Aminostratigraphy of Peruvian and Chilean Quaternary marine terraces

Abstract

Amino acid enantiomeric ratio ( d l ) data for over 200 molluscs from Pleistocene marine terraces on the coast of Peru and Chile are reported. They are used to evaluate the utility of this dating method for terraces in this region. Analyzed samples represent both local relative age sequences and regionally-correlative deposits identified over a broad latitude range (14–31°S). Aminozones are defined on the basis of data for Protothaca, supplemented with results for Mulinia and other genera. Electron spin resonance (ESR) data serve to calibrate two aminozones from Peru (ca. 15°S) as being correlative with Oxygen Isotope Stages 5 and 7 of the marine isotope record. The latitudinal trends of enantiomeric ratios for Stage 5 samples, plotted against current mean annual temperature (CMAT), are similar to those observed for Protothaca from the North American Pacific coast. The sea level record preserved in the Peru-Chile terraces is complex and usually not clearly resolved geomorphically. Typical uplift rates of 0.1–0.2 m/ka are inferred from terrace age and elevation data, with higher rates being observed where the Nazca Ridge is being subducted beneath the coast at about 15°S. Evidence of terrace reoccupation by sea levels with substantially different ages is found at several sites of apparent low uplift.