Clays and Clay Minerals, Vol. 56, No. 1, 100–111, 2008.
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Authors
Day-stirrat, Ruarri J.
Aplin, Andrew C.
S´rodon´, Jan
Van Der Pluijm, Ben A.
Issue Date
2008
Type
Article
Language
Keywords
Periodicals , Geology , Diagenesis , Fabric , Mudstone , Phyllosilicate , Shale , Textural Goniometry
Alternative Title
Diagenetic Reorientation Of Phyllosilicate Minerals In Paleogene Mudstones Of The Podhale Basin, Southern Poland
Abstract
We used high-resolution X-ray texture goniometry to quantify changes in the mm-scale orientation of phyllosilicate minerals in a suite of Paleogene mudstones from the Podhale Basin in southern Poland. The sample set covers an estimated range of burial depths between 2.4 and 7.0 km, corresponding to a temperature range of 60-160ºC. Although mechanical compaction has reduced porosities to ~10% in the shallowest samples, the phyllosilicate fabric is only modestly aligned. Coarser-grained (>10 mm) detrital chlorite and mica appear to be more strongly aligned with (001) parallel to bedding, suggesting their deposition as single grains rather than as isotropicfloc s or aggregates. From 2.4 to 4.6 km, R0 illitesmectite with 40-50% illite layers changes to R1 illite-smectite with 70-80% illite layers. At the same time kaolinite is lost and diagenetic chlorite is formed. The mineralogical changes are accompanied by a strong increase in the alignment of illite-smectite, chlorite, and detrital illite, parallel to bedding and normal to the presumed principal effective stress. We propose that the development of a more aligned I-S fabricre sults from the dissolution of smectite and the growth of illite with (001) normal to the maximum effective stress. Water released by illitization may act as a lubricant for the rotation of all platy minerals into nanoporosity transiently formed by the illitization reaction. At greater depths and temperatures, further illitization is inhibited through the exhaustion of K-feldspar. After the cessation of illitization, a further 2.4 km of burial only results in a small increase in phyllosilicate alignment. At such small values for porosity and pore size, increasing stress does not substantially reorient phyllosilicates in the absence of mineralogical change.
Description
Clays and Clay Minerals, Vol. 56, No. 1, 100–111, 2008. Diagenetic Reorientation Of Phyllosilicate Minerals In Paleogene Mudstones Of The Podhale Basin, Southern Poland. Ruarri J. Day-stirrat; Andrew C. Aplin; Jan S´rodon´; Ben A. Van Der Pluijm. DOI: 10.1346/CCMN.2008.0560109. Copyright © 2008, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 56, No. 1, 100–111, 2008.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society