Abstract:
Based on stratigraphic redivision and recorrelation of Tanan depression,its lower cretaceous can be divided into 3 firstorder sequences, 4 secondorder sequences and 6 thirdorder sequences according to seismic data,drilling data,logging data,paleontological data,geochemical data,and tectonic evolution characteristics.There are 6 main sedimentary systems in all sequences,such as alluvial system,fan delta system,braided river delta system,meandering river delta system,turbidite fan system and lacustrine system.Alluvial system is now found primarily in SQ1,whereas fan delta system primarily in SQ1 to SQ2,braided river delta system primarily in SQ3~SQ5,meandering river delta system primarily in SQ6,turbidite fan system primarily in SQ4 and lacustrine system in all 3 firstorder sequences.Sedimentary systems evolution is under control by palaeogeomorphology formed during Tanan depression tectonic evolution.Small lake basins filling at intermountain remnant basin stage formed SQ1,and SQ2~SQ3 formed in broad and gentle palaeogeomorphology environment at passive rift stage,SQ4 formed under complex small faulted lake basins background at initial active rift stage,whereas SQ5~SQ6 formed in wide basin with deepwater environment at stage of faulted basin transform to depression.