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Title: Integrated structural, sedimentological and diagenetic evaluation of fault-fracture controlled dolomite, Hammam Faraun Fault Block, Gulf of Suez
Author: Hirani, Jesal
ISNI:       0000 0004 8510 1539
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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Fault-controlled dolomite bodies have been described as potential reservoir units, formed by the upward flux of fluids which migrate out into higher permeability beds. This study focuses upon dolomite bodies adjacent to the Hammam Faraun Fault (HFF) and a present day hot spring system, in the HFF block, Gulf of Suez. The block-bounding normal HFF was activated in the Late Oligocene, with the onset of extension within the Suez Rift. Dolomitisation in the pre-rift Eocene Thebes Formation occurs in the footwall of the HFF in two principle forms: i) stratabound bodies preferentially dolomitising debris flows and grainflows, with associated zebra dolomite-like textures and dedolomitisationii) massive, non-facies selective dolomite pods with dolomite tongues extending away from the massive bodies. These dolomite bodies are located in close proximity to the HFF and show local evidence of hydro-brecciationFollowing extensive fieldwork and detailed sampling, a conceptual model has been formed that invokes the flux of dolomitising fluids along the HFF. Fluid migration away from the fault is facies controlled, which is dictated by the surface area and chemical reactivity of the precursor limestone, rather than the mechanical or petrophysical properties. Stable isotope analysis indicates that the delta13C of both dolomite bodies resembles whole rock values measured in unaltered pelagic limestone (delta18O = -3.1 to -6.8‰ and delta13C = -1‰ to 1‰). However, the delta18O values of the stratabound dolomites have more constrained values (delta18O = -4.1 to -8.0‰) compared to the lighter and wider-ranging values of the massive dolomites and their associated tongues (delta18O = -4.4 to -12.0‰). The REE signatures of both dolomite bodies are consistent with replacement from seawater-derived fluids. 87Sr/86Sr ratios were analysed, with the stratabound dolomite bodies characterised by 87Sr/86Sr ratios that fall within the range of late Oligocene seawater. However, the massive dolomite bodies have a wider spread of 87Sr/86Sr ratios which coincide with late Oligocene to middle Miocene seawater, indicating that the two types of dolomite bodies have formed as separate events during rift evolution. This data is used to calculate the temperature of dolomitising fluids forming the stratabound dolomite bodies between 62°C and 87°C, which is in good agreement with fluid temperatures calculated using the clumped isotopes (Delta47). The fluid temperature for the massive dolomite bodies and associated dolomite tongues is calculated between 68°C and 121°C. However, the clumped isotopes measure a much lower apparent temperature between 51°C and 72°C, and a back-calculated delta18Ofluid value that suggests alteration (calcitisation) by meteoric fluids, similar to that issued at the present day hot springs. A conceptual model of fluid flux will therefore be presented, tied to the evolution of the Suez rift, which will assess the relative importance of matrix and fracture permeability, fluid composition and kinetic factors on the size, shape and distribution of the replacive dolomite bodies.
Supervisor: Hodgetts, David ; Hollis, Catherine Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geochemistry ; Fault-fracture conrolled ; Dolomite