Diagenesis in Pelleted Limestones: ABSTRACT

Abstract

The abundant pelleted limestones encountered in the geologic record are of polygenetic origin. Selected examples, biased by the author's personal field experience, are used to illustrate various textures and structures involving different pellet and matrix types. Lithification is the most important problem. A remarkable lack of features apparently due to compaction characterizes all pellet limestones. Volume reduction by stylolitization is common, but the basic limestone fabric remains intact and essentially uncompressed. Apart from stylolitization which appears to be a late stage diagenetic effect, detectable pressure solution at points of grain contact is minor. Calcite filling of apparent raises the question of what constituted a void? It is suggested that more stable crystals could grow equally as well in voids largely filled by metastable crystals as in fluid-filled space and the source problem is lessened. The presence of sparry of fibrous calcite is not necessarily evidence of a pre-existing void. Drop in relative sea-level and exposure to fresh water probably promoted lithification but they were not the prime control. The course of lithification depended more on the primary distribution of carbonate minerals, particularly aragonite. Dolomitization and silicification are only to be mentioned from the point of view of their bearing on lithification and the development of porosity. End_of_Article - Last_Page 517------------