What Is the Frontal Suture?

It is a type of pressure-soluble structure. A common fracture structure in carbonate rocks. Its cause is controversial, but most people think that it is mainly affected by the pressure and temperature of the overlying formation to form erosion. The profile is jagged on the cross section; the surface is uneven, uneven; and the three-dimensional columns are concave and convex in size. The magnitudes are quite different, and some of the fluctuations are very obvious, while others are flatter and gradually disappear in line with the level. ^[1]

Sutures (stylolites) are mainly produced in relatively pure carbonate rocks, and sometimes also appear in quartz sandstone, salt rock, and siliceous rock. They refer to the cross section of two adjacent rock formations or two in the same rock formation. Jagged seams joining adjacent parts. It is actually a reflection of the suture plane on the cross section. Most of the rocks on both sides of this line are connected in irregular canine teeth staggered or intersected. Sutures are often enriched with insoluble residues of this type of rock, such as clay, organic matter, and sand.

The undulation amplitude of the suture, that is, the distance between the fingertips on both sides of the suture varies greatly, the small can be less than 1 millimeter, generally a few centimeters to a dozen centimeters, and the large can reach 1 meter. It is usually divided into visible sutures visible to the naked eye and micro sutures that can be recognized under the microscope according to their magnitude.

There are five common geometric shapes of sutures: 1) simple wave shape; 2) complex curved shape; 3) sharp tooth shape; 4) square tooth shape); 5) seismic wave shape. In fact, there are many transition shapes between them. Sometimes a suture can change from one shape to another in a lateral direction.

According to the relationship between suture and layer, they can be generally divided into: 1) horizontal suture parallel to the layer; 2) oblique suture intersecting with the layer; 3) vertical suture perpendicular to the layer; 4) mesh suture Threads, interwoven meshes or complex sutures with a mutual cutting relationship composed of the above two or three kinds of sutures.

The causes of sutures have not been completely solved, but they tend to be considered to be related to the pressure-dissolution in the diagenetic-epitagene stage. ; Specifically, the formation of sutures is the result of the selective dissolution of adjacent rock formations under pressure in the Xiuyan-metageneous stage. Under directional stress conditions, where rock components have different stress solubility, one component will dissolve faster than the other. For example, calcareous biological bone debris in carbonate rocks is less soluble than mud-crystal matrix under stress conditions. Therefore, when the adjacent rock; stone component undergoes stress dissolution, the more soluble part is dissolved away, while the less soluble part is left and extends into the space generated by the dissolution accordingly, thus forming Undulating dentate dissolution seams. The dissolved material is removed in a solution state along this dissolution joint, or it is re-precipitated as a cement in the nearby rock formation. Insoluble residues remain in this gap. ^[2]