Sequence Stratigraphic Model of Nonmarine Sediments in Cretaceous, Songliao Basin

Key words: 
• seqence stratigraphy /
• Soliao Basin /
• nonmarine deposits /
• sequence boundary /
• system tract model /

Abstract: The main foundations of using the basic concepts of sequence stratigraphy in Songliao Basin and the fundamental characteristics of nonmarine seqences in Cretaceous are dealt with in the present paper. Around the sequence boundaries some erosional or exposure evidences in cores were found such as palaeosol or rootlet bed, fluvial lag conglomerate, transgressive lag conglowerate, subaqueous slumping, caliche nodules as well as geological record of the facies that changed abruptly, and there were tempestite, alluvial fan, deltatic front sheet flow deposit, oolitic limestone, bioclastic limestone, sandstone with excellent porosity and penetrability and volcanics upon the sequence boundaries. The logging responses of sequence boundaries were characteristic of progradation to retrogradation gradually, aggradation to retrogradation abruptly, progradation to aggradation or progradation to progradation and so on. It could be seen that on the seismic sections there were some reflecting configurations of truncation, onlap and downlap near the sequence boundaries. On the basis of the comprehensive interpretations of cores, well logs and seismic lines, the paper principally demonstrated the features of depositional system tracts of the major oil payzones. Based on these studies mentioned above, the authors constructed the idearlized models of sequence stratigraphy for the nonmarine Sonliao Basin. The lowstand system tract was composed of alluvial fan, river mouth bar, "incised valley" guests, sluming, debris flow deposit, turbidite and deltatic front flow deposits. The transgressive system tract consisted of tempesitite, sand bank and sand bar, carbonate shoal, sheet sandstone in deltatic front, stromatolite and so forth. The typical condensed section, which is located on the top of TST and on the bottom of HST, was composed of dark shales with marine nannofossils. The highstand system tract was mainly made up of delta, fan delta and meandering stream systems.