PALEOENVIRONMENTAL RECONSTRUCTIONS FROM THE PENNSYLVANIAN-PERMIAN ABO AND BURSUM FORMATIONS IN NEW MEXICO USING STABLE ISOTOPIC GEOCHEMISTRY OF PALEOSOLS

Comparison of current atmospheric CO₂ concentrations to pre-historical values preserved in ice cores reveals that modern values have not occurred in the past 800,000 years, with increasing rates of change in recent times that have no documented equivalent in the geological record. Yet, paleoclimate reconstructions from various periods of geological history have served to inform climate change through analog studies. In particular, the Pennsylvanian-Permian transition, a time associated with global environmental change, serves as the only analogous icehouse to greenhouse transition on a vegetated world, and as such, may be useful in predicting future climate change and corresponding floral and faunal changes. To that end, we present analyses of Pennsylvanian-Permian paleosols in order to estimate paleoenvironmental changes during the time of their formation. In particular, paleosols with pedogenic calcite (i.e., Calcisols, vertic Calcisols, calcic Vertisols) are used to reconstruct concentrations of CO₂ (pCO₂) and mean annual precipitation (MAP) from the Pennsylvanian-Permian Bursum and Abo Formations near Socorro, NM. Stable carbon values of calcite from the Bursum and Abo formations range from -7.9‰ to -3.6‰ and -7.5‰ to -4.5%, respectively. Organic matter co-existing with paleosol carbonate in the Bursum and Abo formations ranges from -26.0‰ to -23.6‰ and -25.5‰ to -24.7‰, respectively. These isotope values correspond to pCO₂ levels that ranged from 1017 to 4377ppmV for the Pennsylvanian Bursum Formation, which increased in the Permian to 1254 to 8695 ppmV during deposition of the Abo Formation. MAP was calculated from co-existing calcite and organic materials and ranged from 19.6 cm/yr to 26.6 cm/yr in the Bursum Formation and between 14.7cm/yr to 23.2cm/yr in the Abo Formation. These interpretations from the carbon isotope values from calcite and organic matter suggest a more nuanced climate story in paratropical region paleoenvironments throughout the Pennsylvanian-Permian climate transition.