Serravallian soft sedimentary deformation structures of the Ain Kihal Formation in shallow marine deposits (Tafna Basin, northwestern Algeria)

The Serravallian shallow-water marine deposits of the Ain Kihal Sandstone Formation from the Tafna Basin (northwestern Algeria) have been studied. The sandstone marl succession revealed numerous sedimentary structures (e.g., ripple marks, hummocky cross stratification, and linguoid ripples). However, the most striking feature of these Serravallian deposits is the abundance of soft-sediment deformation structures (SSDS), such as slumps, convolutions, pseudonodules, dish and pillars structures, autoclastic breccias, contorted laminations, pillow bed, ball and pillow structures, load casts, flame structures, dykes and water escapes structures. The microscopic investigation displayed fine-medium to coarse quartz grains, with feldspar, and oyster fragments. Based on sedimentary structures, the depositional environments of these intercalated marls and sandstones range from shoreface to upper offshore. This allowed us to link these SSDS to palaeoearthquakes. Comparison of the observed SSDS with previously published data suggests seismic activity of moderate to strong magnitude (over 5 degrees on the Richter scale).