oa Preservation potential of carbonate and halite polygons of the Abu Dhabi coastline

Polygons have previously been described as ubiquitous features of the Abu Dhabi sabkha and coastline, yet there has been little effort to quantify these features or assess their preservation potential in the stratigraphic record. This study compared the morphology, mode of formation and preservation potential of evaporite polygons from the upper inter-tidal to supra-tidal zones with carbonate polygons from the lower inter-tidal zone of the Abu Dhabi coastline. Very large-scale peritidal polygons were identified as forming in hardgrounds over an extensive area of the peritidal environment. These polygons were sampled and their morphology was accurately mapped to produce a quantitative description of polygon characteristics and a genetic model for their formation. These polygons are interpreted to have developed through lateral expansion due to the growth of displacive calcite cements. In the upper inter-tidal zone a number of sites were defined (1 to 25 square meters) and regularly photographed and described to construct a graphic record of temporal changes in surface morphology. This study demonstrated that the upper intertidal zone is a dynamic sedimentary environment with many of the sabkha surface features in a constant state of flux. Meter-scale halite polygons formed as a result of the evaporation of surface and near-surface pore waters. The precipitation of salts resulted in lateral displacement and uplift of polygon margins as tepee structures. Uplifted margins are susceptible to aeolian abrasion and<br>dissolution during humid summer months. Conversely, episodic winter rainfall ponds in dish-like polygon centers with consequent dissolution of salts to leave a residual rim tepee structure. During extended periods of rainfall total dissolution and removal of halite polygons may occur.