Piotr Migoń

Weathering mantles and their significance for geomorphological evolution of central and northern Europe since the Mesozoic

Abstract Weathering mantles (saprolites) are very widespread in central, western, and northern Europe, where they form thick near-surface residual deposits, often in excess of 50 m. They vary in the type of weathering, the bedrock lithology involved, the topographic setting, and the age and stratigraphic context. This review paper provides information about the distribution and major characteristics of weathering mantles from a number of ‘key areas’, including the British Isles, the Central European belt of mid-mountains and uplands, the Scandinavian Mountains, and the Fennoscandian Shield. It also examines the evidence for weathering (=etched) origin of various landforms, including boulders, tors, inselbergs, basins and some regional landforms assemblages. Major types of regionally important weathering mantles include ferrallitic (lateritic) saprolites, kaolinite-rich saprolites, sandy to grus mantles, and various residuals left after partial dissolution of carbonate rocks. Although dating of weathering mantles is often circumstantial, it appears sufficiently precise to argue for various ages of deep weathering. Mesozoic (pre-Late Cretaceous) mantles are particularly widespread, but there are also Early Tertiary and Miocene saprolites widely present, whilst most grus weathering is likely to be of Miocene to Pleistocene age. Individual upland areas have been subjected to multiple episodes of weathering, whose legacy is the present-day co-existence of different weathering products. Continental and shallow marine deposits around the uplands, particularly in the North Sea and intra-continental graben structures, are often dominated by quartz and kaolinite, pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale. They demonstrate that weathering mantles repeatedly formed and were subjected to erosion, and new cycles of weathering were initiated. We suggest that deep unroofing of basement structures in many parts of Europe has been mainly accomplished by deep weathering and stripping of pre-weathered rock. The phenomenon of deep weathering has been very important for geomorphology. Etched landforms vary in size, from small residual boulders up to regional characteristic landscapes (etchsurfaces), such as joint-valley landscapes of southern Sweden or undulating multi-convex and multi-concave landscapes of many uplands in central Europe. Deep weathering has played a major part in the geomorphological evolution of Europe since at least the Late Triassic, and the concept involving long-term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features.

Grus weathering mantles—problems of interpretation

Abstract 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 following characteristics: sand+gravel 75–100%; silt+clay

Deep weathering through time in central and northwestern Europe: problems of dating and interpretation of geological record

Abstract Upland and shield areas of central and northwestern Europe are characterised by an abundance of relict weathering mantles (saprolites). These saprolites, if accurately dated and interpreted, may serve as an important complementary source of information about long-term environmental history. In this paper, methods used to establish ages of weathering mantles are reviewed, such as stratigraphic and morphostratigraphic dating, clay mineral and stable isotope analysis, K–Ar and cosmogenic isotope dating, particularly with reference to European examples. The record of deep weathering in the Mesozoic and Cainozoic is examined to explain the peculiarities of the evidence and controls on the changing style of weathering through time. Weathering has been a continuous process through time, but general and local geological conditions have resulted in different ages of preserved mantles. An apparent trend from an earlier kaolinitic/ferrallitic style of weathering in the Mesozoic and Early Tertiary, towards a grussic style by the end of the Cainozoic, does not only reflect climate change, but it is also broadly consistent with tectonic/geomorphic history and related changes in land surface stability. Miocene and Plio–Pleistocene saprolites, in particular, show that in different geomorphological and lithological circumstances, different types of weathering mantles could have evolved.

Development of joint-controlled rock basins in Bohus granite, SW Sweden

The granite area of Bohuslan along the Swedish west-coast is characterised by an abundance of rock basins of different sizes. Within a 163 km2 large part of the area over 400 basins occur, ranging ...

Palaeoenvironmental significance of grus weathering profiles: a review with special reference to northern and central Europe

Grus weathering profiles are common signs of bedrock alteration in northern middle and high latitudes and have frequently been used to infer climatic regimes of the past and to develop denudation chronologies. This paper shows that the actual palaeoenvironmental significance of grus weathering is limited, and its potential in such reconstructions is clearly conditioned by local situations. Textural and mineralogical features of grus weathering profiles are rather unreliable indicators of past environments, being influenced by a variety of factors, including parent rock characteristics, topography and geological and geomorphological history. Grus weathering has been operating for at least the last few million years and the known profiles are of different ages, so it is doubtful if there is any narrow range of climatic conditions to which the origin of grus may be ascribed. By contrast, the relatively neglected relationships between grus weathering and topography at different scales of inquiry may be worthy of exploration, because it may help to decipher evolutionary pathways of weathering profiles.

Analysis of digital elevation data for the Scottish Highlands and recognition of pre-Quaternary elevated surfaces

Abstract Remnants of elevated palaeosurfaces in the Scottish Highlands, proposed in numerous earlier studies, have been re-evaluated using digital elevation data from the Ordnance Survey. Histograms of elevation frequency, for areas 5, 10 and 20 km2, display multi-modal distributions which can be interpreted in terms of plateau and base-level components. The effects of glaciation, lithology and faulting can be inferred from patterns in the elevation distribution. The histogram modes reveal a series of elevated surfaces which broadly confirm previous, qualitative models of inclined Tertiary palaeosurfaces, but indicate a much more complex pattern. Many of the elevated surfaces are seen to be inclined towards two major faults, the Great Glen Fault and the Ericht-Laidon Fault. However, the highest surfaces may have crossed these fault zones uninterrupted. A model in which an episode of tectonic reactivation imposes a major change on pre-Quaternary geomorphological evolution in this area is proposed.

Tertiary etchsurfaces in the Sudetes Mountains, SW Poland: a contribution to the pre-Quaternary morphology of Central Europe

Abstract This paper presents the evidence of the major part played by deep weathering accompanied, or followed, by stripping of a weathering mantle in the formation of Tertiary surfaces in the Sudetes. It also highlights the complicated nature of the topography of surfaces developed upon differentiated bedrock over protracted time-scales. The evidence is gained from the available data about weathering mantles and Tertiary sediments, and from the analysis of pre-Quaternary landforms such as rolling plains, scarps and inselbergs. A classification of the Tertiary surfaces, recognized here as etchsurfaces, is proposed for the Sudetes. The palaeosurfaces in the Sudetes are regarded as a part of an extensive etch surface which dominated the Tertiary landscape of Central and Northern Europe.

Evolution of granite landscapes in the Sudetes (Central Europe): some problems of interpretation

Major problems concerning the origin and development of granite landscapes in the Sudetes are discussed, with special reference to particular landforms, such as marginal depressions, inselbergs and related hills, and microforms of rock surfaces. Types of granite terrains and different weathering mantles are also briefly described. Two factors controlling the development of granite forms are considered: structural properties of bedrock and external climatic influences. Discussions about the age and palaeoclimatic significance of individual landforms are summarized.

Rediscovering geoheritage, reinventing geotourism: 200 years of experience from the Sudetes, Central Europe

Abstract The Sudetes is a mountain range in Central Europe and an area of remarkable geodiversity. In recent years, the area has been promoted as a geotourist destination and various initiatives aimed at better understanding geoheritage have been implemented. An interest in scenic landscapes is not new however, and dates back to the end of the eighteenth century. Two areas within the Sudetes are cradles of local nature-based tourism. These are the granite massif of the Karkonosze in the west and the sandstone stepped plateau of Broumov Highland and Stołowe Mountains in the central part of the Sudetes. In both, physical access to the key geosites was provided as early as in the nineteenth century, while an interpretation component was added in the early twentieth century. A side-effect of political change following the end of World War II was the neglect and dilapidation of many sites, as well as the disappearance of geoheritage appreciation from the collective social memory. In the last decade many of those early achievements were rediscovered and provided the foundations for contemporary activities. An educational component based on modern science is now included in the features which were discovered as tourist attractions long ago.

Overlooked Geomorphological Component of Volcanic Geoheritage—Diversity and Perspectives for Tourism Industry, Pogórze Kaczawskie Region, SW Poland

In the West Sudetes (SW Poland), volcanic activity of Oligocene and Miocene age has left a suite of landforms of considerable geomorphological interest. Besides being relevant to the subject of volcanology, they illustrate how volcanism influences interplays with landscape development in the long-term. Three main geomorphological themes are explored: structural geomorphology of ancient volcanic terrain, volcanic remnants as markers of long-term denudation and hillslope evolution under periglacial conditions of the Pleistocene. Volcanic geosites are used as a resource for geotourism and promotion of geoheritage has intensified recently, with the region branding itself as the ‘Land of Extinct Volcanoes’. Ten localities are evaluated as geomorphosites of significant educational potential, taking into account geomorphological values, added values as well as physical accessibility and information supply. Successful interpretation remains a key challenge in further geotourism development, and several associated practical issues are pointed out such as choice of terminology, uncertainties in scientific understanding and stand-alone attractiveness of geoheritage.