Synthesis of late paleozoic and triassic redbed sedimentation in Morocco

Abstract

The Late Carboniferous and Permian strata of Morocco were deposited in late-orogenic, probably fault-bounded basins that formed during the last stages of the Variscan (Hercynian) orogeny. Remnants of a dozen of these basins are exposed in Morocco. They contain reddish-brown alluvial-fan and fluvial conglomerates and sandstones, as well as significant volumes of mudstone of probable floodplain origin. Several also contain intercalated acidic lava flows. Syndepositional and postdepositional tectonism caused structural deformation and erosion of these strata. The next stage of preserved deposition in Morocco began with continental rifting 30–40 million years later in Late Triassic time, and took place in isolated, fault-bounded basins that are aligned along the inherited Variscan structural trends. In southwestern Morocco, these basins were filled with brick-red alluvial-fan and fluvial conglomerates, sandstones, and mudstones; in the northern and coastal-southwestern parts of the country, marine-influenced thick halites and red evaporitic mudstones are the prevalent sedimentary deposits. As localized subsidence of the basins decreased, more regional subsidence began, causing transgression of the Tethys from the east, and of the newly formed Atlantic from the west. Widespread evaporitic mudstones were deposited across Morocco in vast nonmarine mudflats inland, and marine-influenced, muddy sabkhas nearer to the transgressive shoreline. Extensive basalt flows were extruded during deposition of these facies. As subsidence and transgression continued, open-marine Jurassic carbonates were deposited conformably over the mudstones along the High and Middle Atlas trends.