The role of loamy sediment (terra rossa) in the context of steady state karst surface lowering
Section snippets
Foreword
Since the introduction of general systems theory in geomorphology several decades ago (Chorley, 1962, Chorley and Kennedy, 1971) earlier paradigms (see Summerfield, 1991, pp. 457–463) have been abandoned and empirical knowledge about the Earth's surface landforms (Summerfield, 1991, pp. 464–466) has been adapted to new views. Within this context the principle of landscape sensitivity (Summerfield, 1991, p. 465) became crucial. In practice, it reduces to the question of whether particular sets
Materials and methods
Though the total number of terra rossa studies is enormous, information about the prevailing geomorphic conditions is sparse. In view of this limitation two approximately west–east traverses were laid out across Slovenia and the Czech Republic (Fig. 1), comprising nine sample locations in each country. The former traverse runs across the Dinaric Karst of southern Slovenia. Sample locations were spaced approximately uniformly and were chosen in such a way that they cover the most important rocks
Statistics of the raw data
Mineral compositions of insoluble residues and clayey material (terra rossa) from all sample locations were determined by X-ray diffraction (Table 2). Two of the Slovene insoluble residue samples (Čepovan and Komen) failed due to insufficient material being available. Nevertheless, the data obtained from the terra rossa are incorporated in some tables for purposes of comparison.
Based only upon the contrast between the presence/absence of individual minerals at each location, Sokal–Michener
Possible sources of terra rossa material
Starting from the two alternative options of terra rossa origin, and temporarily ignoring Merino and Banerjee's (2008) ideas, a straightforward deduction is that terra rossa material (Fig. 3) is basically:
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Parent rock weathering products (PRWPs). This category covers the material, part of the rock matrix, released during gradual chemical decay of the rock. Dimensions of individual crystals are within the range of calcite crystals or smaller. Its origin might involve material from at least two
Storage ability of the karst surface
Effectively the karst surface is just a sieve, where loamy material from a number of sources accumulates. An obvious problem remains concerning how small mineral grains remain trapped on the karst at all. An equally obvious explanation is that either vegetation or mantles of coarser, or minimally cemented, mineral particles – contained especially in some NRRPs, SRRPs and ASIMs – protect finer fractions of various origins from rain drop impacts, and thus from being washed away. Loam-covered
Discussion
It transpires that the karst surface is primarily a receptor of loamy materials, which are subsequently exposed to specific processes, largely unrelated to the “original” karst rock constituents. Only the loamy fills of cutters are to some extent closely related to the parent rock, whereas other terra rossa bodies are less closely related or not related to it at all. It appears that cutters have not been considered systematically in the past, having normally been explained as relatively
Conclusions
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Terra rossa is not an inherent karst feature but rather an attribute of the inevitable configuration of any karst geomorphic system.
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Explaining the existence of terra rossa on the karst surface involves solving a storage problem rather than a source problem.
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The composition of terra rossa includes arbitrary contributions from several sources, to some extent unified under conditions induced by a specific microenvironment, i.e. karst geomorphic system development.
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Direct comparison of insoluble
Acknowledgements
The research described was partly sponsored under the Slovenian-Czech Intragovernmental Science and Technology Cooperation Programme between 2001 and 2007. We thank the three unknown reviewers for a number of useful suggestions that have improved the manuscript. Dr David Lowe (Nottingham) is thanked for his help and advice in enhancing the English translation.
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