PETROGRAPHIC OBSERVATION ON STYLOLITE COLUMNS IN THE COLUMBUS LIMESTONE AND IMPLICATIONS ON ITS EARLY DIAGENETIC ORIGIN

Stylolite found in Columbus Limestone at the O’Shaughnessy Reservoir Park near Columbus, Ohio is observed in detail under optic and scanning electron microscopes. The observed Columbus Limestone is a fossiliferous limestone deposited in marine environment as a part of the Devonian carbonate platform in Ohio.

Stylolite at this locality shows distinct columns up to 3 cm height. Some commonly known features about stylolite are observed. They include the wall and the cap of column are coated with thin, iron-rich organic material; the amount of residual material along the stylolite is not proportional to the height of column; and the stylolite cuts through large fossils. In addition, several special microscopic features of the stylolite are discovered: 1) Cross sections of the stylolite wall not only show arc-shape grooves on the size of a few millimeter in diameter, but also show multi-level superposition of similar microscopic grooves of various sizes all the way down to a few micron in diameter. 2) The wall surface is smooth along the organic coating and it is also smooth between the organic coating and the rock. 3) The wall surface is covered with numerous pores range in size from less then a micron to about 10 microns. 4) Limestone along the wall is mostly made of very porous, loosely cemented euhedral calcite crystals a few microns in diameter. However, all small crystals aligned very well around a smooth groove surface. 5) The stylolite cut across euhedral calcite crystals about 10 micron diameter in size. 6) No calcite precipitation in the form of overgrowth is observed around the stylolite. 7) Leaching of limestone and deposition of iron oxide in the leached area are common within 1 cm of the stylolite on the upper side of the limestone. 8) No clay particles larger than 1 micron is observed in the residual organic rich material.

Based on the petrographic observations, this particular stylolitization process is likely to take place: 1) in a lithified limestone; 2) mainly through chemical dissolution processes; 3) with little help from clay minerals; and 4) was completed during the early diagenesis of the limestone.