| Tectonic uplift, sea level fluctuations, and local geomorphic conditions have controlled development of emerged marine terraces on the Paracas Block in southern Peru. Terraces extend up to 330 m above sea level on 23 transects between 13.5{dollar}spcirc{dollar} and 17.73{dollar}spcirc{dollar} S. latitude. Because of the arid climate, mollusk shells in the marine cover strata are exceptionally well preserved and provide datable samples for a terrace and sea level chronology.; Amino acid racemization was the most extensively used dating method, with three other numerical dating methods, electron spin resonance (ESR), Uranium-series, and radiocarbon ages used to calibrate the amino acid ages. D-alloisoleucine/L-isoleucine (A/I) ratios of {dollar}>{dollar}200 mollusks shells belong to six statistically and geomorphically defined aminozones. Aminozone IIa correlates with the last Interglacial (deep-sea oxygen isotope Stage 5e) based on 12 ESR ages and the similarity of the IIa ratios to those determined from calibrated last Interglacial sites on the Pacific Coast, U.S. Calibrated amino acid ages for the other aminozones are; I = {dollar}>{dollar}45,000 yr B.P. and {dollar}leq{dollar} 87,000; IIb = 211,000 yr B.P.; III = 297,000 yr B.P.; IV = 496,000 yr B.P.; and V {dollar}geq{dollar} 945,000 yr B.P. The calibrated ages agree with ESR, Uranium series, and radioactive ages.; On segments of the Peruvian coast where uplift rates have been {dollar}leq{dollar}0.3 m/1000 yr, strata of aminozones IIa, IIb, and occasionally III are found on a single, broad terrace at about 30 m. The aminozone IIa, IIb, and III marine terraces are only well resolved at 15.2{dollar}spcirc{dollar} S. latitude where the uplift rate is 0.47 m/1000 yr.; The pattern of terrace deformation can be approximated by a simple geometric model in which the subconducting Nazca Ridge migrates obliquely southeastward as a rigid trapezoid beneath the forearc. The model correctly predicts a pattern of marine terrace deformation with the highest elevations located above the southern flank of the Nazca Ridge and subsidence above the northern flank. The topography, pattern of marine terrace deformation, and Quaternary rates of uplift of the Paracas Block are determined by oblique subduction of the aseismic Nazca Ridge. |
