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Érudit est un consortium interuniversitaire sans but lucratif composé de l'Université de Montréal, l'Université Laval et l'Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. Érudit offre des services d'édition numérique de documents scientifiques depuis 1998. Pour communiquer avec les responsables d'Érudit : erudit@umontreal.ca Article Allan Pentecost et Heather Viles Géographie physique et Quaternaire, vol. 48, n° 3, 1994, p. 305-314. Pour citer cet article, utiliser l'information suivante : URI: http://id.erudit.org/iderudit/033011ar DOI: 10.7202/033011ar Note : les règles d'écriture des références bibliographiques peuvent varier selon les différents domaines du savoir. Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter à l'URI http://www.erudit.org/apropos/utilisation.html Document téléchargé le 26 March 2014 12:27 "A Review and Reassessment of Travertine Classification" Géographie physique et Quaternaire, 1994, vol. 48, n" 3, p. 305-314, 2 fig., 2 tabl. Essais A REVIEW AND REASSESSMENT OF TRAVERTINE CLASSIFICATION Allan PENTECOST and Heather VILES, Division of Life Sciences, King's College London, Camden Hill Road, London W8 7AH, United Kingdom, and St. Catherine's College, Oxford 0X1 3UJ, United Kingdom. ABSTRACT This paper provides a review of the classification of travertines with emphasis on their morphology. Three criteria are used to describe them: geochemistry, microfabric and morphology. Geochemically, travertines may be divided into two groups, the meteogene travertines, where the carrier carbon dioxide originates in the soil and epi- gean atmosphere, and the thermal (thermo- gene) travertines where the carbon dioxide comes from thermally generated sources. Many travertine fabrics are influenced by bacteria and plants. These include 'stroma- tolitic' forms, many oncoids, shrubs, tufts, mats and moss travertines. Morphologically, travertines are conveniently divided into autochthonous (spring mounds and ridges, cascades, barrages, fluvial and lacustrine crusts, paludal deposits and cemented rudi- tes) and the allochthonous or clastic traver- tines (valley-fills, back-barrage deposits, alluvial cones). Travertine deposits often include a wide range of fabrics and morpho- logies in one system. They are influenced locally by discharge, slope, vegetation, cli- mate and human activity. Intergradations occur, both within travertine types but also with other freshwater deposits, e.g. calcrete and lake chalk. The influence of travertine deposition on the local hydrology and geo- morphology is also discussed. The review emphasises the significance of scale and hydrology and aims to provide a unified scheme of travertine classification. Manuscrit reçu le 23 août 1993; manuscrit revisé accepté le 16 février 1994. RÉSUMÉ La classification des travertins : revue et réévaluation. Cette revue met l'ac- cent sur la morphologie des travertins. Leur description repose sur trois critères : la géo- chimie, la microfabrique et la morphologie. Du point de vue de la géochimie, les traver- tins peuvent être divisés en deux groupes : les travertins d'eau météorique, où le dioxide de carbone provient du sol ou de la surface, et les travertins d'eau thermale, où le dioxide de carbone provient de sources thermales. La fabrique des travertins est souvent influ- encée par la présence des bactéries et des plantes, ce qui comprend des stromatolithes, de nombreux oncolithes et diverses formes caractéristiques. Du point de vue de la mor- phologie, les travertins sont autochtones (monticules, cascades, barrages, encroûte- ments fluviatiles ou lacustres, dépôts palustres et rudites cimentées) ou allochto- nes (dépôts de remblaiement de vallée, de remplissage amont de barrage, de cônes alluviaux). Les dépôts travertineux com- prennent souvent un assortiment de fabriques et de morphologies comprises dans un seul ensemble selon le débit, la pente, la végétation, le climat et les activités humaines. On discute également de l'effet de la mise en place du travertin sur l'hydro- logie locale et la géomorphologie. Cette revue fait ressortir l'importance de l'échelle et de l'hydrologie et tente de faire ressortir une vision intégrée de la classification des travertins. ZUSAMMENFASSUNG Ûberblick ùber und Neubewertung der Travertinklassifi- zierung. Dieser Aufsatz gibt einen ûberblick ùber die Klassifizierung der Travertine unter Hervorhebung ihrer Morphologie. Bei ihrer Beschreibung werden drei Kriterien benutzt: Geochemie, Mikrostruktur und Morphologie. Geochemisch kann man die Travertine in zwei Gruppen aufteilen: die Verwitterungs- Travertine, wo das Trâger-Kohlendioxyd aus dem Boden und der epigenetischen At- mosphâre stammt, und die thermischen Travertine, wo das Kohlendioxyd aus ther- misch erzeugten Quellen kommt. Viele Travertin-Strukturen sind durch Bakterien und Pflanzen beeinfluBt. Dies umfaBt "stromatolithische" Formen, zahlreiche Onkoide, Straucher, Bûschel, Matten und Moos-Travertine. Morphologisch teilt man am besten die Travertine in autochthone (Bodenerhebungen und Rùcken Wasser- fàlle, Dàmme, FIuR- und Seeverkrustungen, Sumpfablagerungen und verkittete Rudite) und in allochthone oder klastische Travertine (Tal-Auffùllungen, Ablagerungen hinter Dâmmen, alluviale Kegel). Die Travertin- Ablagerungen enthalten oft eine groBe Auswahl von Strukturen und Morphologien in einem einzigen System. Sie sind ôrtlich beeinfluBt durch Wasserfùhrung, Bôschung, Vegetation, Klima und menschliche Aktivitâten. Intergradation kommt vor, sowohl innerhalb der Travertin-Typen aber auch mit anderen Frischwasser-Ablager- ungen, z.B. Kalkkrusten und See-Kreide. Auch wird der EinfluB der Travertin- Ablagerung auf die ôrtliche Hydrologie und Géomorphologie diskutiert. Der ûberblick hebt die Bedeutung von MaBstab und Hydrologie hervor und suent ein vereinheil- lichtes Schema der Travertin-Klassifikation zu geben. Manuscrit reçu le 23 août 1993; manuscrit révisé accepté le 16 février 1994 306 A. PENTECOST and H. VILES INTRODUCTION The word travertine is a corruption of lapis tiburtinus, a Roman building stone mentioned by several early authors {e.g. Plinius, Statius, Vitruvius). The stone was quarried near the town of Tibur (Tivoli) and probably brought to Rome by boat along the Anio, but the original quarries have not been located and have most likely been excavated out of existence. Another, softer rock known as tufo is mentioned around the same time and was also used for building, but extant descriptions appear to refer to forms of consolidated volcanic ash which are very extensive around Rome. However, the term was exported at an early date — probably before the 12th Century, to Britain, France and Germany where it was termed 'Tuff, 'tufa', 'towfë, or 'tuff, and used for both volcanic ash and softer, poorly consolidated freshwater carbonates. In the early 19th century various prefixes, e.g. 'Kalktuff. 'tuf cal- caire', 'calcareous tufa' show that a distinction was being sought between volcanic ashes and travertine. Today, both travertine and calcareous tufa are applied to a wide range of freshwater fluvial and lacustrine carbonates. The terms are to a degree interchangeable. We know pre- cisely what is meant by travertine, as it is still quarried at Tivoli, and the term is frequently reserved for resilient forms, sufficiently strong to be sawn and used as load-bearing masonry. Most people use the term calcareous tufa for the softer varieties which would be unsuitable for building (e.g. Flugel, 1982; Burger, 1990). Recently, Hubbard and Herman (1990) advocated the use of 'travertine-marl' as a general term for surficial carbonates deposited from springs and streams, including unconsolidated deposits containing some clay, while Julia (1983) uses travertine as a general term for "all the carbonate incrustation on plant remains (in place and debris) without reference to pore volume or density". The distinction between travertine and tufa is based mainly on the degree of cementation, which is neither easy to define in terms of its limits nor measure. The need to dis- tinguish between travertines, tufas and deposits such as lake- chalks, calcretes and stromatolites has been recognised for many years and a number of schemes have been proposed but there is still much confusion. No 'standard' classification exists because most authors have described deposits from limited areas, of which few if any, contain the whole range of known travertines. The delimitation of rock types with respect to their forma- tion processes facilitates the recognition and understanding of freshwater carbonate faciès throughout the geological rec- ord. It is indispensible in survey work where a researcher may only be interested in a particular travertine type. With a sub- stantial literature on the recognition and classification of trav- ertines, particularly in the last decade, we decided to look at all of the descriptions, seek common ground and provide a summary of available knowledge. Our principal aim is to pres- ent a unified classification, emphasising travertine morphol- ogy and its influence on other landforms. The review covers both actively forming and inactive travertines and the classi- fications should be appropriate to travertine deposits of all ages. However, less is known of travertines deposited prior to the Pliocene, and most of our examples belong to the Quaternary. TRAVERTINE CLASSIFICATION SCHEMES Three main criteria have been used for travertine classifi- cation; 1) geochemical 2) fabric and 3) morphology. Classification schemes based on these criteria are not mutu- ally exclusive, but it is convenient to consider them separately. GEOCHEMISTRY A recent proposal by Pentecost (1993) separates the trav- ertines according to the origin of the carrier carbon dioxide. This is reflected to a considerable degree in their composition (bulk and isotopic) and provides a division dependent upon the source and interaction of the carbon dioxide. Two classes of travertines are recognised: a) the meteo- gene travertines and b) the thermal, or thermogene traver- tines. In the former, the carrier CO2 originates in uploads/Geographie/ formation 1 .pdf