Cahuachi, the largest adobe ceremonial site in the world, is located on the coastal desert of Peru (Nasca Province), one of the driest zone of the Earth. It was the main centre of the Nasca culture (Orefici, 2012). In the nineties, an hypothesis of destruction of the site due to a Mega-El Niño event, based on a geological reconstruction, was proposed by Grodzicki (1990). Although some questions arose among the scientific community about this catastrophic interpretation (Bonavia, 1995), such a hypothesis finally led to believe that Cahuachi was covered by a huge flood that would have deposited conglomerates even on top of the highest buildings. A stratigraphic section was measured in correspondence of the bedrock of the "Pirámide Sur" at Cahuachi. The section consist of mudstones, siltstones, sandstones and conglomerates. Our sedimentologic and petrographic studies clearly allow us to correlate the whole sedimentary deposits to the local geology, as defined by Montoya et al. (1994). The investigated succession can be referred to the Changuillo Formation having an Upper Pliocene-Lower Pleistocene age (Montoya et al., 1994) rather than to the Holocene alluvial terraces (Grodzicki, 1990). The conglomerate deposits at the top of the section could be also interpreted as a lateral facies of the base of Canete Formation and unequivocally underlie the ceremonial buildings. Most likely, Grodzicki and his collaborators had not good exposures of the bedrock and interpreted these deposits as a recent alluvial terrace, also following a subjective aerial photo interpretation (Ostaficzuk, 1990). The epistemological implications of the geological interpretations are evident. The hydrogeological hazard assessed at Cahuachi (e.g. the occurrence of huaycos, debris flows triggered by extreme rain events) and the intense local earthquake activity are consistent with the influence of hydrological and seismic damages on the decline of the Nasca culture as asserted by Orefici (2012). However, the geological observation allow us to overcome the paradigm of the Nasca culture destruction due to a Mega-El Niño event.
Overcoming the paradigm of the destruction of Nasca culture due to a Mega-El Niño event: a clue from the stratigraphic survey at Cahuachi (Peru)
Marco Delle Rose;
2014
Abstract
Cahuachi, the largest adobe ceremonial site in the world, is located on the coastal desert of Peru (Nasca Province), one of the driest zone of the Earth. It was the main centre of the Nasca culture (Orefici, 2012). In the nineties, an hypothesis of destruction of the site due to a Mega-El Niño event, based on a geological reconstruction, was proposed by Grodzicki (1990). Although some questions arose among the scientific community about this catastrophic interpretation (Bonavia, 1995), such a hypothesis finally led to believe that Cahuachi was covered by a huge flood that would have deposited conglomerates even on top of the highest buildings. A stratigraphic section was measured in correspondence of the bedrock of the "Pirámide Sur" at Cahuachi. The section consist of mudstones, siltstones, sandstones and conglomerates. Our sedimentologic and petrographic studies clearly allow us to correlate the whole sedimentary deposits to the local geology, as defined by Montoya et al. (1994). The investigated succession can be referred to the Changuillo Formation having an Upper Pliocene-Lower Pleistocene age (Montoya et al., 1994) rather than to the Holocene alluvial terraces (Grodzicki, 1990). The conglomerate deposits at the top of the section could be also interpreted as a lateral facies of the base of Canete Formation and unequivocally underlie the ceremonial buildings. Most likely, Grodzicki and his collaborators had not good exposures of the bedrock and interpreted these deposits as a recent alluvial terrace, also following a subjective aerial photo interpretation (Ostaficzuk, 1990). The epistemological implications of the geological interpretations are evident. The hydrogeological hazard assessed at Cahuachi (e.g. the occurrence of huaycos, debris flows triggered by extreme rain events) and the intense local earthquake activity are consistent with the influence of hydrological and seismic damages on the decline of the Nasca culture as asserted by Orefici (2012). However, the geological observation allow us to overcome the paradigm of the Nasca culture destruction due to a Mega-El Niño event.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
