Impact of Parent Sediments on Soil Salinity and Gypsum Accumulation along the Rio Grande in Presidio County, Texas

Gypsiferous, saline lacustrine deposits of Late Tertiary-Quaternary age are associated with ancestral basins along the Rio Grande Rift, subsequently breached with development of the Rio Grande drainage. In the Presidio Bolson in Presidio County, soils formed in these clayey lacustrine parent sediments (Changas soils) have both high electrical conductivity (EC) and gypsum content. Soils formed in sediments derived from these lacustrine deposits and deposited on alluvial flats (Melado soils) inherit the high salinity, but lower gypsum content, than the present in the parent materials. Low salt and gypsum accumulations have been observed in soils that formed in these sediments on low gravelly stream terraces (Fancho soils). Soil salinity that is increasing on the Rio Grande flood plain is likely (at least in part) related to salinity inherited from these gypsiferous, saline lacustrine deposits.