华南上扬子区早-中奥陶世疑源类古环境意义

PALAEOENVIRONMENTAL SIGNIFICANCE OF THE EARLY—MIDDLE ORDOVICIAN ACRITARCHS FROM THE UPPER YANGTZE PLATFORM,SOUTH CHINA

对上扬子区 7个剖面早—中奥陶世疑源类研究表明 ,这些疑源类组合在分异度及属种组成上呈现有规律的变化 ,这种变化是上扬子区古环境变化的反映。在上扬子区西部 ,近岸碎屑岩相沉积的滇东红石崖组所产疑源类组合分异度低 ,为个体较小、壳饰较简单的分子 ;上扬子区中部 ,以黔北湄潭组为代表的浅海相碎屑岩和灰岩沉积中 ,疑源类分异度较高 ,并出现许多个体较大、壳饰较复杂的分子 ;而在上扬子区东部鄂西宜昌大湾组陆棚相灰岩与泥岩中 ,疑源类分异度继续增高 ,其中个体大、具粗大、长而复杂突起的分子占优势。

Investigation on the Early—Middele Ordovician acritarchs from seven sections of the Upper Yangtze Platform indicates that these assemblages vary in their diversities and compositions. The variation reflects the palaeoenvironmental changes. The Hongshiya Formation of eastern Yunnan,the near-shore facies clastic rocks in the western part of the Upper Yangtze Platform, yields low-diversity, small-sized and simple-processed taxa; the central Upper Yangtze Platform assemblages of the shallow-water clastic and carbonate rocks, which is represented by the Meitan Formation of northern Guizhou, become more diversified and contain many large-sized, complex-processed taxa; while in the eastern part of the Upper Yangtze Platform, the shelf carbonate and mud stones of the Dawan Formation of western Hubei, acritarch assemblage is high-diversity and dominated by the large-sized, thick, long and complex-processed taxa.