Exploration and Development ��esearch Institute of Daqing Oilfield Company Ltd�� ��Daqing 163712��Heilongjiang��China

Guided by the theories of sequence stratigraphy and rupture zone analysis��the authors recognized the stratigraphic framework of Nantun Formation of South Wu Sag in Hailaer Basin��based on integrated study of core��logging��mud-logging��seismic and its test data�� Nantun Formation is divided into two third-order sequences and eight fourth-order sequences�� The sediment system and sediment facies were studied under the stratigraphic framework��and four sediment systems (underwater fan near the coast��fan delta��turbidite fan and lake) were de- termined�� The underwater fan near the coast mainly distributed on the western abrupt slop of South Wu Sag��fan delta mainly distributed on its eastern gentle slope��turbidite fan mainly distributed in deep lake facie of its center�� and the lake mainly distributed in the center of South Wu Sag and on the both sides of underwater fan and fan del- ta�� The underwater fan near the coast facies changed to deep or semi-deep lake from western fault zone to the center of South Wu Sag; the fan delta changed gradually to beach shallow lake and deep or semi-deep lake from eastern slight grade to the center of South Wu Sag�� All these sediments distributed entirety differently along north-south�� and constituted band zone along east-west direction�� During the geologic time��the distribution of sediment facies changed everywhere��exhibitting the water changed from shallow to deep��and then became shallow again��and the areas of sedimentations gradually expanded��