2022 KIRK BRYAN AWARD: THE EKLU’UM PALEOSOL, GROUNDWATER, AND CLIMATE: MULTIPROXY MODELS OF ANCIENT MAYA WETLAND FIELD FORMATION IN THE MAYA LANDS (Invited Presentation)

This paper is the 2022 Kirk Bryan Award Lecture for the Quaternary Geology & Geomorphology Division. Kirk Bryan was a research leader exploring human interactions in geomorphology, climate impacts, and geoarchaeology, especially of arid lands. This paper builds on these foundations but in tropical wetlands. Wetland farming systems developed around the world near coasts and wetlands that stabilized with sea levels in the Mid-Holocene. Within the Maya world these manifest as fields that rise ~1 meter above canals in cobwebs and grid-like patterns. Scientists have been studying this patterned ground since the 1960s. This work led to different interpretations about formation and chronology, which we present in five conceptual models based on multiple lines of evidence. First, model 1 arose from historical and ethnographic information from ‘chinampas’ in the Basin of Mexico and was applied to field islands in the Maya tropical lowlands theorized as an intensive subsistence strategy for high Maya Classic (1700 to 1100 BP) populations. Researchers at this time were mindful of natural processes that might explain these patterns such as gilgai and discovered the mid-Holocene Eklu’um Paleosol with deep hand cores. Second, deeper excavations, vibracoring, and water-pumping revealed the widespread paleosol that the Preclassic Maya (4000 to 1700 BP) ditched and farmed. Model 2 argued wetland farming became untenable in the Maya Classic with higher water tables and erosion-induced aggradation and gypsum accumulation that raised the fields via gypsum precipitation in the root zones that also made soils infertile. A third model from 20-50 km farther from the coast and ~5 meters higher in elevation provides a compromise with continued farming into the Late Classic like Model 1 and similar high gypsum levels like Model 2. A fourth model based on recent work has indicated that farming and intensive uses of the field systems continued well into the Maya Postclassic (600 BP), perhaps as oases through the Maya droughts of 1200-900 BP. The fifth model extends models 2 and 3 and argues that gypsum precipitation elevated fields or tree islands by transpiration inducing more groundwater flow to the fields during the Maya droughts, thus creating a climate change-induced landform. We evaluate these models through multiple lines of geological and archaeological evidence.