下扬子地区青龙群上部角砾岩成因问题

ORIGIN OF THE BRECCIAS FROM THE UPPER PART OF THE QINGLONG GROUP IN THE LOWER YANGTZE AREA

摘要:

1989—1990年,安徽省地质科学研究所与德国下萨克森州不伦瑞克大学地质古生物研究所在下扬子地区合作进行了中三叠统的蒸发岩沉积特征及含钾性评价的研究,对下扬子地区青龙群上部(东马鞍山组)地表角砾岩层进行了详细的野外地质工作。我们认为这套以往一直被看作盐溶倒塌成因的角砾岩,主要是碎屑流沉积的结果,有少量构造角砾岩、膏溶崩坍角砾岩。碎屑流沉积发育于长江北岸的宿松、安庆、巢湖、无为和长江南岸的贵池、铜陵、繁昌、南京、镇江、溧阳等地,呈北东—南西向带状展布,分布广泛、规模大,最大沉积厚度超过百米以上,十分引人注目。

Abstract:

The breccias from the upper part of the Qinglong Group (East Ma'anshan Formation) in the Lower Yangtze area, which were previously interpreted to be the gypsum-solution products, consist mainly of debris flow breccias, with small amounts of tectonic breccias and gypsum-solution breccias. The gravel fragments from the debris flow breccias are derived from: (1)the tidal flat deposits in the lower member of the East Ma'anshan Formation. This kind of the fragments are composed dominantly by dolostones and mixed dolomitic and calciferous rocks, with small amounts of limestones, and (2)the platforms generated prior to the East Ma'anshanian. This kind of fragments are composed mostly of limestones, with small amounts of siliceous rocks, carbonaceous shales and clastic rocks. The matrix in the breccias consists principally of dolomite, calcite and carbonate rock fragments, including small amounts of siliceous rock fragments and quartz. The breccias are matrix-and grain-supported, and exhibit massive and stratified structures. In general, the debris flow breccias in the study area are confined to the slope zone; tectonic brecciass to the gypsum basin, slope and tidal flats and gypsum-solution breccias to the gypsum basin.