Abstract:

To understand the dynamic mechanisms of post-rift subsidence in Songliao Basin, the backstripping and strain rate inversion methods are used to study the stratigraphic sections and boreholes in Changling sag and Shiwu sag on the southern edge of Songliao Basin by analyzing the relevant data. The post-rift anomalous subsidence is computed as the discrepancy between observed and predicted post-rift subsidence based on modeling exponential thermal cooling following earlier lithospheric thinning events. The modeling results of 13 wells show clearly that the anomalous subsidence during the post-rift stage is between 160 m and 800 m in the study area. With averagely maximium subsidence rate reaching 16 m/Ma and strain rate reaching 6 Ga-1, the rapid subsidence periods in the study area occurred at 99.6-91.4 Ma(Quantou Formation) and 84.7-79.1 Ma(Nenjiang Formation). The Cretaceous anomalous post-rift subsidence in the southern Songliao Basin was primarily induced by downdrag pressure of subducting in western Pacific slab and deep mantle flow under Songliao Basin. The basement faulting in Songliao Basin during Early Cretaceous and normal faulting in the post-rift stage also make contribution to anomalous post-rift subsidence.

Key words: Songliao Basin, tectonic subsidence, anomalous subsidence, strain rate inversion, Changling sag, Shiwu sag