EGU2020-11908, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-11908
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Interaction among biogenic, climate and tectonic processes influences tufa precipitation, Araripe Basin, Brazil

Jaqueline Lopes Diniz1,2, Francisco Manoel Wohnrath Tognoli1,2, Tiago Siqueira de Miranda2,4, Alcides Nóbrega Sial4, Laís Vieira de Souza2, Leonardo Campos Inocêncio2,3, Juliano Bonato1,2, Caroline Modica Custódio2, and Aline Fernanda Spaniol2
Jaqueline Lopes Diniz et al.
  • 1Graduate Program on Geology, Unisinos University, São Leopoldo, Brazil (jaquelineld@edu.unisinos.br)
  • 2VizGEO Research Group, Unisinos University, São Leopoldo, Brazil (ftognoli@unisinos.br)
  • 3Graduate Program on Applied Computing, Unisinos University, São Leopoldo, Brazil (lcinocencio@unisinos.br)
  • 4Graduate Program on Geology, Federal University of Pernambuco, Recife, Brazil (tiagogeoufpe@gmail.com)

Tufas are continental freshwater carbonates common in epi-karst zones. They are composed of micrite and microsparitic crystals of calcite with variable primary moldic and fenestral porosity and with the frequent presence of biogenic content. By definition, tufa petrogenesis depends on climate processes and usually has precipitation induced by biological activity. Our examples include two morphotypes resulting from weathering of limestone of the Crato Formation, Araripe Basin, NE Brazil, and precipitated along vugular fractures. To understand how the climate and the biological activity act on precipitation of these rocks, we integrate structural data, petrography, and δ18O and δ13C values. Tufas are always associated with joints and faults in the northern boundary of the basin. The block where tufas occur has a dip angle between 5º and 30º, which differs from the regional average of 0° to 3º. The tufas fill vugular steep fractures with preferential planes oriented N50E and N30W and have a pipe-shaped growth pattern with top-down and center-out growth direction. The presence of organic filaments and mollusk shells are recurrent in all samples. Isotopic values measured on 32 samples indicate δ18O VPDB between -11,4‰ and -1,7‰ and δ13C VPDB between -12,1‰ and -5,1‰. The enrichment of 16O reveals the composition of meteoric water, responsible by the limestone dissolution and tufa precipitation. Organic fractioning induced by photosynthesis of the C4 plants result in 12C enrichment in the tufas. Macro and microscopic analysis revealed bryophyte filaments. Moreover, the porosity pattern strongly evidences the presence of these plants in tufa diagenesis. The close association of these rocks with the boundary faults suggests a relationship with climate denudation processes. The Araripe Basin is part of a set of continental rift basins in the Brazilian Northeast affected by uplifting. Thus, there are two stages recognized; the first one corresponds to the exhumation and reworking of the basement, probably in the early Cenozoic; and in the second stage a more intense weathering under semi-arid climate during Oligocene, or later.

How to cite: Lopes Diniz, J., Wohnrath Tognoli, F. M., Siqueira de Miranda, T., Nóbrega Sial, A., Vieira de Souza, L., Campos Inocêncio, L., Bonato, J., Modica Custódio, C., and Spaniol, A. F.: Interaction among biogenic, climate and tectonic processes influences tufa precipitation, Araripe Basin, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11908, https://doi.org/10.5194/egusphere-egu2020-11908, 2020

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