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Linking mineralisation process and sedimentary product in terrestrial carbonates using a solution thermodynamic approach

Rogerson, M.; Pedley, H. M.; Kelham, A.; Wadhawan, J. D.

Authors

H. M. Pedley

A. Kelham

Abstract

Determining the processes which generate terrestrial carbonate deposits (tufas, travertines and to a lesser extent associated chemical sediments such as calcretes and speleothems) is a long-standing problem. Precipitation of mineral products from solution reflects a complex combination of biological, equilibrium and kinetic processes, and the different morphologies of carbonate sediment produced by different processes have yet to be clearly demarked. Building on the groundbreaking work of previous authors, we propose that the underlying control on the processes leading to the deposition of these products can be most parsimoniously understood from the thermodynamic properties of their source solutions. Here, we report initial observations of the differences in product generated from spring and lake systems spanning a range of temperature–supersaturation space.We find that at high supersaturation, biological influences are masked by high rates of physico-chemical precipitation, and sedimentary products from these settings infrequently exhibit classic “biomediated” fabrics such as clotted micrite. Likewise, at high temperature (>40°C) exclusion of vascular plants and complex/ diverse biofilms can significantly inhibit the magnitude of biomediated precipitation, again impeding the likelihood of encountering the “bio-type” fabrics. Conversely, despite the clear division in product between extensive tufa facies associations and less spatially extensive deposits such as oncoid beds, no clear division can be identified between these systems in temperature–supersaturation space. We reiterate the conclusion of previous authors, which demonstrate that this division cannot be made on the basis of physico-chemical characteristics of the solution alone. We further provide a new case study of this division from two adjacent systems in the UK, where tufa-like deposition continuous on a metre scale is happening at a site with lower supersaturation than other sites exhibiting only discontinuous (oncoidal) deposition. However, a strong microbiological division is demonstrated between these sites on the basis of suspended bacterial cell distribution, which reach a prominent maximum where tufa-like deposits are forming. We conclude that at high supersaturation, the thermodynamic properties of solutions provide a highly satisfactory means of linking process and product, raising the opportunity of identifying water characteristics from sedimentological/petrological characteristics of ancient deposits. At low supersaturation, we recommend that future research focuses on geomicrobiological processes rather than the more traditional, inorganic solution chemistry approach dominant in the past.

Journal Article Type Article
Publication Date Apr 1, 2014
Journal Earth surface dynamics
Print ISSN 2196-6311
Electronic ISSN 2196-632X
Publisher European Geosciences Union
Peer Reviewed Peer Reviewed
Volume 2
Issue 1
Pages 197-216
Institution Citation Rogerson, M., Pedley, H. M., Kelham, A., & Wadhawan, J. D. (2014). Linking mineralisation process and sedimentary product in terrestrial carbonates using a solution thermodynamic approach. Earth surface dynamics European Geosciences Union, 2(1), 197-216. doi:10.5194/esurf-2-197-2014
DOI https://doi.org/10.5194/esurf-2-197-2014
Keywords Terrestrial deposits; Sedimentary products
Publisher URL http://www.earth-surf-dynam.net/2/197/2014/esurf-2-197-2014.html
Copyright Statement © Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License. See: http://creativecommons.org/licenses/by/3.0/
Additional Information Copy of article first published in: Earth surface dynamics, 2014, v.2, issue 1

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Copyright Statement
© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License. See: http://creativecommons.org/licenses/by/3.0/



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