粤北丹霞盆地丹霞组砾岩特征及物源分析

Characteristics and Provenance Analysis of the Danxia Formation Conglomerates in the Danxia Basin,Northern Guangdong Province

丹霞盆地上白垩统丹霞组是丹霞山世界地质公园丹霞地貌形成的主要岩石组合,目前缺乏对其砾岩物质组成及其物源的深入研究。本次通过14个丹霞组巴寨段砾岩露头的观测,统计其砾石的大小、岩性、磨圆度、球度及风化程度,进而结合盆地基岩特点,探讨砾岩的物质来源及形成条件。结果表明,丹霞组砾岩的砾石成分复杂,分选性较差,磨圆程度中等,风化程度较低,为半干旱-干旱气候条件下河流主导的冲积扇相粗碎屑沉积,具有明显的多物源和近距离堆积的特点;盆地北部的晚古生代灰岩、石英砂岩地层提供了主要的碎屑物质,仁化东部的花岗岩可能也提供了少量物源。

In the Danxiashan UNESCO Global Geopark,the Late Cretaceous Danxia Formation is the dominant rock foundation for the formation of Danxia landform.At present,the composition and its provenance significance of the Danxia Formation conglomerates remain poorly known.In this study,the gravel size,lithology,roundness,sphericity,and weathering degree of the Danxia Formation conglomerates are studied through pebble counting at 14 conglomerate outcrops.The results show that the conglomerates are featured by complex composition,poor sorting,moderate roundness,and low weathering degrees.Both the sediment sources and depositional conditions of the conglomerates are analyzed and discussed in combination with characteristics of the basement strata in the basin.The results show that the conglomerates were dominantly coarse clastic deposits of alluvial fan facies under the semi-arid to arid climate during Late Cretaceous,which is characterized by multiple provenances and rapid sedimentation.The Late Paleozoic limestones and quartz sandstones in the north probably provided the dominant sediments to the basin.