Fault-controlled dolomitization in a rift basin

Hollis, Cathy; Bastesen, Eivind; Boyce, Adrian J.; Corlett, Hilary; Gawthorpe, Robert L.; Hirani, Jesal; Rotevatn, Atle; Whitaker, Fiona F

doi:10.1130/g38s394.1

Cited by 87 publications

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References 11 publications

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“…On the Hammam Faraun Fault (HFF) block, Gulf of Suez, non-stratabound dolomitization is observed in proximity to the HFF, with numerous, discontinuous stratabound dolostone bodies extending into the footwall for up to 2 km. Hollis et al (2017) demonstrated that in this wellexposed example, the stratabound dolostone pre-dates, and is not genetically related to, cross-cutting non-stratabound dolostone. This is contrary to the interpretation of many dolostone bodies formed in proximity to faults.…”

Section: Introductionmentioning

confidence: 66%

“…2 Massive dolostone bodies, up to 500 m wide (distance from the HFF) and 60 to 80 m thick. Dolostone tongues associated with these massive bodies extend for up to 100 m away from the massive dolostone bodies, forming 1 to 5 m thick bands (Hirani, 2014;Hollis et al, 2017). This paper focuses on the stratabound dolostone bodies and the major controls associated with their formation.…”

Section: Field Observationsmentioning

confidence: 99%

“…2A)showing the distribution and extent of stratabound dolostone bodies relative to the Hammam Faraun Fault and the Gebel Fault, superimposed onto a Google Earth Ó image. The origin of the massive dolostone bodies in the study area are further discussed inHollis et al (2017).…”

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Controls on the formation of stratabound dolostone bodies, Hammam Faraun Fault block, Gulf of Suez

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Dolomitization is commonly associated with crustal‐scale faults, but tectonic rejuvenation, diagenetic overprinting and a fluid and Mg mass‐imbalance often makes it difficult to determine the dolomitization mechanism. This study considers differential dolomitization of the Eocene Thebes Formation on the Hammam Faraun Fault block, Gulf of Suez, which has undergone a simple history of burial and exhumation as a result of rifting. Stratabound dolostone bodies occur selectively within remobilized sediments (debrites and turbidites) in the lower Thebes Formation and extend into the footwall of, and for up to 2 km away from, the Hammam Faraun Fault. They are offset by the north–south trending Gebel fault, which was active during the earliest phases of rifting, suggesting that dolomitization occurred between rift initiation (26 Ma) and rift climax (15 Ma). Geochemical data suggest that dolomitization occurred from evaporated (ca 1·43 concentration) seawater at less than ca 80°C. Geothermal convection is interpreted to have occurred as seawater was drawn down surface‐breaching faults into the Nubian sandstone aquifer, convected and discharged into the lower Thebes Formation via the Hammam Faraun Fault. Assuming a ca 10 Myr window for dolomitization, a horizontal velocity of ca 0·7 m year−1 into the Thebes Formation is calculated, with fluid flux and reactivity likely to have been facilitated by fracturing. Although fluids were at least marginally hydrothermal, stratabound dolostone bodies do not contain saddle dolomite and there is no evidence of hydrobrecciation. This highlights how misleading dolostone textures can be as a proxy for the genesis and spatial distribution of such bodies in the subsurface. Overall, this study provides an excellent example of how fluid flux may occur during the earliest phases of rifting, and the importance of crustal‐scale faults on fluid flow from the onset of their growth. Furthermore, this article presents a mechanism for dolomitization from seawater that has none of the inherent mass balance problems of classical, conceptual models of hydrothermal dolomitization.

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Section: Introductionmentioning

confidence: 66%

Section: Field Observationsmentioning

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Controls on the formation of stratabound dolostone bodies, Hammam Faraun Fault block, Gulf of Suez

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“…5 km of maximum displacement (Suez Rift, Egypt; Figure ). Dolomitization occurs in the form of discrete, non fabric selective bodies that cross‐cut stratigraphy and older, stratabound dolostone bodies (Hirani et al., ; Hollis et al., ). The outcrop provides an opportunity to understand the controls on the localization of dolomitization within a relatively young (Tertiary) extensional basin that has not undergone subsequent tectonic rejuvenation.…”

Section: Introductionmentioning

confidence: 99%

Structural controls on non fabric‐selective dolomitization within rift‐related basin‐bounding normal fault systems: Insights from the Hammam Faraun Fault, Gulf of Suez, Egypt

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Fault-controlled dolostone bodies have been described as potential hydrocarbonbearing reservoirs. Numerous case studies have described the shape and size of these often non fabric selective dolostone bodies within the vicinity of crustal-scale lineaments, usually from Palaeozoic or Mesozoic carbonate platforms, which have undergone one or more phases of burial and exhumation. There has been little attention paid, however, to fault-strike variability in dolostone distribution or the preferential localization of these bodies on particular faults. This study focuses on dolostone bodies adjacent to the Hammam Faraun Fault (HFF), Gulf of Suez. This crustalscale normal fault was activated in the Late Oligocene, coincident with the onset of extension within the Suez Rift. Dolomitization in the prerift Eocene Thebes Formation occurred in the immediate footwall of the HFF forming two massive, non facies selective dolostone bodies, ca. 500 m wide. Facies-controlled tongues of dolostone on the margins of the massive dolostone bodies extend for up to 100 m. The geochemical signature of the dolostone bodies is consistent with replacement by Miocene seawater, contemporaneous with the rift climax and localization of strain along the HFF. A conceptual model of dolomitization from seawater that circulated within the HFF during the rift climax is presented. Seawater was either directly drawn down the HFF or circulated from the hanging wall basin via a permeable aquifer towards the HFF. The lateral extent of the massive dolostone bodies was controlled by pre-existing HFF-parallel fracture corridors on the outer margins of the damage zone of the fault. The behaviour of these fracture corridors alternated between acting as barriers to fluid flow before rupture and acting as flow conduits during or after rupture. Multiple phases of dolomitization and recrystallization during the ca.10 Ma period in which dolomitization occurred led to mottled petrographical textures and wide-ranging isotopic signatures. The localization of dolomitization on the HFF is interpreted to reflect its proximity to a rift accommodation zone which facilitated vertical fluid flow due to perturbed and enhanced stresses during fault interaction. It is possible that the presence of jogs along the strike of the fault further focused fluid flux. As such, it is suggested that the massive dolostones described in --

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“…In addition, other mechanisms could have produced a weak thermal gradient, such as a little geothermal anomaly related to the transtensional tectonic setting that was active in Gargano Promontory at the time of dolomitization. In such a tectonic setting, dolomitization models that rely on geothermal convection of former seawater circulating along faults (Corbella et al, 2014;Hollis et al, 2017) can explain the dolomitization in Gargano Promontory; especially the fault-plane convection model proposed by Hollis et al (2017). This model relies on seawater that descends down discrete, surface-breaching faults (Fig.…”

Section: Model Of Fault-controlled Dolomitizationmentioning

confidence: 99%

Fault‐controlled dolomite bodies as palaeotectonic indicators and geofluid reservoirs: New insights from Gargano Promontory outcrops

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The Upper Jurassic to Lower Cretaceous platform-slope to basinal carbonate strata cropping out in Gargano Promontory (southern Italy) are partly dolomitized. Fieldwork and laboratory analyses (petrographic, petrophysical and geochemical) allowed the characterization of the dolomite bodies with respect to their distribution within the carbonate succession, their dimensions, geometries, textural variability, chemical stability, age, porosity, genetic mechanisms and relation with tectonics. The dolomite bodies range from metres to kilometres in size, are fault-related and fracture-related, and probably formed during the Early Cretaceous at <500 m burial depths and temperatures <50°C. The proposed dolomitization model relies on mobilization of Early Cretaceous seawater that flowed, downward and then upward, along faults and fractures and was modified in its isotopic composition moving through Triassic and Jurassic strata that underlie the studied dolomitized succession. Despite the numerous cases reported in literature, this study demonstrates that hydrothermal and/or high-temperature fluids are not necessarily required for fault-controlled dolomitization. Distribution and geometries of dolomite bodies can be used for palaeotectonic reconstructions, as they partly record the characteristics (size, attitude and kinematics) of the palaeo-faults, even if not preserved, that controlled dolomitization. In Gargano Promontory, dolomites record Early Cretaceous palaeo-faults from metres to kilometres long, striking north-west/south-east to east/west and characterized by normal to strike-slip kinematics. Dolomitization increases the matrix porosity by up to 7% and, therefore, can improve the geofluid storage capacity of tight, platform-slope to basinal limestones. The results have a great significance for characterization of geofluid (for example, hydrocarbons) reservoirs hosted in similar dolomitized carbonate successions. Distribution, size and shapes of reservoir rocks (i.e. dolomite bodies) could be broadly predictable if the characteristics of the palaeo-fault system present at the time of dolomitization are known. © 2017 The Authors. Sedimentology © 2017 International Association of Sedimentologist

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Fault-controlled dolomitization in a rift basin

Cited by 87 publications

References 11 publications

Controls on the formation of stratabound dolostone bodies, Hammam Faraun Fault block, Gulf of Suez

Controls on the formation of stratabound dolostone bodies, Hammam Faraun Fault block, Gulf of Suez

Structural controls on non fabric‐selective dolomitization within rift‐related basin‐bounding normal fault systems: Insights from the Hammam Faraun Fault, Gulf of Suez, Egypt

Fault‐controlled dolomite bodies as palaeotectonic indicators and geofluid reservoirs: New insights from Gargano Promontory outcrops

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