Clays and Clay Minerals, Vol. 54, No. 4, 500-514, 2006.
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Authors
Aplin, Andrew C.
Matenaar, Ingo F.
McCarty, Douglas K.
Pluijm, Ben A. Van Der
Issue Date
2006
Type
Article
Language
en_US
Keywords
Periodicals , Geology , Compaction , Gulf of Mexico , High-resolution X-ray Texture Goniometry , Microfabric , Mudstone , Shale , Smectite
Alternative Title
Influence of Mechanical Compaction and Clay Mineral Diagenesis on the Microfabric and Pore-scale Properties of Deep-water Gulf of Mexico Mudstones
Abstract
We report on how the effects of mechanical compaction and clay mineral diagenesis have affected the alignment of phyllosilicates in a suite of Miocene-Pliocene mudstones buried to sub-seabed depths of between 1.8 and 5.8 km in the deep-water Gulf of Mexico. Mechanical compaction has reduced the porosity of the samples to 15% at 5 km, with modal pore sizes between 10 and 20 nm. High-resolution X-ray texture goniometry data show that the intense mechanical compaction has not resulted in a strongly aligned phyllosilicate fabric. The muds were apparently deposited with a weak or isotropic phyllosilicate fabric which was not substantially realigned by mechanical compaction. Unusually, X-ray diffraction of <0.2 mm separates shows that: (1) there is no illitization trend between 90 and 120ëC; and (2) discrete smectite persists to ~120ëC, coexisting with R1 I-S or R0 I-S with 30ÿ40% expandable layers. Between 120 and 130ëC, discrete smectite disappears and the expandability of I-S decreases to ~25ÿ30%. We propose a two-stage diagenetic process involving (1) the alteration of volcanic glass to smectite and (2) the illitization of smectite and I-S; the alteration of glass results in smectite without a preferred orientation and retards the illitization reaction. We suggest that the lack of a strongly aligned phyllosilicate fabric reflects the apparently limited extent of illitization, and thus recrystallization, to which these mudstones have been subjected.
Description
Citation
Clays and Clay Minerals, Vol. 54, No. 4, 500-514, 2006.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018.