Facies and early diagenesis of rainwater-fed paleospring calcareous tufas in the Kurkur oasis area (southern Egypt)

Abstract

AbstractThe Quaternary calcareous tufas precipitated in the Kurkur Oasis area in the southern Western Desert of Egypt were analyzed to determine their implications for the construction of environmental conditions during their formation. X-ray diffraction analysis showed that the tufas consist of low-Mg calcite, whereas macroscopic and microscopic analyses showed the presence of both allochthonous (clastic) and autochthonous components consisting predominantly of pisoliths, oncoids, intraclasts, lithoclasts, stromatolites and encrusted plant materials. These tufas form four facies associations that represent pisolitic intraclastic/lithoclastic oncoidal rudstones, phytohermal /bryophyte framestones, stromatolite-algal boundstones, and speleothem-like flowstones. These tufa associations were formed within a karstified carbonate terrain by a rainwater-fed paleospring system comprising waterfalls, slopes, dammed areas, lacustrines-paludal, and fluvial channel margin environments. Early diagenetic features are cementation, neomorphism and subaerial dissolution. Isotope-geochemical analysis indicated that the negative δ18O values (between – 13.26 and – 8.89‰ V-PDB) and the negative δ13C values (between – 3.16 and – 1.62‰ V-PDB) of the studied tufas are consistent with carbonates deposited from meteoric water in regions with much precipitation.