Triassic paleosol catenas associated with a salt-withdrawal minibasin in southeastern Utah, U.S.A.

Abstract

Catenas for lithified paleosols have been rarely described in the literature because they are seldom preserved and, where present, are difficult to trace laterally. This study focuses on paleocatenas associated with a Triassic salt-withdrawal minibasin (rim syncline). The catenary surfaces formed during an episode of pro-longed landscape stability along a margin of a salt-withdrawal minibasin and were identified by a series of continuous, high-resolution photopanoramas of canyon outcrops. The paleocatenas had paleoslopes of ∼1%, and were laterally extensive over distances ranging from ∼2.8 to ∼7.9 km. Paleocatenas within the Chinle are associated with lateral taxonomic differences in paleosol morphology. A paleocatena formed on the upper boundary of the lower Chinle has well-drained alfisols on its upper slopes and a poorly drained, over-thickened inceptisol at the toe of the slope. A second paleocatena documented within the upper Chinle includes inceptisols with carbonate nodules characterized by thick paleosols on upper slopes and thin paleosols at the toe slope. Solum thickness, horizon thickness, color, and profile development index (PDI) values were evaluated relative to slope position. Solum thickness, E horizon thickness, Bt horizon thickness, and PDI values have relatively robust covariance to slope position, which suggests that they were influenced by pedotopographic factors. The Bw horizon thickness, Bk horizon thickness, and BC horizon thickness have less robust correlation to slope, and may instead, reflect the influence of other soil forming factors. Both paleocatenas were probably unstable, a conclusion supported by evidence for downslope sediment movement. Upper-slope paleosols have truncated surfaces whereas toe-slope paleosols were either buried or over thickened due to cumulic aggradation. Soil development along the paleocatenas was influenced primarily by erosion, deposition and soil-moisture processes, similar to modern catenas. Thus, landscapes associated with these salt tectonic features significantly influenced paleosol morphology in the Chinle.