GSA Connects 2021 in Portland, Oregon

Paper No. 20-8
Presentation Time: 9:50 AM


BEACH, Tim1, DOYLE, Colin2, SMITH, Byron1 and BEACH, Sheryl3, (1)Department of Geography and the Environment, University of Texas at Austin, 305 E. 23rd Street, Austin, TX 78712, (2)Department of Geography and the Environment, University of Texas at Austin, Austin, TX 78712, (3)University of Texas at AustinGeography RLP 3.306, 305 Deloss Dodds Way, Austin, TX 78712-1804

Because pollen does not usually preserve in tropical soils, soils are tricky to date, and other fossil lines of evidence often have equivocal evidence for ancient Maya land use, scientists have measured carbon isotopic ratios of soil organic matter to understand vegetative profile changes between C4 and C3 species. We now have studies that have examined profile shifts in many types of soil environments from ancient to modern agricultural terraces to floodplains and wetland fields. Here we present synthesized and new evidence from three wetland field complexes in the floodplains of the Rio Bravo near the ancient Maya sites of Birds of Paradise, Chawak But’o’Ob, and Wari Camp. All of these soil profiles have AMS dating from charcoal through the sequences that helps constrain the timing of these changes in vegetation of the floodplain. The Birds of Paradise is a well-studied wetland complex, which we synthesize to compare with these more recently analyzed wetland fields. Stable carbon isotope sequences of these ancient wetland field sites reveal shifts to more C4 dominated organic matter during Maya occupation both in the pre-raised field floodplain as well as in the raised fields. These sites are likely to indicate locations where intensive Maize agriculture persisted long enough to shift the stable carbon isotope signature of the soil organic matter. We discuss these shifts and their possible equifinalities and complexities.