广西合山煤田中的滨岸带海绵骨针岩及其地质意义

发育在晚二叠世合山组主采４煤层及其分层底板的硅质岩含有大量的海绵骨针，向陆过渡为黑色泥岩或具根化石的铝土质粘土岩，向海则相变为燧石灰岩，这种海绵骨针硅质岩为原生沉积成因，在沼泽化过程，炎热潮湿的气候及繁盛的植物使原先的沉积岩发生强烈的化学风化作用，由此产生的胶状ＳｉＯ２随地表水进入滨岸地带，与海水中带有正电荷的电解质发生化学反应，沉淀下来，而富含ＳｉＯ２的海水及极少陆源碎屑供给又为硅质海绵的生存提

LITTORAL SPONGE-SPICULE ROCKS IN LATE PERMI AN HESHAN FORMATION IN GUANGXI

The silicalite floors of the main minable seam No. 4 developed in the Late Permian Heshan Formation contain a great quantity of spongesplcules. The silicalite floors change into dark mudstone or light grey bauxitic root clay towards land and into flint limestone towards sea.They were formed in shallow littoral area.The colloform silica formed from strong chemical weathering of previous carbonate rocks was transported into littoral areas by surface drainage and acted with dielectric with positive charge to precipitate In shallow littoral area.The seawater body with a great quantity of silica and little terrigenous supply provided the essentlal living conditions for the siliceous Sponges.The absence of sponge-splcule silicalite floorstowards the land and the sea indicates that the sponges could only live in the littoral area.Therefore,the sponge-spicule silicalie floors can be regarded as a mark of paleocoastline,and can represent the maximum spreading of the seawater body towards the land.