Sedimentary and tectonic evolution of Qaidam areas in Late Paleozoic

Key words:  Qaidam Basin  Late Paleozoic  sedimentary tectonic framework  paleocurrent  volcanic rocks

Abstract:

According to the restoration of paleocurrent data collected in the field and the study on geochemical behavior of Neopaleozoic volcanic rocks, sedimentary and tectonic evolution features of Qaidam areas in Late Paleozoic were studied. The results show that the land sources of the eastern part of the basin generally come from the north, which reflects that the direction of transgression is from south to north and the deposition center lies in the southern part of the basin. The tectonic settings were intraplate tension in later stage of collision in Late Devonian, intracontinental tension in Early Carboniferous and ocean continent underthrust in Late Carboniferous. The Qaidam Basin Block Mass developed a series of slim graben like basin or ocean trough and formed the prototype of Qaidam Basin central uplift (Niubiziliang ancient land) because of tension from Late Devonian. The Carboniferous depositional basin, with a depression and uplift palaeogeographic framework, is a differential subsidence basin, formed by Hercynian movement on the basis of Late Devonian rift trough. It was a rift basin deposited with neritic facies carbonate rocks and was extensivly transgressed. Lagoon, fan dalta (or braided river dalta) of transitional facies and coal bearing deposition of paludal facies were formed around the ancient land. Permian Period had the same sea area as that of Carboniferous Period, which still located in epicontinental faulted depression and belonged to clasolite carbonate construction with stable shallow marine deposition.