Methane-related Mg-calcite cements in Recent tidal flat sediments from the Firth of Forth

Andrews, JE (1988) Methane-related Mg-calcite cements in Recent tidal flat sediments from the Firth of Forth. Scottish Journal of Geology (24). pp. 233-244. ISSN 2041-4951

Full text not available from this repository.

Abstract

Recent, intertidal, medium-coarse grained silts from the Firth of Forth have been partially cemented. This cementation is selective, restricted to planar-horizontal crusts and thalassinid burrow fills. Stained thin sections and XRD show that the cement is composed of sub-micron sized, non-ferroan calcite containing 12–14 mole% MgCO3. Stable carbon and oxygen isotope analyses of the cements give a mean d 18O of 0.57‰ PDB and a mean d 13C of -29.8‰ PDB. The d 18O value is consistent with precipitation of Mg-calcite from seawater at a temperature around 9.5°C diluted by about 17% with meteoric water. The d 13C value is not indicative of normal marine bicarbonate, or derivation from microbial sulphate reduction and is diagnostic of methane oxidation. Methane is inferred to have formed below the sulphate reduction zone by biogenic reactions. Methane migrating upwards in the pore waters was oxidised by anaerobic bacteria near the base of the sulphate reduction zone. An increase in pore water alkalinity accompanied methane oxidation, resulting in the precipitation of CaCO3. Preferential cementation of thalassinid burrows suggests that this silt was permeable, acting as a conduit for sulphate-rich pore water to diffuse into the fermentation zone, and a site for bacterial methane oxidation. Projection of the cemented silts above the present tidal flat surface shows that they are now being exhumed, but it is not certain whether cementation is still occurring deeper within the sediment.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Related URLs:
Depositing User: Rachel Snow
Date Deposited: 03 Mar 2011 12:44
Last Modified: 11 Oct 2017 06:04
URI: https://ueaeprints.uea.ac.uk/id/eprint/25615
DOI: 10.1144/sjg24030233

Actions (login required)

View Item