GSA Connects 2021 in Portland, Oregon

Paper No. 20-2
Presentation Time: 8:20 AM


BEACH, Sheryl, University of Texas at Austin Geography RLP 3.306, 305 Deloss Dodds Way, Austin, TX 78712-1804, BEACH, Tim, Department of Geography and the Environment, The University of Texas at Austin, Austin, TX 78712, DOYLE, Colin, Department of Geography and the Environment, University of Texas at Austin, Austin, TX 78712, KRAUSE, Samantha Marie, Texas State University, Geography, 601 University Dr, San Marcos, TX 78666-4684 and SMITH, Byron, Department of Geography, University of Texas at Austin, Austin, TX 78712

There exists a growing corpus of carbon isotope ratios from soil profiles of the tropical forests of the Maya Lowlands. This research first started with investigations on the agricultural terraces at the Maya site of Caracol to understand if they provided evidence for C4 plants, i.e. maize, production in antiquity. This paper will review the techniques, general findings, and potential pitfalls of the carbon isotope records from multiple sites. First, we consider sample preparation such as the use of the humin fraction versus acid fumigated soil organic matter. Second, we consider a typology of soil environments including sinkholes, floodplains, wetland fields, agricultural terraces, and slope toposequences. Third, we present a range of AMS-dated carbon isotopic profiles from sequences that have evidence of past C4 species. These include profiles from areas with pollen or phytolith evidence for maize and grasses dated to ancient Maya times or have contemporary evidence of modern pastures or crops with topical C4 grasses like sugarcane. Then we compare these with carbon isotopic profiles that appear to have no evidence of past C4 species influences on the soil organic matter such as from old growth forests. Finally, we present an assessment of the strengths and weaknesses of carbon isotopes as proxies in soils archaeological work in these tropical lowlands.