Recognition of Milankovitch Cycles in the Natural Gamma–Ray Logging of Upper Cretaceous Terrestrial Strata in the Songliao Basin

Abstract

Abstract: Spectrogram analysis of seven natural gamma‐ray logging of Member 1 of the Qingshankou Formation (K 2 qn 1 ) and Member 1 and 2 of the Nenjiang Formation (K 2 n 1–2 ) of Late Cretaceous age in the Songliao Basin reveals sedimentary cyclicities controlled by Milankovitch climate periodicities. The recognition of Milankovitch cycles allows estimation of an average accumulation rate of ∼7.55‐8.62 cm/ka for the K 2 qn 1 sections, and ∼6.69‐10.16 cm/ka for the K 2 n 1–2 sections. Two marine transgression events occurred during the deposition of K 2 qn 1 and K 2 n 1–2 and their ages are at ∼0.74‐1.10 Ma and ∼2.38‐4.84 Ma, respectively. Identification of Milankovitch cycles from fine‐grained deep lake sedimentary rocks in the Songliao Basin may provide great potential for high‐resolution stratigraphic subdivisions and correlations.