Pressure Solution During Diagenesis

Pressure is durable problem in geology. It has engendered continuing arguments on its mechanism, thermodynamic basis, and geo­ logical significance. Recently, it has drawn renewed attention both for its important role in the diagenesis of sedimentary rocks and for its relation to rock deformation. Pressure is defined as process by which grains dissolve at intergranular or intercrystalline contacts. This process is presumably related to the higher solubility under nonhydrostatic stress at the contacts than at free grain surfaces. The process often, although not always, is accompanied by reprecipitation at adjacent free grain surfaces. Nevertheless, it is not justifiable to treat pressure as recrys­ tallization process. Two common types of pressure are recognized: intergranular pressure and stylolitization. The former, occurring at individual grain contacts, was first described by Sorby (1863) based on experiments and theoretical predictions by Thompson ( l862a,b). The latter produces a surface or contact that is marked by an irregular and interlocking penetration of the two sidcs, and is supposedly formcd diagenctically by differential vertical movement under pressure, accompanied by solution (Bates & Jackson 1980). Here we use the term for surface that involves an of grains (the aggregate stylolite of Park & Schot 1968), originating exclusively by dissolution under nonhydrostatic stress.