Quaternary marine terraces, sea-level changes and uplift history of Patagonia, Argentina: comparisons with predictions of the ICE-4G (VM2) model of the global process of glacial isostatic adjustment

Abstract

Quaternary marine terraces have been investigated along a 1000 km stretch of the coast of Argentinian Patagonia. Fossil mollusc shells, most in living position and collected from raised beaches, were dated using the U-series, ESR and 14 C methods. Our analyses show that Holocene sea-level in this region culminated 7000 to 8000 BP at 6–7 m amsl. This beach slightly increases in altitude southward. The last interglacial stage (5e) was identified at 16–17 m amsl whereas the highest and morphologically most distinctive radiometrically dated terrace at 250,000 to 330,000 BP exists at an elevation of 33–35 m amsl. We estimate a constant rate of tectonic uplift of 0.09 m/1000 yr since the middle Pleistocene. Using this estimate of the local rate of tectonic uplift we correct relative sea-level (r.s.l) observations for the Holocene epoch. In turn, the inferred Holocene sea-level histories are compared with those predicted using the ICE-4G (VM2) model of the global process of glacial isostatic adjustment. This model accurately predicts r.s.l history from all sites along the northern part of the east coast of the South American continent (Venezuela, Brazil). However, along the southern part of the coast of Argentinian Patagonia there is evidence of an influence that is not accurately represented in this version of the model of the global process of glacial isostatic adjustment. We suggest that this influence could be connected to the presence of the broad continental shelf that is located offshore of this region, but the influence of significant neotectonic uplift cannot be dismissed.