Characteristics and Genesis of Sequence Boundaries on Subaqueous 〖JZ〗Gentle Slope of Lacustrine Basin:a case study on Upper Cretaceous in Talaha region of Songliao Basin

Key words: 
• sequence stratigraphy /
• sequence boundary /
• genetic analysis /
• gentle slope /
• Songliao Basin

Abstract: Talaha region in Songliao Basin is the gentle slope which was covered with water in long term during the depositional periods of the Fourth Member of Quantou Formation to Third Member of Nenjinag Formation. On the basis of sequence stratigraphy studies, it is found that there are 7 types of sequence boundaries manifestation in the drilling well data, such as: (1)boundary between uppercoarsing cycle and upperfining cycle within the sandrich part of well profile; (2) boundary between uppercoarsing sandrich cycle and upperfining mudrich cycle of well profile; (3) boundary between uppercoarsing mudrich cycle and upperfining sandrich cycle of well profile; (4) boundary between uppercoarsing cycle and upperfining cycle within carbonaterich part of well profile; (5) boundary between uppercoarsing carbonaterich cycle and upperfining mudrich cycle of well profile; (6) boundary between uppercoarsing mudrich cycle and upperfining carbonaterich cycle of well profile; (7) boundary between uppercoarsing cycle and upperfining cycle within mudrich part of well profile. The secondorder and thirdorder sequence boundaries dominated by the boundary between uppercoarsing cycle and upperfining cycle within the sandrich part of well profile, respectively is 92% and 39%. The fourthorder sequence boundaries are provided with diversity, there are near equal probability of 7 types of sequence boundaries. The characteristics of sequence boundaries are controlled by fluctuation of lake level, supply of source and intensity of evaporation.