CHARACTERIZATION OF TRACE ELEMENTS IN MISSISSIPPIAN PENNINGTON FORMATION PALEOSOLS AT POUND GAP, KY: A NEW PALEOCLIMATE INDICATOR?

Paleoclimate studies rarely use trace elements in paleosols as a proxy record, and instead mainly focus upon molecular ratios based on major elements (K, Ca, Mg, Si, Al) and or stable isotopes of C and O measured in calcite, Fe-oxides, and sphaerosiderite. Here we provide data from the Pennington Fm. (Upper Miss., Chesterian) paleosols, which demonstrate temporal patterns of changes in trace element concentrations possibly useful as a new tool for paleoclimate interpretation. We infer Late Miss., high-frequency climate change based on field observation, micromorphologic description, and bulk geochemical analysis of over 30 paleosols exposed in 280 m of outcrop section. Paleoprecipitation estimates (employing the chemical index of alteration minus potassium (CIA-K) proxy) range from 519-1331 mm/yr, and increase generally up-section, but with cyclical fluctuations (200-400 mm) approaching the Miss.-Penn. Boundary. Paleoclimate generally fluctuated between wetter and drier conditions, as evidenced by poorly drained/gleyed paleo-Vertisols, -Entisols, and –Histosols formed during wetter conditions, and reddened, calcic paleo-Vertisols and –Alfisols developed during drier conditions. Concentrations of many trace elements appear related to degree of chemical weathering, assuming no change in parent materials and negligible change in texture. Rare-earth elements Ce and La exhibit a coupled trend with their highest concentrations associated with well-drained paleo-Vertisols (MAP = 1290 mm) and –Entisols (MAP = 1390 mm) and lowest concentrations coinciding with poorly drained paleo-Histosols (identified by an A-horizon/coal) -Entisols and -Vertisols. Other “immobile” trace elements (Ga, Ge, Hf, Nb, and Ta) also display tightly coupled trends with like associations. Chemical weathering rates are retarded during deposition of poorly drained/gleyed soils, most particularly Histosols, and conversely those rates would increase with wetter, well-developed and better-drained paleo-Vertisols and -Alfisols. Trace elements can be utilized as a paleoclimate indicator for deep-time climate studies, when used in association with other paleosol climate proxies.