Formation of Shale by Compaction of Flocculated Clay--A Model

Abstract

Compaction is a major physical diagenetic process responsible for the final fabric in many argillaceous rocks. This chapter discusses the role of compaction (mechanical rearrangement of particles) in shale formation. It is commonly agreed that most clay-rich sediment settles out in sea water as aggregates or floccules. The “flocculated model” (see section on PREFERRED PARTICLE ORIENTATION IN SHALE) shows how parallel particles result from an original random orientation. Here, a model is described by which the flocculated fabric of sediment may change into that of shale. Presented is a composite of SEM micrographs of clays of various orientations assembled to illustrate hypothetical successive stages of shale formation. Although from different clays from different environments, the examples are useful in providing an idea of particle orientation at different stages of compaction. An actual case study of fabric change with depth in marine sediment is presented by Bennett et al. (1979).