Sequence Configuration and Sedimentary Evolution of Nenjiang Formation in the Songliao Basin

Key words: 
• sendimentary evolution /
• sequence configuration /
• Nenjiang Formation /
• Songliao Basin

Abstract: In the Upper Cretaceous, Nenjiang Formation have been formed a progradation-retrogradation type stratigraphy in the second lacustrine flooding Period, according to the tectonic unconformity, sedimentary unconformity, lake flooding surface and regressive surface and so on, which totals eleven sequence boundaries, the Nenjiang Formation was divided into one secondorder sequence, two third-order sequences and ten fouth-order sequences, restored the sedimentary filling evolution histories in the fourth-order sequence stratigraphic framework. During the first member of the Nenjiang Formation deposition, the SB07 the maximum flooding surface was formed on the top of strata, which resulted in the retrogradation sequence has the characteristic of low-angle retrogradation delta sediment with the lake level constantly rise, meanwhile the large scale turbidite channels and turbidite fans are observed in the delta front. By uplifting the basin during the second-order and fifth-order member of Nenjiang Formation deposition, developed a series east to west into the area of high-angel delta is characterized by the deposition of retrograding sequences, because of the slumping in the delta front slopes, the forepart of lacustrine zone discovered a series of slump turbidite fan bodies. Retrograding sequences usually incurred the direction 90^o change of the deposition material source, its the mainly difference compare with progradation sequence, whereas the structure of progradation sequence and sedimentary characteristics indicated that the oil shale (at the bottom of the Nenjing second member) is  formed  in the process of shrinking lake, not in maximum lake flooding through to the sea invasion.