Title: Reconstruction of high-resolution lake level and its astronomical forcing during the Paleogene
Meng Wang (1) & Mingsong Li (2)
School of Earth Resources, China University of Geosciences, Wuhan, China (1); Department of Geosciences, Pennsylvania State University, USA (2)
Event: Abstract GeoUtrecht2020
Challenges in continental sequence stratigraphy and typically limited resolution in geochronology hinder the understanding of paleolake evolution and hydrocarbon exploration in terrestrial basins. The Dongpu Depression in North China is a lacustrine basin with abundant hydrocarbon resources. An accurate geochronology for the Paleogene stratigraphy in the Dongpu Depression is lacking, and the mechanism of lake-level variations remains unclear.
We utilize high-resolution gamma ray logs to conduct a cyclostratigraphic analysis of the Shahejie Formation, which is a Paleogene succession in the Dongpu Depression characterized by sandstones and dark mudstones interbedded with thin salt rocks. Time series analysis reveals evidence for 405 kyr eccentricity cycles in the gamma ray series. Tuning of the gamma ray data to this 405 kyr eccentricity cyclicity enables a 14.37-Myr-long astronomical time scale. This astrochronology is anchored to the recalibrated age of the Dongying Formation/Shahejie Formation boundary (28.86 Ma) in the Bohai Bay Basin, providing an absolute timescale for the studied interval that extends from 28.86 Ma to 43.59 Ma. Furthermore, based on a recently established sedimentary noise model for inferring sea level change in marginal marine settings, we propose that variations in sedimentary noise in paleolake environments can be linked to lake level fluctuations. Sedimentary noise modeling of the tuned gamma ray series reveals high-resolution sedimentary noise changes indicative of lake-level variations linked to million-year scale astronomical forcing. These inferred changes in lake level are supported by previously published sequence stratigraphic interpretations. Moreover, an evolutionary correlation coefficient (eCOCO) analysis of the gamma ray series also indicates recurrent distortions in sedimentation that may link to lake level changes. This study provides new methods for the assessment of paleolake level variations and provides insights into the connection between astronomical forcing over long-time scales and lake evolution in terrestrial basins.