Anais da Academia Brasileira de Ciências (2018) (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201820170526 www.scielo.br/aabc | www.fb.com/aabcjournal

Stratigraphic Relations of the Ipubi Formation: Siliciclastic- Evaporitic Succession of the Araripe Basin

CARLOS E. FABIN1, OSVALDO J. CORREIA FILHO1, MÁRCIO L. ALENCAR1, JOSÉ A. BARBOSA2, TIAGO S. DE MIRANDA1, VIRGÍNIO H. NEUMANN2, IGOR F. GOMES3 and FELIPE R. DE SANTANA1

1Programa de Pós-Graduação em Geociências, Universidade Federal de Pernambuco, Avenida Acadêmico Hélio Ramos, s/n, Cidade Universitária, 50740-530 Recife, PE, Brazil 2Laboratório de Geologia Sedimentar e Ambiental, Departamento de Geologia, Universidade Federal de Pernambuco, Avenida Acadêmico Hélio Ramos, s/n, Cidade Universitária, 50740-530 Recife, PE, Brazil 3Laboratório de Métodos Computacionais em Geomecânica, Departamento de Engenharia Civil, Universidade Federal de Pernambuco, Avenida Acadêmico Hélio Ramos, s/n, Cidade Universitária, 50740-530 Recife, PE, Brazil

Manuscript received on July 10, 2017; accepted for publication on December 5, 2017

ABSTRACT The Ipubi Formation represents the Aptian-Albian siliciclastic-evaporitic succession of Araripe Basin, NE Brazil. This succession comprises siliciclastic rocks (bituminous shales and claystones) and evaporites (gypsum and secondary anhydrite) and represents part of the lacustrine-shallow marine post-rift phase I. This study used sequence stratigraphy concepts to define the relations between changes in the relative lake level and the formation of Ipubi deposits. Results show that the organic-rich shales of the Ipubi Formation formed during a transgressive pulse that covered large areas of the proximal domains. These deposits overlie a regional unconformity that marks the end of the deposition of the underlying Crato Formation. A High Stand stage that followed the transgression influenced the formation of evaporitic deposits. Climate conditions played a major role in influencing the triggering and stopping of evaporite deposition. Thus, a new relative lake level fall event caused the exposure of the Ipubi Formation deposits, and created another regional subaerial unconformity accompanied by widespread karstification of evaporite beds. A posterior transgression caused the deposition of siliciclastic rocks of the Romualdo Formation over the Ipubi Formation strata, and also promoted a new event of karstification of the Ipubi upper evaporite beds. Key words: Araripe Basin, evaporite succession, interior basins, Ipubi Formation, sequence stratigraphy.

INTRODUCTION conditions, as well as a lack of terrigenous input, allow evaporites to form in saturated brines Evaporites represent sedimentary rocks that (Collinson and Thompson 1982, Cavalcante and normally form in saline aqueous bodies under Ramos 2010, Warren 2006, 2010, Mohriak et al. arid conditions with high evaporation rates. Such 2008, Ortí et al. 2017). Tectonic processes are also Correspondence to: Osvaldo José Correia Filho E-mail: [email protected] important in forming and sustaining evaporitic * Contribution to the centenary of the Brazilian Academy of systems due to the formation of restrictive conditions Sciences. in lakes and epeiric seas. Topographic barriers can

(An Acad Bras Cienc (2018 2 CARLOS E. FABIN et al. restrict water circulation in gulfs, shallow seas and claystone and limestone beds and discontinuous lakes, and mountain chains can limit atmospheric evaporite layers that can reach from few meters to circulation, which carries humidity (Warren 2006). tens of meters thick and mainly comprise gypsum, In a large number of both marginal and interior followed by anhydrite (Silva 1986, 1988, Assine sedimentary basins, evaporite deposits present 1992, Assine et al. 2014). Silva (1988) suggested complex deformation processes associated with salt that these evaporite beds can reach thicknesses of tectonics (Hudec and Jackson 2007). Evaporites 20-30 m, and were formed in systems of salinas present very low permeability and plastic response and sabkhas, and that they were preceded by to deformation, which makes their seal capacity black shales and algal limestones. The few studies more competent than of brittle rocks, and that developed on the Ipubi Formation found difficult allows these rocks to be used for the excavation to define the relations between evaporite layers of storage facilities for the disposal of toxic and and other lithologies that compose the formation radioactive waste (Munson et al. 1991). In the same due to the lateral discontinuity of the evaporite way, evaporites also represent an important part bodies (Silva 1988, Assine 1992, 2007, Assine et in many petroleum systems, because they form al. 2014). Evaporite beds are found in proximal good seal rocks and strongly influence migration regions of the Araripe Basin, with good outcrops and accumulation of hydrocarbons (Mohriak et al. in the southwestern and northern borders, which 2008, Bengaly 2003, Medeiros 1999, Szatmari and attracted the mining industry. There is no record Milani 2016, Warren 2017). Abundant deposition of evaporite deposits in distal domain of the basin, of evaporites occurred in many marginal basins in over the main depocenters (Assine 1992, 2007, Brazil during the Upper Aptian period (Hashimoto Rios-Netto et al. 2012), where the thickness of et al. 1987, Uesugui 1987, Mohriak et al. 2008, sedimentary succession can reach up to 1500-1700 Szatmari and Milani 2016). m (De Castro and Castelo Branco 1999). Due to To avoid misconception regarding the names, the large extension of the Araripe Lake in post-rift or the stratigraphic status, of the sedimentary phase, it is difficult to define regional stratigraphic units belonging to the post-rift phase I of the relations across proximal and distal domains. Araripe Basin, a few comments are necessary. The stratigraphic division of this succession (Barbalha, Based on chemical evidence, some authors have Crato, Ipubi and Romualdo formations) remained a suggested that marine ingressions occurred during matter of debate for decades. Along the time, some the evaporite deposition (Silva 2017). However, authors proposed that these sequences represented the Romualdo Formation, which overlies the members of a formation (Assine 1994, 2007), or Ipubi Formation, is the only unit that exhibits proposed different names for some units (Martill clear evidence of marine influence represented 2007). However, the proposition made by Neumann by the fossils of marine organisms (Assine et al. and Cabrera (1999) prevailed as the more consistent 2014). Ipubi Formation exhibits important lateral (Kellner et al. 2013, Assine et al. 2014). Thus, our variations, in a relative thin succession, that are investigation is based on the stratigraphic division related to the physiography of the basin and the proposed by these authors. involved depositional systems. This makes it The Ipubi Formation represents a siliciclastic- difficult to establish a general stratigraphic model evaporitic succession of the Araripe Basin, which for the entire basin (Fabin 2013), that covers an is the largest interior basin in northeastern Brazil. area of approximately 7.200 km² (Assine et al. This formation is composed of bituminous shales, 2014).

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A new characterization of the stratigraphic 1977, Van Schmus et al. 1997, 2008, Brito Neves relations of the siliciclastic-evaporitic Ipubi et al. 2000, Santos et al. 2010, Neves et al. 2012, Formation is presented in this study, based on new Araujo et al. 2013) (Fig. 1). The TZD is bounded stratigraphic and sedimentological information. to the north by the Patos Shear Zone, which The investigation focused the characteristics of strongly influenced the basin, and to the south the stratigraphic boundaries of the succession by the Pernambuco Shear Zone. The basement with the overlying Romualdo Formation, and of the Araripe Basin comprises the Piancó-Alto the underlying Crato Formation (Assine 1992, Brígida Terrain (Fig. 1), that represents a Neo- Neumann 1999, Neumann et al. 2003, Assine et Proterozoic fold belt mainly composed of low- al. 2014). The research analyzed outcrops and grade metasedimentary rocks with plutonic exposures of quarries on the southwestern and intrusions formed during the Brasiliano orogenic northern borders of the basin, near the cities of event (Almeida et al. 1977, Van Schmus et al. 1997, Araripina and Nova Olinda (Fig. 1), respectively. 2008, Brito Neves et al. 2000, Santos et al. 2010, The record of a new stratigraphic well drilled near Neves et al. 2012, Araujo et al. 2013). the city of Crato on the northern border (Fig. 1) is Geophysical studies based on gravimetric and also described. The research applied the sequence magnetometric data revealed that the structural stratigraphy concepts to define the relationships framework of the basin comprises two main between the major oscillations of the relative lake depocenters, or sub-basins: the western and eastern level and the development of the siliciclastic- depocenters correspond to the Feitoria and Cariri evaporitic succession of the Ipubi Formation. The Sub-basins, respectively (Rand and Manso 1984, investigation adopted the concept of depositional Miranda and Assine 1986). These depocenters are sequences (Mitchum 1977, Vail 1987, Catuneanu separated by the central Dom Leme Horst (Assine 2002) meaning a pulse of deposition influenced 1992) (Fig. 1). De Castro and Castelo Branco by the relative lake level, that is separated from (1999) confirmed the existence of the two main depocenters and the central high, and estimated a the adjacent depositional sequences by regional maximum depth about 1,600 m. unconformities, created by major regressive The tectono-sedimentary evolution of the events. The proposed relative lake level curve basin encompasses four stages, with five tectono- comprises two regressive-transgressive cycles that stratigraphic phases (Assine 1992, 2007, Neumann controlled the deposition in the proximal areas 1999, Neumann and Cabrera 1999, Assine et al. during the studied interval. The formation of two 2014): regional unconformities that mark the base and top a) Syneclise phase (Silurian-Devonian) that is boundaries of Ipubi Formation is discussed. characterized by tectonic quiescence in the GEOLOGICAL SETTINGS Borborema Province. It is represented by the deposits of the Cariri Formation, that include The origin of the Araripe Basin is linked to tectonic medium to coarse-grained quartz sandstones, processes that occurred in the Borborema Province locally conglomeratic, deposited in large (NE Brazil) including Tithonian pre-rift and the braided fluvial systems (Assine 1992, 1994, Berriasian-Hauterivian rift phases (Assine 1992, 2007, Assine et al. 2014); Matos 1992, 1999). The basin is located in the b) Pre-rift phase (Jurassic-Tithonian) that is Transversal Zone Domain (TZD), a central tectonic characterized by the mechanical subsidence domain of the Borborema Province (Almeida et al. due to lithosphere thinning that preceded

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the rift. It is represented by the Brejo Santo Santos 2005, Fara et al. 2005, Martill 2007, Formation, that comprises red shales and Saraiva 2008, Vila Nova et al. 2011). This claystones, and the Missão Velha Formation, formation recorded the marine ingression that constituted by medium to coarse-grained involved the Araripe Basin (Maisey 1991, quartz-feldspathic sandstones, locally Martill 1993, Kellner 2002), and other interior conglomeratic, that contains entire trunks basins and created a large seaway throughout and fragments of silicified wood Dadoxilon( the Borborema Province during the Albian benderi) conifer (Assine 1992, 1994, 2007); (Valença et al. 2003, Parméra et al. in press). c) Rift phase (Cretaceous-Berriasian-Hauterivian) e) Post-rift II phase (Albian-Cenomanian) that is characterized by increasing mechanical that is characterized by a major sag phase, subsidence that created a system of grabens and and is formed by two stratigraphic units: half grabens. It is represented by the Abaiara the Araripina Formation, that occurs in the Formation, that includes shales, siltstones, western region of the basin and is composed sandstones and conglomerates (Assine 1992, by rhythmites and heterolithic layers of 1994, 2007); reddish, purplish and yellowish fine-grained d) Post-Rift I phase (Aptian-Albian) that is sandstone and mudstone (Assine 2007); and characterized by thermal subsidence. The the Exu Formation, that comprises medium-to- Santana Group was formed during this stage coarse grained sandstones, fine grained clayey and comprises four stratigraphic units: the sandstones and local conglomeratic beds Barbalha Formation, that represents a fluvio- (Beurlen 1962, Assine 2007). lacustrine phase and is composed of red and gray shales, siltstones and claystones (Assine MATERIALS AND METHODS 2007); the Crato Formation that is composed of six intervals of laminated limestones (C1 to A detailed investigation was carried out on C6), interbedded with calciferous siltstones and the Ipubi Formation and its lower and upper marls (Neumann 1999, Neumann and Cabrera boundaries in two study areas (Fig. 1). These 1999, Neumann et al. 2003), and is very analyses provided detailed descriptions of the rich in fossils of vertebrate and invertebrate Ipubi sedimentary facies and its stratigraphic organisms (Martill 1988, 2007, Kellner and framework. The investigation involved the creation Campos 1999); the Ipubi Formation, that of photopanels from the main exposures available is mainly composed of organic-rich, black- in quarries, samples collecting, study of samples greenish bituminous shales, claystones and through cuttings and macrophotography, and algal limestones that are interbedded with petrographic analysis. Data collected in the field gypsum-anhydrite beds (Silva 1988, Fabin were integrated with satellite images and a digital 2013, Assine et al. 2014, Silva 2017); and elevation terrain model created with SRTM (Shuttle the Romualdo Formation, that represents a Radar Topography Mission) data (90 m spatial calciferous siliciclastic succession composed resolution). Topographic and geological models of fine to medium-grained sandstones, helped the correlation of interpreted stratigraphic argillaceous siltstones, calciferous shales, and surfaces. The interpretation of the new borehole limestones (Assine 1992, Neumann et al. 2003, lithostratigraphic record is also compared with Assine et al. 2014), very rich in fossils (Beurlen previous stratigraphic models that are based in 1963, Kellner and Campos 1999, Carvalho and outcrops and the boreholes of the Santana Project

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Figure 1 - Geological map (Assine 2007) and digital elevation model of the Araripe Basin. The two black rectangles mark the study areas: one in the southwestern border (Araripina region) and another in the northern border (Nova Olinda region). (Brazilian Geological Survey-CPRM) (Assine Formation is characterized by the formation of a 1992, 2007, Rios-Netto et al. 2012, Assine et al. calcrete formed under subaerial conditions with 2014). The present study also used information small clasts of limestones and local silicification. obtained with a new stratigraphic borehole, 2-AR- Figure 2 shows the interpretation of the well core SR-01a-CE (continuous coring), drilled in the Sítio (litholog), with the division of the main units Romualdo locality, near the city of Crato (Fig. 1), according to the recent proposition for the basin on the northern border of the basin. This drilling stratigraphy (Assine et al. 2014). was funded by the research cooperation project STRATIGRAPHIC AND SEDIMENTOLOGICAL agreement developed between UFPE and Petróleo ASPECTS OF THE IPUBI FORMATION AND ITS Brasileiro S.A. (PETROBRAS) (Projeto Três Furos SEQUENCE BOUNDARY WITH THE UNDERLYING no Andar Alagoas). This new borehole crossed all CRATO FORMATION three units analyzed in this study (Crato, Ipubi and In the northern border of the Araripe Basin (Fig. 1), Romualdo Formations) (Cabral 2017). evaporite deposits of the Ipubi Formation overlies RESULTS deposits of Crato and Barbalha formations (post-rift phase) and older deposits from the pre-rift and rift SEQUENCE BOUNDARIES OBSERVED IN THE phases (Assine 1992, Neuman 1999, Assine et al. DRILL HOLE 2-AR-SR-01a-CE 2014). In the southwestern border, in the Araripina The analysis of the 2-AR-SR-01a-CE well cores region (Fig. 1), record from the groundwater wells (Fig. 1) showed no evidence of interfingering of shows that the siliciclastic-evaporitic sequence the main lithologies of the three units (Crato, Ipubi rests directly on the basement, suggesting an onlap and Romualdo) (Fig. 2). The division proposed relationship. In quarries located near the Rancharia here is similar to previous studies, based on the village (Araripina), black shales (Fig. 3e), that analyses of other stratigraphic wells drilled across form the base of siliciclastic-evaporitic succession the basin (Rios-Netto et al. 2012). The top of Crato has been deposited directly above the basement.

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Figure 2 - Litholog of the 2-AR-SR-01a-CE elaborated from core description and detailed view of the cores across the contact between the Crato and Ipubi formations. An interval of cemented calcrete, with local silicification, occurs at the top of the Crato Formation and records evidence of subaerial reworking, as can also be observed in outcrops. Stratigraphic column based in Assine (2007) and Assine et al. (2014).

Between the Porteiras and Santana do Cariri of limestone and siliciclastic grains. The upper localities on the northern border (Fig. 1), the top part of the laminites also present local silicification of the Crato Formation, represented by laminated (Neumann 1999) (Fig. 3). Abundant wavy limestone beds (C6), records evidence of subaerial laminations in the top of the C6 layer possibly exposure, which is mainly represented by a represents occurrence of microbial structures calcrete containing reworked oxidized fragments (Fig. 3e). Recent works have indeed discussed

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Figure 3 - Details of the C6 laminated limestone that marks the top of the Crato Formation in the Porteiras, Nova Olinda and Satana do Cariri regions. a) and b) Exposure of the C6 layer, exhibiting evidence of subaerial erosion and reworking represented by a calcrete containing oxidized and angulated fragments of limestone (yellow arrows), in Nova Olinda region; c) Exposure of the C6 layer showing evidence of subaerial erosion and reworking, near Porteiras, Mina Branca site, represented by a thin layer of calcrete that contains reworked and oxidized clasts of limestone (yellow arrows); d) Exposure of the C6 layer near Santana do Cariri, with a calcrete layer that contains clasts of limestone and quartz grains (yellow arrows); e) detail of samples from the upper part of the C6 interval, collected in Nova Olinda region, with wavy laminations that possibly represents algalic structures; f) Detail of a shale bed and a gypsum bed (Ipubi Formation) deposited directly above the C6 layer in nova Olinda Region. the microbial influence in the formation of these shales are calciferous, bituminous and fossil-rich laminites (Catto et al. 2016). (fish remains, plant fragments, ostracods), and its The succession deposited over the TOC content reaches up to 25% of TOC (Souza unconformity that marks the top of Crato Formation Neto et al. 2013), and are mainly composed of in the northern border is composed of black shale, expansive clay minerals, such as illite and smectite, clayey siltstone and greenish claystone beds. Black and they record important contents of barium (up

(An Acad Bras Cienc (2018 8 CARLOS E. FABIN et al. to 2%). Evidences suggest that these basal deposits the shale interval and the evaporite beds, can reach of the Ipubi Formation formed under anoxic 30 to 40 m. However, its average thickness, which conditions (Souza Neto et al. 2013, Nascimento Jr is observed in many quarries, is approximately 15 et al. 2016, Silva 2017). m. Figure 4a shows the contact between the basal Data collected in quarries in the southeastern black shale and the gypsum at the Rocha Nobre border, integrated with available record of Quarry in the southwestern border. However, the boreholes, indicate that the basal interval of the transition between the basal siliciclastic interval Ipubi Formation comprises calciferous black shales and the evaporite beds can be also gradual with the and thin beds of calciferous siltstone claystone interbedding of gypsum and thin limestone lenses. and limestone (Fig. 4). In this border region, the Evaporite beds comprise three main facies: 1 siliciclastic interval ranges in thickness from 2 to - banded gypsum, with millimetric bands of fine- 15 m. The upper portion of the siliciclastic interval grained, brown, gray and white gypsum crystals present interbedding thin gypsum lenses and (Figs. 5, 6 and 7); 2 - microcrystalline/micronodular, bedding-parallel fibrous gypsum veins possibly light brown to light gray, homogenous gypsum; 3 - formed by overpressure hydraulic fracturing laminated gypsum, which is formed by millimetric during burial processes (Meng et al. 2017). The laminae of prismatic, gray, white, yellow or total thickness of the Ipubi Formation, including brown gypsum crystals. Anhydrite occurs in the

Figure 4 - Detail of the black shale that compose the base of the Ipubi Formation in outcrops and quarries in the Araripina (Fig. 1). a) Detail of the contact between the massive shale (below) and the gypsum (above), Rocha Nobre Quarry, Ipubi; b) pavement of bituminous shale, Campevi mine, Araripina; c) detail of plant fragments and ichnofossils in the black shale.

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Figure 5 - Samples of evaporites from the Ipubi Formation. Figure 6 - Samples of evaporites of the Ipubi Formation. a) a) Sample of massive, microcrystalline gypsum. The cutting Sample of massive anhydrate (anid), showing light brown surface shows small white nodules of recrystallized gypsum branching veins of fine gypsum (gip) (diagenetic);b ) sample of (black arrows); b) sample of recrystallized gypsum (rosettes); nodular anhydrite with diagenetic recrystallized gypsum veins c) sample of laminated gypsum with white laminae of anhydrite and rosettes; c) samples of mosaic gypsum (gip); d) nodular (blue arrows). Red arrows indicate rosettes of recrystallized anhydrite (anid) showing zones where it is altered to gypsum gypsum; d) sample of banded gypsum showing colors ranging (gip). from light to dark brown to white. Laminae are formed of fine grains of gypsum. Red arrows indicate recrystallized gypsum (rosettes). and fine veins of gypsum within anhydrite masses (Fig. 6). Rosette gypsum also formed from form of massive lenses within gypsum beds, as primary gypsum deposits. Petrographic analyses isolated laminae in banded gypsum and as isolated of the present study suggest that part of the original nodules (Figs. 5 and 6). Facies interpretation herein gypsum was dehydrated during eo-diagenesis to proposed for the evaporites of the Ipubi Formation form anhydrite; and anhydrite was altered again supports many ideas formerly presented by Silva to form gypsum (mosaic gypsum, microcrystalline (1986). gypsum, and gypsum veins). Two main types of diagenetic alterations are observed: 1 - fibrous gypsum that filled fractures; UPPER STRATIGRAPHIC BOUNDARY OF THE IPUBI FORMATION AND ITS RELATION WITH THE and 2 - gypsum rosettes formed by dissolution of OVERLYING ROMUALDO FORMATION primary deposits (Figs. 5, 6 and 7). The alteration of anhydrite to gypsum represents the main process In all quarries where the top of the uppermost that resulted in the formation of rosette gypsum evaporite layer is exposed, it records evidence of

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Figure 7 - Samples of evaporites of the Ipubi Formation. a) Folded, laminated gypsum that has been deformed due to diagenetic processes (gypsum dehydration/anhydrite hydration); b) folded, laminated gypsum with a fracture that has been filled by fibrous gypsum; c) detail of fibrous gypsum filling a large fracture (vein). Black-greenish clay was injected in the fracture and formed thin laminae and lenses within the fibrous gypsum. the subaerial exposure and erosion that preceded the above the unconformity bounding the Ipubi and deposition of the Romualdo Formation (Fig. 8). This Romualdo formations. It is locally conglomeratic stratigraphic surface is marked by the occurrence and contains abundant clasts of gypsum, shale of reworked, angulated and oxidized clasts of and sandstone formed by the reworking of Ipubi gypsum, shale, quartz pebbles and fine-to-medium deposits (Fig. 8f, h). Evidences suggest that this sand grains. Locally, it forms a cemented, usually bed represents a “transgressive lag”, formed during few centimeters thick paleosol (gypcrete) (Fig. 8a, the new expansion of the lake (Fig. 8f). e). The subaerial exposure and erosion of the Ipubi The mechanical removal of Romualdo evaporite layers had already been discussed by Formation deposits during the mining of the gypsum Silva (1983, 1986, 1988), who mentioned that the beds exposed the karst paleosurface formed at the top of the Ipubi Formation is marked by a regional top of the evaporite (Fig. 9). This surface records karst surface. This author suggested that after the large isolated columns and scattered escarpments, deposition of the siliciclastic-evaporitic succession, the deposits of the Ipubi Formation were exposed pits and depressions (Fig. 9). The formation of the and eroded, what created a karst paleorelief. Recent karst paleosurface may have lasted for thousands works have also associated this karst surface with a of years and once represented an impressive sequence boundary delineating the top of the Ipubi ruiniform landscape. The filling of the irregular Formation (Fabin 2013, Assine et al. 2014). karst topography caused large thickness changes In both studied areas a medium to coarse- in the basal strata at the base of the Romualdo grained, 20-30 cm thick sandstone bed occurs Formation (Fig. 8g, h).

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Figure 8 - Sequence boundary at the top of the Ipubi Formation and the basal beds of the Romualdo Formation. a) Regional surface that marks the separation between the gypsum layers in the basal deposits of the Romualdo Formation; b and c) truncation surface at the top of the deformed gypsum layer; d) sample of banded gypsum from the top of the Ipubi Formation (São Jorge Quarry, Trindade), showing the truncation surface that formed a cemented pavement; e) cemented surface (gypsum crust) showed in (d), which is a few centimeters thick and contains oxidized clasts of gypsum, shale, and quartz; f) detail of local coarse-grained sandstone at the base of the Romualdo Formation, that contains abundant reworked clasts of shale and gypsum; g) deposits of the Romualdo Formation deposited above an erosive surface, showing the influence of the syn-depositional dissolution of the gypsum (Vale do Gesso Quarry, Araripina); h) detail of the truncation surface showed in (g). The Romualdo deposits rest directly on the unconformity (Pedra Branca Quarry, Nova Olinda).

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within isolated levels of the Romualdo Formation (Fig. 11). Collapse and faulting continued after the Cretaceous, probably due to the exposure of the Romualdo and Ipubi formations caused by denudation of the basin during the Cenozoic, which increased the percolation of meteoric fluids. Examples of present active subsidence caused by evaporite karstification are well known in regions where underground evaporite deposits, especially gypsum, represent geological hazards in Spain,

Figure 9 - Exposure of the top of the gypsum in the Sombra France, England and United States (Gutiérrez et al. da Serra Quarry, Araripina, after the removal of the Romualdo 2002, 2008b, Yilmaz et al. 2011). Formation deposits. The exposed paleorelief appears to be a In Figure 12a, a series of moderate- to high- ruiniform landscape formed by intense karstification. angle faults are seen in a large exposure of deposits from the Romualdo Formation. The geometry Bed thickness at the base of the Romualdo created by the faults and the collapse structure Formation reflects syn-sedimentary generation of formed a sagging synform (Fig. 12) (Gutiérrez et accommodation space caused by the dissolution al. 2008a). Although some features indicate that and collapse of upper evaporite beds of Ipubi these faults are syn-depositional, the propagation Formation. This process created large folds and of fault planes through Neogene deposits over the listric faults in the deposits of Romualdo Formation Romualdo Formation indicates that this process (Figs. 10 and 11). The structures seen in Figure 10b continued until recently, albeit on a smaller scale. represent examples of syn-depositional sagging In Figure 12b, a collapse structure is shown. It sinkhole structures (Gutiérrez et al. 2008a). The exhibits variation in the lateral thicknesses of Romualdo transgression also caused the injection the beds around the collapse indicating that this of water saturated siliciclastic deposits into local subsidence is syn-depositional, caused by fractures and vugs (Fig. 10d, e). As deposition initial dissolution of the evaporite bed. However, continued, the load caused new failures and the the collapse probably occurred after deposition collapse of karst, which generated the faulting of due to continued dissolution of the gypsum bed. the Romualdo Formation strata to accommodate This collapse structure can be classified as a the syn-depositional deformation (Figs. 10, 11 and sagging+suffosion structure (Gutiérrez et al. 2008a). 12). Large areas over evaporite layers underwent Suffosion represents the downward migration collapse and subsidence, which generated of the cover through dissolution conduits and is continuous fault propagation (growth faults) coeval with ductile accommodation (Gutiérrez et within the Romualdo Formation. This deformation al. 2008a). occurred when deposits were not completely DISCUSSION consolidated, which created a series of soft- deformation structures, including convolute beds, The results here presented indicate that the top of microfaults and folds. The deformation of more the Crato Formation is a regional unconformity ductile beds caused the propagation of listric faults caused by a relative lake level fall that exposed

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Figure 10 - Contact between the Ipubi and Romualdo formations. a) Boundary between both units (yellow lines), with no evidence of karstification (Pedra Branca Quarry, Nova Olinda); b) example of dissolution feature formed at the top of the gypsum (synform sagging), with syn-sedimentary filling of the karst structure by the deposits of the Romualdo Formation (Conceição Preta Quarry, Santana do Cariri); c) the surface of the gypsum layer is exposed after the mechanical removal of the Romualdo Formation deposits on the right side. On the left side, the folded deposits of the base of the Romualdo Formation can be seen (Supergesso Quarry, Araripina); d) and e) clayey deposits infiltrated into fractures and small sinkholes during the transgression of the Romualdo Formation (Puluca Quarry, Ipubi). these deposits in proximal areas. This unconformity Directly overlying the unconformity at the top marks a major retreat in the relative lake level of the Crato Formation are the bituminous black (Neumann 1999, Assine et al. 2014), following a shales of the Ipubi Formation, which contain up series of pulses of expansion that culminated with to 25% TOC. This lithology represents evidence the formation of the uppermost interval of laminated of a transgressive pulse caused by a relative lake limestones (C6 interval) (Fig. 3). The top of the C6 level rise (Fig. 4). Occurrence of these shale beds interval is marked by evidence of subaerial erosion, is recorded across the basin in proximal domains, reworking and pedogenetic features (calcretes with in wellbores and outcrops on the northern borders. local silicification) (Fig. 3). On the northern border, these shale beds overlie the

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Figure 11 - Deposits of the Romualdo Formation exposed in the Pedra Branca Quarry, Nova Olinda. The paleorelief created by karstified surface of the gypsum controlled the geometry of the basal beds. Syn-sedimentary karstification (sagging+suffosion) caused collapse (red arrow) and influenced deposition by creating additional accommodation space. Additionally, the instability created by the continuous effect of karstification caused the deformation of beds that were not completely consolidated (upper bedding), thus forming complex sets of listric faults (yellow lines), folds, and rollovers.

Figure 12 - Deposits of the Romualdo Formation in the Sombra da Serra Quarry, Araripina. a) Detail of a large exposure showing syn-sedimentary faults caused by the syn-depositional dissolution of the gypsum; b) syn-depositional faults (yellow lines) created by local subsidence due to the dissolution of the gypsum. The left side of the panel shows a collapse structure (suffosion) created by a sinkhole (pink lines) (Gutiérrez et al. 2008a, b). Note that the faults control bed thickness (accommodation space).

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Crato Formation deposits, whereas at the southern deposits, and the diagenetic aspects involved in border, they were deposited over the basement. its evolution. They proposed that the shale and On the southern border, these shale beds are more evaporite beds formed in a shallow environment, often intercalated with calciferous siltstones, characterized by anoxic water bodies locally sandstones and thin limestone beds. Deposition of hypersaline under seasonal variations of relative shale beds over previously exposed proximal areas lake level. Nascimento Jr et al. (2016) also suggests that this new transgression expanded the suggested that the deposition occurred in playa lake domains of the lake beyond its previous limits. systems under some influence of hydrotermalism, These bituminous black shales, formed under and that these rocks underwent shallow burial due anoxic conditions, indicate that the water column to the frequent occurrence of primary gypsum. was at least a few tens of meters deep (Tourtelot The possible tectonic influences that may have 1979, Farouk et al. 2016, Jiang et al. 2016). The triggered the Ipubi inundation, including marine abundance of organic matter and high sedimentation ingressions, remain a topic of debate (Assine et rates, as well as some restriction of circulation, are al. 2014, Nascimento Jr et al 2016). The Ipubi and important processes that have also influenced the Romualdo formations are Aptian-Albian in age, enrichment on organic matter (Tourtelot 1979). which corresponds to the post-rift phase of this After the transgressive pulse, with the stagnation interior basin. However, the rift phase lasted until of the relative lake level (high stand conditions), the Upper Aptian-Early Albian in the equatorial arid conditions may have prevailed and influenced margin and the eastern margin of the South Atlantic the formation of salinas, or coastal sabkhas, which (Matos 1992, 1999), which could have represented allowed the formation of evaporite deposits (Figs. some post-rift influence in marine transgressions to 5 to 7). Coastal sabkhas represent water bodies that the interior basins. are filled with brine and form during the retreat of Evaporite deposits in modern salinas include seaways (Warren 2006, Warren et al. 2010). The halite, gypsum, laminites, organic carbon-rich present study found that during the diagenesis the siliciclastic sediments, and carbonates (Warren alteration of anhydrite to gypsum within the Ipubi 2006). The occurrence of isolated brines that Formation caused pervasive folding and fracturing formed over small depressions, where restrictive of the gypsum layers (Fig. 7). This process conditions created stratified brines, could explain increased during the exhumation of deposits (under the formation of the discontinuous evaporite layers meteoric influence) along Cenozoic. Similar of the Ipubi Formation. Another important point, aspects regarding the effects of dehydration on confirmed by available boreholes in the basin, primary gypsum are described by Abrantes Jr et is the fact that evaporites did not form in distal al. (2016) for the Paleozoic siliciclastic-evaporitic domains; this implies that the physiography and deposits of the Parnaíba Basin, Brazil. Silva (1986) climate conditions drove evaporite deposition, proposed that primary textures of evaporites from which predominantly occurred in proximal regions Ipubi Formation are represented by laminated (Fig. 14). The deposition of carbonate-prone or gypsum composed of prismatic crystals, nodular fine-grained siliciclastic sediments continued in anhydrite and laminated anhydrite. According to distal regions. this author, secondary textures are represented Then, a new subaerial unconformity formed by microcrystalline gypsum, rosette gypsum, and during the maximum of the subsequent relative fibrous gypsum that fills veins. Nascimento Jr et lake level fall, and erosion affected the evaporite al. (2016) studied the origin of the Ipubi Formation beds and other lithologies of the Ipubi formation

(An Acad Bras Cienc (2018 16 CARLOS E. FABIN et al. deposited in proximal zones. A correlative conformity overlying other lithologies certainly formed in the distal regions of the lake (Fig. 13), thus representing the continuation of the subaerial unconformity (Catuneanu 2006, Catuneanu et al. 2009, 2011) (Fig. 14). The formation of this correlative conformity may have been associated with low sedimentation rates caused by the reduction of hydraulic potential and the influx of sediments under arid conditions. Figure 13 shows a schematic model to represent the relations between the main changes in the relative lake level and the formation of unconformities. In this Figure 13 - Schematic model of variations in the relative base model, a tectonic-influenced basal unconformity level of the lake and the formation of unconformities. The major separated deposits of the rift phase from those of basal unconformity separates the deposits of the rift phase from those of the post-rift sequences. The unconformities within the the post-rift depositional sequences. Within the post-rift sequences were caused by variations in the relative post-rift succession subaerial unconformities and base level of the lake driven mainly by climate fluctuations. correlative surfaces are formed in proximal and These unconformities comprise subaerial erosional surfaces distal regions, respectively, and the composite (proximal) and correlative conformities (distal) (modified surface created represent the idealized sequence from Catuneanu 2006). boundaries between the Crato, Ipubi, and Romualdo formations (Figs. 13 and 14). carbonate and evaporites in evaporitic systems. An important unknown aspect of the erosive However, the interdigitation of laminated event that affected the top of the siliciclastic- limestones and evaporites is not observed in evaporitic depositional sequence is its temporal borehole records (Fig. 2), nor in outcrops. In magnitude and the diachronism associated with addition, the existence of a regional erosive the formation of the correlative conformity across unconformity separating the facies associations of the basin. The frequency of relative lake level the Crato and Ipubi formations has been widely cycles (Figs. 13 and 14) is greatly influenced by recognized (Neumann 1999, Assine et al. 2014). climate factors, which suggests that diachronism Thus, the proposition of a sequence boundary of stratigraphic events of the Araripe Basin could between these units that occurs in proximal areas be shorter than observed in stratigraphic events in is consistent. marginal basins (Pietras and Carroll 2006). STRATIGRAPHIC MODEL FOR THE IPUBI An important question still remains concerning FORMATION the lateral relationships between the lithologies of the Ipubi Formation and their distal coeval Here, a depositional model is proposed for the counterparts, that formed within areas not affected formation of the siliciclastic-evaporitic succession by subaerial erosion. Bobco (2014) proposed that of the Ipubi Formation on the proximal regions the Crato and Ipubi Formations were deposited of the Araripe Basin. The model shows how contemporaneously and that their different evolution of major changes in relative lake level lithologies are the result of lateral variations. The influenced the deposition and the formation of author pointed to the aerial distribution of these regional unconformities, considering an adaptation lithofacies and the common relationships between of the original concepts of sequence stratigraphy.

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The model is based in the assignment of the main dominated by calciferous organic-rich black shales, relative lake level stages (Transgressive System were deposited above the unconformity of the top Tract, High Stand System Tract and Low Stand of the Crato Formation. These deposits mark the System Tract) throughout the studied succession, base of the Ipubi Formation (Fig. 14). encompassing six episodes (Fig. 14): Stage IV - After the transgressive pulse, the Stage I - Pulsating expansion of the Araripe stagnation of the relative lake level established a Lake during the post-rift phase created few high stand, under increasingly arid conditions, that depositional sequences (Neumann 1999), including led to the formation of isolated salinas or coastal the Crato Formation (Neumann and Cabrera 2002, sabkhas along the proximal regions. Increasing Silva et al. 2015) (Fig. 14). There is no evidence of stagnation and small oscillations in the relative major relative lake level falls during the deposition lake level possibly are the causes of the main phase of the Crato Formation, although the presence of of evaporites deposition of the Ipubi Formation stratigraphic levels recording the mass mortality of (Fig. 14). Most of the evaporite deposits formed young specimens of fishes (Dastilbe elongatus) and under subaqueous conditions and are intercalated halite pseudomorphs suggests that hydrological/ with fine-grained siliciclastic deposits (Fig. 14). biological conditions (eutrophication, salinity and These isolated salinas or sabkhas may have been oxygenation) may have experienced oscillations. intermittently connected with the lake waters, The formation of halite pseudomorphs (hoppers) which caused occasional interruptions in evaporite (Martill 2007) may indicate that minor relative deposition. lake level falls or severe climate periods occurred, Stage V - Another expressive relative lake although carbonate deposition continued (Martill level fall ended the deposition of siliciclastic- 2007, Heimhofer et al. 2010). These oscillations evaporitic succession in proximal regions. This may have intensified the dense-stratified effect forced regression exposed the proximal zones, of the water column, thus increasing the anoxic and triggered the karstification processes of conditions in the deeper regions of the lake. evaporite beds (Fig. 14). The consequent erosion Stage II - At the end of the cycle that formed and reworking of evaporite deposits, and other the Crato Formation, a major fall in the relative lake lithologies, created a new sequence boundary (Silva level caused the subaerial exposure of proximal 1986, Fabin 2013) that marks the upper limit of the regions (Fig. 14). This caused an erosional process Ipubi Formation. According to the biostratigraphic that affected the deposits of this unit (Neumann record obtained from boreholes across the basin, 1999). The lowest position of the relative lake level siliciclastic sedimentation continued within the marks the maximum expression of the subaerial depocenters, what indicates that the relative lake erosion and the first sequence boundary of the level was not completely depleted, and a correlative studied succession. surface probably formed across distal regions. The Stage III - A new relative lake level rise karstification processes of the evaporite layers, occurred and caused an important transgression created a ruiniform relief featuring escarpments, over the proximal areas, including regions not depressions and sinkholes. previously covered by the basin domains. This Stage VI - A new transgressive event event possibly caused the drowning of sedimentary triggered by a new relative lake level rise created sources. The balance of sedimentary influx and the depositional sequence that comprises the organic production influenced the establishment of Romualdo Formation what overlies the Ipubi anoxic conditions. Siliciclastic deposits, which are Formation (Fig. 14). The marine influence on this

(An Acad Bras Cienc (2018 18 CARLOS E. FABIN et al. transgression, that established a seaway in the studied interval is proposed (Fig. 15). It represents interior of Northeast Brazil, is well documented a tentative approach based on the adaptation of by abundant occurrence of marine fossils (sharks concepts of sequence stratigraphy to establish a and rays) (Martill 1988, Kellner 2002, Saraiva model for the Araripe Lake evolution during the 2008). This new transgression, that followed the studied interval, which can be further tested in erosion of evaporite beds, caused a renewed syn- future stratigraphic investigations with the addition depositional karstification of these deposits. The of new borehole and/or seismic data. new inundation caused syn-depositional variations The proposed relative lake level curve was in accommodation space due to the increase in divided into three main pulses of transgression dissolution and collapse of the upper evaporite bounded by two regional unconformities. The bodies, as well as the syn-depositional deformation major trigger of the major and minor changes in of the strata of the Romualdo Formation. the relative lake level may have been the climate. Tectonic pulses (post-rift reactivations) that PROPOSED CURVE OF RELATIVE CHANGES IN could have influenced marine ingressions remain ARARIPE RELATIVE LAKE LEVEL DURING THE DEPOSITION OF THE IPUBI FORMATION a topic of debate. Interpretation of the relative lake level changes presented here corroborates A curve comprising the changes in the Araripe some propositions made by Neumann (1999) relative lake level during the deposition of the and Assine et al. (2014), about the establishment

Figure 14 - Schematic model of the evolution of the depositional sequences corresponding to the Crato, Ipubi and Romualdo formations. Major variations in the Araripe Lake level controlled the formation of these sequences.

(An Acad Bras Cienc (2018 SEQUENCE STRATIGRAPHY OF IPUBI FORMATION, ARARIPE BASIN 19 of depositional sequences controlled by the high values of TOC. The following relative lake expansions and retractions of Araripe Lake during level stagnation and increasingly arid conditions the post-rift phase I. influenced the establishment of a high stand stage that led to the formation of coastal sabkhas or FINAL CONSIDERATIONS salinas. This high stand stage allowed the formation The application of sequence stratigraphy concepts of isolated masses of gypsum and anhydrite to guided the identification of the relationships occur, which culminated in the deposition of between variations in the relative level of Araripe discontinuous evaporite beds at the top of the Lake and the formation of depositional sequences succession. A second major relative lake level fall within the post-rift phase I during the Aptian- generated a regional subaerial unconformity that Albian. Data collected from outcrops and boreholes affected the Ipubi deposits (mainly the evaporites). indicate that the Ipubi Formation is separated from Extensive pedogenetic processes and karstification the underlying Crato Formation and the overlying then occurred, which created a paleorelief. A new Romualdo Formation by regional unconformities transgression followed and caused the deposition in proximal domains. The lower unconformity of the carbonate-siliciclastic succession of the separates the top of the Crato Formation, which Romualdo Formation over the Ipubi Formation. The is mainly represented by its uppermost interval deposition of the Romualdo strata was influenced of laminated limestones (C6), from the basal by the continuation of the karstification processes black shales and claystone deposits of the Ipubi within the Ipubi evaporites. This process created Formation. These basal deposits formed due to collapse structures, the infiltration of siliciclastic the transgressive event that expanded the relative sediments into the fractures and karsts of the Ipubi lake level beyond the previous extension of the Formation, and the syn-depositional deformation of Crato Formation over the adjacent basement areas. the Romualdo deposits with the formation of listric During the Ipubi transgression, anoxic conditions faults, local convoluted deformation and folding. influenced the formation of basal black shales with The occurrence of syn-depositional deformation during the deposition of the Romualdo Formation, due to the dissolution and collapse of evaporite deposits, represents an important example of the influence that evaporite karstification can exert on depositional processes.

ACKNOWLEDGMENTS

We would like to acknowledge the ANP-UFPE Programa de Formação de Recursos Humanos (PRH-26), the Agência Nacional do Petróleo, Gás Natural e Biocombustíveis (ANP), the “Turing” R&D cooperation project and the “Três Furos no Andar Aalgoas” R&D cooperation project, Figure 15 - Schematic curve of changes in the relative base both funded by the Petróleo Brasileiro S.A. lake level of Araripe Lake during the depositional period of the Ipubi Formation (time span related to the distinct cycle (PETROBRAS) and developed by the Laboratório frequencies are from Neumann 1999). de Geologia Sedimentar (LAGESE) from

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Universidade Federal de Pernambuco (FADE/ CABRAL FAA. 2017. Caracterização das microfácies e UFPE/PETROBRAS). A special thank you to evolução diagenética dos calcários do topo da Formação Crato, Bacia do Araripe, NE do Brasil, 120 p. Dissertação Professor Paulo Paim, UNISINOS, who shared de Mestrado. Programa de Pós-Graduação em Geociências, his expertise and thereby helped to improve the Recife. (Unpublished). manuscript. CARVALHO MSS AND SANTOS MECM. 2005. Histórico das pesquisas paleontológicas na Bacia do Araripe, nordeste do Brasil. Anu Inst de Geoc UFRJ 28(1): 15-34. REFERENCES CATTO B, JAHNERT RJ, WARREN LV, VAREJÃO FG AND ABRANTES JR F, NOGUEIRA ACR AND SOARES JL. ASSINE ML. 2016. The microbial nature of laminated 2016. Permian paleogeography of west-central Pangea: limestones: Lessons from the Upper Aptian, Araripe Basin, Brazil. Sediment Geol 341: 304-315. Reconstruction using sabkha-type gypsum-bearing CATUNEANU O. 2002. Sequence stratigraphy of clastic deposits of Parnaíba Basin, Northern Brazil. Sediment systems: concepts, merits, and pitfalls. J Afr Earth Sci Geol 341: 175-188. 35(1): 1-43. ALMEIDA FFM, HASUI Y, BRITO NEVES BB AND FUCK CATUNEANU O. 2006. Principles of Sequence Stratigraphy. RA. 1977. Províncias Estruturais Brasileiras. In: VIII Elsevier, Amsterdam, 375 p. Simpósio de Geologia do Nordeste, Campina Grande, p. CATUNEANU O ET AL. 2009. Towards the standardization 363-391. of sequence stratigraphy. Earth-Sci Rev 92: 1-33. ARAUJO CEG, WEINBERG RF AND CORDANI UG. 2013. CATUNEANU O, GALLOWAY WE, KENDALL CGC, Extruding the Borborema Province (NE-Brazil): a two- MIALL AD, POSAMENTIER AP, STRASSER A AND stage Neoproterozoic collision process. Terra Nova 26(2): TUCKER ME. 2011. Sequence Stratigraphy: Methodology 157-168. and Nomenclature. Newsl Stratigr 44(3): 173-245. ASSINE ML. 1992. Análise estratigráfica da Bacia do Araripe, CAVALCANTE AD AND RAMOS VC. 2010. Ajuste de Nordeste do Brazil. Braz J Geol 22(3): 289-300. Parâmetros Para Modelo Viscoelástico de Fluência com ASSINE ML. 1994. Paleocorrentes e paleogeografia na Bacia Aplicações em Rochas Salinas. In: Dvorkin E, Goldschmit do Araripe, nordeste do Brasil. Braz J Geol 24(4): 223-232. M and Storti M (Eds), Mecânica Computacional. XXIX ASSINE ML. 2007. Bacia do Araripe. Bol Geo Petr 15(2): Buenos Aires: Asociación Argentina de Mecánica 371-389. Computacional, p. 8579-8591. ASSINE ML, PERINOTTO JAJ, CUSTÓDIO MA, COLLINSON JD AND THOMPSON DB. 1982. Sedimentary NEUMANN VH, VAREJÃO FG AND MESCOLOTTI Structures. George Allen & Unwin, London, 207 p. PC. 2014. Sequências deposicionais do Andar Alagoas da DE CASTRO DL AND CASTELO BRANCO RMG. 1999. Bacia do Araripe, Nordeste do Brasil. Bol Geo Petr 22(1): Caracterização da arquitetura interna das Bacias do 3-28. Vale do Cariri (NE do Brasil) com base em modelagem BENGALY AP. 2003. Modelagem Geométrica e Termal gravimétrica 3-D. Rev Bras Geof 17: 129-144. Tridimensional de Corpos Salíferos em Bacias FABIN CE. 2013. Mapeamento geológico à sudoeste da cidade Sedimentares, 132 p. Dissertação de Mestrado, de Araripina: Contexto estratigráfico da Formação Ipubi, Universidade Federal do Rio de Janeiro, Rio de Janeiro. sequência evaporítica da Bacia do Araripe, 129 p. Trabalho (Unpublished). de Conclusão de Curso. Departamento de Geologia, BEURLEN K. 1962. A geologia da Chapada do Araripe. An Universidade Federal de Pernambuco. (Unpublished). Acad Bras Cienc 34: 365-370. FARA E, SARAIVA AAF, CAMPOS DA, MOREIRA, BEURLEN K. 1963. Geologia e estratigrafia da chapada do JOÃO KR, SIEBRA DC AND KELLNER AWA. 2005. Araripe. In: XVII Congresso Brasileiro de Geologia – Controlled excavations in the Romualdo Member of the SBG, Recife, p. 1-47. Santana Formation (Early Cretaceous, Araripe Basin, BOBCO FER. 2014. Caracterização faciológica, petrográfica northeastern Brazil): stratigraphic, palaeoenvironmental e isotópica dos evaporitos do Membro Ipubi, Bacia do and palaeoecological implications. Palaeogeogr Palaeocl Araripe, nordeste do Brasil, 147 p. Trabalho de Conclusão 218: 145-160. de Curso. Universidade Federal do Rio Grande do Sul. FAROUK S, AHMAD F, MOUSA D AND SIMMONS (Unpublished). M. 2016. Sequence stratigraphic context and organic BRITO NEVES BB, SANTOS EJ AND VAN-SCHMUS geochemistry of Palaeogene oil shales, Jordan. Mar Petrol WR. 2000. Tectonic History of the Borborema Province, Geol 77: 1297-1308. Northeast Brazil. Tectonic Evolution of South America. In: GUTIÉRREZ F, CALAFORRA JM, CARDONA F, ORTÍ 31st IGC, Rio de Janeiro, p. 151-182. F, DURÁN JJ AND GARAV P. 2008b. Geological and

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