Depositional Characteristics and Provenance Analysis of the Miboshan Formation, Helan Mountain

Key words: 
• Helan Mountain

Abstract: Miboshan Formantion in the southern Helan Mountain mainly consisted calcareous breccia, conglomerate, interbedded sandstone or pebbled sandstone, and shale, pebbled shale and grain limestone, and it is very thick Slope facies that is regionally lowgrade metamorphic terrigenous turbidite in deep water, which has experienced different degree deformation and the flysch rhythmic layering and typical Bouma sequence are well developed. Our results shows that the deposition duration of the Middle Ordovician Miboshan Formation is corresponding to the active stage of Helan cold rift, which is particularly important to understand the early Paleozoic tectonic framework and lithofacies paleogeography of Helan Mountain. Our geochemical analysis found that eigenvalue of La, Ce, ∑REE and δEu are similar to that of continental island arc and active continental margin setting. With further information from the tectonic environment and local background, it is concluded that the source of Miboshan Formation is from its southern region of Qilian orogenic belt and its adjacent area of Alashan massif, which is a near source sedimentation that is binary provenance.