Sonia H. Tatumi

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.

Optical properties of Nd doped Bi2O3-PbO-Ga2O3 glasses.

The optical properties of a new family of neodymium doped BPG (Bi2O3-PbO-Ga2O3 ) glasses are presented. We measured a high refractive index, of 2.5, and a transmission cutoff in the far infrared at 8microm. Three intense emission bands are observed centered at 877nm, 1066nm and 1341nm. The emission cross-section is 10 -20 cm 2 and the total spectral linewidth is 30nm at 1066nm. The Judd-Ofelt parameters are calculated and used to evaluate transition probability, radiative lifetime and branching ratios. The optical properties of these Nd:BPG glasses show promise for their use as a new active laser material.

OSL age determinations of Pleistocene fluvial deposits in Central Amazonia

Absolute dating methods have been used in chronological studies of geological processes and sedimentary units of Quaternary age in Central Amazonia, Brazil. Although radiocarbon dating has been very useful in archaeological research and soil studies, the temporal interval of this method is inefficient in evaluating the sedimentation aspects and geological events from the beginning of the Quaternary in the Amazon basin. The use of crystal luminescence dating has been one of the most promising tool for determining the absolute dating of Quaternary deposits in the Amazonian region. Optically stimulated luminescence (OSL) dating, following the MAR and SAR protocols, in a tectonic-sedimentary study of Quaternary fluvial deposits in the confluence area of the Negro and Solimoes rivers, indicated ages from 1.3 (Holocene) to about 67.4 kyears (Late Pleistocene) for these sediments. Low radioactive isotope concentrations were found about 2ppm for 235 U and 238 U; 5ppm for 232 Th; and the 40 K concentrations were almost zero. A comparison

Geologia e geomorfologia do quaternário costeiro do estado do Rio Grande do Norte

O objetivo deste trabalho e a apresentacao de um mapa geologico-geomorfologico preliminar para o Quaternario costeiro do Estado do Rio Grande do Norte, com destaque para os depositos eolicos. O mapa foi elaborado a partir de fotografias aereas, escala 1:70.000, imagens de satelite (P/B, banda 4), escala 1:100.000, mapas topograficos e trabalhos de campo. Foram feitas datacoes 14C em rochas praiais e depositos de paleomangues e datacoes por termoluminescencia em sedimentos eolicos e marinhos. Nos depositos eolicos foram identificados tres dominios geomorfologicos de dunas inativas e um de dunas ativas. Eles formaram-se no Quaternario a partir de retrabalhamento de areias da propria planicie costeira e de sedimentos da Formacao Barreiras. As idades TL de 36 amostras indicam que os depositos eolicos foram formados durante seis intervalos principais: 390.000 - 326.000, 270.000 - 240.000, 210.000 - 150.000, 63.000. - 24.000, 11.000 - 9.000 e, 6.500 anos - presente. Essas idades sugerem sua deposicao tanto durante estagios glaciais como interglaciais, relacionados a niveis relativos de mar baixos e altos respectivamente. Dois terracos marinhos foram identificados, com idades de 210.000 a 214.000 anos e 110.000 a 120.000 anos. O primeiro ocorre entre Natal e Baia Formosa, onde a costa se orienta na direcao N - S; o segundo encontra-se no trecho da costa entre Sao Bento e Zumbi, com orientacao E - W. Extensos depositos de intermare holocenicos, principalmente de arenitos praiais, estao localizados na costa orientada N - S e apresentam idades entre 7.000 - 6.000 anos AP. e 5.500 - 4.500 anos AP.

Spectroscopic properties of lead fluoroborate and heavy metal oxide glasses doped with Yb3

Abstract A new glass of heavy metal oxide (25.0Bi2O3–57.0PbO–18.0Ga2O3 (mol%)) doped with Yb3+ is presented and compared with lead fluoroborate glass (43.5H3BO3–22.5PbCO3–34.0PbF2 (mol%)), also doped with ytterbium. The interest in Yb3+ for laser action and short pulse generation under diode pumping has been reported in the literature. Spectroscopic properties were studied for both glasses doped with 0.5 mol% of Yb2O3. The absorption cross-section of the heavy metal oxide glass is (2.20±0.15)×10−20 cm2 at the absorption peak wavelength of 968 nm and its emission cross-section is (0.75±0.05)×10−20 cm2 at the extraction wavelength of 1012 nm. A fluorescence effective linewidth of 86 nm and a fluorescence lifetime of 0.40 ms were measured. In the case of the lead fluoroborate glass used for comparison, these values change to (2.56±0.18)×10−20 cm2 (absorption cross-section), (1.07±0.08)×10−20 cm2 (emission cross-section at 1022 nm), 60 nm (fluorescence effective linewidth) and 0.81 ms (fluorescence lifetime). Calculations of the minimum pump intensity are also presented. Both have spectroscopic properties for laser applications that are similar to those of other known glasses (phosphate and tellurite laser glasses) used as active laser media. The large emission bandwidth measured for the heavy metal oxide is of interest for tunable lasers.

Spectroscopic properties of lead fluoroborate glasses doped with ytterbium

A new lead fluoroborate glass (PbO-PbF2-B2O3) doped with ytterbium (Yb:PbFB) is presented. Samples with different concentrations of Yb3+ were produced and had their emission cross-sections, fluorescence lifetimes and minimum pump intensities determined. They have high refractive index of 2.2 and a density of 4.4 g/cm3. For a doping level of 1.153x1020 ions/cm3, the fluorescence lifetime, after excitation at 968 nm, is 0.81 ms, which is comparable to Yb:tellurite laser glass. Also, an emission band at 1022 nm is measured with emission cross-section of approximately 1.07x10-20 cm2 and fluorescence effective linewidth of 60 nm, which is comparable to Yb:phosphate laser glass.

Upper Pleistocene deposits of the Comprida Island (São Paulo State) dated by thermoluminescence method

The Cananeia (Upper Pleistocene) and the Comprida Island (Holocene) formations, outcropping in the Comprida island (SP) have been mapped using geomorphological and lithological criteria. Only one sample of the Cananeia Formation, collected in the homonymous island in front of the Comprida Island, was beyond the limit of the standard radiocarbon method. But since the publication of the geological map of the area in 1978, there has been some doubt on the real occurrence of Pleistocene deposits in southern extremity of Comprida Island. This paper deals with the results of thermoluminescence (TL) ages of eight samples from Comprida Island, which corroborate the Pleistocene age assumed during mapping surveys of these deposits. On the other hand, possible interpretations of the obtained ages, in relation to their depositional environments and related northern hemisphere Quaternary glaciations, are presented.

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.

Glasses of heavy metal and gallium oxides doped with neodymium

Abstract Optical and physical properties of a new family of Nd: BPG (Bi2O3-PbO-Ga2O3) glasses are presented at 1 mol% Nd doping level. Knoop hardness of 321 kg/mm2 and density of 4.63 g/cm3 were measured. These high refractive index glasses present a very large absorption cross section of 2.5 × 10−20 cm2 at 800 nm. Emission occurs at three bands centered at 877 nm, 1066 nm and 1341 nm with a fluorescence lifetime associated to these transitions of 110 μs. At 1066 nm, the spectral linewidth is 30 nm. These properties make these glasses good candidates for laser action.