Marcio Yee

Late Pleistocene marine terrace deposits in northeastern Brazil: sea-level change and tectonic implications

Abstract Coastal areas of passive margins are among the best places to examine the reality of sea-level changes. Elevation of marine terraces is central to interpretation of their approximate age in this kind of tectonic setting. The recognition of Pleistocene shorelines on the South American eastern continental margin is becoming increasingly common, but data are commonly imprecise in both time and space, and the resulting chronology is based mainly on geomorphological attributes. Nine thermoluminescence dates and four optically stimulated luminescence dates of 220–206 ka and 117–110 ka were obtained for two marine terrace deposits along 340 km of coast in Rio Grande do Norte State, northeastern Brazil. They are correlated with the highstands of marine oxygen-isotope substages 7c and 5c sea level, respectively. The older deposit occurs mainly on the N–S-trending coast and ranges in elevation between 7.5 and 1.3 m. The latter is found along the E–W-trending coast at altitudes that vary between 1 m and 20 m. It indicates relative downfaulting of the 220–206-ka marine terrace and uplift of the 117–110-ka marine deposit, which is locally about 12 m higher than deposits of similar age described 1000 km to the south. It follows that elevation alone is an unreliable tool for establishing a Quaternary sea-level change chronology also on passive margin coastal areas.

Pleistocene-Holocene sedimentation of Solimões-Amazon fluvial system between the tributaries Negro and Madeira, Central Amazon

In the scope of Solimoes-Amazon fluvial system between the Negro and Madeira tributaries, three levels of Quaternary fluvial terraces overlie the Alter do Chao and Novo Remanso formations further than 100 km southward its current main channel. Smooth undulated topography presenting low drainages density formed by sparse secondary plain channels and rounded lakes characterizes these deposits. Internally, they show point bars morphology constituted by intercalated layers of mud (silt and clay) and sand forming an inclined heterolithic stratification. The asymmetric distribution of fluvial terraces allied to the records of old scroll-bars features and paleochannels in many extensions of the Solimoes River suggests the predominance of a meander pattern between 240 to 6 kyears. On the other hand, the development of the current anabranching pattern took place in the last six kyears due to the Holocene sea-level rise, besides the action of neotectonics and rainforest establishment related to the increase of humidity in Amazonia.

Dating human occupation at Toca do Serrote das Moendas, Sao Raimundo Nonato, Piaui-Brasil by electron spin resonance and optically stimulated luminescence

Excavation of Toca do Serrote das Moendas, in Piauí state, Brazil revealed a great quantity of fossil wild fauna associated with human remains. In particular, fossils of a cervid (Blastocerus dichotomus) were found, an animal frequently pictured in ancient rock wall paintings. In a well-defined stratum, two loose teeth of this species were found in close proximity to human bones. The teeth were independently dated by electron spin resonance (ESR) in two laboratories. The ages obtained for the teeth were 29 ± 3 ka (thousands of years) and 24 ± 1 ka. The concretion layer capping this stratum was dated by optically stimulated luminescence (OSL) of the quartz grains to 21 ± 3 ka. As these values were derived independently in three different laboratories, using different methods and equipment, these results are compelling evidence of early habitation in this area.

Compatibilization mechanism induced by organoclay in PMMA/PS blends

In this work, the effect of adding organoclay (Cloisite 20A) to a poly(methyl metacrylate) (PMMA)/polystyrene (PS) blend was evaluated in order to understand the compatibilization mechanism taking place. The blend morphology was quantified using micrographs obtained by scanning electron microscopy and observed by transmission electron microscopy. The state of dispersion of the clay was studied using small angle X-ray scattering and wide angle X-ray scattering and by applying the Carreau-Yasuda with a yield stress model to small amplitude oscillatory shear (SAOS) data. Morphological analyses revealed that the clay was intercalated, that its addition resulted in a decrease in the size of the dispersed phase and that it was preferentially located at the interface, except in the case of saturated interfaces, in which case the remaining clay was dispersed in PMMA. By applying the simplified Palierne model to SAOS experiments, the interfacial tension between the polymers forming the blend was inferred and shown...