DEDOLOMITIZATION OF DOLOCRETE DEPOSITS IN KUWAIT, ARABIAN GULF

Dedolomitization of a dolocrete profile hosted in Mio-Pleistocene sili ciclastic deposits in the area of Kuwait City, Arabian Gulf was invest igated. Dolocrete dolomite crystals vary considerably in size, shape a nd internal structure; however, they are mostly zoned. Zonation is usu ally due to the alteration of cloudy and clear zones. The cloudy zones , which are mostly formed of disordered metastable dolomite, are more susceptible to dedolomitization than the stable, well ordered clear zo nes. Two modes of dedolomitization were recognized; the first involves complete dissolution of the metastable dolomite followed by precipita tion of intracrystalling cavity-filling calcite. The second is a pseud omorphic replacement of dolomite by calcite. This replacement takes pl ace by the simultaneous dissolution of dolomite and precipitation of c alcite in such a manner that the original dolomite fabrics are inherit ed in the dedolomite. Exposed and near-surface dolocrete profile (less than 5 m deep) are almost completely dedolomitized and altered to sec ondary calcrete whereas subsurface profiles are slightly dedolomitized . Dedolomitization of the sub surface dolocrete profiles may indicate the effect of flushing by fresh groundwater; which flows from west to east, whereas the alteration of the exposed dolocrete profile could be attributed to be an effect of meteoric water. A new mode of calcrete genesis by dedolomitization and/or complete calcitization of precursor dolocrete is suggested.