LAMINATED SEDIMENTS ASSOCIATED WITH ARCHAEOLOGICAL STRUCTURES IN NORTH COASTAL PERU: A RECORD OF PREHISTORIC EL NIÑO ACTIVITY

Proxy records for El Niño should be located in areas where the impacts of ENSO are most direct and least equivocal, such as in the eastern, tropical Pacific. Linear archaeological structures (e.g., canals and walls) located in hyperarid north-coastal Peru cross ephemeral streams that flow only during El Niño events. These archaeological structures impede runoff and produce laminated sediments that can serve as proxy records for past El Niño activity. Preliminary excavations of ponded sediments associated with the A.D. 1160 Moche-Chicama Intervalley Canal at Quebrada del Oso (7° 50' S. lat.) revealed a sequence of 33 graded fine sand and silty deposits formed by El Niño rainfall and runoff. Combined ¹⁴C and ¹³⁷Cs dating of stratigraphy indicates that the runoff frequency varied from one per ~22 years (A.D. 1160-1660) to one per ~41 years (A.D. 1660-1950) to one per ~16 years (1950-2000). These results support other proxy evidence of changing ENSO activity during the late Holocene including increased El Niño frequency during the late 20th century. Laminated sediments associated with linear archaeological features in the Peruvian Desert provide a more complete record of past El Niño activity than overbank flood deposits associated with rivers and can be used to assess the spatial and temporal variability of El Niño flooding in Peru over the last ~4000 years.