Controls on Stylolite Development: Morphologic, Lithologic, and Temporal Evidence from Bedding-Parallel and Transverse Stylolites from the U.S. Appalachians

Abstract

Quantification of morphology of bedding-parallel and transverse (or "tectonic") stylolites from the southern Appalachians reveals that, regardless of tectonic setting or stylolite orientation, lithologic heterogeneity controls stylolite development. For example, stylolites in more heterogeneous carbonate lithologies (packstones and grainstones) are more serrate than those in wackestones and mudstones. Similarly, early-forming stylolites are more serrate than late-forming stylolites, and computer simulations suggest that decreases in porosity or other lithologic heterogeneity cause the less serrate nature of late-forming stylolites. The linkage of a stylolite's morphology to its time of development should allow field estimation of timing of stylolitization and thus of timing of loading or compression. Although bedding-parallel and transverse stylolites generally result from different kinds of compression, morphological relations indicate that their development follows the same fundamental patterns. Bedding-parallel stylolites are, on average, thicker and less serrate than transverse stylolites, but that difference may only reflect the development of some bedding-parallel stylolites in clay-rich beds. Bedding-parallel stylolites can predate or postdate transverse stylolites that they intersect, illustrating that bedding-parallel stylolites, which are commonly considered "diagenetic," can have a tectonic origin, either from loading by thrust sheets or from loading by orogenically derived sediments. Transverse stylolites, which provide the best record of the lithology in which pressure dissolution began, are found in host rocks with insoluble residue contents ranging from 2 to 21 wt %. The broad range of clay contents disproves previous claims that stylolites form only in clay-poor carbonate rocks, and it suggests that the role of clays in pressure dissolution may depend on whether clays are the only source of permeability in the host rocks.