The significance of giant seismites in the Plio-Pleistocene Baza palaeo-lake (S Spain)

Abstract

Giant load-type seismites, uncommon in the geological record, are described in Plio-Pleistocene lacustrine deposits of the Baza Basin (Betic Cordillera, S Iberia). Deformed beds of the marginal lacustrine and distal alluvial facies of the Baza palaeo-lake can be traced continuously for several kilometres. Soft-sediment deformation is represented by load-type structures of large dimensions (pillows around 4 m in width and 2 m in height). Three-dimensional exposures show ellipsoidal pillows separated by fluidized channels without any preferred orientation. The final size of these load-type seismites is strongly influenced by sedimentary factors such as the presence of a reverse density gradient in sediments and the bed thickness. The giant seismites of the Baza basin are located in a region, which is unlikely to have been subjected to high magnitude earthquakes (maximum around 7.0). Therefore, magnitude is not the main factor that controls the size of these load-type structures.