Facies analysis, provenance and tectono-depositional evolution of the Ediacaran Hammamat molasse sediments, Umm Tawat area, North Eastern Desert, Egypt

Abstract

The Ediacaran Hammamat Sediments in the Umm Tawat basin of the Egyptian North Eastern Desert are exposed with an ENE-trend, along with the Dokhan Volcanics and various phases of intrusive rocks. Different lithofacies of molasse-type deposits exist, with a debate about their tectono-depositional setting, provenance, and diagenesis versus metamorphism. In this study, we present a new insight into the facies and evolution of Umm Tawat sediments using an integrated structural, sedimentological, and mineralogical approach. Lithofacies analysis revealed their deposition in continental suites of alluvial fans, braided fluvial channels, and lacustrine environments. The sediments were derived from proximal heterogeneous sources of intermediate and acidic igneous rocks and a subordinate sedimentary provenance conveyed from uplifted basin margin hinterlands. Petrographic, SEM-EDX, and XRD data imply that the HS were affected by diagenesis to very low-grade metamorphism and local thermal metamorphism in contact with the intrusive younger granite. Carbon smears possibly derived from organic matter in shale were observed. Two reconstructed paleostress phases derived from fault slip data with the sedimentological analysis constrain the tectono-depositional evolution of the Umm Tawat molasse basin. We propose an early development of ENE-asymmetric sedimentary depocenter associated with the N–S-directed extensional strike-slip stress regime. Syn-tectonic deposition of the Hammamat Sediments occurred during this phase in three stages with variable sediment provenance and accommodation/sediment influx ratios. This phase was accompanied by the three phases of younger granites and the Dokhan volcanics. Positive inversion with N–S-directed compressional strike-slip stress regime caused ENE-to NE-folding and reverse reactivation for the pre-existing ENE-trending dextral faults. Up on the regional correlation, the Ediacaran Umm Tawat molasse basin differs somewhat from other molasse basins in the central Eastern Desert regarding their facies and tectono-depositional model. This basin probably formed as a continental intra-arc basin located in the northern region of the Nubian Shield.