Hart, E.A.; Stapor, F.W.; Enrique Novoa Jerez, J., and Sutherland, C.J., 2017. Progradation of a beach ridge plain between 5000 and 4000 years BP inferred from luminescence dating, Coquimbo Bay, Chile.

Luminescence dating was carried out to determine the depositional history of a 2-km-wide, shore-parallel, beach ridge sequence at Coquimbo Bay, Chile, for which no direct dating had previously been done. The beach ridge plain at Coquimbo Bay represents one of the most extensive Holocene depositional features preserved along the Pacific Coast of South America. Both optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dates indicate a rapid period of beach ridge progradation lasting approximately 1000 years at an average rate of 2 m y−1. However, based on previously reported luminescence deficiencies of geologically “young” quartz, it is proposed that IRSL dates are more representative of the actual depositional age of the beach ridges. These IRSL ages indicate that the beach ridge plain at Coquimbo Bay was formed between ca. 5000 and 4000 years BP, after the hiatus of eustatic sea-level rise in the mid-Holocene, and that a relatively stable shoreline location has likely prevailed over the last 4000 yrs. The height of beach ridges 8 to 10 m above modern sea level is difficult to interpret but is likely the result of several factors, including the build-up of an eolian cap on each beach ridge at the time of its formation, the height of wave runup, and tectonic uplift. Although uncertain, the cumulative effect of all three of these factors appears to be insufficient to account for all of the present beach ridge elevation, and thus a fall in sea level after the mid-Holocene at this location cannot be ruled out. Archaeological and geomorphic evidence support the idea of a mid-Holocene sea-level high stand and a 1 to 2 m mid-Holocene high stand is well established at many other circum-Pacific, far-field locations.

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