BURIED SOILS AND WETLAND–AGRICULTURE INTERACTIONS WITHIN THE RIO BRAVO FLOODPLAIN OF NORTHWEST BELIZE

This paper compares two distinct wetland soil sequences along the carbonate rich Rio Bravo floodplain of northwest Belize. Here we focus on the lower basin that is seasonally saturated in gypsum and compare it to the gypsum restricted upper basin. Our interests center on how these soils developed incongruently of one another and how those distinct geochemical environments affected human use along this floodplain. We present soil evidence from excavations and cores near the ancient Maya settlements of Gran Cacao and Chawak But’o’ob that reveals soils buried underneath ancient architecture. What makes these regions significant is their history of wetland field cultivation and geochemical divergence. To characterize floodplain stratigraphy, we analyzed particle size distributions to determine soil texture; X-Ray Fluorescence (XRF) to quantify the soil’s elemental composition; loss on ignition (LOI) to measure for the presence of organics and carbonates; carbon isotopes to estimate relative amounts of C₄ and C₃ species; magnetic susceptibility to estimate ferric iron (Fe) inputs; and accelerated mass spectroscopy (AMS) for chronology. The resulting investigation uncovered depositional sequences in both regions with paleosols of varying ages that extend as far back as 2,340 BP. Our findings also indicate differential sedimentation rates along the floodplain that likely reflect environmental and land use contributions. Together, these data allow us to compare geochemical and anthropogenic factors of soil formation within zones of ancient, intensive, indigenous cultivation.