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Neoproterozoic to Early Paleozoic Deposits Of

Neoproterozoic to Early Paleozoic Deposits Of

U N I V E R S I D A D D E C O N C E P C I Ó N DEPARTAMENTO DE CIENCIAS DE LA TIERRA 10° CONGRESO GEOLÓGICO CHILENO 2003

IGCP 478: PROVENANCE IN NEOPROTEROZOIC TO EARLY PALAEOZOIC SUCCESSIONS OF SW : THE STATUS QUO AT THE BEGINNING OF A NEW IGCP INTIATIVE

ZIMMERMANN, U.1, FRIMMEL, H.2, GAUCHER, C.3, GERMS, G.1, POIRE, D.4, BLANCO, G.3, GOMEZ PERAL., L.4 and VAN STADEN, A.1

1 Dep. of Geology, RAU University, POB524, Auckland Park 2006, Johannesburg, South , [email protected] 2Univ. of Cape Town, Dep. of Geological Sciences, Rondebusch 7701, , [email protected] 3INGEPA, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay, [email protected] 4CIG, CONICET-UNLP,1 Nº 644, 1900 La Plata, . [email protected]

INTRODUCTION Neoproterozoic to early Paleozoic successions are common on both sides of the southern Atlantic in Brasil, Uruguay and Argentina on the western side and Angola, and South Africa on the eastern side. These successions form part of southwestern Gondwana. Our “provenance” research project is part of the IGCP-Project 478 (Neoproterozoic-Early Paleozoic Events in SW- Gondwana) and focuses on the qualitative and quantitative petrological and geochemical characterization of clastic deposits in combination with biostratigraphy. The purpose of the project is to characterize source areas and depositional loci of clastic sediments in order to reconstruct the paleotectonic evolution (including the assembly) of southwest Gondwana during the Neoproterozoic to early Paleozoic (Fig. 1). The primary study targets are: the Arroyo del Soldado Group in Uruguay, the Sierras Bayas Group in Argentina, the Damara and Gariep Supergroups in Namibia and the Gariep and Malmesbury Supergroups and Nama, Vanrhynsdorp, Klipheuwel and Gamtoos Groups in South Africa. Associated are studies on Neoproterozoic successions on the western border of the Rio de la Plata , the , to understand the evolution of the latter craton better. The mentioned successions contain important fossils from a biostratigraphic and palaeobiologic point of view, and a variety of rock types, such as carbonates, /mudstone intercalations and tillites, locally associated with banded iron formations.

GENERAL AND SAMPLING

1. URUGUAY: ARROYO DEL SOLDADO GROUP (ASG) This lithostratigraphic unit was defined by Gaucher et al. (1996), to include thick (>5000 m) marine shelf deposits, which occur in the Nico Pérez of Uruguay (Fig. 2). The boundaries of the terrane also represent the boundaries of the occurrences of the ASG. To the north, the occurrences of the ASG are covered by Phanerozoic sedimentary units and volcanic rocks of the Paraná Basin. The northernmost outcrops of the Group have been recognized and described by Gaucher (2000) in the so-called Isla Cristalina de Rivera, near the boundary with Brazil. The unit lies with erosional and angular on: (1) a Mesoproterozoic

Todas las contribuciones fueron proporcionados directamente por los autores y su contenido es de su exclusiva responsabilidad. metasedimentary complex (Gaucher et al., 1996), (2) Archean (3.4-2.7 Ga) metasedimentary units (Hartmann et al., 2001); (3) Palaeoproterozoic Rapakivi granites (1784 ± 5 Ma: Heaman, in Bossi et al., 1998) and (4) Puntas del Santa Lucía Batholith (granites, granodiorites and monzogranites) that yielded U/Pb SHRIMP age of 633±12 Ma (Bossi et al., 2001).

The stratigraphy after Gaucher (2000) starts with the Yerbal Formation, which is a siliciclastic, deepening-upward sequence, and is characterized by thin conglomerates and arkoses at the base, passing into green siltstones and banded siltstones at the top. Oxide-facies BIF with up to 30 wt % iron oxides occur at the top of this unit. The Yerbal Formation is concordantly overlain with a sharp contact by the Polanco Formation, which marks the development of a large carbonate ramp in the basin. The unit is characterized by bluish grey to black -dolostone rhythmites, frequent carbonatic tempestites, pure calc-siltites and dolosiltites, and rare oolitic calcarenites. In the shallowest areas of the basin, carbonates of the Polanco Formation are concordantly overlain by conglomerates and arkoses of the Barriga Negra Formation, recording a major regression. This unit passes upwards into and siltstones of the basal Cerro Espuelitas Formation. In the deepest sections, the Polanco Formation shows a direct transition into the Cerro Espuelitas Formation. The latter unit is made up of an alternation of dark shales, thick chert-deposits and oxide-facies BIF with up to 35% magnetite and/or hematite (Gaucher & Schipilov, 1994; Gaucher et al., 1996, 1998). The Cerro Espuelitas Formation is truncated by an erosive surface that probably marks an important regression. The Cerros San Francisco Formation was deposited above this surface, and is characterized by very mature quartz-arenites with wave and current ripples, hummocky cross-stratification and low-angle cross bedding (comp. in Gaucher, 2000). Finally, the Cerros San Francisco Formation passes upwards into stromatolitic and oolitic of the Cerro Victoria Formation, which contains ichnofossils of probable age (comp. in Gaucher, 2000). The ASG has been folded and intruded by granites 540-510 Ma (Bossi and Navarro, 1991), Kawashita et al. (1999)), and syenites during the Cambrian. K-Ar age data of illite-rich pelites belonging to the Group yielded recrystallization ages between 532 ± 16 Ma and 492 ± 14 Ma (in Gaucher, 2000), in accordance with ages obtained for intrusive granites. Considering these ages, the orogenic event that determined deformation of the ASG can be taken as a terminal event of the Brasiliano Megacycle or, more probably, represents a separate (Río Doce Orogeny), recording the collision of a Brasiliano-block (Cuchilla Dionisio Terrane) with a cratonized block, onto which the Arroyo del Soldado-shelf developed.

Biostratigraphy Gaucher (2000) assigns both assemblages of organic-walled microfossils found in the ASG (Leiosphaeridia-Lophosphaeridium and Bavlinella-Soldadophycus) to the upper Vendian Kotlin-Rovno assemblage, characterized worldwide by low diversity, simple leiosphaerids, abundant Bavlinella faveolata, cyanobacterial sheaths, rare small acanthomorphs and vendotaenids of the genera Vendotaenia and Tyrasotaenia. The occurrence of Cloudina riemkeae Germs (1972) in the Yerbal Formation is of great biostratigraphic significance. According to Knoll (1996), the range of Cloudina extends from 565 to 543 Ma, coinciding with the depauperate Kotlin-Rovno acritarch assemblage. U/Pb ages of volcanic ash beds interbedded with fossiliferous, Cloudina-bearing strata of the outlined by Grötzinger et al. (1995), determined support the above mentioned upper limit for the biostratigraphic range of Cloudina.Finally, trace fossils occurring in the Cerro Victoria Formation denote quite complicated and diverse behavioural patterns of the organisms that caused them. Above all, burrows are not confined to bedding planes and are often perpendicular to them, indicating, according to Seilacher (1999), a Cambrian age. Biostratigraphic data thus suggest that most of the

ASG is upper Vendian in age (595-543 Ma). The uppermost units (Cerro Victoria and possibly also the Cerros San Francisco Formation) were deposited in the lowermost Cambrian.

Chemostratrigraphy Gaucher (2000) presents a curve of δ13C variations in carbonates of the Arroyo del Soldado Group, based on the data reported by Boggiani (1998). Kawashita et al (1999) present δ13C data and 87Sr/86Sr for the base of the Polanco Formation. More recently, Gaucher et al. (2002; 2003) report high-resolution C-isotopic profiles of the lower and middle ASG (Yerbal, Polanco and lower Cerro Espuelitas formations). The profiles reveal a series of positive and negative δ13C excursions, which correlate well with published δ13C-curves for the upper Vendian. The upper Yerbal-lower Polanco positive δ13C excursion of +5.3 PDB, along with 87Sr/86Sr ratios of 0.7078, point to an age of ca. 580 Ma for the Yerbal-Polanco transition (Jacobsen & Kaufman 1999, Walter et al. 2000). Finally, Gaucher (2000) suggests that negative values obtained by Boggiani (1998) for the Cerro Victoria Formation could be correlative with the sharp negative excursion recorded in the basal Cambrian worldwide. This has been recently confirmed by a detailed δ13C -curve presented by Gaucher et al. (2003) for the Cerro Victoria Formation, allowing to place the -Cambrian boundary in the upper-middle Cerros San Francisco Formation.The location of the Arroyo del Soldado Group makes it a key unit to unravel the relationships between Vendian to lowermost Cambrian units of southern Brazil, Argentina, Namibia, South Africa and Uruguay. Furthermore, its rich fossil content allows relatively precise age constraints and correlations with other units. Provenance studies will aim to confirm the provenance of Arroyo del Soldado sedimentary rocks from old cratonic areas of the Río de la Plata Craton. Comparison of the provenance of the ASG with other Neoproterozoic (volcano)sedimentary successions occurring in Uruguay is another major goal. These successions include: Lavalleja and Rocha Groups, Las Ventanas, Playa Hermosa and Piedras de Afilar Formations. Some of this units, like the Rocha Group, contain zircon populations with a strong component around 1.0 Ga, which could indicate provenance from the Kalahari Craton (M. Basei, pers.comm., 2003). On the other hand, the Playa Hermosa Formation shows a palaeocurrent pattern suggesting provenance from the Kalahari Craton too. All these hypothesis can be tested by means of detailed provenance studies, and compared to results obtained for the Arroyo del Soldado Group, which is the only Vendian-Cambrian unit demonstrably deposited on the Río de la Plata Craton. Samples from the Arroyo del Soldado and Lavalleja Group have been collected, and ongoing field work will focus on the Rocha Group, Las Ventanas and Playa Hermosa Formations.

2. ARGENTINA Neoproterozoic rocks in Argentina are widely distributed in the country (Fig. 1). However, two key can be described: 1. northwestern and central part of Argentina and 2. Sierra Tandil located in the Province of Buenos Aires (Fig. 3). The outcrops of the so-called Puncoviscana Formation (Turner, 1960) and equivalents (Willner, 1990) in northwestern Argentina are stretched from the Bolivian boundary to Mendoza. Only of marginal interest for our described goal above, the formation can give important information about the tectonic evolution of the western border of the Rio de la Plata Craton during the Neoproterozoic. Unfortunately, several problems are masking the interpretation of the paleotectonic evolution of that part of Gondwana: a detailed lithostratigraphy is unknown, the extent of the formation, the tectonic setting of the deposition as well as the characters of the source areas, and a long lasting discussion is concentrated on the hypothesis if low-grade meta-sedimentary successions are upper-crustal

equivalents of widely distributed medium- to high-grade meta-sedimentary rocks (see Willner, 1990 and Mon & Hongn, 1991). Members of the working group of the IGCP 478 are trying to carry out a first comprehensive data set for the whole formation from the point of a modern provenance analysis.Undeformed, unmetamorphosed siliciclastic rocks combined with carbonates were deposited on a complex in the Sierra Tandil in the south of Buenos Aires (Fig. 3). The stratigraphy was described in detail by Poiré (1987) and starts with the formation of paleosoil on mainly granites and gneissic basement rocks (2.2–1.7 Ga according to Dalla Salda et al. 1988). The Neoproterozoic sedimentary succession is composed of the Villa Mónica, Cerro Largo and Loma Negra formations (Sierras Bayas Group) and the Cerro Negro Formation (Spalletti and Poiré, 2000). Above these formations rests a diamictite of unknown age (Volcán Formation; Spalletti and Del Valle, 1984), by mainly siliciclastic rocks (Balcarce Formation), which are interpreted as deposited during the Upper Cambrian to Lower (Spalletti and Del Valle, 1984). The Sierras Bayas Group and the Cerro Negro Foramtion are grouped into four depositional sequences: Tofoletti (I), Malegni (II) Villa Fortabat (III) and La Providencia (IV) sequences (Spalletti and Poiré, 2000). The oldest depositional sequence (Tofoletti, 52m thick; Fig. 2) is equivalent to the Villa Mónica Formation, and shows two sedimentary facies associations: a) quartz-arkosic arenites at the base and b) dolomites including shallow marine stromatolitic dolomites and shales at the top. The dolomite and facies association (36m thick) is composed of laminated stromatolitic dolomites, interdolomitic green shales and supradolomitic red shales with associated mudstones. Eight sedimentary facies have been recognised along these vertical sections. The dolostones of the Villa Mónica Formation support a very good assemblage of , which is composed of Colonella fm., Conophyton ?resotti, Conophyton fm., Cryptozoon fm., Gongylina fm., Gymnosolem fm., Inzeria fm., Jacutophyton fm., Jurusonia nisvensis, Katavia fm., Kotuikania fm., Kussiella fm., Minjaria fm., Parmites fm., Parmites cf. cocrescens and Stratifera fm. (Spalletti and Poiré, 2000). An 800-900 Ma age for the assemblage of Villa Mónica Formation has been suggested by Poiré (1987), based on -wide stromatolite biostratigraphy e.g. Semikhatov (1976). The 793 +/- 32 Ma Rb/Sr age (Kawashita et al., 1999), for the interpreted diagenesis of Villa Mónica Formation coincide with the proposed age of the stromatolites by Poiré (1987). An unconformity is reported at the base of the second depositional sequence (Malegni, 75 m thick) consists of a basal succession composed of chert breccia, fine-laminated glauconitic shales, and fine-grained , followed by cross-bedded quartz arenites which are in turn covered by siltstones and claystones. This sequence represents a shallowing upward succession from subtidal nearshore to intertidal flat deposits. A depositional age of older than 725±36Ma has been interpreted by Rb/Sr data reflecting early diagenetic ages on whole rock samples (Kawashita et al., 1999). The youngest pre-Vendian depositional sequence (Villa Fortabat) is a 40 m thick unit composed almost exclusively of brownish (lower section) and black (upper) micritic limestones, originated by suspension fall-out in open marine ramp and lagoonal environments, and separated by an unconformity from the underlying deposits. On top of the Sierras Bayas Group a regional unconformity is recognised. This surface has been related to eustatic movements. Meteoric dissolution of the carbonatic sediments is interpreted as a karstic surface on which residual clays and brecciated chert have been accumulated. The Vendian (?) Cerro Negro Formation (La Providencia depositional sequence) appears on top of the mentioned unconformity. The formation is a more than 100 m thick unit characterised by claystones and fine-grained sandstone-claystone intercalations, mainly formed in upper to lower intertidal flats. Radiometric dating for the Cerro Negro Formation on whole rock samples with Rb/Sr proposes an early diagenetic age of around 734±48Ma (Kawashita et al., 1999). Preliminary chemostratigraphic

data were carried out by Valencio et al. (1985). A detailed C-O stratigraphy for both the dolomites and limestones will be presented soon. Unpublished data of the dolomites of the Villa 13 18 Mónica Formation shows excursion of δ CCarb between –0.6‰ and 2.22‰, and δ O between – 2.1‰ and –6.6‰. TOC (total organic carbon) values are between 0.7% and 1.2%, TIC (total inorganic carbon) between 9.3% and 11.9%, TC ranging from 10.2% and 12.8%. The limestones of the younger Loma Negra Formation contain a TOC (total organic carbon) value between – 0.15% and 0.35%, TIC (total inorganic carbon) between 8.4% and 11.3%, TC between 8.4% and 13 18 13 11.6%. δ CCarb between +2.8 and +4.5‰, and δ OCarb between –14.1‰ and –7‰. The δ Corg lies constantly between –27.1 and –28.1‰. This shows a clear shift from more negative δ13C values from the dolomites to positive values for the limestones and stronger negative δ18O values for the limestones. Interpreting the between the different cycles as short time intervals, as the radiometric data show, then both carbonate successions can be seen as a continuous stratigraphic column. A preliminary interpretation, without the necessary diagenetic studies and geochemistry on the rocks, leads to the possibility of a data comparison with the Bambuí Group in Brazil (Sete Lagoas Formation; according to Santos et al. (2000)) with depositional ages around 800 Ma. Comparisons with the C-O excursions after Jacobsen and Kaufman (1999) and Walter et al. (2000) two time intervals are probable: ±740 Ma and ± 840 Ma, respecting the interpretations of the Rb/Sr and stromaolithic age constraints.In several projects the clastic content of the whole stratigraphy will be sampled and under modern provenance approach characterized. We will concentrate on geochemistry and zircon dating to develop more information about the age of the source area and probable changes in source composition, related to erosional factors or regional tectonics. However, biostratigraphic work has to be done and intensified on the rocks to get a more elaborated time-resolution for the deposits.

3. NAMIBIA The Neoproterozoic to early Paleozoic sediments of Namibia mainly occur in the Damara and Gariep orogenic belts, and Nama Group which is associated (related) with these two belts (Fig 4).

The Damara orogenic belt comprises a northern coastal branch, the Kaoko Belt and an inner branch, the Khomas Belt. The Neoproterozoic to early Paleozoic sedimentary rocks of the Kaoko and Khomas Belts are mainly represented by the Damara Supergroup. The platform facies of the Damara Supergroup of the Kaoko Belt and the northern part of the Khomas Belt from the bottom upwards consists of the clastic Nosib, the carbonate-rich Otavi and clastic Mulden Groups, which represent - and drift-related and deposits respectively (Miller, 1983). At least two tillites occur in the Damara Supergroup (Miller, 1983; Kennedy et al., 1998). The platform facies of the Damara Supergroup of the southern part of the Khomas Belt consist of the basal clastic Nosib and overlying carbonate-rich Witvlei Groups (Hegenberger, 1993). The Blaubeker tillite occurs at the base of the Witvlei Group. The Nosib, Witvlei and overlying Nama Groups are considered to represent drift-, rift- and foreland basin deposits forming a major geotectonic cycle (Germs, 1974, 1995).The Neoproterozoic to early Paleozoic sediments of the Gariep Orogenic Belt (Fig. 4) are represented by the Gariep Supergroup. The Gariep Supergroup is represented by two tectono-stratigraphic units namely the allochthonous Marmora Terrane in the west and the para-autochthonous Port Nolloth Group in the east. The youngest age obtained from intrusive rocks of the pre-Gariep basement is 771 ±6 Ma (Frimmel et al., 2001b) implying a maximum age of ca. 771 Ma for the onset of the sedimentation of the Port Nolloth Group. The Port Nolloth Group is subdivided stratigraphically upwards into the predominant clastic

Stinkfontein Subgroup, the diamictite containing Kaigas Formation, the clastic and carbonate- rich Hilda Subgroup and the diamictite and iron-containing Numees Formation overlain by the clastic and carbonate-containing Holgat Formation (Frimmel et al., 2002). The two diamictites occurring in the Port Nolloth Group, i.e. the Kaigas and Numees diamictites, are glaciogenic and respectively correlated with the global ca.750 Ma Sturtian and ca. 580 Ma Marinoan glaciations (Frimmel et al., 2002).The Nama Group (ca. 550 – 535 Ma) unconformable overlies the Gariep Supergroup. The Nama Group is subdivided into three lithological units: the Kuibis, Schwarzrand and Fish River Subgroups. The most prominent unconformities occur at the base of the Kuibis Subgroup, at the bases of the Nomtsas and Vergesig Formations of the upper Schwarzrand Subgroup and at the base of the Fish River Subgroup (Germs, 1983). The Precambrian/Cambrian boundary (± 543 Ma) (Grötzinger et al., 1995) occurs at the base of the Nomtsas Formation (Germs, 1972a, 1974). The detrital sediment supply of the Kuibis Subgroup was predominantly very quartz-rich, whereas the material of the Schwarzrand Subgroup appears predominantly greenish and not as quartz-rich. The sedimentary rocks of the Fish River Subgroup are mostly reddish in colour and more feldspathic. The Kuibis and Schwarzrand Subgroups document depositional environments ranging from braided-stream to subtidal marine conditions. Intertidal to shallow subtidal conditions seem to have prevailed for much of the period during which the lower two subgroups were deposited. In the upper Schwarzrand Subgroup fluvial deposits become increasingly significant and in the Fish River Subgroup they constitute the dominant facies. In southern Namibia a minor glaciation or coldwater period took place during deposition of the lower Schwarzrand Subgroup. A possible second glaciation may have occurred just prior and/or during deposition of the basal Nomtsas Formation (i.e. near the Precambrian/Cambrian boundary). Both “glacial” events correspond with low δ13C isotope ratios (Kaufman et al., 1991). Some volcanic tuffs occur in the Kuibis and Schwarzrand Subgroups (Germs, 1972a, 1974). These have been dated at 548 ± 1Ma (Kuibis Subgroup), 545 –543 ± 1Ma (middle Schwarzrand Subgroup) and 539 ± 1Ma (uppermost Schwarzrand Subgroup) (Grötzinger et. al., 1995). The Nama Group is well known for the occurrence of an fauna in its lower part, and contains important trace fossils (Germs, 1972b, Crimes and Germs, 1982), skeletal fossils such as Cloudina (Germs, 1972c; Grant, 1990) and (Grötzinger et al., 2000) as well as a low diversity assemblage of organic-walled microfossils (Germs et al., 1986). The upper Nama Group is Cambrian in age as indicated by the trace fossil pedum (Germs, 1972b, 1974). The biostratigraphy of the Nama Group is described in Germs (1972a, 1974, 1983, 1995).

The Port Nolloth and Nama Groups form one major geotectonic cycle. The Stinkfontein and Hilda Subgroups of the Port Nolloth Group are rift- and drift-related respectively and the Nama Group accumulated in a foreland basin setting.The Damara (the Khomas and Kaoko) and the Gariep orogenic belts formed as a response to the collisions of the West-Congo, Rio de la Plata and Kalahari (e.g. Stanistreet et al., 1991; Germs, 1995. Biostratigraphic studies and paleocurrent analysis suggest that the Kaoko Belt formed prior to the Khomas Belt and the Khomas Belt prior to the Gariep Belt. The above implies that the West-Congo and the Rio de la Plata cratons collided first, then the West-Congo and Kalahari cratons and finally the Rio de la Plata and Kalahari cratons (Germs 1983, 1995).Our proposed provenance studies intend to decipher the history of these three collisions during the Neoproterozoic to early Paleozoic and establish if magmatic arcs and/or micro were also involved in these collisions. This could be reflected in a change of source compositions and ages, using zircon populations and other single-crystal studies on heavy minerals. It will also be important to determine whether the Fish River sediments with southern and eastern paleocurrents have the same or different

provenance characteristics. Thus far in Namibia only provenance samples of the Nama Group have been taken, whereas data for the Marmora Terrane are in preparation (pers. com. H. Frimmel, 2003).

4. SOUTH AFRICA The Gariep Supergroup and Nama Group in the northwestern part of South Africa are the southern extensions of the Gariep Orogenic Belt and Nama Group in Namibia and are similarly subdivided.Near Vanrhynsdorp (Fig. 4) the correlate of the Gariep Supergroup is named Gifberg Group (Gresse, 1992, De Beer et al., 2002). The Gifberg Group is subdivided into the basal probably glaciogenic diamictitic Karoetjes Kop Formation, the predominantly carbonate- containing Widouw Formation, the predominantly phyllite containing Aties Formation and the upper Blaupoort Formation which comprises the (upper) glacial diamictite. The two diamictites are respectively correlated with the Kaigas and Numees diamictites of the Gariep Supergroup (Frimmel et al., 2002). In the Vanrhynsdorp the correlate of the Nama Group is the Vanrhynsdorp Group. It has been given a different name since it differs lithologically from the classic Nama Group (Germs and Gresse, 1991; Gresse and Germs, 1993). The Vanrhynsdorp Group stratigraphically is subdivided in the Kwanous, Knersvlakte and Brandkop Subgroups (Gresse, 1992; De Beer et al., 2002). The basal Kwanous Subgroup (Flaminkberg Formation) consists predominantly of greyish conglomerates and quartzites. The middle Kwanous Subgroup (Grootriet Formation) predominantly comprises carbonates and the upper Kwanous Subgroup, and the overlying lower and upper Knersvlakte Subgroup greenish sandstones and shales. The first red beds appear locally in the uppermost Knersvlakte Subgroup (Astynskloof Formation). Typical red beds occur in the overlying Brandkop Subgroup. The basal conglomerate (Van Zylkop Formation) of the Brandkop Subgroup is a correlate of the basal Nomtsas conglomerate of the upper Nama Group (Germs and Gresse, 1991). Cherts interpreted as of volcanic origin occur in the Gannabos and Besonderheid Formations of the Knersvlakte Subgroup (Gresse, 1992). The detrital input into the basal Vanrhynsdorp Group (Kwanous Subgroup) were mainly transported from the eastern Kalahari craton. The first evidence of sediment supply from the western Gariep Orogenic Belt can be found in the middle Vanrhynsdorp Group (Besonderheid Formation, middle Knersvlakte Subgroup) according to paleocurrents (Gresse, 1992). Thus far only trace fossils have been found in the Vanrhynsdorp Group. The ichnofauna occurring in this group, similar to that of the Nama Group (Crimes and Germs, 1982), seems to be of low diversity (Gresse, 1992). The Cambrian trace fossils Oldhamia and Treptichnus pedum have been found in the lower Knersvlakte (Gannabos Formation) and middle Knersvlakte Subgroup (Besonderheid Formation). Treptichnus pedum and Monomorphichnus have been reported from the Brandkop Subgroup (Germs, 1983).Provenance samples have been taken in the Vanrhynsdorp region from the Gifberg and Vanrhynsdorp Groups with the aim to reconstruct the collision of the Rio de la Plata and Kalahari cratons.The Saldania Orogenic Belt is a low grade Neoproterozoic to early Paleozoic orogenic belt (Fig. 4) with syn- to post- and anorogenic granoitoids (Rozendaal et al., 1999). It is composed of a number of inliers unroofed in mega- anticlinal hinges of the permo- along the southern tip of South Africa. The main exposure north of Cape Town is known as the Malmesbury Group. This group is subdivided into three by prominent northwest trending and shear zones (Rozendaal et al., 1999). These terranes are from southwest to northeast the Tygerberg, Swartland and Boland Terranes. The highly variable succession of phyllites, greywackes, conglomerates, limestones, cherts and arkosic sandstones of the Malmesbury Group reflect coarse, fluvial-marine, shelf, shore and deltaic sediments, possibly deposited along a highly irregular northeastward transgressive coast line (Rozendaal et al, 1999).

The early Paleozoic Klipheuwel Group may have been accumulated in a late orogenic strike-slip basin (Gresse and Scheepers, 1993).East of Cape Town other small exposures of the Saldania Belt have been preserved (Fig. 4). They are the Kaaimans (Kaaimans Group), Kango (Kango Group) and Gamtoos (Gamtoos Group) Inliers. The Kaaimans Group consists of meta- sedimentary rocks and granites, which reflect a complicated tectonic and metamorphic history (Gresse, 1983; Frimmel and van Achterbergh, 1995). The Kango Group is exposed near Oudtshoorn. The Kango Group is now equivalent to a lower, Precambrian, Cango Caves Group (previously Goegamma Group) and the upper, Cambrian, Kansa Group (Frimmel et al., 2001a). The Cango Caves Group consists of shallow to relatively deep clastics and carbonates and turbidites (Le Roux and Gresse, 1983). The clastic molassic Kansa Group, similar to the Klipheuwel Group, was probably deposited in a late orogenic strike-slip basin (Rozendaal, 1999). The Gamtoos Group is exposed in a mega-anticline in the Port Elizabeth region. The Gamtoos Group is subdivided in tectono-stratigraphic units, which, from the base upwards, are the Lime Bank, Kleinfontein, Kaan and Van Stadens Formations (Hill and Nolte, 1989; Nolte, 1990). Most of these formations are thrust bounded and Nolte (1990) ascribed the Lime Bank Formation to thrust duplication of part of the Kaan Formation. The Lime Bank and Kaan formations are dominated by thick limestone units predominantly intercalated by phyllites. The Kleinfontein Formation mainly consists of phyllite with intercalations of carbonates, quartzites and conglomerates. In contrast the upper molassic Van Stadens Formation is more arenaceous and predominantly consists of cross-bedded arkoses with a discontinuous conglomerate near its base. Mudstones and phyllites are common in the upper part of the Gamtoos Formation. The Van Stadens Formation is probably of early Paleozoic (Cambrian?) age and the formations of the Gamtoos Group stratigraphically below it, of Neoproterozoic age.The Saldania Orogenic Belt is most probably originated by the collision of the Rio de la Plata, Kalahari and cratons. Some magmatic arcs and micro continents may also have been involved in these collisions. The aim of our provenance studies is to reconstruct the assembly of these plates. Thus far, provenance samples have only been taken by us from the Kango and Gamtoos Groups.

CONCLUSIONS Biostratigraphical-, chemostratigraphical- as well as structural data of some Neoproterozoic to early Paleozoic successions of southwestern Gondwana are available but hardly any quantitative source area data exist. The scarcity of the latter data and the large areal extend of lithologically similar Neoproterozoic to early Paleozoic deposits in southwestern Gondwana made us start this provenance project. Various Ph.D. students in and southern Africa are also involved in this provenance project, which is part of the IGCP 478 Project. The provenance project mainly focuses on basin fills and on quantitative petrography, geochemistry (if possible) on whole rock samples and single grains using SEM and microprobe techniques. The facilities available for zircon dating at the Rand Afrikaans University will enable us to determine the age of the provenance areas. The first provenance data will be available in 2003. These data, based on similar data sets, will elucidate the Neoproterozoic to early Paleozoic tectono-magmatic evolution of southwestern Gondwana.

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Figure 1: Outcrop locations related to the here presented project. 1= Arroyo del Soldado (Uruguay), 2=Sierra Bayas (Argentina), 3= Puncoviscana (Argentina), 4=Damara Belt, 5=Gariep Belt and Nama with Vanrhynsdorp successions (Namibia, South Africa), 6= Malmesbury, Gamtoos, Kango, Kaimaans (South Africa) (after Trompette, 1997).

Figure 2: Outcrop locations of the Arroyo del Soldado Group (Uruguay) and Sierra Bayas deposits (Argentina) (after Gresse et al. 1996).

Figure 3: Distribution of the here discussed Neoproterozoic successions in southern Africa (after Trompette, 1997).

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