浙西虎山公园丹霞地貌成景地层的沉积相分析

FACIES ANALYSIS OF THE BEDROCK OF DANXIA LANDSCAPE IN THE HUSHAN PARK OF WESTERN ZHEJIANG PROVINCE

浙江省江山市虎山公园位于金衢盆地西部,下白垩统衢江群中戴组以发育红色碎屑岩,是构成景区丹霞地貌的岩石基础,目前对虎山成景地层的沉积相认识还比较薄弱。研究区的丹霞地貌以孤峰为主,属于演化晚期阶段。研究结果表明,景区红层砾石成分以紫红色凝灰岩为主(78%),大小主要为0.6～4.0cm,以次棱角状—次圆状为主(92%)。砂岩样品主要为砖红色细粒岩屑石英砂岩,碎屑颗粒大小为0.12～1.5 mm、主要为次棱角—次圆状、分选性较差,在粒度曲线上以跳跃组分为主。通过野外露头沉积构造和室内镜下显微组构研究,认为该套红层为冲积扇沉积体系的产物。这些厚度巨大的砾岩和砂岩地层被后期地壳抬升、断层切割、风化侵蚀后形成丹霞地貌。

The Hushan Park is located in the western part of the Jinhua-Quzhou Basin in Jiangshan City of Zhejiang Province. The Early Cretaceous Zhongdai Formation of the Qujiang Group is dominated by red elastic rocks, which form the bedrock of the Danxia landform in the scenic spot. Little is known about depositional facies of the scenery redbeds. The Danxia landscape of the study area consists of isolated peaks, thus they are interpreted to represent the state of landscape evolution. In this study, a detailed sedimentological investigation was conducted through the observation and measurement of outcrop profile, pebble counting in the field, and thin section and grain size analysis of sandstone samples. The results show that pebble lithology is dominated by the purplish red tuff （78%） with clast size ranging from 0.6 to 4.0 cm. Pebbles are mainly subangular to subrounded （92%）. The sandstone samples mainly are brick-red fine-grained lithic quartzose sandstones. The grains of sandstone samples are subangular to subrounded, and 0.12-1.5 mm in diameter. Both the outcrop sedimentary structures and the microscopic textures indicate that the redbeds is the product of alluvial fan deposition system. The Danxia landforms were formed in these thick succession of conglomerates and sand- stones by tectonic uplift, fault cutting and weathering.