新疆伊犁晚二叠世非海相Ophiomorpha

The Upper Permian Nonmarine Ophiomorpha of the Yily Basin, Xinjiang

新疆伊犁盆地上二叠统主要为一套湖相碎屑岩夹碳酸盐沉积，厚约２７００ｍ。在晓山萨依组下部灰岩夹层中产丰富的Ｏｐｈｉｏｍｏｒｐｈａｃｆ．ｎｏｄｏｓａ遗迹化石，标本由一系列代表不同阶段个体所留下的粗细不同的潜穴组成。潜穴具一个明显加厚的、由内外两层粪瘤构成的衬壁构造。潜穴呈简单直管状或盲肠状，不分叉，以水平和斜伸类型为主；内部充填具粒序性，说明沉积速度较快，且可作为良好的地层示顶构造。这些特征说明沉积基底的沉积速度较快，松软。Ｏｐｈｉｏｍｏｒｐｈａ分布特征表明这种造迹生物的掘穴主要与水体的含氧性和沉积基底的性质有关，而与基底成分、水体含盐度、水深等无明显的关系。

Yili Basin, developed in the central Tianshan orogenic belt, accommodates a huge thickness (about 5 000-9 000m) of continental Permian strata. The Upper Permian is chiefly composed of lacustrine clastic sedimentary rocks interbedded with limestone, including the Xiaoshansayi, Hamist, Tiemulike and Bakaluesayi Formations in ascending order, 2 700m in total thickness. Ophiomorpha is rich in a shallow lacustrine limestone bed in the lower part of the Xiaoshansayi Formation, with a suit of burrows different in diameter, probably representing developing stages of the burrowmaker. The burrow wall, conspicuously doublelayered, consists of pellets ovoid, or irregular in shape. They are tubelike or caecumlike, predominantly horizontal and oblique in level, neither showing divergent branching of Ophiomorpha type. Infill is passive, indicating upward grading, reflecting a rapid depositional condition. It could be used as topindicating structure. Above characteristics illustrate that the burrowmaker is inclined to penetrate soft sedimentary floor where relatively high rate of deposition took place, and scarcely controlled by composition of the substrate, waterdepth, and salinity.