Stylolite Formation

摘要

Stylolites are traditionally seen as the result of pressure dissolution. Pressure dissolution is probably at work in the formation of fitted fabric, and may play a role in the formation of stylolites in highly indurated limestones. For stylolites in the porous and easily compactable chalk this theory may not be appropriate. 12 chalk samples from the Dan, Skjold, and Tyra fields of the Danish North sea were chosen for study. The samples bear stylolites, some near horizontal stratiform, and some inclined tectonic. Some samples bear burrowed clay layers of sedimentary origin. The samples were subjected to bulk porosity determination, chemical and mineralogical analysis of bulk sample and insoluble residue, petrography in a hand specimen, thin section, by SEM of the broken surface and polished surface, and, finally, mapping of distribution of porosity and chemical constituents, over selected mm size areas, by the microprobe. Stylolites were found in chalk with porosity of over 40% and with no signs of post stylolite leaching of matrix. The often quoted role of clay as a localizing factor for dissolution is also questinable: Clay rich zones of obvious sedimentary origin may be associated with microstylolites or may not. Apart form the well known depletion in calcite, the stylolites described are depleted in silica. Inclined, tectonic stylolites can not be distinguished from stratiform horizontal by chemistry or mineralogy or porosity distribution. The material of the clay drape shows signs of being transported and recrystallized. 127 refs. (ERA citation 14:011499)