14
One, two or no record of late neoproterozoic glaciation in South-East Cameroon? V. Caron a,, G. Mahieux a , E. Ekomane b , P. Moussango c , M. Babinski d a FRE 3298 Géosystèmes, Faculté des Sciences, 33 Rue St Leu, 80000 Amiens, France b Laboratoire de Géologie des Ensembles Sédimentaires, Université de Yaoundé I, Cameroon c Centre de Recherche Géologique et Minière, Garoua, Cameroon d Centro de Pesquisas Geocronológicas, Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, São Paulo, SP 05508-080, Brazil article info Article history: Received 7 May 2010 Received in revised form 15 September 2010 Accepted 15 September 2010 Available online 22 September 2010 Keywords: Neoproterozoic Cameroon Marinoan Gaskiers Hirnantian Dolostone abstract Severe climate changes culminating in at least three major glacial events have been recognized in the Neoproterozoic sedimentary record from many parts of the world. Supportive to the global nature of these climatic shifts, a considerable amount of data have been acquired from deposits exposed in Pan- African orogenic belts in southwestern and western Africa. By comparison, published data from the Pan-African belts in Central Africa are scarce. We report here evidence of possibly two glacial events recorded in the Mintom Formation that is located on the margin of the Pan-African orogenic Yaoundé belt in South-East Cameroon. In the absence of reliable radiometric data, only maximum and minimum age limits of 640 and 580 Ma, respectively, can at present be applied to the Mintom Formation. The formation consists of two litho- stratigraphic ensembles, each subdivided in two members (i.e., in ascending stratigraphic order the Kol, Métou, Momibolé, and Atog Adjap Members). The basal ensemble exhibits a typical glacial to post-glacial succession. It includes diamictites comprising cobbles and boulders in a massive argillaceous siltstone matrix, and laminated siltstones followed by, in sharp contact, a 2 m-thick massive dolostone that yielded negative d 13 C values (< 3V-PDB) similar to those reported for Marinoan cap carbonates elsewhere. However, uncertainty remains regarding the glacial influence on the siliciclastic facies because the diamictite is better explained as a mass-flow deposit, and diagnostic features such as dropstones have not been seen in the overlying siltstones. The Mintom Formation may thus provide an example of an unusual succession of non-glacial diamictite overlain by a truly glacial melt-related cap-carbonate. We also report the recent discovery of ice-striated pavements on the structural surface cut in the Mintom Formation, suggesting that glaciers developed after the latter had been deposited and deformed during the Pan-African orogeny. Striations, which consistently exhibit two principal orientations (N60 and N110), were identified in two different localities, in the west of the study area on siltstones of the Kol Member, and in the east on limestones of the Atog Adjap Member, respectively. N60-oriented striae indicate ice flow towards the WSW. Assigning an age to these features remains problematical because they were not found associated with glaciogenic deposits. Two hypotheses can equally be envisaged, i.e., either the striated surfaces are correlated: (1) to the Gaskiers (or Neoproterozoic post-Gaskiers) gla- ciation and represent the youngest Ediacaran glacial event documented in the southern Yaoundé belt; or (2) to the Late Ordovician Hirnantian (Saharan) glaciation, thereby providing new data about Hirnantian ice flows in Central Africa. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Prolonged glaciations and short-living glacial pulses have oc- curred repeatedly at mid- to low latitudes between 750 and 580 Ma, and left their marks on continents formerly within Rodinia (Kennedy et al., 1998; Evans, 2000). Lithostratigraphic and chemo- stratigraphic data from Neoproterozoic rocks provide evidence for two Cryogenian glaciations, during the Sturtian Epoch (ca. 750 Ma; Frimmel et al., 1996) and the Marinoan Epoch (ca. 640 Ma; Hoffmann et al., 2004; Williams et al., 2008), respectively, and for one post-Marinoan glaciation during the Ediacaran referred to as the Gaskiers glaciation at ca. 580 Ma (Bowring et al., 2003; Knoll et al., 2004; Alvarenga et al., 2007). The worldwide distribution of glacial debris associated with these episodes of global refrigeration has led to much controversial proposals of models for partly (Hyde et al., 2000) versus entirely frozen oceans (Hoffman et al., 1998; Hoffman and Schrag, 2002). 1464-343X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2010.09.004 Corresponding author. E-mail address: [email protected] (V. Caron). Journal of African Earth Sciences 59 (2011) 111–124 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci

One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

  • Upload
    v-caron

  • View
    236

  • Download
    10

Embed Size (px)

Citation preview

Page 1: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Journal of African Earth Sciences 59 (2011) 111–124

Contents lists available at ScienceDirect

Journal of African Earth Sciences

journal homepage: www.elsevier .com/locate / ja f rearsc i

One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

V. Caron a,⇑, G. Mahieux a, E. Ekomane b, P. Moussango c, M. Babinski d

a FRE 3298 Géosystèmes, Faculté des Sciences, 33 Rue St Leu, 80000 Amiens, Franceb Laboratoire de Géologie des Ensembles Sédimentaires, Université de Yaoundé I, Cameroonc Centre de Recherche Géologique et Minière, Garoua, Cameroond Centro de Pesquisas Geocronológicas, Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, São Paulo, SP 05508-080, Brazil

a r t i c l e i n f o

Article history:Received 7 May 2010Received in revised form 15 September2010Accepted 15 September 2010Available online 22 September 2010

Keywords:NeoproterozoicCameroonMarinoanGaskiersHirnantianDolostone

1464-343X/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.jafrearsci.2010.09.004

⇑ Corresponding author.E-mail address: [email protected] (V. Ca

a b s t r a c t

Severe climate changes culminating in at least three major glacial events have been recognized in theNeoproterozoic sedimentary record from many parts of the world. Supportive to the global nature ofthese climatic shifts, a considerable amount of data have been acquired from deposits exposed in Pan-African orogenic belts in southwestern and western Africa. By comparison, published data from thePan-African belts in Central Africa are scarce. We report here evidence of possibly two glacial eventsrecorded in the Mintom Formation that is located on the margin of the Pan-African orogenic Yaoundé beltin South-East Cameroon.

In the absence of reliable radiometric data, only maximum and minimum age limits of 640 and 580 Ma,respectively, can at present be applied to the Mintom Formation. The formation consists of two litho-stratigraphic ensembles, each subdivided in two members (i.e., in ascending stratigraphic order theKol, Métou, Momibolé, and Atog Adjap Members). The basal ensemble exhibits a typical glacial topost-glacial succession. It includes diamictites comprising cobbles and boulders in a massive argillaceoussiltstone matrix, and laminated siltstones followed by, in sharp contact, a 2 m-thick massive dolostonethat yielded negative d13C values (<�3‰ V-PDB) similar to those reported for Marinoan cap carbonateselsewhere. However, uncertainty remains regarding the glacial influence on the siliciclastic faciesbecause the diamictite is better explained as a mass-flow deposit, and diagnostic features such asdropstones have not been seen in the overlying siltstones. The Mintom Formation may thus providean example of an unusual succession of non-glacial diamictite overlain by a truly glacial melt-relatedcap-carbonate.

We also report the recent discovery of ice-striated pavements on the structural surface cut in theMintom Formation, suggesting that glaciers developed after the latter had been deposited and deformedduring the Pan-African orogeny. Striations, which consistently exhibit two principal orientations (N60and N110), were identified in two different localities, in the west of the study area on siltstones of theKol Member, and in the east on limestones of the Atog Adjap Member, respectively. N60-oriented striaeindicate ice flow towards the WSW. Assigning an age to these features remains problematical becausethey were not found associated with glaciogenic deposits. Two hypotheses can equally be envisaged,i.e., either the striated surfaces are correlated: (1) to the Gaskiers (or Neoproterozoic post-Gaskiers) gla-ciation and represent the youngest Ediacaran glacial event documented in the southern Yaoundé belt; or(2) to the Late Ordovician Hirnantian (Saharan) glaciation, thereby providing new data about Hirnantianice flows in Central Africa.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Prolonged glaciations and short-living glacial pulses have oc-curred repeatedly at mid- to low latitudes between 750 and580 Ma, and left their marks on continents formerly within Rodinia(Kennedy et al., 1998; Evans, 2000). Lithostratigraphic and chemo-stratigraphic data from Neoproterozoic rocks provide evidence for

ll rights reserved.

ron).

two Cryogenian glaciations, during the Sturtian Epoch (ca. 750 Ma;Frimmel et al., 1996) and the Marinoan Epoch (ca. 640 Ma;Hoffmann et al., 2004; Williams et al., 2008), respectively, andfor one post-Marinoan glaciation during the Ediacaran referred toas the Gaskiers glaciation at ca. 580 Ma (Bowring et al., 2003; Knollet al., 2004; Alvarenga et al., 2007). The worldwide distribution ofglacial debris associated with these episodes of global refrigerationhas led to much controversial proposals of models for partly (Hydeet al., 2000) versus entirely frozen oceans (Hoffman et al., 1998;Hoffman and Schrag, 2002).

Page 2: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Fig. 1. (A) Distribution of alleged Neoproterozoic sedimentary rocks in Africa. (B) Simplified geological map showing the outcropping location of Neoproterozoic stratasurrounding the Congo Craton, including the Mintom Basin in South-East Cameroon.

112 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

There is a considerable amount of data documenting the occur-rence of Neoproterozoic glacial and glacially-influenced eithermarine or terrestrial deposits in the Pan-African orogenic belts ofWest Africa (e.g., Ponsard et al., 1988; Proust and Deynoux,1994; Porter et al., 2004; Deynoux et al., 2006; Alvaro et al.,

West Congo(DRC)

Fouroumbala BasinBakouma

(CAR)

Bang(C

Upper Mixtite Fm.

Cap carbonate

HautShilohangoSubgroup

Lower Tillite Fm. Lower Tillite Fm.

Cap carbonate

BakoumaDolomite

Fm.

Bili Limestone Fm.

Dialinga Fm.

BougboulouSubgroup

Bonda Tillite Fm.

Kembe NakandoSandstone

Mbania pelite

SansikwaSubgroup

BaLimest

Schisto-Calcaire

SubgroupBimbo S

F

Conglo

Pan-

Afric

an O

roge

nyan

d na

ppe

tect

onic

s

Mpioka Molasse

Fig. 2. Lithostratigraphy of Neoproterozoic strata in Central Africa, including the study aCAR: Central African Republic; DRC: Democratic Republic of Congo. The age of the Mintoshown by opposite black arrows.

2007), and southwestern Africa (e.g., Fölling et al., 2000; Föllingand Frimmel, 2002; Halverson et al., 2004). By comparison, pub-lished data from the Pan-African belts located north of the Congocraton in Central Africa are few (Frimmel et al., 2006; Wendorffand Key, 2006; Poidevin, 2007). Little is known about the

ui BasinAR)

Southeast Cameroon(This study)

Cryogenian Tonian

Ediacaran

GaskiersGlaciation(580 Ma)

MarinoanGlaciation(635 Ma)

(660 Ma)Sturtian

Glaciation(750 Ma)

Lower Dja series(Age unknown)

nguione Fm.

andstonem.

merates

?

Min

tom

For

mat

ion

Kol Diamictite ?

MétouDolostone ?

Momiboléargillaceous and

calcareous siltstone

Atog AdjapLimestone

GlacialEvents

rea in South-East Cameroun (modified after Frimmel et al. (2006), Poidevin (2007)).m Formation is not radiometrically constrained, hence its given arbitrary duration is

Page 3: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Fig. 3. (A) Simplified geological map of Cameroon showing major lithotectonic units and location of the study area (arrowed). (B) Lithostratigraphy of the Mintom Formation(Caron et al., 2010). Thicknesses are given according to field observations. Estimated thicknesses from drill cores for the Momibolé and Atog Adjap Members are displayed inbrackets. (C) Geological map of the study area showing distribution of the sedimentary units and striated pavements within and above the Mintom Formation, respectively(complemented and modified after Vanhoutte and Salley (1986), Caron et al. (2010)). Insert shows the A–B transect in C. Vertical scale exaggerated.

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 113

Neoproterozoic deposits fringing the Yaoundé Belt in Cameroon, andit was not until recently that the lithostratigraphy of Neoproterozoicstrata has been described in detail in South-East Cameroon (i.e., theMintom Formation; Figs. 2 and 3; Caron et al., 2010).

Two distinct glaciogenic units have been recognised withinNeoproterozoic formations from the West and the North of theCongo Craton. The Sturtian event is represented by tillites, whichare not capped by carbonate beds, namely the lower Mixtite ofthe West-Congolian Group, the Akwokwo tillite (Lindian) of theeastern Democratic Republic of Congo (DRC), the ‘‘GrandConglomérat’’ in southeastern DRC, and the lower tillite of theFouroumbala Basin in Central African Republic (CAR; Key et al.,2001; Wendorff and Key, 2006; Poidevin, 2007). The Marinoanevent might be represented by the Upper Mixtite Formation ofthe West-Congolian Group (Frimmel et al., 2006) and the thin

Banda tillite of the Fouroumbala Basin (Fig. 2). These are overlainby cap carbonates referred to as the Schisto-calcaire Subgroup inthe West-Congolian Group and the Bakouma dolomites in theFouroumbala Basin (Fig. 2; Frimmel et al., 2006; Poidevin, 2007).Direct evidence of younger glaciogenic deposits recording theGaskiers glaciation have not been documented from the latestNeoproterozoic Formations from eastern DRC to southern Camer-oon. It must be acknowledged, however, that this apparent lackof syn-Gaskiers deposits in Central Africa might be due to the ab-sence of radiometric dating for many glaciogenic sediments recog-nized in the region.

The stratigraphy of the Neoproterozoic deposits in South-EastCameroun (Figs. 2 and 3), formerly referred to as the older lowerDja series and younger upper Dja series, is poorly documented,and their stratigraphic position is uncertain with respect to the

Page 4: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

114 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

neighbouring Neoproterozoic strata in the DRC and CAR. The upperDja series has recently been redefined as the Mintom Formation oflikely late Cryogenian to early Ediacaran age (Caron et al., 2010).Despite the limited extent of outcrops located on the banks ofthe Dja River, four lithostratigraphic units have been recognizedallowing reconstruction of the sedimentary architecture (Fig. 3)and interpretation of the deposits as being either lacustrine or la-goonal, confined in an isolated intracratonic basin (Caron et al.,2010).

This work is focused on the analysis of the basal succession,which includes in ascending stratigraphic order diamictites, lami-nated siltstones and a thin dolostone bed (Fig. 3). Findings of recentfieldwork are reported. In addition, previously unpublished andsome new stable isotopic data are presented. We particularly ad-dress the apparent discrepancy of having a typical glacial topost-glacial sedimentary succession, which in the light of pub-lished works on sedimentology and chemostratigraphy of Neopro-terozoic glacial deposits elsewhere could originate in the lateCryogenian (Marinoan Epoch) glaciation, and the absence of somediagnostic glaciogenic features in the deposits such as facetedclasts and dropstones.

We further document the recent discovery of striated pave-ments on top of the Mintom Formation, and discuss the possiblecorrelation of this younger glacial event to either the Late Neopro-terozoic Gaskiers glaciation or a post-Neoproterozoic glaciation,namely the Ordovician Hirnantian glaciation.

2. Analytical procedures

The major element concentrations of samples were investigatedwith inductively coupled plasma-atomic emission spectroscopy(ICP-AES). Samples were subjected to an alkaline fusion in theLiBO2 and the remaining material was treated with HCl. About5 ml of filtered fusion solution was subsequently diluted with35 ml of HNO3, and these quantities were doubled or tripled forstandards and drift corrector. The recovered solutions were ana-lyzed on a Vista Pro (Varian) device.

Isotopic analysis for Pb composition of the Momibolé Membercarbonates were carried out at the Center of Geochronological Re-search, University of São Paulo, and followed the proceduresdescribed by Babinski et al. (1999). Only the second leachate (L2)was analyzed. Samples were loaded with silica-gel and phosphoricacid onto Re filaments and the isotopic compositions were deter-mined on a VG 354 multicollector mass spectrometer. Pb isotopicratios were corrected for a mass fractionation factor of 0.10%amu�1 determined based on analyses of Common Pb StandardNBS 981 done during, and previously to, this work. Blanks were84 pg and had negligible effect on measured isotopic compositions.Isochron age was determined using the Isoplot software (Ludwig,1999); errors are reported at 95% confidence level.

Three samples were collected from weakly fractured portions ofthe Métou dolostone and powdered for carbon and oxygen isotopeanalysis at the National Museum of Natural History. Carbonatesamples weighing 25 to 50 mg were reacted for 180 s with 100%phosphoric acid at 70 �C in individual vessels in an automatedcryogenic distillation system (Kiel IV device) interfaced with aDelta V Advantage isotope ratio mass spectrometer. Analytical pre-cision is 0044% for d18O and 0013% for d13C. Delta (d) values are re-ported relative to the international PDB standard.

3. Geological setting and stratigraphy

The main geological features of Central Africa are intimatelyrelated to the late Neoproterozoic Pan-African orogeny, and consistin Cameroon of stacked south-verging thrust nappes, which

collectively constitute the Yaoundé Fold Belt, also referred to asthe Oubanguide Fold Belt in CAR (Fig. 1). Rocks in the belts aremetasedimentary and volcano-sedimentary (various schists andgneisses, migmatites, amphibolite and quartzite), and metapluton-ic (gabbro, garnet–pyroxene bearing diorite and granitoids). Insouthern Cameroon, the Yaoundé nappe was thrust directly ontothe Congo Craton, whereas in the Lomié region, the Yaoundé nappewas thrust over the Dja series composed of schists and dolerite, theage of which has not been precisely established (Fig. 1; Poidevinand Pin, 1986; Vicat et al., 1997). The Mintom Formation, whichforms the Neoproterozoic infill of the Mintom Basin located imme-diately north of the northernmost limit of the Congo Craton in thearea (Fig. 3A), is geologically part of the Yaoundé belt (Fig. 1), andas such underwent deformation and metamorphism during thePan-African orogeny (Vanhoutte and Salley, 1986; Caron et al.,2010). The southward vergence of folds together with evidencethat the succession has been locally either metamorphosed undergreenschist-facies conditions or is unmetamorphosed (Caronet al., 2010), are of particular importance as they provide some rel-ative age constraints in the absence of reliable radiometric dating(see below).

Recent geochronological and structural studies have indeeddemonstrated that the Pan-African orogeny in Central Africa hasa multi-stage deformation history, characterized between 640and 580 Ma by two major phases of tectonic shortening referredto as D1–D2 (ca. 640–620 Ma) and D3 (ca. 620–600 Ma), with dif-fering directions of broadly west–east and north–south, respec-tively (Toteu et al., 2004). Ages obtained from granitoids andmetaplutonic rocks indicate that the onset of nappe tectonicswas likely diachronous westward and northward, starting at ca.660–640 Ma in the Lomié region, ca. 620–600 Ma in the Yaoundéregion, and ca. 600–580 Ma near Bafia (Fig. 3A; Toteu et al., 2004,2006). In either sector of the belt, however, metamorphic assem-blages indicate that the nappe tectonics was initiated underhigh-grade conditions reaching the granulite facies in the deepernappes, and ended under medium to low-grade greenschist-faciesconditions in the shallowest nappes (Nédelec et al., 1986; Pin andPoidevin, 1987; Nzenti et al., 1988; Penaye et al., 1993; Toteu et al.,2001). Collectively, these data provide a minimum age for the Min-tom Formation of 580 Ma and a maximum age of 640 Ma (Caronet al., 2010). Unfortunately, this age interval of 120 Ma could notbe refined using the Pb–Pb isochron method. The age of528 ± 150 Ma obtained from six carbonate samples of the Momi-bolé Member is not reliable. The isotopic ratios are extremelyhomogenous (207Pb/204Pb = 15.8–16.5) and may represent post-depositional disturbance, and widespread resetting of the Pb isoto-pic system, possibly in relation to either the Pan-African metamor-phism and orogeny, or late tectonic activity allowing circulation ofpolluted fluids from basement rocks. Rehomogeneization of the Pbisotope system and incorporation of old Pb into carbonates via per-colating thermal fluids have thus been envisaged elsewhere toexplain the wide range of Pb–Pb isochron ages determined onNeoproterozoic carbonate rocks (Babinski et al., 1999; Trindadeet al., 2004).

The sedimentary successions within the Mintom Formationhave formally been subdivided in four lithostratigraphic units,which are, in ascending order: the Kol Member and the MétouMember, followed by the Momibolé and Atog Adjap Members(see Figs. 2 and 3). The latter depositional couplet lacks evidenceof open marine conditions as reported from Neoproterozoic car-bonates in Central Africa such as stromatolitic and oolitic facies,and cross-stratified beds (e.g., Poidevin, 1977; Alvarez, 1995;Alvarez et al., 1995). It has instead been interpreted as a shallow-ing-upward lacustrine or lagoonal succession from laminated silt-stone with slumps, to cm- to dm-scale bedded limestone withmicrobial mats, evaporitic pseudomorphs, and fenestrae fabrics

Page 5: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 115

(Caron et al., 2010). As the aim of this paper is to document anddiscuss the possible record of glacial events in the Mintom basin,our work will be focused on: (1) the lower Kol and Métou Mem-bers, which strikingly resemble Neoproterozoic glaciogenic andpost-glacial deposits reported from all around the world; and (2)striated pavements identified in two sectors of the study area.

4. The Kol and Métou Members succession

Field investigation along the Dja River and also up streams pe-netrating the tropical forest permitted to locate a few tens of out-crops that exceptionally extended for more than a hundred squaremeters. The lower part of the Mintom Formation is restricted to thewestern sector of the study area (Fig. 3C), and was not intersectedduring the drilling campaign of Vanhoutte and Salley (1986) in thecentre of the basin. These limitations have complicated establish-ment of stratigraphic relations between facies, and particularlyrecognition of bounding contacts. However, outcrop-based faciesanalysis, complemented by petrographic description of representa-tive samples, made it possible to define three distinct facies thatrecord contrasted depositional conditions.

4.1. Lithofacies of the Kol Member

The Kol Member includes a basal diamictite grading upwardsinto laminated siltstone.

The diamictite consists of a massive to crudely stratified boul-der-rich deposit resting unconformably upon the Congo craton(Fig. 3). The single outcrop found on the western outskirt of theMintom basin is 5 m-thick. The section begins with structurelessdiamictite consisting of pebble- to boulder-sized clasts of gneiss

Fig. 4. Examples of some typical lithologies of the Kol and Métou Members at the basewithin the diamictite (white arrows) and the unconformable contact with the underlyinbedded Kol siltstone overlying the basal diamictite. (C and D) Typical outcrop features ofbrown dolospar laminae in D (arrowed). Scale is 20 cm high.

and quartzite in a silty matrix. Clasts are mostly sub-rounded torounded (Fig. 4A). Elongate pebbles occur but no preferential ori-entation could be estimated due to the absence of outcrop surfacesparallel to stratification that may have allowed orientation mea-surements. The diamictite is normally graded and passes upwardinto boulder-poor diamictic argillite. Towards the top of the sec-tion the matrix includes randomly scattered pebbles, and appearsfaintly laminated.

Outcrops of the overlying laminated siltstone facies occur spo-radically down river from the previous site, and are typicallypoorly exposed. The best section is located at the mouth of theMétou River (Fig. 3C). Although the contact with the basal faciesof the Mintom Formation has not been directly observed, it is likelyrapidly transitional based on facies similarities between the top ofthe diamictite and the overlying siltstone.

The siltstone facies is brown to dark grey, finely laminated withlaminae parallel planar, and thinly bedded from cm to dm thick inplaces (Fig. 4B). Current-related features, scours or tidal troughcross-beds are absent. Neither outsized clasts nor evidence of bio-logical activity, such as microbial mats and stromatolites, havebeen found. Composition of the siltstone facies consists mostly ofillite, subsidiary CaCO3, and rare detrital quartz (Caron et al.,2010). Petrographic features include alternating infra-millimetricmicrocrystalline translucent laminae and dark clayey cryptocrys-talline centimetric planar layers. Occasional dolomite rhombs (ca.50 lm) occur together with rare manganese dendrites.

4.2. Palaeoenvironmental interpretation

Caron et al. (2010) suggested that the Kol Member diamictite isa subaqueous massive flow deposit emplaced in a toe-of-slope

of the Mintom Formation. (A) Kol Diamictite. Note the rounded quartzite bouldersg Congo craton (black arrows). (B) Stair-case folded (arrows), laminated and thinlythe Métou dolostone showing tectonic folding in C (white line and black arrow), and

Page 6: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

116 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

setting rather than a glaciogenic deposit, based on the followinglines of evidence: (1) the apparent absence of preferential orienta-tion of clasts; (2) the fining-upward, gradational succession frombasal diamictite to laminated siltstone facies; (3) the absence ofoutsized clasts in the siltstones; (4) missing faceted or striatedclasts; (5) the local rather than extrabasinal provenance of quartz-ite and gneiss clasts in the diamictite (Fig. 3); and (6) the massiverather than stratified structure of the Kol diamictite.

In addition, the observed sedimentologic and petrographic fea-tures of the overlying laminated siltstone interval support calmdepositional conditions below wave influence or in environmentsdevoid of current activity allowing settlement of fine particles insuspension, which are compatible with toe-of-slope settings wheremass-flows are deposited.

4.3. Lithofacies of the Métou Member

The Métou Member sits within finely laminated siltstone bedbelow and above, namely the Kol Member and Momibolé Member,respectively (Figs. 2 and 3). The contact between the Kol Memberand the Métou Member has not been observed. The latter is patch-ily distributed along the Métou River (Fig. 2), and is typicallypoorly preserved (Fig. 4C and D). Although, the stratigraphic con-tact with the overlying Momibolé Member has not been directlyrecognized (Fig. 3), it is likely sharp, though possibly rapidly tran-sitional, based on outcrop features and contrasted facies attributesbetween the deposits. The Momibolé Member siltstone consists ofrhythmically alternating centimetre-scale cream calcareous andbrown to purple argillaceous beds. The rhythmic interval becomesupwards progressively enriched in carbonate layers, which arelocally disturbed by slumps and display symmetrical ripples.

Fig. 5. Transmitted (A) and cathodoluminescent (B) light photomicrographs of the Métoufracture of the red luminescent brecciated dolomicrite exhibits a deep red luminescence

Table 1Major element concentrations and stable isotope ratios for the Métou Member dolostone. Mthe analysed samples.

Sample Si (ppm) Al (ppm) Fe (ppm) Mn (ppm) Mg (ppm) Ca (ppm

07MET1 253 79 66 5 117200 20610007MET2 262 86 50 5 117200 21020007MET3 383 80 51 4 115100 192900

The thickness of the Métou Member at the type section isapproximately 2 m. Rocks are pale-yellow to pinkish white, faintlylaminated in places, but appear more commonly massive due toweathering. Cross-stratifications, such as trough or planar obliquebedding, have not been recognized. The Métou Member is textur-ally a dolomicrite and locally a dolomicrosparite that is character-istically brecciated (Fig. 5). Faint peloidal textures are present indolomicritic facies.

The diagenetic microstratigraphy, established using transmittedlight microscopy complemented by cathodoluminescent petrogra-phy, has enabled identification of successive porosity-occludingand porosity-opening phases as follow: (1) brecciation and fissuring;(2) precipitation of deep red luminescent dolomicrospar followed bydolospar; (3) precipitation of yellow luminescent mosaic calcite(Fig. 5); (4) solution producing corroded irregular outer crystalboundaries; and (5) precipitation of quartz mosaics.

The occurrence of macrocrystalline dolomite precipitates infractures between breccia indicates circulation of dolomitizingfluids, and suggests that the dolomicritic texture of the MétouMember may not be primary but instead could have resulted fromdolomitization of microcrystalline calcite or aragonite during eitherearly or burial diagenesis.

d13C values range between �3.6‰ and �3.4‰. Samples werenot analysed for 87Sr/86Sr due to low Sr contents, typically<60 ppm (Table 1). Prior to envisaging comparison of these resultswith other reported d13C and d18O values from neighbouring Neo-proterozoic deposits, the degree of post-depositional alteration inrelation to either meteoric diagenesis, dolomitization or metamor-phism must be evaluated. Various authors have provided parame-ters for assessing whether carbonates retained their primarycomposition or were diagenetically modified (e.g., Brand andVeizer, 1980, 1981; Banner and Hanson, 1990; Kaufman et al.,

Member dolomicrite. First generation of dolomicrospar and dolospar cement (do) in, whereas the following stage of calcite cementation (ca) is yellow luminescent.

n/Sr < 0.1, Fe/Sr < 2 and d18O > �8‰ suggest non-altered carbon isotope signatures in

) Sr (ppm) Na (ppm) Mn/Sr Fe/Sr d13C (‰/PDB) d18O (‰/PDB)

54 7 0.09 1.2 �3.326 �7.37883 1 0.06 0.6 �3.517 �7.14485 1 0.05 0.6 �3.364 �6.883

Page 7: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 117

1993). Particularly, carbonate samples with d13C ratios close to pri-mary composition were found to have low Mn/Sr and Fe/Sr ratiosof <3 and <50 respectively, and d18O values >�10‰ (Jacobsenand Kaufman, 1999; Fölling and Frimmel, 2002). The MétouMember dolostone samples yielded Mn/Sr < 0.1, Fe/Sr < 2 andd18O > �8‰ (Table 1), suggesting non-altered carbon isotopesignatures in the analysed samples.

The relatively low d18O values and trace element contents mayindicate that dolomitization of the Métou Member was neither re-lated to the percolation of seawater nor derived from 18O-enrichedevaporitic brines (Warren, 2000; Melim and Scholle, 2002), butinstead that the diagenetic fluid may have been meteoric.However, there is no evidence of subaerial exposure of the MétouMember prior to the deposition of the overlying MomiboléMember. Further investigation must be carried out in order toaddress this discrepancy.

4.4. Palaeoenvironmental interpretation

In addition to the lack of current- and wave-generated sedimen-tary structures, including hummocky cross-stratifications, indica-tors of subaerial exposure and/or shallow-water environments,such as desiccation structures, evaporitic pseudomorphs, fenestraefabrics, oolitic and stromatolitic facies are absent. The presence ofoccasional peloids is not particularly informative because of theiruncertain origin, though likely microbial (Riding, 2000), and theirwide environmental spectrum, from marine to continental. Collec-tively the aformentioned attributes suggest deposition of theMétou Member below storm wave base. The micritic texture ofthe sediments is consistent with suspension settling of micriteand low energy conditions, while fine-grained peloidal laminaecould originate in episodic sediment input by turbidity currents.

The brecciated microfacies has been interpreted as result fromdifferential strain response to compaction during early burial be-tween the Métou Member micritic sediments and the underlyingKol Member siltstone unit (Caron et al., 2010).

5. Is a glacial to post-glacial origin for the Kol-Métou depositsplausible?

The occurrence of diamictites containing polygenic faceted andstriated clasts, and associated features such as striation and/ordeformation of underlying beds, constitutes an undisputable indica-tor of glacial influence in relation to either an ice-sheet cover or thepassage of glaciers (Deynoux, 1985; Williams, 1996; Rodrigues-Nogueira et al., 2003; Evans et al., 2006).

However, if it happens that one or more of these features are ab-sent from the sedimentary deposit, as is the case for the Kol Mem-ber diamictite, then its glaciogenic origin can be questioned andalternative genetic processes can be envisaged, the most commonones being gravity-driven (Schermerhorn, 1974). It follows thatcomplementary criteria must be sought to allege a glaciogenic ori-gin for sedimentary successions that include diamictite.

In this regard, many Neoproterozoic strata around the worldhave yielded remarkable lithostratigraphic records of global glaci-ations that include not only truly glacial deposits, but also sedi-ments produced during glacier retreat, and the ensuing rise ofsea level. Thus, Neoproterozoic glacial to post-glacial conditions,particularly during the late Cryogenian, are generally embodiedby a recurring lithostratigraphic pattern that consists in ascendingorder of glacial diamictites, siltstones containing dropstones, andcarbonate strata termed ‘‘cap carbonates’’ (e.g., Kennedy, 1996;Hoffman et al., 1998; Prave, 1999; James et al., 2001; Kennedyet al., 2001; Halverson et al., 2004; Alvaro et al., 2007; Corsettiet al., 2007).

However, this tripartite stratigraphy is not always complete,and cap carbonates may locally or regionally sit on non-glacialdeposits, either marine or terrestrial (e.g., Deynoux, 1982; Jameset al., 2001), including diamictites lacking robust evidence for aglacial origin (e.g., Calver and Walter, 2000; Corsetti et al., 2007).It follows that despite interpretation of the diamictite and lami-nated siltstone interval defining the Kol Member as a mass-flowdeposit, the likelihood of a glacial influence on the overlying dolo-stone cannot be totally ruled out, and must be addressed on thebasis of sedimentological and geochemical data.

5.1. Discussion

In most published models, Neoproterozoic cap carbonates areshown to form at the end of global glacial events, the melting of iceand glaciers promoting changes of seawater properties that fa-voured carbonate precipitation (Shields, 2005). A consequence ofthis intimate relation with large-scale deglaciation and ensuingtransgression is that cap carbonates constitute event marker bedspotentially distributed over several continents (Knoll et al., 2004,2006; Williams et al., 2008) and, notwithstanding some local varia-tions, are stunningly similar in sedimentary attributes and stableisotope composition. Table 2 summarizes the Métou Memberdolostone properties compared with those of true cap carbonatesand non-glacial carbonates documented from various localities inAfrica and elsewhere. Although not lying on glacigene rocks, theMétou Member dolostone shares many more sedimentary attributeswith cap carbonates, than with interglacial Neoproterozoic carbon-ates documented in Central Africa for example. Such depositstypically accumulate on ramps bearing oolitic shoal crests and evap-oritic lagoons, with common microbially laminated muddy sedi-ments, domal stromatolites, tidal rhythmites, seafloor-precipitatedfans, evaporitic pseudomorphs, and occasional microfossils (e.g.,Poidevin, 1977; Proust and Deynoux, 1994; Alvarez, 1995; Frimmelet al., 2006).

By contrast, the thickness, colour, fine-scale lamination andfine-crystal size of the Métou Member dolostone resemble thosedescribed from dolostone strata interpreted as deep-water, off-shore-to-basinal cap carbonates, deposited below wave influence(Kennedy, 1996; James et al., 2001; Shields, 2005). However,some features often associated with cap carbonates, such as pseu-do-tepee structures, and seafloor precipitates such as barite andaragonite fans in overlying limestone units, have not been recog-nized (Table 2). This discrepancy may be explained by: (1) thelimited extent of the Métou Member dolostone outcrops; and(2) the absence of limestones sitting upon the Métou Memberdolostone, but instead the occurrence of poorly calcareoussiltstones.

Chemostratigraphic studies have revealed the temporal varia-tion of C and Sr isotopes in seawater through the NeoproterozoicEra (e.g., Halverson et al., 2005), which enables characterizationof post-glacial transgressive carbonates and distinction of glacialevents.

A common feature to Neoproterozoic cap carbonates is the re-cord of pronounced negative d13C excursions in contrast to thehighly positive d13C values that characterize much of Neoprotero-zoic time (Fig. 6; Kennedy et al., 1998; Fairchild and Kennedy,2007). These characteristics have been used to correlate otherwisebiostratigraphically and radiometrically poorly- or unconstrainedNeoproterozoic strata (e.g., Kaufman et al., 1997; Kennedy et al.,1998; Porter et al., 2004). Inspite of recent interrogations on thereliability of stable carbon isotopes for chemostratigraphic correla-tion (Frimmel, 2010), due for example to some fundamental prob-lems in the interpretation of negative d13C anomalies (Knauth andKennedy, 2009), the approach may prove successful at least on aregional scale.

Page 8: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Table 2Sedimentary properties of the Métou Member dolostone compared with those of true cap carbonates and non-glacial carbonates documented from various localities in Africa andelsewhere. This comparison shows that the Métou dolostone shares many more attributes with Neoproterozoic cap carbonates than with other Neoproterozoic non-glacialcarbonates. CAR: Central African Republic. DRC: Democratic Republic of Congo.

Sedimentary attributes Neoproterozoic cap carbonates Métou Dolostone (This study) Neoproterozoic non-glacial carbonates in Central Africa

Stratigraphic position Above glacially-influenced rock:– glacial diamictites (tillites)– laminated siltstones with dropstones

Above non-glacial diamictite-laminated siltstone coupletinterpreted as mass-flow depositsin a toe-of-slope setting

Above:– cap carbonates (Schisto-Calcaire Subgroup in DRC)– pelitic facies (Haut Shiloango limestone in DRC)– sandstones (Bangui Limestone in CAR)

Thickness Typically a few metres, but up to a fewtens of metres

2 m Tens up to hundreds of metres thick

Sedimentary structures Thinly laminated (mm- to cm-scale) Faintly laminated (cm-scale) Trough and hummocky cross-stratificationsNormal or reverse grading of beds Massive Tidal rhythmitesOccasional hummocky cross-stratifications

Brecciated Tempestites and carbonate turbidites

Brecciated SlumpsPresence of pseudo-tepee structures Dessication cracks, brecciation

Colour Pale brown, pinkish Pinkish to greyish white Dark grey, creamy, brownishMineralogy Dolomite and occasional calcite

(primary)Dolomite Calcite, aragonite, dolomitized limestone

Sediments Microcrystalline (dolomicrite) andminor macrocrystalline (dolospar)

Microcrystalline (dolomicrite)and minor macrocrystalline(dolospar) in fractures

Oolitic, oncolitic, and peloidal grainstone and packstone

Peloids Occasional peloids Evaporitic pseudomorphs after gypsumMinor siliciclastic contents Variable amounts of siliciclastic contents (sand and gravel

beds, conglomerates intercalated)Low organic content

Fossil content Stromatolitic domes and tubes possible None Frequent stromatolitic and microbially-induced structuresMicrobial films common Occasional to common microfossils

Diagenesis Likely dolomitization of primary calcite Likely dolomitization of primarycalcite

Complex, includes seafloor precipitates

Silicification Silicification Common evidence of subaerial exposure and karstdevelopment

Does not obliterate primary structures DolomitizationDepositional environment Typically below wave base but peritidal

environments possibleBelow wave base In inner to outer ramp settings

Peritidal and lagoonal evaporite settingsFrequently above wave base under storm influence

Stable isotope composition d13C negative anomaly d13C < �3‰ From slightly negative to more typical positive d13C values�6‰ < d13C < �1‰

Nature of overlying beds Condensed barite-bearing horizons Laminated argillaceous siltstonewith slumps developing upwardsinto bedded lacustrine orlagoonal limestone

Glacial diamictites (Mixtite supérieure above the HautShiloango limestones in DRC)

Seafloor aragonite fans Sandstones and schists (Mpioka Subgroup above theSchisto-Calcaire Subgroup in DRC)

Transgressive siltstonesThick limestones forming ramps andcomprising warm water oolitic,stromatolitic and evaporitic facies

118 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

The negative d13C anomaly around �3.5‰ of the Métou Mem-ber dolostone is characteristic of cap carbonates worldwide, andon a regional scale is similar to that of the cap carbonate bed floor-ing the Schisto-Calcaire Subgroup of the West-Congolian Group(�3‰ < d13C < �1‰; Frimmel et al., 2006), the Bwipe cap dolo-stone in the Volta Basin (�3.7‰; Nédélec et al., 2007), and thecap dolostone of the Bowal Member in the southwestern TaoudéniBasin (�6.4‰ < d13C < �2.3‰; Shields et al., 2007) (Fig. 6). Not-withstanding the limitations of the chemostratigraphic approachacknowledged earlier, the above lines of evidence may providesupport for the interpretation of the Métou Member dolostone asa ‘‘cap carbonate’’ unit. If correct, then to which glaciation does itbelong?

5.2. Age of the Métou (cap) dolostone

In the absence of reliable radiometric data, the age of theMintom Formation, bracketed between 580 and 640 Ma, can onlybe speculated upon. Within this time interval, cap carbonates thatformed during the global ice meltdown following the late Cryoge-nian (Marinoan) and Ediacaran (Gaskiers) glaciations (Figs. 2 and6) are potential correlatives with the Métou (cap) dolostone. The

age may nevertheless be further constrained when comparison ismade with neighbouring Neoproterozoic strata. As previouslymentioned, Gaskiers glaciogenic deposits are not known from east-ern DRC to southern Cameroon. Instead, Marinoan glacial units aremore frequent (Fig. 1). In particular, the Métou dolostone comparesremarkably with the cap dolostones identified at the base of theSchisto-Calcaire Subgroup of the West Congo belt in DRC (Alvarez,1995), and the Bakouma dolomites in the Fouroumbala basin inCAR (Figs. 1 and 2; Poidevin, 2007). The proposed correlation ofthe Métou Member dolostone to Marinoan cap carbonates maybe subject to caution because, unlike these units, the former doesnot develop into a carbonate ramp with abundant stromatolitesand oolitic facies, but instead is overlain by about 70 m of shallow-ing-upward laminated siltstones with slumps and wave-ripples.However, interpretation of these deposits as lagoonal or lacustrinesediments confined into an isolated intracratonic basin, possiblyepisodically subject to marine influence (Caron et al., 2010), satis-factorily explains the contrasted facies attributes described herein.

In conclusion, correlation of the Métou (cap) carbonate with thelate Cryogenian deglaciation event, following the Marinoan ice age,is favoured until better age constraints are available for Neoprote-rozoic strata in Central Africa.

Page 9: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

δ31

)BDP‰(

C

0

-5

-10

10

5

Tonian Cryogenian Ediacaran

850 800 750 700 650 600 550Age (Ma)

Age window for the Mintom Fm.

Western Africa

STU

RTI

AN G

LAC

IATI

ON

MAR

INO

AN G

LAC

IATI

ON

GAS

KIER

SGLA

CIA

TIO

N

NamibiaSouth Congo CratonWest Congo Craton Vingerbreek Event

Shuram-Wonoka anomaly

Fig. 6. Compilation of carbon isotope data from various sources (in grey – modifiedafter Fairchild and Kennedy, 2007). Some values reported from African capcarbonates are displayed as symbols with their geographical area indicated in theupper left corner. Horizontal dashed line within the age box for the MintomFormation indicates the carbon isotope data yielded by samples of the Métoudolostone.

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 119

6. A new glacial striation record in Central Africa

We report in the following section the recent discovery of twosets of glacial striae on rock surfaces of the Mintom Formation,and discuss their correlation to either the Gaskiers or the Hirnan-tian glaciation.

6.1. Characteristics of the striated pavements

Striations are present in two localities about 30 km apart in theeastern and western sector of the study area, respectively (Fig. 3).They were not found associated with glaciogenic deposits. Rocksbearing striated pavements include laminated siltstones of theKol Member and bedded limestones of the Atog Adjap Member(Fig. 3). Striated surfaces are not intercalated between sedimentarydeposits but instead occur atop low relief erosional surfaces cutinto rock substrates. The abrasion features interpreted to be of gla-cial origin consist of: (1) polished and smoothened surfaces (Fig. 7Aand D); (2) sets of parallel straight striae a few millimetres deepand tens of centimetres in length (Fig. 7C and G), locally superim-posed on shallow grooves from 5 to 10 cm large (Fig. 7B and F); (3)faceted outcrops with their upper surface polished and striae in-scribed on their lateral facets (Fig. 7G); (4) stair-cased groovestructures up to 20 cm in size exhibiting small-scale stoss- andlee-side topography (Fig. 7E); and (5) crosscutting relationshipsbetween striae with marked different orientations (Fig. 7H).

Orientations of striae and glacial grooves were systematicallymeasured, and indicate two principal N60 and N110 orientations(Fig. 7), remarkably identical in both localities where striated pave-ments were identified. The direction of ice flow could be deter-mined with confidence from the N60 striations, using stair-casedstoss- and lee-side features (Vorren, 1979), but remains uncertainfor the N110 striations in the absence of robust criteria. N60 striaefound at the western site indicate ice flow towards the WSW(Fig. 7E). The following ice-flow sequence can be established fromthe eastern outcrop: N60 striae truncate N110 striae (Figs. 3 and7H).

6.2. Discussion

The identical striae orientations measured in the two study sitesdemonstrate that the striated pavements are correlated.

Striated pavements in the Mintom Basin do not fit in the variousmodels of soft striated surfaces, i.e., striated surfaces that formedby subglacial erosion and scouring following the passage of gla-ciers, icebergs or sea ice over unlithified frozen sediments(Deynoux and Ghienne, 2004). By contrast the glacial abrasion fea-tures reported here formed on hard lithified surfaces as indicatedby the following lines of evidence: (1) there is no indication of softsediment deformation associated with the striations (Visser,1990); (2) striations are not interstratified as would be expectedfrom intraformational décollement surfaces in subglacial unlith-ified deforming beds (Deynoux and Ghienne, 2004); (3) observedpolished surfaces are more likely to develop on lithified substratesbeneath sliding ice than on unlithified, even frozen, sediments; and(5) grooves and internal striae at the western outcrop crosscut tec-tonic fractures (Fig. 7C).

Ice-flow related glacial striae that truncate striae indicative ofolder flows have been reported from particularly widespread gla-cial landform systems (e.g., the North American Laurentide IceSheet; Veillette et al., 1999; Janson et al., 2002). Two hypothesescan be envisaged to account for the observed crosscutting relation-ships. Either the N60 and N110 striae indicate ice-flow directionalchanges during a single glacial event, or they record distinct glacialperiods. Veillette et al. (1999) documented from northern Québec asequence of striated facets characterized by not only differingice-flow directions, but also by differential ferro-manganese stain-ing, the older stained striated facets being truncated by youngerunstained striations. They interpreted the staining as a record ofdeglaciation separating two glacial ice-flow events. Such stainingis not present in the first generation of striae found atop the Min-tom Formation outcrops. Although it is possible weathering mighthave been low in a hypothetical interglacial period, this character-istic suggests instead that both sets of striae formed during thesame glaciation. In addition, the older N110 striae are not onlypresent on protected facets of outcrops but occur also on the sameerosional surfaces as their N60 counterparts (Fig. 7H). This obser-vation satisfies the hypothesis of moderate erosional processesduring a single glaciation. Indeed, in the case of two glaciations,erosion during glaciers retreat, interglacial exposure to surficialprocesses, and new glaciers advance would have probably obliter-ated older glacial abrasion features present on moderately hardsubstrates. This interpretation is strengthened by the fact thatthe preservation potential of glacial abrasion features was lowerupon the Mintom Formation argillaceaous siltstones (Kol Member)and limestones (Atog Adjap Member) than it was upon the graniticbedrocks in Québec.

6.3. Age of the striated pavements

Ice-striated pavements on the structural surface formed by theMintom Formation suggest that glaciers developed after the latterhad been deposited and deformed during the Pan-African orog-eny. Age of the glacial abrasion features must therefore be580 Ma, the minimum age of the Neoproterozoic deposits in theMintom Basin, or younger. Notwithstanding minor pulses ofcooling, four major post-Marinoan cooling events, associated withabundant glaciogenic deposits and glacial landforms, have beenrecognized, namely the Ediacaran Gaskiers glaciation, the LateOrdovician Hirnantian glaciation also referred to as the Saharanglaciation, the Permo-Carboniferous Gondwanan glaciation, andthe various low to high-frequency Cenozoic cooling events. Inaddition, evidence exist for possibly two Neoproterozoic post-Gaskiers glaciations, namely the Vingerbreek event at or around

Page 10: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Fig. 7. Examples of glacial abrasion features from striated pavements discovered in the western (photos A–F – Kol siltstone) and eastern (G and H – Atog Adjap limestone)sector of the Mintom Basin (Fig. 3). (A) Polished surface with shallow groove (white arrow). (B) Set of parallel striae superimposed on shallow groove about 5 cm large. (C)Smoothened surface. (D) Thin, shallow, and straight striae oriented N110 upon Kol siltstone. White arrows point to fractures crosscut by striae. (E) Stair-cased striated groovestructures oriented N60. Stoss- and lee-side topography of the abrasion feature indicates palaeo-ice flow towards the WSW (black arrow). (F) About 20 cm large set of parallelstriae oriented N60. (G) Low relief faceted outcrop of Atog Adjap limestone with its upper surface polished (upon which geologist sits), and its lateral facets striated (thickwhite arrows). Note that N110 orientation compares with that of striations from previous outcrop located about 30 km upstream (Fig. 3C). (G) Crosscutting relationshipsbetween N65 and N110 striations allow the sequence of ice flow to be established (as indicated).

120 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

the Precambrian/Cambrian boundary (Germs, 1995; Gaucher et al.,2004), and the Shuram-Wonoka anomaly between 555 and551 Ma (Fig. 2; Condon et al., 2005; Halverson et al., 2005; Fikeet al., 2006).

Palaeogeographic reconstructions based on the extent of gla-cially-influenced marine and terrestrial sediments indicate thatneither the Permo-Carboniferous nor the Cenozoic ice sheetsreached the Central African region (e.g., Crowell, 1999; Eyles,

Page 11: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Fig. 8. Geographical distribution of Ediacaran glacial deposits worldwide showing location of the Mintom Basin. Radiometrically constrained rocks are indicated as fullcircles. Empty circles are uncertain assignments or poorly constrained data. Full stars locate some Neoproterozoic post-Gaskiers glacial deposits (Germs, 1995; Bowring et al.,2003; Calver et al., 2004; Condon et al., 2005; Gaucher et al., 2004, 2005; Fairchild and Kennedy, 2007; Trindade and Macouin, 2007).

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 121

2008). This leaves the 580 Ma Gaskiers, the latest Neoproterozoic,and the 440 Ma Hirnantian glacial events as possible source forthe abrasion features atop the Mintom Formation, unless theywere produced by Pan-African mountain-type syn-orogenic gla-ciers. In the absence of glacial deposits associated with the striatedpavements from the Mintom Basin, correlation to any of the afore-mentioned events remains highly speculative.

No direct glacial influence has been documented from the latestNeoproterozoic Formations from eastern DRC to southern Camer-oon (Fig. 8; Poidevin, 2007). Provided that the short-lived GaskiersIce Sheet expanded over the actual Central African region, glacialinfluenced facies may either have been eroded or have not yet beenidentified due to the lack of detailed geological mapping in this areaand robust age constraints for the known glaciogenic facies. In addi-tion, there is apparently no expression of Ediacaran glaciation in thefar better documented western African Taoudéni and Volta Basins(Deynoux et al., 2006), and in the West Congo region (Frimmelet al., 2006). In the latter example, however, it is noticeable thatthe late Neoproterozoic glacial diamictites, such as the Upper Mix-tite Formation (Fig. 2), have not been dated. In Africa, syn-Gaskiersglacial deposits, robustly constrained by radiometric data, are re-stricted to the Gariep Belt in Namibia (Fig. 8; Gaucher et al.,2005). It is beyond the scope of this paper to discuss why glacial fea-tures are more frequent in regions formerly in Laurentia and Balticathan in Africa or South America (Fig. 8). This question remains to beaddressed, but various controlling factors must have combined toaccount for the distribution of the Gaskiers glaciation occurrences,including palaeogeography for the latitudinal distribution of land-masses and subsequent development of ice covers, and regionaltectonics for the creation of depocentres and preservation of glacialremnants (Trindade and Macouin, 2007; Eyles, 2008).

The same critical questions apply to the post-Gaskiers coolingevents. Attribution of known glacial deposits to either one of thelatest Neoproterozoic glaciations cannot unequivocally be madein the absence of good U–Pb zircon age data.

The sedimentary records of the Late Ordovician (Hirnantian)glaciation are dominated by glacio-fluvial and fluvio-deltaic silici-clastic facies (e.g., Ghienne, 2003), and include various palaeo-iceflow indicators such as impressive striated surfaces in Lybia,

Mauritania, Algeria, and Saudi-Arabia (Fig. 9; Beuf et al., 1971;Vaslet, 1990; Deynoux and Ghienne, 2004). Palaeomagnetic dataindicate that the Hirnantian palaeo-South Pole was located in wes-tern Central Africa (Smith, 1997), and that the Ordovician ice sheetexpanded outward from the sub-Saharan region, reaching Arabia,South Africa, and central South-America (Fig. 9; Scotese et al.,1999). However, there is still uncertainty regarding the extent ofthe Hirnantian ice-sheet over Gondwana, and it is unclear as towhether the inland ice developed during a single or a multistageglaciation. For example, identification of at least two major subgla-cial striated erosion surfaces bounding Hirnantian glacial depositsfrom northern Africa and South Africa has been interpreted torecord two pulses of ice-sheet growth possibly tuned on orbitalcycles (Sutcliffe et al., 2000). Published data on Palaeozoic glacialdeposits in Central Africa are particularly scarce, and their attribu-tion to a given glaciation faces the same difficulties as for the gla-cial features in the Mintom Basin, i.e., lack of microfossils andabsence of reliable radiochronology. Censier and Lang (1992)reported on the occurrence of glacio-fluvial sediments in CAR,containing faceted clasts and flattened pebbles, to which they as-signed a lower Silurian to Carboniferous age interval. They deducedthe direction of ice flow towards the north after identification ofthe sediment source south of their study site. This south-northdirection contrasts markedly with our own measurements on theglacial striae in Cameroon. This may indicate that either: (1) thenorthward path envisaged by Censier and Lang (1992), which isbased on sediment provenance but not on physical evidence ofice flow, is not correct; (2) the glacial features are correlated butpoint to regional differences in ice movements; and (3) the MintomBasin and CAR records relate to distinct glaciations. We have noargument in favour or against either of these hypotheses, exceptthat the ice flow towards the WSW measured in Cameroon is com-patible with the directions of ice-sheet advance from Central Africaduring the Hirnantian glaciation (Fig. 9).

On this basis and the hypothetical absence of glacial featuresassociated with the Neoproterozoic Gaskiers and post-Gaskiersglaciations in Central Africa, we favour with due caution correla-tion of the striated pavements in the Mintom Basin to the LateOrdovician glaciation.

Page 12: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

Arabia

SouthAmerica

OutcroppingHirnantian glacialdeposits

Hirnantianice flow

Sequence of ice flow insoutheast Cameroon

minimum scenario maximum scenario

2500 km

Direction of ice flow knownunknown

Extent of Hirnantian Ice Sheet

2 3

1 Successive position of the Ordovician south pole

Pakhuis

Cancaniri

Gondwana highlands

1

?This study

This study

Fig. 9. Palaeogeographic reconstruction of Gondwana and ice-sheet extent during the late Ordovician glaciation showing palaeo-ice flow indicators (e.g., Beuf et al., 1971;Vaslet, 1990; Scotese et al., 1999; Deynoux and Ghienne, 2004). Note that ice-flow data collected from the Mintom Basin are compatible with the existing Hirnantian ice-flowdirections and location of a geographic South Pole located in western Central Africa (Smith, 1997). Question marked black arrow: ice-flow direction from Censier and Lang(1992) for (?) Silurian or Carboniferous glacial strata in Central African Republic.

122 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

7. Conclusions

The results of the present study are twofold:

(1) The Mintom Formation of late Neoproterozoic age(ca. 640–580 Ma) contains a basal diamictite–siltstone–dolostone sedimentary succession, which resembles that ofglacially-influenced Neoproterozoic strata documentedworldwide. However, the deposits identified in the MintomBasin differ from the typical interpretative pattern in beingnot fully glacial. The basal diamictite-siltstone couplet isbetter explained as a mass-flow deposited in a toe-of-slopesetting than as a glaciogenic diamictite. By contrast, thedolostone bed is virtually identical to other late Cryogenian(Marinoan Epoch) cap carbonates in Central Africa andelsewhere. It records a negative d13C anomaly around�3.5‰ that compares with values reported from Marinoancap carbonates in the Central African Republic (base ofBakouma dolomite), and in the Democratic Republic ofCongo (base of Schisto-Calcaire Subgroup). In spite of theabsence of radiochronometric data, we preliminary interpretthe dolostone unit to be a glacial Marinoan cap carbonate.The Mintom Formation thus provides example of an unusualsuccession of non-glacial diamictite overlain by a trulyglacial melt-related cap-carbonate.

(2) Glacial striated pavements of unknown age have been iden-tified that truncate two stratigraphically distinct sedimen-tary units of the Mintom Formation, thereby indicatingthat glacial abrasion occurred after the Pan-African nappe

tectonics and subsequent deformation of the study deposits.Striations, showing consistent N60 and N110 orientations,were not found associated with glaciogenic strata. Knownextensions of post-580 Ma glacial ice sheets in Central Africaseem to rule out the possibility that the glacial features arecorrelated with the Permo-Carboniferous and CenozoicGlacio-Epochs. This leaves the latest Neoproterozoic Gask-iers, post-Gaskiers, and late Ordovician (Hirnantian) glacialevents as possible correlatives. We favour with due caution,i.e., until better age constraints are available, correlationwith the Hirnantian glaciation because: (a) there is so farno record of the Gaskiers and post-Gaskiers glaciations inthe widespread and better exposed Neoproterozoic stratafrom western Africa (Taoudéni Basin) and the West Congobelt (West Congo Group); and (b) the palaeo-ice flowtowards the WSW, measured on the N60 striations, is com-patible with the directions of ice-sheet advance from CentralAfrica during the Hirnantian glaciation.

The recent discovery of glacial features in South-EastCameroon adds to the known occurrences of Neoproterozoic gla-cial deposits in Central Africa, and to the Marinoan Epoch isotopestratigraphy. In addition, we report on striated pavements, whichcould constitute the first evidence of either the Gaskiers or theHirnantian glaciation around the Yaoundé-Oubanguide Belt.However, in the absence of robust radiometric constraint, thequestion remains open as to whether one or two Neoproterozoicglacial records (i.e., Marinoan and Gaskiers) are preserved inSouth-East Cameroon.

Page 13: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124 123

Acknowledgements

We thank Joël Ughetto for stable isotope analysis at theNational Museum of Natural History.

Accommodation at Mékoto was kindly provided by PhilémonZo’o Zame from the Bureau of Economical, Technical and FinancialAffairs. Contribution of Marie-Laure Dufossé towards organizationof the fieldtrip to Cameroon is gratefully acknowledged. We aregrateful to H.E. Frimmel and an anonymous reviewer, as well asassociate editor S. Muhango, who kindly reviewed and improvedthis manuscript.

References

Alvarenga, C.J.S., de Figueiredo, M.F., Babinski, M., Pinho, F.E.P., 2007. Glacialdiamictites of Serra Azul Formation (Ediacaran, Paraguay belt): evidence of theGaskiers glacial event in Brazil. Journal of South American Earth Sciences 23,236–241.

Alvarez, P., 1995. Evidence for a Neoproterozoic carbonate ramp on the northernedge of the Central African craton: relations with Late Proterozoic intracratonictroughs. Geologische Rundschau 84, 636–648.

Alvarez, P., Chauvel, J.-J., Van Viet-Lanoë, B., 1995. Obruchevella, cyanobactériefossile du Protérozoïque supérieur du Congo. Implications sur l’âge dugroupe Schisto-calcaire et de la glaciation fini-Protérozoïque. Comptes Rendusde l’Académie des Sciences Paris 320, 639–646.

Alvaro, J.J., Macouin, M., Bauluz, B., Clausen, S., Ader, M., 2007. The Ediacaransedimentary architecture and carbonate productivity in the Atar cliffs, Adrar,Mauritania: palaeoenvironments, chemostratigraphy and diagenesis.Precambrian Research 153, 236–261.

Babinski, M., Van Schmus, W.R., Chemale, F., 1999. Pb–Pb dating and Pb isotopegeochemistry of Neoproterozoic carbonate rocks from the São Francisco basin,Brazil: implications for the mobility of Pb isotopes during tectonism andmetamorphism. Chemical Geology 160, 175–199.

Banner, J.L., Hanson, G.N., 1990. Calculation of simultaneous isotopic and traceelement variations during water–rock interaction with application to carbonatediagenesis. Geochimica et Cosmochimica Acta 54, 3123–3137.

Beuf, S., Biju-Duval, B., De Charpal, O., Rognon, P., Gariel, O., Bennacef, A., 1971. Lesgrés du Paléozoïque inférieur au Sahara. Institut Français du Pétrole, Technip,Paris, vol. 18, 464 p.

Bowring, S., Mysrow, P., Landing, E., Ramezani, J., Grotzinger, J., 2003.Geochronological constraints on terminal Neoproterozoic events and the riseof metazoans. Geophys. Res. Abstr., EGS Nice, 13219.

Brand, U., Veizer, J., 1980. Chemical diagenesis of a multicomponent carbonatesystem: 1. Trace elements. Journal of Sedimentary Petrology 50, 1219–1236.

Brand, U., Veizer, J., 1981. Chemical diagenesis of a multicomponent carbonatesystem: 2. Stable isotopes. Journal of Sedimentary Petrology 51, 987–997.

Calver, C.R., Black, L.P., Everard, J.L., Seymour, D.B., 2004. U–Pb zircon ageconstraints on late Neoproterozoic glaciation in Tasmania. Geology 32, 893–896.

Calver, C.R., Walter, M.R., 2000. The late Neoproterozoic Grassy Group of KingIsland, Tasmania: correlation and palaeogeographic significance. PrecambrianResearch 100, 299–312.

Caron, V., Ekomane, E., Mahieux, G., Moussango, P., Ndjeng, E., 2010. The MintomFormation (new): sedimentology and geochemistry of a Neoproterozoic, Paralicsuccession in south-east Cameroon. Journal of African Earth Sciences 57, 367–385.

Censier, C., Lang, J., 1992. La Formation glaciaire de la Mambéré (RépubliqueCentrafricaine): reconstitution paléogéographique et implications à l’échelle duPaléozoique africain. Geologische Rundschau 81, 769–789.

Condon, D., Zhu, M., Bowring, S., Wang, W., Yang, A., Jin, Y., 2005. U–Pb ages fromthe Neoproterozoic Doushantuo Formation, China. Science 308, 95–98.

Corsetti, F.A., Stewart, J.H., Hagadorn, J.W., 2007. Neoproterozoic diamictite-capcarbonate succession and d13C chemostratigraphy from eastern Sonora, Mexico.Chemical Geology 237, 129–142.

Crowell, J.C., 1999. Pre-Mesozoic Ice ages: their bearing on understanding theclimate system. Geological Society of America Memoir 192, 106 p.

Deynoux, M., 1982. Periglacial polygonal structures and sand wedges in the LatePrecambrian glacial formations of the Taoudeni Basin in Adrar of Mauritania(West Africa). Palaeogeography Palaeoclimatology Palaeoecology 39, 55–70.

Deynoux, M., 1985. Terrestrial or waterlain glacial diamictites? Three case studiesfrom the Late Precambrian and Late Ordovician glacial drift in West Africa.Palaeogeography Palaeoclimatology Palaeoecology 51, 97–141.

Deynoux, M., Affaton, P., Trompette, R., Villeneuve, M., 2006. Pan-African tectonicevolution and glacial events registered in Neoproterozoic to Cambrian cratonicand foreland basins of West Africa. Journal of African Earth Sciences 46, 397–426.

Deynoux, M., Ghienne, J.-F., 2004. Late Ordovician glacial pavements revisited: areappraisal of the origin of striated surfaces. Terra Nova 16, 95–101.

Evans, D.A.D., 2000. Stratigraphic, geochronological, and paleomagnetic constraintsupon the Neoproterozoic climatic paradox. American Journal of Science 300,347–433.

Evans, D.J.A., Phillips, E.R., Hiemstra, J.F., Auton, C.A., 2006. Subglacial till: formation,sedimentary characteristics and classification. Earth-Sciences Review 78, 115–176.

Eyles, N., 2008. Glacio-Epochs and the supercontinent cycle after 3 Ga: tectonicboundary conditions for glaciation. Palaeogeography, Palaeoclimatology,Palaeoecology 258, 89–129.

Fairchild, I.J., Kennedy, M.J., 2007. Neoproterozoic glaciation in Earth System.Journal of the Geological Society, London 164, 895–921.

Fike, D.A., Grotzinger, J.P., Pratt, L.M., Summons, R.E., 2006. Oxidation of theEdiacaran ocean. Nature 444, 744–747.

Fölling, P.G., Frimmel, H.E., 2002. Chemostratigraphic correlation of carbonatesuccessions in the Gariep and Saldania Belts, Namibia and South Africa. BasinResearch 14, 69–88.

Fölling, P.G., Zartman, R.E., Frimmel, H.E., 2000. A novel approach to double-spikePb–Pb dating of carbonate rocks: examples from Neoproterozoic sequences insouthern Africa. Chemical Geology 171, 97–122.

Frimmel, H.E., 2010. On the reliability of stable carbon isotopes for Neoproterozoicchemostratigraphic correlation. Precambrian Research, doi:10.1016/j.precamres.2010.01.003.

Frimmel, H.E., Klötzli, U., Siegfried, P., 1996. New Pb–Pb single zircon ageconstraints on the timing of Neoproterozoic glaciation and continental break-up in Namibia. The Journal of Geology 104, 459–469.

Frimmel, H.E., Tack, L., Basei, M.S., Nutman, A.P., 2006. Provenance andchemostratigraphy of the Neoproterozoic West Congolian Group in theDemocratic Republic of Congo. Journal of African Earth Sciences 46, 221–239.

Gaucher, C., Sial, A.N., Blanco, G., Sprechmann, P., 2004. Chemostratigraphy of thelower Arroyo del Soldado Group (Vendian, Uruguay) and palaeoclimaticimplications. Gondwana Research 7, 715–730.

Gaucher, C., Frimmel, H.E., Germs, G.J.B., 2005. Organic-walled microfossils andbiostratigraphy of the upper PortNollothGroup (Namibia): implications for thelatest Neoproterozoic glaciations. Geological Magazine 142, 539–559.

Germs, G.J.B., 1995. The Neoproterozoic of southwestern Africa, with emphasis onplatform stratigraphy and paleontology. Precambrian Research 73, 137–151.

Ghienne, J.F., 2003. Late Ordovician sedimentary environments, glacial cycles, andpost-glacial transgression in the Taoudeni Basin, West Africa. Palaeogeography,Palaeoclimatology, Palaeoecology 189, 117–145.

Halverson, G., Hoffman, P.F., Schrag, D.P., Maloof, A.C., Rice, A.H.N., 2005. Toward aNeoproterozoic composite carbon isotope record. Bulletin Geological Society ofAmerica 117, 1181–1207.

Halverson, G.P., Maloof, A.C., Hoffman, P.F., 2004. The Marinoan glaciation(Neoproterozoic) in northeast Svalbard. Basin Research 16 (3), 297–324.

Hoffman, P.F., Schrag, D.P., 2002. The snowball earth hypothesis: testing the limitsof global change. Terra Nova 14, 129–155.

Hoffmann, K.-H., Condon, D.J., Bowring, S.A., Crowley, J.L., 2004. U–Pb zircon datefrom the Neoproterozoic Ghaub Formation, Namibia: constraints on Marinoanglaciation. Geology 32, 817–820.

Hoffman, P.F., Kaufman, A.J., Halverson, G.P., Schrag, D.P., 1998. A Neoproterozoicsnowball earth. Science 281, 1342–1346.

Hyde, W.T., Crowley, T.J., Baum, S.K., Peltier, R.W., 2000. Neoproterozoic ‘Snowball’simulations with a coupled climate/ice-sheet model. Nature 405, 425–429.

Jacobsen, S.B., Kaufman, A.J., 1999. The Sr, C and O isotopic composition ofNeoproterozoic seawater. Chemical Geology 161, 37–57.

James, N.P., Narbonne, G.M., Kyser, T.K., 2001. Late Neoproterozoic cap carbonates:Mackenzie Mountains, northwestern Canada: precipitation and global glacialmeltdown. Canadian Journal Earth Sciences 38, 1229–1262.

Janson, K.N., Kleman, J., Marchant, D.R., 2002. The succession of ice-flow patterns innorth-central Québec-Labrador, Canada. Quaternary Science Reviews 21, 503–523.

Kaufman, A.J., Jacobsen, S.B., Knoll, A.H., 1993. The Vendian record of Sr- and C-isotopic variations in seawater: implications for tectonics and paleoclimate.Earth and Planetary Science Letters 120, 409–430.

Kaufman, A.J., Knoll, A.H., Narbonne, G.M., 1997. Isotopes, ice ages, and terminalProterozoic earth history. Proceedings of the National Academy of Sciences ofthe USA 94, 6600–6605.

Kennedy, M.J., 1996. Stratigraphy, sedimentology and isotope geochemistry ofAustralian Neoproterozoic post glacial cap dolostones: deglaciation, d13Cexcursions, and carbonate precipitation. Journal of Sedimentary Research 66,1050–1064.

Kennedy, M.J., Christie-Blick, N., Prave, A.R., 2001. Carbon isotopic composition ofNeoproterozoic glacial carbonates as a test of paleoceanographic models forsnowball Earth phenomena. Geology 29, 1135–1138.

Kennedy, M.J., Runnegar, B., Prave, A.R., Hoffmann, K.H., Arthur, M.A., 1998. Two orfour Neoproterozoic glaciations? Geology 26 (12), 1059–1063.

Key, R.M., Liyungu, A.K., Njamu, F.M., Somwe, V., Banda, J., Mosley, P.N., Armstrong,R.A., 2001. The western arm of the Lufilian Arc in NW Zambia and its potentialfor copper mineralization. Journal of African Earth Sciences 33, 503–528.

Knauth, L.P., Kennedy, M.J., 2009. The late Precambrian greening of the Earth.Nature 460, 728–731.

Knoll, A.H., Walter, M.R., Narbonne, G.M., Christie-Blick, N., 2004. A new period forthe geologic time scale. Science 305, 621–622.

Knoll, A.H., Walter, M.R., Narbonne, G.M., Christie-Blick, N., 2006. The EdiacaranPeriod: a new addition to the geologic time scale. Lethaia 39, 13–30.

Ludwig, K.R., 1999. User’s manual for Isoplot/Ex Version 2. A geochronologicaltoolkit for Microsoft Excel. Berkeley Geochronological Center Spec. Publ. 1a,Berkeley, CA, USA, 47 p.

Page 14: One, two or no record of late neoproterozoic glaciation in South-East Cameroon?

124 V. Caron et al. / Journal of African Earth Sciences 59 (2011) 111–124

Melim, L.A., Scholle, P.A., 2002. Dolomitization of the Capitan Formation forereeffacies (Permian, west Texas and New Mexico): seepage reflux revisited.Sedimentology 49, 1207–1227.

Nédélec, A., Affaton, P., France-Lanord, C., Charrière, A., Alvaro, J., 2007.Sedimentology and chemostratigraphy of the Bwipe Neoproterozoic capdolostones (Ghana, Volta Basin): a record of microbial activity in a peritidalenvironment. Comptes Rendus Geosciences 339, 223–239.

Nédelec, A., Macaudière, J., Nzenti, J.P., Barbey, P., 1986. Evolution métamorphiqueet structurale des schistes de Mbalmayo (Cameroun). Implications pour lastructure de la zone mobile panafricaine d’Afrique centrale, au contact ducraton du Congo. Comptes Rendus de l’Académie des Sciences, Paris 303, 75–80.

Nzenti, J.P., Barbey, P., Macaudière, J., Soba, D., 1988. Origin and evolution of the latePrecambrian high-grade Yaoundé gneisses (Cameroon). Precambrian Research38, 91–109.

Penaye, J., Toteu, S.F., Van Schmus, W.R., Nzenti, J.P., 1993. U–Pb and Sm–Ndpreliminary geochronologic data on the Yaoundé series, Cameroon: re-interpretation of the granulitic rocks as the suture of a collision in the‘‘Centrafrican belt’’. Comptes Rendus de l’Académie des Sciences Paris 317, 789–794.

Pin, C., Poidevin, J.L., 1987. U–Pb zircon evidence for a Pan-African granulite faciesmetamorphism in the Central African Republic. A new interpretation of high-grade series of the northern border of the Congo craton. Precambrian Research36, 303–312.

Poidevin, J.L., Pin, C., 1986. 2 Ga U–Pb zircon dating of Mbi granodiorite (CentralAfrican Republic) and its bearing on the chronology of the Proterozoic of centralAfrica. Journal of African Earth Sciences 5, 581–587.

Poidevin, J.-L., 1977. Les formations du Précambrien supérieur de la region deBangui (République centrafricaine). Bulletin de la Société Géologique de France18, 999–1003.

Poidevin, J.-L., 2007. Stratigraphie isotopique du strontium et datation desformations carbonatéess et glaciogéniques néoprotérozoïques du nord et del’ouest du craton du Congo. Comptes Rendus Geosciences 339, 259–273.

Ponsard, J.F., Roussel, J., Villeneuve, M., Lesquer, A., 1988. The Pan-African orogenicbelt of southern Mauritanides and Northern Rokelides (Southern Senegal andGuinea, West Africa): gravity evidence for a collisional suture. Journal AfricanEarth Sciences 7, 463–472.

Porter, S.M., Knoll, A.H., Affaton, P., 2004. Chemostratigraphy of Neoproterozoic capcarbonates from the Volta Basin, West Africa. Precambrian Research 130, 99–112.

Prave, A.R., 1999. Two diamictites, two cap carbonates, two d13C excursions, tworifts; the Neoproterozoic Kingston Peak Formation, Death Valley, California.Geology 27 (4), 339–342.

Proust, J.N., Deynoux, M., 1994. Marine to non-marine sequence architecture ofintracratonic glacially related basin. Late Proterozoic of the West Africanplatform in western Mali. In: Deynoux, M.M., Miller, J.M.G., Domack, E.W., Eyles,N., Fairchild, I.J., Young, G.M. (Eds.), Earth’s Glacial Record. Cambridge Univ.Press, pp. 121–145.

Riding, R., 2000. Microbial carbonates: the geological record of calcified bacterial-algal mats and biofilms. Sedimentology 47, 179–214.

Rodrigues-Nogueira, A., Riccomini, C., Nóbrega-Sial, A., Veloso-Moura, C., Fairchild,T., 2003. Soft-sediment deformation at the base of the Neoproterozoic Puga capcarbonate (southwestern Amazon craton, Brazil): confirmation of rapidicehouse to greenhouse transition in snowball Earth. Geology 31 (7), 613–616.

Schermerhorn, L.J.G., 1974. Late Precambrian mixtites: glacial and/or nonglacial?American Journal of Science 274, 673–824.

Shields, G.A., 2005. Neoproterozoic cap carbonates: a critical appraisal of existingmodels and the plumeworld hypothesis. Terra Nova 17, 299–310.

Shields, G.A., Deynoux, M., Culver, S.J., Brasier, M.D., Affaton, P., Vandamme, D.,2007. Neoproterozoic glaciomarine and cap dolostone facies of thesouthwestern Taoudéni Basin (Walidiala Valley, Senegal/Guinea, NW Africa).Comptes Rendus Geosciences 339, 186–199.

Scotese, C.R., Boucot, A.J., McKerrow, W.S., 1999. Gondwanan palæogeography andpalæclimatology. Journal of African Earth Sciences 28, 99–114.

Smith, A.G., 1997. Estimates of the Earth’s spin (geographic) axis relative toGondwanaland from glacial sediments and palaeomagnetism. Earth-SciencesReviews 42, 161–169.

Sutcliffe, O.E., Dowdeswell, J.A., Whittington, R.J., Theron, J.N., Craig, J., 2000.Calibrating the late Ordovician glaciation and mass extinction by theeccentricity cycles of Earth’ orbit. Geology 28, 967–970.

Toteu, S.F., Van Schmus, W.R., Penaye, J., Michard, A., 2001. New U–Pb and Sm–Nddata from north-central Cameroon and its bearing on the pre-Pan Africanhistory of central Africa. Precambrian Research 108, 45–73.

Toteu, S.F., Penaye, J., Poudjom Djomani, Y.H., 2004. Geodynamic evolution of thePan-African belt in Central Africa with special reference to Cameroon. CanadianJournal of Earth Sciences 41, 73–85.

Toteu, S.F., Yongue Fouateu, R., Penaye, J., Tchakounte, J., Seme Mouangue, A.C., VanSchmus, W.R., Deloule, E., Stendal, H., 2006. U–Pb dating of plutonic rocksinvolved in the nappe tectonic in southern Cameroon: consequence for the Pan-African orogenic evolution of the central African fold belt. Journal of AfricanEarth Sciences 44, 479–493.

Trindade, R.I.F., D’Agrella-Filho, M.S., Babinski, M., Front, E., Brito Neves, B.B., 2004.Paleomagnetism and geochronology of the Bebedouro cap carbonate: evidencefor continental-scale Cambrian remagnetization in the São Francisco craton,Brazil. Precambrian Research 128, 83–103.

Trindade, R.I.F., Macouin, M., 2007. Palaeolatitude of glacial deposits andpalaeogeography of Neoproterozoic ice ages. Comptes Rendus Geosciences339, 200–211.

Vaslet, D., 1990. Upper Ordovician glacial deposits in Saudi Arabia. Episodes 13,147–161.

Veillette, J.J., Dyke, A.S., Roy, M., 1999. Ice-flow evolution of the Labrador Sector ofthe Laurentide Ice Sheet: a review, with new evidence from northern Quebec.Quaternary Science Reviews 18, 993–1019.

Vanhoutte, M., Salley, P., 1986. Reconnaissance des calcaires de Mintom – Projet derecherches minières, sud-est Cameroun. United Nations Development Program,Unpublished Report 91, 59 p.

Vicat, J.-P., Pouclet, A., Nkoumbou, C., Semé Mouangué, A., 1997. Le volcanismefissural des séries du Dja inférieur, de Yokadouma (Cameroun) et de Nola (RCA) –signification géotectonique. Comptes Rendus Académie Sciences Paris 332,671–677.

Visser, J.N.J., 1990. Glacial bedforms at the base of the Permo-Carboniferous DwykaFormation along the western margin of the Karoo Basin, South Africa.Sedimentology 37, 231–245.

Vorren, T.O., 1979. Weichselian ice movements, sediments and stratigraphy onHardangervidda, South Norway. Norges Geologiske under Sokelse 350, 1–117.

Warren, J., 2000. Dolomite: occurrence, evolution and economically importantassociations. Earth Science Reviews 52, 1–81.

Wendorff, M., Key, R.M., 2006. Sedimentary facies, stratigraphy and SHRIMP agedating of the glaciogenic Grand Conglomerat Fm., Neoproterozoic of CentralAfrica. Abstracts: Snowball Earth 2006, Monte Verita, Switzerland, July 16–21.pp. 114–115.

Williams, G.E., 1996. Soft-sediment deformation structures from the Marinoanglacial succession, Adelaide foldbelt: implications for the palaeolatitude of lateNeoproterozoic glaciation. Sedimentary Geology 106, 165–175.

Williams, G.E., Gostin, V.A., McKirdy, D.M., Preiss, W.V., 2008. The Elatina glaciation,late Cryogenian (Marinoan Epoch), South Australia: sedimentary facies andpalaeoenvironments. Precambrian Research 163, 307–331.