Carbonate Sequence Stratigraphy and Petroleum Geology of the Jurassic Deep Panuke Field, Offshore Nova Scotia, Canada

Weissenberger, John A.W.; Wierzbicki, Richard A.; Harland, Nancy

doi:10.1306/1215883m883275

Cited by 6 publications

(6 citation statements)

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“…In contrast, effective fault‐fracture‐related dolomite reservoirs commonly have planar matrix dolomite with intercrystalline porosity and/or connected vugs related to net volume reduction during limestone dolomitization and coeval or subsequent dissolution events (e.g. Smith, ; Weissenberger et al ., ). Dissolution may be a consequence of thermal or chemical disequilibrium between hydrothermal fluids and the limestones they invade, and also requires a means of exporting the dissolved carbonate (Esteban & Taberner, ; Machel, ).…”

Section: Economic Implicationsmentioning

confidence: 97%

Origin, characteristics and distribution of fault‐related and fracture‐related dolomitization: Insights from Mississippian carbonates, Isle of Man

et al. 2014

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Viséan limestones on the Isle of Man host numerous examples of fault‐controlled and fracture‐controlled dolomitization, which have been investigated to determine their macro‐scale to micro‐scale characteristics, geofluid origin, timing and relation to basin evolution. Geobodies composed of fabric destructive, ferroan, non‐planar dolomite range from several centimetres to >300 m wide and tens to hundreds of metres long parallel to faults and/or fractures; they have sharply defined margins, cross‐cut stratigraphy and locally finger out along beds or bed boundaries for tens of metres. Larger geobodies accompany NNE–SSW extensional faults with substantial breccia zones. One of these bodies hosts a sphalerite‐rich breccia deposit cemented by dolomite. Saddle dolomite lines or fills vugs and fractures within dolomite geobodies, and is a minor late diagenetic phase in undolomitized limestones. Replacive dolomite has low matrix porosity owing to non‐planar texture and associated cementation, and there is no evidence for subsequent leaching. Three dolomite stages are discriminated by texture, cathodoluminescence petrography and electron microscopy. Disseminated ‘Dolomite 1’ is substantially replaced and may be residual early diagenetic dolomite. Pervasive ‘Dolomite 2’ and ‘Dolomite 3’ have overlapping carbon–oxygen–strontium isotopic and fluid‐inclusion characteristics that indicate precipitation from allochthonous, high‐temperature (98 to 223°C) and high‐salinity (15 to 24 wt% NaCl eq.) brines. These variably equilibrated with host limestones and mixed with resident pore fluids. Overlying mudrocks formed a seal for ascending fluids. Integration of data from the mineral deposit suggests that fault‐fracture systems tapped different deep‐seated fluid reservoirs at different temperatures, and implies fluid interactions with both metamorphic basement and sedimentary cover in large‐scale circulation systems. This phenomenon probably took place during Mesozoic rifting, although an earlier event at the end of the Early Carboniferous cannot be discounted. In either case, a transient heat flow anomaly, previously unrecognized in the Irish Sea region, may be required to account for the hottest fluids.

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Section: Economic Implicationsmentioning

confidence: 97%

Origin, characteristics and distribution of fault‐related and fracture‐related dolomitization: Insights from Mississippian carbonates, Isle of Man

et al. 2014

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“…This suggests that Mg drawdown by fault-related dolomitisation in areas of very high localised heat flux may be significant, but it is likely to be subsidiary to dolomitisation driven by geothermal ("Kohout") convection within platform carbonates. The absence of permeable conduits or high basal heat flux mean much lower rates of dolomitisation in these systems (Whitaker and Xiao, 2010), but this is amply compensated for by the vast area of major carbonate platform systems globally (currently some 800 000 km 2 of lowlatitude oceans; Milliman, 1993). Further resolution of these fluxes is key to critically assessing the role of dolomitisation relative to weathering and seafloor spreading in determining secular changes in the Mg/Ca of global ocean (Hardie, 1996;Holland and Zimmermann, 2000;Shalev et al, 2019).…”

Section: Model Limitations and New Insights From Simulations Of Dolommentioning

confidence: 99%

“…Following the early work of Wilson et al (2001) and Jones and Xiao (2005), over the past decade process-based numerical modelling of heat and fluid flow coupled with the simulation of water-rock reactions using reactive transport models (RTMs) have contributed to the understanding of shallow, relatively low-temperature dolomitisation (Al-Helal et al, 2012;Garcia-Fresca, 2009;Whitaker and Xiao, 2010;Xiao et al, 2013). RTM simulations of HTD have focused on understanding controls on the nature of dolomitisation fronts, which are characteristically sharp in fault-related dolomites, and on the development of fault-associated stratabound dolostone bodies (Corbella et al, 2014;Xiao et al, 2013;Yapparova et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Understanding controls on hydrothermal dolomitisation: insights from 3D reactive transport modelling of geothermal convection

et al. 2020

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Abstract. The dominant paradigm for petrogenesis of high-temperature fault-controlled dolomite, widely known as “hydrothermal dolomite” (HTD), invokes upwelling of hot fluid along faulted and fractured conduits from a deep over-pressured aquifer. However, this model has several inherent ambiguities with respect to fluid sources and their dolomitisation potential, as well as mechanisms for delivering enough of these reactive fluids to form substantial volumes of dolomite. Here, we use generic 2D and 3D reactive transport simulations of a single transmissive fault system to evaluate an alternative conceptual model whereby dolomitisation is driven by seawater being drawn down into the subsurface and heated. We examine the evolution of fluid chemistry and the distribution of diagenetic alteration, including predictions of the rate, distribution, and temperature of HTD formation, and consider the possible contribution of this process to the Mg budget of the world's oceans. The simulations suggest that it is possible for convection of seawater along the fault damage zone to form massive dolomite bodies that extend hundreds of metres vertically and along the fault within a timescale of a few tens of thousands of years, with no significant alteration of the country rock. Dolomitisation occurs as a gradient reaction by replacement of host limestones and minor dolomite cementation, and it results in the discharge of Mg2+-poor, Ca2+-rich fluids to the sea floor. Fluids sourced from the basement contribute to the transport of heat that is key for overcoming kinetic limitations to dolomitisation, but the entrained seawater provides the Mg2+ to drive the reaction. Dolomite fronts are sharper on the “up-flow” margin where Mg2+-rich fluids first reach the threshold temperature for dolomitisation, and the “down-flow” dolomite front tends to be broader as the fluid is depleted in Mg2+ by prior dolomitisation. The model demonstrates spatial contrasts in the temperature of dolomitisation and the relative contribution of seawater and basement-derived fluids which are also commonly observed in natural fault-controlled dolomites. In the past, such variations have been interpreted in terms of major shifts in the system driving dolomitisation. Our simulations demonstrate that such changes may also be a product of emergent behaviour within a relatively stable system, with areas that are dolomitised more slowly recording the effect of changes in fluid flow, heat, and solute transport that occur in response to diagenetic permeability modification. Overall, our models robustly demonstrate that high-temperature fault-controlled dolomite bodies can form from mixed convection and act as a sink for Mg in the circulating seawaters. In addition, comparison of our 3D simulations with simplifications to 2D indicate that 2D models misrepresent critical aspects of the system. This has important implications for modelling of systems ranging from geothermal resources and mineralisation to carbonate diagenesis, including hydrothermal karstification and ore genesis as well as dolomitisation.

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“…The economic importance of HTD often lies in the associated hydrothermal dissolution and/or mineralisation, in particular Mississippi Valley-type Pb-Zn ore deposits (Davies and Smith, 2006;Qing and Mountjoy, 1994). More controversially, fluids thought to have formed fault-related HTDs have also been interpreted as responsible for formation or overprinting of large volumes of matrix-replacement dolomite forming important hydrocarbon reservoirs, inferring basin-wide hydrothermal activity (Al-Aasm, 2003;Davies and Smith, 2006;Sharp et al, 2010;Weissenberger et al, 2006). Machel and Lonnee (2002) were particularly critical of this suggestion and argued strongly against the use of the term hydrothermal (as distinct from geothermal) without evidence that the dolomites formed at temperatures of at least 5-10 °C higher than the country rock.…”

Section: Introductionmentioning

confidence: 99%

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

Benjakul¹,

Hollis²,

Robertson³

et al. 2020

Preprint

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Abstract. The dominant paradigm for petrogenesis of high-temperature fault-controlled dolomite, widely known as “hydrothermal dolomite” (HTD), invokes upwelling of hot fluid along faulted and fractured conduits from a deep over-pressured aquifer. However, this model has several inherent ambiguities with respect to fluid sources and their dolomitisation potential, as well as mechanisms for delivering enough of these reactive fluids to form substantial volumes of dolomite. Here, we use generic 2D and 3D reactive transport simulations of a single transmissive fault system to evaluate an alternative conceptual model whereby dolomitisation is driven by seawater being drawn down into the subsurface and heated. We examine the evolution of fluid chemistry and distribution of diagenetic alteration, including predictions of the rate, distribution, and temperature of HTD formation, and consider the possible contribution of this process to the Mg-budget of the World’s oceans. The simulations suggest that it is possible for convection of seawater along the fault damage zone to form massive dolomite bodies that extend hundreds of meters vertically and along the fault within a timescale of a few tens of kyr, with no significant alteration of the country rock. Dolomitisation occurs as a gradient reaction by replacement of host limestones and minor dolomite cementation, and results in discharge of Mg2+-poor, Ca2+-rich fluids to the sea floor. Fluids sourced from the basement contribute to the transport of heat that is key for overcoming kinetic limitations to dolomitisation, but the entrained seawater provides the Mg2+ to drive the reaction. Dolomite fronts are sharper on the “up-flow” margin where Mg2+-rich fluids first reach the threshold temperature for dolomitisation, and the “down-flow” dolomite front tends to be broader as the fluid is depleted in Mg2+ by prior dolomitisation. The model demonstrates spatial contrasts in the temperature of dolomitisation and the relative contribution of seawater and basement-derived fluids which are also commonly observed in natural fault-controlled dolomites. In the past, such variations have been interpreted in terms of major shifts in the system driving dolomitisation. Our simulations demonstrate that such changes may also be a product of emergent behaviour within a relatively stable system, with areas that are dolomitised more slowly recording the effect of changes in fluid flow, heat and solute transport that occur in response to diagenetic permeability modification. Overall, our models robustly demonstrate that high-temperature fault-controlled dolomite bodies can form from mixed convection and act as a sink for Mg in the circulating seawaters. In addition, comparison of our 3D simulations with simplifications to 2D, indicate that 2D models misrepresent critical aspects of the system. This has important implications for modelling of systems ranging from geothermal resources and mineralisation to carbonate diagenesis, including hydrothermal karstification and ore genesis as well as dolomitisation.

show abstract

Carbonate Sequence Stratigraphy and Petroleum Geology of the Jurassic Deep Panuke Field, Offshore Nova Scotia, Canada

Cited by 6 publications

References 0 publications

Origin, characteristics and distribution of fault‐related and fracture‐related dolomitization: Insights from Mississippian carbonates, Isle of Man

Origin, characteristics and distribution of fault‐related and fracture‐related dolomitization: Insights from Mississippian carbonates, Isle of Man

Understanding controls on hydrothermal dolomitisation: insights from 3D reactive transport modelling of geothermal convection

Understanding controls on hydrothermal dolomitisation: insights from 3D Reactive Transport Modelling of geothermal convection

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