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Burial diagenesis and specific catalytic activity of illite-smectite clays from Vienna Basin, Austria

W. D. Johns and Thomas E. McKallip
Burial diagenesis and specific catalytic activity of illite-smectite clays from Vienna Basin, Austria
AAPG Bulletin (April 1989) 73 (4): 472-482


A sequence of Tertiary shales from the Vienna basin, Austria, contains a series of illite-smectite (I/S) clays that are the source of catalytic activity as measured by the method developed by Goldstein in 1983. The source of this activity is Bronsted acidity resulting from the dissociation of water molecules bonded to exchangeable cations in the interlayers of the smectite and on the external basal surfaces of illite platelets. This specific catalytic activity (SCA) is exchangeable cation dependent and correlates directly with increasing interlayer charge and tetrahedral substitution accompanying the diagenetic formation of thin interlayer illite particles with high-charge external surfaces. As a result, diagenetic transformation of smectite to illite in this series results in increased catalytic activity. From consideration of cation exchange capacity and interlayer charge of end-member components of this I/S series, we show that a cation site resulting from tetrahedral substitution of Al3+ for Si4+ has an activity about 40 times greater than a site of octahedral origin. The endmember illite particles of this I/S series have calculated mean thicknesses of about 80Aa (eight 2:1 mica layers). The linear relationship between SCA values and estimated platelet thickness for three different micas and illites confirms the role of cation sites on external basal surfaces as sources of catalytic activity. The possibility of direct involvement of catalytically active diagenetic illite in natural kerogen pyrolysis, acting simultaneously with a fluid release mechanism and its geopressure development, may provide optimum conditions for hydrocarbon generation and migration during I/S diagenesis. The presence of high-surface-area illite in diagenetically altered reservoir sandstones suggests the possibility for modifying the hydrocarbon constitution of crude oils within buried reservoirs. The effects of exchange cation composition on catalytic properties of I/S clays show that formation water chemistry must be considered in evaluating the effectiveness of clay catalysts in hydrocarbon-forming reactions.

ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 73
Serial Issue: 4
Title: Burial diagenesis and specific catalytic activity of illite-smectite clays from Vienna Basin, Austria
Affiliation: Univ. Mo., Dep. Geol., Columbia, MO, United States
Pages: 472-482
Published: 198904
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Accession Number: 1989-029909
Categories: Economic geology, geology of energy sourcesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N48°00'00" - N49°00'00", E16°00'00" - E17°34'60"
N46°15'00" - N49°00'00", E09°30'00" - E17°15'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1989
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