Unique Soil and Landform Features On the Edwards Plateau of Central Texas.

The Edwards Plateau in Central and Western Texas is a unique landform constructed of Cretaceous-age limestone bedrocks that features unique soil and geomorphic attributes.  It has garnered research of numerous geoscientists interested in differentiating pedogenic from lithogenic carbonates, construction of soil climosequences, synthesis of calcic and petrocalcic horizons, contribution of dusts to pedogenesis, dye tracers to monitor water transport, aquitards in soil and limestone bedrock systems, and environmental implications of on-site wastewater effluent applications. In the Edwards Plateau proper there are many “terra rosa-like” soils in which their thickness and mineralogy belie formation directly from subjacent limestone residua. Likewise, evidence of major aeolian contributions to these soils is wanting. They likely formed, partially or in total, from limestone weathering residua derived from superjacent limestone bedrocks. Petrocalcic horizons on bedrock surfaces formed directly from in situ short-range dissolution/re-precipitation transformations of unweathered fossiliferous limestone. Hydraulic discontinuities within sediments at the bedrock interface also favor genesis of calcic and petrocalcic horizons.  These processes are perhaps augmented by microorganism activity. In the Hill Country of Central Texas bordering the Edwards Plateau along the Balcones Escarpment, weathering and erosion of limestone bedrocks of differing physical, chemical, and mineralogical stability result in stair-stepped hillslopes with riser and tread microtopographic couplets.  These microtopographic elements (micro terrain units) yield striking differences in soil depth, soil/geomorphic processes, and function over a scale of meters. Soil distribution patterns, soil development, biogeochemical properties, and hydrological function are locally bedrock-controlled by riser and tread repeating microtopographic units (risers typically are 1-2 m high and treads 10-20 m long).  Numerous misnomers about soil quality, geomorphic stability, hydrology, and environmental implications have been uncovered by recent research on soils of these stepped terrains.