Stylolites in Sandstones

Stylolites occurring as definite seams or as fine sutures at grain contacts are common in many sandstones. Most seams are parallel to bedding, but some have formed along fractures at an angle to bedding. The stylolite columns range from a fraction of a millimeter to 5 cm. in length and are largest in quartzose sandstones. Seams are generally small and closely spaced in highly calcareous and argillaceous sandstones. Stylolites in sandstones are clearly the result of pressure solution. Mutual solution occurs not only between quartz grains but also between quartz and calcite, feldspar, mica, and, to a limited extent, heavy minerals. In the Appalachian area most of the stylolitic solution along seams occurred before folding and without the aid of meteoric waters. Pressure solution greatly modifies the size, angularity, and sphericity of grains in many places. Porosity may be almost entirely eliminated in fine-grained beds where solution occurs at grain contacts. The silica dissolved along seams may be an important source of cement in sandstones; however, there is no simple relationship between the amount of stylolitic solution and the amount of cement in a local area.