Aeromagnetometry and aerogammaspectrometry integrated with U-Pb zircon geochronology of northern Bossoroca ophiolite, Brasiliano Orogen

Age delimitation integrated with aeromagnetometric and aerogammaspectrometric survey advances the understanding of ophiolite evolution in the Brasiliano Orogen. We focused on the Bossoroca ophiolite, because oceanic crustal and mantle rocks contain zircon in metasomatic chloritite. A metadiorite and a metavolcanoclastic rock were also studied to delimit relationship between ophiolite and island-arc infrastructure and superstructure. Zircon crystals were dated by laser ablation inductively coupled plasma emission spectroscopy. Ages of zircon from Campestre metavolcanoclastic rock are 920-840 (peak 842) Ma, Bossoroca chloritite 900-800 (peak 868 Ma) and Capivaras metadiorite 698 Ma. Ages 920-800 Ma correspond to processes in the oceanic crust, whereas 698 Ma was a late magmatic intrusion (Capivaras metadiorite) into the island-arc infrastructure. Aeromagnetometric and aerogammaspectrometric data delimit the occurrence and structure of the ophiolite. These are major multiproxy markers of geotectonic processes early in the Brasiliano Orogen

Umbria-Marche Basin, Central Italy: A Reference Section for the Aptian-Albian Interval at Low Latitudes

Within the Cretaceous Period, the Aptian-Albian interval (125–99.6 Ma, Ogg et al., 2008) was a critical time on a global scale. This is evident from 1) changes in the nature of the ocean-climate system brought about by increased ocean crust production coupled with active midplate and plate margin volcanism in a shifting paleogeography (Skelton et al., 2003); 2) cyclic deposition and preservation of common “black shales”, some of them termed Oceanic Anoxic Events(OAE1a to OAE1d) (Schlanger and Jenkyns, 1976; Arthur et al., 1990); 3) periodic changes in redox conditions at the ocean bottom (Oceanic Red Beds, ORBs) (Wang et al., 2009); and 4) rapid biotic radiations and turnovers (Leckie et al., 2002). The Aptian-Albian time is also of interest for one of the most noteworthy geomagnetic events, namely the post-M0r “Cretaceous Quiet Zone”. This long and constant normal polarity superchron without any convincing true reversal to date (Satolli et al., 2008) precludes usage of reversals magnetostratigraphy from the Aptian through the Santonian. The Poggio le Guaine core was designed to provide a high-resolution age model and a high-resolution relative magnetic paleointensity reference curve for the Aptian-Albian interval of the long normal Cretaceous superchron; it was also designed to understand the causal linkages among geological, biogeochemical, oceanographic and climatic eventsas well as their consequences. The core was drilled at Poggio le Guaine, where the most continuous, complete, and best preserved Aptian-Albian succession is exposed throughout the Umbria-Marche Basin (UMB) of the northern Apennines of central Italy (Fig. 1). It represents a continuous record of fossiliferous pelagic rocks extending from the Albian-Cenomanian boundary down to the uppermost Barremian (99.6–126 Ma). In this progress report we present the first preliminary findings of this ongoing project

Aplicações de isótopos de oxigênio e carbono na reconstrução paleoambiental do interior da Lagoa dos Patos, RS, Brasil: um estudo de caso.

O trabalho apresenta uma reconstrução paleoambiental, a partir de um testemunho extraído da célula sul da Lagoa dos Patos (Rio Grande do Sul – Brasil), com base em análises de isotópos estáveis de carbono e de oxigênio, realizadas em conchas de moluscos. O testemunho está localizado entre a saída do rio Camaquã e o município de Bojuru. Três zonas distintas foram observadas: uma zona inferior marinha composta pelos moluscos Carycorbula tryoni, Acteocina bidentata e Tawera gayi, mostrando um comportamento espelhado com relação à profundidade entre os valores de δ18O e de δ13C,  uma temperatura média de 17°C e a idade do 14C é de 3876 – 4004 AP a 2,5 m. Uma zona de transição, onde não são encontrados moluscos fósseis, e uma zona superior mixohalina, com o molusco Erodona mactroides, de comportamento concordante entre os valores negativos de δ18O e de δ13C. Nesta zona, a temperatura aumenta em 5°C, chegando a 22°C. A 1,2m, a idade radiocarbono é de 3.054 ± 27 anos AP. A 0,3m de profundidade, o comportamento do δ13C e do δ18O passa a ser estável, refletindo o provável fechamento da Lagoa dos Patos (2.080 AP), pertencente a Série Meghalayan da parte Superior do Holoceno. Este estudo corrobora com a variação do nível do mar e com a história evolutiva da formação de ilhas barreira no litoral sul-brasileiro em função da presença de espécies marinhas na base do testemunho e de espécies mixohalinas no topo