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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 11. (November)

First Page: 2417

Last Page: 2425

Title: Significance of Fracture Sets Associated with Stylolite Zones: GEOLOGIC NOTES

Author(s): R. A. Nelson (2)


Stylolite zones consist of an irregular seam and often a variety of associated fracture sets. The geometry of this zone can be used to determine paleostress directions. Of the fracture sets commonly observed in close proximity to stylolites, one is generally induced by the coring procedure (unloading fractures), and another is natural and possibly associated with stylolites of tectonic origin (so-called "tension gashes.").

Within a unit possessing abundant stylolites the stylolites are most common in zones of relatively low porosity. In addition, because of the relatively compact, poorly sorted, fine-grained nature of the seam itself, stylolite zones commonly have much reduced permeability compared to the undeformed rock above and below. Laboratory-measured permeability associated with stylolite zones can, however, be misleadingly large owing to the presence of unloading fractures and/or tension gashes. These fractures may dramatically increase laboratory permeability but commonly are either not present in the reservoir or are relevant only to the size of the laboratory measurement sample. It is critical, therefore, to understand the origin and scale of associated fracture development in interpreting su h data.

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