Many continental large igneous provinces coincide with climate perturbations and mass extinctions. When basaltic plumbing systems traverse carbon-rich sedimentary rocks, large volumes of greenhouse gases may be generated. We document how intrusive sills of the Mesozoic High Arctic Large Igneous Province affected surrounding fine-grained, organic-rich siliciclastic rocks of the Sverdrup Basin in the Canadian Arctic Archipelago. Petrographic and X-ray diffraction data from samples located near sills show the presence of high-temperature metamorphic phases (diopside, andalusite, garnet, and cordierite). Raman thermometry on organic matter yields peak temperatures of 385−400 °C near sill contacts, tailing off to far-field temperatures of ≤230 °C. Samples located >20 m from sills show no systematic change in vitrinite reflectance and have a VRo eq% value of ∼2.5%, which indicates a temperature of ∼210 °C. The finite element thermal modeling tool SUTRAHEAT was applied to the 17-m-thick Hare Sill, emplaced at 3 km depth at 1105 °C. SUTRAHEAT results show that contact-proximal rocks attain temperatures of >700 °C for a brief period (∼1 year). By 5 years, the Hare Sill is completely solidified (<730 °C), and the temperature anomaly collapses rapidly thereafter as the thermal pulse propagates outward. By 10 years, all rocks within 10 m of the Hare Sill are between 450 °C and 400 °C, rocks at 20 m from the contact attain 200 °C, yet far-field temperatures (>50 m) have barely changed. When multiple sills are emplaced between 4 km and 6 km depth, all rocks between sills reach ∼250 °C after 100 years, showing that it is possible to raise regional-scale background temperatures by ∼150 °C for the observed High Arctic Large Igneous Province sill density. Vitrinite reflectance data and pyrolysis results, together with SILLi thermal modeling, indicate that much of the hydrocarbon-generating potential was eliminated by High Arctic Large Igneous Province intrusions. The SILLi model yields ∼20 tonnes/m2 of organic equivalent CO2 (all carbon gas is reported as CO2) from the Hare Sill alone when emplaced into Murray Harbour Formation rocks with 5.7 wt% organic carbon, and ∼226 tonnes/m2 by emplacement of multiple sills throughout the 2-km-thick Blaa Mountain Group with 3 wt% organic carbon. On a basin scale, this yields a total of ∼2550 Gt CO2 from the Hare Sill, with ∼13,000 Gt CO2 being generated by the multiple sill scenario, similar to estimates from other large igneous provinces. Much of the Blaa Mountain Group rocks now have organic carbon contents of <1 wt%, which is consistent with large volumes of carbon-species gas having been generated, likely a mixture of CO2, CH4, and other species. However, organic-rich Murray Harbour Formation rocks show no obvious reduction in organic carbon content toward the Hare Sill intrusive contacts, which suggests that not all of the carbon was lost from the sedimentary package hosting High Arctic Large Igneous Province magmas. We suggest that some of the gas generated by contact metamorphism failed to drain out for lack of high-permeability conduits, and then back-reacted to form calcite cements and pyrobitumen during cooling.
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Research Article|
September 13, 2023
Basaltic sills emplaced in organic-rich sedimentary rocks: Consequences for organic matter maturation and Cretaceous paleo-climate
Jean H. Bédard;
Jean H. Bédard
1
Geological Survey of Canada, CGC−Québec, 491 de la Couronne, Québec, Québec G1K 9A9, Canada
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Keith Dewing;
Keith Dewing
2
Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7, Canada
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Stephen E. Grasby;
Stephen E. Grasby
2
Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7, Canada
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Peter Nabelek;
Peter Nabelek
3
Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA
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Thea Hatlen Heimdal;
Thea Hatlen Heimdal
4
Lamont-Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, New York 10964, USA; and Centre for Earth Evolution and Dynamics, University of Oslo, Post Office Box 1028, Blindern, NO-0315 Oslo, Norway
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Chris Yakymchuk;
Chris Yakymchuk
5
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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Sean R. Shieh;
Sean R. Shieh
6
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
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Justin Rumney;
Justin Rumney
6
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
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Frances M. Deegan;
Frances M. Deegan
7
Uppsala University, Department of Earth Sciences, Natural Resources and Sustainable Development, Villavägen 16, Uppsala, Sweden
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Valentin R. Troll
Valentin R. Troll
7
Uppsala University, Department of Earth Sciences, Natural Resources and Sustainable Development, Villavägen 16, Uppsala, Sweden
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Jean H. Bédard
1
Geological Survey of Canada, CGC−Québec, 491 de la Couronne, Québec, Québec G1K 9A9, Canada
Keith Dewing
2
Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7, Canada
Stephen E. Grasby
2
Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7, Canada
Peter Nabelek
3
Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA
Thea Hatlen Heimdal
4
Lamont-Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, Palisades, New York 10964, USA; and Centre for Earth Evolution and Dynamics, University of Oslo, Post Office Box 1028, Blindern, NO-0315 Oslo, Norway
Chris Yakymchuk
5
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Sean R. Shieh
6
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
Justin Rumney
6
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
Frances M. Deegan
7
Uppsala University, Department of Earth Sciences, Natural Resources and Sustainable Development, Villavägen 16, Uppsala, Sweden
Valentin R. Troll
7
Uppsala University, Department of Earth Sciences, Natural Resources and Sustainable Development, Villavägen 16, Uppsala, Sweden
Publisher: Geological Society of America
Received:
24 Feb 2023
Revision Received:
06 Jun 2023
Accepted:
18 Jul 2023
First Online:
13 Sep 2023
Online ISSN: 1943-2674
Print ISSN: 0016-7606
© 2023 Geological Society of America
GSA Bulletin (2023)
Article history
Received:
24 Feb 2023
Revision Received:
06 Jun 2023
Accepted:
18 Jul 2023
First Online:
13 Sep 2023
Citation
Jean H. Bédard, Keith Dewing, Stephen E. Grasby, Peter Nabelek, Thea Hatlen Heimdal, Chris Yakymchuk, Sean R. Shieh, Justin Rumney, Frances M. Deegan, Valentin R. Troll; Basaltic sills emplaced in organic-rich sedimentary rocks: Consequences for organic matter maturation and Cretaceous paleo-climate. GSA Bulletin 2023; doi: https://doi.org/10.1130/B36982.1
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