Page 82 - Sedimentology and Stratigraphy

5

Field Sedimentology, Facies

and Environments

The methodology of analysing sedimentary rocks, recording data and interpreting them
in terms of processes and environments are considered in a general sense in this
chapter. Geology is like any other science: the value of the interpretations that come
from the results is determined by the quality of the data collected. The description of
rocks in hand specimen and thin-section has been considered in previous chapters, but a
very high proportion of the data used in sedimentological analysis comes from fieldwork,
during which the characteristics of strata are analysed at a larger scale. The character of
sediment in any depositional environment will be determined by the physical, chemical
and biological processes that have occurred during the formation, transport and deposi-
tion of the sediment. In the subsequent chapters the range of depositional environments
is considered in terms of the processes that occur in each and the character of the
sediment deposited. By way of introduction to these chapters the concepts of deposi-
tional environments and sedimentary facies are considered here. The examples used
relate to processes and products in environments considered in more detail in subse-
quent chapters.

5.1 FIELD SEDIMENTOLOGY tary environments and their stratigraphic context
requires a sound basis of field data, so the first part
A large part of modern sedimentology is the interpre- of this chapter is concerned with practical aspects of
tation of sediments and sedimentary rocks in terms of sedimentological fieldwork, followed by an introduc-
processes of transport and deposition and how they tion to the methods used in interpretation.
are distributed in space and time in sedimentary
environments. To carry out this sort of sedimentolo-
gical analysis some data are required, and this is 5.1.1 Field equipment
mainly collected from exposures of rocks, although
data from the subsurface are becoming increasingly Only a few tools are needed for field studies in sedi-
important (2.2). A satisfactory analysis of sedimen- mentology and stratigraphy. A notebook to record