Año 2012, Boletín IFG vol. 82
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Ítem Acceso Abierto First meeting of the Research Group for Paleobiology and biostratigraphy of the ammonites(Instituto de Fisiografía y Geología. Facultad de Ciencias Exactas, Ingeniería y Agrimensura. Universidad Nacional de Rosario, 27/12/2012) Bert, Didier; Bersac, StéphaneThe Laboratory of the “Research Group for Paleobiology and biostratigraphy of the Ammonites” (G.P.A; homepage: http://laboratoire.gpa.pagespersoorange. fr) is localised in Southeastern France, in the Alpes de HauteProvence near DignelesBains. This area is famous since the 19th century for its abundant ammonite localities and because of the Geological Reserve of HauteProvence, which protect them. The G.P.A. is organized around a working group of scientific colleagues from diverse countries and different research laboratories or universities, and of some amateur collaborators, all interested in ammonites and research on related issues. The “1s t Meeting” of the “Research Group for Paleobiology and biostratigraphy of the Ammonites” (G.P.A), organized by Didier Bert, was held in La MureArgens (France) from September 15 to 16, 2012. Eight communications were presented on various subjects about ammonites and nautiloids, their evolution, phylogeny, taxonomy and their use in biostratigraphy, especially with examples of the Upper Jurassic (Kimmeridgian) and the Lower Cretaceous (Barremian and Aptian).Ítem Acceso Abierto A plastic rheology phenomenological 201 . model that explains the Andes evolution in northern Argentina(Instituto de Fisiografía y Geología. Facultad de Ciencias Exactas, Ingeniería y Agrimensura. Universidad Nacional de Rosario, 27/12/2012) Introcaso, Antonio; Giménez, Mario; Martínez, María Patricia; Ruiz, FranciscoA plastic rheology, partially phenomenological model is presented to explain the isostatically compensated Andean relief formation. This model considers a combination of lithospheric heating with long period relaxation and successive crustal shortenings on a north section of Argentina located at 24°S latitude. The present size of the Andean root –related to the Andes construction– was obtained by inverting regionalized Bouguer anomalies, also consistent with geoid undulations. The relief of 1520 km is balanced both with a thermal root of 70.63 km located at the lithospheric mantle and 2 with an evolutionary crustal root originated by shortenings. A pretended contradiction must be noted: lateral compressive shortenings and side moving tending to squash and to widen the high relief. For better understanding the problem, a linear model is first presented. Then, a nonlinear model of plastic rheology is considered with a stability coefficient depending on width and elevation. We have assumed that isostatic balance keeps on the whole orogenic construction. We also impose an empirical stability relationship. If this relationship does not hold, there will be an extra relief and therefore an extra root that will plastically flow until reaching stability.Ítem Acceso Abierto Microfacies and palaeoenvironments of the Lower Carboniferous Mobarak Formation in the Kiyasar section, Northern Iran(Instituto de Fisiografía y Geología. Facultad de Ciencias Exactas, Ingeniería y Agrimensura. Universidad Nacional de Rosario, 28/12/2012) Falahatgar, Mostafa; Mosaddeg, HosseinCarboniferous rocks outcrop over vast areas in the Alborz Mountains. The Mobarak Formation outcrops in the studied area near the Kiyasar town, south-east of Sari, Northern Iran. The petrographic study produced the recognition of fifteen different microfacies types. Based on microscopic studies, four facies belts have been characterized: (1) an intertidal facies belt, (2) a lagoonal facies belt, (3) a barrier (shoal) facies belt and (4) an open-marine facies belt. They are respectively interpreted as inner, middle and outer-ramp carbonates developed in a shallowing-upward sequence.