TY - JOUR
T1 - Evaluating new fault‐controlled hydrothermal dolomitisation models: Insights from the Cambrian Dolomite, Western Canadian Sedimentary Basin
AU - Koeshidayatullah, Ardiansyah
AU - Corlett, Hilary
AU - Stacey, Jack
AU - Swart, Peter K.
AU - Boyce, Adrian
AU - Robertson, Hamish
AU - Whitaker, Fiona
AU - Hollis, Cathy
N1 - Funding Information:
University of Manchester provided the funding for AK PhD work through Presidential Doctoral Award. Fieldwork and analytical costs are supported by a NERC-CDT grant to CH and JS. HR was funded by the PD3 consortium at University of Manchester, supported by Tullow Oil, Woodside Energy and Wintershall DEA. We thanked IAS and AAPG postgraduate grants for AK in providing additional support for this study. Help from colleagues at the Williamson Research Centre, University of Manchester, Alberta Geological Survey and Stable Isotope Laboratory, University of Miami, are gratefully acknowledged. We are grateful for the kind support from Matthew Steele-MacInnis and Pillar Lecumberri-Sanchez for the fluid inclusion analysis. Stable isotope analysis was funded through a NERC grant IP-1759-1117 at the NERC Isotope Geoscience Facility in East Kilbride to AB, CH and AK. Anping Hu is acknowledged for the help with strontium isotope analysis. Constructive comments from Editor Giovanna Della Porta, Associate Editor Hairuo Qing, Jeff Lonnee and two anonymous reviewers are greatly acknowledged and have improved the clarity of the paper.
Publisher Copyright:
© 2020 The Authors. Sedimentology published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/3/11
Y1 - 2020/3/11
N2 - Fault‐controlled hydrothermal dolomitisation in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep‐seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitisation. With development of new concepts in hydrothermal dolomitisation, the study aims in particular to test the hypothesis that dolomitising fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilising the Cambrian Mount Whyte Formation as an example. Here, the large‐scale dolostone bodies are fabric‐destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross‐cut by low amplitude stylolites, dolomitisation is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitisation to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ18Owater and 87Sr/86Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitisation from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO2‐rich fluids. This study highlights that large‐scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.
AB - Fault‐controlled hydrothermal dolomitisation in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep‐seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitisation. With development of new concepts in hydrothermal dolomitisation, the study aims in particular to test the hypothesis that dolomitising fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilising the Cambrian Mount Whyte Formation as an example. Here, the large‐scale dolostone bodies are fabric‐destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross‐cut by low amplitude stylolites, dolomitisation is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitisation to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ18Owater and 87Sr/86Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitisation from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO2‐rich fluids. This study highlights that large‐scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.
KW - Dolomite
KW - Western Canada Sedimentary Basin
KW - fluid mixing
KW - hydrothermal
KW - magnesium
KW - serpentinites
U2 - 10.1111/sed.12729
DO - 10.1111/sed.12729
M3 - Article
SN - 0037-0746
VL - 67
SP - 2945
EP - 2973
JO - Sedimentology
JF - Sedimentology
IS - 6
ER -