Geological evidences as a guide to OSL dating interpretation and northern occurrence of MIS 7e barrier at Southern Brazil

摘要

The chronology of Pleistocene strandplains remains a challenge to this day. The lack of reliable geochronology methods arises from the fact that ages from the Pleistocene sequences are beyond radiocarbon age limit method and, sometimes, near the saturation limits to luminescence dating on quartz, which may introduce uncertainties in the results. Also, choosing different curve fits for the dose-response curve leads to geological incoherent results. In this paper, we evaluated three approaches on curve fit equations (single saturating exponential (SSE), double saturating exponential (DSE) or the SSE + Linear (E + L). We also compared the three scenarios with geological evidences such as sedimentary structures, like plane-parallel lamination, and the presence Ophiomorpha nodosa ichnofossil at Paranagua and Superagui strandplains, Southern Brazil. Since geological evidences indicate deposition under wave-dominated shoreline, the comparison to Quaternary sealevel curves restricts the beach ridges deposition to high relative sealevel intervals. Our results show that, despite being mathematically consistent, DSE and E + L curve fits lead to geological inconsistent results. The luminescence results using SSE curve fit are geologically consistent and suggest the occurrence of MIS 7e barrier on Paranagua and Superagui strandplains, the farther north occurrence of the Barreira II (195-220 ky) correspondent to the Rio Grande do Sul strandplain. However, we stress out that luminescence dating results near the saturation limit must be interpreted with caution, and preferably supported by other evidences.