Graded limestones and limestone-quartzite couplets: Possible storm-deposits from the Moroccan Carboniferous

摘要: Abstract The Lower Carboniferous (Visean) successions of the Meseta region central Morocco are dominated by mixed marine carbonate and terrigenous facies bearing biological sedimentological hallmarks deposition in a neritic environment. This study concerns two inter-related types sedimentary unit, relatively uncommon but displaying features not readily compatible with depositional mechanisms conventionally envisaged for such an They described reference to three sections which they well represented. Graded limestones texturally immature, broadly lenticular or channel-fill units calcarenite calcirudite variable thickness, exhibiting general upwards diminution modal maximum grain size somewhat irregular sequence internal structures, often including large-scale cross-stratification. compound units, here termed limestone-quartzite couplets , generally comprise lower member, frequently graded, succeeded more quartzose arenite, invariably finer size. Six main couplet distinguished primarily on nature contact between members. From review published data modern ancient shelf deposits it is concluded that periodic storm-generated transportation considerable geological importance. Two categories storm-induced modification “normal” sedimentation processes recognised: (1) storm-stirring erosion; (2) lateral transfer storm-mobilised sediment. A process-response model developed involves introduction coarse sediment storms substrate indigenous Comparison theoretical sequences produced graded commonly encountered field strongly indicates these anomalous associations result from rapid, addition detritus (from local elevations as reefs shell-banks) slightly deeper environments muds sands were being deposited protracted processes.