Origin and diagenesis of Quaternary travertine shrub fabrics, Rapolano Terme, central Italy

Origin and diagenesis of Quaternary travertine shrub fabrics, Rapolano Terme, central Italy ABSTRACT Millimetre to centimetre sized arborescent shrub‐like calcite precipitates are common constituents of hot water travertine shallow pool deposits of Quaternary age at Rapolano Terme, Tuscany, Italy. In the presently forming travertines, the shrubs consist of apparently random associations of (i) micrite aggregates and (ii) subhedral to euhedral rhombic spar crystal aggregates. In thin section, the micrite aggregates appear dark and the spar‐rhomb aggregates light, giving the shrubs a mottled appearance. Travertines are basically produced by CaCO3 precipitation due to degassing and evaporation of the spring waters, although biological influence may also stimulate precipitation. The formation of masses of erect shrubs, rather than dense crystal crusts that form on slopes, is probably due to limited water flow in the pool environments. Microbes, including bacteria and diatoms, are important influences on shrub microfabric and external shape. The micrite aggregates are associated with bacteriform bodies, seen as tiny rods and spheres. The micrite precipitates around these bodies and in adjacent biofilm. Spar‐rhomb precipitation appears to be external to the biofilm, and may be related to the presence of diatoms which are locally closely associated with the spar‐rhombs, although an essentially inorganic origin, particularly for the more euhedral rhombs, cannot be ruled out. In the older Quaternary travertines, the original microfabric of the shrubs has been diagenetically altered. The original mottled appearance of the shrubs has become uniformly dark and micritic, and the evidence for the dual micritic and spar‐rhomb origin of the shrubs is obscured or destroyed. Spar‐micritization of the shrubs is probably due to abiotic, and locally biotic, dissolution. Previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Sedimentology Wiley

Origin and diagenesis of Quaternary travertine shrub fabrics, Rapolano Terme, central Italy

Sedimentology, Volume 41 (3) – Jun 1, 1994

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Publisher
Wiley
Copyright
Copyright © 1994 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0037-0746
eISSN
1365-3091
DOI
10.1111/j.1365-3091.1994.tb02008.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT Millimetre to centimetre sized arborescent shrub‐like calcite precipitates are common constituents of hot water travertine shallow pool deposits of Quaternary age at Rapolano Terme, Tuscany, Italy. In the presently forming travertines, the shrubs consist of apparently random associations of (i) micrite aggregates and (ii) subhedral to euhedral rhombic spar crystal aggregates. In thin section, the micrite aggregates appear dark and the spar‐rhomb aggregates light, giving the shrubs a mottled appearance. Travertines are basically produced by CaCO3 precipitation due to degassing and evaporation of the spring waters, although biological influence may also stimulate precipitation. The formation of masses of erect shrubs, rather than dense crystal crusts that form on slopes, is probably due to limited water flow in the pool environments. Microbes, including bacteria and diatoms, are important influences on shrub microfabric and external shape. The micrite aggregates are associated with bacteriform bodies, seen as tiny rods and spheres. The micrite precipitates around these bodies and in adjacent biofilm. Spar‐rhomb precipitation appears to be external to the biofilm, and may be related to the presence of diatoms which are locally closely associated with the spar‐rhombs, although an essentially inorganic origin, particularly for the more euhedral rhombs, cannot be ruled out. In the older Quaternary travertines, the original microfabric of the shrubs has been diagenetically altered. The original mottled appearance of the shrubs has become uniformly dark and micritic, and the evidence for the dual micritic and spar‐rhomb origin of the shrubs is obscured or destroyed. Spar‐micritization of the shrubs is probably due to abiotic, and locally biotic, dissolution. Previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity.

Journal

SedimentologyWiley

Published: Jun 1, 1994

References

  • Microenvironmental controls on mineralogy and habit of CaCO 3 precipitates: an example from an active travertine system
    Chafetz, Chafetz; Patrick, Patrick; Utech, Utech
  • Two mechanisms of microbial carbonate precipitation
    Deelman, Deelman
  • Travertine formation in Plitvice National Park, Yugoslavia: chemical versus biological control
    Emeis, Emeis; Richnow, Richnow; Kempe, Kempe
  • Microbial micritic carbonate in uppermost Permian reefs, Sichuan Basin, southern China: some similarities with Recent travertines
    Guo, Guo; Riding, Riding
  • Aragonite laminae in hot water travertine crusts, Rapolano Terme, Italy
    Guo, Guo; Riding, Riding
  • On the precipitation of aragonite on the surface of marine bacteria
    Krumbein, Krumbein
  • Holocene pisoliths and encrustations associated with spring‐fed surface pools, Pastos Grandes, Bolivia
    Risacher, Risacher; Eugster, Eugster

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