浙江江山藕塘底组陆源碎屑与碳酸盐混合沉积特征及其构造意义

Characteristics and Tectonic Significance of Mixing Sediments of Siliciclastics and Carbonate of Outangdi Formation in Jiangshan,Zhejiang Province

浙江江山藕塘底组是晚石炭世威宁期陆源碎屑与碳酸盐的混合沉积 ,包括两种组分在同一岩层内相互混杂形成混积岩和陆源碎屑岩与碳酸盐岩互层形成混积层系。藕塘底组是海陆交互环境的沉积产物 ,剖面结构具有下细上粗的岸进序列。混积岩形成于滨岸浅滩环境 ,由沿岸流和回流将河口或滨岸海滩的石英砂带到滨岸浅滩和潮坪相碳酸盐沉积区混杂而成。具两种混积层系类型 ,即浅海滨岸环境中砂岩与碳酸盐岩互层、河流相碎屑岩与海相碳酸盐岩互层。研究表明 ,混合沉积成因属“相混合” ,主要受区域构造隆升、全球海平面上升和盆地水介质条件特性控制。区域海平面周期性变化和岸进序列可能是华夏古陆强烈隆起的结果。作者还讨论了混合沉积的分类和命名 ,将陆源碎屑与碳酸盐层相互交替构成的互层和夹层组合称为“混积层系” ,并建议将“混积岩”一词用来表征两种组分相互混杂这种特殊沉积事件 。

Outangdi Formation in Jiangshan, Zhejiang is the mixing deposits of terrigenous clastics and carbonate in Weiningian of late Carboniferous. The mixing deposits include the interbedding which constitutes a series of interbedded clastic beds and carbonate beds and the mixing within in the same bed which forms the 'Hunji rock'. Outangdi Formation has the features of intercalated marine and terrestrial deposits with the progradational sequences with lower fine and upper coarse of sedimentary granularity in the section. Hunji rock is formed in seashore environment, mixed carbonate sediment in beach or tideland facies with quartz sand taken from bayou or beach by coastwise flow and circumfluence. There are two kinds of Hunji sequences: interbeds of sandstone and carbonate rock in seashore environment, interbeds of clastics in river facies and carbonate rock in ocean facies. It is indicated that mixing deposition belong to 'facies mixing', affected mainly by regional toctonic uplift, rise of global sea level and dynamics of water medium in the basin. Regional sea level periodic change andprogradational sequences were probably due to intense uplift of the oldland called Cathaysia. The classification and name of mixed sediments are also discussed in this paper. Interbeds and alternated beds of clastic and carbonate beds are named as 'hunji sequence', a new genetic term. It is suggested that Hunji rock means a special sedimentary event of mixing of terrigenous clastics and carbonate instead of a term of specific rock.