Based on regional distribution of gypsum-salt and the detailed analysis of lithological features, the origin of Middle Triassic Leikoupo Formation gypsum and salt in the Sichuan basin was studied, and migration and evolution of gypsum and salt pot and their structural significance were further discussed. The Leikoupo Formation contains two lithological assemblages and distribution patterns. One occurs as laminated gypsum salt intercalated with massive gypsum salt during the Lower submember of the 1st Member of Leikoupo Formation and the Lower submember of the 3rd Member of Leikoupo Formation depositions. It has a thin thickness and stable distribution, suggesting a lagoon origin. The other occurs as massive anhydrite and halite with greatly varied thickness and quick horizontal change. In contrast to the previously-formed gypsum-salt, the depocenter of gypsum-salt migrates westward and northward, suggesting an origin of gypsum-salt pot. Both reflect a structure signature that tectonic stress field of the Sichuan basin was in the transition from tensile stress to compression stress during the Middle Triassic Leikoupo Stage, in which the basin was in tranquil during deposition period of the Lower submember of the 1st Member of Leikoupo Formation and the Lower submember of the 3rd Member of Leikoupo Formation sections, whereas the basin was in active during the period of the Middle submember of the 3rd Member of Leikoupo Formation and the Middle submember of the 4th Member of Leikoupo Formation. NW-SE-trending and NE-SW-tending compressive stress in the basin tended to be active, thus the new depocenter formed. In addition, extensive evaporation caused the gypsum-salt to precipitate quickly in depressed areas. With the basin being more active due to compression, gypsum-salt pots of the Middle submember of the 3rd Member of Leikoupo Formation, the Upper submember of the 3rd Member of Leikoupo Formation and the Lower-Middle submember of the 4th Member of Leikoupo Formation were formed distributing from north to west. West Sichuan depression started and developed at the Middle submember of the 3rd Member of Leikoupo Formation period, and had an initial shape at the Lower-Middle submember of the 4th Member of Leikoupo Formation period. Above understanding will provide new information for studying the origins of Leikoupo gypsum-salt of the Sichuan basin.%通过详细的岩石学特征分析,结合区域分布,研究了四川盆地中三叠统雷口坡组的膏盐岩成因,进而讨论了其反映的膏盐盆迁移和演化及构造指示意义.雷口坡组总体存在两种岩性组合和分布特征的膏盐岩,一类出现于雷一段雷三段下亚段沉积时,表现为纹层状膏盐岩夹块状膏盐岩,厚度较小,横向分布稳定,属于泻湖成因；另一类出现在雷三段中亚段—雷四段中亚段沉积时,以块状硬石膏岩和石盐岩为主,厚度差异巨大,横向变化较快,并且膏盐岩沉积中心出现向西、向北迁移的趋势,与早期的膏盐岩形成了鲜明对比,属于膏盐盆成因.由此反映出构造信息,四川盆地中三叠世雷口坡期的构造应力场总体处于由张应力向挤压应力转换,其中,雷—段—雷三段下亚段沉积时盆地总体处于构造平静期,为张应力向挤压应力转换的过渡期；相比而言,雷三段中亚段—雷四段中亚段沉积时为构造活跃期,盆内北西—南东向和北东—南西向应力挤压趋于活跃,新的沉降中心形成,强烈的蒸发作用使得膏盐岩在凹地快速沉积,并随挤压的阶段性活跃,发育向北、向西迁移趋势的雷三段中亚段、雷三上亚段、雷四段下—中亚段沉积期三期膏盐盆,川西凹陷的形成与演化从雷三段中亚段沉积期已经开始发育,并在雷四段下—中亚段沉积期已具雏形.这些认识为四川盆地雷口坡组膏盐岩成因研究提供了新基础参考信息.
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