Depositional processes of the Zhushadong and Mantou formations (Early to Middle Cambrian), Shandong Province, China: roles of archipelago and mixed carbonate–siliciclastic sedimentation on cycle genesis during initial flooding of the North China Platform

Abstract

To understand the depositional processes and environmental changes during the initial flooding of the North China Platform, this study focuses on the Lower to Middle Cambrian Zhushadong and Mantou formations in Shandong Province, China. The succession in the Jinan and Laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone, dolostone, stromatolite, thrombolite, purple and grey mudstone, and sandstone. A detailed sedimentary facies analysis of seven well‐exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments, including local alluvial fans, shallowing‐upward carbonate–siliciclastic peritidal cycles, oolite dominant shoals, shoreface and lagoonal environments. These facies associations successively show a transition from an initially inundated tide‐dominated carbonate platform to a wave‐dominated shallow marine environment. In particular, the peritidal sediments were deposited during a large number of depositional cycles. These sediments consist of lime mudstone, dolomite, stromatolite and purple and grey mudstones. These shallowing‐upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea‐level. The carbonate production was, however, interrupted by frequent siliciclastic input from the adjacent emergent archipelago. The depositional cycles thus formed under the influence of both autogenetic changes, including sediment supply from the archipelago, and allogenic control of relative sea‐level rise in the carbonate factory. A low‐relief archipelago with an active tidal regime allowed the development of tide‐dominated siliciclastic and carbonate environments on the vast platform. Siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea‐level. This study provides insights on how a vast Cambrian carbonate platform maintained synchronous sedimentation under a tidal regime, forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea‐level during the early stage of basin development in the North China Platform.

Facies and platform development of a microbe‐dominated carbonate platform: The Zhangxia Formation (Drumian, Cambrian Series 3), Shandong Province, China

“…The upper part of the Mantou Formation, underlying the depositional unit 1, consists of purple mudstone, cross‐stratified sandstone (Figure ) which represents lagoon and tidal flat environments with tidal channels (Lee & Chough, ). Unit 1 started with deposition of oolite and thrombolite bioherms of ooid shoal environments (FA 1) over the siliciclastic‐dominated succession.…”

“…During the middle to late Early Cambrian, the North China Platform was gradually inundated from the south‐east, and mixed‐siliciclastic and carbonate succession formed under tide‐influenced shallow marine environments (Meng, Ge, & Tucker, ). Continued transgression resulted in the submergence of the oldlands which caused a decrease in the supply of siliciclastic sediments to the platform (Lee & Chough, ; Meng et al, ). The shrinking of siliciclastic deposition along with other conditions including continuous rise in sea level and warm climate was favourable for carbonate production.…”

“…The North China Platform was a vast epeiric platform with relatively flat but uneven sea floor (Lee & Chough, ; Meng et al, ). A large amount of siliciclastic sediments was supplied to the platform from the exposed islands scattered on the platform and formed wave‐ and tide‐ dominated siliciclastic facies of the Mantou Formation (Lee & Chough, ). Continued flooding resulted in the submergence of the entire platform and coastal lowlands, which reduced input of siliciclastic sediments.…”

Triassic orocline in East Asia: Insights from a transition from passive margin to foreland basin in eastern North China Block

“…The Paleozoic succession was only discovered in the Luxi region, comprising thick and mixed carbonate and siliciclastic sedimentary rocks (Chen & Lee, ), and has been recently redefined using detailed sedimentological methods based on the major exposures in this region (Lee & Chough, ).…”

“…Furthermore, the Changqing Group rocks were deposited in a closed or semiclosed sedimentary environment by the continental margin (BGMRSP, ), whereas the Jiulong Group rocks developed in an open freshwater platform, which postdated lower Paleozoic clastic deposits, and typically formed a passive margin with minor igneous activities. All the sedimentary evidence indicates that Neoproterozoic rift‐related tectonic settings are adopted by Early Paleozoic tectonic evolution, followed by continuous drifting as a transgression in the whole NCB from the east and the south (Figure a; Chough, ; Lee & Chough, ; Zhong & Fu, ).…”