Michael F. Thomas

University of Stirling · Department of Biological and Environmental Sciences

The rapidly expanding literature on the related subjects of geodiversity, geosites and their place in understanding and conserving our geoheritage has produced several proposed protocols for defining and valuing key sites and landscapes. Distinctions between geosites as well-defined features of our geological heritage and geodiversity sites as land...

The rapidly expanding literature on the related subjects of geodiversity, geosites and their place in understanding andconserving our geoheritage has produced several proposed protocols for defining and valuing key sites and landscapes.Distinctions between geosites as well-defined features of our geological heritage and geodiversity sites as landsc...

Although broad-based tourism is well established in the countries bordering the Mediterranean Sea and to some extent in South Africa, across the rest of the continent there is an emphasis on wildlife and cultural tourism. Sustainability concerns focus mainly on habitat loss and support for rural communities. The single UNESCO Geopark in Morocco ref...

New keywords in the geosciences such as geodiversity, geoconservation, geoheritage and geotourism are now in common use, with a rapid increase in the delineation of geosites and geomorphosites on the ground, usually with an intention to establish geoparks for promotion of geotourism and geoconservation. Geodiversity, as the abiotic equivalent of bi...

New keywords in the geosciences such as geodiversity, geoconservation, geoheritage and geotourism are now in common use, with a rapid increase in the delineation of geosites and geomorphosites on the ground, usually with an intention to establish geoparks for promotion of geotourism and geoconservation. Geodiversity, as the abiotic equivalent of bi...

The concept of geodiversity has its roots in the need for conservation of fossil localities and other sensitive geological sites, but the field has now widened to embrace concerns at the landscape scale as well as the geoscience input to ecosystem management. The geomorphological component of geodiversity becomes central in these wider contexts and...

A geomorphological approach to geodiversity - its applications to geoconservation and geotourism Geodiversity is becoming widely considered alongside biodiversity by conservation agencies and has importance for geotourism. Geomorphology has a central role in understanding geodiversity, particularly at regional and local scales. By focusing on the p...

The concept of geodiversity has its roots in the fossil record as part of the Earth’s biodiversity and in the need for conservation of fossil localities and other sensitive geological sites. The geomorphological component of geodiversity is central to landscape conservation and is examined as a response to the operation of magmatic and surface proc...

The Conference, ‘Engaging with Geodiversity—Why it Matters’, December 2010, addressed the wider relevance of geodiversity in Scotland. A key challenge is to integrate geodiversity within existing policy relating to the way we work and live, and therefore to inform better the decisions we make about a sustainable future for our environment. This wil...

Sanqingshan and Huangshan, two areas of granite mountains in eastern China with World Heritage status, form iconic landscapes. Granites were intruded within a Palaeozoic orogenic zone during the Mesozoic and have been repeatedly uplifted to form striking mountain scenery. At Sanqingshan, a triangular pattern of faults delimits an area of towering r...

The understanding of climate impacts on tropical rivers and catchments has developed, in part, from models developed for temperate landscapes, and a common rhythm is often apparent when millennial-scale studies are compared. At this level issues arising from the complex response of rivers to internal and external factors appear less important than...

Samples of alluvial and colluvial deposits from the coastal plain and coastal valleys north and south of Cairns (17°S) have been dated using optically stimulated luminescence (OSL) protocols, with additional thermoluminescence (TL) and Radiocarbon assays. Coarse fanglomerates from elevated coastal terraces date back to 81 ka, but most are clustered...

Historically, geomorphologists have applied uniformitarian principles based on a temperate normality to all water-worn landscapes. Isolation of tropical landforms within formal morphogenetic regions, which arose during the early history of the subject, has persisted. However, in a global geomorphology, plate tectonic motion, Milankovich cycles of c...

Unusual exposure of the drift stratigraphy of a typical, vegetated hillslope in the Northern Highlands of Scotland has allowed reconstruction of its Holocene history. Graphic logging of palaeogully fill, sediment analysis, radiocarbon dating and microscopic investigation of horizon boundaries, link periodic slope instability to changes in hydrology...

Ideas concerning what is now usually termed “landscape sensitivity” have been a part of geomorphological thinking for half a century, illustrated by the concepts of biostasie and rhexistasie formulated by Erhart (1955) to describe the switch from biogeochemical equilibrium and chemical sedimentation to conditions of erosion and clastic sedimentatio...

A millennial scale of ‘rapid’ change during the Quaternary is recorded in GRIP and GISP2 ice-core records, and is also found in tropical oceans. Rapid warming episodes followed by gradual cooling, associated with sub-Milankovich cycles implies an asymmetry in the behaviour of climate that is likely to be reflected in landscape responses. Slope fail...

Inherited saprolite stores and continued weathering in Quaternary time juxtapose abundant clay and fresh rock in tropical landscapes. This influences sediment fluxes and affects the interpretation of sediment sequences derived from tropical watersheds. Detrital kaolinites derive from inherited saprolite sources as well as from soil clays and appear...

Grus is an ill-defined product of deep weathering of coarse-grained rocks whose relationships to other weathering changes remain unclear. This paper attempts to address this issue by reviewing a number of examples of coarse saprolites from a variety of climatic and topographic settings. Grus is the category of weathering mantle that possesses the f...

Unconsolidated sediments in the humid tropics range from highly altered weathering products involved in minimum, low energy transport, to coarse fans and landslide deposits. But most can be regarded as colluvium and alluvium showing imprints of episodic sedimentation. These deposits may span the entire Cenozoic, but 14C dating has led to a focus on...

Extensive alluvial‐fan and debris‐flow deposits occur along the base of the escarpment of the east Australian highlands in the wet tropics of northeast Queensland. Luminescence and radiocarbon dating show that these deposits accumulated between 27 ka and 14 ka, which was the driest phase of climate during the last full glacial cycle. Climatic desic...

There is now a wide agreement that temperature depression in the humid tropics during the Last Glacial Maximum (LGM) was at least 5°C. Most estimates of precipitation reduction at the LGM range from 25–30% to 50–65%, based on proxy data, but the recent CCM1 model envisages only around 12%. Dates obtained from river sediments indicate major changes...

Landscape sensitivity may be discussed in terms of the response of landscape systems to perturbation on different time and spatial scales. Unstable systems behave chaotically but may show self organised criticality, while stable systems resist change until threshold values of system parameters are exceeded. Spatial sensitivity is expressed in diffe...

Ice core and ocean-drilling records now confirm the evidence from lakes, rivers and mires, concerning temperature depression in the humid tropics during the LGM by at least 5°C on land and this accords with the recent CCM1 model output. There is less agreement about fluctuation in precipitation amount, intensity and seasonality during the late Quat...

Late Quaternary climate and vegetation changes are thought to have induced important changes to landscape dynamics throughout the tropics, including the savanna areas of central Africa. Evidence is presented of high energy landforms in the Chipata District of eastern Zambia, comprising landslides, debris slides and coarse fan deposits. Local geolog...

The morphology and geochemistry of weathering profiles in Miocene granodiorites from the coastal lowlands of NW Kalimantan, Indonesia (1°N lat.), indicate long-term weathering rates, landform development and mechanisms for the formation of `white sands' found widely in valleys and depressions. Samples are analysed from convex hill, piedmont glacis,...

The concept of landscape sensitivity was introduced into thinking about geomorphological systems by Brunsden and Thornes (1979) and has been developed in the context of environmental change (Thomas and Allison 1993). When resistance to change is exceeded by the magnitude of the disturbing forces the environmental system will adjust to create a new...

Although seismic shocks and storm events act as trigger mechanisms for most landslides, weathering leads to the weakening of rock fabrics, often to great depths and may lead to the development of vulnerable saprolite mantles under favourable conditions. Deep karstification has also been implicated in major landslides in Papua New Guinea, while thic...

Dated alluvial stratigraphies indicative of late Quaternary environmental change in the humid tropics have increased, but the database remains inadequate and the intensity and duration of wet-dry oscillations and responses of hillslopes and river systems remain poorly understood. Dry conditions at the Last Glacial Maximum were marked by semi-arid l...

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The data base concerning late Quaternary environmental change in the humid tropics is dependent on records from scattered sites; the intensity and duration of wet-dry oscillations remain speculative, and the responses of hillslopes and river systems are based on over-simplified models. However, available evidence indicates that prolonged aridity af...

Models for pre-glacial relief along passive continental margins must reflect the style and rate of uplift, and the rates of weathering and erosion, during at least the last 100–150 Ma. Passive margins have varied elevation, patterns of rifting, uplift and flexuring. A distinction is recognised between low-lying and steeply rising margins, the latte...

Studies of alluvial placer deposits from tropical cratons in West Africa, NW Australia and Indonesia, indicate common features important to exploration strategy and to geomorphic theory. Alluvial placer concentrations tend to occur in tectonic-topographic "lows' within larger, emergent crustal upwarps, probably subject to continuing neotectonic cru...

Temporal patterns in floodplain genesis and alluvial sedimentation in lowlands tropical rain forest zones of Ghana, Sierra Leone and western Kalimantan (Indonesian Borneo) based upon 14C age determinations are described.Alluvial low terraces or buried sediments in West Africa yielded ages of 36-21 ka. In west Kalimantan a widespread episode of allu...

The exploration geomorphologist must attempt to build a depositional model for a targetted deposit, including the morpho-tectonic setting, long-term landform development, and the application of studies into formative processes. In many tropical valleys this applies particularly to sedimentation over the last 60 000 years. The methodology involves a...

Widespread Quaternary alluvial sediments occur around the coastal margins of western Kalimantan. These strongly podzolised "white sands' occur as major alluvial bodies that may be 15-20 m higher than Holocene/contemporary floodplains inland but converge and pass beneath them towards a near coastal hinge line. It is presumed that the sediments conti...

Progressive differentiation of relief during the last 100 Ma, has been largely a result of differential chemical etching accompanying or following non-orogenic uplift and tilting. Accumulation of chemical residua as duricrusts allows profile deepening, but friable saprolites elsewhere are lowered in dynamic equilibrium or subject to stripping and t...

The early development of the concept of the etched plain was hesitant and the definitions and descriptions offered have led to ambiguity. Yet the phenomenon is so close to Budel's concept of Doppelten Einebnungsflachen that the terminology was combined in the translation of his Climatic Geomorphology. A revised and expanded terminology designed to...

Superficial deposits (residual, colluvial, alluvial) are important as environmental resources in tropical environments. An understanding of their formation through varying time periods is essential to a correct interpretation of their economic and hazard potentials. This requires an integration of process studies with a reconstruction of longer ter...

Emphasis in geomorphology on short-term surface process studies needs to be balanced by enquiry into exogenetic and endogenetic forces in the longer term if the speculative status of most theory concerning long-term landform evolution is to be advanced. Applications are discussed in relation to etching under both palaeotropical and temperate condit...

Examination of the diamondiferous sediments of the Birim River floodplain in Ghana using radiocarbon dating allows the recognition of three chronostratigraphic units: 13 000-11 000, 9000-7000, and 2100 years BP to the present, while older sediments rest on bedrock benches and form terraces. The late Pleistocene sediments infill deeper, scour channe...

The geomorphology and diamond distribution within the Koidu alluvial diamond field in Sierra Leone are examined to provide a methodology for palaeoplacer appraisal within a humid tropical environment of diverse relief and headwater drainage containing local diamond sources. Valley floors including headwater swamps and stream floodplains provide a r...

The formation of etched plains was first described by E. J. Wayland in 1934. The combination of deep weathering and subsequent stripping, the interpretation of stone lines and the evidence from alluvial terraces are discussed. Particular attention is paid to alluvial profiles from diamond workings. Etch planation seems to be episodic and related to...

PHYSICAL Scotland's Environment during the last 30,000 years. By Robert J. Price. 25.5 x 19, 224pp. Numerous illustrations, figures and tables, bibliography, index. Scottish Academic Press, Edinburgh, 1983. £27.50. HISTORICAL An Historical Geography of Scotland. G. Whittington and I. D. Whyte (eds.). 23.5 x 15.5, 342 pp. 28 illus. Tables, reference...

PHYSICAL GEOGRAPHY Hillslope materials and Processes. By M. J. Selby. 25 × 19, 264 pp., 199 figs., 99 photos, 30 tables. Oxford University Press, 1983. £9.95 (paper) or £19.95 (hardback). Slopes and Weathering. By R. J. Small and M. J. Clark, 26 × 18, 112 pp. Figures, plates, tables, references. Cambridge University Press, 1982. £6.95. Geomorpholog...

The Human Impact. By Andrew Goudie. 316 pp., 24.5 × 17, 39 photographs, numerous figures and tables, references, index. Basil Blackwell, Oxford, 1981. £6.50.

The paper describes 37 14C dates determined from organic clays and wood contained within alluvial deposits exposed by diamond mining in valleys in areas of monsoon rain forest. Alluvial sands and coarse gravels lie beneath the surface organic clay loams in all valleys. The 14C dates fall into four groups: 1) 36 000-20 500 BP; 2) 12 500-7800 BP; 3)...

Sierra Leone includes planation surfaces which have been assigned ages from the Jurassic onwards. The evidence is uncertain: the supposed Jurassic Gondwana surface is not easily identified even if it is real, while duricrusts are not readily dated. The field evidence from four areas is reviewed, and four essentially different modes of landform deve...

GEOLOGY AND GEOMORPHOLOGY Stratigraphy of the British Isles. By Dorothy H. Rayner. 9 ¼ × 6 ¼. Pp. 453 and maps. Cambridge University Press, 1967. 70s. Landform Studies from Australia and New Guinea. Edited by J. N. Jennings and J. A. Mabbutt. 9 ⅝ × 7 ⅜. 434 pages. 36 plates. 113 figures. Cambridge University Press, 1967. £5 5s. Glacial and Periglac...

Examination of drilling and seismic logs from constructional and mining operations in Nigeria reveals a variety of deep weathering patterns. Transverse valley sections and contour maps of the basal surface of weathering have been constructed for a number of widely distributed sites. These reconstructions show that irregularity, particularly the occ...