Sedimentary characteristics and interactions among volcanic, terrigenous and marine processes in the Late Permian Kuishan Member, Eastern Block of the North China Craton

Abstract

Understanding the variability of depositional environment and depositional processes of the Late Permian Kuishan Member, North China Craton, is crucial for unraveling the evolution of sedimentary basin and epicontinental sea in Shandong tectonic domain. The Kuishan Member in the Eastern Block of the North China Craton, formed in association with general regression of an epicontinental sea, is composed of abundant volcanic deposits and nearshore sedimentary deposits. Three lithofacies assemblages together with eleven lithofacies are identified in the study area, including volcanic deposits of the turbidity lithofacies assemblage, epiclastic deposits of the nearshore lithofacies assemblage, and mixed volcaniclastic and epiclastic sedimentary deposits of the terrestrial lithofacies assemblage. These alternating volcanic-epiclastic lithofacies assemblages illustrate the depositional environments induced by volcanic activities and nearshore wave influence. Syn-eruptive lithofacies, in the shallow water area, were formed by high density turbidity currents and ash fall into water introduced by rising sea levels and high rainfall due to volcanic eruptions to the north, whereas thin-bedded shallow marine silty mud developed in the distal area. Inter-eruptive lithofacies were represented by tuffaceous mudstone deposited in an exposed and oxidized setting due to falling sea level, whereas epiclastic nearshore deposits accumulated by wave or current flow regimes. Paleocurrent measurements show that the predominant regression direction changes from uniform southwest to divergent southwest and southeast during volcanic inter-eruptive periods. The Kuishan succession therefore can be regarded as a volcano-related sequence, in which the input of volcaniclastic and epiclastic deposits were significantly modulated by controls of volcanism, with frequently changing coastline position of the epicontinental sea and alternating depositional environments.