T315 Deciphering Climate Change and Climate Variability in the Geologic Record Using Palaeosols, Loess, Palaeoweathering Profiles, Pedosedimentary Sequences, and Polygenetic Soils: Their Applications and Limitations as Terrestrial Proxies in Understanding Impacts of Climatic Changes

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Skagit 3

INFLUENCES OF MODERN PEDOGENESIS ON PALEOCLIMATE ESTIMATES FROM PENNSYLVANIAN AND PERMIAN PALEOSOLS, SOUTHEAST OHIO

Paper number: T315-5
Program: Technical Sessions
Time: 9:00 AM – 9:15 AM

Authors

Abstract

Exposed paleosols are subject to modern pedogenic processes which are expected to alter paleosol chemistry and subsequent paleoclimate estimates to reflect conditions at the time of exposure rather than the time of formation. Although paleosol geochemistry is widely used in paleoclimatic reconstruction, current research typically does not address the influence of modern weathering. Understanding the degree that paleosol geochemistry is affected by modern pedogenesis will lead to improved sampling methodologies and correction factors for use in future research.

Pennsylvanian and Permian paleoVertisols and paleoInceptisols with known durations of exposure were described and sampled from five roadcuts in southeast Ohio. For each paleosol, samples were collected from identified cambic and argillic horizons through excavation and coring at depths of 0, 25, 50, 100, and 150 cm from the outcrop surface. Two series of samples were taken 6-9 m apart from each paleosol to account for lateral variation. Each type of paleosol was sampled from the top and base of the roadcut to account for variation due to slope position. A total of 176 40g samples were analyzed for major oxide concentrations (Ca, Fe, K, Mg, Na, Al, Si, Mn, P, Ti) using X-ray fluorescence. These data were used to calculate molecular weathering ratios including hydrolysis, leaching, lessivage, calcification, salinization, and chemical index of alteration excluding potash (CIA-K). Salinization ratio and CIA-K were used to estimate paleotemperature (MAT) and paleoprecipitation (MAP). For paleoVertisols, percent CaO, coefficient of linear extensibility (COLE), cation exchange capacity (CEC), and pH were also calculated and CALMAG was used to estimate MAP.

Preliminary results suggest that depth from outcrop surface affects bulk geochemistry; however, the effect is oxide dependant. Despite attempts to exclude calcareous paleosols from sampling, Ca was the most variable. Ratios including sum of bases, CIA-K, Ca/Ti, percent CaO, COLE, CEC, and MAP by CIA-K and CALMAG also varied, likely due to Ca being a component of each ratio. Fe and Mn also varied with depth, likely due to the presence of microconcretions. Concentrations of other oxides as well as pH and MAT were consistent with depth. Samples taken from more lithified paleosols had less variability with depth.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302577

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