Variation in kaolinite morphology with growth temperature in isotopically mixed pore-fluids, Brent Group, UK North Sea

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Authors:Osborne, M.; Haszeldine, R. S.; Fallick, A. E.
Author Affiliations:Primary:
Glasgow University, Department of Geology and Applied Geology, Glasgow, United Kingdom
Scottish Universities Research and Reactor Centre, United Kingdom
Volume Title:Issue devoted to papers read at a conference on Diagenesis, overpressure and reservoir quality
Volume Authors:Bain, D. C., editor; Hall, P. L.; Shaw, H. F.; Spears, D. A.
Source:Clay Minerals, 29(4), p.591-608; Diagenesis, overpessure and reservoir quality, Cambridge, United Kingdom, March 26, 1993, edited by D. C. Bain, P. L. Hall, H. F. Shaw and D. A. Spears. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1994
Note:In English. 46 refs.; illus., incl. 3 tables, sketch map
Summary:Diagenetic kaolinite in reservoir sandstones of the Brent Group precipitated following the dissolution of detrial feldspar. Two distinct morphologies of kaolinite occur: (1) early diagenetic vermiform kaolinite which is often associated with expanded detrital micas; (2) later diagenetic 'blocky' kaolinite. Combined hydrogen and oxygen isotopic studies suggest that vermiform kaolinite precipitated at 25-50°C, and blocky kaolinite at 50-80°C, from pore-waters of a similar isotopic composition (δ18O = -6.5 to -3.5 ppm). These pore-waters are interpreted to be either a mixture of meteoric and compactional waters, or alternatively a meteoric water that had evolved isotopically due to water-rock interaction. Kaolinite precipitation occurred predominantly during the late Cretaceous to early Eocene. Influx of meteoric water into the Brent Group, probably occurred during the Palaeocene. Fluid flow across the entire basin was driven by a hydrostatic head on the East Shetland Platform palaeo-landmass to the west. The development of the two kaolinite morphologies is possibly related to the degree of supersaturation at the time of precipitation. At low degrees of supersaturation, vermiform kaolinite precipitated slowly upon detrital mica surfaces. Blocky kaolinite precipitated more rapidly into open pore-space at higher degrees of supersaturation. Precipitation of blocky kaolinite was perhaps triggered by the decay of oxalate.
Subjects:Bajocian; Brent Group; Clastic rocks; Clay mineralogy; Clay minerals; Crystal growth; D/H; Deuterium; Hydrogen; Isotope ratios; Isotopes; Jurassic; Kaolinite; Mesozoic; Middle Jurassic; Mineral-water interface; Morphology; O-18/O-16; Oxygen; Petroleum; Pore water; Reservoir rocks; Sandstone; Sedimentary rocks; Sheet silicates; Silicates; Stable isotopes; Temperature; Atlantic Ocean; East Shetland Basin; North Atlantic; North Sea; Areal studies
Coordinates:N600000 N620000 E0030000 E0010000
Abstract Numbers:95M/3630
Record ID:1995025465
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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