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Fossil Freshwater Molluscs from Simanya in the Kalahari System, Northern Namibia

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Fossil freshwater molluscan shells and steinkerns have been found at Simanya, on the Southwestern Bank of the Cubango River in Northern Namibia. The occurrence of fossils resembles those reported from other sites in the « Grès Polymorphes » subunit of the Kalahari System of Central Africa. The aim of this paper is to describe and interpret the Simanya fossils and to discuss their strati-graphic and palaeoenvironmental contexts. The silicified deposits (chert, chalcedony) in which the snails occur were extensively used by prehistoric peoples for manufacturing of stone tools.
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Fossil Freshwater Molluscs from Simanya in the Kalahari System, Northern Namibia
Helke Mocke
, Alma Nankela
, Martin Pickford
, Brigitte Senut
and Loïc Ségalen
1. Geological Survey of Namibia, 1, Aviation Road, Windhoek.
(e-mail: <>)
2. National Heritage Council of Namibia, Windhoek.
3. Sorbonne Universités (CR2P, UMR 7207 du CNRS, Département Histoire de la Terre, Muséum National
d’Histoire Naturelle et Université Pierre et Marie Curie) case postale 38, 57 rue Cuvier, 75005 Paris.
(e-mail: <>)
Abstract: Fossil freshwater molluscan shells and steinkerns have been found at Simanya, on the
Southwestern Bank of the Cubango River in Northern Namibia. The occurrence of fossils resembles
those reported from other sites in the « Grès Polymorphes » subunit of the Kalahari System of Central
Africa. The aim of this paper is to describe and interpret the Simanya fossils and to discuss their strati-
graphic and palaeoenvironmental contexts. The silicified deposits (chert, chalcedony) in which the
snails occur were extensively used by prehistoric peoples for manufacturing of stone tools.
Key Words: Chert; Chalcedony; Grès Polymorphes; Plio-Pleistocene; Gastropods; Fossils; Namibia.
To cite this paper: Mocke, H. Nankela, A. Pickford, M. Senut, B. & Ségalen, L. 2016. Fossil Freshwater Mol-
luscs from Simanya in the Kalahari System, Northern Namibia. Communications of the Geological Survey of
Namibia, 17, 66-84.
Submitted November 2015
In 2013, the discovery of fossil gastro-
pods at Simanya River Lodge on the south-
western bank of the Cubango River, was re-
ported to the Geological Survey of Namibia by
the owners of the lodge.
A visit to the site by HM and AN re-
sulted in the collection of additional fossils
which included ampullariids, pomatiopsids and
planorbids as well as small fragments of silici-
fied wood.
The aim of this note is to identify and
interpret the snail fossils from Simanya and to
discuss their importance within the context of
the fossil record of the Grès Polymorphes of
the Kalahari System.
Geological Setting
The Simanya silicified deposits occur
on the southwestern flank of the Kavango
(Cubango) River at Simanya River Lodge (S
17°32’27.6’’: E 18°32’00.1’’) at an altitude of
1113 m (GPS set to WGS 84) (Fig. 1). The
locality is just outside the eastern flank of the
Cubango Megafan (Miller et al. 2010) and as
such, the sediments underlying the silicified
horizon (1 - 1.5 m thick) comprise poorly con-
solidated fluviatile pale grey-yellow sandy silts
and sandstones with millimetric quartz peb-
bles, over 20 metres thick (exposed down to
river level) and are overlain by 1-2 metres of
unconsolidated red sands (Fig. 2).
Figure 1. Relief map of Namibia depicting occurrences of silicified rock rich in fossil freshwater molluscs at
Simanya, Ekuma and the Sperrgebiet.
The silicified deposits at Simanya oc-
cur principally as loose blocks in the slopes
leading down to river level (Fig. 3) where
masses of cobbles have accumulated in certain
places in the shallows (1090 metres above sea
level) (often aligned by local inhabitants to
make fish traps) (Fig. 4). Limited outcrops oc-
cur in situ beneath the crest of the valley where
its southwestern slopes fade out upwards into
the Kalahari Plains to the southwest.
In the broad valley bottom of the
Cubango River, there are younger silts and
marls (Late Pleistocene to Recent) which are
also fossiliferous (snails, plant remains) but
which show no signs of silicification. These
younger deposits correspond, for the most part,
to floodplain silts and marls overlain by, or
comprising eutric fluvisols (Jones et al. 2013).
The pale grey indurated marly beds are ex-
ploited locally for brick-making as they are
easy to excavate and to cut to size with ma-
Figure 2. Local geology of the region around Simanya River Lodge. 1 - West Bank of the Cubango River with
poor exposures of fluvio-paludal sands and silts, silicified just beneath the top of the slope; 2 - Kalahari Red
Sands and interdune vlei silts (which accumulated in small endorheic depressions and shallow valleys); 3 -
Floodplain deposits of the Cubango River dominated by indurated marls and eutric fluvisols. Orange star: richly
fossiliferous silicified sand and marl (chert, chalcedony) beneath the Kalahari Red Sands, Yellow stars: fossilif-
erous moderately indurated marl of the Cubango floodplain deposits (Map modified from Google Earth).
Examination of the Simanya silicified
deposits under the hand lens reveals that the
cherty fractions are comprised of fine sand and
marl with occasional well-rounded millimetric
quartz pebbles, all intensively silicified to pro-
duce a dark brown, homogeneous flint-like
rock, often with a porous surface.
The chalcedonic deposits are pale yel-
low to light brown and are less densely silici-
fied, and some of them appear to correspond to
silicified marls (and eutric fluvisols). Both
rock types are fossiliferous and contain pre-
dominantly gastropods, but also ostracods,
plant rootlets and rare small pieces of silicified
Material and methods
The fossils described herein are curat-
ed at the Geological Survey of Namibia, Wind-
hoek, under the abbreviation « Sim » followed
by the catalogue number (Table 1). They were
measured with sliding calipers to the nearest
tenth of a mm. Images were captured with a
Sony Cybershot Camera and enhanced using
Photoshop Elements 03.
Comparisons were made with extant
gastropods from Africa (Brown, 1980; Connol-
ly, 1939) and fossils from the Grès Polymor-
phes (Leriche, 1928, 1933; Mouta & Dart-
evelle, 1952; Newton, 1920; Polinard, 1933b).
Nomenclature of shell parts is based on West
et al. 2003.
Due to the limitations of the preserved
parts of the shells (half the specimens are
steinkerns) it would be illusory to pretend to be
able to identify all the specimens to the species
level. Therefore, we describe the specimens
and provide tentative identifications to species
where the evidence warrants it. Otherwise we
remain at the heirarchical level of the genus.
Figure 3. Blocks of silicified sands and marls at Simanya River Lodge, Namibia, at shallow depths near the
southwestern edge of the Cubango Valley. Note the grass-rich Miombo Woodland vegetation and the thin cover
of red sand. The site yields abundant fossil freshwater snails.
Figure 4. Concentrations of blocks of silicified sediment in the bed of the Cubango River, arranged by local in-
habitants into artisanal fish traps. Note the pale silts and eutric fluvisol forming the bank of the river (on the right
of the image) and the Simanya River Lodge in the background.
Table 1. Catalogue of fossil specimens and stone tools from Simanya, Northern Namibia (measurements are in
Locality Catalogue Identification Description Breadth Height
Simanya 1 Pila steinkern 55.5 52.9
Simanya 2 Tomichia section 1.3
Simanya 3 Bulinus shell 6.7
Simanya 4 Pila shell fragment
Simanya 5 Pila shell
Simanya 6 Pila shell fragment & operculum
Simanya 7 Pila shell
Simanya 8 Pila fragment
Simanya 9 Pila steinkern 38.4
Simanya 10 Pila steinkern 32.0
Simanya 11 Pila mould of spire 27.2
Simanya 12 Pila shell
Simanya 13 Pila shell
Simanya 14 Pila shell
Simanya 15 Pila shell 30+
Simanya 16 Pila shell
Simanya 17 Pila mould
Simanya 18 Pila shell 35.5
Simanya 19 Pila mould
Simanya 20 Ceratophallus shell 2.7
Simanya 21 Bulinus shell 4.8
Simanya 22 Bulinus + ostracod shell
Simanya 23 Various snails shells
Simanya 24 Bulinus shell 4.2
Simanya 25 Unidentified dextral snail shell 1.8
Simanya 26 Ceratophallus shell 2.1
Simanya 27 Ceratophallus shell
Simanya 28 Bulinus shell 2.7
Simanya 29 Bulinus shell 3.2
Simanya 30 Bulinus shell
Simanya 31 Bulinus shell 4.5
Simanya 32 Bulinus shell 5.0
Simanya 33 Bulinus shell
Simanya 34 Ceratophallus shell
Simanya 35 Bulinus shell
Simanya 36 Bulinus shells 3.5, 2.4
Simanya 37 Bulinus shell
Simanya 38 Ceratophallus shell 2.7
Simanya 39 Ceratophallus impression 2.1
Simanya 40 Bulinus shell 4.5
Simanya 41 Bulinus elongate form shell 1.3
Simanya 42 Various snails shells
Simanya 43 Various snails shells
Simanya 44 Pila + Ceratophallus shell
Simanya 45 Bulinus shell
Simanya 46 Ceratophallus shell 3.4
Simanya 47 Plant wood
Simanya 48 Ceratophallus shell 1.7
Simanya 49 Ceratophallus shell 1.8
Simanya 50 Bulinus shell 2.2
Simanya 51 Bulinus section 2.9
Simanya 52 Bulinus spire 2.9
Simanya 53 Bulinus shell
Simanya 54 Various snails sections
Simanya 55 Ceratophallus impression
Simanya 56 Various snails shells
Simanya 57 Bulinus shell 1.7
Simanya 58 Bulinus shell 2.7
Simanya 59 Bulinus mould
Simanya 60 Snail shell
Simanya 61 Snail sections
Simanya 62 Ceratophallus small shell
Simanya 63 Tomichia, Ceratophallus, Bulinus shells 1.8
Simanya 64 Bulinus shell
Simanya 65 Plant roots
Simanya 66 Snail mould
Simanya 67 Ostracod? shell
Simanya 68 Bulinus shell
Simanya 69 Chert Tool
Simanya 70 Chert Tool
Simanya 71 Chert Tool
Simanya 72 Chert Flake
Simanya 73 Chert Flake
Simanya 74 Chert Flake
Simanya 75 Chert Flake
Simanya 76 Chert Flake
Simanya 77 Chert Flake
Simanya 78 Chert Flake
Simanya 79 Chert Flake
Simanya 80 Chert Flake
Simanya 81 Chert Flake
Simanya 82 Chert Flake
Simanya 83 Chert Flake
Simanya 84 Chert Chopper
Simanya 85 Ceratophallus impression 2.0
Simanya 86 Pila impression
Systematic organisation
The descriptions of the Simanya fossil snails
follow the systematic scheme presented by
Brown (1980) with modifications following
West et al. (2003).
Table 2. Systematic schema of fossils described in this paper.
Class Gastropoda Cuvier, 1798
Family Ampullariidae Gray, 1824
Genus Pila Röding, 1798
Family Pomatiopsidae Stimpson, 1865
Subfamily Pomatiopsinae Stimpson, 1865
Genus Tomichia Benson, 1851
Family Planorbidae Rafinesque, 1815
Subfamily Planorbinae Rafinesque, 1815
Genus Ceratophallus Brown & Mandahl-Barth, 1973
Subfamily Bulininae Oken, 1815
Genus Bulinus Müller, 1791
Descriptions of Simanya fossil Gastropoda
Genus Pila Röding, 1798
Several medium to large dextral glo-
bose shells from Simanya with depressed conic
apices are confidently attributed to the genus
Pila, and probably to the species wernei (Fig.
5, A-E).
The shells have shouldered whorls, a
relatively low spire and the aperture is appre-
ciably taller than its breadth, as in the species
Pila wernei in contrast to the broader aperture
of Pila ovata. The umbilicus is open but not
very broad.
The shells range in diameter from 35.5
to 55 mm. The tallest individual has a height of
52.9 mm.
Genus Tomichia Benson, 1851
Two small dextral elongate conic
shells from Simanya are close in dimensions
and shell morphology to extant Tomichia. The
specimens are 1.3 mm and 1.8 mm in width.
The sutures are impressed, the whorls
rounded and the shell surface smooth (Fig. 6,
G, H). The Simanya specimen is similar in
shell features (dimensions, whorl number, ratio
of breadth to height, degree of impression of
the suture) to several species of Tomichia such
as T. lirata.
Figure 5. Shells and steinkerns of Pila cf wernei from Simanya, Northern Namibia. A) Sim 11, impression of
apex of shell (A1 - stereo image of impression, A2 - stereo images reversed to produce positive relief image of
the apex); B) Sim 18, damaged shell in chert nodule (B1 - lateral view, B2 - apical view); C) Sim 10, steinkern
(C1 - stereo apical view, C2 - stereo apertural view, C3 - lateral view); D) Sim 9, steinkern (D1 - stereo apical
view, D2 - lateral view); E) Sim 1, partly shell, partly steinkern (stereo images of E1 - apical view, E2 - apertural
view, E3 - basal view, E4 - lateral view, E5 - back view) (scales - 10 mm).
Figure 6. Fossil molluscs from Simanya, Northern Namibia. A) Sim 46, Ceratophallus, stereo image; B) Sim
48, Ceratophallus stereo image; C) Sim 49, Ceratophallus stereo image; D) Sim 50, associated shells of planor-
bid and Bulinus, stereo images; E) Sim 40, planorbid and Bulinus shells, stereo image; F) Sim 39, impression of
planorbid shell in chert; G) Sim 63, Tomichia, stereo image; H) Sim 2, cross section of Tomichia, stereo pair; I)
Sim 57, Bulinus apex in stereo view; J) Sim 41, elongate Bulinus, stereo image of back of shell; K) Sim 62, Buli-
nus steinkern lacking its apex, stereo image (scales: 1 mm).
Genus Ceratophallus Brown & Mandahl-Barth, 1973
Planorbid shells are quite common at
Simanya. They possess a rounded periphery,
an extremely broad umbilicus and sunken spire
(Fig. 6, A, B, C, F). Attribution to Afrogyrus,
Armiger, Gyraulus, Lentorbis, Segmentorbis,
Biomphalaria, Helisoma and Indoplanorbis
can be ruled out on the basis of the breadth to
height ratio of the shells, or on the absence of
angulation in the body whorl, or on the breadth
of the umbilicus, or on the absence of external
shell ornamentation. The closest resemblances
of the Simanya shells are to Planorbis and
Ceratophallus, but the more rounded whorl
without a basal angulation shifts the balance
towards Ceratophallus. One of the specimens
in particular (Fig. 6a) resembles Ceratophallus
Genus Bulinus Müller, 1791
Small sinistral shells are common at
Simanya, and they show a diversity of shell
shapes, indicating the presence of at least three
The first form has a low spire like Bu-
linus angolensis (Fig. 6, E, I, K; Fig. 7, A), the
second has a taller spire with a pointed apex,
like Bulinus tropicus (Fig. 6, D; Fig. 7, B, D,
E, F) while the third is elongated, somewhat
like the species Bulinus scalaris (Fig. 6, J).
Figure 7. Silicified gastropods in chert and chalcedony from Simanya, Northern Namibia. A) Sim 21, apex of
Bulinus, A1 - apical and A2 - apertural views; B) Sim 33, Bulinus, stereo view of back of shell; C) Sim 25, uni-
dentified dextral shell, basal view; D) Sim 36, Bulinus, stereo view of back of shell; E) Sim 31, Bulinus shell in
chert; F) Sim 32, Bulinus steinkern lacking the apex (scales: 1 mm).
Genus indet.
There is a small dextral shell from
Simanya (Sim 25) with an open umbilicus,
almost circular body whorl and clear but irreg-
ular growth lines or rugosities (Fig. 7, C). The
apex and the upper half of the aperture are not
visible which makes it difficult to identify, but
it does not resemble any of the other material
from the site. There are several African fresh-
water snails which show the same degree of
opening of the umbilicus and the rounded body
whorl, including Valvata, some species of Ga-
biella and Funduella. More complete material
is required to determine the affinities of this
Figure 8. Relief Map of Africa showing the approximate extent of the Kalahari System (inside the black lines)
and the occurrence of silicified freshwater molluscs (black dots) in the sub-equatorial half of the continent. Ex-
tent of the Kalahari System is modified from Cahen & Lepersonne, 1952. (Position of Burman Bush is after
Frankel, 1964, and Ngami is after Shaw & Thomas, 1988, Thomas & Shaw, 1991, and Shaw, 1985).
The Grès Polymorphes
The fossil freshwater snails from Sim-
anya occur in silicified fine sand and marl,
which can be described as chert (for the dense,
dark brown varieties) and chalcedony (for the
less dense, paler deposits). In the past, similar
deposits which occur in DR Congo, Angola
and Zimbabwe, were grouped into the Grès
Polymorphes subunit of the Kalahari System
(Polinard, 1932; Leriche, 1932; Mouta, 1954;
Mouta & O’Donnell, 1937) (Fig. 8).
These strata are in part homonymous
with the Kalahari Group of the Owambo Basin
as defined by Miller et al. (2010). According to
Mouta (1954) the Kalahari System comprises
the Kamina Stage at the base (known only in
the DR Congo), followed by the Grès Poly-
morphes in the middle, and Red Sandy Depos-
its (limons sableux ocres) at the top (Anony-
mous, 1947) which are widespread throughout
Congo and Angola, extending as far east as the
Victoria Falls, Zimbabwe, and as far south as
northern Namibia and Botswana. Through
much of Angola, the Red Sandy Deposits are
hundreds of metres thick.
Veatch (1935) proposed the following
succession for the Post-Karroo rocks of the
Kasai-Lunda region:-
Terrace Gravels and Sands - Pleistocene to
Plateau Gravels and Sands - Late Pliocene to
Early Pleistocene
High Plateau Sands - Miocene
Generally silicified sands, chalcedonic quartz-
ite, with freshwater fossils - Oligocene
Conglomerates - Oligocene
He recognised two geomorphological
surfaces (peneplains); the so-called « Miocene
Peneplain » which formed later than the sands
of the high plateaux, and the « End-Tertiary
Peneplain » which formed later than the Plat-
eau Gravels and Sands. Lepersonne (1945) and
Cahen & Lepersonne (1952) agreed in general
with these stratigraphic and geomorphological
interpretations and extended them from the
Congo Basin southwards to South Africa, alt-
hough they noted that there were localised dif-
ferences from the overall scheme.
Gastropods from the Grès Polymorphes
Studies of gastropods from the Grès
Polymorphes were mostly done during the first
half of the 20th Century. The nomenclature of
gastropods has evolved in the meantime, with
the creation of new genera, such as Cera-
tophallus Brown & Mandahl-Barth, 1973. The
fossils described in these pioneer papers need
to be re-examined, because it is clear that au-
thors were employing the genus names Bulinus
and Planorbis, for example, in rather different
ways than they would be used today. In the
following discussion, the original names are
recorded as published.
At Mount Bunza (DR Congo - NE An-
gola) the fossiliferous chalcedony overlies
Karroo strata (Leriche, 1928; Maufe, 1929a,
1929b). Leriche (1928) described Planorbis sp.
and Physa Parmentieri (sic) associated with
Chara Rauwi (sic) and ostracods (Cypris
Farnhami (sic). Leriche (1925, 1928) conclud-
ed that, on the basis of the presence of Bulinus
and Planorbis, the oldest that the Mount Bunza
fossils could be is Upper Jurassic, but such an
estimate was quickly challenged by Polinard
(1933a, 1933b, 1933c) who thought they were
much more recent. Mouta (1954) wrote that the
fossiliferous «Grès Polymorphes» or «Chalce-
donic Quartzites» repose upon an upper Creta-
ceous surface (the Gondwana Surface of King,
1951) whereas the Kalahari System covers a
younger erosion surface, the African Surface
of King (1949, 1951). For Mouta (1954) there
was a third phase of erosion resulting in the
End-Tertiary Surface, which is unconformably
overlain by reworked Kalahari sand and gravel
deposits and even by much younger fossilifer-
ous silicified formations (Pleistocene).
Newton (1920) listed Viviparus and
Hydrobia in the Chalcedony of Southern Rho-
desia (Zimbabwe). Following this lead, Maufe
(1929b) listed several gastropod genera from
the silicified deposits of the Zambezi Valley
(27°- 28°30’ E : 19° S). Viviparus (Paludina),
Hydrobia Paludestrina»), Melania (doubt-
ful), Limnaea and Isodora (a junior synonym
of Bulinus) which are accompanied by the
charophyte Chara. Leriche (1928) considered
the Zambezi chalcedony to be a silicified lime-
Polinard (1933b) described the fresh-
water fauna from chalcedony found near Lu-
budi, Katanga, DR Congo. Accompanying os-
tracods and charophyte gyrogonites, there was
a low diversity of gastropods, Planorbis Fon-
tainasi (sic), Bulinus (Pyrgophysa) Cayeni
(sic), and Bulinus (Pyrgophysa) sp. He con-
cluded that the Lubudi fauna was close to that
of Mont Bunza described by Leriche (1928)
despite the different names given to the fossils.
He deduced that the Lubudi fossils could be of
any age between Jurassic and Quaternary.
Leriche (1933, 1938) recorded a suite
of snails associated with charophytes from
partly silicified limestones in the valley of the
Kampemba (eastern edge of the Kundelungu
Plateau - see also Brien, 1921): Physopsis afri-
cana var. didieri, Limnaea (sic) cf. africana,
Limnaea (sic) sp. and Planorbis sp. On the
basis of these identifications, he estimated an
Upper Pliocene to Pleistocene age for the oc-
Dartevelle (in Mouta & Dartevelle,
1952) identified a variety of snails from silici-
fied deposits (Chalcedony) in the « Grès Pol-
ymorphes » at several sites near Cassanje
(Malanje, Angola) associated with charophytes
and ostracods. There were Lymnaea of the
Lymnaea (Radix) natalensis group, three forms
of Biomphalaria (groups sudanicus, cho-
anomphalus and adowensis), Anisus, four
forms of Bulinus (Bulinus (Bulinus) sp. Buli-
nus (Pyrgophysa) cfr cristalinus, Bulinus (Pyr-
gophysa) cfr forskali and Bulinus (Parabythin-
ia) sp?), Ancylidae sp?, and two forms of Pila
(Pila wernei and Pila sp.). There were also
questionable remains attributed to a streptaxid
land snail and a bivalve, Caelatura. Despite
the difficulty of interpreting the fossils from
Cassanje, due to their fragmentary and poorly
preserved condition, Mouta & Dartevelle
(1952) were inclined to correlate them to the
Pleistocene (probably Middle Pleistocene) on
account of the fact that none of the taxa are
known from the Early Tertiary, and all of them
occur in Africa at the present day. Leriche
(1938) reiterated that these deposits are rich in
shells of Pila (Ampullaria).
In brief, the ages of the various strati-
graphic units which comprise the Kalahari Sys-
tem remained uncertain during the 20th Centu-
ry, just as they do today. Rocks attributed to
this unit span the vast time period from post-
Karroo to Recent. Pertinent to understanding
the complexity of the situation are fossil
freshwater molluscs from Etosha (the gastro-
pod Bellamya and mutelids of middle Pliocene
age in silicified sands of the Ekuma Delta
Member: Pickford et al. 2014, 2016; Miller et
al. 2010) and the Sperrgebiet (hydrobiids,
planorbids and lymnaeids of Bartonian age in
chalcedonic limestone at Silica North, Silica
South, Chalcedon Tafelberg, Steffenkop and
Eisenkieselklippenbake: Pickford et al. 2008;
Pickford, 2015). These occurrences resemble
those found in the Kalahari System, not only
by their mode of preservation, but also by the
taxa represented, but in addition they are asso-
ciated with mammalian fossils which provide
confident estimates of their geological ages.
This means that, on their own, Tertiary fresh-
water gastropods of Africa do not generally
yield accurate biostratigraphic information (in
contrast to deep graben lake assemblages such
as those from Palaeolake Obweruka, Uganda,
which provide important exceptions: Van
Damme & Pickford, 1995, 1999, 2003, 2010;
Van Damme et al. 2010).
From this it is concluded that freshwa-
ter snails on their own, do not provide reliable
biostratigraphic information for estimating the
ages of the strata included in the «Grès Poly-
Palaeoenvironmental indications and
silicification environment
The composition of the freshwater gas-
tropod fauna from Simanya indicates that the
water bodies in which they lived were fresh
and generally well-oxygenated (for Pila), and
probably shallow and marshy (Bulinus, Cera-
tophallus). The cherty fossiliferous blocks of-
ten contain well-rounded sand grains and small
well-polished quartz pebbles (up to 2-3 mm in
diameter) consistent with deposition close to or
within a fluvial system. The more chalcedonic
facies resembles the marls associated with eu-
tric fluvisols which occur today in the flood-
plain of the Cubango, with the exception that
the Simanya samples have been silicified.
Combining the faunal evidence with the sedi-
mentary facies suggests that the fossiliferous
deposits accumulated in a floodplain close to
the Palaeo-Cubango, probably as short-lived,
shallow, somewhat swampy depressions. They
were subsequently buried by further fluvial
deposition, followed by accumulation of the
Kalahari Red Sands (largely aeolian sands),
and were then silicified close to the ancient
land surface. Mouta & Dartevelle (1952) were
of much the same opinion about the deposi-
tional environment of the chalcedonic rocks of
the Grès Polymorphes.
There has been little detailed discus-
sion concerning the mode of silicification, or
the processes that led to near-surface silicifica-
tion of the chalcedonic rocks of the Kalahari
System. Mouta & Dartevelle (1952) thought
that it occurred under desert conditions, but the
distribution of the siliceous deposits in the re-
gion is closely associated with Miombo Wood-
land (savannah) (Fig. 9) in contrast to desert
such as in Kaokoland in which near-surface
induration has produced immense quantities of
« calcrete » and no silicified deposits.
The Simanya occurrence indicates that
silicification occurred near the land surface (1-
2 metres beneath the surface) comprised of red
unconsolidated sands, and that silicification
affected not only deposits of fine sand, but also
marls related to eutric fluvisols. Similar near-
surface masses of silicified rocks occur widely
in DR Congo, Angola, Botswana, Namibia and
parts of South Africa (Mouta, 1954, personal
observations MP) almost invariably associated
with a sand cover and Miombo Woodland veg-
etation (or near equivalents often referred to as
savannah). These silicified rock layers are sel-
dom more than 2-3 metres thick, and are usual-
ly underlain by bedrock or by less consolidated
fluvio-paludal and terrestrial deposits (the case
at Simanya).
In stark contrast, near-surface indura-
tion of rocks in Mopane Woodland and related
vegetation types, which grow in more arid are-
as than Miombo categories, such as for exam-
ple, in Kaokoland, Namibia, almost invariably
comprises calcification to produce « calcrete »
of various sorts (calcisols and derivatives,
Jones et al. 2013), but likewise seldom more
that 2-3 metres thick, overlying bedrock or
poorly indurated sediments. There can be little
doubt that climatic conditions largely deter-
mined not only the processes of silicification
and calcification but also the type of vegetation
that grew in the regions.
The silica in the chert and chalcedony
at Simanya could have been derived from opal
phytoliths (Miombo Woodland is rich in grass
cover) or it could have been derived from the
dissolution of silica from the superficial sands
which blanket the country throughout the re-
There is a possibility that subterranean
fungus plays an important role in silica diagen-
esis in Miombo Woodland settings. Fungus
communities are diverse and well-developed in
such sub-humid conditions, and often concen-
trate sugars in their hyphae, producing an alka-
line chemical environment in which silica is
more prone to dissolve than in acid environ-
ments. Reduction of alkalinity by whatever
means results in silica precipitation. Because
fungal hyphae are concentrated in the superfi-
cial layers of the soils, then this is where silici-
fication will preferentially occur.
Figure 9. Location of Simanya (Northern Namibia) and other localities which have yielded silicified fossilifer-
ous freshwater deposits attributed to the so-called Grès Polymorphes of Central and Southern Africa (The extent
of Miombo Woodland and closely related vegetation types is based on the map of White, 1983).
Comparison of the Simanya molluscan fauna
with the extant fauna of the Cubango River
Extant molluscs collected in the
Cubango River comprise the gastropod Bella-
mya unicolor and the bivalve Coelatura sp.
Neither of these molluscs was found in the
Simanya chalcedony and chert, but both of
them occur in the Pliocene silicified sandstone
at Ekuma in Etosha National, Park (Pickford et
al. 2014). The difference in these faunas is
probably related to a differences in habitat –
flowing, well-oxygenated water in the Cuban-
go, and probably swampy, somewhat stagnant
water for the Simanya fossil fauna.
Simanya Chert as raw material
for manufacturing stone tools
An abundance of lithic instruments and
flakes is scattered over the flanks of the valley
near the Simanya River Lodge. In places it is
possible to observe concentrations of flakes sug-
gesting that stone tools were made on site, close
to the outcrops of chert. Various completed tools
were collected, including discoids worked bifa-
cially all around the circumference (Fig. 10),
flakes which show signs of secondary retouch,
and « pebble tools » with one end flaked bifa-
cially, the other end left in a natural condition.
The raw material for most of the stone tools ap-
pears to have been mined from outcrop, or ob-
tained as loose blocks dug up from the soil pro-
file near the oucrops, but a few implements
comprise water-worn pebbles probably retrieved
from the Cubango River bed or river bank,
where blocks of water-polished chert occur.
The bulk of stone tools observed com-
prise what could loosely be called the Middle
Stone Age complex, but some of the « pebble
tools » resemble specimens of the more ancient
Oldowan culture.
Figure 10. Discoidal, bifacial stone tools from Simanya, Northern Namibia, fabricated from fossiliferous chert-like
rock. Specimens are about 5 cm in diameter.
Silicified sands and marls at Simanya,
Northern Namibia, contain abundant fossil gas-
tropods, ostracods and a few indeterminate plant
remains. Among the gastropods there are several
examples of the large ampullariid Pila cf wernei,
and there is an abundance of sinistral snails
(three species of Bulinus), planorbids (Cerato-
phallus) and small dextral snails (Tomichia and
an unidentified taxon).
The silicified horizon occurs in situ near
the top of the southwestern bank of the Cubango
River, and is underlain by weakly consolidated
fluviatile sands and marls (poorly exposed down
to river level). It is overlain by unconsolidated
red sand which is widespread in the Kalahari
region. In the floor of the Cubango Valley, there
is a series of fossiliferous floodplain deposits of
Recent age, comprising marls and eutric fluvi-
sols, which provide a depositional analogy for
the origin of the silicified deposits prior to their
Silicification of the Simanya sands and
marls appears to have occurred at shallow depths
in a savannah environment (notably Miombo
Woodland). The stratigraphic and geomorpho-
logical position of the Simanya silicified depos-
its suggest that they are likely to be of Plio-
Pleistocene age. They are older than the Middle
Stone age on the grounds that the chert has been
extensively exploited to manufacture of stone
We thank the Simanya River Lodge (Mr
Hendrick Kruger and Mrs Francesca Kruger) for
alerting us to the existence of fossil molluscs on
their property. Support for the palaeontological
surveys of the site were provided by the Geolog-
ical Survey of Namibia (Ministry of Mines and
Energy), the French Ministry of Foreign Affairs
and Sorbonne Universités (CR2P, UMR 7207 du
CNRS, Département Histoire de la Terre,
Muséum National d’Histoire Naturelle et Univer-
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