8/13/2019 Pressure Dissolution and Stylolites Features

1/3

11/22/13 Pressure Dissolution Features

www.gly.uga.edu/railsback/PDFintro1.html 1/3

An Atlas of Pressure Dissolution Features

L. Bruce Railsback

Department of Geology, University of Georgia

INTRODUCTION

BASIC CONCEPTS AND FEATURES

Pressure dissolutionis the petrologic process wherein mineralsdissolve as the result of pressure

applied externally to them. This may happen because minerals under pressure (and thus undergoing elastic

or temporary strain) are more soluble than unstressed minerals, and/or because deformation (permanent

strain) due to stress leaves minerals more soluble. Because pressure dissolution leadsto a reduction of

volume of the rock in which it occurs, it is also called "chemical compaction".

At the microscopic scale, pressure dissolution occurs at contacts between grains, because stress is

localized at grain contacts if surrounding pore volumes support no load. The result is intergranular

compaction, which is most strikingly visible as sutured intergranular contacts. Flattened contacts and

concavo-convex contacts may also be the result of pressure dissolution, although in some cases they may

instead be the result of mehanical deformation and thus be attributed to mechanical (rather than chemical)

compaction. If no intergranular compaction has occurred, most intergranular contacts are tangential,

although in limestones the diverse shapes of carbonate grains may allow some primary or unmodified flat

or even concavo-convex contacts merely as the result of coincidental grain shapes.

Figure I-1. Tangential (A), flattened (B), concavo-convex (C) and sutured (D) intergranular contacts

as seen in thin section. Rectangular backgrounds are same size for all four panels; note reduction

of sediment volume.

Extensive intergranular pressure dissolution reduces intergranular porosity as grains move together.

Intergranular pressure dissolution also generates dissolved solidsthat may be precipitated in nearby pores,

occluding porosity abd eventually precluding further intergranular pressure dissolution. Intergranular

pressure dissolution may also stop as the areas of grain contacts expand to provide surfaces sufficient tosupport the force previously focused on smaller areas as greater stress. In that case, remaining

intergranular pore space may be filled by cements precipitating by advexting fluids. If intergranular

pressure dissolution proceeds to destroy all pore space with no cementation, so that the rock consists of

8/13/2019 Pressure Dissolution and Stylolites Features

2/3

8/13/2019 Pressure Dissolution and Stylolites Features

3/3