Evidence for Upper Cretaceous seismites in the Abu Tartur area, Western Desert, Egypt

Abstract

Upper Cretaceous tidal-flat sediments of the Abu Tartur region, Western Desert of Egypt, contain a variety of soft-sediment deformation structures (SSDSs) in the Mut Member of the Quseir Formation and the overlying Duwi Formation. Here, we document recognition of a set of SSDSs characterized by complex morphology and large size. The SSDS include: 1) water-escape structures, 2) minor recumbent, chevron, and slump folds, 3) syn-sedimentary minor faults, 4) neptunian dykes, 5) regular ball-and-pillow structures, flattened pseudo-nodules, and load casts, 6) syn-sedimentary undulations, 7) fractures and joints, 8) sand injectites, and 9) autoclastic breccia and brecciated siderite clasts. The dimensions of the SSDSs range from a few centimeters to several decimeters. Both extensional and contractional forces appear to have been involved in development of these structures. A detailed analysis of facies relationships, combined with consistent orientations of SSDSs and the regional tectonics of the target area suggests earthquakes as the triggering mechanism for sediment deformation and large-scale mass failure. The deformed strata are consistent with most of the well-known criteria of typical seismites. Thus, syn-sedimentary liquefaction was identified as the primary driving force in most of the observed deformation horizons for these Upper Cretaceous SSDSs in the Abu Tartur area.