EFFECTS OF MARINE HYDROMORPHISM FROM PALEOVERTISOLS IN THE PENNINGTON FORMATION (UPPER MISS.), EAST-CENTRAL TENNESSEE

Interpreting geochemical climate proxy estimates for paleoVertisols underlying marine rocks is complicated by the potential for overprinting as paleosols contact marine water as sea level rises. Understanding the basis of each proxy and how soil chemistry is affected by marine water allows for improved critical interpretation of proxy results. Coastal-margin soils experiencing marine inundation may become enriched in base cations and depleted in redox-sensitive metals and trace metals at the soil surface. Based on this, we hypothesized that (1) geochemical overprinting due to marine hydromorphism will be detectable in paleoVertisols, and (2) paleoclimate proxies based on paleosol B-horizons will underestimate mean annual precipitation (MAP) and overestimate mean annual temperature (MAT).

A mass-balance approach identified additions and losses of major oxides with depth in four paleoVertisols from the Pennington Fm. (Upper Miss.) that underly marine-brackish rocks. MAT (PPM1.0 and salinization ratio) and MAP (CIA-K, CALMAG, PPM1.0, and RFMAP) were calculated for each profile and superjacent marine rocks. Patterns of enrichment differed based on overlying sediment composition, degree of profile development, and laterally between replicates of a single paleosol. Horizons with extensive pedogenic carbonate or carbonate cements were geochemically distinct, though less so than the marine units. Well-developed paleoVertisols beneath dolomicrite were enriched in base cations and manganese at the surface; but this pattern was less evident in composite profiles or in paleoVertisols beneath clastic siltstone. MAP increased with depth in paleoVertisols underlying dolomicrite, but remained relatively consistent in other profiles. When applied to marine units, MAP proxies did not agree (PPM1.0 overestimated MAP, others underestimated versus the paleosol surface). MAT estimates were highest in marine units, but a corresponding increase in MAT in the upper paleosol profile was not always observed; RFMAP appeared to be more sensitive to geochemical variability within a profile than the salinization ratio.

These results indicate that paleosol researchers must consider marine hydromorphism in paleoclimate studies of coastal-margin paleosols.