The Earliest Clastic Sediments of the Xiong’er Group: Implications for the Early Mesoproterozoic Sediment Source System of the Southern North China Craton

Abstract

The volcanic activity of the Xiong’er Group and its concomitant sedimentation are related to the stretching–breakup of the Columbia supercontinent. The Dagushi Formation overlies the Paleoproterozoic Shuangfang Formation with an angular unconformity. The Dagushi Formation, as the earliest clastic strata of the Xiong’er Group and the first stable sedimentary cover overlying the Archean crystalline basement in the southern margin of the North China Craton, provides tectonic evolution information that predates Xiong’er volcanic activity. By distinguishing lithologic characteristics and sedimentary structures, we identified that the sedimentary facies of the Dagushi Formation were braided river delta lake facies from bottom to top. The U–Pb ages of the detrital zircons of the Dagushi Formation can be divided into four groups: ~1905–1925, ~2154–2295, ~2529–2536, and ~2713–2720 Ma, indicating the provenance from the North China Craton basement. Based on the geochemical characteristics of the Dagushi Formation, we suggest that the sediments accumulated rapidly near the source, which were principally felsic in nature, and were supplemented by recycled materials. The provenance area pointed to the underlying metamorphic crystalline basement of the North China Craton as the main source area with an active tectonic background. The Chemical Index of Alteration (CIA) values of the Dagushi Formation sandstone samples ranged from 60.8 to 76.7, indicating that the source rocks suffered from slight to moderate chemic chemical weathering. The Index of Composition Variability (ICV) values ranged from 0.8 to 1.3, which indicates the first cyclic sediments. The vertical facies and provenance changes of the Dagushi Formation reflect a continuous crust fracturing process that occurred in the North China Craton.