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Characterization of environmental conditions during microbial Mg-carbonate precipitation and early diagenetic dolomite crust formation: Brejo do Espinho, Rio de Janeiro, Brazil

By
Anelize Bahniuk
Anelize Bahniuk
Geological Institute, ETHZ, 8092 Zurich, SwitzerlandUniversidade Federal do Paraná, UFPR/DGEOL/LAMIR, 81651–980 Curitiba, Brazil
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Judith A. McKenzie
Judith A. McKenzie
Geological Institute, ETHZ, 8092 Zurich, Switzerland
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Edoardo Perri
Edoardo Perri
Dipartimento di Biologia, Ecologia, e Scienze Della Terra, Università della Calabria, Rende (CS), Italy
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Tomaso R. R. Bontognali
Tomaso R. R. Bontognali
Geological Institute, ETHZ, 8092 Zurich, Switzerland
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Natalie Vögeli
Natalie Vögeli
Institut des Sciences de la Terre, Université Joseph Fourier, BP53, 38041 Grenoble Cedex, France
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Carlos Eduardo Rezende
Carlos Eduardo Rezende
Universidade Estadual do Norte Fluminense, Centro de Biociências e Biotecnologia, Laboratório de Ciências Ambientais, UENF, 28013-602 Campos dos Goytacazes, Rio de Janeiro State, Brazil
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Thiago Pessanha Rangel
Thiago Pessanha Rangel
Universidade Estadual do Norte Fluminense, Centro de Biociências e Biotecnologia, Laboratório de Ciências Ambientais, UENF, 28013-602 Campos dos Goytacazes, Rio de Janeiro State, Brazil
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Crisogono Vasconcelos
Crisogono Vasconcelos
Geological Institute, ETHZ, 8092 Zurich, Switzerland
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Published:
January 01, 2015

Abstract

For many years, sedimentary dolomite rocks have been considered to be primarily a replacement product of the calcium carbonate components comprising the original limestone, a process known as secondary replacement dolomitization. Although numerous dolomite formations in the geological record are composed of fine-grained crystals of micritic dolomite, an alternative process, that is, direct precipitation, is often excluded because of the absence of visible or geochemical indicators supporting primary precipitation. In this research, we present a study of a modern coastal hypersaline lagoon, Brejo do Espinho, Rio de Janeiro State, Brazil, which is located in a special climatic regime where a well-defined seasonal cycle of wet and dry conditions occur. The direct precipitation of modern high-Mg calcite and Ca-dolomite mud from the lagoonal waters under low-temperature hypersaline conditions is associated with the activity of microbial organisms living in this restricted environment. The mud undergoes an early diagenetic transformation into a 100% dolomite crust on the margins of the lagoon. The biomineralization process, characterized by the variations of the physico-chemical conditions in this environment during the annual hydrological cycle, is integrated with isotopic analysis to define the early diagenetic processes responsible for the formation of both dolomitic mud and crust. The carbon isotope values indicate a contribution of respired organic carbon, which is greater for the crust (δ13C=−9.5‰ Vienna Pee Dee Belemnite (VPDB)) than mud (δ13C=−1.2‰ VPDB). The oxygen isotope values reflect a moderate degree of evaporation during mud formation (δ18O=1.1‰ VPDB), whereas it is greatly enhanced during early diagenetic crust formation (δ18O=4.2‰ VPDB). The clumped isotope formation temperature derived for the Brejo do Espinho mud is 34 °C, whereas it is 32 °C for the crust. These temperatures are consistent with the upper range of measured values during the dry season when the lagoon experiences the most hypersaline conditions.

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Geological Society, London, Special Publications

Microbial Carbonates in Space and Time: Implications for Global Exploration and Production

D. W. J. Bosence
D. W. J. Bosence
Royal Holloway, University of London, UK
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K. A. Gibbons
K. A. Gibbons
Nexen Petroleum UK Ltd, UK
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D. P. Le Heron
D. P. Le Heron
Royal Holloway, University of London, UK
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W. A. Morgan
W. A. Morgan
Morgan Geoscience Consulting, LLC, USA
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T. Pritchard
T. Pritchard
BG Group, UK
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B. A. Vining
B. A. Vining
Royal Holloway, University of London, UK
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Geological Society of London
Volume
418
ISBN electronic:
9781862397163
Publication date:
January 01, 2015

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