A High-Resolution Record of Late Quaternary Aeolian Activity at Witpan, South Africa: Palaeoclimatic and Palaeoenvironmental Implications

Matt Telfer

Prof. Dave ThomasDr Mark Bateman

Title

Background

• Much of the Kalahari landscape is characterised by vegetated linear dunes• These have long been interpreted as evidence of former arid periods• Until the 1990s and the advent of luminescence dating, the chronology for these landforms was extremely vague

Title

Background

• Stokes et al (1997) represented the first systematic dating study of dune forms in this area

• Periods of “dune-building (arid)” identified at 9–16, 20–26, 41–46 and 95–115 kyr

Title

Background

So what is there still to do?

• The southwestern Kalahari is represented by only 8 dates, and the earlier two phases are not recorded here.

• Samples are taken from hand-dug pits on the surface of the dunes – generally 3m deep at most.

• Many dunes represented by a small number of dates – is deposition between these ages continuous or are these discrete phases?

• The sites involved are over 1000km apart – different climatic controls?

Title

Aims and Objectives

• Investigate the preservation potential of the Kalahari’s dunes, and improve process knowledge of how an aeolian chronology is preserved

• Extend the aeolian record with coring techniques

• By using a high-resolution strategy within cores as well as within the locale, investigate the continuity of dune records

Title

Field site

• Southwestern Kalahari of the Northern Cape, South Africa

Title

Field site

• Southwestern Kalahari of the Northern Cape, South Africa.

• Witpan contains a range of landforms which may act as palaeoenvironmental indicators – a pan-lunette complex set amongst linear dunes.

Title

Field site

• Southwestern Kalahari of the Northern Cape, South Africa.

• Witpan contains a range of landforms which may act as palaeoenvironmental indicators – a pan-lunette complex set amongst linear dunes.

• Detailed sampling strategy.433

3

4

410

4

6

1 1

411

214

173

10

Spatial variation of lunette deposition

Kal 02/21

Kal 02/20

Kal 02/5

Kal 02/4

Kal 02/6

0.14 ± 0.02

0.45 ± 0.03

1.1 ± 0.1

0.46 ± 0.03

0.60 ± 0.04

0.66 ± 0.04

0.97 ± 0.06

0.08 ± 0.010.20 ± 0.021.1 ± 0.1

2.0 ± 0.1

1.8 ± 0.11.7 ± 0.1

2.2 ± 0.11.8 ± 0.1

0.07 ± 0.01

0.57 ± 0.04

0.53 ± 0.03

All ages in ka

Spatial variation of lunette deposition

Kal 02/21

Kal 02/5

Kal 02/6 2.1Geochemistry

0.3 58

5.1

CaO

(%

)

Sr

(ppm

)

594

310– mean values for all samples at a site

0.3 60

CaO

(%

)

Sr

(ppm

)

Linears

1.6 419Pan

Title

Coring

Linear deposition – intra-core variation

9.0 ± 0.6

1.8 ± 0.1

10.2 ± 0.6

9.8 ± 0.6

9.1 ± 0.6

10.0 ± 0.5

9.3 ± 0.6

10.9 ± 0.7

10.8 ± 0.7

10.5 ± 0.7

3.5 ± 0.2

5.9 ± 0.4

8.9 ± 0.5

0.16 ± 0.02

Kal 02/7

Dep

th

(m)

Age (ka)

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Linear deposition – inter-core variation

12.2 ± 0.8

56 ± 3

76 ± 8

73 ± 7

72 ± 7

12.1 ± 0.8

12.3 ± 0.7

Kal 04/6 Kal 02/1

0.15 ± 0.02

3.1 ± 0.3

4.9 ± 0.3

0.16 ± 0.02

10.1 ± 0.6

9.2 ± 0.6

10.3 ± 0.6

12.7 ± 0.8

57 ± 3

10.4 ± 0.6

9.4 ± 0.5

Dep

th

(m)

Age (ka)

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100

3m

Linear dune OSL histograms

Probability density function of southwestern Kalahari linear dune ages (Stokes et al 1997)

0%

10%

20%

30%

0 10 20 30 40 50 60 70 80 90 100 110 120

Age (ka)

Pn = 5

Linear dune OSL histograms

Probability density function of southwestern Kalahari linear dune ages (Stokes et al 1997; Thomas and Shaw

2002; Bateman et al 2003)

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

0 10 20 30 40 50 60 70 80 90 100 110 120

Age (ka)

Pn = 19

Linear dune OSL histograms

Probability density function of southwestern Kalahari linear dune ages (Stokes et al 1997; Thomas and Shaw

2002; Bateman et al 2003; this study)

0%

1%

2%

3%

4%

5%

0 10 20 30 40 50 60 70 80 90 100 110 120

Age (ka)

Pn = 88

Linear dune OSL histograms

Evidence of wet interval at c.8-5ka:Wonderwerk Cave (Butzer 1984)Kathu Vlei – pollen and clastics

(Beaumont 1984)Namibian valley silts (Eitel et al 2001)

Linear dune OSL histograms

Evidence of dry interval at c.14-9ka:Kathu Vlei pollen (Beaumont et al 1984)Otavi cenotes (Brooke et al 1998) Tsodilo Hills lakeshores (Thomas et al 2003)

Linear dune OSL histograms

“Short-lived dry interval from 20-19ka”(Brook et al 1998), South African tufas and Botswanan caves

“Lake stands indicating wetter regional conditions than present… at 27–12 ka with a possible drying out at 22–19 ka” (Thomas et al 2003) Tsodilo Hills

Title

Conclusions

• Much of the lunette is even younger than suspected previously – full-depth (9m) reworking/deposition over the past 1000 years.

• The response of the lunette dune itself is subject to the influence of differing sediment supply along its length.

• The linear and lunette dunes at Witpan respond in different ways to environmental stimuli.

• A major period of dune building near Witpan occurred at 10-11ka, although there has been near-continuous low-intensity Holocene deposition. Previous periods of dune activity are recorded in this area.

Title

Summary

So how are we doing?

• The southwestern Kalahari is represented by only 8 dates, and the earlier two phases are not recorded here.

• Samples are taken from hand-dug pits on the surface of the dunes – generally 3m deep at most.

• Many dunes represented by a small number of dates – is deposition between these ages continuous or are these discrete phases?

•The sites involved are over 1000km apart –different climatic controls?

Implications for further work

• The Kalahari’s linear dunes have the potential to record long – albeit discontinuous – sequences of aeolian deposition.

• A highly detailed and rigorous sampling strategy is required to discern details of the aeolian record.

• Palaeoclimatic interpretation as to what these depositional events mean is greatly aided by the application of further proxies.