Synsedimentary deformation and the paleoseismic record in Marinoan cap carbonate of the southern Amazon Craton, Brazil

Synsedimentary deformation and the paleoseismic recordin Marinoan cap carbonate of the southern Amazon Craton, Brazil

Joelson Lima Soares a,*, Afonso César Rodrigues Nogueira a, Fábio Domingos b,Claudio Riccomini c

a Programa de Pós-Graduação em Geologia e Geoquímica, Faculdade de Geologia, Universidade Federal do Pará, Instituto de Geociências, Av. Bernardo

Sayão, s/n, Guamá 66075-110, BrazilbUniversidade Federal do Pará, Instituto de Geociências, Faculdade de Geofísica, Av. Bernardo Sayão, s/n, Guamá 66075-110, BrazilcDepartamento de Geologia Sedimentar e Ambiental, Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, 05508-080 São Paulo, SP, Brazil

a r t i c l e i n f o

Article history:

Received 19 December 2012

Accepted 2 August 2013

Keywords:

Synsedimentary deformation

Event Layers

Earthquakes

Neoproterozoic

Cap carbonate

a b s t r a c t

Event Layers in Neoproterozoic cap carbonates of Brazil’s southwestern Amazon Craton record post-

Marinoan synsedimentary seismicity. The 35 m-thick cap carbonates overlie glaciogenic sediments

related to the Marinoan glaciation (635 Ma) and are comprised of two units: the lower cap consists of

dolomite (w15 m thick) and the upper cap is limestone (w25 m thick). The cap dolomite includes

pinkish crystalline dolostone with even parallel lamination, stratiform stromatolites, eventual tube

structures and megaripple bedded peloidal dolostone interpreted as shallow (euphotic) platform

deposits. The cap limestone onlaps the cap dolomite and consists of red marl, gray to black bituminous

lime mudstone, bituminous shale with abundant calcite crystal fans (pseudomorphs after aragonite) and

even parallel lamination interpreted as moderately deep to deep platform deposits. Five successive

events of synsedimentary deformation were recognized in the cap carbonates exposed at Mirassol

d’Oeste and Tangará da Serra, in Central Brazil: Event 1 e large to small-scale load cast structures in the

contact between dolostones and glaciogenic sediments; Event 2 e stromatolitic lamination truncated by

tube structures; Event 3 e vertical to subvertical fractures and faults, and large-scale synclines and

anticlines with chevron folds; Event 4 e conglomerate and breccia filling neptunian dykes limited by

undeformed beds; and Event 5 e slump and sliding deposits found only in the upper part of the cap

limestone. Event 1 was produced by hydroplastic dynamics likely induced by isostatic rebound during ice

cap melting in the final stages of the Marinoan glaciation. Events 2 and 5 are autocyclic in nature, and

related to depositional processes. Event 2 is linked to fluid and methane escape from organic degradation

of microbial mats and domes that formed tubestones; Event 5 is associated to collapse and sliding/

slumping in the platform and slope. The reliable orientations of synsedimentary faults, and fractures and

folds of events 3 and 4 are consistent with regional extensional tectonics associated with earthquakes

that triggered sediment deformation. The 200 km that separate the occurrences of cap carbonates

suggest that important seismic events took place during the early Ediacaran in the southern Amazon

Craton.

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1. Introduction

Current interpretations of stratigraphic sequences are related toa cyclic origin throughout the world. As such, short and episodicintervals in the sedimentary record have been described in several

deposits of marine and continental environments (Dott, 1996;Einsele, 1996; Einsele et al., 1996). These episodic or catastrophiclayers are well documented in Phanerozoic successions generallyinterpreted as resulting from regional and global mechanismsrelated to seismicity, storms/tsunamis and meteorite impact(Ringrose, 1989; Pratt, 1994; Cita et al., 1996; Einsele et al., 1996;Alvarez et al., 1998; Bhattacharya and Bandyopadhyay, 1998;Bouchette et al., 2001; Hassler and Simonson, 2001; Pratt, 2001,2002a, 2002b). While meteorite impact deposits display specificfeatures such as shocked quartz and deformed beds around craterimpact morphology (Alvarez et al., 1998; Lana et al., 2007), seismic

* Corresponding author.

E-mail addresses: [email protected] (J.L. Soares), [email protected]

(A.C.R. Nogueira), [email protected] (F. Domingos), [email protected]

(C. Riccomini).

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disturbances are poorly understood and there is a lack of specificcriteria for their recognition in Precambrian and Phanerozoicdeposits. On the other hand, much work concerning paleo-seismicity in sedimentary deposits of Quaternary ages has beenpublished. These deformed deposits are associated to subductionzones in the USA (Adams,1990), and to isostatic rebound in cratonicareas of Canada (Adams,1989) and Sweden (Mörner, 2005), and canbe used as modern analogs for the Precambrian synsedimentarydeformations in carbonate rocks of the southern Amazon Craton inBrazil. Generally these layers have deformed beds which arecorrelated over a long distance, and a specific stratigraphic interval(Allen, 1986; Adams, 1989, 1990; Mörner, 2005; Audemard et al.,2011).

Precambrian deformed beds in carbonates have been recordedby several authors. Pratt (1994) was the first to explain the defor-mation of carbonate rocks of the Mesoproterozoic Altyn Formation(USA) as the product of seismicity related to earthquakes. Kennedy(1996) described in detail the deformational features in a Neo-proterozoic cap carbonate of Australia, without discussing possibletrigger mechanisms. Neoproterozoic cap carbonates are found inseveral cratonic regions of the world and generally display negatived13C excursions (Hoffman and Schrag, 2002; James et al., 2001;Lorentz et al., 2004; Halverson et al., 2005; Nogueira et al., 2007).At the base of Neoproterozoic cap carbonate, exposed in Brazil’ssouthern Amazon Craton, Nogueira et al. (2003) described large-scale load cast structures and, upsection, slump features andneptunian dykes induced by isostatic rebound and seismicity.These deformational structures were observed in new exposures ofcap carbonate, found in the Tangará da Serra region. They weredescribed in detail and correlated at a regional scale. The synsedi-mentary origin is indicated by the presence of distinct deformedlayers in the cap carbonate succession. This work contributes to theunderstanding of the trigger mechanism which result in deforma-tional processes recorded in Brazil’s Neoproterozoic cap carbonates.

This paper presents a detailed reappraisal of the synsedi-mentary deformational layers in approximately 50 m-thick occur-rences of Ediacaran cap carbonates in the southern Amazon Cratonstudied by Nogueira et al. (2003). The cap carbonate exposed inBrazil’s southern Amazon Craton belongs to the base of the ArarasGroup, and is characterized by pinkish dolostone that overliesglaciogene diamictites. Limestone with crystal fans covers the capdolomite and is interpreted as deep platform deposits. These car-bonate successions are a post-glacial record of the Neoproterozoiclow-latitude glaciations (Hoffman et al., 1998; Hoffman and Schrag,2002; Halverson et al., 2005;Moczyd1owska, 2008). In this workwealso discuss the mechanisms of soft deformation attributed toearthquake activity from early tectonic events which occurred inthe southern margin of the Amazon Craton.

2. Geologic setting and cap carbonate

2.1. Stratigraphy and tectonic setting

The carbonate platform studied here is the Ediacaran ArarasGroup, with excellent exposure in the southern Amazon Craton andParaguay Belt of central Brazil (Fig. 1a). The studied carbonatesuccession corresponds to the Mirassol d’Oeste and Guia forma-tions which constitute the base of the Araras Group (Fig. 1b), ac-cording to the stratigraphic proposal by Nogueira and Riccomini(2006). These units immediately overlay the Neoproterozoic gla-ciogenic diamictites of the Puga Formation, with no evidence of asignificant depositional hiatus. The contact is characterized by asharp undulated surface (Fig. 2a). Marinoan cap carbonatesexposed in the southern Amazon Craton are considered the mostcomplete succession for displaying all of the typical features

described worldwide (Allen and Hoffman, 2005; Nogueira andRiccomini, 2006; Soares and Nogueira, 2008). The main occur-rences of these cap carbonates are found in the Mirassol d’Oesteand Tangará da Serra regions (Figs. 1a and 2b).

The southern Amazon Craton region was affected by the Brasi-lianePan African Tectonic Collision that ended at the Cambrian tolower Ordovician (540e490Ma) and formed the Paraguay Belt. Thistectonic event is also defined as Paraguay Orogenesis (Basei andBrito Neves, 1992). The amalgamation of the Gondwana in theNeoproterozoiceCambrian lead to the closing of the EdiacaranClymene Ocean between the Amazon Craton and Central Gond-wana (Tohver et al., 2010). An extensional event during the finalphase of the Cambrian period produced granitogenesis dated at518 Ma (McGee et al., 2012). The Early Paleozoic was marked by theinstallation of the Paraná and Parecis Basins (Fig. 1a).

In the southeast region of the Amazon Craton, the undeformedand unmetamorphosed sedimentary rocks show subhorizontalbedding, dipping gently to the northwest. Diamictites of the PugaFormation and carbonate rocks of the Araras Group are exposed atthe edge of the Amazon Craton (Nogueira et al., 2003, 2007). Sili-ciclastic rocks of the Alto Paraguai Group covered unconformably(i.e., they are erosive and sharp) the diamictites and carbonaterocks (Silva Júnior et al., 2007). This siliciclastic unit in the ParaguayBelt records the filling up of a foredeep basin after the final amal-gamation of western Gondwana in the earliest Phanerozoic(Bandeira et al., 2012).

According to Nogueira and Riccomini (2006), the 1200-m thickAraras Group consists of four lithostratigraphic formations (Fig.1b):Mirassol d’Oeste (dolostones and stromatolites), Guia (limestonesand shales), Serra do Quilombo (dolostones and breccias) andNobres (dolostones, stromatolites and sandstones). The Mirassold’Oeste and Guia Formations, respectively interpreted as capdolostone and cap limestone, are exposed only at the southernmargin of the Amazon Craton. The Mirassol d’Oeste Formation is15 m thick, and contains fine pink dolostone, stromatolites andpeloidal dolomite interpreted as a shallow (euphotic) to moder-ately deep platform. The Guia Formation is approximately 35 mthick, onlaps the cap dolomite and consists of red marl, gray toblack bituminous lime mudstone and shale with calcite crystal fans(pseudomorphs after aragonite) and even parallel laminationinterpreted as a moderately deep to deep platform. The start of theEdiacaran Period in South America is represented by the Mirassold’Oeste cap dolostone, which represents an important globalstratigraphic boundary (Nogueira et al., 2003, 2007).

Puga diamictite is abruptly covered by the cap carbonates of thebasal Araras Group, recording the drastic changes in climatic con-ditions brought about by the greenhouse effect, which is consistentwith the Snowball/Slushball Earth hypotheses (Hoffman andSchrag, 2002; Nogueira et al., 2003). These hypotheses suggestthat the planet was covered in ice, with the exception of theequatorial zone, for millions of years (Kirschvink, 1992; Hoffmanet al., 1998; Hyde et al., 2000). The sudden disappearance ofthese paleoclimatic conditions was followed by fast ice-melting,over a few hundred years, culminating in the onset of the green-house effect triggered by volcanic eruptions. Such global eventsoccurred at least twice, with widespread glaciations during theCryogenian (w725 Ma and w635 Ma). Gaskiers is a youngerglaciation dated at w580 Ma, and which occurred locally; it is notoverlaid by cap carbonate and is laterally correlated with carbonatesuccessions displaying negative d13C values (Halverson et al., 2005).

2.2. Age

The age of sedimentary rocks of the southern margin of theAmazon Craton was estimated to range between 630 and 520 Ma,

J.L. Soares et al. / Journal of South American Earth Sciences 48 (2013) 58e72 59

based on d13C isotope, 87Sr/86Sr ratios and paleomagnetic data

(Trindade et al., 2003; Alvarenga et al., 2004; Tohver et al., 2006).Theminimumdepositional age of 541�7Ma for these sedimentaryrocks in the Amazon Craton and Paraguay Belt is based on UePbdating of detrital zircon of the Diamantino Formation (Bandeiraet al., 2012). Babinski et al. (2006) used PbePb to date at627 � 32 Ma the depositional ages of Mirassol d’Oeste Formationdolostone in the Mirassol d’Oeste region. Romero et al. (2013) usedthe same method and obtained depositional ages of 622 � 33 Mafor the limestone at the base of the Guia Formation in Tangará daSerra (Figs. 1b and 2a). These authors also suggested ages between620 and 630 Ma, based on 87Sr/86Sr ratios. Font et al. (2010) usedpaleomagnetic data and stromatolitic laminationmeasurements onmodern analogs to estimate the depositional time of Brazil’s capcarbonate as ranging from 104 to 106 years old.

2.3. Paleoenvironment

2.3.1. Restricted euphotic sea

In the 15-m thick dolostone of the Mirassol d’Oeste Formation,evidence of restricted euphotic seas is recorded by stromatoliticdolostone with fenestral lamination (Fig. 3a), tube structures,

peloidal dolostone with megaripple bedding (Fig. 3b) and evenparallel and quasi-planar lamination to low-angle truncations(Fig. 3c). Stromatolites at the base of the Mirassol d’Oeste Forma-tion are generally stratiform and irregularly undulate, whilst upsection they have a locally domal shape (Fig. 3a).

Synsedimentary faults and fractures locally displace anddeform the stromatolitic lamination. Tube structures arecommonly found in the stromatolites. These tube structures areunique to the cap dolostone, and always associated with the top ofdomal stromatolites (Romero et al., 2011). Convolute laminationsand breccia levels occur locally, deforming the even parallel andstromatolitic laminations. The upper part of the Mirassol d’OesteFormation is characterized by dolostone with quasi-planar lami-nation to low-angle truncations and megaripple bedding (Fig. 3band c). Variations in the thickness of the quasi-planar laminationreflect the different sizes of the microcrystalline peloids (Soaresand Nogueira, 2008).

The megaripple bedding is complex, formed by internal climb-ing wave-ripple-lamination. Megaripples exhibit 3 m long crestsand change laterally to even parallel lamination, with wavelengthsranging from 0.15 to 2 m and amplitudes ranging from 10 up to20 cm. The even parallel lamination is up to 2 mm-thick and has a

Fig. 1. Geologic aspects of southern Amazon Craton and Northern Paraguay Belt, Central Brazil. a) Tectonic setting. b) Lithostratigraphy. Ages data were obtained by (*) Bandeira

et al. (2012), (**) Romero et al. (2013) and (***) Babinski et al. (2006). Modified from Nogueira et al. (2003) and Bandeira et al. (2012).

J.L. Soares et al. / Journal of South American Earth Sciences 48 (2013) 58e7260

high concentration of bitumen. The crests of megaripple beddingand climbing wave-ripple-lamination trend predominantly SW.

Stratiform, domal and irregular undulated stromatolites inMirassol d’Oeste dolostone were interpreted as originating in lowenergy conditions, below the stormwave base. According Nogueiraet al. (2003), the main evidence supporting this interpretation in-cludes: (1) the predominance of micritic lamination; and (2) thelack of sedimentary structures suggestive of shallow waters (tidal,wave, storm or exposure features).

The occurrence of even parallel lamination, quasi-planar withlow angle truncated lamination and megaripple bedding iscompatible with moderately deep-waters above the storm wave-base (Soares and Nogueira, 2008). These structures were formedby alternating suspension and oscillatory flows. The abundance ofpeloids indicates intense microbial activity inducing carbonateprecipitation (James et al., 2001; Halverson et al., 2004; Soares andNogueira, 2008).

The megaripple bedding indicates bedform migration inducedby oscillatory flow, sometimes with a predominantly unidirectionalvector. This condition is illustrated by a succession of structuresranging from even parallel to quasi-planar lamination andsupercritically-climbing wave-ripple-lamination. The stacked bed-form crests displaying an upward swing suggest oscillatory flow(De Raaf et al., 1977). Allen and Hoffman (2005) suggested thatmegaripples in cap carbonates were formed under conditions of

extremewinds. The paleocoast’s direction is approximately parallelto the SW trend observed in the megaripple crests measured in thefield.

Based on an analysis of biomarkers, the microbial origin ofpeloids and organic matter, usually bitumen, in cap dolostone wasproposed by Elie et al. (2007). Molecular fossil red algae andphotosynthetic sulfur bacteria (green algae) within bitumen indi-cate typical deposits of mixed zones of carbonate and sulfate-richenvironments. According to Elie et al. (2007), red algae haveinhabited turbulent waters and nutrient-rich inflow of continentalinto the euphotic zone, where the base of this zonewould be anoxicand inhabited by photosynthetic sulfur bacteria.

2.3.2. Moderately deep platformThe moderately deep platform is characterized by layers of

crystal fan-rich limestone, interbedded with bituminous shalesbelonging in the first 25 m of the Guia Formation (Fig. 3d). Thecontact between cap dolostone and cap limestone is marked by alaterally discontinuous layer of marl of a thickness ranging between20 cm and 1.60 m. The thickest intervals of marl are associated withthe onlap filling in synforms in the dolostone of the Mirassold’Oeste Formation.

The base of the cap limestone is characterized by locallyterrigenous limestone with megaripple bedding. The megaripplesare generally covered by mud drapes and display wavelengths and

Fig. 2. Measured sections of Araras Cap carbonate in southern Amazon Craton. Sedimentary facies and paleoenvironmental interpretation are indicated in the profiles of Tangará da

Serra (I) and Mirassol d’Oeste (II) regions in the central Brazil. Gray bands identify the correlated synsedimentary deformation zones (explanations in text). Lithostratigraphic

surfaces (1e6) are indicated in circles. Modified from Nogueira and Riccomini (2006) and Soares and Nogueira (2008). Ages data were obtained by (*) Babinski et al. (2006) and (**)

Romero et al. (2013).


amplitudes varying from 1.10 up to 1.3 m and from 11 to 35 cm,respectively. Asymmetric ripple marks occur in a more isolatedfashion and are apparently associated with the top of megaripples.Marl beds up to 10 cm thick draping megaripple bedding andconvolute lamination occur locally.

Limestone layers with calcite crystal fans interbedded withshale are the dominant facies in the cap limestone, and are laterallycontinuous for hundreds of kilometers. The crystal fans are verysimilar to those in Neoproterozoic cap carbonates found elsewhere(Clough and Goldhammer, 2000; James et al., 2001; Hoffman andSchrag, 2002; Corsetti et al., 2004; Lorentz et al., 2004). The crys-tal fans are columnar, isolated or connected laterally by a thin crustof fibrous crystals. They exist in a variety of sizes, normallyexceeding 5 cm long at the top of the cap limestone. The laminationis undeformed and flat at the base of the crystals, and stronglydeformed in the upper portion and between individual crystal fans.Ripple marks occur locally at the top of the crystal fans and showinterference patterns.

Marl layers onlapping depressions on the cap dolomite indicatethe infilling of a paleorelief during sea level rise. The presence ofsiliciclastic grains indicates the first terrigenous influx into theplatform (Soares and Nogueira, 2008). Themegaripple bedding wasgenerated by the migration of bedforms induced by currents andwaves (De Raaf et al., 1977). The megaripple bedding is generallyindividualized by marls and mud drapes suggesting deposition in aregion of low energy, possibly related to proximal offshore areas(Aigner, 1985; Faulkner, 1988).

The abundance of calcite crystal fans (pseudomorphs afteraragonite) suggests that this facies was formed in a CaCO3-super-saturated and highly alkaline deep water environment, below thebase of stormwaves (Corsetti et al., 2004; Lorentz et al., 2004). Thepresence of ripple marks on the top of layers with crystals indicatesweak currents in an environment of low energy.

The main cause for the precipitation of aragonite would bechanges in ocean circulation and temperature combined with at-mospheric CO2, which together would have produced a rapid in-crease in aragonite saturation (Sumner, 2002). The sedimentation

rate was another important factor in the formation of these crystalfans in the cap carbonate from Brazil, since they are found indepositional environments with low sedimentation rate and spo-radic influx of terrigenous material.

3. Description of Event Layers

Five intervals (Event Layers) showing evidence of synsedi-mentary deformation were identified in cap carbonates of theMirassol d’Oeste and Tangará da Serra regions (Fig. 2a). Event Layer1, at the basal cap carbonate contact, is very irregular with isolatedundulations up to 1 m deep. Event Layer 2 displays microbiallaminites with a fenestral fabric cross-cut by vertical tube struc-tures. Event Layer 3 is characterized by fault-related-folds. EventLayer 4 includes locally brecciated, faulted, and fractured limestonebeds at the base of the Guia Formationwith neptunian dykes. EventLayer 5 is characterized by small-scale convolute laminations pro-duced by slumping and sliding.

3.1. Event Layer 1: small-scale load cast structures

Event Layer 1 comprises pinkish dolomudstone that overliesmassive glaciogenic diamictite containing pebble-sized striatedlithic clasts (sandstone, granite, volcanic) in a sandy clay-rich ma-trix. The dolomudstoneediamictite contact is sharp and showsirregular to undulate geometry (Fig. 4). The diamictite immediatelybelow the contact shows weakly developed lamination parallel tothe contact surface. The dolostone forms convex downward ge-ometry, 0.5e2 m across and 0.3e0.7 m high, with small, postulatebasal protuberances. Within the first meter of the cap, the dolo-stone exhibits incipient planar laminationwith dips up to 6�, fillingin onlap mainly the deep depressions with 0.7 m high. The beddingdips change upward to low angles up to 3� and finally to sub-horizontal beds. Laterally, the contact becomes less irregular anddisplays slight undulations that reflect small-scale load castedstructures (Fig. 4). The depressions show SSW trending axial zone.

Fig. 3. Araras Cap carbonate features. a) Pinkish dolostone with domal stromatolite. b) Megaripple bedded peloidal dolostone with lamination highlighted by bitumen (dark color).

c) Macropeloids between quasi-planar lamination to low-angle truncated of cap dolostone. d) Centimeter crystal fans in undulated beds of the Guia limestones.


3.2. Event Layer 2: stromatolitic lamination cross-cut by tubestructures

Event Layer 2 displays microbial lamination truncated by tubestructures (Fig. 5a; tubestones). Tube structures or tubestones arefeatures of microbialite sedimentary rocks of the Ediacaran,considered as evidence of post-Marinoan glaciation sequencesfound in cap carbonates worldwide, including in Africa (OtaviGroup e Maieberg Formation; Hoffman and Schrag, 2002),Western Canada (Ice Brook cap dolostone; James et al., 2001), theUnited States of America (Noonday Dolomite, Death Valley; Cloudet al., 1974; Corsetti and Grotzinger, 2005) and Brazil (ArarasGroup e Mirassol d’Oeste Formation; Nogueira et al., 2003;Corumbá Group e Bocaina Formation; Boggiani et al., 2010). Thetube structures are limited exclusively to stratigraphic intervals ofheterogeneous thickness associated with the presence ofstromatolites.

The tube structures occur in metric stromatolitic dolomitebioherms and biostromes as sub-cylindrical structures displayingsimilar diameter in map view and cross sections (Fig. 5b, c). Theydisrupt the dolostone lamination, forming vertical cylindricalstructures with straight and sharp edges. The filling in the tubesis characterized by alternating thicker, brighter and dark, thindolomicrite with subordinated dolomicrospar. Tubes ranging inlength from centimeter to decimeter were observed in the Mir-assol d’Oeste Formation, spatially distributed as clusters, associ-ated with the flattest part on the top of the stromatolitic mounds(Fig. 5a).

3.3. Event Layer 3: small-scale fault and fold

Event Layer 3 comprises 4 m-thick intervals of dolostone thatextends over dozens of kilometers, limited above and below by un-deformed layers (Figs. 6a, b and 7a). Synsedimentary normal faults(Figs. 6c and7b, c) showoffsets of stromatolitic andplanar laminationof up to 30 cm, associated with meter-scale open folds. The defor-mational features are located preferentially at the upper portions ofthe Mirassol d’Oeste Formation and along the contact separating theMirassol d’Oeste and Guia Formations (Figs. 6a and 7a).

Synsedimentary N to NE trending normal faults (Figs. 6b, c and7b, c) dippingmoderately (30� up to 45�) to the E or SE, respectively(see stereonets in Fig. 6e), cross-cut the laminated dolostone pro-ducing offsets of up to 2.5 m (Fig. 6b, c). Faults are restricted to theMirassol d’Oeste Formation and do not propagate to the overlyingGuia Formation. Drag and chevron folds (Fig. 6d, e) were foundassociated with the development of normal listric faults (Fig. 6a, b).Fault related folds form meter scale antiformesynform arrays thatextend laterally over tens of meters and are onlapped by unde-formed layers of marl and limestone of the Guia Formation (Fig. 6a,b). Drag folds are parallel and open with sub-vertical fold axes andfold hinges plunging shallowly towards the NW. The chevron folds(Fig. 6d, e) show wavelengths of tens of centimeters and occurpredominantly on the limbs and hinges of the meter-scale folds.The orientation of axial planes and fold hinges of the chevron andmeter-scale folds are similar. Joints show a heterogeneous spatialdistribution with higher densities closer to or adjacent to the mainfaults.

Fig. 4. Event Layer 1. Deformed contact between Puga diamictites and Mirassol d’Oeste dolomicrite, Terconi quarry, Mirassol d’Oeste region. The dolostone forms convex downward

geometry with small, postulate basal protuberances interpreted as overload structures (compass 18 cm length). Massive bedding is observed in the right lobe. Stereograms show the

bedding dip.


Fig. 5. Event Layer 2. a) Illustration of the relationship between the domal stromatolites and tube structures (Romero et al., 2011). Vertical and plan view of tubes in (a) Mirassol

d’Oeste and (b) Tangará da Serra regions.

Fig. 6. Event Layer 3. a) Photomosaic showing the contact of deformed Mirassol d’Oeste Formation and undeformed Guia Formation in the Tangará da Serra quarry. Rectangles

indicate the position of the photos above. b) Photointerpretation of the metric folds associated with synsedimentary faults. Marl are overlying and filling the synforms. Stereograms

show the dip of bedding and trend faults. c) Synsedimentary normal fault in fold flank. d) Chevron folds in pinkish dolomicrite. e) Several small-scale folds in synform.


3.4. Event Layer 4: fractures and small-scale faults, neptunian dykes

Event Layer 4 was identified at the base of the Guia Formationand includes a 4 m-thick interval of stratigraphically distinct layers(Figs. 7a, and 8a, c) that display the following synsedimentaryfeatures: levels of limestone intraformational breccias, normal andreverse faults (Fig. 9a, b, d), calcite- and silica filled fractures, slumpstructures and neptunian dykes (Figs. 8 and 9). The layers occurclose to the contact between the Guia and Mirassol d’Oeste For-mations; they are limited at their base by detachment planes andgrade laterally to undeformed layers (Fig. 8a, c, e).

The synsedimentary breccia bodies which fill neptunian dykeshave tabular subhorizontal geometries, parallel to the bedding,with widths ranging from 2 m up to 3 m (Figs. 8b, d, f and 9c).Successive layers of fibrous calcite overlay the breccia clasts(Fig. 8b). Clast- and matrix supported breccias coexist, composed ofimbricated pebbles, boulders of limestone and randomly orientedfibrous crystals, cemented by calcite spar and dolomite. The brecciaclasts are poorly sorted and comprised predominantly of angular,tabular fragments of shale and limestones from the Guia Formationthat are few centimeters long. Clast distribution is heterogeneous inthe neptunian dykes, with greater clast density in the lower andintermediate sections of the dykes, decreasing gradually toward thetop section. Fibrous or coarse calcite spar cements the clasts andoften shows discrete evidence of deformation.

3.5. Event Layer 5: slump and sliding structures

Event Layer 5 is represented by fine-grained limestones whichdisplay beds with convoluted lamination, metric limestone blocks,intraformational breccias, open folds and slump structures (Fig.10a,b). Micritic convoluted beds intercalated with laminated lime-stones occur subordinately and show relatively undeformed, flat

geometries at their base (Fig. 10c, e). Slump planes comprise 5-mthick beds that represent most of the synsedimentary deforma-tional features (Fig. 10a). Internally, the slump facies display severaldomains of deformed layers of limestone interbeddedwithmassivelimestone/marl and subordinate blocks of limestone of the GuiaFormation, up to 1.60 m long (Fig. 10d).

The fine-grained, pale pink limestones are intensely fracturedand cross-cut by synsedimentary faults. Convolute laminations anddetachment planes are the dominant synsedimentary deforma-tional features in this facies. These features occur in limestonedeposits between 1 and 4 m thick, laterally continuous and boun-ded by undeformed layers of limestones limited by irregular faultplanes. The contacts separating deformed and undeformed layersare characterized by hundreds of meters-long, irregular fault sur-faces that cross-cut all deposits of the carbonate succession andonly part of the dolomitic sequences (Fig. 10a). The contact planesare sub-horizontal, dipping gently at 2� and 6� toward the proximaland distal parts of the slump surface (Fig. 10a).

The slump deposits associated with Event Layer 5 are charac-terized by weakly deformed, tabular layers displaying convolutefolds, synsedimentary faults and meter scale faulted blocks(Fig. 10d). Convoluted bedding was observed in subordinated thinlayers of shale interbedded in laminated limestones, and in rela-tively thick layers of limestone (Fig. 10e). The base of the thinconvoluted bedding is generally flat with limited or no evidence ofdeformation, whilst the top displays NE trending hinges of theconvolute folds. The convolute folds in thicker limestone layershave irregular chaotic geometries. Synsedimentary fault planes arewidespread in the slump facies and can reach up to 1 m in length.They disturb the original bedding in the portions adjacent to thefault tips.

Matrix supported calcareous breccias form discontinuous layersup to 2 m long within the deformed limestone. The breccia clasts

Fig. 7. Deformed beds in the cap carbonate exposed in the Terconi quarry, Mirassol d’Oeste Formation. a) Panoramic section locating the Event Layer 3 that occur below of

stratigraphic surface 3 while the Event Layer 4 is found above that and limited by surface 4. b and c) Pinkish peloidal dolomudstone with megaripple bedding (mb) are displaced by

synsedimentary normal fault generating drag and chevron folds. The faulting interval is cover by undeformed beds (ub). The locations of some figures cited in the text are indicated

by boxes. Surfaces keys are marked with numbers in circles (see abbreviations in Fig. 1).


Fig. 8. Deformational features of Event Layer 4 in Terconi quarry, Mirassol d’Oeste region. a) Panoramic section with deformed intervals (in gray and numbered I to III), alternating

layers of lime-mudstone with undeformed crystals fans. Detachment surface is observed on the base of the interval I. b) Breccia with tabular clasts of mudstone outlined by crystals

fans (cr) and fibrous crystals fringes (fr). c) Neptunian dike detail (d) filled with breccias and covered with undeformed layers (ud). d) Wall of the Neptunian dyke with irregularities

filled by breccia whose major axis of the clasts is parallel to the dike wall. e) Detail of deformed layers. f) Detail of clasts parallel to the dike wall.

Fig. 9. Features of Event Layer 4 in Tangará da Serra region. a) Neptunian dike that cuts through the tabular layers of Guia Formation limestone. b) Faults, fractures (black arrows)

and deformed layers that occur at the same stratigraphic level of the neptunian dike. c) Breccia with rectangular clasts that occur filling the neptunian dykes and are oriented

parallel to the dike wall. d) Synsedimentary normal fault in the limit of neptunian dykes.


are composed of pale pink dolomite and gray or red limestone fromthe Guia Formation, in varied proportions. Clasts are poorly sorted,tabular, angular, randomly oriented with an average size of a fewcentimeters (Fig. 10b). They are heterogeneously distributed alongthe breccia layers, with greater concentrations near the contactbetween the Guia and Mirassol d’Oeste Formations. The brecciamatrix is pink or pale pink massive carbonate.

4. Discussion

4.1. Genesis of Event Layers

Synsedimentary deformation features are ubiquitous in theAraras cap carbonate. They are characterized by load structures,tubestones, faults and folds, slumps and neptunian dykes. Thesedeformed deposits (Event Layers) extend laterally for tens of kilo-meters, and are limited vertically by undeformed deposits.

The irregular basal contact that characterizes the Event Layer 1was interpreted as an overload structure formed by plastic flow andliquefaction processes similar to those described in sand/mud(Anketel et al., 1970; Lowe, 1975; Plaziat et al., 1990). The preser-vation of the primary lamination in locally deformed dolostoneconstitutes evidence of hydroplastic flow processes, and theconvolute lamination indicates fluidization and liquefaction pro-cesses (Lowe, 1975). The incipient even parallel and slightly un-dulated laminations in diamictites are approximately parallel to the

contact. The latter suggests that these sediments underwent lowshear stress, and were mainly affected by liquefaction. Thixotrop-ismmay have reduced the strength of carbonate sediment that wasdenser in relation to the diamicton. Laterally spaced overload bit,similar to sagging (cf. Alfaro et al., 1997), was formed where theviscosity dynamic was greater within the diamictite.

Nogueira et al. (2003) described and interpreted deformationstructures at the contact between the glacial diamictites and capdolostone as the result of seismicity possibly induced by post-glacial rebound. The onlap features observed in dolomicrite arecharacterized by a progressive decrease in the inclination angle ofthe even parallel lamination, away from the contact with the dia-mictites. This evidence suggests that the glacial sediments werepartially lithified when the carbonate sediments were deposited.The irregular morphology of the Puga diamictites may be associ-ated with irregularities in the surface of the glacial deposit base-ment due to the movement of icebergs and/or the deposition ofdiamicton. Postglacial faults formed by flexural stress very soonafter deglaciation may have caused the irregular morphology inthe boundary of diamictite and dolostone (see Adams, 1989), butthe unconsolidated and weathered diamictite does not confirm theoccurrence of faults. Thus, a permafrost morphology during thedeposition of the diamicton could be analogous to the present daymoraines in glacial continental environments.

Synsedimentary breccias were produced by the fragmentationof consolidated carbonate. Convoluted lamination and massive

Fig. 10. Deformational features of Event Layer 5, Tangará da Serra region. a) Slump deposits of the Guia Formation upon the Mirassol d’Oeste Formation dolostone. The contact is

abrupt, irregular and the slip plane shows slight dip. b) Breccia layers in the basal slump deposits. c) Deformed limestone with convolute bedding. d) Photointerpretation of the

slump deposits, with slip planes (characterized by thicker lines), blocks of Guia limestone and deformed layers (Db), orientation NW. e) Convolute bedding (black arrow) in shale

interbedded with deformed limestone.


bedding were formed by liquefaction and/or fluidization processesthat affected the even parallel laminations when the carbonatesediments were partially unconsolidated.

Event Layer 2 is characterized by tube structures that truncatethe fenestrate, even parallel and stromatolitic laminations of thedolostones. The origin of the tube structures in Neoproterozoic capcarbonate is controversial. Cloud (1968) interpreted these struc-tures as “Scolithus” ichnofossil generated by fossil metazoans, butthere was no material evidence to support this interpretation.Cloud et al. (1974) reinterpreted the observations described byCloud (1968) and proposed a mechanism of fluid escape producedby domal stromatolite to explain the origin of the tubes. They alsosuggested that the tubes being limited in occurrence to the middleand apical portions of the stromatolite domes indicates their lateorigin in relation to the formation of the stromatolites. However,these authors did not propose a mechanism explaining the gener-ation of the tubes.

Tube structures in the Mirassol d’Oeste Formation were firstdescribed by Nogueira et al. (2003), who attributed them to theescape of gases produced during microbial activity related to thedegradation of stromatolitic mats. Such a hypothesis was alsoanalyzed. A strong negative excursion of C isotopes was related tothe destabilization of methane hydrates (Kennedy et al., 2001).Similarly, Font et al. (2006) analyzed C and O isotopes from car-bonates in the tubes of the Mirassol d’Oeste Formation and pro-posed that these structures were formed by discharges of methaneseeps. Deformations associated with methane seepage in Quater-nary deposits are common in the Fennoscandian Shield, Sweden,and are interpreted as earthquake events (Mörner, 2011). However,a methane source was never found in cap carbonate deposits.

Evidence presented in this work is in agreement with the fluidescape hypothesis used to explain the genesis of the tube structuresobserved in outcrops of the Terconi Quarry. Font et al. (2006)analyzed d

13C in the sedimentary infill of some tubes found in theTerconi quarry. However, this represents a limited amount of dataand only a more robust and systematic sample set, together withmorphological analyses, could provide a better understandingabout their origin. It would also be valuable to compare thesestructures with other similar features described in cap carbonatesworldwide.

The tube structures were also linked to stromatolitic growth.Corsetti and Grotzinger (2005) proposed that tube structures canresult from the contemporaneous interplay between stromatolitegrowth and sedimentation/cementation. These authors discardedfluid or gas escape as a mechanism for the formation of the tubes.A more detailed study of these structures was carried out byRomero et al. (2011), who described the tube patterns in the stro-matolites of the Mirassol d’Oeste Formation. They found that tubestructures frequently occur in the central and upper portions ofdomal stromatolites. Their findings agree with those of Cloud et al.(1974), who studied stromatolites of Death Valley, California.

The homogeneous filling of the Mirassol d’Oeste tubes and theirspatially localized distribution in the stromatolitic mounds indicatethat pre-existing sediment was injected and later redeposited in ahomogeneous mass within the tubestones during eodiagenesis(Romero et al., 2011). These intriguing features seem to betemporally restricted to the Ediacaran. They show morphologicalsimilarity in Marinoan cap carbonates worldwide. However, theirorigin is still controversial and poorly understood.

Event Layer 3 extends laterally over hundreds of kilometers andis characterized by faults, folds and fractures that deform thedolostones with stromatolitic, even parallel lamination and mega-ripple bedding. Normal faults offset the dolostone layers, formingmeter-scale open- and chevron folds. The folds’ geometry iscompatible with brittleeductile deformation, which affected the

dolostone when partially lithified. Event Layer 3 is limited aboveand below by undeformed layers, which supports the synsedi-mentary nature of the deformation. The presence of these extensivedeposits, showing extensional brittle features limited within thesame stratigraphical level, suggests that a regional tectonic eventaffected the southern Amazon Craton shortly after the deposition ofthe cap dolomite (e.g. Adams, 1996a,b; Mörner, 2005). The tectonicevent likely took place during the stages of basin opening andsubsidence, as suggested by the normal faults and chevron folds.

Event Layer 4 at the base of Guia limestones has the sameextension as Event Layer 3, and corroborates with regional brittletectonics which generated neptunian dykes, faults, fractures,breccias and, locally, slump structures. Neptunian dykes can beformed by sliding associated with stretching, slope collapse, gasexpansion, diapirism, overloading and earthquakes (Montenatet al., 2007). These features were interpreted as having formed inmoderately deep and calm waters, and breccia-filled dykes wererelated to the fracturing and dilation of dyke-walls caused by brittleprocesses. The clasts would accumulate in the lower portion of thedyke, contemporaneously with micrite sedimentation on the oceanfloor. Montenat et al. (2007) highlighted that the dykes can remainopen for a long time after fracturing. The imbricated clasts parallelto dyke walls suggest subsequent flow transport downward. Thefibrous and spar calcite marine cement-outlined clasts precipitatedafter the fragmentation of the dyke wall.

Themetric succession of limestones displaying slump structuresand intraformational breccias of Event Layer 5 were interpreted asoriginating from the gravitational mass flow of sediments on agentle slope, as proposed by Coleman and Prior (1988) and Mulderand Cochonat (1996). This process partially removed the carbonatedeposits of the Mirassol d’Oeste and Guia Formations.

Convolute folds are very complex deformation structures thatcan be generated mainly by overload or sliding/slumping processes(Lowe, 1975). Convoluted beds in the Guia Formation occurbetween undeformed layers. The presence of these features con-stitutes evidence of synsedimentary soft deformation, caused byliquefaction or overload involving layers with contrasting densities(Visher and Cunningham, 1981; Mills, 1983). The poorly sorted,matrix-supported breccia were formed by fast deposition of lithi-fied masses (clasts and blocks) mixed with soft sediments (mudand sand). This process was interpreted as being related to land-slides associated with gravitational instability in a deep submarineramp. The gravitational instability was generated on a slope due tothe progressive accumulation of carbonate on the margin of theplatform (Coniglio and Dix, 1992).

4.2. Trigger mechanism

Deformation in carbonate platforms can be associated withvarious processes including an intensification of carbonate accu-mulation, storms, earthquakes, gravity flow and overload (Plaziatet al., 1990; Coniglio and Dix, 1992; Einsele, 1991; Obermeier,1996; Cozzi, 2000; Kahle, 2002). Synsedimentary deformations incarbonate platforms are characterized by brittle and ductile fea-tures, usually produced on slopes, reefs and in peritidal environ-ments and related to processes of liquefaction, fluidization andtectonic stress (Read, 1985; Cisne, 1986; Coniglio and Dix, 1992;Bourrouilh et al., 1998; Cozzi, 2000; Vernhet et al., 2006; Spallutoet al., 2007). Earthquake seismicity is responsible for severaldeformation features observed in the studied stratigraphic in-tervals. Paleoseismicity events are widely documented in silici-clastic and carbonate deposits (Adams, 1996a,b; Marco et al., 1996;Mörner, 2005; Montenat et al., 2007; Patil Pillai and Kale, 2011).

The deformed stratigraphic intervals (Events Layers) of capcarbonate in Brazil under study here were interpreted as having


formed under distinct deformation mechanisms (Fig. 11). EventLayers 1, 2 and 5 occur locally, while Event Layers 3 and 4 are morewidely distributed, extending laterally for hundreds of kilometers.Event Layers 1, 2 and 5 are related to autochthonous environmentalfactors such as overload, gas escape and gravitational instabilities(Fig. 11). On the other hand, Event Layers 3 and 4 display featuresindicative of regional scale tectonics that affected the rocks of thesouthern Amazon Craton.

The deformation structures observed in Event Layer 1 can beinterpreted as having been formed by induced seismicity or byisostatic rebound. However, deformed features of the contact zonewere observed only in the Mirassol d’Oeste region and moredetailed studies are required in order to better constrain theirtrigger mechanisms. We suggest that the deformation of the basalcontact partially results from hydroplastic adjustments in muddy-sandy diamicton and dolomite mud. Early cementation may havelimited the overhead deposition of dolomite mud. Load caststructures show no preferred orientation and their apparent plasticbehavior indicates that the carbonate sediments were unconsoli-dated to partially consolidated during the deformation. The recur-rence of deformed layers between undeformed layers alsoeliminates post-depositional tectonics as a potential cause.

The fast accumulation rate of carbonate (5 cm ky�1) was sug-gested by Hoffman et al. (1998) to explain the deformation featuresobserved in the Maieberg cap carbonate of Namibia. However, newdata on the deposition rates of cap dolomite indicate longer in-tervals of deposition of approximately 105 years, and reinforce the

idea that liquefaction processes were the primary mechanism inthe formation of these features. Plaziat et al. (1990) and Alfaro et al.(1997) associated the generation of load cast structures, similar tothose observed in the cap carbonate, with seismic shocks. Ac-cording to Mörner (2005), the rapid uplift during the deglaciationperiod is characterized by seismic activity which was high to super-high in amplitude and frequency, but the seismic activity decreasedwith time. Deformed features in cap carbonate result from seismicshock, when the short-lived upward hydraulic force and suddenreductions in intensity near the surface are released (Pratt, 1994;Munson et al., 1995; Obermeier, 1996; Kahle, 2002). The presenceof small-scale load structures was induced by seismicity of mod-erate to high magnitude, probably greater than 5 (Proved byAudemard and De Santis (1991) with contemporary earthquakes)(Ambraseys, 1988; Audemard and De Santis, 1991). The presence ofplastic deformation at the basal contact of the cap carbonate con-stitutes sedimentological evidence of dolomite precipitationshortly after melting, indicating a change from icehouse to green-house conditions in the cap carbonate (Nogueira et al., 2003). Thisinterpretation is valid for the first meters of cap carbonate.

Other deformation features observed on both cap dolostone andcap limestone are consistent with a seismic origin and include: theformation of metric folds, neptunian dykes, synsedimentary faultsand fractures in particular intervals. Event Layers 3 and 4 may beassociated to extensional tectonic events with associated earth-quakes (Marco et al., 1996; Cozzi, 2000; Montenat et al., 2007).Neptunians dykes are commonly interpreted as features generated

Fig. 11. Event Layers origin. Schematic diagrams for the origin of synsedimentary deformation in the Araras cap carbonate (no scale intended). In Event Layer 3 A and B correspond

to Mirassol d’Oeste and Tangará da Serra regions, respectively. Tubes model is Romero et al. (2011).


at the seafloor during extensional tectonic movements associatedwith seismic events, but without the occurrence of subaerialexposure features (Lehner, 1991; Winterer and Sarti, 1994;Bourrouilh, 2000; Montenat et al., 2007; Kandemir and Yilmaz,2009). Bourrouilh et al. (1998) indicated that features such asneptunian dykes resemble high frequency fractures caused byrecent earthquakes that occurred in California (Loma Prieta earth-quake) and Kyoto, both of magnitude greater than 7 on the Richterscale. Thus, neptunian dykes are usually caused by extensionalfracturing of platformal lithified deposits associated with earth-quakes and filled by micrite sediments or marine carbonate ce-ments beneath substantial hydrostatic pressure (Lehner, 1991).

The origin of metric-scale and chevron folds is related to thedevelopment of synsedimentary normal faults related to openingor subsidence of the basin during extensional tectonic periods.During this process, seismic shocks occurred and were recurrentthroughout the deposition of cap limestone, also leading to thebrittle processes with the formation of neptunian dykes. Marcoet al. (1996) describe unusual earthquake-induced structuresassociated with slip events in the Dead Sea Graben, similar tosynsedimentary deformations found in our study area. These au-thors identified mixed layers (breccias, faults and folds) associatedto metric synsedimentary normal fault displacement on the sedi-mentewater interface. Each mixed layer corresponds to an earth-quake event of magnitude greater than 5 or 6. Extensional tectonicsin the southern Amazon Craton, with episode intervals marked byearthquakes, may be related to the formation of the Clymene Ocean(Tohver et al., 2010).

No seismic features were observed in the association of faults,slump structures and breccia that occur in the upper part of thesuccession found in Tangará da Serra. These associations areinterpreted here merely as progressive layer rupture and plasticdeformation, re-sedimentation and synsedimentary cementationevents. Such gravitational instabilities in partially lithified sedi-ments can be interpreted as originating in deep water, possiblyrelated to the ramp slope on the seafloor. Turbidity currents wereresponsible for the generation of the normal gradation found inlimestone layers, separated by intervals of suspension (shale),consistent with a deep marine paleoenvironment. The plastic andbrittle deformation in Event Layer 5 displays discontinuousslumping and sliding features devoid of preferential orientation,which are suggestive of gravitational flow.

Deformed intervals between undeformed layers associated withstructures of the different types of deformation (plastic and brittle)are typical of seismic shocks (Marco et al., 1996; Obermeier, 1996;Mörner et al., 2000; Kahle, 2002; Mörner, 2005; Audemard et al.,2011). Therefore, multiple seismic events could explain the recur-rence of deformed intervals inserted in the cap carbonate succes-sion (see Pratt, 1994; Adams, 1996a,b). The extension of thesesynsedimentary deformations over hundreds of kilometers in theState of Mato Grosso, and the different types of features suggestearthquakes between 6 and 8 in magnitude. This interpretation hasbeen suggested to explain the deformation of the contact betweenthe Mirassol d’Oeste and Guia Formations (Nogueira et al., 2003),called Event Layer 1 here, and may also apply to Event Layers 3 and4. However, detailed mapping of these earthquake-induced struc-tures is necessary for a better understanding of the distribution,frequency and amplitude of great tectonic events registered in theNeoproterozoic cap carbonate of central Brazil.

5. Conclusions

The Marinoan Araras cap carbonate exposed in the southernAmazon Craton has five deformed intervals limited above andbelow by undeformed deposits. These intervals include deformed

carbonate deposits from a restricted euphotic sea (Event Layers 1e3) and moderately deep platform (Event Layers 4e5). Event Layers1, 2 and 5 are locally distributed, whilst Event Layers 4 and 5 occurat a regional scale.

Event Layer 1 is characterized by the presence of deformationfeatures that occur at the contact between the diamictites and capdolomite, and which were likely produced by isostatic reboundafter the ice retreated during the final stages of the Marinoanglaciation.

Event Layer 2 is related to fluid and methane escape followingthe organic degradation of microbial mats and domes that formedtubes. Event Layer 5 is associated with processes of collapse andsliding/slumping on the platform’s slope not associated withearthquakes (Observation: Not exempt of being associated withearthquakes).

The brittle and ductile structures recorded in Event Layers 3and 4 are compatible with extensional regional tectonics duringthe opening of the Araras Basin. These tectonic movements trig-gered earthquakes of magnitudes ranging from 5 up to 7. Seismitesin the cap carbonates are confirmed by the lateral continuity ofthese deposits which extend over hundreds of kilometers, andindicate recurrent allocyclicity during the deposition of the Ararascap carbonate. The exceptional lateral extensions of thesedeformed beds make them reliable stratigraphic markers for theNeoproterozoic successions exposed in the southwestern AmazonCraton.

Acknowledgments

This research was supported by INCT/GEOCIAM program andMCT/CNPq 15/2007-Universal project and MCT/CNPq 14/2010-Universal 484290/2010-0 project. This is a work of GSED-UFPAresearch group. We thank José Bandeira, Roberto César and RickOliveira for their help in field work. We acknowledge to CalcárioTangará S.A. for logistical support and the mine engineer SávioSantos for his valuable collaboration.We thank Frank Audemard forhis useful suggestions in reviews of the manuscript and twoanonymous readers also provided useful critiques.

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Synsedimentary deformation and the paleoseismic record in Marinoan cap carbonate of the southern Amazon Craton, Brazil

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