Calcretized Ferricretes Around the Jaisalmer Area, Thar Desert, India: Their Chemistry, Mineralogy, Micromorphology and Genesis


Abstract: Ferricrete, an iron duricrust, caps Tertiary and Mesozoic rocks around Jaisalmer in the Indian desert. These ferricretes are associated with two distinct present-day landforms. The upper unit is a high-level dissected, rocky structural plain and the lower one a colluvial flat with soft ferricrete gravels. This study pertains to the first situation wherein field observations, micromorphological features and regolith chemistry suggest an in situ origin for the ferricretes, as in the case of the Walther profile. Subsequent tectonism and changes in base level resulted in a shift in processes from weathering to erosion. Episodes of erosion resulted in inversion of relief whereby low but resistant areas with in situ weathering profiles remain as high-level structural plains, mesas and buttes after erosion of the softer material around them. Destruction of nodules and pisoliths, removal of nodules, and formation of cavities suggest destruction of duricrust and the associated weathering profile. A subsequent shift in climatic regime from warm humid conditions of the Neogene period to hot arid conditions of the present resulted in a change in the weathering processes from ferricretization to calcretization. In all, three phases of calcretization are superimposed on the dissected ferricrete profiles.

Keywords: ferricrete, calcrete, micromorphology, inversion of relief, Thar Desert

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