Formation conditions and diagenetic evolution of sand roses in clastic sabkhas along the Arabian Gulf Coastal Region, Eastern Saudi Arabia

This field, petrographic and geochemical study aims at con straining the formation and diagenetic evolution of sand roses (desert roses) in interdune sabkhas in Eastern Saudi Arabia. These “roses”, which are mainly cemented by gyp sum, car bon - ate, and clay minerals, occur as disc-shaped and spherical flower-like crystals. Sands, within the sand roses, are moderately-sorted, me dium-grained, and sub-arkosic. Gypsum typically exceeds 20% of the volume of the roses, and locally gyp sum is partly transformed to anhydrite. In addition to gypsum and anhydrite, early diagenetic modifications include precipitation of grain coating clay, dissolution of unstable grains (e.g., feldspar grains), and weak mechanical compaction. Iron oxide cement was formed when the sand roses exposed to the surface. The XRD and petrographic data indicate an increase in amounts of gypsum cement from the water table upward towards the sabkha surface. The sand roses also are larger and lighter in colour away from the water table. The formation of sand rose at the water table is attributed to the nonpedogenic process where dynamic interactions between meteoric vadose and phreatic zone occur. This study is expected to provide a better understanding of the mode of sand roses formation in the interdunes areas, as well as the diagenetic alterations in both phreatic and vadose zones.