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CHEMOSTRATIGRAPHY OF MICROBIALITES AND CLUMPED ISOTOPES THERMOMETRY OF CAPIRU FORMATION, SOUTHERN RIBEIRA BELT-BRAZIL

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Abstract

The Capiru Formation is a metassedimentary sequence composed of carbonates and siliciclastic rocks, embedded in the Curitiba Terrain supracrustal record, related to neoproterozoic collisions of the Southern Ribeira Belt-South Brazil. Metamorphic and deformation records are marked by zones with incomplete paragenesis of greenschist facies (chlorite zone), tectonically interbbeded with strata displaying preserved primary structures, indicative of a shallow marine environment deposition. A variety of stromatolitic morphological features were observed along the zones where sedimentary structures were preserved such as columnar, club-shaped, conophyton, pseudocolumnar, parallel-branching, divergent-branching and delicate-branching, in addition to lamina and thrombolytic morphologies. Environment deposition is associated with a shallow sea in a regressive trend. Deformation segments are characterized by massive, venular or brecciated aspetcs. Single-isotope data define patterns for distinct microbial facies, with a more particular trend in stromatolite (-1.57 to-0.40‰ δ 13 C and-8.21 to-3.94‰ δ 18 O) and lamina facies (-1.89 to 1.29‰ δ 13 C and-7.32 to-3.55‰ δ 18 O). Isotopic signature in recrystallized facies is different from microbial facies, retaining the most depleted values (-2.16‰ δ 13 C and-14.02‰ δ 18 O). Chemostratigraphic profiles of stable isotopes are separated into two major intervals. Located at the botton of the profile, the first interval does not exhibit a specific isotopic trend and is further subdivided into three smaller units by facies associations. Unit I has a broad range for both isotopes (-1.75 to 0.40 δ 13 C and-2.34 to-8.16 δ 18 O), reflecting post deformational signatures associated to venulation, which is developed heterogeneously. Unit II is characterized by thrombolythics signals spanning between-6.35 and-4.11‰ for δ 18 O and-1.43 to 0.40‰ for δ 13 C; the last unit is marked by a wide variation of facies, mainly supratidal, and isotope signals display values of-1.89 to 1.29‰ for δ 13 C, and-7.32 to-3.31‰ for δ 18 O. Upwads in the profile, the second interval is exclusively associated to microbial facies, displaying more uniforme signatures with depleted values of δ 13 C and δ 18 O and a slight enrichment indicating the change of intratidal and supratidal environments (Unit IV-1.32 to-0.81‰ δ 13 C and-8.17 to-6.25‰ δ 18 O) to supratidal lagoons (Unit V-1,35 to-0,41‰ δ 13 C and-8,20 to-5,49‰ δ 18 O). Clumped isotope thermometry temperatures for microbial facies range between 206.07 up to 307.58°C , expressing low-grade regional metamorphism. Recrystallized facies exhibit a lower formation temperature (122.29 ± 7.07°C), developed, therefore, in a late restricted tectono-thermal event.
49º Congresso Brasileiro de Geologia
20 a 24 de agosto de 2018 – Rio de Janeiro
CHEMOSTRATIGRAPHY OF MICROBIALITES AND CLUMPED ISOTOPES
THERMOMETRY OF CAPIRU FORMATION, SOUTHERN RIBEIRA BELT –
BRAZIL
Lange, L.L.1; Titon, B.G. 1; Figueiredo, T.T. 1; Bahniuk, A.M. 1; Cury, L. F.1
1 Laboratório de Análises de Minerais de Rochas da Universidade Federal do Paraná / LAMIR-UFPR
The Capiru Formation is a metassedimentary sequence composed of carbonates and
siliciclastic rocks, embedded in the Curitiba Terrain supracrustal record, related to
neoproterozoic collisions of the Southern Ribeira Belt South Brazil. Metamorphic and
deformation records are marked by zones with incomplete paragenesis of greenschist facies
(chlorite zone), tectonically interbbeded with strata displaying preserved primary structures,
indicative of a shallow marine environment deposition. A variety of stromatolitic morphological
features were observed along the zones where sedimentary structures were preserved such as
columnar, club-shaped, conophyton, pseudocolumnar, parallel-branching, divergent-branching
and delicate-branching, in addition to lamina and thrombolytic morphologies. Environment
deposition is associated with a shallow sea in a regressive trend. Deformation segments are
characterized by massive, venular or brecciated aspetcs. Single-isotope data define patterns for
distinct microbial facies, with a more particular trend in stromatolite (-1.57 to -0.40‰ δ13C and
-8.21 to -3.94‰ δ18O) and lamina facies (-1.89 to 1.29‰ δ13C and -7.32 to -3.55‰ δ18O).
Isotopic signature in recrystallized facies is different from microbial facies, retaining the most
depleted values (-2.16‰ δ13C and -14.02‰ δ18O). Chemostratigraphic profiles of stable
isotopes are separated into two major intervals. Located at the botton of the profile, the first
interval does not exhibit a specific isotopic trend and is further subdivided into three smaller
units by facies associations. Unit I has a broad range for both isotopes (-1.75 to 0.40 δ13C and
-2.34 to -8.16 δ18O), reflecting post deformational signatures associated to venulation, which is
developed heterogeneously. Unit II is characterized by thrombolythics signals spanning
between -6.35 and -4.11‰ for δ18O and -1.43 to 0.40‰ for δ13C; the last unit is marked by a
wide variation of facies, mainly supratidal, and isotope signals display values of -1.89 to 1.29‰
for δ13C, and -7.32 to -3.31‰ for δ18O. Upwads in the profile, the second interval is exclusively
associated to microbial facies, displaying more uniforme signatures with depleted values of
δ13C and δ18O and a slight enrichment indicating the change of intratidal and supratidal
environments (Unit IV -1.32 to -0.81‰ δ13C and -8.17 to -6.25‰ δ18O) to supratidal lagoons
(Unit V -1,35 to -0,41‰ δ13C and -8,20 to -5,49‰ δ18O). Clumped isotope thermometry
temperatures for microbial facies range between 206.07 up to 307.58°C , expressing low-grade
regional metamorphism. Recrystallized facies exhibit a lower formation temperature (122.29 ±
7.07°C), developed, therefore, in a late restricted tectono-thermal event.
KEY-WORDS: METADOLOMITE; PRECAMBRIAN MICROBIALITES; CLUMPED ISOTOPES
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