WEATHERING AND DEGRADATION OF SHALES
*S. G. Fityus
The University of Newcastle
University Drive
Callaghan, Australia, 2308
(*Corresponding author: stephen.fityus@newcastle.edu.au)
WEATHERING AND DEGRADATION OF SHALES
ABSTRACT
Shales and mudstones undergo weathering in the near-surface geological environment, and degradation
when directly exposed at the surface. Despite having superficially similar appearances, many shales have
very different degradation behaviours. For example, some shales break down readily upon exposure whilst
others remain more or less intact. Further, for those shales which break down, the style of degradation can
vary greatly. A phenomenon is described where fresh shale blocks that are exposed at the surface undergo
rapid breakdown to a fragmented texture which then persists for relatively long times, without further
breakdown to fine soil. This is illustrated for some coal mine wasterocks. Furthermore, this metastable
fragmented texture seems to be particular to each particular type of shale. The paper presents a conceptual
model for this physical breakdown of shales which accounts for the differences in fragmental texture that
are observed. The importance of several factors including strength, permeability and expansive clay
content are identified for their contribution to the degradation behaviour of different shales.
KEYWORDS
Weathering, degradation, shale, mudrock, fragmentation