Wednesday, November 15, 2006 - 9:15 AM

Micromorphology and Stable Isotope Investigation of Lacustrine Petrocalcic Horizons on the Southern High Plains of Texas and New Mexico.

Dusten Russell, Wayne Hudnall, and B.L. Allen. Texas Tech Univ, Lubbock, TX 79409

Petrographic analyses and δ18O and δ13C isotope were used in the investigation of depositional and pedogenic processes of lacustrine petrocalcic horizons on the Southern High Plains, which existed during late Pliocene to early Pleistocene. These petrocalcic horizons are multideveloped with varying degrees of laminae and pisolitic characteristics. Macromorphology and micromorphology of the petrocalcic horizons show extensive influence of pedogenic processes.
Petrographic analysis show unique spheroids of dolomite inherited from lithogenic precipitation weathering into calcite. Relic bedding plains observed within the thin sections of the petrocalcic horizons influences the multiple processes inherited during the development. Isotopic values from the soil carbonate were used as identifiers of carbon whether derived from the atmosphere or from photosynthetic process of plants.  Isotopes have also been used to identify climatic conditions and depositional processes for soils.  δ13C values confirm pedogenic processes were operative within the petrocalcic horizons. δ18O values suggest that during the formation of the  lacustrine sediments climatic conditions were relatively uniform and similar to that of present day, although there remains the possibility of more recent overprinting.