Surface and subsurface reworking by storms on a Cambrian carbonate platform: evidence from limestone breccias and conglomerates

Abstract

Some limestone breccias and conglomerates from the Furongian (Late Cambrian) Chaomidian Formation (Shandong Province, China) were investigated in order to understand the depositional and deformational processes induced by storms. The sediments under study occur in a hummocky cross-stratified peloidal grainstone layer. The limestone conglomerates consist of well-rounded clasts that are mostly flat-lying or imbricated, and have erosional bases. They formed by surface reworking (erosion and rip-up) of thin-bedded grainstones by storm waves and currents. The limestone breccias consist of subangular to subrounded clasts of grainstone, which are often associated with small-scale grainstone clastic dykes. The breccias and dykes resulted from subsurface soft-sediment deformation (i.e., differential liquefaction and fluidization of heterogeneously cemented carbonate grains), most likely triggered by storm-wave loading. The limestone breccias and conglomerates bear important implications for understanding the reworking mechanisms of storms on ancient carbonate platforms.

Depositional history, tectonics, and provenance of the Cambrian-Ordovician boundary interval in the western margin of the North China block

“…Clasts produced by erosion and rip-up of early-cemented carbonate sediment during storms were transported by stormgenerated waves and associated currents, and in instances by gravity forces (Myrow et al, , 2012Chen, 2014). Mostly fl at-lying clasts indicate constant reworking of waves, whereas imbricated clasts indicate reworking by currents.…”

“…Flat-pebble conglomerate is thought to result from storms in shallow-marine environments (Mount and Kidder, 1993;Myrow et al, 2004Myrow et al, , 2012Chen, 2014). Clasts produced by erosion and rip-up of early-cemented carbonate sediment during storms were transported by stormgenerated waves and associated currents, and in instances by gravity forces (Myrow et al, , 2012Chen, 2014).…”

“…1; Meng et al, 1997;Feng et al, 2002). Much is known about the strata in the eastern part of the North China block with respect to sedimentary processes, paleontology, stratigraphy, and tectonic evolution (e.g., Kwon et al, 2006;Chough et al, 2010;Chen et al, 2011Chen et al, , 2012Lee and Chough, 2011;Chen andLee, 2013, 2014), but little is known of its western margin. There, a thick succession of strata was deposited in the Helan aulacogen, a tectonic feature that formed along this margin during the Mesoproterozoic, and then experienced uplift during the Neoproterozoic and renewed subsidence during the latest Neoproterozoic (Sun and Liu, 1983;Lin et al, 1991).…”

The distinctive character of lumpy limestones (Early Jurassic, Lusitanian Basin, W Portugal)

“…Several physical processes can account for the failure of firmer sediments or for their differentiated attributes when alternated with softer and/or water‐impregnated deposits. The designation of aspect and end products resulting from a variety of different processes includes intraclast lag deposits, early diagenetic concretions, hiatus concretions, (lime) mud clasts, mobile rockgrounds, limestone or carbonate breccias, autoclastic breccias, unusual intraclastic limestones, autoconglomerates (Bouchette et al, ; Chen, ; Chough, Kwon, Choi, & Lee, ; Gupta, ; Hesselbo & Palmer, ; Krajewski, Olchowy, & Felisiak, ; Li et al, ; Palmer & Wilson, ; Wignall & Twitchett, ; Zatoń, ; Zatoń et al, ). Interestingly, none of these contributions mention the term “lump,” although some reported features comparable with certain aspects of the lumpy limestones here under investigation, justifying the potential of physically dominated processes to explain the presence of particular lump types.…”

“…A detailed analysis of the lithic elements encased in ancient carbonate deposits can provide insights on depositional conditions and basin evolution by elucidating on an array of processes involved in forming and/or delivering these materials to their final destination (e.g., Alfaro et al, ; Coimbra et al, ; Coimbra, Immenhauser, & Olóriz, ; Gupta, ; Jenkyns, ; Li, Li, Shan, Gong, & Yu, ; Ungureanu et al, ). For this purpose, several aspects are typically investigated, including sedimentological analysis, macro‐ to microfacies analysis, morphometric evaluations, and geochemical composition (Bouchette, Séguret, & Moussine‐Pouchkine, ; Chen, ; Coimbra, Immenhauser, Olóriz, Rodríguez‐Galiano, & Chica‐Olmo, ; García‐García et al, ; Hesselbo & Palmer, ; Wignall & Twitchett, ). When treated in a quantifiable manner, new numeric parameters arise, generating complementary information, which can be integrated in previous knowledge, as structural dynamics or paleoenvironmental evolution.…”