Kaolinite growth during pore-water mixing; isotopic data from Palaeocene sands, North Sea, UK

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Authors:Stewart, R. N. T.; Fallick, A. E.; Haszeldine, R. S.
Author Affiliations:Primary:
University of Glasgow, CRAG - Centre for Research into Applied Geoscience, 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.627-636; 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. 37 refs.; illus., incl. 1 table, sketch map
Summary:Stable isotopic and petrographic data have been used to interpret conditions for the formation of authigenic kaolinite within Lower Palaeocene sands, Central North Sea. Two wells within the Witch Ground Graben were sampled (1975 m to 2795 m). Texturally early calcite concretions have isotopic compositions (δ18O = 18.3-21.6 ppm SMOW) which indicate that they were precipitated in predominantly meteoric waters. The isotopic composition of later vermiform kaolinite (δ18O = 14.8-17.7 ppm SMOW and δD = -53 to -71 ppm SMOW) indicates that kaolinite precipitated at around 45-70°C, from a mixed meteoric-marine pore-water (δ18O = -5 to -3 ppm SMOW). These modelled precipitation temperatures are consistent with the paragenetic sequence and consequently post-precipitation hydrogen isotope exchange between kaolinite and the pore-waters is presumed not to have occurred. It is inferred that the original depositional marine pore-waters were flushed out during the late Palaeocene (54.8 Ma) by a head of meteoric water from the East Shetland Platform. The Lower Palaeocene aquifer became closed to meteoric influx after marine transgression during the late Palaeocene (54.0 Ma). The remaining meteoric pore-waters in the sandstones became mixed with water from compacting marine muds surrounding the hydrostatically pressured sandstones.
Subjects:Cenozoic; Clastic sediments; Clay mineralogy; Clay minerals; Crystal growth; Isotope ratios; Isotopes; Kaolinite; Mineral-water interface; Mixing; O-18/O-16; Oxygen; Paleocene; Paleogene; Pore water; Sand; Sediments; Sheet silicates; Silicates; Stable isotopes; Tertiary; Atlantic Ocean; North Atlantic; North Sea; Areal studies
Coordinates:N580000 N590000 E0020000 W0010000
Abstract Numbers:95M/3632
Record ID:1995025467
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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