Stratigraphy, Petrography and Grain-Size of Sedimentary Lithologies at Cahuachi (South Peru): ENSO-Related Deposits or a Common Regional Succession?

Several central Andean pre-Columbian sites struck by hydrogeological disasters due to El Niño-Southern Oscillation (ENSO) events are reported in the literature. The mainstream explanation for the decline and demise of Cahuachi (pampa of Nazca, south Peru) implies the damage and burial of such a ceremonial center as a consequence of two catastrophic river floods, which occurred around 600 CE and 1000 CE, respectively. Therefore, geological studies at Cahuachi are mandatory with regard to both the correlations of ENSO-related deposits ("event-strata") among different Peruvian sites and the assessment of the millennium-scale climate variability. In particular, the latter is crucial to evaluate the environmental and economic consequences due to the incoming fluctuations of ENSO. In this paper, stratigraphic, grain-size distribution, and petrographic investigations on a sedimentary section exposed close to one of the main temples of Cahuachi are reported. They represent the first test for the current mainstream explanation. The preliminary finding indicates that the studied stratigraphic interval may belong to the common regional succession of the pampa of Nazca rather than the ENSO-related deposits described in the literature. However, further geological research will be necessary to unravel this issue in more detail.