Luminescence dated Late Pleistocene wave-built terraces in northeastern Brazil

This study presents field and chronological investigations along the coast of northeastern Brazil from ~4°S to 9°S latitude, which corresponds to ~700 km of coastline under a semi-diurnal mesotidal regime. We investigated wave-built terrace deposits and dated sediments using the optically stimulated luminescence and thermoluminescence methods on quartz grains. The wave-built terraces yielded two main age groups: 200-230 ka and 100-130 ka, which we interpreted as depositional ages. We correlated these age groups with oxygen-isotope stages 7c and 5e, respectively. These events correspond to the antepenultimate and penultimate transgressions along the Brazilian coast. The deposits occur mainly in patches on low-lying flat plateaus along the littoral zone and incision valleys that cut across coastal tablelands. The altitude of the base of the 200-230 ka terraces ranges from 10 m above mean sea level (asl) to -2m asl, whereas the base of the 100-130 ka varies from 12 m asl to -2 m asl. Both terraces were deposited in the foreshore and upper shoreface zones. We noted a coincidence between sea-level highstand chronologies in northeastern Brazil and those in the Bahamas and Bermuda.<br>Este estudo apresenta uma investigação de campo e geocronológica realizada ao longo da costa nordeste do Brasil entre ~4°S e 9°S de latitude, o que corresponde a ~700 km de costa submetida a um regime de meso-maré. Nós investigamos terraços marinhos construídos por ondas e datamos sedimentos usando luminescência oticamente estimulada e termoluminescência em grãos de quartzo. Os terraços marinhos forneceram dois grupos de idades: 200-230 ka e 100-130 ka, que interpretamos como idades de deposição. Nós correlacionamos estas idades com idades do estágio isotópico do oxigênio 7c e 5e, respectivamente. Estes eventos correspondem a antepenúltima e penúltima transgressões que ocorreram ao longo da costa brasileira. Os depósitos ocorrem predominantemente em faixas sobre plateaus horizontais e de baixa altitude ao longo da zona litorânea e em vales incisos que cortam os tabuleiros costeiros. A altitude da base dos terraços de 200-230 ka varia entre 10 m e -2 m anm (acima do nível do mar), enquanto a base do terraço de 100-130 ka varia entre 12 m e -2 m anm. Ambos os terraços foram depositados na zona de frente de praia e zona de antepraia superior. Nota-se umaa coincidência entre a cronologia de níveis marinhos elevados no nordeste do Brasil e aquelas das Bahamas e Bermudas

Environmental changes recorded in the Holocene sedimentary infill of a tropical estuary

12 páginas.-- 7 figuras.-- 2 tablas.-- 79 referencias.-- Supplementary data related to this article can be found at https://doi.org/10.1016/j.quaint.2018.03.006 .--Early-to late Holocene sedimentary infill of the Potengi-Jundiai Estuary (Brazil) was studied in a 31.5 m long sediment core. The borehole was drilled in a mangrove area within the central part of the flood tide delta. The sedimentary record, encompassing the last 10 kyr, was studied for sediment texture and for the n-alkanes composition of organic matter (OM). Sediments rich in OM and bivalve shells accumulated during the period of sea-level rise, mostly in an intertidal environment of mangrove forest, mudflat and subtidal estuarine flood delta. The characterization of n-alkanes (C10-C33) and lignin methoxyphenols by means of direct analytical pyrolysis (Py-GC/MS) technique allowed determining the sources of the extant OM. Downcore fluctuations were observed in n-alkanes and in several n-alkane based indices, such as long chain carbon preference index (CPI C24-C33), long to short chain ratio (L/S) and average chain length (ACL), as well as in the relative proportion of lignin derived compounds. The n-alkanes distribution points to changing sources of OM input to the estuarine sediments over most of the Holocene period. Major inputs of terrestrial vegetation alternated with periods of mixed input from aquatic macrophytes as the rate of sea-level rise changed over time. The n-alkanes distribution and the lignin markers were useful for reconstructing paleoenvironmental conditions, particularly during the early Holocene when the lower Potengi River valley (now an estuarine area) could accommodate terrestrial forest vegetation before switching to halophytic mangroves as sea levels rose.This study has been carried out within the framework of the project PVE 060/2012 - MUNIM, funded by CAPES, Ciência sem Fronteira, program of the Brazilian Government. We would like to express our gratitude to Professors F. Pinheiro Lima Filho and F.H. Rego Bezerra for their invaluable help during all phases of field work. Also acknowledge is EU Erasmus Mundus Joint Doctorate fellowship administered by FUECA, University of Cádiz, Spain to Mukesh Kumar. Research was supported by EU contract numbers FP7-ENV-2011, Grant agreement No. 282845, and FP7-ENV-2012 Grant agreement No. 308392 and MINECO Spain project INTERCARBON (CGL2016-78937-R). Alba Carmona Navarro, and Desire Monis Carrere from IRNAS-CSIC are thanked for their technical assistance.Peer reviewe

Analytical pyrolysis (Py‐GC/MS) of sediments: sea‐level rise episodes During the holocene in the potengi–jundiai estuary, ne brazil

Póster presentado en el la XVI Reunión Científica de la Sociedad Española de Cromatografía y Técnicas Afines (SECyTA2016) P‐ENV‐31Eds: González-Pérez, José Antonio.-- Almendros Martín, Gonzalo.-- González-Vila, Francisco Javier.-- Rosa Arranz, José M. de laUnderstanding sea‐level changes on various time‐scales is important because it is usually associated to climate changes [1]. Sediments in estuaries may retain a continuous record of climatic and environmental markers surrogated to factors like relative sea level (RSL), vegetation cover, and connectivity with the open ocean. Sediments accumulated since the last glacial maximum (LGM; c. 20 kyr.) are particularly informative and encompass valuable information to infer accurate RSL curves. Lipid biomarkers are preserved in sediments and include molecular markers like n‐alkanes and n‐alkanoic acids increasingly used for paleoclimate and paleoenvironmental reconstructions [2]. In this communication analytical pyrolysis (Py‐GC/MS) is used to study the structure of organic matter (OM) contained in dated sediments from core IG‐8 (31 m depth). This technique has been previously used to monitor past environmental changes in the area [3]. The core was drilled in the area of central flood delta of Potengi‐Jundiai estuary, through the sedimentary sequence accumulated since ca 9,8 kyr cal BP [4]. Marked compositional differences between the OM of different ages were found. Specifically the n‐alkane series were found particularly informative in discriminating OM sources (terrigenous vs marine). In the surface, the alkane series is characterized by a high average chain length (ACL) value indicating a clear influence from terrestrial vegetation. From 6.5 to 11.5 m depth an increase in the terrigenous contribution is observed by an increase in ACL values in correspondence with δ13C depletion. At 22.8 m depth and at 26.6 m there are again inputs from terrestrial plants, but for short periods of Time. Bellow 26.6 m the influence is marine and ends at 29.45 m with a neat alteration of sediment isotopic signature with a δ13C enriched layer with no organic markers and indicating the occurrence of sedimentary conditions favouring carbonate formation. Below this depth, the OM in the sediments shows a conspicuous terrestrial influence (depleted conductivity and δ13C and increase in alkanes ACL and long vs short chain length (L/S) ratio) that increase towards bottom of the core down at 30.95 m. This possibly indicates a drastic sea‐level change during this period of time.[1] G. Milne, A&G 49 (2008) 2.24‐2.28. (doi: 10.1111/j.1468‐4004.2008.49224.x) [2] T.I. Eglinton, G. Eglinton, Earth Planet. Sc. Lett. 275 (2008) 1‐16. (doi: 10.1016/j.epsl.2008.07.012) [3] T. Boski, R.J. Angulo, M.C. Sousa Bezerra, E.G. Barboza, H. Knicker, J.A. González‐Pérez, F.J. González‐Vila, J. Quat. Sc. 30 (2015) 9‐18. (doi: 10.1002/jqs.2753) [4] T. Boski, F.H.R. Bezerra. L.F. Pereira, A.M. Souza, R.P. Maia, F.P. Lima‐Filho, Marine Geol. 365 (2015) 1‐13. (doi: 10.1016/j.margeo.2015.04.N

Hypogenic origin, geologic controls and functional organization of a giant cave system in Precambrian carbonates, Brazil

This study is focused on speleogenesis of the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR), the longest caves in South America occurring in the Neoproterozoic Salitre Formation in the São Francisco Craton, NE Brazil. We employ a multidisciplinary approach integrating detailed speleomorphogenetic, lithostratigraphic and geological structure studies in order to reveal the origin of the caves, their functional organization and geologic controls on their development. The caves developed in deep-seated confined conditions by rising flow. The overall fields of passages of TBV and TBR caves represent a speleogenetically exploited large NE-SW-trending fracture corridor associated with a major thrust. This corridor vertically extends across the Salitre Formation allowing the rise of deep fluids. In the overall ascending flow system, the formation of the cave pattern was controlled by a system of sub-parallel anticlines and troughs with NNE-SSW dominant orientation, and by vertical and lateral heterogeneities in fracture distribution. Three cave-stratigraphic stories reflect the actual hydrostratigraphy during the main phase of speleogenesis. Cavities at different stories are distinct in morphology and functioning. The gross tree-dimensional pattern of the system is effectively organized to conduct rising flow in deep-seated confined conditions. Cavities in the lower story developed as recharge components to the system. A laterally extensive conduit network in the middle story formed because the vertical flow from numerous recharge points has been redirected laterally along the highly conductive unit, occurring below the major seal - a scarcely fractured unit. Rift-like and shaft-like conduits in the upper story developed along fracture-controlled outflow paths, breaching the integrity of the major seal, and served as outlets for the cave system. The cave system represents a series of vertically organized, functionally largely independent clusters of cavities developed within individual ascending flow cells. Lateral integration of clusters occurred due to hydrodynamic interaction between the flow cells in course of speleogenetic evolution and change of boundary conditions. The main speleogenetic phase, during which the gross cave pattern has been established and the caves acquired most of their volume, was likely related to rise of deep fluids at about 520. Ma or associated with rifting and the Pangea break-up in Triassic-Cretaceous. This study highlights the importance of speleogenetic studies for interpreting porosity and permeability features in carbonate reservoirs

Variation of thickness, internal structure and petrophysical properties in a deformation band fault zone in siliciclastic rocks

We studied the geometry and petrophysical properties of fault core and damage zones of a deformation band fault zone in the arkosic sandstones of the Cretaceous Antenor Navarro Formation in the Rio do Peixe Basin, Brazil. The present work includes results from fieldwork and laboratory measurements. We performed structural, geometric, and permeability measurements in the field. These measurements were performed on a longitudinal scanline along the fault core and 18 orthogonal scanlines crossing both fault core and damage zones in the footwall and hanging wall. Drone images were taken from the field locality to study the geometric relation between fault core and individual deformation bands in the damage zone. Porosity, capillary pressure and grain size analyses were performed on the samples. The studied fault is normal and composed of three linked segments, a central E-W segment which is hard-linked to two NE-SW segments tipping toward east and west. Our results show that fault core is the thickest on the E-W segment. The damage zone is narrower around the central part (E-W segment) of the fault and widens westward in both hanging wall and footwall, beyond this point the hanging wall damage zone is wider than the footwall damage zone. The thickest part of fault core has the lowest porosity and permeability and the highest capillary threshold pressure, therefore, increasing the fault sealing capacity. Permeability measurements parallel and perpendicular to fault dip show an anisotropy, in which the permeability perpendicular to fault dip is one order of magnitude lower than dip-parallel permeability measurements. This work highlights the effect of hard linkage between the E-W and NE-SW segments of the studied fault on the petrophysical properties of fault rocks and emphasizes the influence of such linkage on hampering the fluid flow along the breached segment of the fault

Superposed folding and associated fracturing influence hypogene karst development in Neoproterozoic carbonates, São Francisco Craton, Brazil

Porosity and permeability along fractured zones in carbonates could be significantly enhanced by ascending fluid flow, resulting in hypogene karst development. This work presents a detailed structural analysis of the longest cave system in South America to investigate the relationship between patterns of karst conduits and regional deformation. Our study area encompasses the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves, which are ca. 107 km and 34 km long, respectively. This cave system occurs in Neoproterozoic carbonates of the Salitre Formation in the northern part of the São Francisco Craton, Brazil. The fold belts that are around and at the craton edges were deformed in a compressive setting during the Brasiliano orogeny between 750 and 540 Ma. Based on the integrated analysis of the folds and brittle deformation in the caves and in outcrops of the surrounding region, we show the following: (1) The caves occur in a tectonic transpressive corridor along a regional thrust belt; (2) major cave passages, at the middle storey of the system, considering both length and frequency, developed laterally along mainly (a) NE-SW to E-W and (b) N to S oriented anticline hinges; (3) conduits were formed by dissolutional enlargement of subvertical joints, which present a high concentration along anticline hinges due to folding of competent grainstone layers; (4) the first folding event F1 was previously documented in the region and corresponds with NW-SE- to N-S-trending compression, whereas the second event F2, documented for the first time in the present study, is related to E-W compression; and (5) both folding events occurred during the Brasiliano orogeny. We conclude that fluid flow and related dissolution pathways have a close relationship with regional deformation events, thus enhancing our ability to predict karst patterns in layered carbonates

Sea-level rise episodes during the Holocene in the Potengi¿Jundiai Estuary, NE Brazil inferred from direct analytical pyrolysis (Py-GC/MS) of sediments

Understanding sea-level changes on various time-scales is important because it is usually associated to climate changes (Milne, 2008). Sediments in estuaries may retain a continuous record of climatic and environmental markers surrogated to factors like relative sea level (RSL), vegetation cover, and connectivity with the open ocean. Sediments accumulated since the last glacial maximum (LGM; c. 20 kyr.) are particularly informative and encompass valuable information to infer accurate RSL curves. Lipid biomarkers are preserved in sediments and include molecular markers like n-alkanes and n-alkanoic acids increasingly used for paleoclimate and paleoenvironmental reconstructions (Eglinton and Eglinton, 2008). In this communication analytical pyrolysis (Py-GC/MS) is used to study the structure of organic matter (OM) contained in dated sediments from core Ig-8 (31.5 m depth). This technique has been previously used to monitor past environmental changes in the area (Boski et al., 2015a). The core was drilled in the area of central flood delta of Potengi-Jundiai estuary, through the sedimentary sequence accumulated since ca 10 kyr cal BP (Boski et al., 2015b). Direct pyrolysis was performed in a double-shot pyrolyzer (Frontier Lab 2020i) attached to a GC/MS system (Agilent 6890N + 5973MSD). Detailed chromatographic conditions can be found elsewhere (Boski et al., 2015a). In short, samples were thoroughly homogenized and samples introduced (1 mg) into a preheated micro-furnace at 500 ºC for 1 min and evolved gases transferred to the GC/MS for analysis. Compounds assignment was done via single-ion monitoring and by comparison with published and stored (NIST and Wiley libraries) data.The Spanish Ministry of Economy and Competitiveness (MINECO) is acknowledge for project (CGL2016-78937-R). The authors wish to thank Alba Carmona and Desiré Monis for their valuable technical assistance in Py/GC-MS analysis.Peer Reviewe

Fracture Network Patterns from the Brejões Outcrop, Irecê Basin, Brazil

Fracture patterns in the Neoproterozoic carbonates of the Salitre Formation from the Brejoes outcrop, Irece Basin,Brazil, digitised from drone photogrammetry using an automated fracture extraction tool. The fracture traces are georeferenced to a local coordinate system (EPSG:32724, WGS 84 / UTM zone 24S). The data contains: - shapefile of the fracture network, basemap orthomosaic and P21 fracture intensity raste