The Serra da Cangalha impact structure, Brazil: Geological, stratigraphic and petrographic aspects...

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Journal of South American Earth Sciences xxx (2013) 1e15

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The Serra da Cangalha impact structure, Brazil: Geological, stratigraphic andpetrographic aspects of a recently confirmed impact structure

Marcos Alberto Rodrigues Vasconcelos a,*, Alvaro P. Crósta a, Wolf Uwe Reimold b,c, Ana Maria Góes d,Thomas Kenkmann e, Michael H. Poelchau e

a Institute of Geosciences, University of Campinas, Campinas, SP, BrazilbMuseum für Naturkunde, Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, GermanycHumboldt Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germanyd Institute of Geosciences, University of São Paulo, Brazile Institut für Geowissenschaften, Albert-Ludwigs-Universität Freiburg, Germany

a r t i c l e i n f o

Article history:Received 18 October 2012Accepted 18 March 2013

Keywords:Serra da CangalhaStratigraphyShock features

* Corresponding author. Tel.: þ55 1983318909.E-mail addresses: [email protected] (M

ige.unicamp.br (A.P. Crósta), [email protected] (A.M. Góes), thomas.kenkm(T. Kenkmann), [email protected]

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a b s t r a c t

Serra da Cangalha is a complex impact structure with an apparent diameter of 13.7 km located inessentially undisturbed sedimentary rocks of the Parnaíba basin in northeastern Brazil. The stratigraphyof the crater region includes, from bottom to top, the Longá, Poti, Piauí and Pedra de Fogo formations ofDevonian to Late Permian age. The age of the impact event is constrained to <250 Ma by stratigraphy e

the youngest formation affected by the event is the w250 Ma Pedra de Fogo Formation. The structurecomprises a w5.8 km wide central uplift involving the Piauí, Poti and Longá formations and a prominentw3 km wide collar of Poti Formation rocks. We divided Serra da Cangalha into four distinctive structuraldomains (ieiv), from the innermost zone outward. (i) The central domain, with an inner collar w1.5 kmradius from the center, yielded all the samples with microscopic shock features identified so far. Theseinclude planar deformation features (PDF), feather features (FF), and planar fractures (PF) in quartz grainsfound in polymict breccias and shatter cones from the central depression. Furthermore, significantcementation with iron oxide is observed in the rocks of Serra da Cangalha, especially in the Poti For-mation and in the polymict breccias, conferring to them a peculiar red color. Macroscopic deformationinvolves faulted, folded and subvertical strata within a w2.9 km radius from the center. (ii) The annularbasin domain has limited outcrops; its most prominent features are two concentric annular ridgesformed by chert breccias and fossilized wood-bearing folded strata of the Pedra de Fogo Formation. (iii)The crater rim and (iv) external domains comprise undisturbed strata of the Pedra de Fogo and Piauíformations with well-preserved sedimentary structures. Whilst the existing literature on Serra da Can-galha has focused on the structure morphology, general geology and some shock features, we presenthere a detailed description of the stratigraphy and the geology of each formation in the interior andaround Serra da Cangalha, as well as further detailed microscopic shock feature analysis. This providessignificant evidence that the rocks of the central uplift have undergone shock pressures of, at maximum,10 GPa.

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1. Introduction

The Serra da Cangalha (SdC) structure (first referred by Dietzand French, 1973; McHone, 1986) is located in Tocantins state,northern Brazil, centered at 8�050S/46�520W, w40 km south of the

.A.R. Vasconcelos), [email protected] (W.U. Reimold), goes@[email protected] (M.H. Poelchau).

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elos, M.A.R., et al., The Serrad impact structure, Journal

Riachão Ring (another impact structure e Maziviero et al., 2012)(Fig. 1). SdC is a complex impact structure with an apparentdiameter of about 13.7 km, with a central uplift of 5.8 km width(Kenkmann et al., 2011a). This impact structure was formed inundeformed Paleozoic sedimentary rocks of the Parnaíba Basin(Fig. 2), an intracratonic sedimentary basin containing strata of LateSilurian to Triassic age (Góes, 1995). The presumed age of thestructure (<250 Ma) is not well constrained: it is based merely onthe regional stratigraphy (Fig. 2) and on the age of the Pedra deFogo Formation, the youngest strata that were affected by the for-mation of the crater (Góes and Feijó, 1994).

da Cangalha impact structure, Brazil: Geological, stratigraphic andof South American Earth Sciences (2013), http://dx.doi.org/10.1016/

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Fig. 1. Digital elevation model based on Shuttle Radar Topography Mission (SRTM) data showing the location of Serra da Cangalha. Inset shows a map of Brazil with the location ofthe SRTM image. Further to the NE is the Riachão Ring, a second smaller impact structure (D ¼ 4.5 km).

M.A.R. Vasconcelos et al. / Journal of South American Earth Sciences xxx (2013) 1e152

The circular structure of SdC has been known since the late1960s, when it was described by Ojeda and Bembon (1966) withinthe scope of a regional geological survey for oil exploration pur-poses carried out by Petrobras (the Brazilian oil company). The firstreference to SdC as an impact structure was made by Dietz andFrench (1973), who proposed its impact origin based on itsmorphology, as seen on early Landsat satellite images. They pointedoute as indications of the impact nature of SdCe its nearly circularshape and the presence of a conspicuous central uplift. McHone(1979) and Santos and McHone (1979) reinforced the impactorigin hypothesis of SdC, after finding breccias and possible shockdeformation features in sandstone. Further geological studies,including reconnaissance fieldwork, were done by McHone (1986),which resulted in a preliminary map of SdC and the disclosure ofpossible shock features. A first published review of the meteoritic

Please cite this article in press as: Vasconcelos, M.A.R., et al., The Serrapetrographic aspects of a recently confirmed impact structure, Journalj.jsames.2013.03.007

impact structures in Brazil by Crósta (1987) referred to SdC as animpact structure, based on the bona fide shock evidence reportedby the previous authors.

In the early 1970s the Brazilian Department of Mineral Pro-duction (DNPM) drilled three boreholes into the central depressionof SdC, as part of a regional campaign for diamond exploration. Atthat time, DNPM geologists interpreted the structure as beingrelated to a buried kimberlite intrusion, as a number of these areknown in the Parnaíba Basin (DNPM, 1972). Each borehole reachedw200 m depth, whereby only intensely deformed strata attributedto the Devonian Longá Formation were found.

In recent years, geological, geophysical and remote sensingstudies have been conducted at SdC, aiming at the characterizationof this complex structure. Almeida-Filho et al. (2005) employedASTER (Advanced Spaceborne Thermal Emission and Reflection


Fig. 2. Stratigraphic column of the Parnaíba Basin (modified from Góes, 1995). The widths of the strata indicate the lateral extension of the basin at a given time.

M.A.R. Vasconcelos et al. / Journal of South American Earth Sciences xxx (2013) 1e15 3

Radiometer) data for characterizing its main morphological char-acteristics, whereas Reimold et al. (2006) analyzed topographicinformation provided by Shuttle Radar Topography Mission (SRTM)data, combined with satellite imagery acquired by the LandsatThematic Mapper (TM). These authors suggested a morphologicalconfiguration for SdC comprisingmultiple ring structures (used as amorphological term), with a prominent inner ring at 1.6 km radiusfrom the center, a 1st intermediate ring at about 3 km, and a 2ndintermediate ring at about 6.7 km from the center. Kenkmann et al.(2011a) investigated the structural elements of SdC based ondetailed remote sensing and ground-based structural analysis witha special emphasis on the central uplift region. The authors sug-gested an oblique impact from a southerly direction based on theoverturned and folded strata combined with a certain asymmetryof the central uplift. However, the directional analysis washampered by the existence of preexisting joint sets, which stronglyinfluenced the cratering process.

Geophysical studies carried out by Adepelumi et al. (2004,2005a, b) and Vasconcelos et al. (2010a) involved gravity andaeromagnetic analysis, as well as resistivity and magnetotelluricmodeling. According to Adepelumi et al. (2005b), the crystallinebasement underneath SdC occurs at a depth of 1e1.5 km. However,Vasconcelos et al. (2010a), based on regional aeromagnetic data,interpreted the average depth of the basement as 2.4 km, an esti-mation corroborated by data from an oil exploration boreholelocated 70 km north of SdC. According to Vasconcelos et al. (2010a),SdC exhibits an annular gravity low and a 10 nT magnetic high overthe center of the structure, a geophysical signature which is inaccordance with those of impact craters of similar dimensionsformed in sedimentary target rocks (Pilkington and Grieve, 1992).

Kenkmann et al. (2011a) also presented the results of structuralanalysis, as well as general geological and petrographic aspects ofSdC. They emphasized the importance of a more detailed shock


petrographic analysis in order to characterize the deformation ofthe target rocks of SdC. Hence, this article complements the resultsand conclusions of Kenkmann et al. (2011a), based on recentgeological results focusing on the local stratigraphic and sedi-mentary aspects, as well as on detailed petrographic analysis.Concerning the latter, we present an analysis of PDF orientations, aswell as a description of shock deformation features in samples fromthe inner collar of the central uplift. Stratigraphic sections wereanalyzed within SdC and in the surrounding region, examining themain characteristics of the stratigraphic units in order to under-stand how the impact deformationmodified the target rocks on themacro- and micro-scale.

2. Methods

2.1. Field work

SdC can be reached along state road TO-226 to the town ofCampos Lindos, located a few kilometers to the NE of the structure.This road cuts across the northern part of the structure, goingthrough the NWand NE parts of the rim and into the annular basin.Road cuts along TO-226 provide access to good exposures of thedeformed strata of the rim monocline, especially at the north-western part of the rim. In the interior of SdC, there is an unpavedroad that goes around the central uplift toward the village ofRancharia located about 10 km south of SdC (Fig. 1), outside thesouthern crater rim. Along this road there are some exposures ofsedimentary rocks of the Piauí and Pedra de Fogo formations. Be-sides this single unpaved road within SdC, there are a number ofminor dirt tracks covering around 70% of the annular basin be-tween the collar and the crater rim. Access to the collar of thecentral uplift and to the inner depression is more difficult andrestricted to hiking trails.



A panchromatic WorldView-1 satellite image (0.5 m spatialresolution) was used in combination with a digital elevationmodel (DEM) derived from ASTER satellite data, with a 30 mspatial resolution, to support geological mapping of SdC. Field datawere collected along several transects covering all sectors of thestructure, with a larger number of observation points in the raisedcollar and inner depression (annular basin) of the central upliftzone. Particular attention was given to sedimentary structures andsedimentological data which, combined with petrographic anal-ysis of samples from outcrops and drill cores, allow the distinctionof the different strata. Geological data from the areas surroundingSdC structure were collected mainly from outcrops along road TO-226.

2.2. Rock types and sampling

Sampling was carried out during several field campaigns be-tween 2008 and 2010 and was focused on the search for shockevidence, not clearly stated in the previous work by McHone(1986). Sample collection was concentrated in the area of thecentral uplift and its immediate surroundings, as these areas wereconsidered themost likely to have undergone higher levels of shockdeformation (e.g., Grieve et al., 1981; Grieve, 1987) in an impactstructure believed to be deeply eroded (McHone, 1986; Kenkmannet al., 2011a,b). Furthermore, the quartz-rich character of thesandstones that occur in this area is more suitable for the forma-tion, preservation and detection of unique shock-deformation fea-tures in quartz (e.g., Stöffler and Langenhorst, 1994; Grieve et al.,1996) than in the other rock types.

2.3. Sample analysis

The Longá Formation was analyzed based on samples from theboreholes drilled in the inner depression of the central uplift, andfrom a few surface outcrops in this area. Drill cores from theseboreholes, designated by the Brazilian Department of MineralProduction (DNPM) as GT-01-GO, GT-02-GO and GT-03-GO, wererecovered from the DNPM core storage facility in Recife (Pernam-buco state).

Thin sections from a number of representative samples fromeach lithostratigraphic unit collected within SdC were analyzed forcharacterization of micro-deformation features and the possiblepresence of shock indicators. Based on the presence or absence ofshock features it is possible to estimate the peak shock pressurereached in each domain of SdC. In this procedure, a universal stagewas employed to measure the planes of the respective shock fea-tures found in the samples from the central uplift. The universalstage was mounted onto a Leitz polarizing microscope and mea-surements were indexed using a template of crystallographic ori-entations in quartz proposed by Ferrière et al. (2009).

3. Geological overview

The Parnaíba Basin has an elongated shape along NEeSW and atotal extent of >600.000 km2. It represents an intracratonic sagbasin formed after the Brasiliano/Pan-African Orogeny (Almeidaet al., 1981), probably during Silurian times (Goes and Feijó,1994). Its basement comprises fold belts (Tocantins-Araguaia,Gurupi, Rio Preto-Riacho do Pontal) and cratonic areas (Amazonian,São Luís and São Francisco) (Santos and Carvalho, 2009; Pedreira daSilva et al., 2003). The most prominent tectonic features of theParnaíba Basin are the NEeSW-trending Transbrasiliano lineamentand the NWeSE-trending Marajó-Parnaíba lineament, whichcontrolled the prevailing direction of the sedimentation during thePaleozoic (Cunha,1986), andwere later reactivated in theMesozoic.


The stratigraphy of the Parnaíba Basin comprises the SerraGrande, Canindé and Balsas groups, representing sedimentary de-posits of Silurian to Triassic age (Fig. 2). The rocks are mostly sili-ciclastic sediments deposited during several transgressiveeregressive cycles, with an average total thickness of 3500 m (Góes,1995; Góes et al., 1997). The oldest strata comprise Silurian clasticsediments of the Serra Grande Group (Caputo and Lima, 1984),starting with conglomerate and continental sandstone of the IpuFormation, deposited under possible glacial influence and gradinginto marine sandstone and shale of the Tianguá Formation. Thiscycle ends with the regressive sedimentation of fluvial sandstoneand conglomerate of the Jaicós Formation. The Canindé Groupconsists of marine deposits, comprising white and thin layers ofsandstone, and gray shale of the Itaim Formation, representing atransgressive event during the deposition of the Pimenteiras For-mation. The next sequence comprises the Devonian glacial dia-mictite and deltaic sandstone of the Cabeças Formation. Thecontinental sandstone grades into shale of the Longá Formation(DevonianeLower Carboniferous) representing a transgressive cy-cle. This cycle ends with a further regressive event that resulted inthe deposition of sandstone of the Poti Formation (Lower Carbon-iferous) (Góes, 1995).

The formation of the Balsas Group began with a continentalsequence of predominantly eolian nature, with short sea incursionsrepresented by sandstone, limestone and anhydrite of the PiauíFormation (Upper Carboniferous). The Piauí Formation is overlainby sandstone, shale and limestone of the Pedra de Fogo Formation(Permian), deposited in a shallow sea. The section terminates withshale and anhydrite of the Motuca Formation (Permian) that wasonly deposited in remnant marine regions. During the Triassic, theregion was subject to desertification, resulting in the deposition ofeolian sandstones of the Sambaíba Formation.

4. Results

4.1. Geology of Serra da Cangalha

SdC is a near-circular structure with a subdued elevated rim andan average apparent diameter of 13.7 km. It comprises, from thelowermost to the uppermost unit, the Longá, Poti, Piauí and Pedrade Fogo formations (Fig. 3). Dark shales of the Devonian/LowerCarboniferous Longá Formation constitute the oldest rocks at SdC,which are poorly exposed only in the inner depression of thecentral uplift. Detailed descriptions of the characteristics of therocks of SdC and surroundings are presented in the next sectionsseparately for each of the domains documented in the crater area:central uplift, annular basin, crater rim and external surroundingsof SdC.

The Poti Formation comprisesmainly red or white sandstones ofEarly Carboniferous age that form the collar of the central uplift.Rocks belonging to this unit do not seem to occur in the vicinity ofSdC outside the collar. The Piauí Formation forms the peripheralzone of the central uplift, as well as most of the geology exposedover the inner area of the structure, and is widely covered by thePedra de Fogo Formation (Fig. 3).

The landscape outside SdC is dominated by mesas of generallyflat-lying, barely deformed (large-amplitude gently undulating)strata. The regional table mountain land results from incisions bythe regional drainage systems. This landscape offers a strikingcontrast with the morphology of the interior of SdC, character-ized by annular ridges and intensely deformed strata. The centraluplift comprises a prominent inner collar at w1.5 km radialdistance from the center (Fig. 3). The collar is formed of 250e370 m high hills of intensely deformed sedimentary rocks, and itsouter limit is marked by concentric annular ridges. At the center


Fig. 3. Simplified geological map of Serra da Cangalha. The external dotted line represents the rim of the crater. Numbered sites correspond to main outcrops referred to in the text.The coordinate system applied is the Universal Transverse Mercator (UTM) system (in meters), zone 23South.


of the collar there is a near-circular depression forming a smallbasin that drains the area bounded by steep inner walls of thecollar.

4.2. Central domain

The central uplift of SdC was defined by Vasconcelos et al.(2010b) and Kenkmann et al. (2011a) as the innermost circularregion of 5.8 km diameter, which is built up by steeply dippingstrata comprising an outer peripheral zone with Piauí Formationoutcrops, a prominent, elevated collar formed by rocks of theweathering-resistant Poti Formation, and a central depressed areawith rocks from the Longá Formation (Fig. 3).

The Longá Formation is dominated by shales and siltstones,which are more susceptible to weathering and erosion than the


other siliciclastic rocks that occur in the SdC structure, in particularthe silicified sandstone that forms the collar of the central uplift. Forthis reason, this innermost unit has only some outcrops of medium-or coarse-grained sandstones in the northern part of the centraldepressed area, which is characterized by a gentle topographicrelief and is generally covered by, in part quite dense, vegetation.This depression contains a basin drained by a stream and an erosiveoutlet in the NNW part that is the only break through the annularraised collar. The innermost area can be reached on foot along a trailthat follows this drainage channel.

Information about the rocks of the Longá Formation comesmostly from the drill cores. The three boreholes were drilledvertically through strongly compacted and deformed dark gray andblack shales and poorly sorted sandstones. The dips of the stratamostly range from 45 to 75� (Fig. 4a), although vertical dips have



also been observed. Deformation features observed in the rocksfrom the cores include intense fracturing and brecciation in coarse-grained sandstone (Fig. 4b), features that are completely unusual inrocks of this unit elsewhere in this region. Palynological age de-terminations carried out on the dark shales by Dr. Paulo Alves deSouza of the University of Rio Grande do Sul (personal communi-cation to the authors, 2011) indicate a Late Famennian age (latestDevonian), which confirms that these rocks correspond to theLongá Formation.

The annular raised collar, as part of the central uplift, isw2.8 kmwide (Fig. 4c) and corresponds to the ‘central ring’ defined byReimold et al. (2006). It has a slightly quadrangular shape with anopen part toward the NNW and is formed by sub-vertical walls offolded red and white Poti sandstone. Rocks of the Poti Formationthat form the collar are intensely silicified and indurated, and havea generally massive structure. Bedding, where recognizable, isintensely deformed, with complex fold patterns (as discussed indetail by Kenkmann et al., 2010, 2011a) ranging from a 1-m to adecameter scale. The intense deformation and silicification appar-ently caused widespread obliteration of the original sedimentarystructures, which compromises the interpretation of the deposi-tional processes that produced these rocks. The present position ofthe Poti sandstones and the Longá shales in the central uplift istopographically above that of the younger Piauí and Pedra do Fogounits that surround the central uplift in the interior of SdC, indi-cating that these two units in the central uplift structure have beenuplifted.

Fig. 4. (a) Drill core of sandstone with mm-sized quartz grains collected from 90 m depthborehole is vertical). (b) Detail of the sample shown in (a) exhibiting a vertical fault and smalemphasizing the longer axis of the slightly elliptical central uplift, measuring about 2.8 km


The Piauí Formation is located in a peripheral zone surroundingthe steep collar of SdC (Figs. 3 and 4c). It can be observed in a fewoutcrops only and is externally bounded by semi-circular ridges ofchert breccia and silicified sandstone forming elongated hills withsteep slopes (Fig. 5a and b). Bedding on these ridges usually exhibitssubvertical dips (Fig. 5c); there are numerous centimeter-scalefaults showing displacement of thin layers of sandstone (Fig. 5d).Characteristics of this sandstone comprise red and sometimeswhite colors, fine to coarse grain size, and subangular to sub-rounded grains that are moderately sorted. Cross-bedding with 5e10 cm amplitudes can still be recognized at some of these outcrops,even after deformation. No direct shock evidence has been foundeither in rocks from these ridges, or in the strata that occur in be-tween them and along the outer rim of SdC.

4.3. Annular basin domain

Nearly 90% of the annular basin comprises rocks of the Pedra deFogo Formation and 10% correspond to the Piauí Formation. Thistopographic depression between the crater rim and the centraluplift corresponds to a topographically low region with a concen-tric drainage system and two well-developed concentric ridgefeatures. The 1st annular ridge occurs at about 2.8 km radius fromthe center, forming an annular morphological feature comprisingsteep, rounded hills; it is reasonably well exposed and marks thecontact of the Pedra do Fogo with the Piauí Formation. Thesediscontinuous hills also mark the outer limit of the central uplift

in Longá Formation at the center of SdC. Note the subvertical dip of the bedding (thel chert fragments. (c) Aerial view of the collar of the Serra da Cangalha central uplift andin NNEeSSW direction (aerial photography by A. Bartorelli e view toward the West).


Fig. 5. General characteristics of the Poti Formation in the interior of SdC. (a) 3D perspective view of the central uplift of SdC showing the collar and the 1st annular ridge (imageacquired by WorldView-1 satellite; vertical exaggeration ¼ 10�). (b) Detail of figure ‘a’ showing the subvertical, folded/faulted layers of the 2nd annular ridge. (c) Generalappearance of the Piauí Formation. Sandstone with high dip angle, in the southern part of the central uplift (295537 E/9103471 N, zone 23S). Sedimentary structures such as cross-stratification, although rotated by deformational processes related to the impact, remain preserved in the same location of ‘c’. (d) Detail of layers sectioned by micro-faults, withmillimeter- to centimeter-scale displacements. (e) Fossil wood of the Pedra de Fogo Formation. Pen for scale is 13 cm long.


(Fig. 5a). The strata exposed in these hills comprise mainly brec-ciated (cataclased) chert layers, as well as silicified sandstone withsubordinate mudstone. The large amount of chert breccia, togetherwith the occurrence of fossilized wood of Psauronius (Fig. 5e), wasused as the criterion to assign these strata to the top portion of thePedra de Fogo Formation (e.g., Plummer, 1946; Lima and Leite,1978; Góes and Feijó, 1994).

In some areas, such as in the northeastern and western parts ofthe annular basin, the Pedra de Fogo Formation exhibits centi-meter- to meter-scale open folds (Fig. 6a,b). This marks the 2ndannular ridge that is located some 6 km from the center of SdC(Fig. 6a). It has the following characteristics: (i) in the northwesternsector, it exhibits open folds and centimeter-thick chert layers thatare also folded (Fig. 6b), similarly to the northeastern sector(Fig. 6c); (ii) in the western sector, the ridges are rounded andcomprise silicified sandstone with folded pre-impact chert breccia;(iii) in the southern region it is characterized by thin chert layers inshallow outcrops. At other locations the 2nd annular ridge is nottopographically prominent, probably due to erosion, but its limitscan still be interpreted based on lineaments extracted from highspatial resolution satellite images.

In the northeastern part of the 2nd annular ridge, near the outerrim, there are intercalations of sandstone and mudstone with chertlayers and lenses, which become more abundant and thicker up-wards (i.e., in direction of the crater rim). The bottom of the sectionat point E-13 (Fig. 3) comprises 4.5 m of fine- to medium-grained


and moderately-sorted white sandstone. This stratum is overlainby red, fine-grained and well sorted sandstone that shows what isprobably the outermost impact-related deformation observed inthe form of layers dipping 30� inward, together with meter- andcentimeter-scale open folds. Despite this deformation, this layerstill exhibits well-preserved, medium-scale tabular cross-bedding.The heterolithic interbedding reflects the impact-related defor-mation, which is characterized by open folds in layers with inter-mediate dip toward the interior of the structure.

4.4. Crater rim domain

This domain is characterized by flat-topped plateaus with hightopographic elevations that mark the outer limit of SdC. Thedomain comprises mostly rocks of the Pedra de Fogo Formation.The plateaus have been eroded in some regions, in particular in theNW and E portions of the rim, exposing the underlying Piauísandstones. The Pedra de Fogo Formation consists of heterolithicdeposits of red with occasional gray laminated mudstone and,subordinately, pink sandstone that is coarse- to medium-grainedand well sorted. The Piauí Formation shows frequent in-tercalations of purple/graymudstone and fine- tomedium-grained,red sandstone, usually with massive bedding or with incipientsigmoidal cross-bedding. At point E-26 (Fig. 3) remarkable thick-ening of themudstone and thinning of the sandstonewas observed.The contact between these two formations is gradational; whereas


Fig. 6. (a) Photo taken from the western collar of the central uplift toward the western outer rim. Note the contact between the Piauí Formation and the curved ridge which marksthe Pedra de Fogo Formation. This curved ridge is here termed the 1st annular ridge. The 2nd annular ridge can be seen in the background, exhibiting a shallower topographicexpression compared to the 1st ridge. CU: Central Uplift. (b) 3D perspective view of the western part of SdC showing the Central Uplift (CU), occurrence of the Pedra de FogoFormation, Piauí Formation (PiF), and folded chert breccias defining the 2nd annular ridge of the Pedra de Fogo Formation. The folded chert layers are the same shown in “a”.Vertical exaggeration ¼ 10�. (c) 3D perspective view of the northeastern part of SdC showing the 2nd annular ridge, the annular basin, the Piauí Formation (PiF) and the Pedra deFogo Formation at the outer rim (PFF). Vertical exaggeration ¼ 10�.


the Piauí Formation has a predominance of sandstone, the Pedra deFogo Formation is dominated by mudstone.

4.5. The external domain

Bedding in the areas outside of the rim of the SdC structure isnearly horizontal, and only very little evidence of deformation ispresent, in the form of gently undulating bedding (large wave-lengths of tens to hundreds of meters, amplitudes of a few metersonly, and dip variation of<10� over such distances). In this externaldomain of SdC, the Piauí Formation is exposed in low-altitudeareas, whereas the Pedra de Fogo Formation occurs strati-graphically and topographically relatively higher, on the plateaus(Fig. 7a). To the south of SdC there is a predominance of fine- tomedium-grained sandstone, with well-sorted and rounded grainsand with large-scale tabular cross-stratification (Fig. 7b). The suc-cession begins with laminated mudstones and medium-grainedsandstone with cross-stratification, which grade into sandstoneintercalated with mudstone, mainly at the top. Differentiation be-tween the Pedra de Fogo and Piauí formations was based on thethickening upwards of the mudstone layers in the Pedra de Fogo.

To the northeast of SdC, along road TO-226 and near the town ofCampos Lindos, outcrops of the Piauí Formation show a remarkablesuccession of facies with well-preserved sedimentary structures insandstones and heterolithic deposits (Point E-33, Fig. 1). Coarse-grained sandstones exhibit medium- to small-scale tabular cross-bedding with well-sorted and rounded grains. They are overlainby sandstone with ripple bedding (Fig. 7c), followed upwards bycream-colored mudstone interbedded with fine-grained sandstoneforming lenticular structures (Fig. 7d). The upper part of the section


consists of medium-grained, red sandstone and yellow mudstonewith flaser bedding.

4.6. Petrographic observations

4.6.1. SandstonesSandstones are themost frequent rock type in the target rocks of

SdC; they can be classified as quartz arenites. The deformationcaused by the impact increases from the rim toward the center ofthe impact structure and is clearly observed in thin sections. Whilstin the rim of the structure the sandstones of the Pedra de FogoFormation do not exhibit any deformation and grains are rounded,close to the central uplift domain the same rocks show deformationexpressed through broken grains causing a false aspect of poorlysorted and high angularity grains, with 50e500 mm size and anabundance of fractured grains (point 184 e Fig. 8a). Similarly, thePiauí Formation closest to the rim does not show any evidence fordeformation, whereas within the central uplift quartz grains arestrongly fractured, resulting from in situ disaggregation of thegrains. As a consequence, grains become sharp-edged and poorlysorted (Fig. 8b).

Different from the Pedra de Fogo and Piauí formations describedpreviously, the rocks of the Poti Formation are exclusivelydeformed in the central uplift of SdC. Sandstones of the Poti For-mation exposed along the collar are typically red and show variabledips due to folding. These sandstones are also apparently poorlysorted with very angular and rounded grains of 50e100 mm size(Fig. 8c). Poorly sorted grains with highly angular shapes are alsoproduced in situ, as shown by grains that, despite being extremelyfractured, still display the contours of the entire grain (Fig. 8d). The


Fig. 7. (a) 3D perspective view showing the southern rim with the location of the Pedra de Fogo Formation (PFF) and Piauí Formation (PiF) (image acquired by the ASTER satellite,bands 1, 2 and 3 in RBG); arrow marked ‘b’ shows the location of the outcrops shown in “b”. (b) High-angle tabular cross-bedding in sandstone with well-sorted and rounded grains.(c) Wave-formed ripple bedding characterized by a symmetrical profile in sandstones. (d) Heterolithic mudstone/sandstone with linsen structure, located outside of SdC.


evolution of this process results in complete disaggregation ofgrains as a consequence of displacement between the producedfragments, as previously shown in Fig. 8c. Furthermore, highamounts of iron oxide cement are sometimes concentrated alongstratification (Fig. 8e), which is responsible for the red color of thesestrata.

Sandstones also occur in the area of Longá Fm, although they arenot themain lithotype of this unit. These rocks exhibit sharp, poorlysorted, fractured grains and a high quantity of iron oxide cement,roughly similar to the fracturing observed in the rocks from the PotiFm. In general, characteristics of the Pedra de Fogo, Piauí, Poti andLongá formations inside the crater are very different from the sameformations outside the crater. The latter include moderately-sortedand rounded, generally non-fractured grains (Fig. 8f).

4.7. Shales and heterolithic deposits

The lithotypes comprising shales, heterolithic deposits andsubordinate sandstones described in this section originate from thethree boreholes close to the center of SdC. These boreholes pene-trated rocks of the Longá Formation comprising mainly shale andshale intercalated with minor amounts (about 1% of the columnsection) of siltstones. Shales contain interbedded finest-grainedsiltstone comprising essentially quartz and phyllosilicateincluding micas <10 mm in size. Siltstones consist of subangular torounded quartz grains with subordinate K-feldspar of 200e600 mmgrain size. Shales exhibit subvertical foliation following the generalstrata dip with heterolithic layers showing linsen structures(Fig. 9a) containing silt; these structures are also commonlyobserved in undeformed shales of the Poti Formation (Góes, 1995).Other common sedimentary structures in these heterolithic de-posits include bioturbation features (Fig. 9bed).

Impact deformation might have overprinted these primaryfeatures through micro-fractures (Fig. 9c), some of them causing


bedding displacement (Fig. 9d). Furthermore, these shales exhibitfolding of the strata in chaotic patterns (Fig. 9e) on the microscopicscale. The overall macroscopic appearance of sandstone layers inthe Longá Formation is a mixture of sub-angular quartz grains>1 mm to sub-mm in size, which exhibit fractures with millimeterdisplacements (Fig. 4b). Microscopically, these sandstones consistof 90 vol% angular quartz and 10 vol% feldspar grains, 0.1e2 mm insize, with iron oxide and, less frequently, calcite cement. Quartzgrains are intensely fractured and show shock deformation featuresthat will be described in the “Microscopic shock features in quartz”section below. The shales occur together with the sandstones and,in some cases, the latter intrude the earlier forming features withconvolution appearance (Fig. 9f).

4.8. Shatter cones

Near the center of the inner depression of the central uplift, twosandstone blocks with shatter cones were found at 295197E/910685N UTM (zone 23S). They occur as loose blocks in the areacorresponding to the domain of the Longá Formation (Points 22 and42 e Figs. 3 and 4). The shatter cones formed in coarse sandstonewith individual cones reaching 8e12 cm in length (for photographsof the shatter cones see Kenkmann et al., 2011a). The specimensconsist of sub-rounded to sub-angular, moderately fractured andmoderately sorted quartz grains varying from 100 to 400 mm ingrain size. Phyllosilicates, iron oxide and silica cement are presentin high amounts. The cement exhibits prominent syntaxial over-growths of quartz on quartz grains which are not observed insimilar rocks outside SdC. However, the cement appears to haveformed prior to the formation of SdC, as the fractures related to theshatter cones crosscut grain boundaries as well as the cement(Fig. 10a). These fractures are observed particularly in the shattercones and correspond to the shatter cone planes observed at themacro-scale. They look different from the other, quite common


Fig. 8. (a) A poorly sorted sandstone of the Pedra de Fogo Fm. (point 184 Fig. 3) (under cross polarized light). (b) In situ fracturing of quartz grains in a sample of sandstone from thePiauí Fm. (under cross polarized light). (c) Apparently poor sorting of quartz grains of Poti Formation as a consequence of total disaggregation of grains, likely caused by impactdeformation (under cross polarized light). (d) Examples of in situ fracturing showing the boundaries of two quartz grains (under plane polarized light). (e) Preferential concentrationof iron oxide cement along a specific band of sandstone of the Poti Fm. (point 109, Fig. 3) (under plane polarized light). (f) Undeformed sandstone of the Poti Fm w70 kmnortheastward away from the crater center (under plane polarized light).


fractures in the rocks of the central uplift, being continuous andextending across several grains. Nevertheless, these fractures arerestricted to portions of the thin section and show randomdirections.

4.9. Polymict breccias

Polymict breccias were found in situ, along the access trail thatcrosses the collar of the Poti Formation at 294981E/9107540N(zone 23S), as previously mentioned by Kenkmann et al. (2011a).The most representative specimens of polymict breccia were foundin the central depression (Point 22 e Figs. 3 and 4). These brecciasare exposed as loose blocks, typically 20e50 cm in size, and are ofkey importance as they contain shock features. They comprisepoorly- to moderately-sorted, angular to sub-angular clasts of up to5 cm size, made up of quartz, siltstone and chert, in a fine-grained(Fig. 10b), red matrix (Fig. 10c). Grains comprise >90 vol% sub-angular quartz, moderately fractured and rarely in contact withother grains. Evidence for in situ fracturing can be seen in largegrains of the breccias and their preserved boundaries can still be


observed (Fig. 10d). Thematrix comprises small (<100 mm), angularquartz and feldspar grains and the red color of the matrix of thebreccias is due to the presence of high amounts of iron oxidecement. The breccias appear to have been formed by fragments ofall the local target rocks, thus comprising remains of the Pedra doFogo, Poti, Piauí and, possibly, Longá formations.

4.10. Microscopic shock features in quartz

Within SdC, the intensity of deformation increases progres-sively from the rim (Pedra de Fogo Formation) toward the center(Longá Formation). In the Pedra de Fogo Formation, all rocksexhibit the original sedimentary characteristics, with non-fractured rounded grains. Sandstones from the Piauí Formationexhibit grain fracturing resulting in apparently poorly sortedgrains. Therefore, they show a bimodal distribution of grain sizes,with larger grains being rounded and smaller grains being highlyangular. Rocks from the collar of the central uplift (Poti Formation)contain grains exhibiting intense and irregular fracturing withshard-like shapes.


Fig. 9. Primary sedimentary structures and micro-deformation patterns observed in samples from boreholes into the Longá Formation. (a) Shale/sandstones with linsen structures.(b) Bioturbation in a heterolithic, flaser-textured sample. (c) Bioturbation fabric cut by fractures roughly perpendicular to the thinesection plane (d) Bioturbation features displacedby micro-faults. (e) Folded sedimentary layers crossed by faults filled with secondary silica. (f) Sandstone domains intruding shale and causing a diapiric mingling pattern.


However, diagnostic shock features have been found only inrocks from the Poti Fm. (collar), the Longá Fm., and breccias/shattercones from the central depression, restricted to an area within a1.5 km radius from the center of the structure.

Feather features (FF) constitute a type of micro-deformationstructure in quartz that has been described in recent years fromseveral impact structures (French et al., 2004; Haines and Rawlings,2002; Poelchau and Kenkmann, 2011). They consist of narrow-spaced, almost parallel to subparallel planes in certain crystallo-graphic directions that branch off from one side of a planar fracture(PF), with the combination forming an unusual and distinctivefeature that resembles the structure of a half feather. At SdC, FFhave been observed in quartz of sandstone from the Poti Fm.(collar), in Longá Fm. polymict breccia (Fig.11a and b), and in quartzof shatter cones (Table 1). The planar fracture of FF is frequentlyfilled by iron oxide cement (Fig. 11a).

Planar fractures (PF) form as parallel sets resembling cleavage inquartz grains at the lower end of the shock pressure regime(>5 GPa) (Stöffler and Langenhorst, 1994). The fractures are typi-cally 5e10 mmwide. Occurring alone, without further corroboratingevidence of shock deformation, planar fractures alone are notconsidered of compelling impact-diagnostic value. At SdC, PF were


also found in rocks from the Longá Fm. and Poti Fm., in polymictbreccias and in shatter cones. In the drill cores from the Longá Fm.they developed in quartz grains of w2 mm size, with the planesdisplaced by shearing (Fig. 11c). PF are not common in the sand-stones of the Longá Fm and, when present, as at point 120, they arepoorly developed with short lengths. In the rocks of the Poti Fm.these features are also not common, although better developedthan in Longá Fm rocks. They are formed in quartz grains ofw200 mm size with angles between 15 and 80� (Fig. 11d). In thepolymict breccias the development of PF (Fig. 11c) occurs prefer-entially associated with FF or in larger quartz grains of 2e5 mmsize, with up to 3 sets of different crystallographic directions. PF inthe breccias are preferentially oriented subparallel to c (0001),whereas in the shatter cones they follow along the x {112} and r/z{101} orientations (Table 1).

Finally, PDF have been found only in coarse sandstones from thedrill cores (Longá Fm.) and in shatter cones. A total of ten PDF setsoriented parallel to the c (0001) axis were identified in ten differentquartz grains of central uplift samples. Nine of themwere observedin sandstone that also contained shatter cones (Fig. 12a, Table 1)and one was found in a sandstone sample from the GT-01-GO drillcore at 90 m depth. Individual planes are typically �1 mmwide and


Fig. 10. (a) Syntaxial cement overgrowth between two quartz grains cut by fractures (F) in the shatter cones; this shows that the shatter cones were formed after the overgrowth.SO1 ¼ syntaxial overgrowth of grain 1; SO2 ¼ syntaxial overgrowth of grain 2. Photomicrograph taken with crossed polarizers. (b) Polymict breccia showing a clast of siltstone (S)and a larger quartz grain (Q) embedded in a particulate matrix of subangular quartz grains. Photomicrograph taken in plane polarized light. (c) Breccia showing extremely frag-mented/shattered quartz grains <50 mm, together with a large quartz grain and groundmass iron oxide cement. Cross polarized light (d) Shattered quartz grain in polymict brecciashowing a conspicuous pattern of intersecting subplanar and subparallel fractures. Cross polarized light.

Fig. 11. Impact-related deformation features developed in quartz grains in samples from the inner depression of SdC’s central uplift, all of them taken in cross polarized light. (a)Feather Features (FF) developed at an apparent angle of w45� to the host planar fracture; fracture planes are partially filled by iron oxide cement (b) Quartz grain from polymictbreccia showing planar fractures (PF) and FF. (c) PF in quartz grain from polymict breccia. Arrows show the displacement along the PF plane. (d) FF developed with feathers at low-apparent angle to the host PF plane in quartz from sandstone at 90 m depth in drill core GT-GO-01.


Please cite this article in press as: Vasconcelos, M.A.R., et al., The Serra da Cangalha impact structure, Brazil: Geological, stratigraphic andpetrographic aspects of a recently confirmed impact structure, Journal of South American Earth Sciences (2013), http://dx.doi.org/10.1016/j.jsames.2013.03.007

Table 1Summary of indexed shock features found at SdC. Numbers correspond to one shockfeature per grain.

Breccia Shatter cone Drill-hole Sandstone

Plane Miller-Bravaisindex

Polarangle (�)

PF PDF PF PDF PF PDF PF PDF

c axis (0001) 0 2 e 39

e 1 2 e

E {104} 18 3 e 2 e 1 e e e

P {102} 32 e e 2 e e e e

X {112} 48 e e 8 e 1 e e e

r/z {101} 52 1 e 7 e 2 e e e

S {111} 66 e e e e e e 1 e


spaced only a few micrometers apart. A stereoplot with orienta-tions of the indexed planes is shown in Fig. 12b with orientations ofthe indexed planes.

5. Discussion

5.1. Stratigraphy and extent of deformation caused by the impact

The Serra da Cangalha impact structure mostly comprisessandstones (w80% of the local host rocks), and the ages of the stratadecrease from the center outward. Older rocks of the Longá Fm areexposed in the innermost depression, which suggests approxi-mately 500 m of stratigraphic uplift, coherent with numericalmodel results for Serra da Cangalha (Vasconcelos et al., in press).

Fig. 12. (a) Photomicrographs showing both basal planar deformation features (PDF)parallel to c (0001) and PF oriented parallel to r/z {101} in a quartz grain from asandstone shatter cone found in the innermost part of the central uplift. (b) IndexedPFs and PDFs in a stereoplot, using a template based on Ferriere et al. (2009).


Apparently, the strongest deformation of strata was recorded bysandstones of the Poti Formation, which form the innermost collar.Strata of the Piauí and Pedra de Fogo formations represent sedi-mentologic key sections inside the SdC structure, as they revealwell-preserved sedimentary features and show that the shockwaves were not strong enough to obliterate primary structurewithin a certain radii.

The results of fieldwork and further analysis of the rocks showthat all macroscopic and microscopic shock features found at SdCoccur in rocks from within a 1.5 km radius from the center of thestructure, corresponding to w5% of the area of SdC only. At theoutcrop scale, only the tilted strata of the outer margin of thecentral uplift and folded strata exposed along the 2nd ridge exhibita deformation pattern unique to the interior of the structure, andnot observed in equivalent stratigraphic rocks outside of it; thismacrodeformation is, therefore, interpreted here as impact-related.This deformation, however, did not overprint original sedimentarystructures, such as cross-stratification, heterolithic structures (e.g.,linsen, wavy, and flaser textures), bioturbation, and others.

The area where shock features were found corresponds to thesame domain for which numerical modeling suggested the highestimpact-induced plastic strain rates (Vasconcelos et al., in press) Thefinal crater shows intermediate and almost constant values ofplastic strain, which could explain the presence of folds anddeformed strata close to the rim. The numerical models presentedby these authors suggest that target rocks at the rim and up to a fewkilometers outside the crater should theoretically display at leastsome plastic deformation effects on the macro-scale. However,according to the estimated amount of erosion at SdC (Vasconceloset al., 2010b; Kenkmann et al., 2011a), these deformed stratacould well have been eroded, leaving only rocks that underwentlow-grade plastic deformation. Impact-diagnostic shock featuresare preferentially concentrated in the shatter cones and the poly-mict breccias of the innermost occurrences of strongly deformed/uptilted Longá Formation rocks.

McHone (1986) reported finding shatter cones at SdC but didnot specify the locations of their occurrence. We have found themat two locations in the innermost depression only. Therefore, therelative scarceness of shatter cones at SdC, together with the factthat they were found in loose blocks rather than in-situ outcrops,suggest removal by erosion of the strata that originally containedmore of these structures, leaving only limited debris that is todayscattered over the current land surface.

5.2. Diagnostic microscopic shock features

Microscopic shock features were noted in 13 quartz grains withPF, 4 quartz grains with FF, and 10 grains with basal PDF. Thefractures are relatively thin (3e10 mm) and may be related to verylow-level shock pressure (>5 GPa) (Stöffler and Langenhorst, 1994;Huffman and Reimold, 1996; French and Koeberl, 2010). Planarfractures apparently reflect very low shock pressures, although it isstill debated whether PF alone can be considered an impact crite-rion, as planar to subplanar cleavage in quartz has also been e

although rarely e reported from non-impact environments (see forexample, Frondel, 1962; French and Koeberl, 2010).

Although PF and FF are not useful to calibrate shock pressure,the presence of single PDF in quartz from the central depression ofSdC indicates that these rocks were subjected to pressures of lessthan 15 GPa (i.e., the lower threshold shock pressure to generatemultiple sets of PDF in quartz; e.g., Grieve and Robertson, 1976;Stöffler and Langenhorst, 1994; Robertson, 1975; Grieve et al., 1996;Poelchau and Kenkmann, 2011). This peak pressure was alsoreached in rocks found at depth, according to the basal PDF found inthe drill core from about 90 m depth. In some samples from the



collar only FF and PF have been found, indicating a shock pressurerange of w5e8 GPa. Outside the collar the peak pressure did notexceed w5 GPa, as the rocks do not exhibit any diagnostic micro-scopic shock features. The fact that non-basal PDF are very scarce atSdC ismost likely related to the current level of erosion experiencedby this impact structure.

The absence of shock features outside the collar and theoccurrence of macroscopic and microscopic deformation featuressuggest deformation at pressures <1 GPa, in agreement with theresults of numerical modeling by Vasconcelos et al. (in press). At thecrater rim, deformation is restricted to folding and small-scalefaulting.

It is known that quartz melting occurs at lower shock pressuresin sedimentary rocks compared to crystalline rocks (see, e.g.,Osinski et al., 2008 for a review of the melting behavior of sedi-mentary rocks in terrestrial impact structures). Only recently haveattempts to determine and calibrate the exact pressures for theonset of various specific shock deformation features in sandstonebeen carried out as part of the MEMIN research group (Kenkmannet al., 2011b; Poelchau et al., 2013; Kowitz et al., 2013). It has thusbecome evident that certain shock effects (e.g., diaplectic glass)may already be initiated in sandstone targets at nominal experi-mental shock pressures as low as 10 GPa. This depends to a largedegree on the presence of porosity (Kowitz et al., 2013;Güldemeister et al., 2013), which is a parameter that can lead tolocal enhancement of shock pressure by a factor of 3e4. Thus, atthis stage, the generally applied values of >5 GPa for formation ofplanar fractures and feather features in quartz, and >8e10 GPa forthe formation of PDF in quartz are currently the only basis onwhichto assign approximate shock pressures experienced by crystallineor sedimentary rock.

Displacement was observed along some FF and PF planes inshocked quartz. Some authors have suggested that these planesrepresent microfaults along planes of high shear stress (Christieet al., 1964; Gratz et al., 1988, 1992; Poelchau and Kenkmann,2011). Christie et al. (1964) interpreted that planar fractures areinitiated by plastic slip on crystallographic planes, which thenpropagates by brittle fracture mechanism. These authors observedthe occurrence of an isotropic phase comprised of Si, Al, O along PFand they interpreted this as quenched glass formed by frictionalmelting. The occurrence of these phases also indicates formation atstress concentrations, and a high mobility allowing elementalmovement along the planar fractures.

Microfolds and faults present in the Longá rocks are indicative ofpseudo-ductile and brittle regimes that occur during the formationof the central uplift. In situ fracturing of rocks of all the stratigraphicunits within SdC gives the target rocks at SdC clearly differentcharacteristics when compared to similar undeformed rocks of theParnaíba Basin. As a result of brittle deformation, broken grainsproduce a false appearance of a poorly-sorted rock. Hence, althoughthese features are not diagnostic of impact, they can be used also tocharacterize the degree of deformation imposed by the impact.

6. Concluding remarks

We present here new detailed observations regarding the stra-tigraphy within the SdC structure, and new findings related tomacroscopic and microscopic impact-induced deformation e

including diagnostic shock features. The occurrence of diagnosticshock deformation features in quartz is restricted to the Carbonif-erous rocks of the Poti and Piauí formations within the innermost,prominent collar of the central uplift and, particularly, to the ex-posures in the central depression corresponding to the Devonian toUpper Carboniferous Longá Formation. The analysis of the shockfeatures provided constraints that allow to estimate shock


pressures ofw5e10 GPa for the rocks of the innermost collar of thestructure. These constraints are based on measurements of severalsets of single PDF (0001 direction) found in quartz of shatter conesfrom the central depression, and one set found in a drill core sampleinto the Longá Formation. Some quartz grains in sandstones fromthe southern part of the collar exhibit PF and FF, thus indicatingpressures <10 GPa. Between 2.8 and 5.8 km from the center (stillwithin the central uplift domain) no microscopic shock featureswere observed, and deformation was accomplished by folding ofthe local strata only. Further out from the center of the crater thereis no macro- or microscopic shock evidence. In the crater rimdomain, as well as in the surrounding areas outside SdC, sedi-mentary structures are well preserved.

As most sedimentary features were obliterated by impact-induced and recrystallization, there is no complete vertical profilefor the interior of SdC. Therefore, the reliable identification ofspecific stratigraphic units within SdC was achieved analyzing theirprimary sedimentary characteristics and relating them to the un-deformed strata outside the structure.

The main criterion for differentiating between the Piauí andPedra de Fogo formations in the outer parts of the SdC structure isthe presence of a significant amount of mudstone in the latter. Thischaracteristic is particularly apparent along the southern rim ofSdC. In the annular basin, rock exposures are rather limited andusually located along the ridges of subvertically oriented rocks.

Red-colored strata, especially breccias and rocks correspondingto the Poti Formation, exhibit extensive cementation by iron oxideand local secondary silicification. This iron staining is still not un-derstood, but similar to many other terrestrial impact structuresand might be related to post-impact alteration and possible hy-drothermal activity caused by the impact event.

Acknowledgments

This project has been supported by a FAPESP research grant(#2008/53588-7) to A.P. Crósta and a DAAD grant to WUR. M.A.R.Vasconcelos acknowledges CNPq for his PhD grant in Brazil, as wellas DAAD support that made possible his research period in Ger-many in 2010. He also thanks the Barringer Family Fund (BFF) for aresearch award that allowed him to carry out field research in Brazilin July 2010. The authors gratefully acknowledge the BrazilianDepartment of Mineral Production (DNPM/Recife) for allowingaccess to and sampling of the drill cores. The authors also thankMr.Giandri Machado, from DigitalGlobe Latin America, for theWordView-1 image provided, Prof. Dr. Paulo Alves Souza for paly-nological data on Longá samples and A. Bartorelli for the wonderfulaerial photo of Serra da Cangalha. We are also grateful for thesupport in the field provided by Mr. Carlos da Serra, from CamposLindos. We also acknowledge the reviewers Dr. G. Osinski, Dr. M.Schmieder and an anonymous reviewer for the contributions thatcertainly improved the quality of the manuscript.

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http://dx.doi.org/10.1111/j.1945-5100. 2012.01430.x

http://dx.doi.org/10.1111/j.1945-5100. 2012.01430.x

http://dx.doi.org/10.1111/j.1945-5100.2011.01199.x

http://dx.doi.org/10.1111/j.1945-5100.2011.01199.x

http://dx.doi.org/10.1111/maps.12030


http://dx.doi.org/10.1029/2010JB007803

http://dx.doi.org/10.1029/2010JB007803



The Serra da Cangalha impact structure, Brazil: Geological, stratigraphic and petrographic aspects...

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