Luminescence characteristics of quartz from Brazilian sediments and constraints for OSL dating

This study analyzes the optically stimulated luminescence (OSL) characteristics of quartz grains from fluvial, eolian and shallow marine sands of northeastern and southeastern Brazil, with especial focus on the applicability of the single-aliquot regenerative dose (SAR) dating protocol. All analyzed Brazilian sediments presented relatively high OSL sensitivity and good behavior regarding their luminescence characteristics relevant for radiation dose estimation. However, some samples from the Lençóis Maranhenses region in northeastern Brazil showed inadequate OSL sensitivity correction, hampering the implementation of the SAR protocol and their ability to behave as a natural dosimeter. While the shallow marine and eolian samples showed a narrow and reliable dose distribution, the fluvial sample had a wide dose distribution, suggesting incomplete bleaching and natural doses estimates dependent on age models

Juntos na costa: zooarqueologia e geoarqueologia de sambaquis do litoral sul catarinense

This paper explores the contribution that zooarchaeological and geoarchaeological analyses can bring to the study of shell sites depositional history combined approach is applied for the study of two that represent part of the diversity of shell deposits in the southern coast of Santa Catarina State: Jabuticabeira II, a monumental cemetery; and Encantada III, a smaller shell deposit that, besides its apparent simplicity, presents a challenge for the definition of its function. In Encantada III, zoo and geoarchaeology contributed to a better characterization of its role as short-term deposit of long lasting permanence. Both shell sites, and their practical and symbolical attributions, represent examples of the complex dynamics of the anthropic construction of a landscape.Neste artigo, explora-se a contribuição que análises zooarqueológicas e geoarqueológicas podem fornecer ao entendimento da sucessão deposicional de sambaquis. Esta abordagem combinada é aplicada ao estudo de dois sambaquis que representam parte da diversidade dos sítios da costa sul de Santa Catarina: Jabuticabeira II, sambaqui-cemitério, cujas pesquisas tiveram papel decisivo para uma compreensão mais detida do ritual funerário; e Encantada III, um sambaqui pequeno que, apesar de sua aparente simplicidade, apresenta um desafio para a definição de sua função. Em Encantada III, tanto a Zooarqueologia como a Geoarqueologia contribuiram para uma melhor caracterização do seu papel enquanto depósito resultante de curto prazo, porém, de permanência duradoura. Ambos os sambaquis, bem como suas atribuições práticas e simbólicas, são exemplos da complexa dinâmica envolvida na construção antrópica da paisagem

Luminescence characteristics of quartz from Brazilian sediments and constraints for OSL dating

This study analyzes the optically stimulated luminescence (OSL) characteristics of quartz grains from fluvial, eolian and shallow marine sands of northeastern and southeastern Brazil, with especial focus on the applicability of the single-aliquot regenerative dose (SAR) dating protocol. All analyzed Brazilian sediments presented relatively high OSL sensitivity and good behavior regarding their luminescence characteristics relevant for radiation dose estimation. However, some samples from the Lençóis Maranhenses region in northeastern Brazil showed inadequate OSL sensitivity correction, hampering the implementation of the SAR protocol and their ability to behave as a natural dosimeter. While the shallow marine and eolian samples showed a narrow and reliable dose distribution, the fluvial sample had a wide dose distribution, suggesting incomplete bleaching and natural doses estimates dependent on age models

Reply to Castro et al. 2018 on “Holocene paleo-sea level changes along the coast of Rio de Janeiro, southern Brazil”.

ABSTRACT Discussions are useful to the advance of science, and we appreciate the opportunity to discuss the paper by Castro et al. (2014) for the second time. Here we maintain the interpretations presented in our discussion paper (Angulo et al. 2016). In the discussion paper we emphasized that the vertical position of a paleo-sea level indicator is not the position of the paleo-sea level. We pointed out that: (1) to reconstruct paleo-sea levels it is crucial to determine the vertical distance between the indicators to their present homologous one; (2) margin of errors can only be established if considering the indicator’s intrinsic characteristics and (3) the interpretation of a sea level 3.0 to 4.5 m below the present one at 11.9 to-11.1 ka BP is in strong contradiction with worldwide established data and would require a detailed discussion. We consider that Castro et al. (2018) do not properly address or answer the comments we made in the discussion paper. More work and discussions are necessary to elucidate several questions that still remain about the sea level behavior in the Holocene

Holocene paleo-sea level changes along the coast of Rio de Janeiro, southern Brazil: Comment on Castro et al. (2014)

ABSTRACT The present work discusses and reinterprets paleo-sea level indicators used to build Holocene sea-level curve for the coast of Rio de Janeiro at former works. We conclude that: (a) the paleo-sea levels inferred by vermetid remains show that sea-level has fallen over the past 4400 years, at least; (b) the paleo-sea level inferred by the beachrock facies and dated shells of Jaconé shows that sea-level was near the present elevation between 8198 and 5786 years before present; and (c) several shells from other beachrocks were deposited probably thousands of years after the specimens died and consequently do not allow precise reconstructions of paleo-sea levels. These conclusions differ from the conclusions of the original paper

Thermoluminescence and optically stimulated luminescence measured in marine sediments indicate precipitation changes over northeastern Brazil

Marine sediment cores offer a great number of proxies for reconstructions of past environmental conditions, such as ocean temperature, salinity, primary productivity, stratification of the upper water column and continental precipitation. Up to date, continental precipitation archived in marine sediment cores is reconstructed based mainly on the hydrogen isotopic composition of plant‐wax compounds (i.e., n‐alkane δD) or on the ratio between terrigenous and marine sediments expressed as elemental ratios (e.g., ln (Fe/Ca)). Although these proxies provide reliable precipitation reconstructions, there are some inherent limitations, as plant‐wax δD application depends on the availability of n‐alkanes in marine sediments and elemental ratios can be influenced by other factors like the relative sea‐level, primary productivity and post‐depositional processes. Here we introduce new precipitation proxies based on optically stimulated luminescence and thermoluminescence signals of quartz and feldspar. The rationale is that when precipitation changes over the catchment through time, different sediment sources regarding weathering intensity and parent rock types are drained, supplying sediments with varying signals of luminescence to the ocean. We compared our new proxy records with records of well‐established proxies, for the same (ln (Fe/Ca)) and neighboring (n‐alkane δD) marine sediment cores. The comparison among all proxies as well as with a state‐of‐art transient climate model run (TraCE‐21ka) demonstrates that the new proxies accurately constrain precipitation changes over northeastern Brazil for the last 30,000 years. The main advantage of these new proxies relies on their fast response to precipitation changes over the continent. Furthermore, they are straightforward to measure and not expensive