Petrography and stable isotope composition of baroque dolomite from the Shuaiba formation (lower cretaceous), Abu Dhabi, United Arab Emirates

Abstract

Integration of petrographic and stable isotopic analyses of dolomite from the reefal facies of the Lower Cretaceous Shuaiba Formation of Abu Dhabi, indicates two types of dolomites: host (very fine to medium crystalline dolomite formed in a meteoric-marine mixing zone) and baroque (white, coarsely crystalline dolomite). The baroque dolomite is characterized by coarsely crystalline mosaics of anhedral to subhedral crystals with undulose extinction, curved crystal faces and cleavage planes, and abundant inclusions. Baroque dolomite from this formation was precipitated in veins and narrow solution channels and is commonly composed of coarse bladed crystals, sometimes fan-shaped toward the center, precipitated as void filling cements that partially occlude porosity. Analysis of the formation of water chemistry and stable isotope for the dolomite of the Shuaiba Formation reveals that it probably formed by mixing seawater or meteoric water in the subsurface, with interstitial brines derived from halite-bearing evaporites. Also, oxygen isotope analyses (δ ¹⁸O PDB values range from −4.8 to −9.6% and δ ¹³C PDB values range from 2.4 to 4.9%) suggest that baroque dolomite formed at temperatures ranging from 67 to 112°C.