关于“龟裂纹灰岩”成因的探讨

扬子区中奥陶统宝塔组普遍发育“龟裂纹灰岩”,对其龟裂构造的成因研究自二十年代以来基本上是沿用“干缩龟裂”理论。而刘特民、陈学时(1981)和盛莘天、姬再良(1984)则认为此“龟裂纹灰岩”是在开阔浅海比较安静的环境下,由生物碎屑灰泥形成一种胶体状态,经由沉积期、成岩期的凝聚、失水收缩等作用所致。提出了所谓的“水下胶体凝缩纹”假说。笔者通过对湘西北慈利地区宝塔灰岩龟裂纹的研究,特别是对岩石薄片观察的成果分析,得出如下结论:水下胶体凝缩论尚不够令人信服,更为合理的解释仍是“干缩龟裂”。

NOTES ON THE ORIGIN OF THE "POIYGONAL MARKING" LIMESTONES

The Middle Ordovician Pogoda limestones in Cili County, Northwest Hunan Province are dominantly composed of the "horse shoe" cracking limestonos or "polygonal marking"limestones. Since 1920's this rock type has been considered as a result of drying and cracking of the lime mud exposed in the tidal environment. In 1981 and 1984, according to their study in Gui-Zhou Province and other places, Liu Teming, Chen Xuoshi and others assumed that the "polygonal marking" limestones were formed by the coagulation-contraction under the water not by drying and cracking, and therefore these limestones seemed not to be deposited in the tidal mud flat. Based on our microscopic observations on the texture,structure and composition of sediments, together with the paleontological evidence, the present writers have reached the conclusion that the origin of the "polygonal marking" structure might result from mud cracking in the tidal flat environment.