川西前陆盆地上三叠统层序地层学研究
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摘要
应用层序地层学方法,通过不整合面、地震反射特征等标志将川西前隆盆地上三叠统划分为4个三级层序;以地层叠置样式、岩性、岩相的变化细分出低位、湖侵和高位体系域。其中低位体系域以扇三角洲、深切谷(辫状河)沉积为特征;湖侵体系域以广泛分布的湖相沉积为特征;高位体系域发育进积式三角洲。在建立前陆盆地层序地层模式的基础上,研究了不同区带岩性圈闭的特征及发育模式。结果表明:冲断带—前渊带为陡坡冲积扇—扇三角洲沉积模式,有利的岩性圈闭为LST时期的辫状河下切谷和TST-HST时期的浊积扇岩性圈闭;斜坡带—隆起带为缓坡三角洲沉积模式,是寻找不整合遮挡、透镜状砂岩圈闭和砂岩上倾尖灭岩性油气藏的理想目标区。
According to unconformities and seismic reflection signatures, 4 third-order sequences are recognized in the Upper Triassic in the western Sichuan foreland basin by using sequence stratigraphy methods. They are subdivided into lowstand system tract (LST), lacustrine transgression system tract (TST) and highstand system tract (HST) according to the patterns of strata superimposition and changes of lithology and lithofacies. The lowstand system tract is characterized by fan delta and incised valley (braided river) facies, the lacustrine transgression system tract features in extensive lacustrine deposits, and the highstand system tract is characterized by prograding deltas. The features and development patterns of lithologic traps at different areas are analyzed on the basis of sequence stratigraphic model of foreland basin. Steep slope alluvial fan-fan delta system is developed in the foreland thrust-foredeep belt, with incised valley of braided river in LST and turbidite fans in TST and HST as favorable lithologic traps. Ramp delta is developed in the ramp slope-uplift belt, where subcrop, lenticular sandstone traps and sandstone updip pinch out traps are favorable lithologic traps.
According to unconformities and seismic reflection signatures, 4 third-order sequences are recognized in the Upper Triassic in the western Sichuan foreland basin by using sequence stratigraphy methods. They are subdivided into lowstand system tract (LST), lacustrine transgression system tract (TST) and highstand system tract (HST) according to the patterns of strata superimposition and changes of lithology and lithofacies. The lowstand system tract is characterized by fan delta and incised valley (braided river) facies, the lacustrine transgression system tract features in extensive lacustrine deposits, and the highstand system tract is characterized by prograding deltas. The features and development patterns of lithologic traps at different areas are analyzed on the basis of sequence stratigraphic model of foreland basin. Steep slope alluvial fan-fan delta system is developed in the foreland thrust-foredeep belt, with incised valley of braided river in LST and turbidite fans in TST and HST as favorable lithologic traps. Ramp delta is developed in the ramp slope-uplift belt, where subcrop, lenticular sandstone traps and sandstone updip pinch out traps are favorable lithologic traps.
引文
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[5]LUO Z.New recognition of basement in Sichuan basin[J].Journal of Chengdu College of Geology,1998,25(2):191-200.
[6]许希辉,刘开时.川西北柘坝场潜伏构造须二上亚段古河道岩性圈闭初探[J].天然气工业,1995,15(3):28-33.
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