Upper Cretaceous (Maastrichtian) paleosols in Trans-Pecos Texas

Fluvial flood-plain deposits of the upper Aguja, Javelina, and El Picacho Formations in Brewster and Presidio Counties of West Texas record multiple episodes of soilformation during Late Cretaceous (Maastrichtian) time. These well-differentiated alluvial paleosols are characterized by pale gray leached (albic) A horizons and purple or red, clay- and iron oxide-enriched (cambic, argillic) B horizons. These characteristics indicate that podzolization and lessivage were important pedogenic processes and suggest that these paleosols are comparable to some modern Al-fisols. Texturally diverse accumulations of calcite nodules, coalesced masses of nodules, rhizocretions, and thin discontinuous hard-pans indicate that calichification also occurred. The compound paleosols thus formed indicate that the Maastrichtian climate in this region may have fluctuated between regimes of humid and semiarid character, each at least several thousand years in duration. -from Author