Paleoenvironmental implications of authigenic magnesian clay formation sequences in the Barra Velha formation (Santos Basin, Brazil)

The characterization of Mg-clays in rock samples (well P1) from the Barra Velha Formation (Early Cretaceous) allowed the establishment of mineral assemblages on the basis of their kerolite and Mg-smectite (stevensite and saponite) content. Kerolite-rich assemblages (A and B) rarely con-tain saponite. Assemblage B is composed of kerolite-stevensite mixed layers, while assemblage A consists of more than 95% kerolite. Mg-smectite-rich assemblages (C and CB) are made up of both Mg-smectites. The predominance of stevensite in the lower interval of the stratigraphic succession suggests evaporative conditions, higher salinity and pH, which would favor its authigenesis by neoformation. In the upper portion, the occurrence of thick kerolite-rich intervals suggests regular water inputs, contributing with a decreasing in salinity and pH, favoring the neoformation of kero-lite and later kerolite-stevensite mixed layering. The saponite would be the result of the transfor-mation from Al-smectite into Mg-smectite in a Mg2+ rich medium. The results indicate that lake hydrochemical processes would have allowed the establishment of a basic depositional sequence, from base to top, as follows: (i) initial lake expansion stage marked by the occurrence of saponite, (ii) later kerolite neoformation, (iii) formation of kerolite-stevensite mixed layer with increasing sa-linity, and (iv) neoformation of stevensite, marking a final stage of maximum salinity (evaporation) and alkalinity of the lak

Characterization of volcanic reservoirs; insights from the Badejo and Linguado oil field, Campos Basin, Brazil

Funding Information: This work was financially supported by Petrobras (CENPES – Research Center and Exploration) projects. Especially the authors of Petrobras appreciate the fruitful discussions with the VMAPP Consortium (Volcanic Margin Petroleum Prospectivity) team and workshops. The authors would like to thank also all those who contributed in some way to make this work possible. Dougal A. Jerram and Sverre Plank acknowledge the support from the Research Council of Norway through its Centres of Excellence funding scheme, project 22372 (CEED).Peer reviewedPostprin

Palinof?cies de uma sequ?ncia sedimentar quatern?ria da Lagoa Preta, Parque Estadual do Rio Doce, MG, Brasil.

Este trabalho apresenta os resultados do estudo de palinof?cies de um testemunho de sondagem quatern?rio da lagoa Preta, Parque Estadual do Rio Doce (PERD), MG, Brasil. A lagoa Preta est? inserida no complexo lacustre do M?dio Vale do Rio Doce, que ? constitu?do por cerca de 160 lagoas. De acordo com estudos pr?vios, a origem do complexo lacustre est? relacionada, principalmente, ? neotect?nica local, que pode ser dividida em duas etapas. A primeira etapa ? caracterizada pela transcorr?ncia dextral E-W e atuou partir do final do Pleistoceno. J? a segunda etapa de movimenta??es tect?nicas ocorreu durante o Holoceno M?dio e ? caracterizada pelo regime extensional NW-SE, que foi respons?vel pela gera??o de falhamentos normais que promoveram desnivelamentos e basculamentos nos leitos dos canais tribut?rios, funcionando como barragens e gerando, desta forma, os lagos. A an?lise de palinof?cies foi realizada em 30 amostras de um testemunho de sondagem de 200 cm, datado na base em 6.620?110 anos A.P. O testemunho de sondagem apresenta uma seq??ncia sedimentar constitu?da por tr?s f?cies de argila de colora??o variada, argila cinza claro na base, argila cinza escuro e argila marrom em dire??o ao topo. A partir da caracteriza??o dos tipos de componentes org?nicos particulados e da correla??o entre as varia??es de seus percentuais, foi poss?vel identificar uma palinof?cies com predom?nio de mat?ria org?nica amorfa (MOA,70-95%), esporos de fungo e fitoclastos opacos como elementos subordinados. A an?lise de palinof?cies nos permite concluir que: a seq??ncia sedimentar da lagoa Preta foi depositada em condi??es an?xicas-dis?xicas, compat?veis com l?mina de ?gua de pouca profundidade depositada em ambiente lacustre ou paludal, devido a grande quantidade de MOA e aus?ncia significativa de algas, e, que a lagoa Preta esteve, provavelmente, em processo assoreamento desde 6.620?110 anos A.P.This paper presents the results of a palynofacies study from a quaternary core of Preta Lake State Park of Doce River (PERD), MG, Brazil. Preta Lake is situated in the Doce River?s Middle Valley lake complex, which consists of around 160 lakes. According to previous studies, the origin of the lake complex is linked mainly to local neotectonics, which can be divided into two phases. The first stage is characterized by E-W dextral transcurrent movements and occurred from the end of the Pleistocene. The second stage of tectonic movements occurred during the Middle Holocene and is characterized by NW-SE extensional regime, which was responsible for the generation of fault-block activity that promoted unevenness and tipping in beds of the tributary channels, acting as dams and thus creating the lakes. The analysis of palynofacies was carried out on 30 samples of a core of 200 cm, dated at the base at 6,620 ? 110 years BP. The core shows a sedimentary sequence that consists of three facies of clay varying in color: light gray clay at the base, dark gray clay and brown clay toward the top. From the characterization of the particulate organic matter components and the correlation between changes in their percentage, a palynofacies was identified with a predominance of amorphous organic matter-AOM (70-95%), fungal spores and opaque phytoclasts as subordinate elements. The palynofacies analysis allows us to conclude that: the sedimentary sequence of Preta Lake was deposited in anoxic-desoxic conditions, consistent with a shallow lake, deposited in a lake or paludal environment, due to large amount of AOM and substantial lack of algae and that Preta Lake has likely been in a filling process since 6,620 ? 110 years BP