~ t Pergamon

1040-6182(95)00092--5

Quaternary International, Vol. 33, pp. 81-95,1996. Copyright © 1996 INQUA/Elsevier Science Ltd

Printed in Great Britain. All rights reserved. 1040-6182/96 $32.00

LATE HOLOCENE ENVIRONMENTS AT VERLORENVLEI, WESTERN CAPE PROVINCE, SOUTH AFRICA

Michae l E. Meadows ,* A n d r e w J. Baxter* and John Parkingtonl" *Department of Environmental and Geographical Science, University of Cape Town, Rondebosch, 7700, South Africa

tDepartment of Archaeology, University of Cape Town, Rondebosch, 7700, South Africa

Evidence on late Quaternary palaeoenvironments of the western and southwestern Cape of South Africa has facilitated detailed reconstructions mainly for the mountains, where organic sediment accumulation has been favoured by relatively humid climates. On the lowlands, particularly those of the west coast region, the search for sites traditionally regarded as suitable for the accumulation of sediments containing preserved fossil pollen has commenced only more recently. This area of the Western Cape Province has, however, provided Quaternary scientists with a rich archaeological record that has yet to be tested against independent lines of palaeoecological evidence. A sequence of sediments which have accumulated in what is today a large freshwater coastal lake, Verlorenvlei, has been sampled at Grootdrift, 15 km inland of the coast. A series of seven sediment cores was extracted during 1991 and three of these have now been sub-sampled, radiocarbon dated and subjected to a range of palaeoenvironmental techniques, in particular pollen analysis, sedimentology and geochemistry. Three pollen diagrams are presented which reveal the vegetation history of both the immediate Grootdrift environment and the wider catchment during several periods over the last 5500 years. A mid-Holocene higher sea-level is evident in two of the cores which were examined for pollen throughout their length. The surrounding area appears at this time to have been somewhat more arid than today. Following a hiatus in sedimentation some time after 4300 BP, the marine conditions at the site disappear and are replaced by fresh water as the dominant hydrological and ecological influence. Around the time of colonial occupation of the region, some 300 years ago, lacustrine conditions prevailed at Grootdrift and greater moisture availability is indicated in the catchment. During the last 300 years, the picture revealed by high resolution palynology of the third core is one of progressive levels of human disturbance both in and around the Verlorenvlei. Evidence from a textural and geochemical analysis of the sediments is consistent with the interpretation based on fossil pollen. The implications of this information are examined against the archaeology and palaeoecology of several cave sites in the vicinity of the vlei. The consistency apparent in the range of types of evidence suggests that some reliance can be placed on the mid-late Holocence palaeoenvironmental reconstruction at Verlorenvlei. The paper thus provides insight into the nature of the complex interactions between late Holocene climate change, sea-level fluctuation, vegetation change, vlei hydrology and human activity in the Western Cape coastal region. Copyright © 1996 INQUA/Elsevier Science Ltd

INTRODUCTION

Information on the evolution and development of patterns of vegetation, especially during the late Pleisto-

cene and Holocene of southern Africa, is progressively emerging as more and more sites suitable for palaeoeco- logical reconstruction are interpreted (see Scott, 1993, for a recent review). Nonetheless, the distribution of such sites remains spatially uneven such that there are large tracts of the sub-continent, particularly in the more arid regions to the west, for which there is relatively little late Quaternary palaeoecological information. The floristically diverse Fynbos Biome (Cowling, 1992), coinciding approximately with the Cape Floristic Region, has only recently been studied from this perspective (Meadows and Sugden, 1993). Relatively few sites have produced reliable and well-dated palaeoenvironmental sequences, mainly from the uplands of the fynbos, where fossil pollen preserved in sediments accumulating in wetlands has revealed a more

detailed late Pleistocene vegetation history (Meadows and Sugden, 1990, 1991a, b, 1993). The fynbos lowlands, however, have remained largely unstudied from this viewpoint, with the notable exception of the chronologi- cally problematic work of Schalke (1973) and the analyses of Martin (1968) and Scholtz (1986).

The identification of sequences of Holocene sediments at Verlorenvlei, near Eland's Bay on the west coast of

81

southern Africa (Fig. 1), represents an opportunity to redress some of the spatial imbalances in distribution of late Quaternary sites in the fynbos. The aim of this paper

is to present the results of a palaeoenvironmental investigation conducted on a series of sediment cores, extracted during the past three years, along a transect across the Verlorenvlei. The investigation is multi- disciplinary in the sense that it focusses not only on the

palaeoecological information (in this case based on analysis of fossil pollen preserved in the deposits) but refers to the sedimentological, geochemical and chron- ological characteristics of the Verlorenvlei sediments. The study is given further impetus courtesy of a detailed archaeological picture which arises from the excavation of several shelter and open sites in the surrounding region. It is therefore possible, at Verlorenvlei, to integrate

interpretations of the palaeoenvironmental circumstances in which late Holocene people occupied the lowland fynbos landscape of the Western Cape Province of South Africa.

The paper begins with a brief review of the physical location and geography of the study site, presents the palaeoenvironmental methods used and follows with an examination of the stratigraphic, chronological, palynol- gical, sedimentological and geochemical results. The results are then analysed in the context of the archae- ological information available for the region.

82

5 10

Scale (km)

Larnberts Bay

M.E. Meadows et al.

,~ ~o ~A A~ F R I C

Cape Town

~' ' ~ / L a ] p o / d t v

',2

E/ands Bay Baboon Point

N Verloren vleJ ~I jSTUDY SITE

Rede/inghuys ,

FIG. 1. The location of Verlorenvlei and the Grootdrift study site.

A BRIEF GEOGRAPHY OF VERLORENVLEI

Verlorenvlei is the colloquial name given to the closed coastal estuarine-lake, river and reed-swamp system located at Eland's Bay, approximately 180 km north of Cape Town, along the west coast of South Africa (Fig. l). The Verlorenvlei river and its tributades are allogenic and intermittent, feeding the swamp and lake system only during the rainfall months of winter and early summer. The open water lake, which extends for 13 km and has a maximum width of 1.5 km, is linked to the sea by a narrow, hydraulically-inactive estuary channel. Occasion- ally, winter flooding or high spring tides have been known to breach the sandbar which overlies the rock- barrier obstruction at the mouth, resulting in an interchange between the sea and the lower lake system (Sinclair et al., 1986).

The catchment, which extends some 87 km inland from the coast, is aligned along a northwest/southeast structural trend which traverses the undulating coastal lowlands or Sandveld (Miller, 1987). Occupying an area of 1890 km 2, the catchment has its origins to the south and east of the Sandveld plains, in the Piketberg and the Olifantsriver Mountains respectively. The regional geology is domi- nated by the low-lying sand fiats (Tertiary to Recent deposits), while sandstone outcrops of the Table Moun- tain Group, fine-grained rocks of the Malmesbury Group

and shales of the Klipheuwel Formation are also present within the catchment (Visser and Toerien, 1971).

Climatically, Verlorenvlei falls within the winter rainfall region of the southwestern Cape, which is classified as Mediterranean. However, with annual average rainfall figures of less than 300 mm yr -~ (Sinclair et al., 1986), the Verlorenvlei area is typically semi-add to sub-arid in nature (Noble and Hemens, 1978). Rainfall frequency and intensity can be highly variable from year to year but generally 80% of the annual rainfall occurs during the months April to September. During the dry summer months, high temperatures undoubtedly contribute to large evaporative losses from the Verlorenvlei system.

Verlorenvlei has long been recognised by botanists for its high plant species diversity (Acocks, 1988). Both the structural and physiognornic variations within the geo- graphy of the region and the transitional location of Verlorenvlei between the fynbos and karroid vegetation types are considered to be the prime factors responsible for the high diversity; it is typical, in fact, of an ecotonal area. Sinclair et al. (1986) have identified a number of different vegetation types in and around Verlorenvlei (Fig. 2), among these are: Strandveld, a drought- deciduous vegetation type of the sandy plains and littoral dunes typically including hardy shrubs, geophytes and grasses and, especially, succulents such as Euphorbiaceae

Late Holocene Environments at Verlorenvlei 83

FIG. 2. Vegetation map of Verlorenvlei region (after Sinclair et al., 1986).

and Mesembryanthemaceae; Lowland fynbos, favouring deep, sandy soils, is dominated by Restionaceae as well as drought-resisting elements such as certain Proteaceae and other sclerophyllous fynbos shrubs; Dry mountainfynbos, particular to the sandstone outcrops to the south of Verlorenvlei, is characterised by small-leaved sclerophyll shrubland with a high percentage of succulent and drought deciduous species. Many of the typical fynbos elements including Ericaceae, Proteaceae and Restiona- ceae are present. In sheltered, fire-protected gullies, scrub forest elements including Olea europaea subsp, africana, Maytenus oleoides and Podocarpus elongatus cling to the sandstone steeps; Karroid shrubland, favouring shale on lower slopes, is dominated by members of the Asteraceae, Mesembryanthemaceae and Euphorbiaceae families and include genera such as Stoebe, Lessertia, Passerina and Elytropappus; Marsh vegetation is highly dependent on conditions of salinity and includes salt-tolerant species such as Sarcocornia natalensis and Scirpus marginatus, while the less saline areas support dense stands of emergent reeds such as Typha capensis, Phragmites australis, Cyperus marginatus and Juncus spp.

MATERIALS AND METHODS OF ANALYSIS

Core Derivation

The decision to core the Verlorenvlei sediments has been contingent upon the need for a relatively undisturbed and continuous sediment profile from which suitable organic samples could be derived for both the analysis of fossil palynomorphs and the generation of radiocarbon dates. The farm Grootdrift, located some 15 km inland of the coast, was selected for its position at the head of the open water lake. The site, although heavily disguised by a proliferation of Typha reeds, appears to represent a contemporary fluvial delta, with the river proper disper-

sing into multiple sinuous channels, finally disappearing into the alluvial sponge that feeds the lake. Coring of the sediments was conducted by means of a portable vibracorer unit, designed and modified along the lines of Lanesky et al. (1979) and Smith (1984). During 1991, seven organic sediment cores, each varying in depth from 4-6 m, were derived from a shore to shore transect across the riverine-lacustrine transition at Grootdrift (Fig. 3). All seven cores were returned to the laboratory, the stratigraphy for each was described and recorded and three were then selected for further investigation. The south bank core, demarcated as GDV1 (with a surface height of 1.4 m a.s.1.) and subsequently, two cores derived from within the shallow-waters of the marsh, GDV2 and GDV4 (see Fig. 3) were subsampled for radiocarbon dating and pollen analysis.

Laboratory Techniques

Preparation of polleniferous materials

For the purpose of pollen analysis, each of the cores was sub-sampled at an interval of 5 cm and a volume of approximately 5 cm 3 was removed from the profile and treated with standard reagents as used in pollen concentration procedures (Faegri et al., 1989; Moore et al., 1991). Initial preparation included measuring the volume and dry weight of samples in order to facilitate the calculation of absolute pollen frequencies and densities. Since the ratio of organic material to clastic sediments is relatively low in the Grootdrift transect (<5- 10% organics by weight), special attention was given to the removal of clastic sediments, including clay and coarse-grained quartzitic material. Mechanical separation by wet sieving procedures was followed by the applica- tion of sodium pyrophosphate (Na4P207) as a defloccu- lant for clays (Bates et al., 1978) and zinc chloride

84 M.E. Meadows et aL

• ~ , ' ; ~ ~ , : - _ ~ ~ = ~ : _ ~ _ ~ _ = ~ _ ~ e ~

~ - = - = Vibracore

Grootdrift Farm ~~ '~

r£~ ~ : Scale { m ) ~ : : : : ~ : ~ : ~ ~ 0 50 1 O0 150 20C

FIG. 3. Grootdrift showing positions of sediment sampling transect and cores GDVI, GDV2 and GDV4.

(ZnCI2) for the separation of heavy minerals (Birks and Birks, 1980). Following acetolysis, staining and mounting (Faegri et al., 1989), pollen counting was facilitated by a Zeiss light microscope at ×400 and ×630 magnification. Identification of the palynomorphs, initially down to family level, was aided by reference to a contemporary collection of over 400 taxa from the Verlorenvlei area.

Pollen data presentation

Absolute pollen counts, derived at each level from a sample of known volume, were based on a minimum pollen sum of 250 identifiable grains. Pollen densities appear to be relatively low with an average of 10 x 103 g-

of sediment.

Sedimentological and geochemical methods

Eleven stratigraphic units were identified in GDV1 (Fig. 4) and approximately 10 g sub-samples were extracted from representative sections of each of these units for sedimentological and geochemical analysis. Grainsize analysis was conducted using a sedimentation tube (cf. Sandford and Swift, 1971) on samples which were first dried and then sieved to separate the gravel fraction. Geochemical analyses were performed by X-ray fluoresence (XRF) on a Philips 1400 Spectrometer, to yield data on SiO2, A1203, TiO2, FeO, MnO, CaO, Na20, K20 and P205 minerals.

TABLE 1. Radiocarbon dates at Verlorenvlei"ady

Core Depth (m) C 14 age Ref.

GDV1 1.35 300±45 GDV1 2.29 4340+60 GDV1 4.0 5070+110 GDV1 4.54 5550+70 GDV4 0.695 200+50 GDV4 0.895 330+50

Pta-5814 Pta-58 l 2 Pta-5809 Pta-5807 Pta-5908 Pta-5910

STRATIGRAPHY AND CHRONOLOGY

The core logs from the seven vibracore samples taken across the Verlorenvlei on the farm Grootdrift reveal a sequence of organic and more clastic sediments which indicate that the site was probably subject to a complex series of hydrological and geomorphological events during the period of sedimentation. Figures 4~5 illustrate the stratigraphic sequences for cores GDV1, GDV2 and GDV4 which have all been utilised for fossil pollen analysis. A relatively thin (up to 250 mm), but distinctive layer of black, organic clay material provides a useful stratigraphic, marker horizon as it occurs consistently in the cores at depths of 0.8-1.2m.

Sediments, vary in character from dark grey to black organic clays and sandy clays to red or orange coarser materials with little or no organics. Such sediments are entirely consistent with an estuarine/lacustrine environ- ment of the Verlorenvlei.

Radiocarbon dating of two of the cores (GDV1 and GDV2) (Table 1) suggests that the sediments, were deposited during the latter half of the Holocene. Closer inspection of the cores suggests that sedimentation at GDV1 began around 5500 BP, continued until after 4300 BP and then recommenced some time during the past 300 years (Meadows et al., 1994). Sedimentation rates (Table 2) vary from around 1-2 mm per year near the base of the core, to approximately 5 mm per year in the sandy unit near the surface of GDV1.

TABLE 2. Sedimentation rates at Verlorenvlei

Depth ( c m ) Radiocarbon years Rate (mm year -1)

CORE GDV 454--400 480 1.1 400-229 730 2.3 454-229 1210 1.9 454-141 1684 1.9 141~) 300 4.7 CORE GDV4 69.5-89.5 130 1.5

Late Holocene Environments at Verlorenvlei 85

oepm

I 0 0

200

300

400

500

STRATIGRAPHY, GDV1, GROOTDRIFT, VERLORENVLEI Llthology Mumell "C Date '~C,~ Organic Carbon

+I .4m (amsi) No ta t l on [mol/mg)

I

i I !

e

Sandy clay turf layer with roots

Medlum grey sand

Fine, mottled brown grey sand

Dark grey clay

Fine mottled brown-grey sand

1 becoming white

Fine black laminated clay

Medium grey sand matrix with clay intrusions

Dark grey clay matrix with coarser sandy mottling

Black clay with rootlets

Medium mottled grey & white sand

Continuous mottled grey clayey sand

Black clay band with quartz pebbles

Dark grey clayey sand with occasional gravel pockets

Grey, mottled medium sand & quartz pebbles

Coarse ferous orange sand

Black clay

Orange and grey mottles In yellow sand matrix

IOYR 411

IOYR 3/I

IOYR 7/3

IOYR 4/I

IOYR 7/3

IOYR 7/I

IOYR 2/I

IOYR 7/2

10YR 4/1

10YR 2/1

10YR 5/1

10YR 411

IOYR 211

IOYR 311

10YR 7/1

10YR 716

IOYR 2/I

IOYR 718

-21.63

-21.98

-23.60

-25.73

300 + 45 -27.67

-26.97

-21.75

4340 + 60 -21.25

-21.09

5070 :~110 -21.9

5550 + 70 -22.01

-23.51

2.05

0.13

0.38

0.08

2.95

0.19

1.17

1.12

0,61

1 , 7 1

1.27

0.02

FIG. 4. Stratigraphy of core GDV1.

86 M.E. Meadows et al.

STRATIGRAPHY, GDV2, GROOTDRIFT, VERLORENVLEI

(cm)

~" .~ ~,, .. ..

100

2OO

300

400

450

+ 0.7m (amsl)

Llthology Munsell Notation

Black lacustrine mud

Mottled brown-grey sand

Grey sand

Mottled brown-grey sand

Fine black laminated clay

Coarse grey sand matrix with clay & fine sand Intrusions

Dark grey clay matrix with sandy mottling

becoming darker

Organic black clay Light grey sandy band

Dark grey clay wlfh sandy mottles

Continuous mottled grey clayey sand

IOYR 2/1

IOYR 7/2

IOYR 511

I OYR 7/2

IOYR 211

10YR 7/I

IOYR 5/I

IOYR 411

IOYR 3/I

10YR 2/I IOYR 6/I

IOYR 4/I

IOYR 3/I

Dark grey clay layer

Mottled grey to white medium sand with occasional gravel pellets

IOYR 4/1

IOYR 712

IOYR 713

FIG. 5. Stratigraphy of core GDV2.

POLLEN DIAGRAMS AND VEGETATION HISTORY

Three pollen diagrams have been constructed (Figs 6, 8 and 9) from fossil analysis on cores GDV1, GDV2 and GDV4. Contemporary pollen analysis is in progress (Baxter, in preparat ion) , but the indications are that the different plant communities around the site produce distinctive pollen spectra, suggesting that the fossil

analysis should produce appropriate models of former vegetation conditions. The results of the fossil pollen analysis are presented sequentially.

GDV1

The pollen diagram for core GDV1 (Fig. 7) is divided into four zones (Meadows et al., 1994) which reflect

Late Holocene Environments at Verlorenvlei 87

STRATIGRAPHY, GDV4, GROOTDRIFT, VERLORENVLEI

Depth Llthology '4C Date 8"C,0, L~inC (cm)

I OO

200

300

400

450

+ 0.7m (amsl) Organic brown clay cap lled-yelicw clay

Ferous

Faintly laminated

Dark brown-yellow clay

Fine black laminated organic clay

Organic grey sand matrlx with clay Intruslons

Dark grey clay matrix

Grey sandy clay matrix with clay intrusions Dark grey clay Dark sandy clay layer Coarse mottled grey and whffe sand

Continuous mottled grey clayey sand interspersed with occasional gravel pockets

becoming lighter

White medium sand with occasional mottles

Mun|ell Noh]tion

IOYR 413 10YR 6/8

10YR 4/6

10YR 3/6

10YR 3/2

IOYR 2/I

10YR 7/I

10YR 3/I

10YR 7/I

10YR 3/I 10YR 2/I 10YR 6/I

IOYR 3/1

I OYR 712

IOYR 712

200±50

300 ±50

-28.00

-27.60

(mollmo)

3.20

3,90

FIG. 6. Stratigraphy of core GDV4.

important environmental changes at the site during times over the past 5500 years in which sediments were accumulating in this part of the Verlorenvlei. The basal parts of the core, represented by zone GDVla and covering the period prior to 5000 BP, is characterised by relatively poor pollen preservation and lower pollen concentrations, although there are indications of a fresh water/terrestrial environment at the site at this time (Typha sp., Juncaceae and low percentages of Restiona-

ceae would be consistent with this interpretation). Zone GDVlb, to after 4300 BP, is dominated by grass pollen (mainly larger than 50 microns in diameter) with small but significant percentages of Chenopodiaceae/Amar- anthaceae pollen. There are low percentages of pollen representing the major fynbos elements and woodland taxa appear to be scarce. The sequence is interpreted as accumulating in an estuarine environment, and while Meadows et al. (1994) suggest that the surrounding

0 0

UL

AQ

D

t

qLA

IID

41

OLA(]9

PLA

OD

II

I

euoz I ~o~}

• y,,., L,,p, ,|,,,~

, --

i

i

I

v~

L-- L--J L_

~

i

1

~A

'd~

J

~L

, c

u~

.~!p

U

,JllU

d L

CIL

~

i

I i

i I I I I I I

! I I

i i.

a vv

v~

vv ~

vv v~

m

dg

OL

Og

00

~ dgOt~

'OO

Z dgO0£

oot

V~

v

~)eo~°° qlde(]

I, IILI ~J • lOlIlU=aUlAUl~L

vv

Late Holocene Environments at Verlorenvlei 89

catchment may have been somewhat more xeric than today, this remains unsubstantiated. This interpretation is consistent with a 2.8 m higher sea-level which is dated to around 4000 BP (Yates et al,, 1986; Miller et al., 1993) and which would have rendered the Verlorenvlei a substantial estuarine/marine embayment at the time, apparently as far inland as Grootdrift. The upper pollen zones of GDV1, show marked changes from this estuarine situation. After a hiatus, sedimentation recommences to reveal pollen spectra (zone GDVlc) which are dominated by elements indicating open fresh water conditions in the vlei (e.g. Nymphaea spp., Typha spp. and higher proportions of Cyperaceae). Clearly the saline elements have retreated westwards with declining sea-level and the immediate environment of the Grootdrift core site is characterised by open, fresh water lacustrine conditions. During the past 300 years the history of vegetation is not visible at GDV1 as the sediments are sandy and largely devoid of well-preserved pollen, although the recent spectra (GDVld) suggest significant anthropogenic influence on the ecology of the region with the introduction of alien trees (especially Pinus spp.) and higher quantities of pollen indicative of annual or 'weedy' elements (e.g. Scrophulariaceae, Oxalidaceae and Stoebe- type). Core GDV4 (see below) documents these devel- opments in considerably greater detail.

GDV2

The sedimentary sequence here has not been separately radiocarbon dated, although its proximity to GDV1 and similar stratigraphy suggest that it too accumulated periodically over the past 5000 years. GDV2 is a shorter core than GDV1 and probably does not extend as far back into the Holocene. The black laminated clay marker horizon, at equivalent depth to that of GDV1, is assumed to represent the recommencement of organic sedimenta- tion in the Grootdrift section of the vlei within the last 300 years. The surface 70 cm and basal 250 cm yielded insufficient pollen for analysis and these are omitted from the pollen diagram (Fig. 8). The diagram is divisible into three zones, GDV2a, GDV2b and GDV2c and is suggestive of a parallel vegetation history to that documented for the equivalent parts of the adjacent core GDV1. This is an encouraging sign, for it confirms that the palynological method of palaeoenvironmental recon- struction used in this instance proves to be reasonably reliable. Zones GDV2a and GDV2b are indicative of estuarine conditions, with relatively high concentrations of Chenopodiaceae/Amaranthaceae pollen and moderate percentages of Poaceae pollen (again, dominated by the larger grains). The persistence of fresh water nearby is apparent in these zones, however, as witnessed by the proportions of Typha pollen, especially between about 230 and 170 cm. The xeric elements, apparent in GDVI, do not make a contribution to these sediments, accumu- lating somewhat further into the centre of the vlei. The major vegetation shift, as at GDV1, occurs in the upper parts of the core. Zone GDV2c, with higher proportions of Typha, Nymphaea and Cyperaceae, record the change

from saline to fresh water conditions at approximately 140 cm, assumed to be coincident with the hiatus at GDV1 and representing a time about 300 years ago in the immediate pre-colonial or early colonial period. The vegetation history of these past few hundred years is well- represented in the sediments, of core GDV4.

GDV4

The GDV4 pollen diagram (Fig. 9) represents the accumulation and subsequent preservation of pollen within the wetland sediments at Grootdrift, Vedorenvlei, since pre-colonial or early colonial times (ca. AD 1600) until the present. The diagram shows a number of synchronous community trends across the pollen spectra which has allowed for the zonation of the diagram into four units (Baxter and Meadows, 1994). The earliest of these, GDV4a, reveals the pollen signature of Verlor- envlei around the time of the arrival of colonial settlers in the region. The pollen spectra reveals that Poaceae (grasses) were far more abundant then than their contemporary distribution suggests is the case today. Regional elements such as fynbos shrubs, although poorly represented in the pollen diagram (being statistically diluted by abundant local wetland indicators) are, none- theless, characteristically diverse and include elements such as Restionaceae, Proteaceae, Rutaceae, Thymeleae- ceae and Pelargonium. Pollen from local wetland communities indicate the presence of an open fresh water lake capable of supporting Myriophyllum spicatum, a submerged fresh water macrophyte. Chenopodiaceae\A- maranthaceae, probably halophytes such as Limonium spp., Salicornia spp. and Chenolea spp., would likely have constituted elements of the local riparian vegetation where extreme summer evaporation is likely to have induced hypersaline conditions. Zone GDV4b is noted for the consistent decline in the frequency of grass pollen while fluctuations in the pollen of wetland and aquatic vegetation are ascribed to changes in water chemistry and nutrient status (Baxter and Davies, 1994). The decline of Chenopodiaceae/Amaranthaceae in favour of predomi- nantly fresh water elements such as, Potamogeton spp. and the aquatic perennial, Nymphaea, suggest the persistence of fresh water all year round at the site. Zone GDV4c marks a dramatic increase in the proportion of Asteraceae pollen and a concomitant decline in grasses and fynbos elements. The increase in Asteraceae is interpreted here, as elsewhere in the fynbos, as being indicative of anthropogenic interaction in the landscape (Meadows and Sugden, 1991a, b). The establishment by colonists of a new mode of agro-pastoralism at Verlor- envlei is likely to have brought with it the impacts of overgrazing, an altered fire regime and wholesale agricultural clearing of indigenous vegetation. The final and most recent zone, GDV4d, reveals a 50% decline in the abundance of grasses since the onset of zone GDV4a, almost certainly a consequence of progressive over- grazing. Fynbos elements seem to decline in favour of non-palatable karroid succulents such as Euphorbiaceae, while disturbance indicators including Stoebe-type Aster-

90 M.E. Meadows et al.

>

>

o @

m

>

%

\

IIII

m

l ° ] "

I

A

A

i P

E F

:o

F F

F F ro

~F ~F ~F

F _ _

A

A

d ~

F ~

F F

_ 0 L'~

~ 0 up P,.

qldoo

eq ;>

o6

d

Late Holocene Environments at Verlorenvlei 91

.

,m G)

m

e-

o m l,m

%

0 ~ ~ N a a a a

\ % .

\ \

.

\ %

\ o -

_- A

i.Am_aL._.....___.. A

A A

__ A i I i

A |

- - A A A

Jm

A

A

am,...._

A

|

A ~ A

A

| i f i l l l l l l l l l l l l l l l l l l l l ] o ~ ~ o ~ o

o

m o o

q ~ d e o

~3

92 M.E. Meadows et al.

TABLE 3. Textural analysis of GDV 1

Stratigraphic unit Label Depth (m) % Fines % Sand

Turf S 1 0-0.3 59.1 40.9 White sand $2 0.3-1.2 2.7 97.3 Black laminated clay $3 1.2-1.35 28.9 71.1 Grey sand $4 1.35-1.85 14.6 84.9 Black clayey sand $5 1.85-2.25 23.9 76.0 Black clay $6 2.25-2.35 36.2 63.8 Dark grey clayey sand $7 2.35-3.95 15.8 84.0 Grey mottled sand $8 3.95-4.05 35.7 64.2 Orange sand $9 4.05-4.50 5.4 94.2 Black clay S10 4.50-4.55 44.4 55.4 Orange-grey mottled sand S 11 4.55-5.0 1.9 97.1

aceae, and Scrophulariaceae increase in frequency. Simultaneously, indigenous scrub forest elements such as Podocarpus and Oleaceae become absent from the spectra, while the pollen from alien vegetation, such as Acacia and Pinus, becomes evident for the first time. Most noteworthy of the riparian and wetland flora, the pollen of Typha and Cyperaceae now reach maximum proportions. The almost total absence of aquatic vegeta- tion indicates that a rapid ecological succession has endured at Grootdrift during the last few hundred years. Given the historical evidence for attempts at causeway construction (Sinclair et al., 1986) and, more recently, the progressive impoundment of the system, it seems possible that the proliferation of Typha may be a function at Grootdrift of rapid development from an open water embayment to that of a fluvial delta and associated alluvial sponge.

SEDIMENTOLOGY AND G E O C H E M I S T R Y

The textural analysis of sediments, at GDV1 (Table 3) reveals that the deposits at Grootdrift are mainly sandy in nature interspersed with facies which are more clay-rich. Closer inspection (Fig. 10) suggests a series of upwardly- fining cycles of sedimentation, although the sediments are insufficiently differentiated with respect to their grainsize statistical parameters (cf. Friedman, 1961) to facilitate their more precise classification as to environment of deposition. The apparent cyclicity may be consequential upon fluctuations in sea-level, or even tidal influence (see Allen, 1964, 1965) but this remains difficult to interpret.

The full implications of the geochemical analyses on major elements of the GDV1 sediments, (Table 4) are discussed elsewhere (Meadows and Asmal, in press). The geochemical classification of the sediments suggests two significant unconformities in the sequence. Samples from the surface to 1.2 m are classified as 'arenaceous', with high silica to aluminium ratios and small proportions of other major minerals; those from 1.2-4.05 m are classified as 'argillaceous' having lower silica to aluminium ratios, less than 90% silica and higher proportions of other major elements (see Table 4). The upper unconformity occurs around 300 BP, consistent with the conclusions drawn from pollen analysis that the

subsequent sediments accumulated relatively rapidly in the Verlorenvlei and coincide with lower sea-level, greater influence of fresh water in the system and increased levels of human disturbance. Poor pollen preservation in the lower portion of the core makes it difficult to be certain of the palaeoecological circum- stances surrounding the lower unconformity, but the possibility, tentatively supported by pollen analysis of GDV1, is that these basal sediments were deposited under terrestrial conditions as opposed to the marine/estuarine environment of the overlying units. In summary, the geochemical analyses of the major elements in GDV1 suggests that the lower and upper sediments were deposited under terrestrial/fresh water conditions, while

S1

$2

S3

S4

$5 .._= e -

= $6 0=

® $7 E

m $8

$9

$10

S l l 0 % weight 1 O0

Sand

Fines

I ~ Top of sedimentary cycle

FIG. 10. Grainsize analysis of core GDV1, illustrating sedimentary cycles.

Late Holocene Environments at Verlorenvlei

TABLE 4. Results of major element analysis in % by weight

93

Sample SiO2 TiO2 A1203 Fe203 MnO MgO CaO Na20 K20 P205

$2 96.95 0.19 1.13 1.66 0.05 0.24 0.19 0.00 0.08 0.05 $3 86.60 0.32 3.64 1.73 0.05 0.23 0.17 0.00 0.43 0.04 $4 84.76 0.36 5.04 2.51 0.04 0.29 0.11 0.00 0.61 0.05 $5 84.77 0.44 5.17 2.73 0.05 0.23 0.09 0.00 0.68 0.02 $6 85.81 0.38 3.85 2.40 0.04 0.21 0.l I 0.00 0.49 0.04 S7(u) 91.78 0.23 2.47 1.75 0.08 0.01 0.06 0.00 0.30 0.03 $7(1) 82.75 0.50 6.88 1.99 0.04 0.23 0.05 0.00 0.93 0.05 $8 95.23 0.22 1.41 1.13 0.04 0.00 0.05 0.00 0.19 0.02 $9 96.39 0.16 0.94 0.83 0.03 0.00 0.05 0.00 0. I 1 0.03 Sll 97,46 0.18 0.84 0.83 0.04 0.00 0.04 0.00 0.11 0.03

S1 and SI0 not analysed geochemically.

the deposits from about 5000 BP onwards were associated with higher sea-level resulting in estuarine conditions at Grootdrift.

PALAEOENVIRONMENTAL SYNTHESIS

The evidence gleaned from the three Grootdrift cores analysed thus far reveals important palaeoenvironmental changes occurring at Verlorenvlei during the latter part of the Holocene. The most significant influence on both the sediments and the fossil pollen preserved therein appears to be fluctuating sea-level. Although the coring site is 15 km from the contemporary mouth of the vlei, the rising sea level after 5000 BP is reflected in changes in the local vegetation and that of the surrounding catchment. The Holocene sea-level curve for the west coast region has been constructed by Miller et al. (1993) and is shown here as Fig. 11. Before the Grootdrift area was inundated by a sea-level up to 3 m higher than present, the conditions on site appear to have been dominated by terrestrial sedimentation and plant communities indicative of available fresh water. Subsequently, the hydrology shifted to estuarine and shallow water marine conditions and the local plant community resembled a salt marsh. Some time after the sea-level high of post-4300 BP, falling sea-levels prompted a cessation in sedimentation (or subsequently

5- D O • • • _ -_ • • •

• ",,A

0 .:77 . . . . . . . g o . . . . . . . . . . . . . . . . . . . . . . • ............................ o. . .~,~: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

¢: 1o ',

i

,o;o 2d00 3000 ,0;0 20;0 6goo ,g00 ~g00 ,o0o RADIOCARBON YEARS BP

FIG, l 1. Holocene sea-level curve for West Coast region o f South Af r ica (after Miller et al. , 1993).

eroded accumulated sediments) such that the next view of the Verlorenvlei environment is one in which open fresh water conditions prevailed in a coastal lake. Thereafter we witness the progressive alteration of both the Verlorenvlei itself and the surrounding landscape under the influence of increasing human disturbance. The sedimentary sequence illustrates the complex interplay of changes in moisture availability, sea-level and degree of anthropogenic activity. It is against this palaeoenvir- onmental backdrop, then, that the successive modes of human occupation of the area have occurred.

ARCHAEOLOGICAL SIGNIFICANCE OF THE HOLOCENE PALAEOENVIRONMENTS AT

VERLORENVLEI

Excavations at rock shelters and caves on the margins of the Verlorenvlei have produced evidence of changes in the status of the lower riverine system as well as the surrounding terrestrial landscape (Parkington et al.,

1988). Most prominent, perhaps, is the complete absence of occupation deposit at any site in the lower Verlorenvlei and adjacent coastline between about 7700 and about 4300 years ago. Two deep sequences show a hiatus in deposition at this time and all other sites either pre-date or post-date this mid Holocene time period. It has been remarkable that the very first set of radiocarbon dates from the vlei floor have produced a date (5550 years) which has proven to be so elusive from archaeological sites. Given the relatively arid environment of the present, it has always been tempting to refer the absence of mid Holocene occupation of the area to an increase in aridity. The notion that circumstances could have been wetter then has seemed less persuasive, assuming that the absence of evidence in the sites is indeed the evidence of absence. The very lack of deposition has, however, prevented us from analysing any proxy environmental indicators. The suggestion from the Grootdrift cores that the mid Holocene was, indeed, drier than today is a promising first step in the search for an explanation for human avoidance of the area for so long.

A second general feature of the archaeological evidence from sites near the Verlorenvlei has been the hints that the lower riverine system has previously been

94 M.E. Meadows et al.

more tidal and more open-mouthed than at present. Evidence from the near-shore deposits (Yates et al., 1986; Miller et al., 1993) has been interpreted as reflecting a mid Holocene relatively higher sea-level of about +3m, which in turn would have inundated the lower vlei and created a relatively broad-mouthed tidal inlet. Signifi- cantly, the eelgrass, Zostera capensis, has been found in archaeological deposits dating before the mid Holocene hiatus and after it until about 1500 years ago. The eelgrass is not found today and prefers fully estuarine conditions with regular exchanges of marine and fresh water. In support of this, there are regular, but low percentages of the razor shell, Solen capensis, in shellfish assemblages dating prior to 3500 years ago, but not thereafter (Jerardino, 1993). Solen prefers clean sand flats in tidally flushed conditions and is not found in the vlei today. The fish species of the late-mid Holocene period--about 4300 to about 1800 years ago---reflect open estuarine condi- tions in the diversity and range of species present compared to later archaeological faunas and the limited range found today (Poggenpoel, 1987). All in all there can be little doubt that the lower Verlorenvlei flooded back about 8000 years ago with rising sea-level, maintained a broad open mouth for several millennia and experienced a closing of the mouth with the gradual lowering of sea- level after the mid Holocene high. Preliminary confirma- tion of this scenario from the Grootdrift cores helps sharpen our understanding of the past condition of the river. More detailed relationships between pattems of archaeological evidence of settlement and palaeoenviron- mental indications of past climate changes can be anticipated.

CONCLUSIONS

Palaeoenvironmental reconstructions are always more reliable when based on multi-disciplinary forms of evidence. The mid-late Holocene environmental condi- tions at Verlorenvlei are revealed through the analysis of data from several different sources, viz: chronology, sedimentology, geochemistry and palynology of a series of cores, coupled with archaeological and palaeoecologi- cal information from several localities in the vicinity of the vlei. Although the sediments examined have not accumulated continuously since 5500 BP, it is now possible to provide a reasoned palaeoenvironmental reconstruction of the vlei and its catchment during much of the latter half of the Holocene. Rising sea-level shortly after the onset of sedimentation at Grootdrift, some 15 km from the contemporary vlei mouth, flooded the vlei as reflected in changes in the local vegetation. The palynological indications of greater aridity in the wider catchment at this time is tentatively correlated with the occupational hiatus at Elands Bay and other archaeolo- gical sites in the region. Sedimentation at the Grootdrift transect site seems to have ceased after 4300 BP (or deposits were subsequently eroded), but the sea-level appears to have remained relatively high for at least a millenium thereafter. The decline in sea-level and

substitution of marine influences with a fresh water hydrology is reflected in the palynology of the more recent sediments at Grootdrift. The past few hundred years have witnessed the replacement of natural environ- mental change with anthropogenic disturbance as the dominant influence on the ecology of Verlorenvlei. These insights provide the first detailed analysis of Holocene environmental changes in the add lowland fynbos of the southwestem Cape coast and suggest that the search for further information on the interplay between climatic change, sea-level fluctuations and the impact of human populations in the region could prove a fruitful exercise.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the financial support of the FRD core programme (MM and JP) and the FRD Special Programme on Rivers (AB). Textural analysis was conducted by Natasha Erlanck. Additional pollen analysis was provided by Terence Adams. We are grateful to Mr P van Zyl, the owner of Grootdrift farm for permission to core the sediments.

REFERENCES

Acocks, J.P.H. (1988). Veld types of South Africa, 3rd edition. Memoirs of the Botanical Survey of South Africa, 57, 1-146.

Allen, J.R.L. (1964). Studies in fluviatile sedimentation: six cyclotherms from the Lower Old Red Sandstone (Devonian), Anglo-Welsh basin. Sedimentology, 3, 163-198.

Allen, J.R.L. (1965). Fining upwards cycles in alluvial successions. Geological Journal, 4, 229-246.

Bates, C.D., Coxon, P. and Gibbard, P.L. (1978). A new method for the preparation of clay-rich sediment samples for palynological investigation. New Phytologist, 81, 459-463.

Baxter, A.L. (in preparation). Late Quaternary palaeoenvironments at Vedorenvlei, southwestern Cape Province, South Africa. Unpub- lished Doctoral thesis, University of Cape Town, Suth Africa.

Baxter, A.L. and Davies, B.R. (1994). Palaeoecological insights for the conservation of aquatic ecosystems in dryland environments: a case study of the Verlorenvlei system, South Africa. Journal of Aquatic Conservation: Marine and Freshwater Ecosystems, 4, 255-271.

Baxter, A.L. and Meadows, M.E. (1994). Palynological evidence for the impact of colonial settlement within lowland fynbos: a high- resolution study from the Verlorenvlei, southwestern Cape Province, South Africa. Historical Biology, 9, 61-70.

Birks, H.J.B and Birks, H.H. (1980). Quaternary Palaeoecology. Edward Arrtold, London, 289pp.

Cowling, R.M. (ed.) (1992). The Ecology of Fynbos: Nutrients, Fire, Diversity. Cape Town, Oxford University Press, 411pp.

Faegri, K., Kaland, P.E. and Krzywinski, K. (1989). Textbook of Pollen Analysis, 4th edition. John Wiley, Chichester.

Friedman, G.M. (1961). Distinguishing between dune, beach and river sands from their textural characteristics. Journal of Sedimentary Petrology, 31, 514-529.

Jerardino, A. (1993). Mid- to late-Holocene sea-level fluctuations: the archaeological evidence at Tortoise Cave, southwestern Cape, South Africa. South African Journal of Science, 89, 481-488.

Lanesky, D.E., Logan, B.W., Brown, R.G. and Hine, A.C. (1979). A new approach to portable vibracoring under water and on land. Journal of Sedimentary Petrology, 49, 654-4557.

Martin, A.R.H. (1968). Pollen analysis of Groenvlei lake sediments, Knysna, (South Africa). Review of Palaeobotany and Palynology, 7, 107-145.

Meadows, M.E. and Asmal, O. (1996). Chronology, sedimentology and geochemistry of sediments at Verlorenvlei (western Cape Province, South Africa) as evidence of anthropogenically-induced land degradation. Zeitschrift far Geomorphologie Supplementband, (in press).

Meadows, M.E. and Sugden, J.M. (1990). Late Quaternary vegetation history of the Cederberg, south-western Cape. Palaeoecology of Africa, 21, 269-281.

Late Holocene Environments at Verlorenvlei 95

Meadows, M.E. and Sugden, J.M. (1991a). A vegetation history of the last 14000 years on the Cederberg, south-western Cape Province. South African Journal of Science, 87, 34--43.

Meadows, M.E. and Sugden, J.M. (1991b). The application of multiple discriminant analysis to the reconstruction of the vegetation history of fynbos, southem Africa. Grana, 80, 325-336.

Meadows, M.E. and Sugden, J.M. (1993). The late Quaternary palaeoecology of a floristic kingdom: the southwestern Cape, South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 101, 271-281.

Meadows, M.E., Baxter, A.J. and Adams, T. (1994). The late Holocene vegetation history of lowland fynbos, Vedorenvlei, southwestern Cape Province, South Africa. Historical Biology, 9, 47-59.

Miller, D. (1987). Geoarchaeology at Veriorenvlei. In: Parkington, J. and Hall, M. (eds), Papers in the Prehistory of the Western Cape, South Africa. British Archaeological Reports International Series, 332, 46- 77.

Miller, D.E., Yates, R.J., Parkington, J.E. and Vogel, J.C. (1993). Radiocarbon-dated evidence relating to a mid-Holocene relative high sea level on the south-western Cape coast, South Africa. South African Journal of Science, 89, 35-44.

Moore, P.D., Webb, J.A. and Collinson, M.E. (1991). Pollen Analysis, 2nd edition. Blackwell Scientific Publications, Oxford.

Noble, R.G. and Hemens, J. (1978). Inland water ecosystems of South Africa: a review of research needs. South African National Scientific Programmes Report, 34, Council for Scientific and Industrial Research, Pretoria.

Parkington, J., Poggenpoel, C., Buchanan, W., Robey, T., Manhire, A. and Sealy, J. (1988). Holocene coastal settlement patterns in the western Cape. In: Bailey, G. and Parkington, J.E. (eds), The Archaeology of Prehistoric Coastlines, pp. 22-41. Cambridge University Press, Cambridge.

Poggenpoel, C.A. (1987). The implications of fish bone assemblages from Eland's Bay Cave, Tortoise Cave and Diepkloof for changes in the Holocene history of Verlorenvlei. In: Parkington, J. and Hall, M. (eds), Papers in the Prehistory of the Western Cape, South Africa. British Archaeological Reports International Series, 332, 212-236.

Sandford, R.B. and Swift, D.J.P. (197l). Comparison of sieving and settling techniques for size analysis, using a Benthos rapid sediment analyser. Sedimentology, 7, 257-264.

Schalke, H.J.W.G. (1973). The upper Quaternary of the Cape Flats area (Cape Province, South Africa). Scripta Geologica, 15, 1-57.

Scholtz, A. (1986). Pallynological and palaeobotanical studies in the southern Cape. Unpublished M.A. thesis, University of Stellenbosch, South Africa.

Scott, L. (1993). Palynological evidence for late Quaternary wanning episodes in southern Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 101, 229-335.

Sinclair, S.A, Lane, S.B. and Grindley, J.R. (1986). Verlorenvlei: Estuaries of the Cape, part II: synopses of available information on individual systems, In: Heydorn, A.E.F. and Morant, P.D. (eds), Council for Scientific and Industrial Research, 431.

Smith, D.G. (1984). Vibracoring fluvial and deltaic sediments: tips on improving penetration and recovery. Journal of Sedimentary Petrology, 54, 660--663.

Visser, H.M. and Toerien, D.K. (1971). Die geologie van die gebied tussen Vredendal en Elandsbaai. Toeligting van blaaie 3218C Doringbaai en 3218A Lambertsbaai. Geological Survey of South Africa Publication, 62813-1, Department of Mines, Pretoria.

Yates, R.J., Miller, D.E., Halkett, D.J., Manhire, A.H. and Parkington, J.E. (1986). A late mid-Holocene high sea-level: a preliminary report on geoarchaeology at Elands Bay, western Cape Province, South Africa. South African Journal of Science, 82, 164-165.