Distribution of carbonate cements within depositional facies and sequence stratigraphic framework of shoreface and deltaic arenites, Lower Miocene, the Gulf of Suez rift, Egypt

This study aims to unravel the spatial and temporal distribution of diagenetic alterations of the Mheiherrat Member, the Rudeis Formation (lower Miocene) of the Gulf of Suez rift, Egypt within depositional facies and sequence stratigraphy. The Mheiherrat member is represented by shoreface calcarenites and hybrid arenites (transgressive and highstand systems tracts; TST and HST; respectively) and deltaic rudites and coarse-grained calcarenites and hybrid arenites (lowstand systems tracts; LST). Petrographic, stable O- and C-isotopes, mineral chemical and geochemical analyses have revealed that the arenites are pervasively cemented by eogenetic carbonates and, to small extent, by zeolite and pyrite as well as by telogenetic palygorskite. The shoreface TST and HST calcarenites and hybrid arenites were dominantly cemented by microcrystalline grain-rimming and inter- and intragranular pore-filling calcite (δ¹⁸O_V-PDB=-3.6‰ to -0.3‰ and δ¹³C_V-PDB=-2.3‰ to -0.7‰) and rhombic dolomite (δ¹⁸O_V-PDB=-3.9‰ to+0.9‰ and δ¹³C_V-PDB=-2.5‰ to -0.7‰). These cements are interpreted to be formed by marine to brackish waters with δ¹⁸O_V-SMOW -1.2‰ to+3.2‰ at temperature of 20-55°C. The deltaic LST coarse-grained calcarenites and hybrid arenites were dominantly cemented by coarse-crystalline, inter- and intragranular pore-filling calcite (δ¹⁸O_V-PDB -4.4‰ to -2.3% and δ¹³C_V-PDB=-2.8‰ to -1.3‰), which are interpreted to have precipitated from pore waters with δ¹⁸O_V-SMOW+3.5‰ to+5.5‰ at temperatures of greater than 55°C. Such pervasive cementation by carbonates is attributed to the occurrence of abundant intrabasinal carbonate grains. The carbonate cement texture is suggested to be controlled by changes in pore-water chemistry owing to transgression and regression events. This case study revealed that better understanding of factors controlling the extent and textural habits of carbonate cements can be achieved when it is linked with depositional facies and sequence stratigraphy.