An event of stratospheric air intrusion and its associated secondary surface cyclogenesis over the South Atlantic Ocean

This work presents an analysis of a lowermost stratospheric air intrusion event over the coast of Brazil, which may have been responsible for a secondary surface cyclogenesis over the southwestern Atlantic Ocean. The surface cyclone initiated at 0600 UTC 17 April 1999 in a cold air mass in the rear of a cold front after a primary cyclone developed over the same region. The analysis of the secondary cyclone revealed the presence of lowermost stratospheric air intrusion characterized by anomalous potential vorticity (PV), dry air, and high concentration of ozone in atmospheric column. The system developed on the eastern side of an upper level core of PV anomaly, which induced a cyclonic wind circulation at lower levels and favored the onset of the secondary cyclone. In midlevels (500 hPa), the cutoff low development contributed to reduce the propagation speed of the wave pattern. This feature seemed to (1) allow the low-level cold/dry air to heat/moisten associated with sensible and latent fluxes transferred from the ocean to the atmosphere, which intensified a baroclinic zone parallel to the coast, and (2) contribute to the long duration of the system. The present analysis indicates that this secondary cyclone development could be the result of the coupling between the PV anomaly in the upper levels and low-level air-sea interaction.

One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Severe climate changes culminating in at least three major glacial events have been recognized in the Neoproterozoic sedimentary record from many parts of the world Supportive to the global nature of these climatic shifts a considerable amount of data have been acquired from deposits exposed in Pan-African orogenic belts in southwestern and western Africa By comparison published data from the Pan-African belts in Central Africa are scarce We report here evidence of possibly two glacial events recorded in the Mintom Formation that is located on the margin of the Pan-African orogenic Yaounde belt in South-East Cameroon In the absence of reliable radiometric data only maximum and minimum age limits of 640 and 580 Ma respectively can at present be applied to the Mintom Formation The formation consists of two lithostratigraphic ensembles each subdivided in two members (i e in ascending stratigraphic order the Kol Metou Momibole and Atog Adjap Members) The basal ensemble exhibits a typical glacial to post-glacial succession It includes diamictites comprising cobbles and boulders in a massive argillaceous siltstone matrix and laminated siltstones followed by in sharp contact a 2 m-thick massive dolostone that yielded negative delta(13)C values (<-3 parts per thousand. V-PDB) similar to those reported for Marinoan cap carbonates elsewhere However uncertainty remains regarding the glacial influence on the siliciclastic facies because the diamictite is better explained as a mass-flow deposit and diagnostic features such as dropstones have not been seen in the overlying siltstones The Mintom Formation may thus provide an example of an unusual succession of non-glacial diamictite overlain by a truly glacial melt-related cap-carbonate We also report the recent discovery of ice-striated pavements on the structural surface cut in the Mintom Formation suggesting that glaciers developed after the latter had been deposited and deformed during the Pan-African orogeny Striations which consistently exhibit two principal orientations (N60 and N110) were identified in two different localities in the west of the study area on siltstones of the Kol Member and in the east on limestones of the Atog Adjap Member respectively N60-oriented striae indicate ice flow towards the WSW Assigning an age to these features remains problematical because they were not found associated with glaciogenic deposits Two hypotheses can equally be envisaged e either the striated surfaces are correlated (1) to the Gaskiers (or Neoproterozoic post-Gaskiers) glaciation and represent the youngest Ediacaran glacial event documented in the southern Yaounde belt or (2) to the Late Ordovician Hirnantian (Saharan) glaciation thereby providing new data about Hirnantian ice flows in Central Africa (C) 2010 Elsevier Ltd All rights reserved

Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

Turkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite-steacyite group was found in evolved peralkaline granites from the Morro Redondo Complex, south Brazil. It occurs with quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO(2), Na(2)O and K(2)O contents of 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE(2)O(3) abundances (5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite-steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluids carrying Ca, the circulation of which was enhanced by deformational events.

Molecular mass distribution of dextran in Brazilian sugar and insoluble deposits of cachaca

The dextran molecular mass distribution profile in 77 sugar samples from Brazil and twelve insoluble deposits (alcoholic flocks) samples from sugared cachacas (Brazilian sugar cane spirit) is described in terms of number-average molecular mass M,,, weight-average molecular mass M(w), Z-average molecular mass M,, and polydispersity. The analyses were performed by size-exclusion chromatography, using a refractive index detector. In most of the sugar samples, it was possible to identify two major groups of dextrans with Mw averages of 5 x 10(6) and 5 x 10(4) Da. Based on the evaluated parameters, the dextran distribution profile is about the same in samples analyzed over five seasons, and, therefore, it is likely that the Brazilian product pattern will not change very much over the years. In insoluble deposits from sugared cachacas, dextrans with Mw values in the order of the 10(5) Da were the most frequent ones, being present in 58% of the samples. (c) 2008 Elsevier Ltd. All rights reserved.