Low uplift rates and terrace reoccupation inferred from mollusk aminostratigraphy, Coquimbo Bay area, Chile

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Abstract
Mollusk aminostratigraphy of Quaternary marine terrace sediments at Coquimbo Bay, Chile, combined with recently available electron spin resonance (ESR) ages, necessitates revision of the northern Chilean relative sea-level and terrace chronology. Protothaca and Muliniad-alloisoleucine/l-isoleucine values define four aminozones which are consistent with available ESR ages. Terrace reoccupation during successive high sea-level stands is inferred on the basis of litho- and aminostratigraphically defined unconformities in terrace sediments. ESR data and a nonlinear kinetic racemization model give approximate numerical ages for the aminozones and thus yield estimates of net uplift rates. These rates, averaged over intervals of one to several hundred thousand years, have ranged from less than 0.1 m/1000 yr to no more than 0.2 m/1000 yr. Such slow uplift is the cause of terrace reoccupation, as the amount of uplift between successive glacioeustatic high sea-level stands is frequently not sufficient to isolate an earlier-formed abrasion platform from rising sea level during a subsequent high stand.