GROUPS AND FORMATIONS AGE LITHOLOGY
2.5 Revised Stratigraphy
The latest informal stratigraphic subdivision (Botha, 1987, Botha pers. comm. 1999) of the Zulu land coastal plain deposits emphasizes a Maputoland Group subdivided into, Uloa, Umkwelane, Port Durnford, Kosi Bay, Kwambonambi and Sibaya Formations (Fig.
2.5.1 and Table 2.5.1)
Table 2.5.1 Summary of the revised stratigraphy of KwaZulu-Natal (Maud and Botha, 2000)
Formation Lithology Age
Sibaya Formation Loose, medium to fine grained sands Present day to Mid forming coastal dune cordon. Holocene
Kwambonambi Brown to grey fine grained, Late Pleistocene and Formation unconsolidated to semi-consolidated Holocene
sands forming inland dunes.
Kosi Bay Formation Lignite and dune sands. Late Pleistocene Port Durnford Formation Mudstones and clayey sand. Middle to late
Pleistocene Umkwelane Formation Aeolianite and calcarenite. Pliocene Uloa Formation Calc-arenites, conglomerates and Mio-Pliocene
coquinas
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., high coastal dll'le cordon SIBAYA
c E
.,
8 100"0 V of calcoceous:l8nd FORMATION
:I:
~
...
inlandS1abtised dll'les KWAMBONAMBIE redistribUted sand (non·
FORMATION
0....
:= ~ calcareous and olll.tomite
...
reddish soil, 'Berea-type' red sand:J
':';::'~.£~.::.:;::: ":;':~;".:£::.:::.:::.::~:.~.
0
§~
~ cross-bedded sand, KOSI BAY
er:
i ~ local calcarenite FORMATION
('J
c: ~
lensioa cartloneceous sand
C>
!! a.:>
~
0
31E beachrock. coral-bearlng
Z
cOQuina<± ,20ka) lignite (78ka) PORT
E fossilllerous mUdrock, DURNFOAD
«
0
~
+I aeolian caJcarenileand red sandstone FORMATION
--l
... « J--
... red sandy soil
..... ... ..........
:J
E ~...
-
...C> .................. .... decalcified UnkwelaneFm.
10 ...
D-
v ........ ... ...
.,'"
«
.,... aeollan
2
.S! E
UMKWELANE
ii:g
.,.
C>v cross-beddedFORMATION
~'" caICarerite
~~ CD
:si
coquinaand ULOA
conglomera1e FORMATION
tylesozolc. ~
Palaeozloc end
~
Precambrlen bedrock
Fig. 2.5.1 Revised stratigraphy of the Zululand coastal Plain after the Cainozoic Task Group (after Botha, 1987).
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2.5.1 Uloa Formation
The Uloa Formation is approximately 10m thick and consists of calcarenites, conglomerates and coquinas (Johnson, 1994). The beds contain a rich assemblage of marine invertebrates, including the distinctive Pecten Beds (SACS 1980). This formation has been dated biostratigraphically as late Miocene to early Pliocene (Johnson, 1994).
The concentration of shells in beds of this formation suggests deposition in lag deposits, most likely related to a marine regression (Johnson, 1994), indicating an overall littoral deposition environment.
2.5.2 Umkwelane Formation
The Umkwelane Formation consists of compact, poorly cemented, medium to coarse grained sandstones, interbedded with free flowing coarse sands (Fockema 1986), with intercalated thin gravel beds formed in slightly incised channel beds. Marine shell fragments occur throughout this formation and are sometimes concentrated in shell beds (Fockema, 1986). The top of the Umkwelane Formation has been re-worked, and forms a red, sandy palaeosoil devoid of fossils (Singh, 1995). Fockema (1986) deduced a biostratigraphically constrained Pliocene Age for these strata. The thin gravel beds are considered to represent f1uvially confined deposition and the gravel beds in association with shell bearing layers an indication of a marginal marine or lacustrine depositional environment. The Umkwelane Formation is of Pliocene Age and considered to have been deposited during a marine transgression (Fockema, 1986). Taking into account the marine character of the shells the formation, it is considered to have been deposited during a marine transgression (Fockema, 1986).
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2.5.3 Port Durnford Formation
The Port Durnford Formation is 4 to 6m thick and, consists of a basal unit of unconsolidated fine-grained sandstones, silts and clays (Johnson, 1994), containing fossil wood and mammal remains as well as fragments of marine invertebrate, and fish (Hobday and Orme, 1974). The Port Durnford Formation is considered to be of mid Pleistocene Age (Singh 1995), and is overlain in places by a lignite bed, up to O.25m thick and unconsolidated medium-grained sands are characterised by large-scale cross- bedding (Hobday and Orme, 1974). The lignite bed is found in the lower 1.5m of the Kosi Bay Formation.
Grain-size characteristics, the lignite bed and the assemblage of both marine and terrestrial animals together with tree logs suggest a lagoonal or perhaps estuarine depositional environment (Hobday and Orme, 1974) for the Port Durnford Formation.
2.5.4 Kosi Bay Formation
There is a marked erosive unconformity between the Port Durnford Formation and the Kosi Bay Formation. The Kosi Bay Formation overlying the Port Durnford Formation has a thickness of up to 100m. Singh (1995), distinguished three distinct units with gradational contacts in the Kosi Bay Formation; a basal unit consisting of a white clay rich sand; an intermediate unit composed of white clay-rich layer with reddish patches that coalesce towards the top of the unit; and an uppermost unit made up of unconsolidated to semi-consolidated red sands.
Singh (1995) interpreted the Kosi Bay Formation as an aeolian deposit and attributed the variation to weathering and interaction with ground water.
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2.5.5 Kwambonambi Formation
The Kwambonambi Formation is composed of brown and grey fine-grained,.
unconsolidated to semi-consolidated sands with large scale cross-bedding and is approximately 50-80m thick. These sands are characterised by well-rounded, partly frosted grains. Johnson (1994) interpreted the Kwambonambi Formation as coastal seif dunes that have a Holocene Age.
2.5.6 Sibaya Formation
The Sibaya Formation consists of loose, medium to fine-grained sands, containing abundant bioclasts and heavy minerals (ilmenite, rutile, zircon and monazite) in high concentrations. The maximum observed dune height in the Sibaya Formation is 100m, containing large-scale, cross-bedding. Abundant low-order truncation surfaces separate the beds into numerous cross-bed sets. The dune sands of the Sibaya Formation are still accumulating as the strong on-shore winds carry beach sands inland.
From the bedding characteristics and relationship to the underlying Kwambonambi Formation Fockema (1986) interpreted the Sibaya Formation as a series of large aeolian dunes resulting from the inland migration of seif dunes.
The depositional environment of the Sibaya Formation is considered to have been very similar to that of the Kwambonambi Formation. Beach sands, enriched in heavy minerals by tidal and wave action, were blown into relatively narrow, parallel series of coastal seif dunes. Westward directed palaeocurrents indicate that the strong on-shore winds were responsible for eventual accumulation of the sands in to prominent high dunes further inland (Force, 1991).
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