四川盆地雷口坡组层序岩相古地理

摘要

The inconsistence in different mining areas of the stratigraphic division schemes of Leikoupo Formation, Sichuan Basin, and the fact that on the karst zone strata sloughed off effected by Early Indosinian movement, brings about a problem of stratigraphic classification and lithofacies paleographic reconstitution. Guided by sequence stratigraphy theories and methods, this paper collates and stipulates the stratigraphic division schemes of Leikoupo Formation on the basin interior and reconstructs stratic lithofacies paleography by using quarternary bedding as constructive units. High precision lithofacies paleographic study demonstrates that Sichuan Basin of Leikoupo stage was in restricted-evaporated sea environment and that platform edge developed near Songpan-Ganzi oceanic trough in northwest Sichuan, where the grain bank of platform internal and fringe constitutes the main prospecting parts of Leikoupo Formation. The evolution of lithofacies paleography indicates that the bed form of basin transformed from dipping eastward to westward by the way of "seesaw" in the period of Leikoupo Formation deposition. Even in the early stage of sequence Ideposition, it still remained what the topographic configuration took on as in early Triassic, which was high westward and low eastward, while the eastward dipping trend disappeared gradually in sequencelll depositional period. Yet, after that period there presented a miniature of uplift-hollow framework in the sequence IV—V depositional period on the basin interior. From sequence VI on, the bed form uplift-hollow framework differentiated intensively accompany with the intensity of the tectonic compression movement, forming macro-thick gypsolyte basin, whose depocencer had an apparent westward dipping trend in the depositional period of sequence VI—X.%针对四川盆地各矿区雷口坡组地层划分方案不统一,且受早印支运动的影响,雷口坡组顶部岩溶带地层垮塌破坏,造成地层内幕划分及岩相古地理恢复困难的难题,以层序地层学理论与方法为指导,重新厘定了盆地内雷口坡组的地层划分方案,以四级层序为作图单元进行层序岩相古地理重建.高精度的层序岩相古地理研究表明,雷口坡期四川盆地处于局限-蒸发海环境,在川西北一带靠近松潘-甘孜海槽一带发育有台地边缘,台地内部颗粒滩和台地边缘颗粒滩构成了雷口坡组的勘探主体.岩相古地理的演化表明,雷口坡组沉积时期盆地底形发生了东倾向西倾“跷跷板”式的转换,在层序Ⅰ早期仍保持了早三叠世西高东低的地形格局,至层序Ⅲ沉积期东倾趋势消失,层序Ⅳ～Ⅴ沉积时期盆地内隆凹格局略具雏形.伴随着构造挤压运动的加剧,从层序Ⅵ开始盆地底形隆凹格局分异加剧,形成巨厚膏盐盆,膏盐盆沉积中心在层序Ⅵ～Ⅹ沉积时期具有明显西移的趋势.