stylolites

Stylolites are irregular, serrated dissolution surfaces that form in sedimentary rocks, most commonly in carbonates such as limestone, dolostone, and marble. They develop by pressure solution: under confining stress, mineral grains dissolve at points of contact and along grain boundaries, and the dissolved material is removed by pore waters. The remaining insoluble residue concentrates along the dissolution surface, producing a dark, seam-like boundary that appears jagged or “tooth-like.”

These seams typically run parallel or subparallel to bedding or grain contacts and may cross-cut earlier structures. Their spacing and thickness vary from millimeters to centimeters, and a single outcrop can display multiple stylolites with different orientations. The boundaries of stylolites are often highly relief, giving a characteristic zigzag or sawtooth appearance.

Geologically, stylolites record the diagenetic history of rocks under differential stress and fluid flow. Their density, spacing, and orientation can reflect the magnitude and direction of ancient tectonic or burial stresses and the duration of pressure solution processes. They are usually signs of post-depositional pressure and chemical weathering rather than primary sedimentary structures.

Formation conditions include the presence of a solvent (water with dissolved ions), elevated pressure, and temperatures that permit calcite dissolution without gross mineral dissolution. Stylolites are common in mature carbonate rocks and can influence porosity and permeability in reservoir rocks by introducing dissolution seams and subsequent cementation or further alteration.