126-3 Connecting Highlands to Coast in the Peruvian Andes: Climate Impacts on the Transport of Water and Sediment to Support Lowland Agriculture

Session: Geoarchaeology of Sites to Landscapes: Current Research on Long-Term Water and Soil Management and Maladaptation, Part II

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Abstract:

The Chicama Valley of northern coastal Peru is a fertile agrarian region in an otherwise hyperarid landscape. For thousands of years, human communities have occupied and shaped this environment, arriving as maritime foragers and adopting raised-field agriculture before later evolving into state-level societies dependent on irrigated floodplain agriculture. The emergence and expansion of these arable landscapes were directly tied to sediment availability and distribution from the Chicama River basin. Around 7.5 ka, rising sea levels formed lagoons in the littoral zone, which were later infilled by river-derived silts, locally expanding cultivable land along the coast. A major shift occurred around 3.8 ka, as increased ENSO activity delivered greater hydrologic input, triggering increased sediment mobilization and increasingly rapid aggradation of the lower valley floodplain. This transformation required the convergence of geomorphic and climatic factors. Fine-grained sediments sourced from mudstone- and sandstone-rich lithologies in the upper catchment were mobilized downslope and deposited in the lower valley. As sea level stabilized and a more permanent shoreface developed, sediment retention at the coast improved. Wetlands further slowed floodwaters, enhancing silt deposition. The extensive anthropogenic canal systems that irrigated the floodplain also facilitated the lateral distribution and reworking of flood-deposited silts to sustain and expand the arable landscape.

This project investigates how sediment transfer from upland to coastal zones shaped the development of arable landscapes and early state-level societies. Field-based sedimentological and geochemical analyses of sink and transfer zone deposits are being used to reconstruct the source-to-sink system and evaluate the role of environmental and anthropogenic drivers in sediment flux and storage. The Chicama Valley provides a compelling case study of the long-term sustainability of human-environment interaction in a dynamic, arid setting. Its history of land use and resilience to climatic perturbations, particularly El Niño-driven rainfall, offers valuable lessons for modern agricultural planning, and climate adaptation strategies in similarly vulnerable regions.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8264

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