UNIVERSIDADE FEDERAL DO RIO GRANDE DO NORTE - UFRN CENTRO DE CIÊNCIAS EXATAS E DA TERRA – CCET
DEPARTAMENTO DE GEOLOGIA – DGEO CURSO DE GEOLOGIA
RELATÓRIO DE GRADUAÇÃO – GLG0001
Brechas em uma caverna hipogênica: petrografia, geoquímica e
implicações para cavernas, um caso da Bacia de Irecê, Bahia, Brasil.
Hypogenic Cave Breccia: petrography, geochemistry and implications for
caves, a case from Irecê Basin, Bahia, Brazil.
Author:
Saulo Henrique Lourenço Bezerra
Natal – RN 2019
Saulo Henrique Lourenço Bezerra
Hypogenic Cave Breccia: petrography, geochemistry and implications for caves, a case from Irecê Basin, Bahia, Brazil.
Report presented on July 4, 2018, as
requirement to obtain a Bachelor's degree in Geology by the department of Geology of the Federal University of Rio Grande do Norte
Examiners:
Prof. Dr. Francisco Hilário Rego Bezerra MsC. Cristiane Paulino de Menezes
MsC. Ingrid Barreto Maciel
Natal – RN 2019
Universidade Federal do Rio Grande do Norte - UFRN Sistema de Bibliotecas - SISBI
Catalogação de Publicação na Fonte. UF
RN - Biblioteca Setorial Prof. Ronaldo Xavier de Arruda - CCET
Bezerra, Saulo Henrique Lourenço.
Hypogenic Cave Breccia: petrography, chemistry and
implications for caves, a case from Irecê Basin, Bahia, Brazil / Saulo Henrique Lourenço Bezerra. - 2019.
46f.: il.
Relatório (Bacharelado em Geologia) - Universidade Federal do Rio Grande do Norte, Centro de Ciências Exatas e da Terra, Departamento de Geologia. Natal, 2019.
Orientador: Francisco Hilário Rego Bezerra.
1. Geologia - Relatório. 2. Breccia - Relatório. 3. Hydrothermal Cave - Relatório. 4. Carbonates - Relatório. I. Bezerra, Francisco Hilário Rego. II. Título.
RN/UF/CCET CDU 551
THERM OF APPROVAL
Saulo Henrique Lourenço Bezerra
Hypogenic Cave Breccia: petrography, geochemistry and implications for caves, a case from Irecê Basin, Bahia, Brazil.
Examiner comission composed by:
_______________________________________________________________ 1º Examiner: Prof. Dr. Francisco Hilário Rego Bezerra
Advisor – Departament of Geology da UFRN
_______________________________________________________________ 2º Examiner: MsC. Cristiane Paulino Menezes
PhD student in Science and Petroleum Engineer at PPGCEP/UFRN
_______________________________________________________________ 3º Examinador(a): MsC. Ingrid Barreto Maciel
PhD student in Geodynamics and Geophysics at PPGG/UFRN
Note of the Author:
This work is a mutual result, from one student and three professors advisors, in alphabetical order:
Armstrong Osbourne, from Sydney University, who went to the field with Hilário, and collected sample and changed many e-mails explaining how a cave system works, what each sample is his perspective.
Francisco Hilário, who went to the field, and project coordinator which this work is related. Also helped improve its, needed, correction.
Narendra Kumar Srivastava, who helped a lot with ideas, suggestions, thin sections descriptions and a lot of text review.
Acknowledgments
This work would not be possible without the dedication, love and raising and all positives words of my parents who also are the biggest founders of this work, encouraging me since my childhood, for them all due respect, recognition and love.
My family, who are great supporters always pushing me forward also helping me with my education, my godfathers had a fundamental paper in my initial years at school and later for life. My uncles and aunts for their words of positivity and my sister who indirectly contributed a lot in my life helping me when needed.
My teachers Narendra and Hilário who gave me the opportunity of this project and many hours of their precious time to evaluate, talk and above all teach, being most of what is written result of his contributions. To all my teachers involved at my graduation, Francisco Oliveira, Vanildo, Frederico, David, Marcella, and all others since school, all did their best effort to develop not only learners but friends and ethical professionals.
To Armstrong Osborne, being responsible to this report be written in English, his contributions and many and many mails changed resulted in this job, which is still have a lot to do, what is amazing, because it showed the potential to better understanding. In addition he and Hilário were the ones who sampled and photographed all samples its his credits to all field activities.
My friends who supported me while exchanging ideas, listening arguing and why not criticizing aspects of this job, special thanks to Genilson, João Paulo, Galdino e Tadeu friends who I want to keep for life. Regards to all my mates who someday shared a class, it’s a group achievement.
My girlfriend, her entrance gave me new inspirations and goals to do a better and complete job, for her all my love and dedication in a hope for the best only life we will have. You are incredible.
Thanks to Petrobras and Capes/CNPq for the scholarship and founding crucial to do SEM and thins section with the high. quality needed. And Caroline Cazarin for the much needed external perspective over the caves. That talk helped me a lot.
Abstract
This works aims to give a pioneer conception of brecciated rocks from the world class caves of Irecê Basin, Salitre Formation, Bahia. Of Proterozoical age those caves are receiving increasing attention due to its easy access and similarities with hydrocarbon reservoirs analogues, in special, pre-salt. Through pre-field activities selected areas were chosen, in field, described and sampled, and in lab photographed, described, analyzed and correlated. A total of twenty two thin sections were done and a variety of sedimentary process were observed, being silicification the most common, followed closely by limonitization. Using a classification adapted from Osborne (2001) we found two mains classes of breccias, sedimentary (collapse breccia) and hydraulic, and despite only one occurrence of hydraulic breccias two findings were curious: Barium concentrated in clay minerals and sedimentary plagioclase. Indicating hydrothermalism, those elements (Ba and Al) can help locate those fractures corridors , which concentrates in a typical reservoir most of the porosity and permeability, being a sweet spot in an increasing competitive market. Overall, we also could tell the cave evolution by the type of breccia found, in juvenile caves, hydrothermal ones tend to be the most common, and with ageing caves are infilled by an intricated system of mixing between surface sediments and bedrock, in which sedimentary process become dominant, with opal, chalcedony and limonite growing as the hypogenic fluid enters in the system changing the system dynamics. Key words: Breccia, Carbonate, hydrothermal, cave.
Resumo:
Este trabalho visa dar uma concepção pioneira de rochas de falha em ambiente de caverna. As cavernas de classe mundial, encontram-se na Bacia do Irecê, Formação Salitre, Bahia. De idade Proterozóica essas cavernas estão recebendo atenção crescente devido ao seu fácil acesso e semelaridades nos processos com análogos de reservatórios de hidrocarbonetos, em especial, o pré-sal. Através de atividades pré-campo, locais e cavernas chave foram escolhidas, em campo, descritas e amostradas, e em laboratório fotografadas, descritas, analisadas e correlacionadas. O total de vinte e duas secções delgadas foram confeccionadas e uma variedade de processos sedimentares foram observados, sendo a silicificação a mais comum, seguida de perto pela limonitização. Usando uma classificação adaptada de Osborne (2001) encontramos duas classes principais de brechas, sedimentar (brecha colapsada) e hidráulica, e apesar de apenas uma ocorrência de brechas hidráulicas, dois achados foram curiosos: Bário concentrado em argilominerais e plagioclásio resultante de processo sedimentar. Indicadores de hidrotermalismo, esses elementos (Ba e Al) podem ajudar a localizar esses corredores de fraturas, que se concentram em um típico reservatório de porosidade e permeabilidade, podendo ser aplicado como indicadores desses corredores, que em um mercado cada vez mais competitivo pode ser uma descoberta interessante. No geral, podemos também dizer a evolução das cavernas pelo tipo de brecha encontrada, em cavernas juvenis, as hidrotermais tendem a ser as mais comuns, que com o passar do tempo vão sendo preenchidas por um intrincado sistema de mistura entre sedimentos superficiais transportados e rocha hospedeira. O processo se torna cada vez mais dominante, com opala, calcedônia e limonita crescendo à medida que o fluido hipogênico entra no sistema, no entanto se observou que mesmo sob forte alteração a textura brechoidal tende a ser preservada.
Sumário
1 Introduction ... 1 2 Geological Settings ... 2 2.1 Regional Geology ... 2 2.2 Local Settings ... 3 2.3 The Caves ... 33 Materials and Methodology ... 6
4 Petrography and Petrology ... 7
4.1 Toca da Boa Vista (TBV) Breccias ... 7
4.2 Toca da Barriguda (TBR) Breccia ... 12
4.3 Toca do Morrinho Cave. ... 15
5 Petrology of Morrinhos Breccias ... 26
5.1 Microporosity ... 26
5.2 Precipitation – hydrothermal activity ... 27
6 Results and discussion ... 32
7 Conclusion ... 35
1 1 Introduction
Caves in carbonate rocks are attracting increasing interest as models for petroleum reservoirs, due to their features such as storage and trap capacity (Cazarin et. al. 2019). As with reservoirs, the capacity and permeability of karst caves is influenced by the presence distribution and properties of materials such as sediments, solutional deposits and breccias filling or partially filling the cave.
This work aims to describe the mineralogy, petrography, geochemistry and origin of breccia deposits in three caves. Developed in the Salitre Formation in the Municipality of Morro do Chapéu, Bahia State, Brazil. They are located in cave cluster and the 111km Toca da Boa Vista (TBV), the longest known cave in South America, the 34km Toca da Barriguda(TBR) the second longest known cave in South America and the much smaller 475m long Toca do Morrinhos(TDM) have been the subject of intensive study since Auler (et. al 2003) where he suggested and an acid-base origin for these caves. This idea changed conclusively after Klimchouk (et. al. 2016) with an hypogenic origin was demonstrated.
TBV and TBR caves are very close, with around 700m far from each other with its entrances located at 10° 09′ 45″S, 40° 51′ 35″W and TBR 10° 08′ 26″S, 40° 51′ 08″W. Morrinhos is a shorter cave located at 10° 12’ 32” S, 40°55’ 05” W. All of them are close to each other within a radius of 10km (Fig. 1.1).
2 2 Geological Settings
2.1 Regional Geology The São Francisco Craton
The SFC it is filled by units of Archean-Paleoproterozoic to younger Proterozoic and Fanerozoic units. The regional setting is defined by domains, from east to West there the Paramirim Aulacogen, which inside it that developed a partially inverted rift system that the Supergroup Espinhaço is located (Alkmim, 2004).
The Rocks of Espinhaço Supergroup contour the whole Irecê basin, acting as substract to Neoproterozoical rocks. The Paraguaçu Group, with circa 1400m thick, shows levels of feldspar sandstones, siltites, shale and rare levels of sandstones, which record a transition of continental until shallow marine environment. The Chapada Diamantina Group, represent a new cycle of sedimentation, with sandstone, pelite, and limestone thus, also showing variations of continental to shallow marine showing a maximum thickness of 1000m.
The São Francisco Supergroup lies in an unconformity over the rocks of Supergroup espinhaço, and it is represented on the region by Bebedouro and Salitre Formations. Bebedouro is composed as rocks of continental nature in a glacial paleoenvironment. The main litotypes are diamictites, pelites and sandstones always with low textural and compositional maturity (Auler, et. al, 2017, in Klimchouk et al, 2017).
The Salitre carbonates are largely dominant in Irecê Basin, and shows rare levels of siliciclasticic successions implying in an extensive sea platform tide dominated. In the main sector of the basin, at the municipalities of Irecê and Lapão, this formation corresponds to a succession of calcilutites, calcarenites, calcirrudites and less commonly phosphatics stromatolites, and siliciclastic sediments arranged in regressive-transgressive cycle (Auler, et. al, 2017, in Klimchouk et al, 2017) (Fig 2.1).
3 Figure 2.1 - Tectonic and stratigraphic setting of study area: (A) Major carbonate units,
location of South America's largest karst system in the São Francisco Craton, and location of the study area (modified from Auler et al., 2001); (B) Detail of the northern part of the São Francisco Craton. Key: RP, Riacho do Pontal belt, 1 )Archean– Proterozoic basement, 2) Mesoproterozoic sedimentary rocks of the Espinhaço Supergroup, 3 ) Neoproterozoic rocks of the São Francisco Supergroup, 4 ) Phanerozoic sedimentary covers, 5 ) Neoproterozoic Folding belts, 6 ) Marginal belts (modified from Bizzi et al., 2003 and Ennes - Silva et al., 2016 , Apud Cazarin et. al 2019).
2.2 Local Settings
The study area is located at Salitre Formation (Una Group) of the Campo Formoso Basin, on the Northern part of SFC. This Formation, is the uppermost unit of Una Group. Being the main exposed occurrence of Campo Formoso Basin, with 530m thick, it shows few siliciclastic lenses and easily outcrops in the SFC.
2.3 The Caves
Entrances of caves occur within a 10km radius (Fig. 2.2) and the access of TBV and TBR caves are very close, approximately 700m apart. They are situated in an underground cluster where TBV (Fig. 2.3) is the largest known cave in South America with 111km of galleries and having 34km TBR (Fig 2.3) is in second, while Morrinhos is
4 a smaller with 475m length (Fig 2.4). Being located in the Sao Francisco Craton they all are of early-Proterozoic age (Auler, et. al, 2017, in Klimchouk et al, 2017).
Figure 2.2 - Location maps for the caves (the exact location of morrinhos was inferred), and
profile view for TBR and TBV. Modified from Ennes -Silva (et. al. 2016).
Few karstfied features are present, as example of collapse dolines, and over the limestone lies a few meters soil cap of weathered chert. There are is little surface exposition, such as few hill scarps it only outcrops discreetly, and even scarcer horizontal outcrops (Auler, et. al. 2017). The hypogenic karstification was not precised, however it is inferred as late-Proteroizoc, due to Pangea breakup context, at early Brasiliano cycle (Klimchouk et. al. 2016).
5 Figure 2.3 – map vie w of caves, showing its dominant NE trend with less often orthogonal
galleries connections. Distance between them the caves are in scale. Retrieved from Auler (et. al. 2017 in Klimchouk et. al. 2017).
Figure 2.4 - Map of Toca do Morrinho cave, showing where each sample was taken.
Important to look, the whole Mo 5 (5 samples) were taken from few meters apart. And Mo -4 shows a range of 70m sampling. This important behavior will be discussed later. Modified from: B ambuí pesquisas esp eleológicas.
6 3 Materials and Methodology
As the author did not participate the sampling during the field trip, the main objective was, sample preparation, description and correlation to existing bibliography about breccias in hypogenic karst environment.
The primary step was to organize all samples with a brief petrographic description, in Excel. After that each sample was photographed. Following the next stage comprised of selecting planes to cut slabs and tablets to thin sections confection.
A total of 22 samples were prepeared, at single size for each sample/site. Overall, trying to be as representative as possible. The objective was to describe the petrography of the fault rocks and distinct characteristics between them. The thin sections were prepeared by the lab Petrografia BR located at Belo Horizonte, MG.
In order to obtain mineral and chemical composition, selected samples were submitted to do XRF analysis. This analysis was performed at Laboratcrushed at Laboratorio de Geoquimica (LABGEO) of Geology department in UFRN to get at least 4 grams necessary to run X-Ray Diffraction (XRD) and some X-Ray Fluorescence (XRF) analysis. Due to contamination concerns the whole process was done manually, initially by using hammer with thick paper protection and later agathe mortar.
A third stage was to submits one total of 8 samples to run Scanning Electron Microscope (SEM). For this some samples needed to be smashed and metalized through the protected hammer and scanned at LABMAT of CTGAS RN.
All samples were submitted to XRD analysis, the XRD is extremely useful to identify mineral phases by its atomic structures which by the deviation of those rays suffer from hitting each structure.
X-Ray Fluorescence was done in fewer samples to determine the composition of each oxide. The machine used, was simple and could only determine elements heavier than Sodium, which in our case is ok as it is a secondary data source to help have a look on the thin section. Few results demonstrated elements at 0.0% which is odd, being described as possible occurrence, perhaps beyond the machine could detect, this occurrence is restricted to hydrothermal breccias.
7 4 Petrography and Petrology
All samples were classified in two categories, based in their textures, grain content and petrography. Their two categories adapted from Osbourne (2001):
Breakdown (collapse breccias): are result of gravitational collapse, as example a doline reaches it full development getting to surface, and this collapse develops a rock with great lithology mixing, such as rounded grains and a high ratio of matrix over clasts. Hydraulic Breccias, are from tectonic origin, with developed jigsaw pattern, however as there is little silicification it suggesting an hypogenical origin for the fluid.
4.1 Toca da Boa Vista (TBV) Breccias
Table 1 – TBV series, as there are fe w samples, they will be discussed in detail, describing
it simi larities and subtle differences.
These samples were collected above the cave, showing intense telodiagenesis alteration, remarkably intense silicification then limonitization which, in degrees, stablish color for all three samples. Recent published (Cazarin et al, 2019, Klimchouk et al 2016) works suggests that these nodules are result of water lixiviation of Cazarin unit 5, as uppermost unit, it suffered intense intemperism both chemical and, causing carbonate dissolution that concentrated strong chert nodules (figure 1). Even so, those samples exhibited breccia like texture (TBR-1A, 1B and 1C in each respective unit), however its grains shape are not typical, as it has lithified rounded quartz and too dissolution over carbonates, that shows no cracks. Because of that, we described this texture as breccioidal (figure 1).
Sample Petrography Texture
TBV-1A Chert with chalcedony, subrounded quartz, limonite few carbonate
Breccioidal texture/Oxidized TBV-1B Chert with chalcedony, subrounded quartz,
limonite relict carbonate
Breccioidal texture/Oxidized TBV-1C Chert with chalcedony, subrounded quartz,
limonite few carbonate
Breccioidal texture/Oxidized
8 Figure 4.1 – Field aspect (A) and hand sample (B) of breccias presents in TBV cave.
TBV-1B shows very little calcite and is cemented by chalcedony with punctual HCl reaction observed. This calcite absence is mostly due to a nearly complete carbonate substitution, which possibly was higher once its exposition became complete. The quartz exhibits roundness rounded to sub rounded implying in a sedimentary origin. In addition relative good sorting was observed, (0,05 to 0,03 mm average) those features suggests its origin should be wind or rain transported. There are some remnants of skeletal calcite consumed by clay minerals (fig 4.3) implying in recent shallow diagenesis alteration.
It is important to notice, that opal is still the second latest mineral present, being only followed by limonite, as it overall shows mineral growing perpendicular to the fracturing, implies in a distensive tectonics. Which may suggest those samples are aggregates of more or less oxidized chert. Yet, there are few skeletal calcites grains, being mostly However, they still have a minor relevant
Overall this site shows a texture similar to a breccia early cemented by calcite (unit 5 common composition), where outside the matrix are several mineralogies, with important clay minerals in chaotic distribution, being later cemented by overgrowthed opal (fig 4.3).
It does have a well-developed porosity, even though it is a compact and indurated rock, which oddly is better developed inside the grains, rather than amid the fractures. It is such well developed, that the blue pigment used interferes greatly on thin section color, and close to well oxidized grains turns the thin section nearly blue.
9 TBV 1-B at hand sample scale is very similar to to 1-A, same textures, color, the main difference is an absence of incrusted chert and a “injection” of possibly clay minerals inside the pale material (fig. 4.2)
Figure 4.2 – Injection like of a matrix, in addition rounded peebles also at hand sample scale. At microscope it is very similar to site 1-A. However at parallel nicols, it does shows two dominant features black and light blue, which is result of a higher developed porosity, both inside carbonates and matrix composed by clay minerals, probably implying in a transport relation between clay minerals and porosity (fig 4.3). The few carbonate grains are remnants of Unit 5 inside the chert.
This rock shows the lightest level of oxidation of all sample, while exhibiting the best developed porosity. The occurring carbonate, is restricted to relict ones, with 3% carbonate, 5% limonite and 92% silica. Between the true tectonic samples, this sample shows the highest porosity, being most of it inter-grain, developed inside the matrix (photo TBV-1C.1), secondarily are intra-grain and less often, fractures. It is estimated 22% porosity.
As the whole TBV series, the opal keeps growing perpendicular to the fractures, implying in distensive tectonics and common evolution, despite the difference in porosity style.
10 Figure 4. 4 – Photomicrography showing typical textures at TBV, in A, there is a matrix composed by clay
minerals, in a chaotic arrangement. In B a well developed chalcedony infills the matrix, in a gigantic way. C and D are // and NX nicols of a carbonate grain, where it is also observed rounded quartz lithified, implying in a long sub-aerial exposition. E and F are pairs of fractured matrix with in a silicified portion of TBV-1C where in the left older grains are smaller, of massive structure and in higher developed porosity the grains overgrows creating a rich mosaic of chalcedony/opal features.
Futheremore, all samples from TBV-1C were submitted to DRX, which shows nearly equal behavior in TBV-1 A and B, having as only difference an increase in calcite in site B, and the increasing in SiO2 reduced greatly the other minerals, the only exception was MgO, being slightly higher in TBV-1B.
11 Figure 4.5 – Graphic showing chemical compositions of TBV samples.
0 20 40 60 80 100 TBV-1A TBV-1B TBV-1C
High SiO2 chert
SiO2 Fe2O3 Al2O3 MgO
12 4.2 Toca da Barriguda (TBR) Breccia
Table 2 – TBR series, as there are few samples, they will be discussed in detail, describing it similarities and subtle differences.
Sample TS Petrography Observation
TBR-1 Y Sandstone From diagenesis + epithermal activity TBR-2 Y Sandstone From Silicification with occasional
calcite
TBR1-A is a fine-grained sandstone and is tricky to affirm if it can be a breccia, as at hand sample scale it does looks like (fig4.4. with strong compaction, showing two mineral generations, one detrital and a second epithermal. There is very little calcite, as seen in other severally silicified samples. Those few grains are in the northern portion of thin section, with mineralogy corresponding to 3% of all minerals. As opposed to samples in TBR there is no opal, and porosity only occurs as inter-grains. From observed in thin section, we can write the following sequence, deposition with strong compaction, and epithermal activity, possibly with intense silicification, a fracture system obliterating nearly any carbonate, and later precipitanting calcite in its borders and pores. This phenomenon explains why in hand sample there is no HCl reaction inside the rock, whereas in few outer portions of the sample it occurs ponctually. Then, the existing calcite must be younger than all quartz (fig. 4.4). Another difference from previous samples is, there is no limonite, possibly due to no to little surface influence. This breccia was classified as tectonic sandstone.
TBR1-B is very much alike 1-A, in terms of porosity development, however there is no calcite at all, this slide showed just silica (4.4), that it might be appropriated to call it a sandstone.
TBR-2A thin section very similar to its TBR’s predecessors, with a major difference, there is a second and larger generation of quartz developed close to fractures, implying that, here silicification happened longer than previous sites (fig. 4.7). Another important difference is the extinction, where in the small, older grains it is wavy, in those younger ones, it is clean, implying in no tectonics after silicification occurred. From those
13 observations we can trace the following event sequence, sandstone
Figure 4.6. Overall look of TBR sandstones (perhaps breccia). Pairs A and B are from sample 1B. Figure
C is from TBR 2-A, photos D and E from TBR 2.B. Photo F from TBR-1A. In common they all show vugular and fracture porosity and nearly entirely SiO2 with still great lithification and compaction, possibly from diagenesis.
deposition, tectonics developing quartzose breccia (fig 4.7), and later silicification infilling partially remaining fractures.
About porosity, the only one present are the fractures remained open after silification occurred.
Sample composed by two generations one detrital with strong compaction, and a second one as result of silification, chalcedony, botryoidal cement smaller and inter grain (fig. 4.7). Porosity are mostly secondary inter grain, with occasional calcite precipitated.
14
Fig. 4.7 Common microtextures for sandstones at TBR, pairs A B shows calcite precipitation related to porosity, implying in its later, maybe reappearance, as result of later epithermal activity. Also, it shows the relative homogeneous size of quartz grains and its angular and straight contacts as result of intense compaction. Pairs C and D showing inter-grain porosity and contrast of younger vs older quartz generation, where younger ones are away from porous and small, and possibly older ones are far. Pairs pore infilled by calcite. And two generations of quartz, a smaller sub-rounded and a younger one better formed, there is also some chalcedony cement product of silicification. In common, all samples demonstrated very well developed secondary porosity.
As already discussed, TBR showed incredibly high SiO2 content, as field description said it was collected close to a fault, suggests a total silica mobilization. TBR-2B showed lower SiO2 content, it might be from the sampling that happened closer to its outer cape, which deposited solid fluid content.
15
Figure 4.8 – Graphic exhibiting chemical compositions of Toca da Barriguda samples.
Interesting to see relative high content of Al in TBR -2B.
4.3 Toca do Morrinho Cave.
Table 3 – Mo series, as there are few samples, they will be discussed in detail, describing it similarities and subtle differences . S* stands for some, which in field selected samples were chosen to further lab analysis.
Sample TS Classification Observation
Mo-1 N Matrix Breccia Hydrothermal
Mo-2 S Sedimentary Breccia A first generation
Mo-3 N Calcite vein Matrix of Sedimentary Breccia
Mo-4 Y Sedimentary Breccia Youngest breccia
Mo-5
Mo-5e
S* Sedimentary Breccia
Tectonic Breccia
More Intense lithification
Present where fracturing was intense, breccioidal texture
Mo-6 Y Sedimentary Breccia Intense lithification from vicinal fractured wall
Mo-7 S* Hydraulic Breccia Same site of Mo-1, has a variety of hydrothermalism
This cave description starts with Mo-2, that at hand scale showed a light brown color, with developed diagenesis reaching external calcite precipitation (fig. 4.9), lithifying chert clasts aggregated to the rock. The thin section was done in the matrix (fig. 4.9), that showed relative homogeneity, suggesting a non-tectonic mixing. Its textures are quite simple, with sub-rounded wavy quartz and chert showing an initial siliciclastic
0 1 1 2 2 3 3
Fe2O3 CaO SO3 Al2O3 CaO K2O ZnO
Almost pure SiO2
16 cementation, syn-cinematically, then an subtle hypothermal dolomitization occurred, followed by calcite, this new event is suggested to be epithermal, where it developed gigantic calcite and dolomite crystals in its borders and in vugular porous (photo Mo-2a.1). The very last stage was the oxidation which even developed minor crystal of iron-hydroxide in porous that remained open. Overall, this sedimentary breccia shows a multi stage evolution, suggesting being an older sedimentary breccia, than the much common Mo-4X.
Figure 4.9 – aspects of Toca do Morrinhos cave. A) is its hand sample, b) the sampled matrix in which the
thin section was made. In C its field appearance, perhaps clasts supported. D and E shows abbudant limonitization, rounded and fractured quartz, as well as, calcite precipitation around pore in a last stage, with zoned growing.
The samples of site 4, Mo-4, were classified as Sedimentary, as there is no tectonics involved they have no sorting, having being karstified epigenically. They are
17 the most common breccia found in Morrinhos cave (fig. 4.10), and there is a whole series of them sampled. In common the seven samples shows intense limonitization, and its color suggests calcite cimentation around collapsed surface soil. Furthermore, all samples have in common clasts of chert, wavy and sub to rounded quartz, thus implying in a mixing from a collapsed doline probably which brought siliciclastic and facilitating carbonate percolation cementing those rocks.
At hand sample scale, it is very porous and friable, with over 80% matrix ratio, and grains does not touch each other at all. Often the red “breccia”, amid bedrock in gray in a chaotic arrangement. In thin section, they showed similar behavior in all samples, so in order to be synthetic its descriptions and phtos were unified.
Overall field view of these samples, this chaotic framework runs through 1/3 of Morrinhos cave, it’s implications will be later discussed. In micro scale, it is a very oxidized rock, with plenty chert.
The quartz is shown in three ways, detrital rounded and wavy extinction, a second one contended as chert, rock, with bigger grainsize having its own fractures (Mo-4.2 cluster), which are older than the actual rock’s lithification, with contemporaneous infilling . From these chert dissolution comes the last quartz variety, opal, in spar texture occurring along bigger chert grains.
The calcite is well spread over the matrix, along with detrital quartz. Its distribution, are related to porosity, suggesting its epigenic transport, then crystalized filling the gaps. It most likely is calcite with some dolomite. To corroborate to this idea, the calcite is growing alongside a implaced quartz grain, thus suggesting, that originally it was not there (fig. 4.10).
18 Fig. 4.10 – main features of site 4, in A) in field, showing the conductor in dark grey. B is from sample site
G and C shows site F, showing important difference in matrix. Possibly as result of higher or not soil contamination. D, is a calcite vein inside a fractured chert, implying in the calcite system is active, and probably is epigenic. E and F shows the typical settings for this site. Intense oxidation, fractured cherts, sub-rounded quartz, and dissolution porosity is abundant.
Site 5 represents the most diverse sequence of sedimentary breccia studied in this report. Starting with a non-tectonic related rock, Mo-5a, which is floatstone, having no porosity, and a particular mineral growth, perpendicular to the bedding. As result seasonal growth, from the rain season, creating its “bedding” and the growth from the gravity that pulls the crystals, photo Mo-5A shows it faces at hand sample scale.The remaining rocks are sedimentary breccia with distinct lithification levels, being Mo-5E the highest among them. In common, the less lithified ones (Mo-5B, C, D have a ratio of 65% matrix over clasts and a strong porosity. Between those, two grains are dominant sub-rounded quartz and chert, (Mo-5 B and D) which indicates transport and less sorting,
19
Figure 4.11- A) shows floatstone found in site A, with “bedding” resulted from seasonal variation, in which each rain season contributes or adds a new layer. B and C are sites B and D showing its fluctuating contact clasts. Photo D, in hand sample in cut, Mo-5E exhibits sub-rounded clasts with no sorting, thus indicating that the fracture process broke the bed rock, while intense flow activity washed away its borders, while precipitating calcite as matrix. Photo E and F are parallel and crossed nicols of common matrix breccias in site 5, finding abundant rounded quartz and chert with millimetric grainsize, in thin section, and lower porosity compared to site 4. Photo G shows sample Mo-5E and its sedimentary bedding still preserved. From its grainsize and homogeneity it is suggested that carbonate came from microbial organisms, such as
20
cyanobacterias. Photo H shows in left matrix and clasts at right where we see the boundary marked by strong porosity.
and those grains possibly came from the surface through a collapsed doline. In addition there is also importante oxidation, forming limonite and later stronger calcite crystalization, as result of being closer to the fractured cave wall than MO-4.
The fault related rocks of site 6 are matrix supported with well-developed secondary porosity, formed by intense fluid flow mainly through two ways: inter clast and fractures. The only cement present in this thin section is calcite which constitutes the matrix (fig. 4.13), mostly occurs as xenomorphs crystals, however few crystals have rhombohedral habit, so it might better develop, as long as there was enough space (Fig. fig 4.13). Overall, there is slightly less matrix than previous sites, with 60% matrix, the clasts yet does not touch each other (fig 4.12).
The incredible porous rocks (fig 4.13) is possibly result of a very and continuous flow system that after the fault system acted, have recrystallized most of the matrix in a process that created the very common inter-grain porosity. Which can overgrow to what is observed in figure Mo-6.3 where the boundary between clast and matrix have a superb porous system.
In field, those breccias are the closest ones to the fractured cave wall, so the quartz shows mostly angular and stronger wavy extinction. Therefore, differently from ther other sites, those samples suggest to be an older breccia or at the collapse core, which the grains fractured/broke during its falling in a straight cavity developed the observed wavy extinction. Furthermore, despite its huge difference in color, these three samples showed to be similar even equal in thin section, and the difference in color (pictures below), is result of the bedrock influence as shown in sample Mo-5E.
21 Overall, those sample shows intense fracturing and important cavities remained open, which is unusual, as they tend to be infilled. This suggests an end of the tectonics activity with only gravity acting, which slowly cracks those samples. On the other hand, it could have been the blocks sampled that broken during its falling. The cracks left open, as seen in thin section (fig 4.13) shows no carbonate inside the chert grains, indicating the flow system has stopped/sealed. Therefore, an explanation can be that, the collapse system migrated to younger sites, as Mo-4, as it also shows little oxidation/limonite, restricted to few infilled areas that was open, but stopped (sub-euhedral calcite photos E nd F in cluster below).
22
Figure 4.13 - Mo-6 Photos A and B shows that, despite its textural and color differences as seen in pairs C/D, from Mo-6A, and E/F from Mo-6C samples Mo-6 A, B and C are basically equal microscopically. Pairs 26 C and D shows no calcite or any recent cement filling pores, therefore no actual lithification process, also it is possible to see its angular grains, which are dominant in this site, and a contrast of matrix supported breccia in the carbonate and grain supported in the chert. Pairs E and F shows rhombohedral calcite in Mo-6C, thus an older system worked previously.
The last site studied in this report, showed to be the most interesting one, with high many calcite/dolomite veins (fig. 4.14). Furthermore, two thin sections shows different behavior with Mo-7D showing intense shrinkage structures, thus gigantic porosity, while Mo-7E is well developed with calcite infilling in its fractures.
Samples MO-7A, B and D are the matrix of the main fault located at cave’s beginning. While Mo-7D is the weathered matrix. It shows chaotic arrangement and fractures, with abundant mobilized calcite (fig. 4.14). Whose seems to appear in two generations, an older, small, fractured, and a secondary one, well-formed filling cavities.
23
Figure 4.14. in A) Sample Mo-7a with brecciated matrix and calcite in different shapes and vugular porosity. B) from sample Mo-7E shows a fractured bedrock block inside a recrystallized matrix calcite. Pair C and D shows at hand and micro scale how dissolution works, firstly the matrix, then bedrock leaving a “mudcrack” texture behind. Pairs E and F are from sample Mo-7E in a nearby area showing plagioclase needles related to fracture system, as well as its oxidation (limonite), the only of this kind in this site.
Therefore differently from site 6, here the system is still open in a continuous cycle of dissolution and crystallization. However, the system seems to work differently, as there is no limonite or oxidation acting. On the other hand, thin section Mo-7E shows few oligoclase needles, with its inclined 5 degrees extinction, which differentiate it from others Na-Ca feldspars. This occurrence is related to fracturing and oxidation being parallel to it and seems to be its precursor. It is a bold assumption, but this feldspar anomaly, can led to an important fracturing from its reaction, thus a cave embryo.
24 Mo-7C is the only example of hydraulic breccia, which is the host of the previous samples (including Mo-1A and B), as shown in the picture below this site has intense calcite mobilization, amid jigsaw texture in the clasts. Comparing to the previous ones, there is less oxidation, no rounded grains, chert or quartz, so this environment is closed, for this reason, must be older, as these conditions does not repeat in other sites.
Figure 4.14 is from where these samples came from, an intensely fractured wall covered by a thick white layer of recrystallized calcite. Such characteristics are known as fractures corridors and described by Auler (et al. 2017) as the controllers of cave development in this area. Having no samples from fractures corridors in TBV or TBR, was assumed they should have had evolved similar in Morrinhos which will be discussed in the results.
25 figure 4.15 - only from Mo-7D and related sample Mo-1 A and B, in A) (backpack as scale) there is the
fractured wall where those hydrothermal breccia were developed, in C a clean polished cut showing the thick veins amid brecciated bedrock in a jigsaw pattern with angular borders. Pairs B and D shows from where samples Mo-1A were collected, its matrix showed to be special, containing barium will be discussed later in chapter 6.
26 5 Petrology of Morrinhos Breccias
Few key samples were selected in order to provide very detailed data, about porosity and hydrothermal activity. Samples Mo-3A, B, C, D and E are scattered matrix of hydrothermal breccia. While samples 7A, B and C are the bedrock. Thus understanding what and how the fluid passed through give a solid idea the recent process affecting recently the Morrinhos and other caves.
5.1 Microporosity
Those rocks are overall, very porous, as described in Mo-7D, initially at hand sample, then thin section scale. This porosity, is related to rock dissolution and fracturing of an already lithified rock. Thus, the following examples of porosity are result from one of those types: moldic, fractures, interpaticle and maybe shrinkage, as happens with Mo-7E. Overall, porosity was observed in all samples, which reflects the incredible absortion capacity observed (fig 5.1).
Figure 5.1 – pair A and B shows a concretiong infilling porem, as result of flow precipitation. Microporosity, there are three main kinds, between calcite grains (D), fracture(C), in the contact between silicification and bedrock(C. In addition, Fe all over the sample shows homogeneous fluid activity in the filled fracture and bedrock.
27 5.2 Precipitation – hydrothermal activity
Mo-7A shows the best examples of hydrothermal activity, always starting with fracturing, then epithermal finishing in hypothermal mineral growing (Photo 5.2). At thin thin section scale we could affirm that the plagioclase was from hydrothermal origin, from its texture, and alignment to fractured zones. However, through SEM is possible to suggest.
Photo – 5.2 A) Clay mineral incrustation possibly lithified by silicification, a process that explain
Plagioclase content in thin sections. Maybe the mineral was carried by water then stuck, clay adsorption, or it is a result of odd mesodiagenesis process. B) EDS, showing anomalous metal content in clay mineral.
5.3 Crystals
Was observed two mineral generations, an initial one, better formed, rhombohedral and a later one, small in agglomerate structures, with high nucleation rates, which indicates fast growing, suggesting an initial supersaturate possibly hot solution, followed by a cooler saturated CaCO3 solution that created many crystals, however of
small size.
EDS analysis from Mo-3A indicated presence of clay minerals amid the calcite matrix. Which can suggest, if related, a broader hypogenic activity through the breccias, as according to figure 2.4 they are separated by 20-30m a plausible radius of action.
28
Photo 5.3.1 Pair A and B from Mo-7C porosity with smaller crystals on the top, suggesting a sequence, pore then new calcite. C and D are from Mo -3A from its mineral composition, is possible to infer clay minerals as reason for anomalous Si, Al, K and Fe, or maybe plagioclase. Compared to figure 5.5 its elements % represents a gain of roughly 1000%. E) From Mo-3A a mosaic of rhomboedral calcite and dolomite, where they grows as agglomerates. F) From Mo-3C a second generation of calcite growing from the pores. G) Crystal habit from sample Mo-3C, interesting calcite rhombohedral habit. H) From Mo-3E similar micro arrangement for crystals in Mo-3E, implying in a overall
29 This part will discuss the laboratorial XRF, which have 10% mistake, however as observed, results in most cases are good enough to make notes on overall authigenic alterations, despite the results probably are not 100% confident, assuming the samples from same site have nearly the same composition we can try to understand how the system works.
Samples Mo-3 are calcite veins that shows a subtle competitive relation between silicification vs dolomitization processes, where they both happen silica seems to be dominant, and from its overall behavior, K, Fe, Dy (REE), suggests Mg origin to be hypogenic, while Si seems epigenic. Observation, Calcium was removed in order to better understand other elements behavior.
0 1 1 2 2 3 3 4
Mo-3A Mo-3B Mo-3C Mo-3D Mo-3E
Morrinhos Calcite veins (No Ca, as it is >93%) Mo-3
30 Site 4, shows again increasing silica content (remarkably chert) reduces the other elements. Silica tends to concentrate itself becoming a sole mineral, where it is abundant.
As Mo-5A and 5E are particular case, the first one nearly pure calcium and the second one a mixing of host + matrix, therefore in order to better understand this site they were differentiated. As observed in epigenic alteration, it shows the reduction in calcium content did increase other elements outer than silicon, but not as much. This suggests silicification happened later and is a dominant process, possibly as result of its abundancy on the crust. Again, dolomite increasing results in reduction of al other elements, implying in a near pure Mg source.
0 10 20 30 40 50 60 70 80
Mo-4A Mo-4B Mo-4C Mo-4E Mo-4F
Site 4
CaO SiO2 Fe2O3 Al2O3 P2O5 MgO K2O
0 10 20 30
Mo-5B Mo-5D Mo-5F
Epigenic alteration
SiO2 MgO Al2O5
P2O5 P2O5 K2O
0 50 100 150
Mo-5A Mo-5B Mo-5D Mo-5E Mo-5F
CaO and MgO vs SiO2
CaO SiO2 MgO Al2O5
31 Sample Mo-6 showed competitivity between silica and silicon, to silicon increase it must replace silica. However, at thin section scale it does seem similar percentages. Therefore, the analytic method is not as reliable as needed.
Both Mo-1 and 7 are from the same site, however as described in chapter 4 they are different lithologies, Mo-1 are pebbles of much altered matrix, its altered elements shows silicon enrichment replacing carbonate, for heavier elements. More importantly it shows barium, a classical indicator of hypogenic alterations. Its low concentration, might be due to the thick sedimentary pack the fluid percolated to crystallize, so it needed a secondary method (likely clay adsorption) to have detectable trace elements.
0 10 20 30 40 50 60 70 80
SiO2 Al2O3 Fe2O3 CaO K2O MgO P2O5
CaO vs SiO2
Mo-6B Mo-6C 0 20 40 60 80 100Mo-1A Mo-1B Mo-7A Mo-7B Mo-7C
Morrinhos Hydrothermal
breccia
SiO2 Al2O3 K2O
CaO Fe2O3 MgO
0 2 4 6 8 10 12 14 16
Mo-1A Mo-1B Mo-7A Mo-7B Mo-7C
Minor alteration elements
Al2O3 Fe2O3 MgO
32 6 Results and discussion
Starting from TBV was observed that even a long period of exposition and all kinds of weathering, was not enough to obliterate certain breccia textures. This can keep them as point of interest for any petroleum company that operates in a known non active are, however was in the past and faults can still be maped, in higher or lower scale, porosity and permeability will be always positively influentiated.
Was seen a strong sequence of events, initiating with hypogenic ones, such as dolomitization, passing by middle ones as chert formation and botryoidal cementation, and in the limonitization, such sequence of events was published by Cazarin (et. al. 2019) and fitted nicely our interpretation (fig 6.1).
We are not sure of what was sampled from TBR, if it is a breccia or sandstone, as it maybe be both. At thin section, it is clear its abundant quartz, compacted and indurated. On the other hand, the hand sample has a chaotic arrangement, cavities, strong porosity, some calcite (fig. 4.6). When sampled was not sure of what was collected, however it does shows interesting features as silicification from epithermal source and two varieties of quartz. As the bigger variety happens closer to the pores (fig 4.7) it is plausible to say it is from silicification, that when well developed can turn the rock massive.
From Morrinhos one feature is interesting, the breccias varies from two colors, blue and its shades between. The blue coloration is from the bedrock, and red (or whatever the soil is) from the surface soil. It was observed that, as red as it gets and matrix rich, overall the breccia tends to be younger. And the shades between are level. This idea of evolution can be applied for a specific cave for time, as way to determine relative age due to the evolution should track the same path, initiating with hydraulic breccias, Mo-7, them tectonic breccia, Mo-5E, and the nearly not breccia at al, as Mo-4, that in some cases are almost conglomerate. It is important to notice, most of samples were matrix supported, as result of its nature, the few cases observed (fig 4.13) is probably from two reasons, recent fracturing or the nature of the grain, as calcite is fragile its pore tend to infill faster the ones of silica, chert.
From Morrinhos was also detected Barium, as proof of hypogenic activity for the hydraulic breccias at clay minerals in pebbles. This secondary enriching can help detect hydrothermal environments can as always as possible help locate these hydrothermal zones. Secondly, and an odd plagioclase that if related to hypogenic activity can work as
33 indicator for it too. It is still unknown, would be necessary more samples and analysis. However, it would be interesting because Al is far more abundant than Ba in most occasions, thus helping reservoir geologists help track these hydrothermal zones, where in our cave is also a fracture corridor.
Field and lab observations have inserted TBV at surface unit 5 of Cazarin (et. al. 2019), from its washed bedrock carbonate (fig 6.2). TBR we are not sure, in field was described as unit 1, and in lab unit 4 (the most siliceous one). And Morrinhos, its grainstone and breccia texture fits Cazarin Unit 5. For Morrinhos was recognized features of intense silicification, this process was explained in Klimchouk (et. al. 2016) and surely fits our findings.
SEM was a interesting tool to approach the same objective, its better result is the finding of clay minerals in Mo-7A and Mo-3C suggesting a stronger hydrothermal pulse and a possible idea of Al and smaller metals be hypogenic. It was also interesting to show again the first hydrothermal activity to be the strongest, while a second one was cooler and quicker, having little influence in porosity.
The geochemical data obtained through FRX, helped to give a analytical point of view for our samples, proofing where was easy to see, SiO2 in TBV and TBR, and unclear situations as Mo-1 and subtle changes as the aluminum content in Mo-3C. As secondary method FRX was incredible to help certificate findings in petrography, as to say it was a plagioclase due to its Al content, and help detect the source of an event.
Chart 6.1 – sequence of diagenetic events. Green represents creation of porosity with generation of karst,
red representes porosity reduction, and gray representes unknown effect. The bar length indicates relative time during diagenesis.
34
Fig. 4.1 Main
features of
stratigraphic units as they occur in the cave. The samples analysed from TBV is from Unit 5, oxidized chert. Unit 4, Sandstone. Unit 5 is the bedrock at Morrinhos cave. Key: Un., stratigraphic unit described in text, M, Mudstone, W, Wackestone, P, Packstone, G, Grainstone, F, Floatstone, R, Rudstone, B, Bindstone, Bf, Bafflestone, Fr, Framestone, C, Crystalline. Modified of Cazarin (et. al. 2019).
35 7 Conclusion
Fault related rocks in carbonates is yet an unknown area, where is still much to learn. Those few samples showed to being able to tell a cave evolution just by its description.
Secondarily this work showed insights on fault related rocks in caves and how they look, and are, its textures, shapes, clasts and processes behind it. Even though, they are not as breccia as expected (Mo-4 series), its origin is result of diagenesis processes, dissolution, transport, lithification. With a continuous cycle of dissolution and precipitation in carbonates.
TBV samples showed breccia textures remains despite intense silicification, and knowing it had a fault there, no matter how old it is, it will influence fluid flow and even an intense telodiagenesis cannot obliterate it.
TBR are tricky samples, as is unknown from where they were collected those sandstones were classified in field by having its carbonates from unit 1 washed out, and in lab perhaps related to unit 4, the most siliciclastic Unit. That left a very massive rock, quartzose, appearing to have undergone intense silicification. Where, a second generation, better formed of quartz was formed, probably showing epigenic fluids rich in SiO2 acting and very calcite flowing as seen in pores.
Morrinhos was better detailed, and it is possible to track its evolution by understanding its breccias. Starting with hydrothermal breccias integrating a fracture corridor it slowly creates the caves (in this case, Morrinhos). In its boundaries the bedrock gets fractured, creating textures like the ones found in Mo-5E, where matrix involves clasts having a lower ratio of matrix/grains. From that we observe the orange breccias, with abbudant calcite cement as example of Mo-6 and which eventually evolve to some of site 5 (F and C)and later the dissolution develop huge cupolas that, with the upper layers mass its weight becomes too much, collapsing on the cave creating breccias with high matrix/clasts ratio, overall those are the most common breccias mostly because the intense mass and fluid transport as seen in site Mo-4.
The best results from this job are the ones from site Mo-7, initially the capture by clay minerals of heavy elements such as Barium, emphasize its potential economic
36 interest, as well as research, because it had the only high enough detectable for this element, helping us affirm with a degree of certain what kind of process is happening.
The most intriguing question from this report is the presence of diagenetic plagioclase which is unknown as it really seems to be happening as result of diagenesis parallel to fractures. Furthermore, XRF showed good amount of Al in site 7, showing it quite relevant there. The implications for this can be many. Since a mere geological curiosity to work as a snitcher for fractures corridors, of great economic interest, as it is much more abundant than Barium (at least in this work) it is easier to detect, as long as, it is from hypogenic source, which is unknown.
37 8 References
Auler, A.S., Klimchouk, A., Bezerra, H.R., Cazarin, C.L., Ennes-Silva, R., Balsamo, F., 2017. In: Klimchouk, A., Palmer, A., De Waele, J., Auler, A., Audra, P. (Eds.), Hypogene Karst Regions and Caves of the World. Cave and Karst Systems of the World. Springer International Publishing, pp. 827–840.
Alkmim F. F. 2004. O que faz de um cráton um cráton? O Cráton do São Francisco e as revelações almeidianas ao delimitá-lo. In:Mantesso-Neto V., Bartorelli A., Carneiro C. D. R, Brito-Neves B. B. (org.) Geologia do Continente Sul Americano: Evolução da obra de Fernando Flávio Marques de Almeida.Beca, p.17-35.
Bizzi, L.A., Schobbenhaus, C., Vidotti, R.M., Gonçalves, J.H. (Eds.), 2003. Geologia, Tectônica e Recursos Minerais do Brasil, Texto, Mapa & SIG. CPRM, Serviço Geológico do Brasil, Brasília, pp. 692.
Cazarin C. L., Bezerra F. H.R., Borghi, L, Santos, R. V., Favoreto, J., Brod, J. A., Auler A. S., Srivastava, N. K., 2019. The conduit-seal system of hypogene karst in Neoproterozoic carbonates in northeastern Brazil. Marine and Petroleum Geology 101, Ennes-Silva, R.A., Bezerra, F.H.R., Nogueira, F.C.C., Balsamo, F., Klimchouk, A., Cazarin, C.L., Auler, A.S., 2016. Superposed folding and associated fracturing influence hypogene karst development in Neoproterozoic carbonates, São Francisco Craton, Brazil. Tectonophysics 666, 244–259
Klimchouk, A., Auler, A.S., Bezerra, F.H.R., Cazarin, C.L., Balsamo, F., Dublyansky, Y., 2016. Hypogenic origin, geologic controls and functional organization of a giant cave system in Precambrian carbonates, Brazil. Geomorphology 253, 385–405. KUCHENBECKER, M.; REIS, H. L. S.; FRAGOSO, D. G. C. Caracterização estrutural e considerações sobre a evolução tectônica da Formação Salitre na porção central da Bacia de Irecê, norte do Cráton do São Francisco (BA). UFMG. 2011. 49p.
OSBORNE R. A. L. Petrography of Lithified Cave Sediments. In: 26th Brazilian Congress of Speleology. Brasília, p 105-109.
