Late- to post-orogenic basins of the Pan-African – Brasiliano collision orogen in southern Africa and southern Brazil

Basin Research (1996) 8, 157–171

Late- to post-orogenic basins of the Pan-African –Brasiliano collision orogen in southern Africa andsouthern BrazilP. G. Gresse,* F. Chemale,† L. C. da Silva,‡ F. Walraven§ and L. A. Hartmann¶*Geological Survey, PO Box 572, Bellville 7535, South Africa†Universidade do Vale do Rio dos Sinos, Caixa Postal 275,

93022–000, Sao Leopoldo, Brasil‡Companhia de Pesquisa de Recursos Minerais, Rua Bancoda Provıncia, 105 90840–030 Porto Alegre, Brasil§Geological Survey, X112, Pretoria 0001, South Africa¶Universidade Federal do Rio Grande do Sul, Av. BentoGoncalves, 9500, 90820–190, Porto Alegre, Brasil

ABSTRACT

Late- to post-orogenic basins formed on both sides of the Pan-African – Brasiliano orogenwhen the Congo and Kalahari Cratons collided with the Rio de la Plata Craton during theformation of western Gondwana. Trace fossil evidence and radiometric age dating indicate thatdeposits on both sides are coeval and span the Cambrian–Precambrian boundary.

A peripheral foreland basin, the Nama Basin, developed on the subducting southern Africanplate. Lower, craton-derived fluviomarine clastics are overlain by marine platform carbonatesand deltaic flysch derived in part from the rising subduction complex along the northern(Damara Belt) and western (Gariep Belt) orogenic margins. Rare, thin volcanic ash layers (tuffsand cherts) are present. Upper sediments consist of unconformable red molasse related tocollisional orogenesis. Orogenic loading from the north and west led to crustal flexure and theformation of a remnant ocean that drained to the south and closed progressively from north tosouth. During final collision SE-, E- and NE-verging nappes overrode the active basinmargins. Although younger than most of the post-orogenic magmatism, its setting on thecratonic edge of the subducting plate precluded marked volcanism or granitic intrusion, theonly exception being the youngest intrusions of the Kuboos-Bremen Suite dated at 521±6 Mato 491±8 Ma.

Two foreland-type basins, perhaps faulted remnants of a much larger NE–SW elongatedretroarc foreland basin, are found west of the Dom Feliciano Belt on the edge of the Rio de laPlata Craton in southern Brazil. In the southern Camaqua Basin, basal fluvial deposits arefollowed by cyclical marine and coarsening-up deltaic deposits with a notable volcanic andvolcaniclastic component. This lower deformed succession, comprising mainly red beds,contain stratabound Cu and Pb–Zn deposits and is overlain unconformably by a fluviodeltaicto aeolian succession of sandstones and conglomerates (with minor andesitic volcanics), derivedprimarily from an eastern orogenic source and showing southerly longitudinal transport. In thenorthern Itajaı Basin, sediments range from basal fluvial and platform sediments to fining-upsubmarine fan and turbidite deposits with intercalated acid tuffs. The Brazilian basins hadfaulted margins off which alluvial fans were shed. They also overlie parts of the Ribeira Belt.Thrust deformation along the orogenic margin bordering the Dom Feliciano Belt was directedwestward in the Camaqua and Itajaı basins, but reactivated strike-slip and normal faults arealso present. Late- to post-orogenic granitoids and volcanics of the Dom Feliciano Belt,ranging in age from 568±6 Ma to 529±4 Ma, occur in the foreland basins and aregeochemically related to some of the synsedimentary volcanics.

© 1996 Blackwell Science Ltd 157

P. G. Gresse et al.

magmatic and volcanic rocks with local metasedimentaryINTRODUCTIONsuccessions on the Brazilian side.

Late- to post-orogenic basins developed on both sidesMobile belts of Neoproterozoic age surround and weldcratons on the African continent and in eastern South of the collision orogen. On the African side the Nama

and Mulden basins (Fig. 1) are typical peripheral forelandAmerica. These Pan-African belts form a three-armsystem along the west coast of the Congo, Angola, basins (Gresse, 1986; Stanistreet et al., 1991) formed by

downward flexure of the crust cratonward of the collisionNamibia and South Africa, recurring across the AtlanticOcean as the Brasiliano belts of Brazil and Uruguay belts showing late, marginal deformation verging towards

the craton. Very few magmatic intrusions invaded these(Fig. 1). The West Congolian Belt, Damara Orogen –i.e. Kaoko, Damara and Gariep belts (in the sense of remote foreland regions on the subducting plate(s). On

the Brazilian side a series of isolated ‘basins’, someHoffmann, 1987) and Saldania Belt on the African sideand the Ribeira and Dom Feliciano belts on the South possibly remnants of a much larger depository, are found

inboard of the older orogenic belts. In southern BrazilAmerican side, respectively, reflect bipolar cratonward-verging and sinistral strike-slip deformation related to a specifically, the Camaqua (Rio Grande do Sul State) and

Itajaı (Santa Catarina State) basins (Fig. 1) overlie fore-N–S-trending collision orogen that sutured the Congo,Kalahari and Rio de la Plata cratons in western land parts of the Dom Feliciano Belt, including the

Ribeira Belt, older Meso- to Palaeoproterozoic volcano-Gondwana. Collision in the south involved north-westward subduction of the Kalahari plate and sequential sedimentary successions and Archaean basement. Some

of the volcanosedimentary successions, for instance theclosure of the proto-Atlantic (Adamastor) Ocean fromnorth to south (Porada, 1979, 1989; Davies & Coward, Tijucas Belt (Fig. 1), have been interpreted in the past

as being part of the Brasiliano cycle (Porada, 1979, 1989;1982; Stanistreet et al., 1991). This orogen consistsmainly of thick rift-related metasedimentary and volcanic Fernandes et al., 1992) but U/Pb zircon dates on, for

example, a metavolcanic unit of the Brusque Groupsuccessions with late- to post-orogenic magmatism onthe African side and voluminous syn- to post-orogenic (Santa Catarina) indicate a pre-Brasiliano age for this

Fig. 1. Pan-African/Brasiliano belts andlate- to post-orogenic basins ofNamibia, South Africa and southernBrazil in the Gondwana context. Areascovered by Figs 5 and 9 are indicated.(Insert modified after Porada, 1989.)

© 1996 Blackwell Science Ltd, Basin Research, 8, 157–171158

Pan-African – Brasiliano basins

belt (Basei, 1985). The late- to post-orogenic deposits in Gresse & Germs, 1993). Sediments of the Zaris andWitputs basins constitute the Nama Group and those ofsouthern Brazil are frequently intruded by late Dom

Feliciano granites. Limited trace fossil evidence and the Vanrhynsdorp Basin, the Vanrhynsdorp Group.Basal clastic and carbonate deposits in the Witputsisotopic age determinations suggest that deposits in these

basins are coeval with their southern African counterparts and Vanrhynsdorp sub-basins, the Kuibis Subgroup andFlaminkberg Formation (Figs 3 and 4), were derivedand span the Precambrian–Cambrian boundary.from the craton and deposited in braided fluvial toshallow-marine environments. Basal Kuibis sediments inINTRABASINAL STRATIGRAPHY ANDthe Zaris sub-basin were partly derived from an elevatedDEPOSITIONAL ENVIRONMENTregion in the Damara Belt (Germs, 1972; Gresse &Germs, 1993; Hegenberger, 1993), suggesting early upliftBasins on the Kalahari Cratonin this belt. The Witvlei Group, an outlier of sediments

The Nama Basin, covering an area of roughly 900 km byunderlying the Nama Group paraconformably in the

300 km, has been interpreted as a peripheral forelandZaris Basin east of Windhoek, was interpreted by

basin by Gresse (1986) and Gresse & Germs (1993). TheHegenberger (1993) as a passive-margin succession

Nama and Vanrhynsdorp groups, each some 2.5 km thickdeposited on the edge of the Kalahari Craton during

at maximum, were deposited in this basin on the flexuredopening of the Damara Ocean.

edge of the Kalahari Craton, partly overstepping sedi-Stanistreet et al. (1991) suggested that the Kuibis

ments of the Damara and Gariep belts in the north-west,Subgroup in the south (Witputs Basin) was deposited on

west and south-west. Three sub-basins, the Zaris Basinan open shelf during orogenesis in the Damara Belt,in the north, the central Witputs Basin and the southernprior to collision in the Gariep Belt. According to them

Vanrhynsdorp Basin, separated by the Osis andthe depository in the south only developed into a

Kamieskroon ridges, have been distinguished (Fig. 2;peripheral foreland basin during deposition of theSchwarzrand Subgroup. Recent sequence stratigraphicand chemostratigraphic work by Saylor et al. (1995)showed that the base of the Kuibis is diachronous andthe lowermost sequence in the Zaris basin correspondsto the second sequence (Kliphoek and Mooifontein mem-bers) in the Witputs Basin, indicating earlier depositionof recognized Nama sediments in the latter. In thisscenario the first sequence of Saylor et al. (1995) in theWitputs Basin may correlate with the upper part ofthe Witvlei Group, implying that both may pre-date theregional Nama transgression and thus belong to thepassive margin stage of the Damara Orogen. Hoffmann(1989) related parts of the Nama Group to ‘deep-water’equivalents in the upper Vaalgras Subgroup of theDamara Belt.

Gresse & Germs (1993) ascribed the regional uncon-formity at the base of the Nama and Vanrhynsdorpgroups, transecting parts of the Gariep and Damaradeposits, to global continental aggradation. Hegenberger(1993) likewise related it to the reversal from spreadingto convergence in the Damara Orogen. Black micriticlimestones of the Kuibis Subgroup are composed ofstromatolitic, oolitic, pisolitic and oncolitic facies rep-resenting barrier reef, barrier bar and forereef deposits.These limestones line the basin margins grading intodeeper water shales offshore and arkosic or quartzosearenites onshore.

During Schwarzrand/Knersvlakte times orogenicsource areas became more prominent in the Damara Beltand also emerged to the west in the Gariep Belt. Withprogressive orogenic uplift a remnant ocean basin thatdrained to the south-east developed. Foredeep sequencesfilled the northern Zaris and southern Vanrhynsdorpbasins whereas thick platform carbonates were depositedFig. 2. Sub-basins of the Nama foreland basin (after Gresse &

Germs, 1993). in the central Witputs Basin. Volcanic ash layers in the

© 1996 Blackwell Science Ltd, Basin Research, 8, 157–171 159

P. G. Gresse et al.

Fig. 3. Generalized stratigraphy of the Nama and Vanrhynsdorp groups (after Gresse & Germs, 1993).

Fig. 4. The lower Nama Group asexposed in the Fish River Canyon,Namibia.

form of chert beds are dispersed through the upper Witputs (and Zaris) Basin defined by the unconformityat the base of the Nomtsas Formation (Fig. 3). If,Kuibis, Schwarzrand and Knersvlakte subgroups. A

SE-prograding, longitudinal flysch fan, fed by the south- however, the successions in the sub-basins are asdiachronous as suggested by Saylor et al. (1995) andeast drainage of the remnant ocean basin, deposited the

Knersvlakte Subgroup in the southern Vanrhynsdorp implied by, for example, the correlation of the GrootrietFormation in the lowermost Vanrhynsdorp Group withBasin. Gresse & Germs (1993) proposed a generalized

sequence stratigraphic model to show the relationship the Huns Member in the Schwarzrand Subgroup (Germs& Gresse, 1991; Gresse & Germs, 1993; Kaufmann et al.,between depositional facies in the foreland sub-basins.

Cambrian trace fossils have been recorded from near the 1993), the whole Vanrhynsdorp Group could be muchyounger than anticipated. Some of the material depositedbase of the Knersvlakte Subgroup and this led them to

suggest that this subgroup represents a hiatus in the in the Knersvlakte lowstand delta fan (Gresse & Germs,



Fig. 5. Geological sketch map of part ofthe Camaqua Basin (see Fig. 1; modifiedafter Ribeiro et al., 1966; Paim, 1994).

1993) was probably eroded from Schwarzrand sediments stretching zone north-west of the similarly elongatedDom Feliciano Belt (Fig. 1). The largest one in the south,uplifted by flexural bulging in the northern and centralthe Camaqua Basin (Fig. 5), measures about 150 km byregions of the foreland basin. The Nomtsas unconformity75 km and is based on granite–gneiss and metasedimentscould therefore be reflected as a conformable lowstand(Vacacaı Supergroup, Cambaı Complex and Porongossuccession in the Vanrhynsdorp Basin.Group) that were deformed and metamorphosed betweenThe Nomtsas represents the first real molasse incursion750 and 650 Ma (Chemale et al., 1995). Based on strati-in the foreland basin. It consists of braided fluvial reddish,graphic analysis and a gravimetric survey (Chemale et al.,polymictic conglomerate and sandstone in the north thatin prep.) the maximum thickness of the Camaqua Groupgrade southward into subtidal sandstone, shale and lime-is estimated to be in the region of 5 km.stone. According to Germs (1972) some of the erosional

Several stratigraphic classifications have been proposedfeatures at the base of the Nomtsas are glacial. Gresse &for the sedimentary fill of the Camaqua Basin. For theGerms (1993) suggested that palaeovalleys up to 100 mpurpose of this study the nomenclature of Ribeiro et al.deep on this unconformity near Koedoelaagte and(1966) was slightly modified, using the depositionalSwartkloof berg, filled with Nomtsas diamictite and con-sequence description of Paim et al. (1992). The Camaquaglomerates, may reflect submarine shelf edge or slope-sediments are subdivided into the basal Maricafront erosion related to flexural bulging at Osis andFormation, the intermediate Bom Jardim Group and theKoedoelaagte. Saylor et al. (1995) proposed that theupper Camaqua Group (Fig. 6). The first two are separ-valleys were incised during regression and filled byated by an erosional unconformity (Paim et al., 1992)gravity-flow deposits during marine flooding of a possiblewhilst the Camaqua Group is separated from the Bomtype-2 sequence boundary. The Van Zylkop conglomer-Jardim Group by an angular unconformity. The Maricaates and sandstones in the Vanrhynsdorp Basin, litho-and Bom Jardim units display brittle to brittle–ductilelogically similar to the Nomtsas, were deposited asdeformation related to the first stage of late orogenesisconformable delta-plain sediments.in the Dom Feliciano Belt. The Camaqua Group isThe Fish River Subgroup is an unconformable, redunaffected by this event.molasse phase consisting of five upward-fining cycles

The Marica Formation (Ribeiro et al., 1966), depositedsourced in the orogenic mountains north and west of thedirectly on the Vacacaı Supergroup and Cambaı Complex,peripheral foreland basin. The sediments grade fromstarts with alluvial fan (near the faulted margins) tobraided fluvial in the north to distal fluvial and tidalbraided alluvial conglomerates and sandstones that grademarine towards the south, but due to erosion no exposuresup into shallow-marine storm deposits and delta-front toare found south of the Orange River.prodelta turbidites (Paim et al., 1992). Thin layers ofacid tuff occur frequently. An alluvial facies is present atBasins on the Rio de la Plata Cratonthe top of the sequence.

In southern Brazil two relatively small occurrences of Overlying the Marica Formation is the Bom JardimGroup (Ribeiro et al., 1966), represented by three forma-late- to post-orogenic deposits are found in a NE-SW


P. G. Gresse et al.

Fig. 6. Generalized stratigraphy of the Camaqua and Itajai basins (modified after Silva & Dias, 1981; Rostirola, 1991; Paim et al.,1992).

tions. The lower Hilario Formation comprises basalts, The Camaqua Group represents the final stage ofdeposition in the Camaqua Basin. It is mostly horizontallytrachybasalts, latites and trachytes as well as pyroclastic,

flow and epiclastic rocks. These rocks have a dominant disposed or slightly tilted and rests with an angularunconformity on the Bom Jardim rocks. The lower Santashoshonitic signature, which was interpreted by Nardi

et al. (1992) as late orogenic volcanism formed from Barbara Formation of this group consists of one upward-fining and two upward-coarsening cycles representingmantle fusion deep in a subducted oceanic plate.

The intermediate Arroio dos Nobres Formation con- prodelta and delta-front turbidites as well as braidedfluvial delta plain facies (Paim et al., 1992). These rockssists of the Vargas and Mangueirao members. The Vargas

Member occurs in lateral association with the Hilario are covered by the Guaritas Formation comprising aeolian(Fig. 8), alluvial plain and alluvial fan deposits, overlainFormation as conglomerates and sandstones deposited in

alluvial fan to braided alluvial settings. These rudites by transgressive deltaic to lacustrine rhythmites andalluvial sediments (Lavina et al., 1985). Palaeocurrentsoften contain up to 80% volcanic pebbles derived from

the Hilario Formation. These systems are followed suggest that sediments of the Guaritas Formation weremainly derived from an eastern source and dispersed byby progradational delta-front facies containing a thick

rhythmite succession, mostly shallow-water turbidites longitudinal currents towards the south (Paim et al.,1992). Andesitic volcanic rocks of the Rodeio Velho(Lavina et al., 1985; Paim et al., 1992) which are included

in the upper Mangueirao Member. The top of the Bom Member cut the basal units of the Guaritas Formation(Paim et al., 1992).Jardim Group is composed mainly of volcanic rocks

oversaturated in silica, the Acampamento Velho Member. In Santa Catarina State sediments in the Itajaı Basinwere deposited on the Archaean Santa Catarina GranuliteIt consists of ignimbritic rhyolite lava (Fig. 7), rhyolite

sills and dykes thought to have been generated post- Complex west of the Dom Feliciano Belt (Fig. 9). Thearea of exposure measures about 60 km by 10–60 km andorogenically (Nardi & Bonin, 1991).



Fig. 7. Flow structure in ignimbriticrhyolite, Bom Jardim Group, CamaquaBasin.

and Silva & Dias (1981). The lower Gaspar Formation(Silva & Dias, 1981; Fig. 6) is composed of alluvial fanconglomerates of polymictic composition interbeddedwith trough cross-bedded brown to red arkosic sandstonesand is found mainly in the north-eastern, south-westernand south-eastern parts of the basin along the faultedbasin boundaries. These deposits are overlain by upward-fining delta-front sandstones and shales displaying sig-moidal bed geometry, climbing ripple cross-laminationas well as hummocky cross-stratification. These tem-pestites with intercalated acid tuff layers are thought tohave formed in shallow platform regions during partialwave reworking of delta-front sands. They are followedby the Campo Alegre Formation, a transgressive package(marine or lacustrine) consisting of basal intercalatedsandstone, siltstone and resedimented conglomerate andan upper turbiditic succession. The lensoid conglomeratesin the lower part are interpreted as submarine channeldeposits in an eroded turbiditic succession exhibitingTbcd, Tcd, Tce and Tde turbidites with associated darkgrey shales and siltstones. The upper part consists ofsilty to muddy turbidites (probably submarine fan tur-bidites) with dark grey to black shales and mudstones.The uppermost unit (Fig. 6) may represent a regressivecoastal system composed of sandstones, mudstones andconglomerates (Silva & Dias, 1981; Rostirola, 1991), butKrebs (1992) interpreted it as a thrust wedge derivedfrom the lowermost part of the succession.

Fig. 8. Aeolian cross-bedding in the Guaritas Formation,Camaqua Basin.

PALA EONTOLOGICAL AGECONSTRAINTS

is complemented by the relatively small (30×20 km),Campo Alegre Basin some 90 km to the north. The two In the Nama Group, Ediacaran-type soft-bodied fossils

from the Kuibis Subgroup such as Ernietta, Namalia,basins are fault bounded and contain comparable strati-graphic columns and are therefore probably remnants of Orthogonium, Pteridinium (Fig. 10) and Rangea and the

shelly fossil Cloudina (Kuibis and lower Schwarzranda much larger depository that was at least 110 km wide.The sediments in the Itajaı Basin have an estimated subgroups) combined with acritarch microfossils, place

these formations in the latest Vendian Period (Germs,thickness of about 3.3 km although some duplication bythrusting has been inferred. The stratigraphic sub- 1972; Crimes et al., 1982; Germs et al., 1986; Grant,

1990). Among others, Neonereites, Enigmatichnus africana,divisions used here are adapted from Rostirola (1991)


P. G. Gresse et al.

Fig. 9. Geological sketch map of the Itajaı Basin (see Fig. 1; modified after Rostirola, 1991).

Fig. 11. Cambrian trace fossil Phycodes pedum in theKnersvlakte Subgroup, Vanrhynsdorp Basin. Scale starts top

Fig. 10. Ediacaran soft-bodied fossil Pteridinium in the Kuibis left with 1-cm bar. (Photograph by J. E. Almond.)Subgroup, Witputs Basin.

Skolithos and Phycodes pedum (Fig. 11) in the Nomtsas Planolites, Rusophycus and Skolithos in the Santa Barbaraand lower Guaritas formations. This provisionally placesFormation, Fish River Subgroup and most of the

Knersvlakte and Brandkop subgroups (Vanrhynsdorp the Precambrian–Cambrian boundary at the base of theCamaqua Group (Fig. 12; Table 1).Group) as well as Oldhamia (Knersvlakte Subgroup)

represent typical Early Cambrian (Tommotian) ichno-faunal assemblages (Crimes & Germs, 1982; Germs, POST-OROGENIC FORELAND1983; Gresse & Germs, 1993). The Precambrian– MAGMATISMCambrian boundary at 545 Ma therefore probably fallsat the base of the Nomtsas Formation or lower down in Deposits of the Nama foreland basin cover a vast area

(270 000 km2) on the western edge of the Kalahari Craton,the Schwarzrand and Knersvlakte subgroups (Gresse &Germs, 1993; Table 1). A preliminary study by but they are, with one exception, not intruded by the

late- to post-orogenic granites of the Damara, GariepNetto et al., 1992) distinguished ichnofossils such asDidymaulichnus, Intrites and Planolites in the middle and and Saldania belts. Most of these granites post-date the

depositional age of the Nama and Vanrhynsdorp groups,upper Marica Formation and the Bom Jardim Groupand Cochlichnus, Cruziana?, Didymaulichnus, Gyrolithes, but are confined to the orogenic belts themselves. The



Tab

le1.

Mai

nfe

atur

esof

late

topo

st-o

roge

nic

basi

nsof

the

Pan-

Afr

ican

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rasi

liano

colli

sion

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en.

Age

cont

rols

base

don

isot

ope

data

and

pala

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olog

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ete

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Bas

in/s

trat

igra

phy

Age

Bas

emen

tSe

dim

enta

ryen

viro

nmen

tFo

ssils

Vol

cani

smPl

uton

ism

Tec

toni

cen

viro

nmen

t

NA

MA

Kui

bis

Subg

roup

<590

Ma

Kib

aran

gnei

sses

,B

raid

edflu

vial

tosh

allo

w-

Ern

ietta

,Nam

alia

,O

rtho

goni

um,P

teri

dini

um,

Tuf

fbe

dsB

rem

engr

anite

,Pe

riph

eral

fore

land

basi

n>5

40M

a90

0–70

0M

am

arin

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atfo

rmR

ange

a,C

loud

ina,

Ber

gaue

ria,

syen

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dG

arub

sedi

men

tary

Buc

hhol

zbru

nnic

hnus

carb

onat

itesu

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sion

Schw

arzr

and

Subg

roup

<590

Ma

toT

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taic

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bona

teR

ange

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teri

dini

um,P

aram

edus

ium

,Nas

epia

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beds

~530

Ma

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lom

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a,C

loud

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lichn

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Phy

code

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s

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al,

tidal

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Skol

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code

s,E

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mat

ichn

usaf

rica

ni>5

21M

am

arin

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RH

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min

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n<5

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es,

Bra

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fluvi

alto

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mar

ine

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pher

alfo

rela

ndba

sin

>540

Ma

900–

700

Ma

sedi

men

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succ

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rsvl

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Subg

roup

~540

Ma

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Old

ham

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beds

>495

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code

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s?,M

onom

orph

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95M

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Gas

par

For

mat

ion

~590

Ma

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Allu

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taic

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alin

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etro

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basi

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prot

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dagr

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gran

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s

Cam

poA

legr

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atio

n>5

35M

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523

Ma

Ero

ded

Alk

alin

erh

yolit

e53

5M

a

CA

MA

QU

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aric

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ion

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Ma

750–

700

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Allu

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taic

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Intr

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lichn

usA

cid

tuff

beds

Shos

honi

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dR

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fore

land

basi

nor

ogen

icbe

ltal

kalin

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anite

Bom

Jard

imG

roup

568

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toA

lluvi

al,d

elta

ic,m

arin

eIn

trite

s,P

lano

lites

Shos

honi

tic,

530

Ma

inte

rmed

iate

rock

s,al

kalin

erh

yolit

e

Cam

aqua

Gro

up<5

30M

aA

lluvi

al,d

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arin

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ochl

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us,D

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Alk

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s


P. G. Gresse et al.

Fig. 12. Comparative stratigraphy andprobable age of the southern Africanand southern Brazilian foreland basins.

exception is the Kuboos–Bremen line of post-orogenic, able host-rocks or structures for ore precipitation andconcentration (Klein, 1991). These attributes are relatedgranitic to syenitic intrusions in the Richtersveld and

southern Namibia (Table 1) which follows an older line to plate tectonic setting and basin dynamics.The Nama foreland basin has a low economic potentialof intrusions thought to mark an early Pan-African failed

rift (Von Veh, 1992). Allsopp et al. (1979) defined a because of its geotectonic setting on the subducting plateand the fact that most of the deposition occurred underU–Pb age of 521±6 Ma (recalculated by Cahen et al.,

1984) for the Bremen syenitic phase that visibly intrudes oxidizing conditions. The general absence of markedvolcanic activity and post-orogenic intrusions precludesthe Nama sediments, and a Rb–Sr age of 491±8 Ma for

the Garub pyroclastic (carbonatitic) sill at the north- possible syngenetic or hydrothermal mineralization.Low-grade Cu-mineralization in green shales of theeastern end of the line with similar intrusive relationships.

In contrast, on the overriding plate in Brazil, large Buschmansklippe Formation near Gobabis is nowregarded as being part of the middle Damara sequencevolumes of late to post-orogenic magmas intruded the

Dom Feliciano Belt as well as the foreland regions. (Hoffmann, 1989; Miller, 1983). Clay pellet conglomerateat the base of the Fish River Subgroup is locally cuprifer-Besides the shoshonitic, late and post-orogenic alkaline

volcanism closely related to the sedimentation in the ous on Schlipmundung.Contrastingly, significant syngenetic and strataboundCamaqua and Itajaı basins, there are also important

plutonic intrusions in these basins (Table 1). The plutonic Cu and Pb–Zn mineralization occurs in the CamaquaBasin, for example at the Minas de Camaqua (Fig. 5).rocks display geochemical characteristics similar to the

volcanic rocks, varying from shoshonitic (e.g. core of the The mineralized horizons are situated in the Arroio dosNobres Formation. Stratabound, diagenetic ores occur inLavras and Sao Sepe granites) to alkaline (e.g. border of

the Lavras, Sao Sepe and Jaguari granites) or even green fluvial conglomerates (Fig. 13) and sandstones andalong NW– NNW-striking fault zones that intersect theperalkaline (e.g. Subida Granite). A whole-rock Rb–Sr

isochron age of 568±6 Ma for the Lavras Granite (Vieira stratabound deposits. The mineralization is confined tothe unoxidized part of the red bed succession and appears& Soliani, 1989) is assumed to be the age of the

Hilario Formation. Field relationships and geochemical to be a typical redox boundary deposit. Mineralizedbrines probably leached metals from the synsedimentarydata suggest that these two suites are related and

roughly coeval (Nardi, 1984; Nardi et al., 1992). The volcanics and volcaniclastics found in the Hilario andAcampamento Velho formations (Fig. 6) and depositedalkaline rocks yield whole-rock Rb–Sr isochron ages

of 519±8 Ma (border of Sao Sepe Granite) and them at the redox front in coarse clastic sediments andfault zones. Proven ore reserves are 28 million tons539±20 Ma ( Jaguari Granite; Soliani, 1985). The sedi-

mentary succession of the Itajaı Basin is intruded by the (Ribeiro, 1992) averaging 0.7–1.3% Cu and 2.12% Pbplus 1.33% Zn, respectively. Gold (0.09 g/t) and silver523±92 Ma alkaline Apiuna Rhyolites and perthitic to

syenitic Subida Granite with an age of 535±22 Ma (6.9 g/t) are the main by-products occurring in thepyrite, chalcopyrite, chalcocite, bornite, galena and(whole-rock Rb–Sr data from Basei, 1985).sphalerite ores. Diagenetic illites associated with the orehave given K–Ar dates of #550–465 Ma (Bonhome &BASE METAL MINERALIZATION Ribeiro, 1983).RELATED TO DIVERGENT FORELAND

SETTINGSCOLLIS ION-RELATED BASIN

Ore-hosted sedimentary basins possess specific inherent TECTONISMmaturation attributes that include metalliferous sourcerocks suitable for leaching, favourable conditions for The Nama foreland basin is deformed on three sides

along its north-western, western and south-westernmigration and drainage of ore-bearing fluids and favour-



Fig. 13. Mineralized conglomerate ofthe Vargas Member, Minas doCamaqua.

orogenic margins (Fig. 14). The rest of the basin is cleaved for 20 km ahead of the nappe stack between529±16 and 493±17 Ma (Ahrendt et al., 1977). Alongundeformed except where flexural bulging caused uplift

and on- or offlapping unconformities as at Osis and the western basin margin (Gariep Belt), sinistral trans-pressive movement to the south-east caused en echelonKoedoelaagte (Germs & Gresse, 1991). Collision-related

fold-and-thrust fronts advanced into the foreland folding and thrusting into the foreland. West ofVioolsdrif, 20 km east of the Gariep Belt, the Namaenvironment in a south-easterly direction along the sou-

thern margin of the Damara Belt, thrusting Damara Group shows inclined folds verging east, reversed faultingand thrusting with slickenside striations indicating bed-rocks over Nama Group sediments in the Naukluft

Nappe Complex. Nama sediments were folded and ding plane slip in a north-easterly direction. Cleavagedevelopment and folding/thrusting decrease rapidly east-wards and disappear within 10–15 km, that is 30 kmfrom the Gariep margin. This deformation pre-dates theintrusion of the post-orogenic Kuboos granite pluton at525±60 Ma (Allsopp et al., 1979) in the Gariep Belt.

Along the south-western Vanrhynsdorp Basin margina NE-verging fold-and-thrust belt was generated bysinistral transpressive movement towards the south-east.Foreland propagating thrusts advanced up to 40 kminto the Vanrhynsdorp Basin from the present Gariepoverthrust margin (Gresse, 1986, 1995). Penetrative fold-ing and transecting cleavage development extends for30 km into the basin. Cleavage micas were dated at495±2 Ma on average (Gresse et al., 1988), but biotitecooling ages stretch to 476±5 Ma (Gresse et al., 1988).As in the Naukluft Nappes, a Gariep thrust stack withan estimated original thickness of 4–7 km, deduced fromthe regional anchi- to greenschist metamorphic grade,overrode the foreland basin sediments during the 500 Malate Pan-African event. There appears to be a youngingof deformation from #530 Ma in the north-west to#525 Ma in the west and #495 Ma in the south-westand this led Germs & Gresse (1991) and Gresse & Germs(1993) to suggest sequential oceanic closure and collisionfrom north to south, following similar proposals byHalbich et al. (1988), Porada (1989) and Stanistreetet al. (1991).

On the opposing plate in southern Brazil, foreland andmolasse basins developed in retroarc environmentscratonward of back-arc fold-thrust belts (Fig. 15; termi-Fig. 14. Orogenic margins of the Nama foreland basin (after

Gresse & Germs, 1993). nology after Dickinson & Suczek, 1979; Dickinson, 1981;


P. G. Gresse et al.

nology after Klein, 1991). The Marica Formation andBom Jardim Group of the Camaqua Basin were deformedprior to the deposition of the Camaqua Group on anangular unconformity (Fig. 6). The Bom Jardim Groupis constrained by ages of around 568 and 530 Ma forvolcanic rocks near the base and top, respectively(Table 1). It follows that the Marica Formation isprobably older than #570 Ma and the Camaqua Groupyounger than #530 Ma. This is confirmed to a certainextent by the preliminary palaeontological studies ofNetto et al. (1992) according to which the Precambrian–Cambrian boundary should coincide more or less withthe boundary between the Bom Jardim Group and theSanta Barbara Formation. It seems that the last pulse ofdeformation in the back-arc fold-and-thrust belt advancedinto the Camaqua Basin causing W-verging thrust-and-fold deformation along the eastern margin. This may becorrelated with the ±500 Ma event (#530–496 Ma) onthe African side. The Camaqua Group represents a post-orogenic phase that may have been shed into the basinfrom the uplifted Dom Feliciano Belt during intrusionof the youngest granitic phases (post #520 Ma) andtranspressional strike-slip faulting. Biotite cooling ages,related to post-orogenic uplift in the opposing DamaraBelt for instance, range up to #420 Ma (Miller, 1983).

The Itajaı Basin is also bound by a major NE-trendingfault zone along its south-eastern margin. These faultsdisplay normal and dextral strike-slip movement (Fig. 9).NW-verging folding and thrusting in the Itajaı Groupintensify towards this faulted margin (Rostirola, 1991)suggesting that it represents an inverted Dom Felicianoback-arc fold-and-thrust belt as inferred above for theCamaqua Basin. Fold axes in the basin strike NE–SWand beds are often overturned or inverted. Krebs (1992)suggested that the uppermost unit of the Campo AlegreFormation (Fig. 6) represents basal formations over-

Fig. 15. Modelled plate tectonic setting of the foreland basinsthrusted to the north-west during late Dom Felicianoof the Pan-African – Brasiliano collision orogen. (Cross-sectiondeformation. The age of this deformation is looselymodified after model by Dickinson, 1981.)constrained by the intrusive Apiuna (Campo Alegre)rhyolites and the Subida granites ranging from 523±92to 535±22 Ma. These dates suggest that the ItajaıIngersoll, 1988). Present-day exposures of the Camaqua

and Itajaı basins are bounded by NE-striking faults along sediments were deformed around #535 Ma (Basei,1985) like the lower Camaqua succession. Metamorphictheir south-eastern and mostly also their north-western

margins (Figs 5 and 9). These faults are characterized conditions range from anchi-grade to lower greenschistfacies. The fact that the Campo Alegre Basin, someby post-collisional, sinistral and dextral strike-slip move-

ment. The ‘basins’ appear to be faulted remnants of 90 km to the north-west, is undeformed supports thededuction that compressional forces were generated inlarger depositories.

Strike-slip faults form the boundary between the gran- the south-east and only affected foreland depositsimmediately bordering the Dom Feliciano Belt.ite-invested Dom Feliciano Belt and the Camaqua vol-

canosedimentary succession. Some of them probablyrepresent original back-arc thrusts reactivated as strike- DISCUSSIONslip and normal faults during subsequent tectonic escapeand inversion events. The voluminous volcanic and A stratigraphic correlation scheme between the

Vanrhynsdorp, Witputs and Zaris basins of the Namavolcaniclastic component in the basin fill as well as therelated plutonism support a proximal arc (retroarc) set- foreland basin was proposed by Germs & Gresse (1991)

and Gresse & Germs (1993). This correlation is basedting. Faulted fragments of volcanosedimentary rocksoccur far to the east in the Dom Feliciano Belt, rep- on lithology (e.g. Van Zylkop – Nomtsas formations) and

broad sequence stratigraphic considerations and is sup-resenting intra-arc or superposed basin settings (termi-



ported by trace fossil evidence and carbon isotopes (e.g. source area in the adjacent Dom Feliciano Belt andsoutherly directed longitudinal sediment dispersal of theGrootriet Formation – Huns Member). Some reinterpret-

ations regarding the synchroneity of deposits in the Guaritas Formation (Paim et al., 1992) in the forelandbasin. The age of this group is apparently younger thandifferent sub-basins may be required following the work

of Saylor et al. (1995). As might be expected from their #530 Ma, which makes it younger than the uppermostmolassic Fish River Subgroup in the Nama Basindiffering tectonic settings on the subducting and over-

riding plates, respectively, there are no direct strati- (Fig. 12).Deformation of the Nama foreland basin occurred ongraphic correlations possible between the southern

African and southern Brazilian successions. three fronts between #530 and 496 Ma and was directedcratonward, subnormal to orogenic trends. Folding andWithin Brazil, the Marica Formation in the Camaqua

Basin and the Gaspar and Campo Alegre formations of tilting of the Fish River Subgroup occurred south-eastof the Naukluft Nappes at around 530 Ma and thethe Itajaı Basin show some similarities – both starting

with alluvial fan deposits and grading up into deltaic and Bremen (521±6 Ma) and Garub intrusions (491±8 Ma)provide further minimum ages for Fish River sedimen-marine sediments containing tempestites and turbidites.

The Apiuna (Campo Alegre) and Acampamento Velho tation (Table 1). On all three fronts the Nama forelanddeposits were only affected by one orogenic event, slightlyrhyolites represent a younger alkaline acid volcanic phase

emplaced close to the Precambrian–Cambrian boundary, later in the south than in the north. In Brazil the ItajaıBasin sediments were affected by thrusting before theas deduced from trace fossils, in these basins. Some

resedimented conglomerates in the Itajaı Basin consist of intrusion of the Apiuna Rhyolite and Subida Granite.The Gaspar and Campo Alegre formations in the Itajaıwell-rounded and well-sorted polymict conglomerates

composed of red cherts, metaquartzite and granitic Basin and the coeval Marica Formation in the CamaquaBasin were therefore deformed by an event older thanpebbles that are very similar to the Nomtsas- and

Van-Zylkop-type conglomerates in the Nama and #535 Ma (Table 1). This early deformation may becorrelated with a #545 Ma event registered as metamor-Vanrhynsdorp basins, suggesting perhaps a common

source in the elevated collision orogen. phic resetting and intrusion throughout the Damara,Gariep and Saldania belts on the opposing plate.As described here, basins on both sides of the collision

orogen display basal fluvial or alluvial successions overlain A subsequent event, younger than #535 Ma andperhaps related to a general #500 Ma Pan-African event,by shallow-marine, deltaic deposits. The southern African

basins are primarily carbonate-dominated, shallow- led to the deposition of the Camaqua Group in theCamaqua Basin. There is no record of such youngmarine platform deposits (excluding the Vanrhynsdorp

Basin) whereas the southern Brazilian basins are mainly (Ordovician) deposits on the African side, with perhapsthe exception of the molassic Klipheuwel Group inshallow-marine deltaic successions with extensive

volcanic and volcaniclastic components (Table 1). the Saldania Belt along the southern tip of Africa.These sediments post-date the Cape Granite SuiteFurthermore, the Brazilian basins contain widespread

intrusions of post-orogenic granites and rhyolites, and (585–510 Ma) and pre-date the Late Cambrian to EarlyOrdovician base of the Cape Supergroup clastics. Quartzcontain important sediment-hosted stratabound (SSC)

copper deposits, whereas the Nama basins are virtually porphyry dykes with a probable age of 506±10 Ma(Gresse & Scheepers, 1993) intrude the Franschhoekdevoid of magmatic activity and economic mineral

deposits. These differences are clear manifestations of Formation, a possible correlate of the Klipheuwel Group.the peripheral foreland (i.e. subducting plate) vs. retroarcforeland (i.e. overriding plate) settings of the two regions ACKNOWLEDGEMENTS(Fig. 15).

We wish to thank Drs Paim and Stanistreet for veryAs illustrated by the case of the ±900-km-long Namacomprehensive reviews and thought-provoking commentsBasin, and possibly also the remnant Brazilian basins,stemming from their own intimate knowledge of thelateral facies differences are to be expected and will beareas involved, serving to improve the original manuscriptrelated to distinct subenvironments within the unevenlysubstantially.subsiding forelands. In such a scenario the coarse clastic

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Field guide to the Nama, Witvlei and related basins in Received 7 August 1995; revision accepted 15 September 1995.


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Late- to post-orogenic basins of the Pan-African – Brasiliano collision orogen in southern Africa and southern Brazil