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@article{1822931,
author = {Bábek, Ondřej and Vodrážková, Stanislava and Kumpan, Tomáš and Kalvoda, Jiří and Holá, Markéta and Ackerman, Lukáš},
article_number = {7},
doi = {http://dx.doi.org/10.1111/sed.12910},
keywords = {Diagenesis; diffuse reflectance spectroscopy; geochemistry; palaeoceanography; sedimentary petrology; stable isotopes of Mo},
language = {eng},
issn = {0037-0746},
journal = {Sedimentology},
title = {Geochemical record of the subsurface redox gradient in marine red beds: A case study from the Devonian Prague Basin, Czechia},
url = {https://onlinelibrary.wiley.com/doi/10.1111/sed.12910},
volume = {68},
year = {2021}
}
TY - JOUR
ID - 1822931
AU - Bábek, Ondřej - Vodrážková, Stanislava - Kumpan, Tomáš - Kalvoda, Jiří - Holá, Markéta - Ackerman, Lukáš
PY - 2021
TI - Geochemical record of the subsurface redox gradient in marine red beds: A case study from the Devonian Prague Basin, Czechia
JF - Sedimentology
VL - 68
IS - 7
SP - 3523-3548
EP - 3523-3548
PB - Wiley
SN - 00370746
KW - Diagenesis
KW - diffuse reflectance spectroscopy
KW - geochemistry
KW - palaeoceanography
KW - sedimentary petrology
KW - stable isotopes of Mo
UR - https://onlinelibrary.wiley.com/doi/10.1111/sed.12910
N2 - Marine red beds are usually interpreted as indicating water column oligotrophy, good bottom-water oxygenation and redox conditions. Lower Devonian successions of the Prague Basin, Czechia, exhibit a distinct centimetre to metre-scale alternation of layers of marine red beds, grey carbonates, marls and black shales. In order to understand why the redox potential fluctuated so rapidly, reflectance spectroscopy, microscopy, elemental geochemistry data and stable isotopes of Mo have been analysed in this paper. Whilst the grey and black facies only contain goethite, the marine red beds are enriched with synsedimentary and early diagenetic, submicronic hematite, which is present in micrite, skeletal interiors, microstromatolites and oncoids. It was formed by microbially mediated precipitation, the replacement of detrital Fe phyllosilicates, and/or by the oxidation of microbially precipitated Fe-bearing aluminosilicate precursors. The marine red beds are frequently enriched in Fe, depleted in U, V, Mo and Cu, and show negative δ98Mo values indicating oxic conditions. Peloidal micrite, microbial coatings and cements with the marine red beds exhibit positive (up to 9) Ce/Ce* anomalies. The non-red facies show opposite patterns. This geochemical variability is probably related to Mn oxyhydroxide cycling and organic matter remineralization along the sediment subsurface redox gradient, particularly by reactions between pore water and various elemental pools. These patterns, combined with the centimetre-scale colour alternation of the sediments, may reflect redox zonation that has been preserved beneath the ancient seafloor. Four zones are recognized: (i) the oxic zone of Fe-oxide precipitation (marine red beds); suboxic zones of (ii) Fe enrichment, and (iii) U-Mo enrichment; and (iv) suboxic–anoxic zone of Cu, V (± Mo) enrichment. The presented model of a marine red bed origin from redox reactions in the sediment subsurface contradicts models of the formation of marine red beds through iron enrichment from Fe2+ supersaturated ocean waters following periods of ocean anoxia.
ER -
BÁBEK, Ondřej, Stanislava VODRÁŽKOVÁ, Tomáš KUMPAN, Jiří KALVODA, Markéta HOLÁ and Lukáš ACKERMAN. Geochemical record of the subsurface redox gradient in marine red beds: A case study from the Devonian Prague Basin, Czechia. \textit{Sedimentology}. Wiley, 2021, vol.~68, No~7, p.~3523-3548. ISSN~0037-0746. Available from: https://dx.doi.org/10.1111/sed.12910.
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