Abstract

Silcretic duricrust is found capping scattered, isolated hills in the southern desert plain of Kuwait. It occurs in genetic association with surface and subsurface calcrete, dolocrete, and gypcrete deposits. Two main types of silcrete were found--quartzitic silcrete and massive silcrete. The first was developed by precipitation of microcrystalline drusy quartz cement in the intergranular pores of sandstones, whereas the second type was formed by replacement of calcrete, dolocrete, and freshwater limestone by microcrystalline quartz. Silica precipitation took place in two stages. In the first, primary silicification caused the development of the main silcrete mass which is usually composed of microcrystalline quartz, syntaxial quartz overgrowth, and quartzine spherulites. A second stage of secondary silicification was responsible for the precipitation of length-fast chalcedony and megaquartz in cavities. The field occurrence and the petrographic characteristics of the silcrete in Kuwait provide support for the Folk and Pittman (1971) hypothesis on the replacement of evaporite and carbonate by quartzine and lutecite. Calcretization of Kuwait Group clastic deposits, which resulted in complete or partial dissolution of siliciclastic grains and precipitation of carbonate minerals, is likely to have provided soluble silica for groundwater. A diagenetic model for the studied silcrete is proposed in which both vertical and lateral translocation of soluble silica in groundwater is considered. Silcrete has played an important role in the landscape development of the southern area of Kuwait.

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