Mega gravitational slides in Cerro Bola and Sierra de Maz Hills (Guandacol Formation), and their relationship with the Late Paleozoic Ice Age, La Rioja, Argentina

La Formación Guandacol en su localidad homónima es conocida por los extensos depósitos de la glaciación gondwánica. Sin embargo ésta área también es importante debido a la excelente exposición de Depósitos de Transporte en Masa (MTD) que debido a sus características y dimensiones, son ejemplos a escala sísmica en el mundo. La gran cantidad de sedimento acumulado rápidamente en una cuenca subsidente, favorecieron al desarrollo de estos depósitos, expuestos debido a la inversión tectónica a lo largo de la falla de Valle Fértil. Este trabajo documenta uno de los ejemplos más completo de una sucesión de MTD´s, desde la cicatriz de deslizamiento hasta el desarrollo de estos depósitos, con todos sus elementos sedimentarios y deformacionales característicos. Se describen tres intervalos de MTD´s: el MTD 1 aflora en los Cerros Bola y guandacol, donde en ésta última área algunos autores sugieren una discontinuidad separando la sección basal en una nueva formación. El MTD 2, de 200 m de espesor, presenta una exposición continua de 10 km en el Co Bola y 4 km en el Co Guandacol. El MTD 3 es más complejo ya que presenta fallas sinsedimentarias, que permiten el desarrollo de conglomerados de ?post-rilling? a lo largo de la superficie de la cicatriz de deslizamiento. Los tres MTDs son perfectamente correlacionables en ambos afloramientos, donde también se muestra cómo cambian facialmente desde un margen hacia el centro de cuenca. Estas sucesiones son ejemplares únicos, ya que una secuencia así, solo ha sido observada en registros sísmicos a la fecha.This paper reports and analyzes the presence of large, seismic-scale, mass transport deposits (MTDs) recorded within the Guandacol Formation. These major submarine landslides seem to be connected with the occurrence of glacial episodes. The Guandacol Formation is part of the Paganzo Basin fill of Norwest Argentina (Fig. 1), and it is well known for recording several glacial cycles of the Late Paleozoic Ice Age. In this contribution we report and describe three major glacial/deglacial cycles (Fig. 1b) of Mississippian/Pennsylvanian age (Valdez et al., 2013). Outcrops of Guandacol Formation in Cerro Bola and Sierra de Maz (Cerro Guandacol) areas preserve those glacial cycles and each consists in the succession from non-glacial deltaic deposits to proglacial and thick mass-transport deposits (resedimented diamictites), which are the aim of this study, and finally postglacial marine varied strata, including sandy turbidites, shales with and without dropstones and some deltaic deposits (Milana et al., 2010; Dykstra et al., 2011). This study focuses on Sierra de Maz and Cerro Bola localities because they show very well exposed seismic-scale MTDs that otherwise would be quite difficult to see (Fig. 2a, b). Thus, these outcrops give the opportunity to compare many characteristics that are usually seen in seismic records, directly on the ground. On this sense, this contribution is mainly oriented to describe the facial and geometrical interrelations between these large MTDs (as there are many minor MTDs) and not the detailed internal architecture or their comparison to specific seismic features. The occurrence of these large MTDs can be explained by the large amounts of sediment delivered to the basin triggered by glacial- deglacial episodes. Due to the scarcity of well-exposed mega-scale MTD successions, a detailed study is being carried out since a few years. The result of detailed mapping of this rough terrain allow an excellent correlation between single MTDs, for several kilometers from Guandacol to Bola Hill outcrops (Fig. 3), and also portraying how a single MTD changes laterally when passing from a basin-margin environment (Guandacol Hill) to a basin-center environment (Bola Hill). The local Guandacol Formation shows three large glacial cycles that are mainly represented by single large MTDs and/or MTD composite intervals. The oldest MTD1 crops out completely in the Guandacol Hill, but only the upper part is present at Bola Hill (Fig. 4). MTD1 particular diagenesis and broad folds caused some authors to separate it from the Guandacol Formation, but we did not find any significant unconformity other than the normal upper relief between it and the following inter-MTD deposits. MTD2 is the largest and occurs as basin widens and more accommodation space is available. Reaching up to 200 m thick, it crops out continuously for more than 10 km in Bola Hill and 4 km in Guandacol Hill (Figs. 5, 6). The MTD3 is more complex due to its encroaching with large syn-sedimentary faults that we interpret as a large-scale slide scar associated to the MTD3 interval (Figs. 9, 10). This potential slide scar is associated with other elements as incised valleys or rilling at the scar surface, which have been observed in subsurface examples. Therefore one of the largest example of MTD successions and probably the best exposed worldwide is documented for the first time as a large, seismic-scale slide-scar cropping out in association to an MTD interval, with all the suite of sedimentary and deformational elements that might be expected for this play. Due to the fact these features are rarely exposed altogether, we expect this outcrop could be a world-class example to observe features cropping out that otherwise could be only studied indirectly from deep-water seismic surveys. This succession also serves as an example of how some sedimentary features could be easily mistaken by tectonic features when the scale of the sedimentary processes involves the discrete movement of large volumes (several km3) of semiconsolidated sedimentary units, as in the case presented here.Fil: Buso, Victoria Valdez . Universidade do Vale do Rio Dos Sinos; BrasilFil: Milana, Juan Pablo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Kneller, Benjamin. University Of Aberdeen; Reino Unid

Megadeslizamientos gravitacionales de la Formación Guandacol en Cerro Bola y Sierra de Maz y su relación con la glaciación del Paleozóico Tardío, La Rioja, Argentina.

La Formación Guandacol es conocida por los extensos depósitos de la glaciación gondwánica y en los cuales se registran diferentes ciclos glaciales del Paleozoico Tardío. Sin embargo, en las áreas del Cerro Guandacol y Cerro Bola (Provincia de La Rioja, Argentina), esta formación adquiere mayor relevancia debido a la presencia y excelente exposición de depósitos de transporte en masa que debido a sus características y dimensiones, conformando ejemplos a escala sísmica como pocos se conocen en el mundo. Estos grandes deslizamientos submarinos parecen estar conectados con la ocurrencia de ciclos glaciales y deglaciales, donde la gran cantidad de sedimento liberado favoreció el desarrollo de estos megadepósitos. En este trabajo se documentan tres ciclos glaciales de edad mississippiana/ pennsylvaniana, donde los depósitos que predominan son diamictitas glacigénicas resedimentadas. Estos depósitos se encuentran intercalados con sedimentos deltaicos o fluvio-deltaicos y marinos postglaciales. Dentro de este contexto, en este trabajo se reporta uno de los ejemplos más completo de una sucesión vertical y variaciones laterales, de depósitos de transporte en masa (a los que llamaremos en el texto por su sigla abreviada en inglés, MTD) incluyendo desde la cicatriz de deslizamiento hasta el desarrollo de estos depósitos, con todos sus elementos sedimentarios y deformacionales característicos. Se describen tres intervalos de MTDs: el MTD1 aflora en los cerros Bola y Guandacol, donde en ésta última área algunos autores sugieren una discontinuidad separando la sección basal en una nueva formación. El MTD2, que alcanza los 200 m de espesor, presenta una exposición continua de 10 km en el Cerro Bola y 4 km en el Cerro Guandacol. El MTD3 es más complejo ya que presenta fallas sinsedimentarias que permiten el desarrollo y preservación de conglomerados de “post-rilling” a lo largo de la superficie de la cicatriz de deslizamiento. Los tres MTDs son correlacionables entre ambos cerros, donde también se muestra cómo cambian facialmente desde un margen hacia el centro de cuenca. Estas sucesiones son ejemplos únicos, ya que una serie de deslizamientos de este porte y nivel de exposición, sólo es comparable a lo observado en registros de sísmica de reflexión a la fecha

Block generation, deformation and interaction of mass transport deposits with the seafloor : An outcrop-based study of the Carboniferous at Cerro Bola, NW Argentina

The research presented here was carried out with support from CNPq-Brazil (National Council for Scientific and Technological Development) in partnership with Shell-Brazil. We thank Massimo Moretti and an anonymous reviewer, whose constructive comments and criticisms helped to improve the text, their efforts are highly appreciated. Finally, we thank Kei Ogata, Gian Andrea Pini and Andrea Festa for editing this volume.Peer reviewedPostprin

Tabularity of individual turbidite beds controlled by flow efficiency and degree of confinement

The authors would like to acknowledge the support of the PRAX 2 Joint Industry Project at the University of Aberdeen, funded by Petrochina, Statoil, BP and Det Norske (now AkerBP), which has allowed us to undertaken this study. We are grateful to Professor Bryan Cronin who provided much assistance and advice in the field. We also wish to thank Jianan Wu and Guilherme Bozetti for their assistance in the field. Three reviewers (Mike Mayall, Georgios Pantopoulos and an anonymous reviewer) provided very constructive and crucial ideas, which have greatly improved the manuscript.Peer reviewedPostprin

Late Palaeozoic glacial cycles and subcycles in western Gondwana : Correlation of surface and subsurface data of the Paraná Basin, Brazil

This work is part of a research project supported by BG Brazil E&P Ltd. entitled “Carboniferous de-Glacial record in the Paraná Basin and its analogue in the Paganzo Basin of Argentina: Impacts on reservoir predictions”. The authors would also like to acknowledge the ANP (Agência Nacional do Petróleo, Gás Natural e Biocombustível) (ANP BG 29) for its support to the project. This project was carried out at the Universidade do Vale do Rio dos Sinos (UNISINOS) in collaboration with the University of Aberdeen, Universidade Federal do Rio Grande do Sul (UFRGS), Universidad Nacional de San Juan (UNSJ), Argentina, and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). The third author would like to acknowledge the long-term support from the Brazilian Research Council (Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq). A special acknowledgment is made to Carla Puigdomenech, Bruno Vaz de Carvalho and Fabiano Rodrigues, who assisted in the field campaigns.Peer reviewedPostprin

The coastal ridge sequence at Rio Grande do Sul: A new geoarchive for past climate events of the Atlantic coast of southern Brazil since the mid Holocene

We present here the first geochronometric analysis of a large succession of coastal ridges that developed south of Rio Grande do Sul inlet, aided by OSL dating of samples taken in this succession that amounts c. 306 coastal ridges. This succession allows defining epochs of enhanced coastal drift or fluvial transport to the river mouth. Additionally, changes in the preservation of ridges also suggest the additional effect of transverse winds that create blow outs, while changes in the ridge packages planview onlap suggest possible changes in the dominant longshore drift. Four OSL samples located strategically allow defining the age of five main stages of this succession. The first stage comprises 2 substages. The first substage shows ridges #1 to #36 onlapping the boundary coastal scarp northwardly, while the second (ridges #37 to #84) shows an inversion of ridge shape wedging out southwards until coast returns to be quasi parallel to the initial coastal scarp estimated to be c. 6 ka. We estimate this first stage to comprise enhanced coastal drift due to higher and sandier ridges, ending at c. 4.1 ka. The second stage (ridges #85 to #124) ridges is marked by a slight unconformity, and indicates a period of enhanced fluvial progradation and less coastal drift suggesting milder winds up to 3.6 ka. The third stage (ridges #125 to #204) initiates with erosion of ridges near the delta front, being higher and sandier ridges, suggesting enhanced coastal drift due to windier conditions, being the windiest time bracketed between 3.3 and 2.35 ka. The fourth stage (ridges #205 to c. #270) shows again, as second stage, a tendency of wedging out southwards, suggesting enhanced fluvial progradation, estimated between 2.34 and 1.7 ka. The fifth stage is defined by a complete change of coastal plain progradation, due to the rapid recycling of beach ridges into a complex of blow outs and arcuate sand dunes. Ridges are sparsely recognized in cases they developed during short lived events of enhanced longshore drift, with an outstanding group (ridges #288 to #290) that we correlate to a 1.1–0.9 ka cooling event. Future studies, improving the chronostratigraphy of the beach ridges succession at Rio Grande and comparing it with the Paraná river delta ridges, will help understanding the complex environmental history of South America, that include a reversal of the longshore drift, given the fact they are among the most complete upper Holocene geoarchives available.Fil: Milana, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Conforti Ferreira Guedes, Carlos. Universidade Federal do Paraná; BrasilFil: Valdez Buso, Victoria. Universidade do Vale do Rio Dos Sinos; Brasi

Stratigraphy and depositional architecture of lobe complexes across a range of confinements: Examples from the Late Paleozoic Paganzo Basin, Argentina

The well-exposed, Late Paleozoic glacially-influenced Paganzo Basin offers a unique opportunity to compare and contrast the stratigraphy and depositional architecture of turbidite sheet/lobe complexes with distinct degrees of basin-scale confinements. These include sandstones deposited in narrow paleofjord (Quebrada Las Lajas), moderately narrow paleovalley (Quebrada Grande) and broad depression (Cerro Bola) that are part of the same synchronous transgressive-regressive succession recorded in the basin. This work emphasizes the importance of scales of observation and the importance in make the distinction between the degree of confinement experienced by individual flows and the degree to which the system as a whole is limited by the basin size and geometry. In Quebrada Las Lajas, sheet-like sandstones form lobe complexes largely reflecting the basin physiography. The succession was subdivided into two turbidite stages (Ts1 and 2), separated by a finer-grained interval (F1) that together represents lobe complexes and interlobe systems. Individual sandstone beds are laterally and longitudinally continuous and onlap the paleofjord walls, suggesting vertically-stacked beds. In Quebrada Grande paleovalley, the succession was subdivided into three stages (Ts1 to Ts3), representing lobe complexes, also separated by finer-grained packages (F1 and 2) ascribed to interlobe phases. Individual sandstone beds are truncated, thinning and pinching out, making them hard to correlate between logged sections. This depositional pattern may suggest that lateral stacking dominates during the construction of lobe complexes. At Cerro Bola, the succession was subdivided into five stratigraphic units (Ts1 to Ts5). These units also onlap the basin margin. Individual sandstone beds of Ts1 and Ts2 are similar to those recorded in Quebrada Grande area, also suggesting compensational stacking dominated systems. However, individual sandstone beds within Ts4 are thicker relative to the other units and more continuous longitudinally, reaching the basin margin thus pointing to larger volume flows ascribed to a vertically-stacked pattern. On the other hand, Ts3 and Ts5 correspond to the thinner sandstone beds in the succession and, as these intervals are as thick as the others, they may be attributed to lobe off-axis to fringe settings. In all three areas, the lobe complex geometry is determined by the basin-scale confinement and, at this scale, all of them are represented by more or less tabular, large sandstone bodies showing more similarities than differences. Each of these three successions record an upward increase in the sand-to-mud ratio, which may denote flow ponding or progradation of up-dip deltas that fed these systems.Fil: Fallgatter, Claus. Universidade Federal de Pernambuco; BrasilFil: Buso, Victoria Valdez. University of Aberdeen; Reino UnidoFil: Paim, Paulo S.G.. Universidad de Vale do Rio dos Sinos; BrasilFil: Milana, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentin

The glacial paleovalley of Vichigasta: Paleogeomorphological and sedimentological evidence for a large continental ice-sheet for the mid-Carboniferous over central Argentina

We present new data on the Vichigasta Carboniferous paleovalley, a glacial trough crucial to understand the type of glaciation that affected western Gondwana during the Late Paleozoic Ice Age (LPIA). The filling of this paleovalley starts soon after the mid-Carboniferous glacial peak. Stage I represents pro-glacial lacustrine deposits with outwash, glacially rafted dropstones, mass transport deposits (MTDs) and turbidites of the trunk and a lateral tributary valley. Base-level drop created the scenario for Stage II outwash deltas and sandur deposits, with westward flow. Stage III represents a flooding at the base of the Bashkirian, characterized by typical transgressive dark shales and distal turbidites. Stage IV represents a highstand prograding turbidite wedge. We worked in a detailed terrain analysis, surveyed the scarce sedimentary record left and recovered a rich palynoflora from mudstones of Stage 3. The almost complete erosion of the fill allowed us to analyze the shape of this paleovalley and compare it to Olta and Malanzán ones. Vichigasta and Malanzán paleovalleys show similar size, a clear U-shape and regular and homogeneous width downslope, a requisite for bypass glacial paleovalleys carved in a subcrop of homogeneous composition (basement), which allow us to interpret them as outlet valleys. Olta paleovalley ranks as tributary as its capacity is only one-third of the others. We also identified a basement high over the Vichigasta valley floor that suggests the presence of a potential drumlin supporting our interpretation as a bypass glacial valley. This post-glacial flooding event is widely observed at other glacial valleys as the Olta-Malanzán herein analyzed and others like Las Lajas and Quebrada Grande. The new data from Vichigasta paleovalley reinforce the hypothesis of a large ice-sheet located to the east of the craton.Fil: Valdez Buso, Victoria. University Of Aberdeeen; Reino Unido. University of Aberdeen; Reino UnidoFil: Milana, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: di Pasquo, Mercedes. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Espinoza Aburto, José Horacio. Universidad de Atacama; Chil

A field guide to the sand-rich turbidite systems of the Taciba Formation, Itararé Group, Paraná basin, Brazil

This field guide provides a detailed outcrop logistics, access and description of the sand-rich turbidite deposits of the Taciba Formation (Rio do Segredo Member), the uppermost unit of the Pennsylvanian Itararé Group (Paraná Basin), which crops out in the Santa Catarina State, southern Brazil. This area has become a classic destination for professional’ field courses and students interested in outcrop analogous to offshore turbidite reservoirs. Although some of the outcrops have been widely described, some localities remain unexplored. These turbidite systems are here subdivided on the basis of their degree of confinement, relative to the Precambrian basin floor topography. The bedrock morphology was shaped during the Late Paleozoic Ice Age. Advance and retreat phases of glaciers are represented by superficial scouring into the crystalline basement. This glacially-carved topography in turn controlled the subsequent sedimentation by forming a basal nonconformity in the Taciba Formation. Thus, the turbidity currents and their deposits, exposed in three main areas along the eastern margin of the Paraná basin, were classified as confined and/or unconfined. This field guide is also valuable for nourishing the ongoing debate on the turbidity currents interpretations based on sedimentological descriptions of the main localities and their major features. Field guides are quite popular in North America and Europe, among other places, but not so popular in Brazilian literature. The present contribution aims to bring details on some little known turbidite-outcropping localities of the Taciba Formation. It also intends, through its format, to attract interest the of national and international geologists on Brazilian key outcrops and offer a synthesis and a starting point for teaching purposes and future studies