We have done several field trips to the Araripe Basin focusing on natural fracture characterization of the Lower Cretaceous Crato Formation – laminated limestone, which can be taken as an analogue of a low permeability carbonate reservoir (eg. Pre-salt layer of the Brazilian marginal basins).
Participants: Texas A&M University – Marcelo Sanches; Petrobras – Flávia Falcão, Eduardo Roemers, Jorge André; UFPE – Profs. Virginio Neumann, Leonardo Guimarães, Igor Gomes, Enelise Kátia e Rafael Santos.
Participantes: Jackson School of Geosciences, the University of Texas, at Austin – Randy Marrett, Lizzy Mckinnon; Petrobras – Thiago Falcão, David Bortollotti (former Petrobras), Gabriel Matos (former Petrobras); UFPE – Márcio Lima Alencar (master’s student of Geosciences)
Participants: Jackson School of Geosciences, the University of Texas, at Austin – Lizzy Mckinnon; Petrobras – Eduardo Roemers, João Menescal; UFPE – Paulo Brandão, Marcio Lima Alencar, Bartolomeu Ribeiro, Hugo Guimarães e Lília Albuquerque.
Participants: ICCR, Heriot Watt University – Patrick Colbert, Helen Lewis, Stephanie Zihms; Petrobras – Jorge André, Thiago Falcão; UFPE – Prof. Virginio Neumann.
Participants: LNCC – Prof. Márcio Murad, Aline, Patrícia; Petrobras – Flávia Falcão, Antonio Cláudio, Eduardo Roemers; UFPE: Profs. Antonio Barbosa, Igor Gomes, Leonardo Guimarães, Aura, Marcela Seixas, Laís Lopes.
Please, find below a summary of the Field Trip Guide of Crato Formation.
UNIVERSIDADE FEDERAL DE PERNAMBUCO
CENTRO DE TECNOLOGIA E GEOCIÊNCIAS
DEPARTAMENTO DE GEOLOGIA
Fracture characterization of Crato Formation, Araripe Basin
*Geological map made by undergrad students
In case of emergencies, call 192 or 190 from your cell phone or the nearest available phone.
Igor Gomes, cell 55 81 994216799; Antonio Barbosa, cell 55 81 986587238; Tiago Miranda, cell 55 81 987439197
Hotel Encosta da Serra: 55 88 35216515
Hospital Regional do Cariri, Rua Catulo da Paixão Cearense, 99, Crato-CE, 55 88 3566 3600
Field trip logistics
Transportation: Two pickup trucks from UFPE and a van (Petrobras).
Level of physical activity involved: Most stops are within short walking distance from the car stop.
Accommodations: Participants pay for their hotel accommodation (which includes all meals), and transportation to and from the meeting.
- Crato-CE: Hotel Encosta da Serra: http://encostadaserra.com.br/
The Aptian Crato Formation (NE Brazil) is renowned in the international scientific community as a lagerstatte deposit that contains pristine body fossils. Despite this, a research has been undertaken on the region’s potential as a naturally fractured reservoir analogue. We present the laminites of the Crato Formation as an analogue for some observed facies in the pre-salt reservoir sequences of the Brazilian marginal basins. This work was carried out to provide a basis for the laminites’ mechanical and fracture stratigraphy, when were then applied to geological-computational modelling.
Keywords: Araripe Basin; Borborema Province; natural fractures; laminites; Cretaceous
For over 100 years the Araripe intracontinental Basin in Northeast Brazil has drawn geologists due it’s renowned fossil deposits (Agassiz, 1841; Beurlen 1966, among others). Despite being well-studied, the basin continues to provide rich research possibilities. For example, the region contains sediments which are ideally suited for comparative studies with pre-salt reservoirs in famous Campos and Santos basins in southeast Brazil (Assine, 2007; Catto et al., 2016).
This field report characterizes the fractures of the Lower Cretaceous Crato Formation. We focus on a prominent representative outcrop near to the city of Nova Olinda in the state of Ceará (Fig. 1). This outcrop contains tridimensional exposures providing a valuable opportunity to collect information on the contribution of fracture networks. Rather than depend on limited subsurface poor-resolution datasets, our data can feed powerful fluid-flow computational models that can potentially optimize recovery.
– Field Trip Agenda
The first day, is devoted to the road trip from Recife (Pernambuco State) to Crato (Ceará State), about 620 km. On the second day, we will have an overview of the structural settings of Crato Formation by visiting some quarries nearby Santana do Cariri. During the third day we we will collect structural data and samples in the Crato Formation in quarries around Nova Olinda. On the fourth day we will drive from Crato-CE to Recife-PE.
– Field trip logistics
Lodging is provided by Casa da Pedra, an outpost created by the Federal University of Rio de Janeiro to support scientific research in the region. Casa da Pedra is located nearby some of the main principal quarries of Crato Formation and has accommodation for up to 60 people, and additionally it offers excellent regional cuisine prepared by local hands. The Araripe Basin also contains the first Geopark founded in South America, the Geopark Araripe, which preserves nine important sites for geoscientific research. For example, Pedras Cariri geosite, which conserves natural outcrops of Crato Formation laminites.
The study area is located in the Araripe Basin, the largest interior basin of Northeast Brasil (Figs. 1, 2). The underlying basement rocks are dominantly Paleo/Mesoproterozoic orthogneisses, ranging in composition from quartz diorite to granite, but metaultramafics, metagabbros, amphibolites and metasedimentary rocks are locally important, as well as a Neoproterozoic granitic intrusion. The basin has an E-W-elongated shape and is positioned between two large shear zones, which divide the major Borborema Province into the northern, central, and southern domains. The shear zones that bound the basin are the Pernambuco to the south and the Patos to the north. Both zones strike E-W and have dextral kinematics (Brito Neves et al., 2000). The Araripe Basin can be divided in two main sub-basins, the Cariri (East) and the Feitoria (West), which are separated by a regional structural high referred to as the Dom Leme (Assine, 1992; Neumann, 1999).
The stratigraphy of the Araripe Basin can be divided into five tectono-sedimentary sequences: a) Paleozoic, represented by the Ordovician-Devonian continental deposits of the Cariri Formation; b) prerift, represented by the Tithonian continental deposits of the Brejo Santo and Missão Velha Formations; c) rift, composed of the Neocomian continental deposits of the Abaiara Formation; d) postrift I, which includes the Aptian-Albian continental deposits of the Barbalha, Crato, and Ipubi Formations and the lacustrine to marine deposits of the Romualdo Formation; and e) postrift II, which includes the Albian-Cenomanian continental deposits of the Araripina and Exu Formations (Fig. 3) (Ponte and Ponte Filho, 1996; Neumann, 1999; Assine, 2007).
The Crato Formation belongs to the postrift tectono-sedimentary sequence and represents the main lacustrine phase of the continental succession of the Araripe Basin (Neumann, 1999). It contains six units of laminated limestones, interbedded with marls, calciferous siltstones, and shales (Neumann et al., 2003).
Miranda et al. (2012) described three main deformation structures in the studied limestone unit C6: 1) shear fractures (normal syn-depositional faults), 2) stylolites, and 3) opening-mode fractures (joints and veins) (Fig. 5) (Fossen, 2012).
Figure 1 – Sketch geological map of the Borborema Province with Araripe Basin location. DN: Norte Domain; DZT: Tranversal Zone Domain; South Domain. Source CPRM (Geological Survey of Brazil).
Figure 2 – Some sedimentary basins located in the northeastern Brazil. ZCPA – Patos shear zone; ZCPE – Pernambuco shear Zone. Source CPRM (Geological Survey of Brazil).
Figure 3 – Stratigraphic chart of Araripe Basin (Neumann & Assine, 2015).
Figura 4 – Simplified geologic map of the Araripe Basin. Green polygon shows the study area, in the region of Nova Olinda, Ceará State. Source CPRM (Geological Survey of Brazil).
Figure 5 – Structures observed in the Crato Formation. The photograph in the background depicts a fault, a stylolite, and an opening-mode fracture in the same location. The stereograms are contoured lower hemisphere projections of poles to structures that are sub-parallel to the photographed structures, and are interpreted as belonging to the same sets: 1) shear fractures, N80E/55NW; 2) vertical stylolite (N05E); and 3) opening-mode fracture filled by calcite (N60E). n = number of measured data (Miranda et al., 2014).
Day 1 – Recife to Crato, 620 km (Fig. 6). We will stop in Arcoverde (PE) to have lunch.
Figure 6 – Google Earth image of the route Recife – Crato, which is about 620 km long.
Day 2 – Trip Crato to Santana do Cariri, about 60 km.
Stop 1: Sítio Tatajuba
PT 13 (9212444N; 408190E, 517m)
- Shear fractures;
- Opening-mode fracture sets
- Vug fractures
Figure 8 – Strike variation of a conjugate pair of shear fractures in the Crato Formation.
Stop 2: Inhumas Quarry, Santana do Cariri
BR-11 (9205270N; 417396E; 435m) Datum: UTM_WGS84.
- Carbonate concretions and related confined fractures (Fig. 10).
Figure 9 – Laminated limestone of Crato Formation. Outcrop showing some carbonate concretions in the Inhumas quarry (note that the vertical linear, fracture-like traces are in fact marks from the cutting machine).
Stop 3: Museu de Paleontologia da URCA (Universidade Regional do Cariri)
The Museu de Paleontologia is a part of the Geopark Araripe (http://geoparkararipe.org.br/) that is located in Santana do Cariri-CE. The Geopark Araripe is the first geopark founded in South America (Fig. 9).
- The region is famous for its pterosaur bone beds and the Crato Fm. is a lagerstätte deposit that preserves pristine body fossils
Figure 10 – The Museu de Paleontologia presents a good overview of the Araripe Basin stratigraphic sequence and it has a large amount of Crato Formation samples and samples from other formations that have a rich-fossil content.
Day 3 – Trip from Crato to Nova Olinda (45 km) – Structural and geomechanical data acquisition in the Crato Formation
Stop 4: Quarries of Nova Olinda
PT 09 (9213808N; 423076E; 527m) – Três Irmãos quarry (Fig. 12).
- Shear fractures;
- Opening-mode fracture sets;
- Vug fractures
- Timing of fractures (shear fractures, stylolite, bed parallel and orthogonal veins);
Figure 11 – Três Irmãos Quarry located in the complex of Nova Olinda’s quarries where the laminated limestone of Crato Formation outcrops.
Stop 4: Pontal de Santa Cruz
The Pontal de Santa Cruz is located at the top of the Chapada do Araripe, which is covered by the Exu Formation – sandstone (Fig. 11).
- Landscape of the Santana-Nova Olinda Canyon, which makes a view of an amazing sunset.
Figure 11 – Landscape from the Pontal de Santa Cruz, Santana do Cariri.
Day 4 – Trip Crato-CE to Recife-PE
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Assine, M.L. 2007. Bacia do Araripe. Boletim de Geociências da Petrobras, 15, 371-389.
Brito Neves B.B., Santos E.J., Van Schmus W.R. 2000. Tectonic history of the Borborema Province. In: Cordani G, Milani E.J., Thomaz Filho A.T., Campos D.A. (Eds.). Tectonic evolution of South America. 31st International Geological Congress, Rio de Janeiro, 151–182.
Fossen, H. 2012. Geologia Estrutural. Oficina de Textos, S jão Paulo, 575 p.
Miranda, T.S. 2015. Caracterização geológica e geomecânica dos depósitos carbonáticos e evaporíticos da Bacia do Araripe, NE Brasil. Tese de doutorado. Programa de Pós-graduação em Geociências-UFPE, 267p.
Miranda, T.S., Barbosa, J.A., Gomes, I.F., Neumann, V.H., Fernandes, R., Matos, G., Queiroz, R., Guimarães, L.J. 2012b. Aplicação da técnica de scanline à modelagem geológica/geomecânica de sistemas de fraturamento nos depósitos carbonáticos e evaporíticos da Bacia do Araripe, NE do Brasil. Boletim de Geociências da Petrobras, 20, 305-326.
Neumann, V. H. & Cabrera, L. 1999. Una Nueva Propuesta Estratigráfica para la Tectonosecuencia post-rifte de la Cuenca de Araripe, Noreste de Brasil. In: Bol. 5º Simpósio Sobre o Cretáceo do Brasil e 1º Simpósio Sobre el Cretácico de América Del Sur. Serra Negra-SP. UNESP, Rio Claro, 279-285.
Neumann, V.H., Borrego, A.G., Cabrera, L., Dino, R. 2003. Organic matter composition and distribution through the Aptian–Albian lacustrine sequences of the Araripe Basin, northeastern Brazil. International Journal of Coal Geology, 54, 21-40.
Ponte F.C. & Ponte Filho F.C. 1996. Estrutura geológica e evolução tectônica da Bacia do Araripe. Recife, DNPM, 68 p.