Regional Fault-Controlled Shallow Dolomitization of the Middle Cambrian Cathedral Formation by Hydrothermal Fluids Fluxed Through a Basal Clastic Aquifer
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Regional fault-controlled shallow dolomitization of the Middle Cambrian Cathedral Formation by hydrothermal fluids fluxed through a basal clastic aquifer Jack Stacey1,†, Hilary Corlett2, Greg Holland1, Ardiansyah Koeshidayatullah1, Chunhui Cao3, Peter Swart4, Stephen Crowley5, and Cathy Hollis1 1 Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK 2 Department of Physical Sciences, MacEwan University, Edmonton, AB, T5J 4S2, Canada 3 Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China 4 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Coral Gables, Florida 33149, USA 5 Department of Earth Sciences, University of Liverpool, Liverpool, L69 3GP, UK ABSTRACT dolomitize the Cathedral Formation. In sum- fault planes, facilitated by basal clastic aquifers mary, these results demonstrate the impor- (e.g., Martín-Martín et al., 2015; Lukoczki et al., This study evaluates examples of hydro- tant role of a basal clastic aquifer in regional- 2019), indicating that fault-controlled dolomitiza- thermal dolomitization in the Middle Cam- scale fluid circulation during hydrothermal tion can occur from fluids that are heated at shal- brian Cathedral Formation of the Western dolomitization. Furthermore, the presence low depths. As such, this study will evaluate re- Canadian Sedimentary Basin. Kilometer- of the Stephen Formation shale above the cently recognized components of the HTD model scale dolomite bodies within the Cathedral platform facilitated the build-up of fluid pres- on the pervasively dolomitized carbonates of the Formation carbonate platform are composed sure during the final phase of dolomitization, Middle Cambrian (509–497 Ma; Miaolingian Ep- of replacement dolomite (RD), with saddle leading to the formation of saddle dolomite- och) Cathedral Formation and determine whether dolomite-cemented (SDC) breccias occur- cemented breccias at much shallower depths this example of HTD is more complex than previ- ring along faults. These are overlain by the than previously realized. ously thought. As the HTD of the Cathedral For- Stephen Formation (Burgess Shale equiva- mation has been considered analogous to many lent) shale. RD is crosscut by low-amplitude INTRODUCTION examples of HTD worldwide (e.g., Davies and stylolites cemented by SDC, indicating that Smith, 2006; Sharp et al., 2010), this has signifi- dolomitization occurred at very shallow Structurally controlled hydrothermal dolomiti- cant implications for our understanding of these depths (<1 km) during the Middle Cambrian. zation (HTD) (Machel and Lonnee, 2002; Davies systems, particularly for the timing and depth of Clumped isotope data from RD and SDC in- and Smith, 2006) has been widely described (e.g., saddle dolomite-cemented breccia formation. dicate that dolomitizing fluid temperatures Sharp et al., 2010; Barale et al., 2016), partly due Fault-controlled dolomite bodies in the Ca- were >230 °C, which demonstrates that do- to the economic importance of HTD bodies as thedral Formation are well exposed in the thrust lomitization occurred from hydrothermal flu- hydrocarbon reservoirs (e.g., Davies and Smith, sheets of the southern Canadian Rocky Moun- ids. Assuming a geothermal gradient of 40 °C/ 2006) and as hosts of Mississippi Valley-type tains and provide an opportunity to study and km, due to rift-related basin extension, fluids (MVT) lead-zinc mineralization (e.g., Vandegin- sample their vertical and lateral extent. Pre- likely convected along faults that extended to ste et al., 2007). Common features of HTD bodies vious studies have primarily focused on the ∼6 km depth. The negative cerium anomalies include faulting, fracturing, brecciation, and zebra Kicking Horse Rim, a fault-controlled, linear of RD indicate that seawater was involved in dolomite textures, world-renowned examples of paleo-topographic feature (Aitken, 1971) that the earliest phases of replacement dolomitiza- which are found in the Paleozoic carbonates of coincides with the trend of the Cathedral Es- tion. 84Kr/36Ar and 132Xe/36Ar data are consis- the Western Canadian Sedimentary Basin (Davies carpment, the gravity-collapsed margin of the tent with serpentinite-derived fluids, which and Smith, 2006). One of the key uncertainties Cathedral carbonate platform (Johnston et al., became more dominant during later phases with the HTD model is the ultimate source of do- 2009). In this area, talc and magnesite are pres- of replacement dolomitization/SDC pre- lomitizing fluids, which are often interpreted to ent (Powell et al., 2006), and MVT mineraliza- cipitation. The elevated 87Sr/86Sr of dolomite be “evolved crustal fluids” based on highly saline, tion (Vandeginste et al., 2007) is hosted in saddle phases, and its co-occurrence with authigenic high temperature fluid inclusions within dolomite dolomite-cemented breccias within replacement quartz and albite, likely reflects fluid interac- crystals (e.g., Wendte et al., 1998; Lonnee and Al- dolomite bodies. To the northeast, talc, magne- tion with K-feldspar in the underlying Gog Aasm, 2000; Nelson et al., 2002; Al-Aasm, 2003; site, and MVT mineralization are absent, but Group before ascending faults to regionally Morrow, 2014). However, recent work (Gomez- examples of zebra dolomite textures are present Rivas et al., 2014; Hollis et al., 2017; Rustichelli in the Beauty Creek and Mistaya Canyon areas Jack Stacey http://orcid.org/0000-0001-8209- et al., 2017; Hirani et al., 2018a; Hirani et al., (Vandeginste et al., 2005). Additionally, zebra 6373 2018b, Benjakul et al., 2020) has shown that HTD dolomite and saddle dolomite-cemented brec- †[email protected]. can occur from the convection of seawater along cias occur at Whirlpool Point (Jeary, 2002). GSA Bulletin; Month/Month 2021; 0; p. 1–23; https://doi.org/10.1130/B35927.1; 13 figures; 5 tables; 1 supplemental file. © 2021 The Authors. Gold Open Access: 1 This paper is published under the terms of the CC-BY license Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/doi/10.1130/B35927.1/5240923/b35927.pdf by guest on 29 September 2021 Stacey et al. The earliest timing proposed for dolomitiza- the Northwest Territories, underlies most of Al- bearing grainstones that are indicative of plat- tion is during the Middle Cambrian by thermal berta, and continues into southwestern Saskatch- form margin facies, whereas Whirlpool Point convection of brines (Jeary, 2002; Powell et al., ewan and the north-central United States. The is characterized by the occurrence of peritidal/ 2006). Yao and Demicco (1997) suggested a Western Canadian Sedimentary Basin has ex- microbially laminated mudstones and biotur- later event in the Middle Silurian to Late Devo- perienced a complex tectonic history that began bated lagoonal mudstones that are interpreted to nian, involving topographically induced flow of with Neoproterozoic rifting (780–570 Ma), dur- represent platform interior facies (Pratt, 2002). basinal brines and mixing with meteoric water. ing which the deep-water, turbidite-dominated Early (pre-Laramide) structural elements at Conversely, Nesbitt and Prochaska (1998) con- Miette Group was deposited (Slind and Perkins, Whirlpool Point are NE-SW–trending normal cluded that dolomitization occurred from re- 1966). Following a period (ca. 700–635 Ma) of faults that intersect the Cathedral Formation. sidual evapo-concentrated brines derived from declining tectonic activity (Collom et al., 2009, Non-stratabound dolomite bodies are sub-paral- Middle Devonian sediments that flowed west- and references therein), renewed rifting occurred lel to bedding and have stratabound (bedding- ward during the Late Devonian to Mississippian during the Early Cambrian (541–509 Ma; Ter- parallel) terminations that extend up to 6.5 km Antler Orogeny. Vandeginste et al. (2005) also reneuvian Epoch–Stage 2) (Bond and Kominz, in length away from the faults. Non-stratabound suggested that dolomitization was related to the 1984), when the quartz arenites of the Gog dolomite bodies are only found within 16 m of Antler Orogeny but favored the expulsion of hot Group were deposited in a subtidal setting the normal faults (3 m and 13 m in the footwall basinal brines from underlying Lower Cambri- (Desjardins et al., 2012). This final rifting epi- and hanging wall, respectively) and are charac- an strata, and Symons et al. (1998) concluded sode ended with regional subsidence during the terized by the occurrence of saddle dolomite-ce- that dolomitization was related to regional fluid Middle Cambrian (Bond and Kominz, 1984), mented breccias, fractures, and zebra dolomite flow induced by the Laramide Orogeny (Creta- although heat flow and tectonic activity poten- textures. This study focuses in detail on one ceous to Paleocene). Additionally, recent work tially remained high (Powell et al., 2006). Dur- brecciated dolomite body that is exposed in a (Koeshidayatullah et al., 2020) on the underlying ing this time, the Cathedral carbonate platform road cut along the David Thompson Highway Mount Whyte Formation suggested that dolomi- developed, with the platform margin located in at Whirlpool Point and also incorporates field tization occurred from fluids that were partially the vicinity of the Kicking Horse Rim (Aitken, mapping of other bodies in the Bourgeau Thrust sourced from, or interacted with, Proterozoic 1971). This paleo-topographic feature likely (Fig. 1). serpentenite during the Middle Cambrian.