An 11 million-year-long record of astronomically forced fluvial-alluvial deposition and paleoclimate change in the Early Cretaceous Songliao synrift basin, China

摘要: Abstract In the Cretaceous Songliao Basin, northeastern China, boreholes have recovered detailed geologic data from sub-basins that developed during early rifting of basin. Among these, Lower Shahezi Formation (K1s) in Songshen 4 (SS4) Well is represented by an 836-m-thick succession fluvial-alluvial deposits, with coals distributed throughout upper part formation. Gamma-ray (GR) logging are quantitatively related to grain size-defined litho-facies recur succession, high GR values mudstones and low sandstones. Cyclostratigraphic analysis log reveals depositional cycling at frequencies consistent those Earth's astronomical parameters. The results also indicate occurrence coal beds occur every ~100 kyr, when development vegetation site was promoted humid climate. We propose a model astronomically forced hydroclimate change explain environments between fluvial alluvial conditions. describes principally environment episodically experienced, one extreme, advancing conditions involving drop base level, lake recession increased aridity (conglomerates coarse sands), other lakeshore rise level humidity (fine sands, silts, muds coal). A floating time scale established calibrating long orbital eccentricity (405-kyr) cycles interpreted along series. duration K1s 11.14 Myr (27.5405-kyr cycles), corresponding average sedimentation rate 6.55 cm/kyr. recognition forcing this fluvial-alluvial-dominated setting offers new framework for interpreting sedimentary cyclicity dynamics rift basins developing scales.