. Nevertheless, our ATS of K2n supports the chronostratigraphic frame constructed by the CA‐ID‐TIMS data of the SK‐1s borehole. This new "floating" ATS provides precise numerical ages for stratigraphic boundaries, biozones and geological events in the Songliao Basin, and can serve as a basis for correlation of strata and events between marine and terrestrial systems. [ABSTRACT FROM AUTHOR]

The International Continental Scientific Drilling Project of Cretaceous Songliao Basin has recovered a complete Cretaceous terrestrial sedimentary record in northeastern China, providing a unique opportunity to understand the terrestrial climate change during the Cretaceous period. In this study, we present high-resolution geochemical records from Members 3 and 4 of the Quantou Formation in the SK-1 South borehole. The findings show that samples from Members 3 and 4 of the Quantou Formation originated from a source area of a homogeneous composition. Most of the samples were sediments that underwent the first round of weathering. The geochemical proxies (Th, CIA, CIW, τ Na) and average value of the CIA proxy indicate that the strata have been subjected to moderate chemical weathering. The weathering intensity trend was divided into four evolutionary stages based on the CIA proxy: the steady lower part (1915–1878 m), the slowly rising lower and middle part (1878–1815 m), the middle and upper part (1815–1800 m) showing the highest values, and the gently fluctuating upper part (1800–1783 m). Precession, obliquity, and short-eccentricity signals were recognized in the proxies of Th, τ Na , corrected CIA, and corrected CIW from Members 3 and 4 of the Quantou Formation, including about seven short-eccentricity cycle periods with a duration of ∼700 ka. The high peaks in short-eccentricity correspond to the high values of Th, corrected CIA, and corrected CIW proxies, and are consistent with the amplitudes of precession signals preserved in τ Na during humid periods. During strong precession, the enhanced seasonal contrasts increased humidity, which intensified chemical weathering. The paleoclimatic pattern of interaction between the monsoon-like system and westerlies in the Cretaceous Songliao Basin may be the underlying interpretation that causes cyclic variation in the chemical weathering proxies in Members 3 and 4 of the Quantou Formation. • Reconstruction of historical chemical weathering using multiple weathering proxies. • Humid climate derived from a non-linear response of the climate system to precession. • Interaction between the monsoon-like system and westerlies may be the interpretation causing cyclic variation. [ABSTRACT FROM AUTHOR]

The Songke-1 north (SK-1n) borehole recovered a continuous, 1541.66 m Late Santonian–Early Danian terrestrial succession in Songliao Basin (SB), northeastern China. It provides a unique record for improving our understanding of continental paleoclimate and ecological system in Cretaceous greenhouse world. Here we use thorium (Th) logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the SK-1n core. Power spectra, evolutionary fast Fourier transformation and wavelet analysis all reveal significant decameter- to meter-scale sedimentary cycles in the Nenjiang (K 2 n), Sifangtai (K 2 s) and Mingshui (K 2 m) formations. The ratios of cycle wavelengths in these stratigraphic units are ∼20:5:2:1, and are interpreted as Milankovitch cycles of 405 kyr and 100 kyr eccentricity, 38.4 kyr obliquity and 20 kyr precession cycles, respectively. An astronomical time scale (ATS) is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution La2010d based on the magnetostratigraphic time framework of the SK-1n borehole. This ATS provides precise numerical ages for stratigraphic boundaries, biozones, geological and geophysical events, and serves as a basis for correlation of strata and events between marine and terrestrial systems. The Cretaceous/Paleogene (K/Pg), Campanian/Maastrichtian, Santonian/Campanian boundaries are estimated at core depths of 318 m, 752.8 m and 1751.1 m, respectively. A ∼3.8 myr-long hiatus between the Nenjiang (K 2 n) and Sifangtai (K 2 s) formations occurs from 76.1 to 79.9 million years ago. The ages and durations of magnetochrons C33r to C30n are precisely estimated and provide new constraints on the Late Cretaceous Geomagnetic Polarity Time Scale (GPTS) and South Atlantic sea-floor spreading rates. [ABSTRACT FROM AUTHOR]