Abstract: Mineralogic and Physical Properties of Gulf Coast Limestone Soils

Wayne C. Isphording

The weathering of Cretaceous and Tertiary limestones in the Gulf coastal plain has produced a residual weathering product unlike that found developed on all other rock types. Though much has been written about the processes that act to break down igneous, sedimentary, and metamorphic rocks when they are exposed to surface weathering, an apparent gap remains when limestones, alone, are considered. Because these rocks characteristically form in marine areas not receiving an abundant contribution of detrital materials, and because they are highly susceptible to chemical attack by meteoric and ground waters, the residual soils that form from their weathering tend to be thin and possess a mineralogy that is highly dependent on the trace constituents in the original limestone p rent rock. This imposes a somewhat more "controlled" mineralogy for the soils and also results in their having certain physical and mechanical properties that differ from those of soils formed by the weathering of other rock types.

A study has been made of the mineralogic and physical properties of soils developed on limestones from two areas in the Gulf coastal plain: (1) the massive limestone platform that extends northward from the Chiapas Laramide deformation belt of Central America (the Yucatan Peninsula), and (2) the Tertiary and Cretaceous limestones of the Alabama coastal plain. The former constitutes the largest area of Cenozoic-age carbonate rock exposed anywhere in the Gulf Coast and further has the unique property of lacking any interbedded detrital sedimentary rocks that could superimpose their characteristics on the resulting residual soils. The Alabama coastal plain limestones are similarly important, for the weathering of these strata has given rise to the economically important soils that now co er the region known as the "black belt."

AAPG Search and Discovery Article #90965©1978 GCAGS and GC Section SEPM, New Orleans, Louisiana