江宁孔山、茨山高骊山组中遗迹化石组合的生态分析

ECOLOGICAL ANALYSIS OF TRACE FOSSIL ASSEMBLAGES FROM DELTAIC SEQUENCE OF THE GAOLISHAN FORMATION IN KONGSHAN, CISHAN MOUNTAINS, JIANGNING, JIANGSU PROVINCE

江宁孔山、茨山高骊山组是一个典型的三角洲层序,可分为三个亚相及若干微相,高骊山组下部的前三角洲亚相中发现Chondrites-Planolites-Palaeophycus组合,中部远岸砂坝微相发现Palaeophycus-?Protopaleodictyon组合;河口砂坝微相见Palaeophycus-trail Phycodes?组合,上部的废异河道微相含有Rhizocorallium jenense-Gyrolithes-Palaeophycus组合。这些组合有着明确的指相意义,遗迹属种、生态类型及组合在剖面上的分布与环境条件有着密切的关系。

The Gaolishan Formation including siltstones, shales, sandstones in Kongshan, Cishan Mountains is a typical deltaic sequence, upper part of which intercalated with lagoon subfacics sediments. The sequence can be divided into three subfacics and a number of microfacics in which four trace fossil assemblages arc recognized: (1) the Chondritcs-Planolites-Palaeophycus assemblage, found in prodclia subfacics of lower Gaolishan Formation, (2) the Palaeophycus-?Protopaleodictyon assemblage, occurred in offshore bar microfacics of middle Gaolishan Formation, (3) the Palaeophycus trail Phycodesl assemblage, restricted to river mouth bar sandstones and siltstoncs upward the offshore bar sediments, and (4) the Rhizocorallium jenense-Gyrolithes-Palaeophycus assemblage, occurred in abandoned river channel mud and sandy mud sediments of upper part of Gaolishan Formation. The vertical distribution of trace fossils in Gaolishan Formation reflects the change of diversity and replacement of behavioral types. The trace fossils of prodelta subfacies sediments have lower diversity, predominately arc of level deposit feeding type. The most abundant trace fossils are found in the sedimentary rocks of delta front subfacics. They have the greatest diversity, among them, not only the horizontal feeding and dwelling traces, but also locomotion trace occurred. The trace fossile included in upper part of Gaolishan Formation mainly appear in the abandoned river channel environment and arc characterized by abundance of low diversity burrows, predominantly of suspension and prcdaccous-feeding animal's dwelling burrows. According ecological analysis of trace fosssils, it is inferred that from the bottom to the top of Gaolishan Formation, the oxygen content in water increase and the water energy strengthens except the situation of the lagoon. The distribution of ichnogenus Chondrites, Plaanolites is related to the oxygen-poor sedimentary environments. The character of the ground and the condition of the water energy control the distribution of Rhizocorallium jenense and Gyrolithes.