Sue McLaren

Geochemical sediments and landscapes

1. Introduction: Geochemical Sediments in Landscapes (David J. Nash and Sue J. McLaren). 2. Calcrete (V. Paul Wright). 3. Laterite and ferricrete (Mike Widdowson). 4. Silcrete (David J. Nash and J. Stewart Ullyott). 5. Aeolianite (Sue J. McLaren). 6. Tufa and travertine (Heather A. Viles and Allan Pentecost). 7. Speleothems (Ian J. Fairchild, Anna Tooth, Andrea Borsato and Silvia Frisia). 8. Rock varnish (Ronald I. Dorn). 9. Lacustrine and palustrine geochemical sediments (Eric P. Verrecchia). 10. Terrestrial evaporites (Allan R. Chivas). 11. Beachrock and intertidal precipitates (Eberhard Gischler). 12. Nitrate deposits and surface efflorescences (Andrew S. Goudie and Elaine Heslop). 13. Analytical techniques for investigating terrestrial geochemical sediments (John McAlister & Bernie J. Smith). 14. Geochemical sediments and landscapes: general summary (Sue J. McLaren and David J. Nash).

Late Pleistocene wetting and drying in the NW Kalahari: an integrated study from the Tsodilo Hills, Botswana

Abstract The sediments and landforms at the Tsodilo Hills, in the northwestern Kalahari desert, provide an opportunity to directly investigate the late Quaternary wetting and drying of the region from evidence at a single site. Lacustrine carbonates, including incorporated molluscs and diatoms, a lake shoreline feature and stabalised linear dunes were investigated for their constituent palaeoenvironmental signals. Chronometric control is provided by calibrated 14 C , AMS and OSL dating. The evidence suggests that linear dune construction has not occurred since the Last Glacial Maximum, with particular development from 36 to 28 ka . Lake stands indicating wetter regional conditions than present occurred at 40– 32 ka , with more seasonal conditions from 36 ka , and at 27– 12 ka with a possible drying out at 22– 19 ka . Data are consistent with other independent studies from the region, and with recent evidence obtained from Atlantic cores off the coast of Namibia. It is concluded that careful consideration of multi-proxy data from a single location can assist in resolving discrepancies that arise from independent studies of lake, cave and dune records in the Kalahari.

Kalahari valley calcretes: their nature, origins, and environmental significance

Abstract Calcretes that form in non-pedogenic settings have been widely reported in the geomorphological and geological literature, yet they are still poorly understood in comparison with pedogenic varieties. This may be because there are assorted types of non-pedogenic calcretes (often loosely referred to as groundwater calcretes, but encompassing groundwater, phreatic, open valley or confined channel calcrete types) forming within vadose and phreatic environments in different geomorphological settings. Relatively few studies have described the detailed petrological characteristics of such calcretes, leading Wright and Tucker (Calcretes; International Association of Sedimentologists Reprint Series, (1991) Vol. 2, Blackwell Scientific Publications, Oxford, p. 10) to suggest that “much more work is needed to define the ‘groundwater calcrete facies’ and to devise criteria for its recognition” so that the various non-pedogenic calcretes can be identified within the Quaternary as well as further back in the geological record. Most descriptions of groundwater calcretes are highly generalistic and do not take into account the variability that may occur as a result of calcretes forming in different positions within a landscape and affected by separate controls. Thus, the range of groundwater calcretes that exists now needs to be studied individually to identify patterns within the distinct types. As a step towards expanding our knowledge of the variety of non-pedogenic calcretes, this paper describes the petrology, micromorphology, and mode of development of one of these types of calcrete, namely that which forms within valley locations (but not in definite fluvial channels). Late Quaternary to Holocene valley calcretes are described from various dry valleys ( mekgacha ) across the Kalahari region of central Botswana, with the majority of samples collected from trunk and tributary valleys of the Okwa. Samples have been analysed in thin section and under scanning electron microscope in order to determine the carbonate matrix type and calcrete micromorphology. In general, most samples consist of grains of quartzose Kalahari sand cemented by fine crystalline, often glaebular, grain-coating and pore-filling micrite. Cement types are fairly consistent and not as micromorphologically variable as has been noted for other Kalahari calcretes. Biological inputs are prevalent in many samples and include networks of calcified rootlets. These characteristics reflect the fact that the calcretes formed in a relatively near-surface environment with relatively high rates of evaporation.

Early-Holocene environments in the Wadi Faynan, Jordan

Evidence for early-Holocene environments in the Wadi Faynan in the rift-margin in souther Jordan is described. The early Holocene of Jordan is not well known and palynology, plant macrofossils and molluscs from Wadi Faynan provide evidence for a much more humid-forest-steppe and steppe-environment than the present stony desert and highly degraded steppe. The early-Holocene fluvial sediments in the Faynan catchment are predominantly fine-grained, epsilon crossbedded and highly fossiliferous. They provide convincing evidence for meandering perennial rivers before 6000 cal. BP. It is probable that this early-Holocene landscape was disrupted by the impact of early farmers and by climate change-the 8.1 ka event appears to be marked by desiccation. By the Chalcolithic, environmental degradation was well advanced.

The reliability of uranium-series mollusc dates from the western mediterranean basin

Abstract Fossil mollusc shells from western Mediterranean raised beach deposits have been dated using U-series techniques. Sub-sampling has allowed intra-shell isotopic variability to be assessed. Although most of the calculated ages appear plausible and some internal consistency exists, closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect. Some previously published U-series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable. Simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells.

Environment and land use in the Wadi Faynan, southern Jordan : The second season of geoarchaeology and landscape archaeology (1997)

AbstractThis report describes the third season of fieldwork by an interdisciplinary team of archaeologists and geographers working to reconstrnct the landscape history of the Wadi Faynan in southern Jordan over the past 200,000 years. The particular focus of the project is the long-term history of inter-relationships between landscape and people, as a contribution to the study of processes of desertification and environmental degradation. The geomorphological and palaeoecological studies have now established the outline sequence of landform changes and climatic fluctuations in the late Pleistocene and Holocene. The complex field system WF4 has now been recorded in its entirety in terms of wall construction, suiface artefacts, and hydrological features, as well as most of the outlying field systems. From these studies, in combination with the analysis of the suiface artefacts, an outline sequence of the water utilization and management strategies they represent can now be discerned. Ethnoarchaeology is als...

Past human activity and geomorphological change in a guano-rich tropical cave mouth: initial interpretations of the Late Quaternary Succession in the Great Cave of Niah, Sarawak

This paper presents initial interpretations of the processes and events responsible for the late Quaternary sequence in the West Mouth of the Great Cave of Niah, in the hot and humid lowland rainforest and swamp forest of Sarawak in Malaysian Borneo. It evaluates the geomorphological context of the site within the known pattern of rapid late Quaternary climate change. Attention is given to the proximity to the sea and the likelihood of humid tropical or cooler drier conditions. The stratigraphic succession is described and four units or lithofacies (2C, 2, 3 and 4) are recognized as being of particular geomorphological and archaeological importance. The key processes operating within the site are the accumulation and subsequent failure and flow of bat and bird guano, hillslope colluviation, and ephemeral stream flow and pond development. Units 2C and 2 contain the critical archaeology, including the Deep Skull from an anatomically modern human, discovered by Tom Harrisson. These were formed by colluviation from a complex cave-mouth rampart and stream flow from within the cave. The stream transported fine-grained sediment to a shallow pond, and both the stream and pond deposits show evidence for prolonged desiccation. Human activity is associated with these surfaces. The human remains and related archaeology are preserved because a mudflow (Unit 3) plowed into and overrode the land surface upon which the humans had lived, resulting in the deformation and burial of the surface and the preservation of the archaeological material. Provisional radiocarbon dates indicate that Units 2C and 2 accumulated from before ca. 45,000 B.P. until ca. 38,000 B.P. Dates bracketing the Deep Skull give this an age of ca. 45,000 B.P. to ca. 43,000 B.P. Overlying the mudflow, Unit 4, a silty diamicton with a relatively high carbonate and organic content, appears to have formed by a mix of natural colluvial and human transport processes, and is associated with human cultural material. Unpublished radiocarbon dates indicate that this deposit formed from before ca. 19,500 B.P. to ca. 8500 B.P. (uncalibrated).This interpretation of the site and its finds has required detailed reconstruction of the changing palaeogeography within and beyond the cave entrance and the nature and rate of geomorphological processes operating within the region, which have been placed within models for rapid Quaternary environmental change. The results suggest that during the earlier period of human presence in the Great Cave of Niah(earlier than ca. 45,000 B.P. until ca. 38,000 B.P.), the climate was episodically wet with much longer periods of relative dryness. During the later period of human occupancy (ca. 19,500 B.P. to ca. 8500 B.P. [uncalibrated]), the evidence is less secure and a slightly moister climate is suggested.

Merged remotely sensed data for geomorphological investigations in deserts: examples from central Saudi Arabia

Image merging has gained acceptance in geological remote sensing, however it has rarely been applied in geomorphology. We report on the usefulness of principal components substitution (PCS) to merge IRS panchromatic data with multispectral Thematic Mapper (TM) imagery, to map commonly encountered desert geomorphological features, and in relative age dating of alluvial surfaces. The merged data were applied to the identification and mapping of geomorphological features along two geolo-gically different mountain fronts in central Saudi Arabia. Two types of geomorphological maps have been created. A morphogenetic map that distinguishes between aeolian landforms, fluvial landforms, desert pavements, and gypsum crusts. Second, a morphochronological map, which shows the relative age of four geomorphic surfaces developed on an alluvial fan. The construction of the two maps is supported by field observations and laboratory measurements. Using the optimum index factor (OIF), a TM band 1, 5 and 7 image (of 20 merged composites) was found to be the optimum colour composite image for the geomorphological features in this arid environment. We discuss our findings in the context of the spatial and spectral properties required for applied geomorphological remote sensing.

Archaeology and Desertification in the Wadi Faynan: the Fourth (1999) Season of the Wadi Faynan Landscape Survey

Abstract This report describes the fourth season of fieldwork by an interdisciplinary team of archaeologists and geographers working together to reconstruct the landscape history of the Wadi Faynan in southern Jordan. The particular focus of the project is the long-term history of inter-relationships between landscape and people, as a contribution to the study of processes of desertification and environmental degradation. The 1999 fieldwork contributed significantly towards the five objectives defined for the final two field seasons of the project in 1999 and 2000: to map the archaeology outside the ancient field systems flooring the wadi that have formed the principal focus of the archaeological survey in the previous seasons; to use ethnoarchaeological studies both to reconstruct modern and recent land use and also to yield archaeological signatures of land use to inform the analysis of the survey data; to complete the survey of ancient field systems and refine understanding of when and how they functioned; to complete the programme of geomorphological and palaeoecological fieldwork, and in particular to refine the chronology of climatic change and human impacts; and to complete the recording and classification of finds.

Radon and 'King Solomon's Miners': Faynan Orefield, Jordanian Desert.

Concentrations of 222Rn were measured in ancient copper mines which exploited the Faynan Orefield in the South-Western Jordanian Desert. The concentrations of radon gas detected indicate that the ancient metal workers would have been exposed to a significant health risk and indicate that any future attempt to exploit the copper ores must deal with the hazard identified. Seasonal variations in radon concentrations are noted and these are linked to the ventilation of the mines. These modern data are used to explore the differential exposure to radon and the health of ancient mining communities.