Distribution and formation mechanism of lime mudstone in Upper Triassic in northwestern Sichuan, China.

The lime mudstone in the oolites of the Upper Triassic Maantang formation has not been examined in detail by many geologists though the intraclast-bearing lime mudstone is obviously different from the underlying and overlying gray oolitic layers in northwestern Sichuan Basin, China. This study presents an interpretation of four newly measured stratigraphic sections for investigating the distribution and thickness of the lime mudstone. The distribution of the lime mudstone is discontinuous, and the deposits vary in thickness. The lime mudstone occurs as lentoids or bands of approximately 0.2-2 m in thickness and ranges in length from about 5 m to more than 30 m in length in the outcrops. Similar complexes occur in other places in the world although there are regional and site-specific variances. However, the phenomenon in the Maantang mudstone formation seems most like those of the modern Bahama bank. The lime mudstone of Maantang is assumed to have formed by sequential historic storms of great strength, much as did the similar Bahama deposits. [ABSTRACT FROM AUTHOR]