The inventory of geological heritage of the state of São Paulo, Brazil: Methodological basis, results and perspectives

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy.The authors acknowledge the Science Without Borders Programme, Process 075/2012, which supported this study and the São Paulo Research Foundation (FAPESP), Process 2011/17261-6. We also thanks C. Mazoca for his help with maps and figures.info:eu-repo/semantics/acceptedVersio

Gondwana Glacial Paleolandscape, Diamictite Record of Carboniferous Valley Glaciation and Preglacial Remnants of an Ancient Weathering Front in Northwestern Argentina

A record of glacier advance and retreat is preserved in Carboniferous strata exposed in an exhumed glacial paleovalley on the eastern side of the Paganzo basin. Previous investigations have focused on the sandstones in the paleovalley and inferred a glacial lacustrine history. New observations have demonstrated that remnants of a preglacial, ancient weathering front, developed under wet tropical conditions and composed of corestones, are found underneath the glaciogenic deposits. Delta and alluvial fan deposits were also recognized, but no inferences were made from the diamictites in the paleovalley regarding glacial events (Andreis et al., Bol Acad Nac Cienc Cordoba 57:3–119, 1986; Buatois and Mángano, J Paleolimnol 14:1–22, 1995; Sterren and Martínez, El Paleovalle de Olta (Carbonífero): Paleoambiente y Paleogeografía. 13º Congreso Geológico Argentino and 3º Congreso de Exploración de Hidrocarburos, Actas, 2, 89–103, 1996). This chapter focuses on the diamictites and provides a link between the sediment infill and the glacial origin of the paleovalley. We describe diamictites and associated sediments at three main locations: at La Chimenea, near the mouth of the paleovalley; at Mid-Valley, near the middle of the paleovalley; and at the Campsite near the head of the valley. We interpret some of the diamictites exposed at La Chimenea and at Mid-Valley to be subglacial tillite. Deformation in the sandstone underlying the tillite indicates warm-based conditions as the glacier advanced over soft deformable sediment. At the Campsite location, a diamictite bed, which is about 1.5 m thick, lies within a sequence of alternating sandstone and siltstone beds. The diamictite bed is interpreted to represent an ice-front readvance during a period of ice retreat. The diamictite may be a debrite originating off the ice front, or a subglacial deposit, i.e., a tillite, or a combination of both. Two additional diamictite beds, exposed higher in this sequence of alternating sandstone and siltstone beds, may also record minor ice-front advances into the flooded valley. Evidence of an ancient, preglacial weathering front (Late Devonian?–Earliest Carboniferous?) has been found in the granitic basement rocks which underlie the glaciogenic deposits, as large corestones included in a weathered regolith. This weathering front was developed under wet tropical conditions, before the onset of Carboniferous glaciations. The tillite and other diamictites overlying the corestones are composed largely of locally derived granitic basement rock. Features observed in the tillite and other diamictites are attributed to rapid rates of deposition, depositional processes, and the susceptibility of pre-weathered granitic basement rock to glacial and other erosional processes. Processes other than glacial erosion and deposition, including mass transport (slumping, rafting, sliding, and debris flow), also operated in the steep-sided valley and contributed large amounts of diamictite and other sediment to the valley fill. Corestones, weathered from the basement rock during a pre-Carboniferous period of intense weathering, constitute the larger clasts in the diamictite and associated deposits. The glacial paleolandscape is very well preserved in detail, after being buried during the Permian and later exhumed in the Cenozoic. The glacial valley was likely a transitional (fjord) environment, as micropaleontological material (Gutiérrez and Limarino, Ameghiniana 38:99–118, 2001) and clay mineral assemblages (Net et al., Sediment Geol 152:183–199, 2002) indicate a marine transgression into the area during the Middle Carboniferous.Fil: Socha, Betty. No especifíca;Fil: Carignano, Claudio Alejandro. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rabassa, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; ArgentinaFil: Mickelson, Dave. University of Wisconsin; Estados Unido

Middle Jurassic-Late Cretaceous Paleogeography of the Western Margin of the Neuquén Basin (34° 30′–36° S)

U–Pb dating of detrital and igneous zircons from the retroarc deposits of the Neuquén Basin has shed light over the Mesozoic evolution of the western border of South America, yet the coeval arc and forearc regions remain mostly indirectly characterized. Furthermore, recent paleogeographic reconstructions consider the arc and forearc regions as a tectonically stable and static region at least until Late Cretaceous. In this chapter, we aim to contribute to the Middle Jurassic-Late Cretaceous paleogeographic reconstructions of the western margin of South America from a western point of view integrating the coeval arc and forearc evolution, between 34° 30′ and 36° S. We focus here in the deposits exposed along the Chilean slope of the Principal Cordillera and use four new detrital zircon age data to determine their ages and main source areas. These ages are compared with 38 published U–Pb detrital zircon ages and integrated into a series of paleogeographic cross sections which illustrate the Mesozoic evolution along the Southern Central Andes encompassing the forearc, arc, and retroarc regions. Our data show that the arc and forearc regions were active at least since the Middle Jurassic. Evidence for this tectonic activity corresponds to the development of forearc basins in the Middle Jurassic and Early Cretaceous times. New ages along the Chilean slope of the Andes allow suggesting an early beginning for the compressive period during the latest Early Cretaceous. The formation of a geographic barrier, as a consequence of the compressive regime, would explain the differences in the sediments provenance between western and eastern deposits during the latest Late Cretaceous. Finally, the almost complete record of Mesozoic ages in the detrital and volcanic deposits of the western slope of the Southern Central Andes constitutes a counter-argument about the null or waning activity proposed for the Middle Jurassic or Late Cretaceous from U–Pb detrital zircon analysis of the eastern Mesozoic deposits. Conversely, our data indicate a continued activity of the arc-related volcanism and magmatism throughout all the Mesozoic time.Fil: Tapia Silva, Felipe Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; ArgentinaFil: Muñoz, Marcia. Universidad Andrés Bello; ChileFil: Farías, Marcelo. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Departamento de Geología; ChileFil: Charrier, Reynaldo. Universidad Andrés Bello; ChileFil: Astaburuaga, Daniela. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Departamento de Geología; Chil

Tectono-Stratigraphic Evolution of the Atuel Depocenter During the Late Triassic to Early Jurassic Rift Stage, Neuquén Basin, West-Central Argentina

The Neuquén basin presents an almost continuous record from the Late Triassic until the Paleocene,making it an excellent case study of the most relevant tectonic stages of southern South America during the Mesozoic. It was initiated in the Late Triassic to Early Jurassic times as a continental rift basin in the context of a widespread extensional stage that affected western Gondwana andculminated with the break-up of the supercontinent.The Atuel depocenter is located in the northern sector of the Neuquén basin. Synrift and sag units are represented by Upper Triassic to Lower Jurassic siliciclastic marine and continental sedimentary rocks including the oldest marine deposits of the basin, of Late Triassic age. The depocenter infill hasbeen deformed and exhumed during the Andean orogeny, being presently exposed in the northern sector of the Malargüe fold and thrust belt. In this review, we have integrated a large set of stratigraphic, sedimentologic, geochronologic and structural data in order to unravel the tectono-sedimentary evolution of the Atuel depocenter, and to evaluate the main controlling factors of thesynrift stage. We analyzed data from the synrift units, such as facies and thickness distribution, sandstone provenance, detrital zircon geochronology data, kinematic data from outcrop scale normal faults, angular and progressive unconformities and subsurface information. Reactivation of preexisting NNW-striking anisotropies under a regional NNE extension resulted in anoblique rift setting, which generated a bimodal distribution of NNW- and WNW-striking major normal faults. Strain and stress tensors obtained from the kinematic and dynamic analysis of structural data show a complex heterogeneity that we interpreted as a result of local stress permutations due to both activity of the larger faults, and to strain partitioning inside the Atueldepocenter.Sedimentologic and petrographic data revealed a complex evolution with strong lateral variations of the depositional environments during the synrift phase, which lasted from Rhaetian to Pliensbachian times. We identified several stages that were controlled by processes of initiation, propagation, growth, linkage and deactivation of new and reactivated faults along the depocenter evolution, in combination with sea level changes related to global eustatic variations. Sandstone provenance data suggest that an important basin reorganization by the Toarcian, probably related to the initiation of the sag stage in this depocenter.Fil: Bechis, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio; ArgentinaFil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Tunik, Maisa Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Suriano, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Lanés, Silvia. Cape Town; SudáfricaFil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentina. Universidad Nacional de Cuyo; Argentin