TECTONIC CLASSIFICATION AND GEOCHEMICAL SIGNIFICANCE OF STYLOLITES IN THE KOMETAN FORMATION (TURONIAN) IN DOKAN AREA, SULAIMANIYAH, NE IRAQ

Stylolites of the Kometan Formation are genetically studied and classified in this paper. Mineralogy and chemistry of the stylolite-seam residual deposits were investigated. Mass and thickness reduction of the limestone, due to pressure-solution, were estimated by geometric and chemical criteria methods. Sedimentary stylolites and younger tectonic stylolites were identified, in addition to several mesoscopic, younger reverse and normal faults, and different types and sets of veins with various age relationships relative to the stylolites. Residual deposits of the stylolite seams are composed of quartz, orthoclase, illite and glauconite. Diagenetic cementation by calcite, pyrite and bitumen is abundant, whereas chert and pyrite nodules are common along the stylolite seams. The least mobilized elements during stylolitization are Ti, Al and K, followed by Fe, Si, Cr and U, whereas Ca, Na, Mg, Mn and Ni are mostly mobilized. Limestone mass reduction due to pressure solution was estimated in the studied section using chemical criteria, by about 5%, whereas limestone thickness shortening was estimated by about 15 cm / one cm stylolite seam thickness using two independent means: (1) geometric methods and (2) chemical and bulk density parameters. The difference in the estimated values is negligible despite the significant variation in the seam thickness and bulk density of the residual deposits as well as the uncertainty of the exact age relationship between the stylolite seams and the segmented cross-cutting veins.