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前言扬子地层区西区大致包括四川盆地西部边缘峨眉、乐山、汉源、凉山州以及云南东部、东北部一带,在大地构造位置上处于扬子地台西部。此区是我国上震旦统至下寒武统发育较好的地区之一。在下寒武统筇竹寺阶中含三叶虫岩层之下,上震旦统含藻白云岩层之上,广泛分布着一套连续沉积的,由白云岩逐渐过渡到碎屑岩的含磷岩系,含大量最古老的带壳微体动物化石(以下简称小壳化石)。这套厚几十米至300米的过渡岩系,现已划入寒武系,为下寒武统最下部一个年代地层单位——梅树村阶。
Foreword The western region of the Yangtze stratigraphic zone includes the Emei, Leshan, Hanyuan, Liangshan and the eastern and eastern parts of Yunnan in the western margin of the Sichuan Basin, and is located in the western part of the Yangtze Platform in the tectonic setting. This area is one of the better developed areas from Sinian to the Lower Cambrian in China. On the Lower Cambrian Qiongzhusi step contains Trilobite formations, the algal dolostone layer on the upper Sinian, widely distributed a continuous deposition of a gradual transition from dolomite to clastic rock phosphate rock Department, with a large number of the oldest shellfish microfossils (hereinafter referred to as shell fossils). This set of transitional rock series that is tens to 300 meters thick has now been assigned to the Cambrian, which is the Meixu village of Meishan, a chronostratigraphy unit in the lowermost part of the Lower Cambrian.