Establishment of Geological Age Under the Constraints of Astronomical Cycles in Dongying Sag

Abstract

The accurate determination of geological age is the key to understanding the evolutionary history and process of earth, but improving the accuracy of geological age has always been a scientific problem. Astronomical cycle analysis is an effective method developed for high-resolution stratigraphic research in recent years. We apply this method to improve the accuracy of the stratigraphic age of the ash-deficient section of lacustrine fine-grained sedimentary rocks in Dongying Sag, which can make up for the lack of isotopic dating. By observing the core (about 198 m thick, well Niu 33), the study interval’s petrological characteristics are found. The study interval is divided into four stratigraphic units according to the GR curve and lithology. After the data preprocessing, the results show that these four stratigraphic units all record the Milankovitch cycles of 405 ka eccentricity, 125 ka short eccentricity, 40.1–38.7 ka obliquity, and 18.7 ka precession. Finally, the 38.7 ka obliquity cycle curves are filtered out, and we find about 202.45 cycles of 38.7 ka in the Es3m of the Dongying Sag, with a cumulative deposition time of 7.83 Ma. Taking the volcanic dating 40.1 Ma of the Es3l and the Es3m as the anchor point, a “floating” astronomical age scale is established, and the geologic age of the top of the Es3m is 32.27 Ma.