龙潭组下部含煤段腕足类的发现及其意义——对龙潭组成煤环境的新认识

DISCOVERY OF BRACHIOPODS FROM COAL-BEARING MEMBER OF LUNGTAN FORMATION AND ITS SIGNIFICANCE—A NEW UNDERSTANDING OF LUNGTAN FORMATION COAL-FORMING ENVIRONMENT

一、问题的提出龙潭组是我国南方经济价值最大的含煤岩系,曾以典型的海陆交替相而闻名于世。过去一向把龙潭组底部中至粗粒长石石英砂岩和煤层作为陆相的标志。然而,十几年来,随着国民经济建设的迅速发展,煤田地质工作的不断深入,在苏南地区的勘探队于这层长石石英砂岩中较普遍发现有指相意义的矿物--海录石(颗粒均较新鲜,大多呈胶体形态充填在碎屑之间)。浙江省煤田地质勘探公司和长广煤矿地质队骆善胜(1980)等先后在苏浙皖交界地区的广德牛头山西边村、龙山洼、王村、查扉村等井田龙潭组下部含煤段的主采煤层(俗称“C”

As the most important coal-bearing rock series in South China, the Lungtan Formation is prominent for its epicontinental marine facies. Being controlled by the Cathysian structure, it extends in the northeast to southwest direction over the vast area from North Jiangsu to north Guangdong. It bears a tripartite character, with the Lower and Upper Coal-bearing Members separated by the Shale Member yielding the Anderssonoceras fauna. Although both members contain the Gigantopteris flora, the Lower Member is more divergent and better preserved, and so are the main workable coal seams. The Upper Coal-bearing Member has mostly changed to ammonites and brachiopods-bearing shales, while the Lower Coalbearing Member has been taken as the typical epicontinental marine facies. However, its facies sequence in ascending order can be recognized as: medium to coarse feldspar-quartz sandstone (con- taining basal conglomerate in some areas)→alumine mudstone→plant-bearing shale or sandy limestone→main workable coal seams→Loping Fauna-bearing limestone→Anderssonoceras fauna-bearing shales, etc., forming a complete sedimentary cycle of transgressive sequence. In recent years, the facies index mineral glaucolite has been discovered from the basal feldspar-quartz sandstone in the Lower Coal-bearing Member of the Lungtan Formation around the border area of Jiangsu, Zhejiang and Anhui which had long since been regarded as indicating the continental facies. Moreover, numerous fossils have been discovered from the dunn bass and basal plate sandy limestone of the coal seams, such as the brachiopods Niutoushania niutoushanensis plicata Liao and Tyloplecta yangtzeensis (Chao); the cephalopod Lopingoceras (Stoyanov); the bivalve Permoperna trapezoidalis (Kayser); the coral Tachylasma sp.; the trilobite Phillipsidae; the bryozoan Fistulipora cf. timorensis Bassler; together with fusulinids, crinoid stems, etc. Combining this discovery with the characters of the Lungtan Formation, such as the wide distribution, the clear cycles structure, and the stable occurrence and high sulphur content in its coal seams, which can be correlated layer by layer, it is obvious that the Lungtan Formation does not belong to the epicontinental marine facies coal-bearing rock series but to the structure of nearshore littoral plain pattern, being dominated by marine facies clastic rocks, and bearing a resemblance to the littorol marsh mangrove coal-forming environment on the Hainan Island of Guangdong. The study of modern environments will open up the entrance to the study of ancient ones, but it can not be taken as an omnipotent key or panacea to solve all problems in this regard, and therefore we must try to establish a model for the ancient environments which different from the modern pattern.