Elsevier

Geomorphology

Volume 106, Issues 1–2, 1 May 2009, Pages 35-45
Geomorphology

The role of loamy sediment (terra rossa) in the context of steady state karst surface lowering

https://doi.org/10.1016/j.geomorph.2008.09.024Get rights and content

Abstract

Reddish, loamy material (terra rossa), found on many karstified surfaces, has long been accepted as a characteristic karst feature. Two basic views of terra rossa formation were distinguished, related to either a residual or a detrital origin. More recently it has been suggested that it could derive from isovolumetric reactions between the parent carbonate rock and airborne material. This paper reviews possible sources of terra rossa, explores its behaviour on the karst surface from the karst geomorphology viewpoint, and considers whether its existence is better explained in terms of a closed or open karst geomorphic system. Two approximately west–east traverses were laid out across Slovenia and the Czech Republic, comprising nine sample locations in each country previously known to be characterized by terra rossa. General geomorphic/speleomorphic conditions were estimated, and loamy material and parent rock samples were collected. Insoluble residues extracted from the rock were processed in the same ways as the loamy material. Basic geochemical and mineralogical investigations were run. The data obtained were processed statistically. Results show that statistical relationships between the adjacent rock insoluble residues and adjacent terra rossa bodies exist only at sampling sites recognised as “vertical”. Most such sites are cutters, which are “karren-like grooves formed beneath the soil, more commonly referred to as subsoil karren” (US Environmental Protection Agency, 2002. A Lexicon of Cave and Karst Terminology. Field, M.S. (Ed.). <http://www.karstwaters.org/files/glossary.pdf>, p.53).

Possible sources of terra rossa material as well as the possibilities of material accumulating on the karst surface are discussed in detail, with special emphasis upon cutters. Theoretical considerations indicate that cutters are the only features that can collect sufficient insoluble residue to be detectable after a period of evolution within a surface that is lowering under steady state conditions. All other accumulations of similar appearance must be admixed materials of diverse origins or be completely allogenic in origin. The most recent approach, which considers terra rossa as an active karst surface agent, is temporarily put aside, though its explanatory potential in the future is acknowledged.

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:

  • 1.

    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

  • Terra rossa is not an inherent karst feature but rather an attribute of the inevitable configuration of any karst geomorphic system.

  • Explaining the existence of terra rossa on the karst surface involves solving a storage problem rather than a source problem.

  • 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.

  • 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.

References (45)

  • WilliamsP.W.

    The role of the subcutaneous zone in karst hydrology

    Journal of Hydrology

    (1983)
  • ChoquetteP.W. et al.

    Introduction

  • ChorleyR.J.

    Geomorphology and general systems theory

  • ChorleyR.J. et al.

    Physical Geography: A systems approach

    (1971)
  • ComerJ.B.

    Genesis of Jamaican bauxite

    Economic Geology

    (1974)
  • ComerJ.B.

    Genesis of Jamaican bauxite—a reply

    Economic Geology

    (1976)
  • DreybrodtW. et al.

    Basic processes and mechanisms governing the evolution of karst

  • FordD.C. et al.

    Karst Geomorphology and Hydrology

    (1989)
  • FordD.C. et al.

    Karst Hydrology and Geomorphology

    (2007)
  • GabrovšekF.

    On denudation rates in karst

    Acta carsologica

    (2007)
  • GamsI.

    Faktorji in dinamika korozije na karbonatnih kameninah slovenskega dinarskega in alpskega krasa

    Geografski vestnik

    (1966)
  • GamsI.

    Types of accelerated corrosion

  • GamsI.

    Kras v Sloveniji v prostoru in času

    Založba ZRC

    (2003)
  • GarnerH.F.

    The origin of landscapes

    (1974)
  • GrundA.

    The geographical cycle in karst

  • GuendonJ.-L. et al.

    Les phenomenes karstiques dans les processus de la bauxitisation sur substrat carbonate

  • HerakM. et al.

    Karst

    Important karst regions of the Northern Hemisphere

    (1972)
  • JacksonM.L.

    Soil Chemical Analysis — Advanced Course

    (1969)
  • KlimchoukA.B.

    Karst morphogenesis in the epikarstic zone

    Cave and Karst Science

    (1995)
  • KuklaJ. et al.

    K problematice výzkumu jeskinních v výplní

    Češkoslovenský Kras

    (1958)
  • LafitteP.

    Traité d'informatique géologique

    (1972)
  • MarićL.

    Terra rossa u karstu Jugoslavije

    Acta Geologica

    (1964)
  • Cited by (0)

    View full text