The Paleocene travertine system of the Itaboraí basin, Southeastern Brazil

Author(s)

Riccomini, C. ; Rodrigues-Francisco, B. H. ; Sial, A. N. ; Carvalho, M. D. ; Moura, C. A. V. ; Sant'Anna, L. G. ^[6]

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 18, n. 1, p. 11-25, dez. 2004.
• Field of knowledge: Physical Sciences and Mathematics - Geosciences

Abstract

The record of pre-Quaternary travertines is restricted to relatively few publications in the geological literature. In this paper, the authors present a petrographic and geochemical study of Paleocene travertines partly exposed in the Itaboraí basin, a small half-graben of southeastern Brazil. Travertine lithofacies were defined mainly from borehole samples, and these data were integrated with available field information. The most representative lithofacies of the travertine system are crystalline crusts that developed around springs at the surface and close to the fault. Other lithofacies, such as pisoid, micritic, and lithoclast travertines and tufas, were deposited distally from the springs. Mn and Fe carried to the surface by rising waters were incorporated in CL-zoned fibrous calcite and precipitated as iron-bearing minerals, respectively. Both goethite in the crystalline crusts and pyrite in the micritic travertine probably formed under biotic mediation. The evolution of this travertine system was related to Cenozoic reactivation of a shear zone in the Precambrian basement at the southern border of the basin. 87Sr/86Sr ratios indicate that groundwaters interacted with subsurface Precambrian marbles and gneisses before reaching the surface. d13C and d18O data suggest that several factors influenced carbonate precipitation in distal settings and that crystalline crusts formed from waters that changed in composition in the spring outlets and/or downflow within the travertine system. (AU)