E.M. BORDY AND R. PREVEC 429

INTRODUCTION

The coal-bearing Emakwezini Formation (AdelaideSubgroup, Beaufort Group, Karoo Supergroup) isrestricted to a narrow, faulted, meridional outcrop andsubcrop belt in the central (Swaziland) and southern(north-eastern KwaZulu-Natal) Lebombo Basin (Figure1). This little-studied formation has been consideredlithostratigraphically equivalent to the Upper PermianNormandien Formation (incorporating the now informalEstcourt Formation) in the eastern and north eastern andthe Balfour Formation in the southern parts of the mainKaroo Basin (Linström, 1987a; SACS, 1980; Joubert, 1994;Johnson et al., 2006). Temporal correlation with theseformations has been based on a few accounts of fossilplants found near Somkele (Etheridge, 1902; Seward,1907; Plumstead, 1970) and Empangeni (Anderson andAnderson, 1985; Van Dijk, 2000). However, these fewrecords and accompanying locality information werevague and conflicting.

This study provides a brief review of earlier accountsof the lithology and flora of the Emakwezini Formation,a sedimentological description of the unit and aclarification of known fossil localities following ourrecent exploration of the region. In addition, somepreliminary findings on previously reported and newly discovered plant fossil localities that have

yielded an abundant and diverse flora are presented. This contribution also provides a palaeoenvironmentalinterpretation of the Emakwezini Formation, serves toconfirm a Late Permian age for the upper half of theformation, and for the first time reports floral elementsassociated with the economically important coal seamsin the lower part of the unit.

GEOLOGICAL SETTING

The Upper Permian Emakwezini Formation constitutesthe sole representative of the Beaufort Group (KarooSupergroup) in the southern half of the Lebombo Basin(or ‘Monocline’; Figure 1), an elongated Phanerozoicdepression that stretches in a north-south directionbetween the Limpopo River in the north and Empangeniin the south for a total of ~700 km.

The type area of the Emakwezini Formation is westand northwest of Empangeni (KwaZulu-Natal), morespecifically railway sections east and west ofEmakwezini siding (from S 28° 30.508’, E 31° 50.354’ toS 28° 33.025’, E 31° 52.743’); road and other cuttingsaround the old collieries near Ntambanana (S 28°36.443’, E 31° 45.487’); various cuttings betweenDukaneni and Kwa-Yaya railway sidings (S 28° 43.895’,E 31° 35.378’ and S 28° 41.767’, E 31° 41.286’) and a fewnatural outcrops (streams, dongas), pit walls of open

Sedimentology, palaeontology and palaeo-environmentsof the Middle (?) to Upper Permian Emakwezini Formation

(Karoo Supergroup, South Africa)

E.M. Bordy and R. PrevecDepartment of Geology, Rhodes University, Grahamstown 6140, South Africa

e-mail: e.bordy@ru.ac.za, rose.adendorff@ru.ac.za

© 2008 December Geological Society of South Africa

ABSTRACT

The little-known Emakwezini Formation (Adelaide Subgroup, Beaufort Group, Karoo Supergroup) crops out in a narrow strip just

inland of the eastern coast of South Africa in northern KwaZulu-Natal. It is an actively mined coal-bearing succession characterised

by fining-upward successions of coarse- to fine-grained sandstones together with mudstones containing a fossil assemblage of

animal traces, insects, molluscs, arthropods, fish and plants. Previously, only Glossopteris leaves and Phyllotheca australis had been

described from this formation, on the basis of a few very small, scattered and poorly provenanced collections.

Recent regional-scale sedimentary facies analysis (based on field relationships, provenance studies, palaeocurrent and

subsurface data) together with palaeobotanical studies of a newly discovered, well-preserved and diverse palaeoflora from the

Emakwezini Formation, have permitted a more detailed interpretation of the depositional environment. The current investigation

also reveals the first evidence of the plant fossils Dictyopteridium flabellatum, Rigbya arberioides, Lidgettonia spp., and Trizygia

speciosa in the upper parts of the Emakwezini Formation, strongly supporting a Late Permian age based on correlation with floras

from Upper Permian units in the main Karoo Basin. In the lower part of the unit, within the partings of actively mined coal seams,

our preliminary investigations also show the presence of a new flora including both the glossopterid fructification Ottokaria sp.

(only known from the Lower Permian in South Africa) and the sphenopsid Schizoneura gondwanensis (typical of the Upper

Permian in South Africa).

With sediments sourced from a north-easterly continental interior, the Emakwezini Formation was deposited rapidly in a fluvio-

lacustrine setting under moist conditions capable of supporting an abundant and diverse biota. The permanently moist environment

in which the Emakwezini Formation was deposited contrasts with that of the time-equivalent lower Beaufort Group units in the

main Karoo Basin where environmental indicators suggest deltaic, lacustrine and meandering fluvial systems developed in a

seasonally dry and more arid setting. Thus, within southern Africa, during the Middle to Late Permian, the environmental

conditions, including climate, were varied leading to a mosaic of continental depositional settings.

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doi:10.2113/gssajg.111.4.426

cast mines and exploration trenches around Somkele (S 28° 20.1’, E 31° 6.5’) (Figure 1). The unit is alsopresent in the subsurface along the western side of theLebombo Basin from Empangeni to at least as far northas Komatipoort (Figure 1).

The study area is a high rainfall, coastal region,where the natural vegetation is dense coastal bushveldand grassland. Most of the region is intensively farmed,with sugar cane fields dominating the landscape. It wasa challenge finding laterally extensive exposures thatwere not heavily weathered or vegetated. Correlationsbetween local exposures were further hampered byextensive faulting and an abundance of doleriteintrusions in the region. An additional difficultyencountered was the high level of crime in much of the region, necessitating the use of armed guards alongthe Emakwezini section of the Richards Bay-Volksrustrailway line.

The Emakwezini Formation consists chiefly offossiliferous, grey, greenish-grey and brown mudstoneswith intercalated coal seams, subordinate white oryellow-white, mainly medium-, but locally coarse-

grained, commonly feldspathic sandstones and veryrare, discontinuous limestone lenses. The mudstone tosandstone ratio is approximately 2 to 1. Planar cross-bedding, current-ripple cross-lamination, and horizontaland massive bedding, and soft-sediment deformationfeatures, are the most common sedimentary structures inthe sandstones. Coal seams (usually <1 m, but locally upto 15 m thick) are associated mainly with the mudstones.It is estimated that the formation attains a thickness of~490 m near Somkele (Marshall, 1966), and ~550 m westof Somkele and at Emakwezini (Watson and McGeorge,1977). From here, it thins southwards to ~370 m west ofEmpangeni (Genis, 1961); however, according to Du Preez (1982), the formation is ~500 m thick in thisarea. North of Somkele, the formation thins dramatically,attaining a thickness of ~130 to 150 m in Swaziland(Davies, 1961) and near Komatipoort (Du Toit, 1918).Further north, between Komatipoort and the LetabaRiver (~S 25° 30’ to ~S 24°), the lack of stratigraphicmarkers preclude the separation of the different Permiancoal-bearing units i.e., equivalents of the Vryheid and/orEmakwezini Formations (own observation based on

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430

Figure 1. Geological maps showing (A) the position of the Lebombo Basin and the study area (small rectangle, enlarged in B) in relation

to the main Karoo Basin and other outcrop areas with Karoo-age deposits in southern Africa and (B) the distribution of the Emakwezini

Formation in the study area. For GPS coordinates, see text. Modified after 1:1000 000-scale geological map of South Africa, Lesotho and

Swaziland (Council for Geoscience, 1997) and Johnson et al. (1996).

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Council for Geoscience borehole data). Intense post-Karoo faulting probably caused the localized duplicationof the unit, but because of poor exposures and lack ofstratigraphic subdivisions, the faulting often remainsundetected and thickness estimations are, therefore, veryuncertain for the whole region. Probably this has givenrise to anomalously large apparent thicknesses in someareas (e.g., ~600-700 m near Vryheid - Linström, 1987b).The strata are inclined fairly consistently eastwards tosouth-eastwards at angles up to 30° (average 15-20°).

This coal-bearing stratigraphic unit has aconformable, gradational (Wolmarans and Du Preez,1986) lower boundary, which is taken at the base of thefirst cross-bedded sandstone located above the grey andblue-grey, commonly micaceous (but non-carbonaceous), carbonate-nodule-bearing, monotonousmudstones of the underlying Volksrust Formation. The Emakwezini Formation has an unconformableupper boundary, which coincides with the base of thefirst coarse- to very coarse-grained, “glittering”,feldspathic sandstone (top of the uppermostcarbonaceous mudstone; Du Preez, 1978, in Linström,1987a).

PALAEONTOLOGY

Palaeoflora There have been several previous reports of fossil plantsin the Emakwezini Formation, although most of thesehave been based either on a few poorly provenancedspecimens, or have been cursory assessments simplyacknowledging the presence of Glossopteris.

Etheridge (1902) and Seward (1907) both describedplant fossils from the Somkele Coalfield. The materialwas collected in the vicinity of the ‘Enseleni River’ (northof Somkhele Mine), and was sent to them by the thenGovernment Geologist of Natal, Mr W. Anderson.Etheridge (1902) described the Nseleni River material asthickly packed mats of fragmentary, poorly preservedGlossopteris leaves in clay shale. He recorded thepresence of Phyllotheca zeilleri, Glossopteris retifera, G. damudica, G. browniana, G. stenoneura, andAngiopteridium (a taeniopteroid leaf form). Seward(1907) recorded Phyllotheca zeilleri, G. browniana, G. indica, G. retifera and Vertebraria from severalpoorly defined localities in the region.

Visser (1957a; b) and Genis (1961) noted anabundance of Glossopteris fossils in several beds in therailway cuttings near the Emakwezini Station, along theRichards Bay-Vryheid railway line. Plumstead’s (1970)account of Glossopteris leaves, Phyllotheca andDictyopteridium in carbonaceous shales associated withcoal seams in SO1 borehole sunk by the South AfricanGeological Survey (S 28° 21’; E 32° 06’) was pivotal inthe assignation of the Emakwezini Formation to theUpper Permian. The fossil specimens are housed in the Bernard Price Institute for Palaeontology at theUniversity of the Witwatersrand. What Plumstead (1970)described as Phyllotheca etheridgei was found at a depth of ~512 m in massive carbonaceous shales.

She considered this taxon to be a good index fossil forUpper Permian deposits, although it was the first recordof this sphenopsid in South Africa. P. etheridgei has sincebeen synonymized with P. australis (e.g., Anderson andAnderson, 1985), which although stratigraphically long-ranging in its Gondwana-wide occurrence, does appearto be typical of Upper Permian deposits in South Africa.What Plumstead (1970) claimed to be specimens ofDictyopteridium sporiferum were found ~3 m higher inthe same borehole (at a depth of ~509 m). Examinationof the purported specimens of Dictyopteridium duringthe current investigation revealed that they are small,narrow Glossopteris leaves and not fertile organs.However, most of these leaf impressions have dense,irregularly dispersed concentrations of insect ovipositionscars on the lamina (Plate III: E; F), and thesesuperficially resemble the seed scars of Dictyopteridium.The distinctive morphology of Dictyopteridium, i.e.,elongate lanceolate receptacle with small, circular,regularly spaced, raised tubercles (in impression fossils) representing seed attachment sites, the marginalrow of these corresponding in position to segments ofan entire, narrow peripheral wing, is absent in these specimens (cf. Dictyopteridium flabellatumin Plate I: A; B).

Anderson and Anderson (1985) documented threeslabs from a railway cutting to the north of Empangeni,at the Emakwezini railway siding. They reported thepresence of Phyllotheca australis (60%) and two speciesof Glossopteris (40% with 5% of the flora represented byopen-meshed leaves assigned to their Rigbya arberioidespalaeo-species). They characterized the Emakwezinilocality as less than 10 m in extent. Photographs of twoof the slabs containing Phyllotheca impressions werelabelled by Anderson and Anderson (1985) as NM 2538and NM 2539, although according to the Natal Museumcatalogue, specimens with these numbers are insectfossils from another locality at Balgowan. Staff at theNatal Museum were unable to provide any catalogueinformation on plant fossil material collected from theEmakwezini Formation or the Empangeni region. VanDijk (2000) suggested that the plants recorded byAnderson and Anderson (1985) from EmakweziniStation, in fact originated from another locality atMevamhlope. However, according to geological maps ofthe vicinity, the Mevamhlope railway siding is a fewkilometres east of Kwa-Yaya, within deposits of theVolksrust and Vryheid Formation. We investigated thisarea, and the few poor and limited exposures we foundwere apparently devoid of plant fossils. It is possible thatVan Dijk’s report represents a misidentification of theKwa-Yaya site, although we think this unlikely due tothe fairly sporadic and infrequent occurrences ofPhyllotheca australis whorls and the clear dominance of Glossopteris leaves at Kwa-Yaya.

PalaeofaunaAssociated with the fossil plants, a protorthopteraninsect Neoliomopterum picturatum (Riek 1976, p. 763),

clam shrimp Estheria greyii (now called Cyzicus)together with ganoid (Etheridge, 1902, p. 75) andCoelacanthus dendrites (Gardiner 1973, p. 33) fish scaleshave been reported. Kynaston (1906, p. 51) alsomentioned “some Ganoid scales and teeth”.Furthermore, unidentified “indistinct casts of Mollusca”were reported in association with some localizedlimestones by Anderson (1907, p. 144).

STRATIGRAPHIC CORRELATION

The Karoo Supergroup in the southern Lebombocontains two Permian carbonaceous successions, whichare now assigned to the older Vryheid and youngerEmakwezini Formations (SACS, 1980; Joubert, 1994).Historically, Anderson (1907) described the uppersuccession as correlative with the Upper Ecca because inhis view there was no satisfactory stratigraphic andpalaeontological evidence to suggest that coal-bearingrocks could also be present in the Beaufort Group.However, most subsequent studies (e.g., Du Toit, 1918;1954), assigned the upper coal-bearing strata to theformer “Lower Beaufort” based on improved plant-basedbiostratigraphic data and/or their stratigraphic positionrelative to the base of the Karoo Supergroup.

Lithostratigraphic correlations The lithostratigraphic equivalents of the EmakweziniFormation (Figure 2) are the Normandien Formation(incorporating the previous Estcourt Formation) in thenorth eastern and eastern parts of the main Karoo Basinand the Balfour Formation in the south-eastern mainKaroo Basin (SACS, 1980; Linström, 1987a; Joubert, 1994;Johnson et al., 2006). This correlation is based chiefly ontheir stratigraphic position relative to the underlyingVolksrust Formation (in case of the NormandienFormation), the diagnostic Late Permian plant,invertebrate and vertebrate fossil assemblages (seesection on Biostratigraphic correlations), and, to someextent, on the coal and carbonaceous mudstone contentof these units. The Emakwezini Formation is litho- andbiostratigraphically most similar to the NormandienFormation, and a brief review of this formation ispresented in the next section. For recent summaries of

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Figure 2. Late Permian to Early Triassic bio- and lithostratigraphy of the Beaufort Group in the eastern half of the main Karoo Basin (MKB)

and southern Lebombo Basin (modified after Botha and Linström, 1977, 1978; Hancox et al., 2002; Rubidge, 2005). A * indicates a

stratigraphic unit not formally recognized by SACS (Johnson, 1994; Johnson et al., 2006; SACS, pers. comm., 2007). Wavy lines indicate

erosional contacts. Note that most lithostratigraphic boundaries are diachronous.

Figure 3. Late Permian palaeocurrents in the southern Lebombo

Basin and the eastern and north eastern part of the main Karoo

Basin (see text for details). 1-6: Emakwezini Formation (own

observations; Linström, 1987); 7-11: Normandien Formation in the

eastern main Karoo Basin (previously Estcourt Formation) (Ryan,

1967; Theron, 1975; Botha and Linström, 1977; Van Dijk et al.,

1978) and 12-15: Normandien Formation in the north eastern main

Karoo Basin (Ryan, 1967; Theron, 1975; Turner, 1977; Groenewald,

1989). Southerly and northerly directions in all areas are weak.

Note that each of our measurements (marked by *) is based on less

than 5 readings in planar cross-bedded sandstones, except for the

south-westerly direction in 2 which is supported by 14 readings

from a single locality.

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the fluvio-lacustrine Balfour Formation, the reader isreferred to Catuneanu and Elango (2001), Catuneanu et al. (2005) and Botha and Smith (2007) and referencestherein.

In the north-eastern main Karoo Basin (i.e., north-western KwaZulu-Natal, north-eastern Free State,southern Mpumalanga), the Upper Permian NormandienFormation contains ~30-40% sandstone and thins from~320 m in the southwest to ~100 m in the northeast(Turner, 1977; Groenewald, 1984; logs in Groenewald,1989). Proximal sedimentary sources situated to thenortheast, east, southeast, and north are suggested byTheron (1975), Turner (1977) and Groenewald (1989)(Figure 3). In this north-eastern region, the formationcontains freshwater conchostracans (Turner, 1977),numerous trace fossils (Turner, 1977; Groenewald,1989), Late Permian plant fossils and Late Permian toEarly Triassic vertebrate fossils (e.g., Rhachiocephalusmagnus, Dicynodon lacerticeps, Lystrosaurus murrayi)(Groenewald, 1984, 1989; Rubidge, 1995).

In the basal part of the formation, the FrankfortMember (<80 m), consists of two upward-coarseningand upward-thickening sequences comprisingrhythmites, carbonaceous shales, siltstones and fine- tocoarse-grained, feldspathic sandstones with minor coalseams (Turner, 1977; Groenewald, 1989; Johnson et al.,1997; Cairncross et al., 2005). In this lower part,sedimentary structures such as flaser-bedding, waveripples, trough and planar cross-bedding and otherfacies relationships suggest a mainly westward-draining,fluvially-dominated deltaic depositional environment(Groenewald, 1989; Cairncross et al., 2005). The rest ofthe formation, consisting of fining-upward successionscomprising (from the base upwards) minorconglomerates with quartz and granite clasts, fine- tocoarse-grained sandstones, and coal-bearing, black,green and grey mudstones together with red to purplemudstones in the upper part (Harrismith Member)(Groenewald, 1989), has been interpreted as deposits ofhigh-sinuosity, mixed-load meandering rivers andoverbank lakes in an increasingly arid climate (Turner,1977; Groenewald, 1989; Hancox et al., 2002).

In the eastern main Karoo Basin, around Mooi River-Bergville-Ladysmith area (western KwaZulu-Natal), theNormandien Formation (representing the now obsoleteEstcourt Formation, Johnson et al., 2006) consists ofdark-grey (red in its uppermost part), carbonaceous,locally calcareous mudstones, fine- to coarse-grained,moderately well-sorted, poorly rounded, feldspar- andgarnet-bearing sandstones with some conglomerates(Botha and Linström, 1977, 1978) and very rare coalseams (Visser and Loock, 1978). It attains a totalthickness of ~400 m (Botha and Linström, 1978), and ischaracterized by coarsening-upward successions in its lower two-thirds, and fining-upward successions in itsupper third (Cadle, 1974; Veevers et al., 1994; Johnson et al., 1997). Palaeocurrents were directed mainly fromthe northeast, southeast, and east, and to a lesser extent,from the north and south (Theron, 1975; Botha and

Linström, 1977; Van Dijk et al., 1978; Figure 3). In thiseastern region of the main Karoo Basin, in addition totrace fossils, freshwater conchostracans, and LatePermian plant fossils, the formation also contains arange of insects, freshwater molluscs, fish scales, fossilfish (Atherstonia) (e.g., Rossouw, 1970; Lacey et al.,1975; Van Dijk et al., 1978; Anderson and Anderson,1985; Linström, 1987a), and, in its upper part, “plentiful”Dicynodon leoniceps (=Daptocephalus) remains(Dicynodon Assemblage Zone, Botha and Linström,1978). According to Dingle et al. (1983, p. 21), theformation also contains Lystrosaurus Zone fossils. A diverse insect assemblage (e.g., Riek 1973; 1976) notonly corroborates the Late Permian age of the formation,but also suggests a palaeoclimate between cold-moistand warm-dry (Riek, 1976; Geertsema et al., 2002).Except for its uppermost part (dominated by red bedsrich in vertebrate remains), the formation has beeninterpreted as comprising deposits of a moist milieu,dominated by a prograding fluvio-deltaic system withsmall river-mouth deltas, swampy floodplains (Bothaand Linström, 1977; 1978) and interdistributary bays (vanDijk et al., 1978). More recently, Selover and Gastaldo(2005) reinterpreted part of the formation as deposits ofa deeper water turbidite system.

Biostratigraphic correlations All previous biostratigraphic correlations of theEmakwezini Formation have been based onpalaeobotanical observations (Etheridge, 1902; Seward,1907; Du Toit, 1954; Plumstead, 1970; Anderson andAnderson, 1985). Etheridge (1902) noted strongsimilarities between the plant fossils he described fromthe Emakwezini Formation near St. Lucia and those ofthe Upper or Newcastle Coal Measures of Australia.Seward (1907) supported allocation of the strata to the Beaufort Group, based on the absence ofGangamopteris, and Du Toit (1954) also considered theplants of the St. Lucia coalfield indicative of the Beaufortrather than the Ecca Group, although he gave noreasons. Plumstead (1970) based her assessment of aLate Permian age for the coal deposits at Somkele on thepresence of Dictyopteridium and Phyllotheca etheridgei,taxa she considered to be diagnostic of this time period.Although Anderson and Anderson (1985) provided noexplanation for assigning strata at the Emakwezinilocality to the Upper Permian, their recognition ofbroad-meshed Glossopteris leaves of the type associatedwith Rigbya arberioides, provided them with a basis forcorrelation with floras of the Normandien (previouslyEstcourt) Formation.

MATERIALS AND METHODS

SedimentologySedimentological fieldwork was carried out in southernLebombo (see Geological Setting for localities) andinvolved compilation of detailed sedimentary logs, fieldsketches and photomosaics. Because of the generallypoor quality of exposures, the spatial variation and

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Figure 4. Sedimentological logs of the Emakwezini Formation detailing vertical facies relationships. All logs show true thicknesses. Zone

A-D = major coal zones. (A) Based on Somkele 1 deep borehole (SO1) (Marshall, 1966); to date, this log is the most complete and reliable

record of the entire formation. Note the two coarsening-upward successions (each <20 m thick) in the lowermost part of the formation,

and a number of faults (F) and dolerite intrusions (do). (B) Sedimentological log recorded along the railway cutting near Emakwezini

station, reproduced from unpublished material (Genis, 1961). It represents the uppermost and middle parts of the formation, intersected

by dolerite (do) intrusions and numerous faults (F) (hence its anomalous thickness). (C) Generalized sedimentological log of the

Emakwezini Formation equivalent in Swaziland based on coal exploration boreholes reported in Davies (1961). * = Volksrust Formation

equivalent unit; ** = Upper Beaufort Group equivalent unit: a ~40 m thick, “grey blue micaceous shale” that starts with a thin clay pellet

conglomerate, and which is then followed by coarser sandstone unit, equivalent of the Molteno/Ntabeni Formations (Davies, 1961).

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Figure 4. (continued)

(D) Generalized sedimentary log of the middle part of the Emakwezini Formation, between Coal Zones B and C at Somkhele Mine

(See Figure 4A for reference). (E) Detailed sedimentary log of the 5th upward-fining succession shown in yellow in D.(F) Detailed

sedimentary log measured in the upper part of the Emakwezini Formation at the type locality near the Emakwezini railway station.

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Tab

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grai

ned

Low

-angl

e cr

oss

-bed

ded

Fr

agm

enta

ry w

oody

Rar

eH

um

pbac

k or

was

hed

-out dunes

under

upper

flo

w

sandst

one

axes

Occ

urs

in e

lem

ents

SS,

DA, CF,

CS

regi

me

conditi

ons

Sr

Fine-

to v

ery

fine-

grai

ned

Rip

ple

cro

ss-lam

inat

ed

None

reco

rded

Moder

atel

y ab

undan

tCurr

ent ripple

s in

low

er f

low

reg

ime

conditi

ons

sandst

one

Occ

urs

in e

lem

ents

SS,

CF,

LA, CS

FlCoar

se to f

ine

silts

tone,

Horizo

nta

lly lam

inat

ed

Pla

nts

(le

aves

, st

ems,

Ver

y ab

undan

tO

verb

ank,

rar

e w

anin

g flow

as

wel

l as

shal

low

clay

stone,

often

hig

hly

roots

), tra

ce f

oss

ils,

Occ

urs

in e

lem

ent O

F, r

arel

y at

the

top

to d

eeper

lak

e dep

osi

ts

carb

onac

eous

inse

cts,

fre

shw

ater

of

finin

g-upw

ard s

ucc

essi

ons,

arth

ropod a

nd f

ish

in e

lem

ents

SS,

CF

FmCoar

se to f

ine

silts

tones

,M

assi

ve

Pla

nts

roots

, Abundan

tPed

oge

nic

ally

alte

red o

verb

ank

and s

hal

low

lak

e m

argi

n

clay

stones

, often

hig

hly

trac

e fo

ssils

O

ccurs

in e

lem

ent O

Fdep

osi

ts

carb

onac

eous

Ca

Car

bonat

e, f

erru

ginous

Mas

sive

to n

odula

r M

ollu

scs

Ver

y ra

rePed

oge

nic

and/o

r dia

genet

ic inorg

anic

pre

cipita

tion

with

rar

e co

ne-

in-c

one

Occ

urs

in e

lem

ent O

F

stru

cture

s

PFi

ne

silts

tone

and c

lays

tone

Colo

ur

and r

oot-m

ottle

dCar

boniz

ed r

oots

Rar

ePal

aeoso

l w

ith i

n s

itu

vege

tal m

atte

r

and r

ootle

tsO

ccurs

in e

lem

ent O

F

CCoal

Finel

y la

min

ated

to

Car

boniz

ed lea

ves

Rar

e Pea

t ac

cum

ula

tion in f

resh

-wat

er s

wam

ps

mas

sive

and w

oody

axes

Occ

urs

in e

lem

ent O

F

E.M. BORDY AND R. PREVEC

SOUTH AFRICAN JOURNAL OF GEOLOGY

437

Tab

le 2

.Cla

ssific

atio

n a

nd d

escr

iptio

n o

f ar

chite

ctura

l el

emen

ts r

ecogn

ized

with

in the

Em

akw

ezin

i Fo

rmat

ion. W

ith m

inor

modific

atio

n, ar

chite

ctura

l el

emen

ts a

nd the

crite

ria

for

thei

r re

cogn

ition

wer

e ad

apte

d f

rom

Mia

ll (1

985,

199

6).

Arc

hit

ectu

ral

un

itA

rch

itec

tura

l el

emen

t Fac

ies

com

po

siti

on

Geo

met

ryB

ou

nd

ing

surf

aces

Coar

se-g

rain

edSu

per

impose

d s

andst

one

Sp >

> S

m, Sl

, Sh

,Sh

eet-lik

e co

mple

xes

exte

ndin

g >10

0 m

lat

eral

ly,

Ero

sive

, pla

nar

to irr

egula

r to

slig

htly

conve

x-dow

n b

asal

surf

aces

.

faci

es a

ssoci

atio

nsh

eets

(SS

)Sr

, m

inor

Flan

d <

4 to

>15

m thic

k (c

om

monly

~4

to 8

m).

Upper

surf

aces

usu

ally

ero

sive

, irre

gula

r to

pla

nar

.

Conta

ined

indiv

idual

tab

ula

r or

lentic

ula

r bed

s ra

nge

Num

erous

flat

inte

rnal

surf

aces

.

from

~3-

5 m

to ~

100

m long

and f

rom

0.0

5 to

2.2

m

(ave

rage

~0.

2 to

0.3

m)

thic

k.

Dow

nst

ream

-acc

rete

dm

ainly

Sp, fe

w S

rW

hal

ebac

k-sh

aped

body

~1–

1.5

m thic

k an

d >

30 m

long.

Pla

nar

to s

lightly

conve

x-dow

n b

asal

surf

aces

. U

pper

surf

aces

dep

osi

ts (

DA)

Ove

rlie

s O

F el

emen

t, ove

rlai

n b

y SS

or

CF

elem

ents

. sh

arp c

onve

x-up, st

rongl

y dow

nw

ard-c

urv

ing.

Inte

rnal

surf

aces

dow

n-c

urr

ent dip

pin

g to

pla

nar

.

Chan

nel

-fill

s of

variab

leSp

>> S

m, Sl

, Sh

Lentic

ula

r bodie

s of

variab

le s

cale

fro

m 1

.5 to >

100

mSh

arp, co

nve

x-dow

n, st

rongl

y upw

ard-c

urv

ing

bas

al s

urf

aces

.

scal

e (C

F)w

ide

and ~

0.5

to >

8 m

thic

k. O

verlie

SS,

DA a

nd O

FU

pper

surf

aces

ero

sive

ly p

lanar

, co

nve

x-dow

n to g

radat

ional

.

elem

ents

, ove

rlai

n b

y SS

ele

men

t. Ver

y ra

re, la

rge-

scal

e

varian

ts m

ay c

onta

in e

lem

ents

SS,

DA, LA

.

Late

rally

-acc

rete

dSp

>> S

m, Sr

,Tap

ered

wed

ge-s

hap

ed b

odie

s an

d ~

1-1.

5 m

thic

k an

dPla

nar

to s

lightly

conve

x-dow

n b

asal

surf

aces

. U

pper

surf

aces

dep

osi

ts (

LA)

min

or

Fl<10

m w

ide.

Ove

rlai

n b

y SS

or

CF

elem

ents

. irre

gula

r to

pla

nar

. In

tern

al s

urf

aces

strai

ght,

slopin

g in

direc

tions

nea

rly

per

pen

dic

ula

r (>

60°)

rel

ativ

e to

the

mai

n

pal

aeocu

rren

t direc

tion.

Fine-

grai

ned

fac

ies

Ove

rban

k fines

(O

F)Fl

, m

inor

Fm,

Late

rally

ext

ensi

ve s

hee

t-lik

e bodie

s, e

xten

din

g >50

0 m

Pla

nar

to irr

egula

r to

slig

htly

conve

x-dow

n, sh

arp to tra

nsi

tional

asso

ciat

ion

C >

Ca,

Pin

len

gth, <0.

5 to

<10

m thic

k. E

rosi

vely

ove

rlai

nbas

al s

urf

aces

. U

pper

surf

aces

shar

p to tra

nsi

tional

.

by

SS, D

A a

nd C

F el

emen

ts, as

soci

ated

with

CS

elem

ent.

Cre

vass

e sp

lay

(CS)

Sm, Sh

, Sr

>> S

pLe

ntic

ula

r to

shee

t-lik

e bodie

s, e

xten

din

g <40

m lat

eral

lyEro

sive

, sh

arp, pla

nar

bas

al s

urf

aces

. U

pper

surf

aces

pla

nar

to

and 0

.1-4

m thic

k. C

om

monly

pas

sing

late

rally

into

undula

tory

to s

lightly

dow

nw

ard-c

urv

ing

or

tran

sitio

nal

.

OF

elem

ents

, an

d a

ssoci

ated

with

sm

all-sc

ale

CF

and O

F el

emen

ts. Ero

sive

ly o

verlai

n b

y SS

ele

men

ts.

relationships of the facies were interpreted usingsupplementary data from Council for Geoscience coalexploration boreholes and unpublished reports. The data were compiled and interpreted according tostandard facies analysis techniques (Miall, 1978; 1985;1996). Palaeocurrent measurements and petrographicstudies (thin-section descriptions) were undertaken tocomplement the field-based facies analysis, in particularto establish the direction of the local and regionalpalaeoslopes and source rock geology.

PalaeobotanyPlant fossils were collected under AMFA Permit number06/01, issued to RP. Specimens from Kwa-Yaya andEmakwezini are impressions, in fine-grained olive-greymudstone, whereas those from Somkhele Mine areimpressions and compressions within highlycarbonaceous, fine-grained siltstone. All material (over900 slabs) is currently housed in the Albany Museum,Grahamstown, and specimens have been assignedtemporary field numbers with the prefix KY (Kwa-Yaya),ES (Emakwezini Station) or SM (Somkhele Mine).Specimens were photographed with a Canon Powershot G6 digital camera under low-angled,unilateral light.

SEDIMENTOLOGY OF THE EMAKWEZINI FORMATION

Vertical profile analysis shows that the EmakweziniFormation is composed of four major clastic-coalsequences (demarcated by Coal Zones A –D; Figures 4A;4B; 4C). These all fine upward, except at Somkele,where the first clastic-coal sequence commences withtwo upward-coarsening successions (<20 m each; seenext section). Each upward-fining clastic-coal sequencerests on a prominent erosion surface and commenceswith coarse-grained sandstones. Furthermore, each ofthese major upward-fining sequences comprisesbetween two and five vertically stacked fining-upwardsuccessions that can be further subdivided into severalsmaller-scale (<10 m thick), fining-upward successions(Figures 4D; 4E; 4F; 6). The coal is always found in theupper part of each major clastic-coal sequence and isinterbedded with other fine-grained lithofacies. In mostinstances, the coal occurs at variable distances from thebase of the succeeding sequence, with the exception ofthe second sequence, where the regionally mostpersistent and uniformly thick coal zone is overlaindirectly (with a sharp erosional contact) by the verycoarse, pebbly sandstones of the third sequence (Figures 4A, 4C). Based on the current scant data,substantial and progressive grain-size differences do notoccur among the four major upward-fining clastic-coalsequences, however, the third sequence appears to becoarsest, and at least in Swaziland, the fourth(uppermost) is the finest (Figure 4C).

Facies analysis Lithofacies data obtained from regional outcrop andsubsurface facies analysis were synthesized, and, based

on this, the Emakwezini Formation can be subdividedinto: i. coarse-grained facies association, comprising several,

~4 to 8 m thick, cylindrical to slightly upward-finingsuccessions dominated by sandstones, withsubordinate siltstone-sandstone interbeds andcarbonaceous mudstones;

ii. fine-grained facies association, comprising mainlymudstones with subordinate fine to very finesandstones, thin coal seams and very rare limestones.

These two facies associations constitute the two mainarchitectural units of the formation, and can be furthersubdivided into six architectural elements, which in turnconsist of a total of eleven lithofacies (Tables 1 and 2).

Coarse-grained facies association Sandstones, constituting ~40% of the entire formationand ~95% of this facies association (Figure 4), are white,yellow-white, dusky yellow or greenish grey to darkgrey, poorly to moderately sorted, and predominantlymedium-grained, but locally fine-grained or evenpebbly, coarse- to very coarse-grained. Mineralogicalcomposition of the locally micaceous (finer) andfeldspathic (coarser) sandstones varies fromsublitharenite to subarkose and quartz arenite. Pebbles,invariably found in stringers at the base of thicklybedded, coarser grained sandstones, are subangular rip-up carbonaceous mudstone clasts predominantly 1 to1.5 cm in diameter, and very rarely 3 to 5 mm,subrounded quartz clasts. At one locality (SomkheleMine), a 10-cm-diameter, subangular granite clast wasalso found at the base of the coarsest sandstone.Furthermore, randomly orientated, whole fossil leavesand impressions of fragmentary logs ranging in size froma few centimetres to decimetres are also found at thebase of some coarser grained sandstones (Figure 5).

The coarse-grained facies association is dominatedby ~4 to 8-m-thick, upward-fining successions with a narrow vertical range of mean grain sizes resulting ina cylincrical grain-size profile (e.g., Figures 4D; 4E; 4F).Thicker (~10 to 15 m) upward-fining successions arealso present, but closer inspection reveals that most ofthese can be further subdivided into smaller, <4-m-thick,upward-fining successions of sandstones (Figures 4D;4E). Most upward-fining successions also displayupward-thinning trends from thicker (up to 2.2 m),normal graded beds in their lower, to thinly bedded (<5 cm), finely laminated, black to grey, carbonaceousand micaceous mudstones in their upper parts. Mostbeds are ~20 to 30 cm thick.

Upward-coarsening grain-size trends have only beenidentified at the base of the formation (both in outcropand subsurface) at a single locality (Somkhele Mine).Representing <10% of the total formation at this locality,these successions are <20 m thick, and commence withblack to grey carbonaceous mudstones that graduallycoarsen up to very fine- and fine-grained sandstones thatcontain abundant soft-sediment deformation features

SOUTH AFRICAN JOURNAL OF GEOLOGY

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438

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and trace fossils. In comparison, upward-coarseningsuccessions constitute over two-thirds of theNormandien Formation in the eastern (i.e., outcrop areaof the previous Estcourt Formation), and approximatelyone-quarter in the north-eastern main Karoo Basin.

Because of the limited lateral continuity ofexposures, the abundance of large-scale macroforms

(e.g., lateral or downstream accreted beds) could not bedetermined with certainty, as in many cases the lateraldimension of even individual beds was difficult toquantify. Nevertheless, the sandstones appear to havetabular to lenticular geometry with variable lateralcontinuity ranging from a few ~3 to 5 m to up to ~100 m in sections oblique to the palaeoflow direction (Figure 6).

Irrespective of their scale, the fining-upwardsuccessions are invariably characterized by sharp, flat toconcave-up, erosional lower contacts with relief of a fewdecimetres or metres. Erosion surfaces within large-scale, composite fining-upward successions havevariable geometries, and in decreasing order ofabundance, they are identified as:1. planar - lending a multi-storey, vertically stacked,

tabular appearance to the strata;2. downward-curving - lending a whaleback

appearance to strata;3. upward-curving - lending a channel-like appearance

to strata; and4. straight, sloping in directions nearly perpendicular

(>60 degrees) to the main palaeocurrent direction(Figure 6).

Primarily, the nature of these surfaces and geometry ofthe contained beds allowed the subdivision of thecoarse-grained facies association into four architecturalbuilding blocks, namely:superimposed sand sheets (SS);downstream-accreted deposits (DA);channel-fills of variable scale (CF); andlaterally-accreted deposits (LA) (Figure 6; Table 1).

Most sandstones in the coarse-grained faciesassociation are medium (> 0.1 m to < 1 m) to thick (> 1 m), planar cross-bedded (facies Sp) (Figure 6), andarranged in erosively-based co-sets 0.4 to 2.2 m thickcomprising individual sets 0.1 to 0.15 m thick. Foresetsand cosets are often draped by a few millimetre thickcarbonaceous mud film.

Strata with no visible sedimentary structures (faciesSm) are also common. However, the proportion ofprimary structureless (including post-depositionalobliteration of syn-depositional structures) to secondarystructureless (massive) sandstones is uncertain given thehighly weathered nature of the outcrops. Low-anglecross-bedded (facies Sl), horizontally laminated (faciesSh) and asymmetrical ripple cross-laminated (facies Sr)sandstones are less common and mainly restricted tofine- to very fine-grained, commonly argillaceous andmicaceous sandstones. Ripple cross-laminated sand-stones are found exclusively towards the upper part ofupward-fining successions, and generally areinterbedded with <5-cm-thick, finely laminated,carbonaceous mudstone.

Soft-sediment deformation features in sandstones arevery abundant and range from slump structures(Marshall, 1966, p. 3), contorted beds and water-escapestructures to overturned cross-beds and load casts(Figures 7A; B).

Figure 5. (A and B) Non-diagnostic, random, impressions of

fragmentary woody axes up to 50 cm long in coarse, massive

sandstone at the base of an upward-fining succession (Emakwezini

railway station). Scale intervals are 1 cm. (C) Random impression

fossils of intact Glossopteris leaves in coarse, massive sandstone at

the base of an upward-fining succession (Emakwezini railway

station).

SOUTH AFRICAN JOURNAL OF GEOLOGY

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440

Fig

ure

6.

Arc

hite

ctura

l el

emen

ts a

nd b

oundin

g su

rfac

es in the

Em

akw

ezin

i Fo

rmat

ion. Photo

mosa

ic a

nd lin

e in

terp

reta

tion o

f a

~10

0 m

-long

artif

icia

l tren

ch a

t So

mkh

ele

Min

e th

at c

ut ac

ross

the

conta

ct

of th

e co

arse

- an

d fin

e-gr

ained

fac

ies

asso

ciat

ions

(see

Coal

Zone

B a

nd o

verlyi

ng

sandst

one

in F

igure

4A), r

ough

ly p

aral

lel to

the

regi

onal

struct

ura

l st

rike

and o

bliq

ue

to p

alae

o-flo

w d

irec

tions.

Sep

arat

ed

from

the

under

lyin

g ca

rbonac

eous

mudst

ones

and c

oal

(el

emen

t O

F) b

y a

stro

ng

erosi

on s

urf

ace,

the

~6-

7 m

-thic

k sa

ndst

one

succ

essi

on (

eroded

) co

nta

ins

super

impose

d s

and s

hee

ts (

SS), c

han

nel

-fill

s

(CF)

of

variab

le s

cale

and l

ater

ally

-acc

rete

d d

eposi

ts (

LA). N

ote

that

obse

rvat

ions

of

such

cle

arly

-def

ined

, sl

opin

g m

ajor-

chan

nel

mar

gins

are

exce

ptio

nal

ly r

are

for

the

Em

akw

ezin

i Fo

rmat

ion,

pro

bab

ly

due

to t

he

poor

qual

ity o

f th

e outc

rops

and t

hei

r orien

tatio

ns

(i.e

., m

ost

ly p

aral

lel

to p

alae

o-flo

w). M

ost

com

mon l

ithofa

cies

are

Sp,

follo

wed

by

Sl i

n t

he

med

ium

, an

d S

h,

Sr i

n t

he

fine

sandst

ones

.

Sedim

ento

logi

cal lo

g (n

ote

its

blo

cky

grai

n-s

ize

pro

file

) on the

righ

t w

as m

easu

red in the

low

erm

ost

upw

ard-fin

ing

succ

essi

on (

see

das

hed

lin

e on the

left f

or

appro

xim

ate

trac

e).

E.M. BORDY AND R. PREVEC

SOUTH AFRICAN JOURNAL OF GEOLOGY

441

Fine-grained facies association This facies association consists mainly of mudstones,subordinate fine to very fine grained sandstones, thincoal seams and very sparse limestones. It forms theupper part of the major clastic-coal sequences attainingthicknesses of up to 50 m (Figure 4). The fine-grainedfacies association commonly has gradational or abrupt lower and sharp, erosional upper (Figure 6)contacts.

Constituting up to ~60% of the entire formation(Figure 4), black, dark to light grey, blue-grey, grey-green and brown mudstones (facies Fl and Fm) havevariable carbon content and grain sizes ranging fromsparse claystones to more common silty claystones andsiltstones. In spite of the generally poor quality of theoutcrops, the bulk of the mudstones have delicatehorizontal laminations, a feature especially prominentwhere regular intercalation of silt- and clay-rich laminaeoccur, resulting in rhythmic bedding. Slight grain sizevariation from silty claystone to very fine sandy siltstoneis also detectable in broken lenticular-beddedmudstones with single, flat, isolated lenses of coarsergrained sediments. In fact, successions of uniform/pureclaystones or siltstones are very rare, and their thicknessseldom exceeds 0.5 m. Because of the generally intenseweathering of the exposures, assessing the proportion ofprimary versus secondary structureless mudstones(facies Fm) is impossible. Very rare ichnofauna (Figure 7C) are associated with the structurelessmudstones.

An additional lithofacies associated with thecarbonaceous mudstones are rare limestones that formlaterally discontinuous (<2 m) carbonate lenses up to~0.2 cm thick (Figure 7D) (facies Ca). These lenses haveknobbly lower and upper contacts, strong ferruginouspigmentation and poorly-developed cone-in-conestructures. During this study, such limestones were onlyobserved at Emakwezini but they have been reported tooccur very rarely at various other localities (e.g., Davies,1961; Wolmarans and Du Preez, 1986), and, in oneinstance, in association with a cast of a mollusc(Anderson, 1907).

Root- and colour-mottled, dark to light grey,bleached white and rusty red-brown (ferruginous)mudstones (clay- and siltstones) (facies P) are associatedwith coal seams (facies C) and highly carbonaceous,locally fossiliferous mudstones. The vegetal matterassociated with these mottled mudstones varies fromhorizontal to subhorizontal, minute, bifurcating andtapering rootlets cross-cutting indistinctly preservedlaminations (Figure 7E) to robust in situ Vertebrariaaxes. Impression fossils of these large, unmistakable,woody roots of the Glossopteris plant have acharacteristically jointed appearance, resulting from thepresence of air chambers in the root that are thought tobe an adaptation to water-logged soils. Most commonly,however, the root remains found in this lithofacies aredisseminated throughout the host mudstones in the formof short (<5 cm), featureless, carbonized axes.

The second-most common lithofacies of the fine-grained facies association are intercalations of silty, veryfine-, to fine-grained and locally medium- and coarse-grained sandstone intercalations. These are locallymicaceous and commonly contain irregularly shaped,locally deformed, rip-up clasts of carbonaceousmudstone up to 8 cm in diameter. Due to the generallypoor quality of the outcrops, their lateral contacts areunclear and very few were observed. Nonetheless, thelimited data suggests that these interbedded sandstonesform fairly continuous, tabular and lenticular strata,several decametres long. Locally, inclined layers withoutdistinct internal sedimentary structures resemble laterallyaccreted surfaces. Upward-fining or -thinning trends arescarce, and, the base of one such upward-finingsuccession of very fine sand to siltstone is marked bypoorly-preserved impressions of large woody axes of upto 30 cm long. These intercalations, which seem to occurin a random manner in the mudstones, can be up to 4 m in total thickness and consist of <10 to >40 cm-thickbeds, usually with sharp, well-defined lower and lessdistinct upper contacts. The very fine to fine sandstonestypically show no internal structures (facies Sm) or havedelicate horizontal lamination (facies Sh), flaser bedding,ripple, trough and low-angle cross-lamination (facies Sr),whereas the coarser grained sandstones are commonlyplanar cross-bedded (facies Sp), horizontally laminated(facies Sh) or structureless (facies Sm). Soft-sedimentdeformation features, especially load casts (Figure 7F)are very common.

Thin (usually <1 m) coal seams (facies C) make upthe remainder of the fine-grained facies association, andconsist of semi-anthracite to anthracite with >75% ofvitrinite (reflectance of 2.4 to 3.1%), ~25% raw ash,<0.015% phosphorus and 0.7 to 0.8% sulphur contents(Bordy et al., 2008). Natural exposures of coal are veryrare; however, they have been reported (often as “LowerBeaufort” coals) to occur from Heatonville in the southto Komatipoort in the north, in the following regions ofthe Lebombo Basin: Somkele-Heatonville area (Visser,1957a; b; Genis, 1961; Marshall, 1966); Nongoma(Snyman, 1998); Swaziland (Davies, 1961) andKomatipoort (Kynaston, 1906; Du Toit, 1918; de Jager,1986). Assessing whether all of these occurrences areindeed within the Middle to Upper Permian successionsis beyond the scope of this study. However, it is evidentthat most of these descriptions refer to coal-bearingstrata that either contain diagnostic Late Permian floralelements or appear above a non-carbonaceous unit (i.e.,Volksrust Formation equivalents) that is underlain by theolder coal-bearing succession (i.e., the Lower PermianVryheid Formation equivalents).

The maximum number of coal seams in the Somkele1 borehole is eleven, with the first major seam occurring~174 m (discounting the dolerite intrusions) above thelower contact of the formation (see Figure 4A –recalculated from Chart 2 of Marshall, 1966). In the samearea, Grant and Snelling (2005) recognized four coalzones of which the first (lowermost) is ~60 m above the

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Figure 7. (A) Contorted beds in coarse-grained sandstone (north of Somkhele Mine). (B) Overturned cross-beds are confined to single

beds (here 35 cm thick) of medium-grained, planar-cross bedded sandstone, and formed due to downcurrent bending and partial collapse

of over-steepened foresets (Emakwezini railway station). (C) Rare, non-diagnostic trace fossils in blue-grey, fine- to very fine siltstones

(facies Fm) (Ntambanana). Scale intervals are 1 cm. (D) Thin, discontinuous limestone lenses with knobbly lower and upper contacts (facies

Ca) (Emakwezini railway station). (E) Close-up of horizontal to subhorizontal rootlets displaying several orders of delicate branching in

white, massive claystones (facies P). These fine, bifurcating and tapering root traces can be several centimetres in length, are less than

1 mm in diameter, and cross-cut weakly preserved bedding planes at low-angle. Their morphology may suggest broadly spreading root

systems with shallow penetration in consistently wet substrates (north of Somkhele Mine). Scale intervals are 1 cm. (F) Soft-sediment

deformation features are very common in the interbedded sandstones and range from water escape structures to load casts and convoluted

bedding (northeast of Somkhele Mine).

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base of the formation, and the second (Coal Zone B)contains the thickest (5.3 m) coal seam (Figure 4A).

At Emakwezini, about eight thin (0.15 to 1 m) coalseams and strongly carbonaceous mudstones werereported, chiefly in the middle to upper part of theformation (du Preez, 1982, p. 58). At Heatonville, twothin (<1.5 m) coal seams are present in an ~18 m-thickcoal zone, some 120 m above the base of the formation(Genis, 1961, p. 15). In Swaziland, the EmakweziniFormation equivalent unit is much more condensed(<150 m thick; Figure 4C), yet the coal zones are againfour in total, of which the lowermost zone is 30 m abovethe basal contact of the formation, and the second oneis again the main zone with an average workable coalseam thickness of ~6 m (Davies, 1961). According toDavies (1961, p. 17), the notable consistency inthickness of the main coal zone and that of thecontained coal seam makes them reliable markers forstratigraphic correlations within Swaziland.

In summary, it appears that the best developed coalzone is in the lower one-third or half of the formation(Figure 4), occurring immediately beneath the coarsestand thickest sandstone package. It is also noteworthythat the average thicknesses of workable coal seams inthe coal zones are similar, even in widely separatedareas such as Swaziland and Somkele, where theaverage thicknesses of the minable coal seam in the main coal zones are ~6 m and 5.3 m, respectively. In light of the ongoing coal exploration efforts in theregion, these stratigraphic distribution patterns mightprove to be important for regional correlations. Datafrom the current geological exploration and miningoperations, especially around Somkhele Mine, willclarify the lateral and vertical facies distribution withinthe Emakwezini Formation.

InterpretationsThe two major facies associations of the EmakweziniFormation represent environments of a swampy fluvio-lacustrine setting, namely (1) a higher energy, low-sinuosity river channel belt and (2) a lower energy,alluvial floodbasin consisting of (a) overbank areas withpermanent lakes, (b) crevasse splays and (c) peatswamps (Figure 8).

Low-sinuosity river channel beltThe building blocks of the coarse-grained faciesassociation are interpreted as fills of shallow, mobile,sand-bed braided channels that were contained inslightly incised valleys. The latter are indicated by sharperosional surfaces at the base of the major channel-fills,commonly overlain by coarse channel lags. The incisionprobably occurred during fluvial base-level fall, and thevalleys were subsequently filled, at times fairly rapidlyand essentially through simple vertical and, to someextent, downstream aggradation (cf. Miall, 1996), duringtimes of fluvial base-level rise.

The multi-storey sequence architecture of themedium-grained sandy bedforms consisting ofindistinctly upward-fining successions, the ratheruniform palaeocurrent patterns (Figure 3) and the lackof features such as cut-banks, sloping channel margins,major lateral accretion surfaces, and point barsuccessions with bell-shaped log profiles, collectivelyimply that deposition in the slightly incised valleysoccurred in low-sinuosity, weakly confined braidedfluvial channels with an overall medium to high energylevel. In addition to the medium grain size, the moderateenergy level of these fluvial systems can be deducedfrom the abundance of planar cross-bedded sandstones(cf. Miall, 1996). The fluctuating current velocities within

Figure 8. Schematic block diagram illustrating the environments of a swampy fluvio-lacustrine setting of the Upper Permian Emakwezini

Formation in the Lebombo Basin.

the channels are indicated by the mud-draped coset andforeset surfaces.

Rapid aggradation rates are suggested by the varioussoft-sediment deformation features that resulted chiefly from water movement through overloaded,unconsolidated sediments (cf. Owen, 1996). In part-icular, overturned cross-bedding indicates a very fastrate of sedimentation, as it results from the drag of high-energy, sediment-laden flows across planar cross-bedded sandbars (cf. Turner, 1981; Owen, 1996).Considering the abundance of soft-sedimentdeformation features in the study area, it is possible thatmany of the massive, structureless sandstones formed asa result of over-rapid ‘dumping’ of sediments orwholesale dewatering during fast accumulation rates(Miall, 1996). The massive sandstones in the lower partof fining-upward successions with randomly orientedplant remains are additional unambiguous indicators ofsuch rapid accumulation of sediments from sporadichyper-concentrated flows. Soft-sediment deformationmight also be taken as indirect evidence for a relativelymoist environment, as the high sedimentation ratessuggested by them are also indicative of high rates ofdenudation, probably driven by increased precipitationin the drainage area.

According to Bridge (2003), upward-fining and -thinning successions with regular upward decrease inthe scale of cross-stratification may be interpreted as theresult of decelerating flow and decreasing sedimenttransport rate over the passage of a single flood.However, the presence of numerous internal erosionsurfaces within these indistinctly upward-finingsuccessions suggests that such multi-storey sand bodiesare products of multiple flooding events during whichpreviously deposited single-flood units were partially ortotally eroded (cf. Miall, 2006). Therefore channel-depthestimates, which are usually based on the scale of anautogenic channel-fill, are not attempted here. However the preserved maximum thickness of planarcross-beds (~2.2 m) allows for the minimum heightestimation of large sand dunes. Based on this, andconsidering that the ratio between the height of sandbars and total bankfull depth is ~0.5 in the modernBrahmaputra River (Bristow in Miall, 2006), theEmakwezini braided channels may have been, at leastlocally, 4 to 5 m deep, implying medium-sized rivers(sensu Fielding - see Miall, 2006). Because the steepstructural tilt and limited lateral continuity of outcropsprevented thorough assessment of three-dimensionalstacking arrangements of strata, other details of fluvialmorphology could only be hypothesized. For example,palaeo-channel widths, the calculation of which requirescontinuous outcrops roughly perpendicular to palaeo-flow, are estimated to have been about 100 m based onthe lateral continuity of some erosion surfaces (e.g.,Figure 6).

Architectural elements (e.g., SS, DA, LA) of thecoarse-grained facies association are interpreted asvarious sandy bedforms within the low-sinuosity

channels. Based on their relative abundance, these mid-channel sand dunes were accreted mainly vertically, lessfrequently in a downcurrent direction and very rarelysideways. The rare, medium-scale channel-fills withstrongly upward-curving basal surfaces (Figure 6) are explained as temporary margins of migratingchannels within the much wider channel belt in theslightly incised valleys. Interpretations of individuallithofacies of the coarse-grained facies association (Table 1) are not repeated in the text as these arestandard features of fluvial facies models (Miall 1978;1985; 1996).

Based on the characteristic depositional features(e.g., contained lithofacies, architectural elements, andgeometry of their internal erosion surfaces), the fluvialstyle of the Emakwezini Formation rivers closelyresembled that of the shallow, perennial, sand-bedbraided river model (Miall 1978; 1996). This similarity is underscored by the relative consistency of thepalaeoflow directions and by the dominance of planarcross-bedded sandstones (facies Sp) that occur inrelatively simple sand sheets (elements SS), and, lesscommonly, as downstream accreted deposits (elementDA). The only difference in the case of the Emakwezini,is the higher proportion of preserved floodplaindeposits, due to the relative confined nature of the mainbraided channel belt (see Discussion below).Considering the numerous recent accounts of the co-existence of shallow, sand-bed braided rivers andassociated extensive floodplains, this discrepancyexemplifies the need for modification of the originalfacies model of this river type (cf. Miall, 1996; Bristow et al., 1999; Allan and Fielding, 2007).

Alluvial floodbasinThe building blocks of the fine-grained facies associationare interpreted as deposits of moist overbank areascharacterized by various micro-relief features, viz. ridgesand swales, locally isolated depressions of variable sizeand relatively level plains. These features are typicallyassociated with different groundwater elevations, occurat different distances from the active channels, andhence reflect different water depths, soil drainage and sedimentary processes.

Overbank area with permanent lakesBased on their fine grain size, the mudstones weredeposited from suspension via low-energy processes inthe overall low-lying area of the overbank region. The finely laminated (facies Fl), rhythmically bedded,non-bioturbated and carbonaceous nature of themajority of the facies association suggests that the overbank area was dotted with deeper stratifiedlakes with restricted water circulation. The lack of waveripples in conjunction with the rhythmic bedding,suggests that these lakes had either a small fetch or steepmargins. Considering the relatively abundant aquaticfauna (e.g., fish, molluscs, concostrachans), it isreasonable to assume that these standing water bodies

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were generally not excessively acidic. Mud-size particleswere brought to the swampy overbank areas viafloodwater incursions and settled out mainly during thewaning phase of floods (cf. Miall, 1996). Primarymassive mudstones (facies Fm) may have originatedpartly in the above low-energy lakes from rapiddeposition during floods, and partly in the inter-lakeareas through homogenization of flood depositsresulting from bioturbation (cf. Collinson, 1996). Wherethe massive mudstones are associated with coal,fossiliferous and/or pedoturbated layers, they are morelikely to be a result of biogenic alteration.

The highly ferruginous carbonate layers (facies Ca)probably precipitated as pedogenic sideriticrhizoconcretions in palaeosols, a common phenomenonin modern reducing, poorly drained soils of the swampyoverbank area (cf. Moore et al., 1992; Ludvigson et al.,1998). The coalescence of the carbonate concretionsinto laterally restricted limestone lenses and theformation of cone-in-cone structures may have occurredin an early diagenetic phase as a consequence ofbiochemically decomposing organic matter (cf. Keighinet al., 1996).

Despite the lack of other pedogenic structures (e.g., angular blocky and wedge-shaped ped structures;pedogenic slickensides) associated with the stronglymottled mudstones (facies P), the morphology andtaphonomy of the contained in situ horizontal and semi-horizontal root remains show strong evidence of landsurface colonization by shallow-rooted plants, hencethese rocks are interpreted as a further evidence poorly-drained palaeosols in a swampy overbank area (cf. McLoughlin et al., 2005).

Crevasse splays The sandstone intercalations in the fine-grained faciesassociation are interpreted as crevasse splay depositsthat formed due to the invasion of the overbank areasby sediment-laden flood waters from the main channels.The vertical and lateral grain-size distributions as well asthe geometry of the crevasse splay deposits werecontrolled by the magnitude of the floods and thetopographic gradient of the overbank area (cf. Miall,1996).

Considering the previously interpreted slightlyincised valleys, crevassing may have occurred duringexceptionally strong floods and their frequency probablyincreased as the vertical aggradation in the slightlyincised valleys accelerated. The high energy and erosivenature of sediment-charged and fast-flowing currents isevidenced by the geometry and internal structures ofthese deposits (e.g., sharp lower contacts overlain byrip-up clasts and fossil logs, abundance of massive bedsand horizontal lamination). The very fast rate ofdeposition associated with these crevassing events issuggested by the profusion of soft-sediment deformationfeatures. The very rare, small-scale channel fills withinclined layers reminiscent of laterally accreted beds andupward-curving, erosional basal surfaces are interpretedhere as deposits of slightly meandering crevasse feederchannels.

Peat swampsCoal seams (facies C) and highly carbonaceousmudstones are interpreted as vegetal matter and organic-rich muds that accumulated in swamps of the overbankarea. Current research has shown that one of the

Figure 9. Schematic illustration of the parameters influencing coal-quality peat accumulation. For optimal peat formation, the surface of

the vegetated swamp and that of the water table should coincide, both of which are dynamic and over time can fluctuate vertically at

variable rates relative to one another and a fixed datum (diagram largely based on McCabe, 1984).

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most important factors influencing coal-quality peatdevelopment in swamps is the stability of a generallyanaerobic, low pH water table at the surface of vegetalaccumulation (Moore and Shearer, 2003). On one hand,the development of such equilibrium conditions, inother words the coincidence of the water table with thedepositional surface of the organic matter, is dependenton a steady balance between the water that enters andleaves the peat swamp (McCabe, 1984). The waterbudget in the swamp is influenced by factors such as the amount of direct precipitation, overland runoff (e.g., floodwaters), groundwater discharge andevapotranspiration rates (Figure 9). On the other hand,the position of a vegetated surface relative to the watertable is dependent on the plant production versus decayrates, subsidence rates (which may be due to tectonicmovements or compaction of the underlying sediment).Another important factor influencing coal formation isthe amount of flood water input to the swamps, whichin addition to providing aerated water, is also the mainsource of clastic sediments, and, in the case of paralicsettings, the source of sulphur and phosphorus(McCabe, 1984; 1987).

In fluvial environments, the influx of clastic sedimentis mainly related to the magnitude and frequency ofoverbank flooding and the lateral and vertical positionof the swamp surface relative to the main fluvialchannels. McCabe (1984, p. 24), who consideredaverage rates of peat accumulation and compactiontogether with frequency of flooding events in fluvialsettings, suggested that coal-quality peat accumulation isa strong indicator of long periods of negligible regionalclastic supply to the swamp.

The low sulphur and phosphorus together with highash content of the Emakwezini coal indicate that theseMiddle (?) to Late Permian swamps were distant frommarine influence, but were relatively close to fluvialsystems (cf. Thomas, 2002). Together with clastics,overbank flooding also supplied moisture, which wasprobably supplemented by direct precipitation andgroundwater discharge. The high vitrinite content of theEmakwezini coal, together with the large size of somefossil roots and woody axes and an abundance oflayered mats of Glossopteris leaves (see Palaeobotanysection), indicates that the swamps were probablyforested (cf. McCabe, 1984; Mastalerz and Padgett,2002).

Provenance and PalaeocurrentsBased on preliminary petrographic studies, the medium-to coarse-grained feldspathic and quartzose sandstonesof the Emakwezini Formation were provenanced fromcraton interior and transitional continental sources. Thedominant medium grain-size and the mineralogicallyand texturally submature sandstones (e.g., subangular tosubrounded and poorly sorted grains) and subroundedquartz pebbles, indicate moderate transportationdistances mainly under intermediate flow conditions.The relatively high feldspar content, in conjunction with

the micaceous facies and occurrence of granite clasts,suggest the dominance of granitoid rocks in the sourcearea. High-consistency palaeocurrent measurements(Figure 3), obtained from the foresets of planar cross-bedded sandstones, indicate low-sinuosity channels thatcarried sediments from a main source area to thenortheast, and to lesser extents to the southeast and east.Southerly or northerly palaeocurrents were notobserved. These results tie in well with the previouslysuggested general westerly palaeocurrents in the north-eastern and eastern part of the main Karoo Basin in theMiddle to Late Permian (see Figure 3). The name the“Eastern Highlands” was coined as by Ryan (1967) forthis predominantly eastern source area. He suggestedthat this mountainous region was an important source ofsediments for the Ecca and lowermost Beaufort Groupsin the eastern part of the main Karoo Basin. Morerecently, based on palaeoflow, palaeogeography anddetrital zircon analysis, Veevers et al. (2007)demonstrated that a granitoid source in centralAntarctica was a dominant and supposedly long-livedsupply of sediments to peri-Antarctic basins during theCambrian–Ordovician, Early Permian and Early Triassic.Similarity of the Emakwezini Formation to the LowerPermian successions in regional palaeocurrents,sandstone composition and regional palaeogeographyindicate that the same central Antarctic granitoid sourcewas also significant in the Middle and Late Permian.

PALAEOBOTANY OF THE EMAKWEZINI FORMATION

Description and assessment of the plant fossillocalitiesEmakwezini StationThe highly weathered railway section at EmakweziniStation is the holostratotype of the formation (Figures 1B, 4B, 4F). Although Visser (1957a) and Genis(1961) recorded the presence of several coal seams andcarbonaceous mudstones in this section (Figure 4B), wewere unable to locate these. We did, however, findseveral fossiliferous horizons containing well-preservedGlossopteris leaves in finely laminated, highly fissilemudstones in the middle and upper part of theformation (Figure 4B). Collections (Table 3) were madeat two of the most productive locations in the middle toupper-middle part of the formation, referred to here asSite 01 (S 28° 31.653’, E 31° 52.221’) and Site 02 (S 28°32.006’, E 31° 52.423’). Both sites expose intercalatedsandstones (mainly element CS), mudstones and sandysiltstones (element OF) of the fine-grained faciesassociation.

The plant fossils at Site 01 appear to beautochthonous, as indicated by an abundance ofVertebraria (rooting structures of Glossopteris) that insome cases transect the bedding planes and apreponderance of impressions of delicately preserved,leafy shoots with intact leaf whorls, belonging to twosphenopsid taxa. These taphonomic characteristics andvarious sedimentological features (such as horizontallylaminated, carbonaceous shales with good lateral

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continuity associated with rhythmites and crevasse splaysandstones), indicate that the deposits probablyrepresent a vegetated lake margin setting in theoverbank area, where there was in situ accumulation ofleaves and rooting of the substratum.

Site 02 is dominated by mats of well-preservedGlossopteris leaf impressions, with sphenopsidscomprising a minor element of the flora (Plates I; II; III).No in situ plant material was found, indicating that thedeposit is probably parautochthonous. This, togetherwith the associated horizontally laminated carbonaceousmudstones, suggests that the localized depositionalsetting at this site was probably a crevasse splay, withinwhich the plants were moved for a short distance beforethey settled out during the waning phase of a crevassingevent together with the suspended mud-size particles.

Kwa-Yaya railway siding This plant fossil locality (Figure 1B) is a railway cutting200 m west of the Kwa-Yaya railway siding,approximately 25 km west of Empangeni along the R34(S 28° 41.915’, E 31° 40.730’). The locality has not, to ourknowledge, been reported previously in the literaturealthough it has been known to geologists working in the

area for many years. Members of the Zululand Rock andMineral Club (ZRMC) have visited the site on severaloccasions (K. Pieterson, pers. comm.). This spatiallyisolated exposure of the Emakwezini Formation is ~2.75m high and ~100 m long, and displays a successionfrom the fine-grained facies association, including twopartial, very slightly upward-fining sandy successionsseparated by a scour surface that is overlain by a basallag with few impressions of (~30 m long) woody axes.Because of spatial isolation, the stratigraphic position ofthis site within the formation is only estimated to becloser to the upper boundary of the unit.

The flora (Table 3) comprises dense mats ofGlossopteris leaf impressions, interspersed withglossopterid ovuliferous and polleniferous fructificationsand several sphenopsid taxa. Examples of in situsphenopsid plants and Vertebraria roots cross-cuttingthe bedding planes were observed. The autochthonousnature of the deposit, together with associatedsedimentary features (such as horizontally laminatedmudstones overlain by an erosively based upward-finingsuccession with vague lateral accretions surfaces),indicates that the site probably represents the in situaccumulation of leaf litter in a vegetated floodplain

Table 3. Preliminary list of fossil plants from re-examined and newly discovered localities in the Emakwezini Formation.

Locality Floral elements Illustrations

Emakwezini Station Glossopteridales Glossopteris spp.

Rigbya arberioides Lacey et al. 1975

Dictyopteridium flabellatum Benecke 1976 Pl. I, B

Lidgettonia africana Thomas 1958 Pl. I, D

Lidgettonia lidgettonioides (Lacey et al. 1975) And. & And. 1985 Pl. I, E

several types of samaropsoid seed Pl. I, G

Eretmonia natalensis du Toit 1932 emend. Lacey et al. 1975

Arberiella sp.

Scale leaves

Vertebraria indica Royle 1834

Sphenopsida Phyllotheca australis Brongniart 1828 emend. Townrow 1955 Pl. II, A

Paracalamites australis Rigby 1966

Raniganjia kilburnensis And. & And. 1985 Pl. II, B

KwaYaya Glossopteridales Glossopteris spp. Pl. I, I, J; Pl. II, D-K;

Pl. III, B

Rigbya arberioides Lacey et al. 1975 Pl. I, F, H

Plumsteadia gibbosa (Benecke 1976) And. & And. 1985 Pl. I, H

Lidgettonia africana Thomas 1958

several types of samaropsoid seeds Pl. I, C

Eretmonia natalensis du Toit 1932 emend. Lacey et al. 1975

Arberiella sp.

Scale leaves

Vertebraria indica Royle 1834

Sphenopsida Phyllotheca australis Brongniart 1828 emend. Townrow 1955

Paracalamites australis Rigby 1966

Trizygia speciosa Royle 1840 emend. Pant & Mehra 1963 Pl. II, C

Incertae sedis Benlightfootia sp.

Somkhele coal mine Glossopteridales Glossopteris spp. Pl. III, A, D

(Coal Zone B) Ottokaria sp. Pl. III, G

Vertebraria indica Royle 1834

Sphenopsida Schizoneura gondwanensis Feistmantel 1876 Pl. III, C

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Plate I. Impression fossils of glossopterid leaves, ovuliferous fructifications and seeds from Emakwezini Station and Kwa-Yaya railway

siding. (A) apex of a Dictyopteridium sp. fructification [ES 190e]; (B) Dictyopteridium flabellatum fructification [ES 205]; note the small,

circular, raised tubercles (seed scars) evenly dispersed on the surface of the receptacle; (C and G) platyspermic, winged, samaropsoid seeds

[KY 28b; ES 185]; (D) dorsiventrally compressed capitulum of the ovuliferous fructification Lidgettonia africana (arrow) [ES 166b];

(E) laterally compressed capitulum of Lidgettonia lidgettonioides (arrow) [ES 190f]; (F) ovuliferous glossopterid fructification Rigbya

arberioides [KY 28a]; (H) partially preserved impression of the veined surface of the fructification Plumsteadia gibbosa (P), and

R. arberioides (R) [KY 19a]; (I) and (J) small, narrow Glossopteris leaves with polygonal meshes (note insect margin feeding traces in the

specimen in I) [KY 75a; KY 79a]; this morphotype is commonly associated with R. arberioides. Scale bars = 10 mm unless otherwise

specified. Square brackets contain the temporary field numbers of the specimens.

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Plate II. Sphenophytes and Glossopteris morphotypes from Emakwezini Station and Kwa-Yaya railway siding. (A) Phyllotheca australis leaf

whorls [ES 08]; (B) highly fused, disk-like leaf whorl of Raniganjia kilburnensis [ES 123b]; (C) Trizygia speciosa leaf whorls [KY 301a];

D to K samples of Glossopteris leaf morphotypes [KY 32; ES 45; KY 7a; KY 315a; KY 78a; KY 301a; KY 75a; KY 63b]: note the insect

oviposition scars to either side of the midrib in (D) particularly towards the apex; (E) a leaf with particularly broad/open meshes, similar

to those attributed by Lacey et al. (1975) to (G) conspicua, and by Anderson and Anderson (1985) to their Estcourtia vandijkii palaeo-

species; morphotypes in D and G to (J) fall within the palaeo-genus Lidgettonia of Anderson and Anderson (1985). Scale bars = 10 mm.

Square brackets contain the temporary field numbers of the specimens.

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Plate III. (A and B) distinctive Glossopteris morphotypes included by Anderson and Anderson (1985) within their palaeo-species Estcourtia

bergvillensis, found at both Kwa-Yaya [B; KY 72], and Somkhele Mine [A; SM 01]; note that the Somkhele specimen is double the size of

the leaf from Kwa-Yaya; (C) an unusually well-preserved specimen of the sphenopsid Schizoneura gondwanensis from Somkhele Mine,

with multiple foliar lobes in attachment [SM 02; scale bar = 50 mm]; (D) Glossopteris morphotype from Somkhele Mine [SM 03; scale bar =

50 mm]; (E and F) impression fossils from the SO1 borehole at Somkele, described by Plumstead (1970) as Dictyopteridium. Note the

abundance of oviposition scars, particularly along the midrib, in the specimen in E, which is the basal portion of a small Glossopteris leaf;

(G) adjacent specimens of the ovuliferous glossopterid fructification Ottokaria sp. (arrows). Scale bars = 10 mm unless otherwise specified.

Square brackets contain the temporary field numbers of the specimens.

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setting in relative close proximity to a wide, shallow,suspended-load, slightly meandering (?crevasse feeder)channel in the overbank area.

The plant fossils found in the Emakwezini Stationand Kwa-Yaya railway cuttings are unusually well-preserved and abundant. Preliminary investigations haverevealed a floral diversity directly comparable to that ofthe Late Permian floras of the main Karoo Basin.

By far the most dominant floral element at both thesesites is Glossopteris. The most common morphotypes areillustrated in Plates I, II and III. The leaves are generallyvery well-preserved, with excellent venation detail,although complete specimens are rare because of theweathered, fractured and fragmentary nature of theslabs. The abundance of material will allow for accurateand detailed characterization of the morphotypespresent, to be described in a future paper. Leaves fallingwithin the circumscriptions of the Estcourtia,Lidgettonia, Rigbya arberioides and Plumsteadia gibbosapalaeo-taxa of Anderson and Anderson (1985) areparticularly abundant (Plates I; II; III).

Although Anderson and Anderson (1985) did notreport the occurrence of R. arberioides fructifications atthe Emakwezini locality, they did note the presence ofleaves they attributed to their R. arberioides palaeo-species, i.e., glossopterid leaves consistently associatedwith this fructification at multiple sites. These leaves areapparently the same as those described by Lacey et al.(1975) from the Mooi River locality as Belemnopteriselongata. Many examples of this long, broad-meshedleaf with small, pointed basal lobes were found at Kwa-Yaya (Plate I: I, J), associated with a surprisingabundance (over 80 specimens) of Rigbya arberioidesfructifications (Plate I: F, H). Rigbya is only known fromthe Late Permian, and has a fairly broad distribution,with reports from Australia (Rigby, 1972; McLoughlin,1990, 1995) and Antarctica (Schopf, 1976).

Several other taxa of ovuliferous glossopteridfructification were found at the Kwa-Yaya andEmakwezini Station localities. These are the firstunequivocal fertile glossopterid organs to be reportedfrom the Emakwezini Formation. Rigbya arberioides,Dictyopteridium flabellatum (Plate I: A; B), Plumsteadiagibbosa (Plate I: H), Lidgettonia africana (Plate I: D) andLidgettonia lidgettonioides (Plate I: E), and thepolleniferous glossopterid organ Eretmonia natalensisare all characteristic elements of the Upper PermianNormandien Formation of the main Karoo Basin inwestern KwaZulu-Natal (Lacey et al., 1975; Benecke,1976; Anderson and Anderson, 1985; Adendorff, 2005).Dictyopteridium in particular is considered to be a usefulbiostratigraphic indicator for the Late Permian, and hasbeen recorded in Upper Permian deposits in India(Surange and Chandra, 1973), South Africa (Benecke,1976) and Australia (Rigby, 1978).

The genus Plumsteadia has a wide-ranging temporaland spatial distribution in Gondwana, probably becauseof its broad circumscription. Plumsteadia gibbosa,however, is a distinctive fructification currently known

only from several Upper Permian South African localitiesin the main Karoo Basin (Loskop, Mooi River, Inhluzani– Anderson and Anderson, 1985; Adendorff, 2005).

Numerous dispersed platyspermic seeds with lateralwings were found at both Kwa-Yaya and EmakweziniStation (Plate I: C; G). Very similar seeds are known tohave been produced by species of Lidgettonia andRigbya arberioides (Anderson and Anderson, 1985;Adendorff, 2005).

Two specimens of the extremely rare leaf typeBenlightfootia were found at Kwa-Yaya. This representsonly the second report of this probable sphenophytefrom South Africa – Lacey et al. (1975) described twoleaves from the Upper Permian Mooi River locality in themain Karoo Basin.

Sphenopsids Phyllotheca australis and Trizygiaspeciosa, both typical Upper Permian elements in themain Karoo Basin, were found at the Kwa-Yaya andEmakwezini Station localities. The deposits atEmakwezini Station (Site 01) contain a high density ofPhyllotheca australis foliage shoots (Plate II: A).Raniganjia kilburnensis (Plate II: B) is also present andhas been found at numerous localities in the UpperPermian Normandien (previously Estcourt) Formation,and a few localities that are thought to be MiddlePermian in age (Lacey et al., 1975; Anderson andAnderson, 1985). Within these localities it is apparentlyrare, and in most cases is recognized from fragmentedspecimens, but at Emakwezini Station there is anunusual profusion of this delicate sphenopsid andseveral specimens with multiple leaf whorls attached toindividual axes were collected.

The Somkele 1 deep borehole (SO1)Although the specimens from this borehole (approx. S28°21’ and E 32°06’ – see Figure 1B; taken ~170 m belowthe upper contact of the formation – see Figure 4A)identified by Plumstead (1970) as Dictyopteridiumappear to have been misidentified, they still provideevidence for a Late Permian age for the upper one thirdof the formation in the Somkele area. The Glossopterisleaves from the SO1 borehole core are very similar tothose consistently associated with the glossopteridfructification Lidgettonia, and which constitute the mostcommonly occurring leaf forms in the Upper Permiandeposits of the main Karoo Basin (Plate III: E; F). A LatePermian age is further supported by the presence ofPhyllotheca australis within the same section of the core,viz. above Coal Zone C (Figure 4A).

Somkhele MineThe recent open-cast mining operations west ofSomkele, at Somkhele Mine (Figure 1B) opened freshexposures of the coal-bearing succession associated withCoal Zones B and C (Figures 4A; 4D; 4E; 6) in themiddle part of the formation. Recent examination ofthese led to the discovery of a new fossil flora withinCoal Zone B (overlain by a prominent erosion surface;~115 m below the SO1 borehole core specimens

documented by Plumstead, 1970; Figures 4A; 6). Wewere able to make a small collection of the fossil flora,but the site was destroyed by mining operations shortlyafterwards.

Preliminary investigations have revealed aGlossopteris-dominated flora with glossopterid fertileorgans and subsidiary sphenopsid elements. Vertebrariaand rooted sphenopsid rhizomes cross-cutting thebedding planes indicate that the deposits areautochthonous. Based on the taphonomic characteristicsof the collected plant material and the associatedsedimentary features (horizontally laminated mudstonesclosely associated with coal seams) (Figure 4A), this siteprobably represents a very low energy, vegetated peatswamp isolated from sites of active clasticsedimentation.

Preliminary investigations have revealed that this isan atypical flora within the context of our currentperceptions of South African Permian biostratigraphy.The two key biostratigraphic indicators in thisGlossopteris-dominated flora are Ottokaria (Plate II: G)and Schizoneura gondwanensis (Plate II: C).

Ottokaria is a genus of glossopterid ovuliferousfructifications that, in South Africa, has only been foundpreviously in Lower Permian rocks (Plumstead, 1956;Anderson and Anderson, 1985; Adendorff, 2005) andmost other Gondwanan records are also restricted to thisinterval. There have been a few reports of this genus inthe Upper Permian of India and Australia (e.g., Banerjee,1978; McLoughlin, 1990) although the atypical wingmorphologies of those specimens suggest they could beplaced in a separate genus. On the other hand, S. gondwanensis is currently known only from theUpper Permian in South Africa, Australia and Brazil(Etheridge, 1903; Du Toit, 1932; Benecke, 1976;Anderson and Anderson, 1985; Rohn and Rösler, 1986;McLoughlin, 1992), although it has been found in bothMiddle and Upper Permian deposits in India(Feistmantel, 1880; Singh, 2000).

The Somkhele Mine flora is dominated byGlossopteris leaves much larger (some over 300 mmlong) than those characterizing the Upper Permian ofSouth Africa (Plate III: D). Although leaf size alone is nota sound biostratigraphic indicator, there is a trend withinSouth African Permian floras for larger Glossopterisleaves to be associated with Lower to Middle Permiandeposits (Anderson and Anderson, 1985). The presenceof broad-meshed morphotypes, very similar in shapeand venation style to those found in the Middle to UpperPermian of the main Karoo Basin (attributed byAnderson and Anderson, 1985, to Estcourtia), maysupport either a Middle or Late Permian age for the flora(Plate III: A; B). Detailed characterization of theGlossopteris morphotypes in this ongoing study willhopefully clarify this further.

PhytostratigraphyA detailed study of the floras is currently underway, butpreliminary results clearly demonstrate a strong

correlation between the upper parts of the EmakweziniFormation (represented by the Kwa-Yaya andEmakwezini Station localities) and the Normandien(previously Estcourt) Formation of the main KarooBasin. A Late Permian age is confirmed by the presenceof a range of taxa typical of this time period in SouthAfrica, including several sphenopsids and a suite ofovuliferous glossopterid fructifications.

The flora from Somkhele Mine (Coal Zone B) hasyielded a new glossopterid assemblage that containselements typical of both Late and Early Permian SouthAfrican floras, precluding a confident age determinationof the host strata within the biostatigraphic frameworkcurrently recognised in South Africa. This unusualcombination of plants, and the generally large size of theleaves present, may indicate that these deposits are nottemporal equivalents of the exclusively Upper Permianstrata at KwaYaya and Emakwezini. Alternatively, theprolonged existence of moist fluvio-lacustrine habitats inthe Somkhele region may have promoted the growthand preservation of plants atypical of floras commonlyassociated with the Upper Permian in the main KarooBasin.

DISCUSSION

Local environmental settingStratigraphic architecture in continental basins removedfrom marine influences is controlled by thesuperimposed effects of autogenic processes (e.g.,channel belt avulsion due to differential compaction),tectonics and climate (Shanley and McCabe, 1994).These are the ultimate controls of the changes in theequilibrium (graded) river profiles (or fluvial base level)and lake and local groundwater levels in fluvial-lacustrine settings (Catuneanu, 2006). Aggradation willoccur in fluvial channels when the fluvial base level isabove the land surface. This can be caused by tectonicsubsidence and/or relatively low discharge periods.Incision of channels will take place when fluvial baselevel falls below the land surface as a consequence oftectonic uplift and/or relatively high discharge periods.

Generally, previous studies have suggested that bythe time Beaufort Group deposition commenced in themain Karoo Basin in the Middle Permian, this part ofsouthern Gondwana was isolated from marineincursions (e.g., Catuneanu and Elango, 2001; Cairncrosset al., 2005; Catuneanu et al., 2005). However, based onthe recently discovered marine bivalve in the VolksrustFormation (Figure 2) of the eastern main Karoo Basin(Cairncross et al., 2005), marine influences cannot beexcluded. Hence, changes in sediment accommodation,at least in the Middle Permian portion of the EmakweziniFormation, may also have been impacted by fluctuationsin eustatic sea levels. However, considering the lowsulphur and phosphorus contents of Emakwezini coal,and the presence of freshwater conchostracans, directmarine incursions can be excluded. The currentdatabase does not allow us to extricate the tangledsignatures of autogenic, tectonic, climatic and possibly

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eustatic influences on fluvial base-level cyclicityrepresented in the Emakwezini Formation.

Sequence architecture of the Emakwezini Formation,including the lateral equivalence of the shallow,perennial, sand-bed braided rivers and extensivevegetated floodbasin, together with the verticalrelationships of four major clastic-coal sequences, isexplained here in terms of large-scale depositional anderosional events dictated by cyclical changes in sedimentaccommodation (e.g., fluvial graded profile).

We hypothesize that the co-existence of relativelyhigh to moderate energy braided fluvial and mainly lowenergy floodplain processes was facilitated by therepeatedly incised nature of the braided channel belts.The incision would have provided an elevationdifference between the depositional surfaces within andoutside the channel belt, and ensured protection offloodplains from influx of sand-size sediment whichonly entered these areas during stronger floods or attimes when the accommodation space within the incisedvalley was reduced, as the valley was gradually filled byvertically accreted sand bodies.

In terms of temporal fluvial base-level changes, thedepositional events that may have taken placethroughout the development of each clastic-coalsequence are the following: Phase 1 – fluvial base-level fall: incision of the valleysand coeval heavy erosion of the floodplain regions (notethat in the case of strong incision, the removal ofsediments deposited in the previous phase could occur). Phase 2 – stasis (relative stability of the system): by-passof sediments in the incised valleys (which acted asconduits in flushing the bedload towards the west andsouthwest), and coeval soil formation in the overbankareas. Phase 3 – during fluvial base-level rise: increasedsediment loads in channels leading to vertical stackingof sandbodies within the incised valleys and significantcoeval peat accumulation in the overbank areas cut offfrom active clastic sedimentation.Phase 4 – during late fluvial base-level rise: increasedaggradation of sediments (and reduced accommodationspace) in the incised valleys leading to more frequentflooding (including crevassing) with a high clastic influxto the overbank area.

A similar configuration of sandy braided channelbelt, associated floodplains and in-channel aggradationinduced by fluvial base-level rise and subsequentcrevasse splay formation has been described from themodern Niobrara River in Nebraska, USA (Bristow et al.,1999). As already mentioned, unravelling the autogenicand allogenic imprints and their effects on these fluvialbase-level changes is not currently possible. However,their magnitude can be deduced from the scale andnature of the architectural appearance (e.g., thickness,grain size, lateral continuity) of the contained sequences.For instance, the great and uniform thickness of CoalZone B at Somkele and in Swaziland (Figure 4A, 4C)suggests an extended period during which clastic influx

to the peat swamps was relatively low and probablycoincided with climatic conditions ideal for peataccumulation on a regional scale. The low sulphurcontent of the coal in combination with relatively lowclastic influx to the peat swamps collectively imply anextended period of relatively fast regional subsidence(cf. McCabe, 1989; Thomas, 2002) during whichdeposition of coarse clastic sediments was confined tothe incised valleys. This regionally fast rate ofsubsidence (phase 3 above) eventually slowed down(phase 4), and the subsidence was ultimately terminatedwhen the strongest fluvial base-level fall of theformation occurred (a new phase 1). This major incisionevent caused the significant down-cutting of thechannels to the level of thick, erosion-resistant peatlayers (Coal Zone B), the removal of the sequencesdeposited during the slower subsidence rates (of phase4) and the development of the prominent erosionsurface at the base of the coarsest (third) clastic-coalsequence. Considering the uncertain age of the floraassociated with Coal Zone B and the confidence withwhich we can deduce a Late Permian age for the rest ofthe succession, this prominent erosion surface aboveCoal Zone B may in fact represent a regionalunconformity.

Regional environmental settingExcept for the two localized coarsening-upwardsuccessions identified at Somkele (both in outcrop andin the subsurface - Figure 4A), diagnostic evidence ofdeltaic sedimentation (e.g., hummocky, herringbone,and wave ripple cross-stratification, bidirectionalpalaeocurrents, mature sandstones) has not beenrecognized in the study area. Therefore, the claim that the Emakwezini Formation has a “fluvio-deltaicorigin” (e.g., Linström, 1987a) is unsubstantiated by thecurrent findings. However, it is possible that the twobasal coarsening-upward successions indicate a short-lived, initial deltaic interlude that was eventuallysucceeded by the dominant fluvio-lacustrinedepositional interval.

A similar change from deltaic to fluvio-lacustrinesettings is present on a regional scale in thestratigraphically equivalent Normandien Formation,which is also characterized in its lower part bycoarsening-upward successions, albeit in differentproportions. These coarsening-upward successions areespecially prominent in the eastern main Karoo Basin(outcrop region of the former Estcourt Formation), anarea that constituted the basinward continuation of themore upslope depositional settings in the northeasternparts of the main Karoo Basin, and the southernLebombo (i.e., current study area) (Figure 3). In additionto palaeocurrent trends, the poor sorting, thearchitecture of the multi-storey sandstones, the higherabundance of upward-fining successions and thepresence of better developed coal seams in theEmakwezini Formation collectively suggest thatdeposition in the southern Lebombo area occurred in

closer proximity to the mountainous source to the eastand northeast, in a wetter, more densely vegetatedsetting than that envisaged for the other Upper Permiansuccessions in the main Karoo Basin.

One of the regional stratigraphic implications of thenewly discovered Emakwezini Formation floralassemblages is that the Ecca-Beaufort transition seems tohave occurred earlier in the southern Lebombo regionthan in the eastern main Karoo Basin (Figure 2). In otherwords, the possible time equivalence of the lowerEmakwezini Formation with the upper lacustro-marine(?) Volksrust Formation, and of the upperEmakwezini Formation with the fluvio-deltaic/lacustrineNormandien Formation, suggests that the overallregressive shrinking of the terminal Ecca lake(?‘Volksrust sea’) took place first from the south, theneast and finally from the north as indicated by thestratigraphic distribution of prograding deltaicsuccessions.

Climate during the Middle(?) to Late PermianLocal climate Coal seams, soft-sediment deformation, autogenic peatswamp limestones and shallow root systems collectivelypoint to relatively high to moderate precipitation and/orrelatively shallow groundwater levels throughout the deposition of the Emakwezini Formation. Theenvironment was continuously moist, a conditionnecessary for coal-quality peat formation andpreservation (cf. Miall, 1996). This permanently moistsetting is further corroborated by the absence in thesouthern Lebombo Basin of at least episodically dryclimate indicators such as raindrop impressions,desiccation cracks or semi-arid palaeosol features (e.g.,evaporitic pseudomorphs and rosettes, pedogeniccarbonate concretions, red colour mottling).Furthermore, the relative abundance of the medium-grained feldspathic sandstones, indicating slow chemicalweathering in this moist milieu, suggests cool, temperate(as opposed to warm, humid) conditions, probably in asetting distal to the montane climate of the EasternHighlands. The relatively wide range of fossil plant andanimal (i.e., trace fossils, insects, molluscs, arthropodsand fish) species reflects the presence of a complexecosystem in the area during the Middle to Late Permian.While individually none of these fossil organisms can beused as a climate indicator, several are aquatic, andhence may be taken as indicators of a fresh-waterwetland setting.

Regional climate Conditions that prevailed during the Late Permian aregenerally considered to have been unsuitable for thedevelopment of coal-bearing successions (e.g., Fuare et al., 1995), with the climate having becomeincreasingly arid (e.g., McLoughlin et al., 1997; Ward et al., 2000; 2005; Kiddler and Worsley, 2004). Thepalaeoclimatic signal of the Emakwezini Formationtherefore has regional implications.

Although Upper Permian coal measures are relativelyabundant in other high palaeolatitude sedimentarybasins of Gondwana with a humid, cool, temperateclimate (e.g., Australia, Antarctica, Chumakov andZharkov, 2003), coal is subordinate in the NormandienFormation and absent in the Balfour Formation in theneighbouring temperate, semi-arid main Karoo Basin(reconstructed at ~50 to 60ºS palaeolatitude, but ~41ºSaccording to Ward et al., 2005, supplement). Notably, insouth-central Africa, Middle Permian coal and UpperPermian mudstones with variable carbon content(Madumabisa Mudstone Formation and equivalents)have also been reported in Zambia, Tanzania, Malawi,etc. (Catuneanu et al., 2005). The latter are mainlyinterpreted as deposits of lake interior and littoralenvironments in a continental temperate climate (meanannual surface palaeotemperatures >10°C) (Yemane et al., 1989; Yemane and Kelts, 1990; Yemane and Kelts,1996; Nyambe and Dixon, 2000; Wopfner, 2002).

Within the lower Beaufort Group of the southern andwestern main Karoo Basin, evaporitic pseudomorphsand rosettes, desiccation cracks, raindrop impressions,pedogenic carbonate concretions and red mudstones arecommon in the Middleton Formation and are sporadic,but nonetheless present in the Balfour Formation(Johnson, 1976; Jourbert, 1994; Smith, 1990, 1995;Catuneanu and Elango, 2001). These features have beenused to interpret the Middleton Formation as deposits ofan arid to semi-arid fluvio-lacustrine setting (Smith,1990), and the Balfour Formation as deposits of “streamsin a semi-arid climate” and “shallow lacustrineenvironments on a cool, seasonally dry (i.e.,predominantly wet) alluvial plain” (Botha and Smith,2007, p. 132). Notably, up-sequence, the Upper Permianunits of the main Karoo Basin have been reported tobecome redder and contain calcareous nodules anddesiccation cracks in increasing abundance, whichaccording to Botha and Linström (1978), Groenewald(1989), Visser (1995) and Botha and Smith (2007) implya gradual aridification in the terminal Permian on aregional scale. Recently, however, these interpretationsof end-Permian aridification have been contested largelybased on geochemical and ichnological data (e.g., Taboret al., 2007; Gastaldo and Rolerson, 2008).

Accepting that the association of red mudstones,calcareous concretions, and desiccation cracks in theUpper Permian of the main Karoo Basin implies relativedryness on a regional scale, the absence of thisassociation from the upper part of the EmakweziniFormation may be explained as due to either (1) non-deposition/-preservation in a relatively moister, morereducing environment, implying a mosaic of differenthabitats in South Africa from the Middle until the veryend of the Permian, or (2) local erosion during aregional-scale denudation event that preceded thedeposition of the overlying ‘Stormberg Group’. The lattercase would imply that close to the end of the Permian,throughout South Africa, a homogeneous distribution ofgradually more arid environments with thin vegetal

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cover and ephemeral rivers and lakes was prevalent.Lack of absolute age indicators and the limitations of thebiostratigraphic resolution currently do not permit theclarification of this dilemma. Nonetheless, the otheroverall facies differences between the EmakweziniFormation and its correlatives in the main Karoo Basinsuggest that in the Middle Permian and for most of theLate Permian, the southern Lebombo was characterizedby a moist milieu with thick vegetation, permanent lakesand slightly incised braided-river belts sourced from theEastern Highlands of Gondwana (Figure 8).

Considering the physical proximity of theEmakwezini Formation and its age equivalents in the main Karoo Basin, it is unlikely that their moisturedifference resulted from palaeolatitude-controlledclimatic variation (e.g., dry, warm vs. wet, cooltemperate). More likely, these local moisture differencesmay be attributed to the topographic effect of theEastern Highlands over the Middle and Late Permiancontinental interior climate of southern Africa (cf. Chumakov and Zharkov, 2003). These north-southmountain ranges and upslope winds from the direction of perennial, internal lakes of southern Africa (e.g., Johnson, 1976, Yemane and Kelts, 1996) possiblyprovided sufficient orographic precipitation in the localhydrological cycle to maintain groundwater flow andrecharge rivers in the drainage basin of the EmakweziniFormation (Figure 8). The study area was, therefore, apermanent wetland that linked the surroundingmountains to the east and northeast to the lowlands inthe main Karoo Basin further to the west, wheresomewhat drier conditions were probably accentuatedby the rain shadow effect of the rising Cape Fold Belt inthe south (cf. Du Toit, 1948; Ward et al., 2000).

CONCLUSIONS

Sedimentary facies analysis and palaeobotanical studiesof the Middle (?) to Upper Permian coal-bearingEmakwezini Formation in the southern Lebombo Basinreveals a mosaic of architectural elements typical of low-gradient, alluvial floodbasins and low-sinuosity fluvialsettings. These permanent lakes, swampy floodplainsand relatively high- to moderate-energy river channelscoexisted, and were continuously recharged in an activehydrological cycle (probably via direct precipitation,overland as well as groundwater flow). The lateral andvertical stacking pattern as well as the indistinctlyupward-fining and chiefly planar cross-bedded nature ofthe multi-storey sandstones with erosional bases,suggest that the braided rivers were shallow, perennial,and sand-bed dominated and probably restricted toslightly incised valleys. Regional palaeocurrents,sandstone composition and regional palaeogeographyindicate that the Emakwezini Formation sediments weresourced from the northeast, east and southeast (from theEastern Highlands of Gondwana that stretchedeastwards, possibly into central Antarctica).

The association of carbonaceous, plant-fossil-bearing, laminated to massive mudstones, palaeosols

with in situ Vertebraria and rootlet horizons, coal, andinterbedded crevasse splay sandstones suggests that,flanking the incised valleys, the extensive vegetatedalluvial floodbasins had an irregular microrelief withdepressions of variable size, permanent lakes andforested swamps. This unit is exceptional in that it hassupplied geological and palaeontological evidence todemonstrate that in the southern Lebombo Basinpermanently moist climatic conditions favourable forcoal-quality peat formation existed in the Middle(?) toLate Permian, in contrast to other parts of westernGondwana, including the southern and north-westernmain Karoo Basin.

ACKNOWLEDGEMENTS

We gratefully acknowledge full financial support fromRhodes JRC (EB), the Palaeontological Scientific Trust(P.A.S.T.) (RP), the National Science Foundation (EAR-0230024) (RP) and the National Research Foundation(African Origins Grant, UID: 65241) (RP).

Thank you to Dr Billy de Klerk, Sean Linkermann,Mamadou Diop, John Hepple and Jenny Abdy for theirfield assistance, and to Sean Linkermann and JennyAbdy for helping with preliminary curation of thespecimens. We are also most grateful to SeanLinkermann for drawing our attention to the Kwa-Yayalocality. Thank you to the South African Police Forceofficials at Ntambanana for their concern and assistance.Data obtained from the Council for Geoscience in theform of coal exploration boreholes and unpublishedreports are gratefully acknowledged here together withthe beyond-the-call-of-duty assistance from Mrs NickyMcilrae, Mr Mxolisi Kota and Dr Johann Neveling.Insightful scientific discussions as well as invaluablefield and logistical assistance at Somkhele Mine (Petmin)were provided by Messrs David Grant, Brian Paull, Mark Snelling and Dr Ricky Pinheiro. We also thank S. McLoughlin and M. Johnson for constructive reviewsof the paper.

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