Beachrock Cementation Patterns Along the Gulf of Aqaba Coast, Saudi Arabia

Beachrocks crop out along the Saudi coast of the Gulf of Aqaba with beds lying at elevations up to 0.8 m above the present sea level and with seaward extents that repeatedly submerge and emerge during high and low water levels. This study discusses the cement composition, petrography and bedding features of beachrocks at 24 different locations, of which a total of eight sites were sampled. The study focuses on the petrographic and microtextural characteristics of the beachrocks to elucidate their cementation environment and diagenetic evolution. The results revealed the predominance of three main cement types: (1) fibrous aragonite cement with morphologies including isopachous rims around grains with or without micritic substrates, pore-filling radial aggregates, pseudospherulite and randomly oriented interlocking aragonite fibers; (2) microcrystalline low-Mg calcite (LMC) cement binding grains and filling inter-and intra-granular pore spaces; and (3) micritic cement in the form of envelopes and/or pore-filling micrite in some samples with meniscus bridges. The last two types also contain infiltrated silt-sized clasts and skeletal remains. The cements indicate precipitation mainly in pore-filled marine phreatic diagenetic zone and, rarely, in the marine vadose zone with the aid of microbial and algal activity. Petrographic investigations and energy-dispersive X-ray spectroscopy of selected samples showed the occurrences of aragonite and LMC.