In the dry corridor of Central Nicaragua lies an extraordinary archaeological site: more than 372 rocky mounds shaped into semicircles and likely built from 300 A.D. onwards. Over the past few years, archaeologists from Leiden University have mapped these mounds. However, their stratigraphy remained unknown. To address this, Dita Auzina (project-leading archaeologist, Leiden) invited geoarchaeologists from AMGC to investigate twenty of them.
Excavation revealed at least three distinct construction phases, challenging the idea that the mounds were built in a single episode. These phases are characterized by layers of poorly sorted pinkish rhyolite , capped by weathered, whitish rhyolite. At the landscape level, this may have created patterns of whitish mounds visible from higher elevations in the past.
The mounds were built over an ancient surface, burying clayey dark soils rich in ceramics, lithics, and metates beneath volcanic deposits (tephra). The parent material of these soils is the same rhyolite found as construction material for the mounds, suggesting that the stone sources were likely located nearby. Further soil micromorphology and geochemistry will better explain the environmental changes and human agency in constructing monumentality in Nicaragua.
Furthermore, the OSL profiling generally mirrored the construction phases identified in the soil and stones stratigraphy but showed marked differences between some mounds. Since luminescence signals are the result not only of age but also of sediment mineralogy and texture, no absolute chronological picture can be painted yet. However, the results indicate that the history of the mounds is neither simple nor uniform. This will be further illuminated once the profiling results are combined with the laboratory OSL dating results.
Axel Cerón González, Ella Egberts, and Dita Auzina