Papers by Caroline Cazarin
This study is focused on speleogenesis of the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR)... more 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 geo-logic 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.
RESUMO-Este trabalho focou sobre os efeitos das fraturas na morfogênese do carste epigênico na Fo... more RESUMO-Este trabalho focou sobre os efeitos das fraturas na morfogênese do carste epigênico na Formação Jandaíra, Bacia Potiguar. A Formação Jandaíra é uma plataforma carbonática Turoniana-Campaniana que se desenvolveu durante a fase pós-rifte da margem Equatorial, durante a separação entre as placas Africana e Sul-americana. Esta unidade é a principal exposição de rochas carbonáticas Cretáceas em bacias sedimentares brasileiras e abriga um grande número de cavernas e outras feições cársticas. O carste epigênico ocorre em carbonatos fraturados submetidos à dissolução química. A metodologia deste estudo compreendeu o uso de imagens de drone e o mapeamento de campo de um amplo afloramento e de cavernas. A área de estudo é o Lajedo Rosário, um afloramento com 1,5km x 0,5km de dimensões, localizado na parte sul da bacia. Os resultados indicam quatro principais direções de fraturas onde ocorre carstificação: NS, EW, ENE-WSW e NW-SE. As estruturas cársticas ocorrem ao longo de sete padrões estruturais: falhas step-over, fraturas en echelon, interconexão de fraturas, no centro de fraturas, ao término de fraturas, dendrítica e padrão misto. Esses padrões estruturais favorecem a concentração de fraturas e, portanto, a dissolução e o desenvolvimento cárstico. Estes resultados podem ser de grande valia para explicar os sistemas cársticos em outras unidades carbonáticas. ABSTRACT-This work focused on the effects of fractures in the morphogenesis of epigenic karst in the Jandaíra Formation, Potiguar Basin. The Jandaíra Formation is a Turonian-Campanian carbonate platform that developed during the post-rift phase of the Equatorial margin, during the drift between the South American and African plates. This unit is the major exposed Cretaceous carbonate unit in Brazilian sedimentary basins, and it hosts a large number of caves and other karst features. The epigenic karst occurs in fractured carbonates undergoing chemical dissolution. The methodology of this study comprised the use of drone imagery and field mapping of a large outcrop and caves. The study area is the Lajedo Rosário, a 1.5 km x 0.5 km outcrop in the southern part of the basin. The results indicate four main trend of fractures, where karstification occurs: NS, EW, ENE-WSW, and NW-SE. The karst structures occur along seven structural patterns: step-over faults, en echelon fractures, interconnection of fractures, at the center of fractures, at the termination of fractures, dendritic, and mixed pattern. These structural patters favor fracture concentration and, therefore, dissolution and karst development. These findings may be of value to explain karst systems in other carbonate units.
Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absen... more Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Janda ıra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post-rift stage of the Potiguar rift (NE Brazil). The Janda ıra Formation in the present onshore domain experienced <1.5 km thermal subsidence and, following Tertiary exhumation, forms outcrops over an area of >1000 km 2. The carbonates have a gentle, <5⁰, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub-vertical veins, and sub-vertical as well as sub-horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Janda ıra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Janda ıra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400–500 m. Deformation was accommodated by a dense network of sub-vertical mode I and hybrid fractures associated with sub-vertical stylolites developed in a stress field characterised by a sub-horizontal r 1 and sub-vertical r 2. The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Ac ßu sandstone underlying the Janda ıra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800–900 m entering a depth interval characterised by a sub-vertical r 1. At this stage, sub-horizontal stylolites developed liberating calcite which sealed the sub-vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre-existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures.
This paper analyzes different types of karst landforms and their relationships with fracture syst... more This paper analyzes different types of karst landforms and their relationships with fracture systems, sedimentary bedding, and fluvial processes. We mapped karst features in the Cretaceous carbonates of the Jandaíra Formation in the Potiguar Basin, Brazil. We used high-resolution digital elevation models acquired using LiDAR and aerial orthophotographs acquired using an unmanned aerial vehicle (UAV). We grouped and described karst evolution according to scale and degree of karstification. These degrees of karst evolution are coeval. Fractures are opened by dissolution , forming vertical fluid conduits, whereas coeval dissolution occurs along horizontal layers. This conduit system acts as pathways for water flow. The enlargement of conduits contributes to the collapse of blocks in sink-holes and expansion of caves during an intermediate degree of karstification. Propagation of dissolution can cause the coalescence of sinkholes and the capture of small streams. Fluvial processes dominate karst dissolution at an advanced degree of karstification. Comparisons with previously published ground-penetrating radar (GPR), borehole and seismic surveys in sedimentary basins indicate that these structures can be partially preserved during burial.
Porosity and permeability along fractured zones in carbonates could be significantly enhanced by ... more 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.
The increasing importance of carbonate rocks as aquifers, oil reservoirs, and for urban problems ... more The increasing importance of carbonate rocks as aquifers, oil reservoirs, and for urban problems is demanding detailed characterization of karst systems, a demand that can be partially satisfied with GPR imaging. However, the goal of imaging and interpreting karstified carbonate rocks is notoriously difficult due to the complex nature of the geometry of the dissolution and the GPR intrinsic limitations. One way forward is the direct comparison of GPR images with similar outcropping rocks. A joint study involving a 200 MHz GPR survey, unmanned aerial vehicle imagery (UAV), and outcrop characterization is presented aiming to improve the interpretation of sedimentary structures, fractures and karst structures in GPR images. The study area is a 500 m wide and 1000 m long carbonate outcrop of the Jandaíra Formation in Potiguar basin, Brazil, where sedimentary, fracture, and karst features can be directly investigated in both vertical and horizontal plan views. The key elements to interpret GPR images of karstified carbonate rocks are: (1) primary sedimentary structures appear in radargrams as unaltered imaged strata but care must be taken to interpret complex primary sedimentary features, such as those associated with bioturbation; (2) subvertical fractures might appear as consistent discontinuities in the imaged strata, forming complex structures such as negative flowers along strike–slip faults; (3) dissolution may create voids along subhorizontal layers, which appear in radargrams as relatively long amplitude shadow zones; and (4) dissolution may also create voids along subvertical fractures, appearing in radargrams as amplitude shadow zones with relatively large vertical dimensions, which are bounded by fractures.
This paper analyzes different types of karst landforms and their relationships with fracture syst... more This paper analyzes different types of karst landforms and their relationships with fracture systems, sedimentary bedding, and fluvial processes. We mapped karst features in the Cretaceous carbonates of the Jandaíra Formation in the Potiguar Basin, Brazil. We used high-resolution digital elevation models acquired using LiDAR and aerial orthophotographs acquired using an unmanned aerial vehicle (UAV). We grouped and described karst evolution according to scale and degree of karstification. These degrees of karst evolution are coeval. Fractures are opened by dissolution , forming vertical fluid conduits, whereas coeval dissolution occurs along horizontal layers. This conduit system acts as pathways for water flow. The enlargement of conduits contributes to the collapse of blocks in sink-holes and expansion of caves during an intermediate degree of karstification. Propagation of dissolution can cause the coalescence of sinkholes and the capture of small streams. Fluvial processes dominate karst dissolution at an advanced degree of karstification. Comparisons with previously published ground-penetrating radar (GPR), borehole and seismic surveys in sedimentary basins indicate that these structures can be partially preserved during burial.
The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant per... more The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation. As a consequence, the Jandaíra Formation accommodated fluid flow only during specific moments in time. We reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements. The Jandaíra Formation, which belongs to the post-rift sequence of the Potiguar Basin in northeast Brazil, was deposited from the Turonian onward until a marine regression exposed it in the Campanian. Due to the subaerial exposure, meteoric waters flushed out marine connate waters, leading to an event of early diagenesis and full cementation of the Jandaíra Formation. Fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing. Fracturing in the Late Cretaceous induced a drastic increase in permeability, giving rise to extensive fluid circulation. Host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network, causing it to regain an impermeable and sealing character. In the research area, fluid flow occurred during early burial of the Jandaíra Formation at estimated depths of 400e900 m. This study documents the first application of fluid inclusion isotope analysis on vein precipitates, which allowed full isotopic characterization of the paleo-fluids responsible for calcite vein cementation. The fluid inclusion isotope data indicate that upwelling of groundwater from the underlying Açu sandstones provided the fluids to the fracture network. In Miocene times, renewed tectonic compression of a lower intensity created a secondary fracture network in the Jandaíra Formation. The density of this fracture network, however, was too low to induce a new episode of fluid circulation. As a result, this tectonic event is associated with the development of barren extensional fractures.
The present study investigates the lithofacies and processes such as karstification, which lead t... more The present study investigates the lithofacies and processes such as karstification, which lead to the generation of the karst province of the Neoproterozoic Una and Bambuí groups, located in the central-eastern part of Brazil. This province comprises several systems of carbonate caves (Karmann e Sanchéz, 1979), which include the Toca da Boa Vista and Barriguda caves, considered the largest hypogenic caves in South America (Auler e Smart, 2003).
O presente estudo investiga as litofácies, os processos diagenéticos e espeleogenéticos que gerar... more O presente estudo investiga as litofácies, os processos diagenéticos e espeleogenéticos que geraram o sistema cárstico Toca da Boa Vista-Toca da Barriguda (TBV-TBR).
O presente trabalho é uma contribuição ao conhecimento geológico dos carbonatos do Cretáceo da Fm... more O presente trabalho é uma contribuição ao conhecimento geológico dos carbonatos do Cretáceo da Fm Ponta do Mel.
In this study was analysed thin sections and plugs from the facies of Jandaira Formation, a Turon... more In this study was analysed thin sections and plugs from the facies of Jandaira Formation, a Turonian-
Campanian carbonate platform in the Potiguar Basin. The focus was in samples from the Rosario outcrop
and a few boreholes. Textural features, framework composition, diagenetic processes, and porosity types
was determined. Were also measured petrophysical properties as permeability and porosity. With
petrografic and petrophysical data we can produce a detail map to support structural and karst analyses in
the study area.
Conference Presentations by Caroline Cazarin
Dissolution along zones of preferential flow enhances anisotropy in geological media and increase... more Dissolution along zones of preferential flow enhances anisotropy in geological media and increases its complexity. Many karst models tend to be descriptive and fail to predict localization and structure of karst systems. Conduit architecture is difficult to derive from borehole data, and it can be hardly mapped even with the advent of 3D seismic techniques. Therefore, analysis of the geometry of karst conduit systems remains elusive where direct access to karst conduits is not possible. The present study investigates the relationship between lithofacies, tectonics and karstification in the Neoproterozoic Salitre Formation, located in the central-eastern Brazil. This unit comprises several systems of caves including the Toca da Boa Vista and da Barriguda hypogenic caves, the largest in South America, and focus of this study. We focused on cave mapping and morphogenetic analysis, determination of petrophysical properties, thin-section description, micro-tomography, and isotopic analysis. The Salitre Fm, deposited in an epicontinental sea, comprises mud/wakestones, grainstones, microbial facies, and fine siliciclastic rocks. The caves comprise 3D mazes with a network/spongework pattern. Passages occur in several levels within ca. 60 m thick cave-forming section, limited at the top by lithofacies with low permeability and fractures. Cave development occurred in phreatic sluggish-flow environment with overall upwelling flow. It rose via cross-formational fractures and distributed laterally within the cave-forming section using geological heterogeneities to eventually discharge up through outlets breaching across the upper confining beds. Cave formations include an assemblage indicating a period of water table conditions. Sediment fill includes deposits of dolomitic sand originated from in situ weathering of cave walls and ceiling. Caves show no relationship with the surface. Our data indicate several events of porosity evolution, such as subaerial exposure, folds and fractures, hydrothermal events (exotic minerals assemblage), sulfuric acid dissolution, dissolution at the water table, condensation corrosion, and faults and fractures reactivation. The major enhancement of secondary porosity was due to hypogene speleogenesis. Hypogene karst process may have implications to carbonate reservoirs not only through porosity enhancement, but also through their influence on regional flow systems, cross-formational communication, and migration of hydrocarbons Reference Cited
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Papers by Caroline Cazarin
Campanian carbonate platform in the Potiguar Basin. The focus was in samples from the Rosario outcrop
and a few boreholes. Textural features, framework composition, diagenetic processes, and porosity types
was determined. Were also measured petrophysical properties as permeability and porosity. With
petrografic and petrophysical data we can produce a detail map to support structural and karst analyses in
the study area.
Conference Presentations by Caroline Cazarin
Campanian carbonate platform in the Potiguar Basin. The focus was in samples from the Rosario outcrop
and a few boreholes. Textural features, framework composition, diagenetic processes, and porosity types
was determined. Were also measured petrophysical properties as permeability and porosity. With
petrografic and petrophysical data we can produce a detail map to support structural and karst analyses in
the study area.