Page 46 - Introduction to Paleobiology and The Fossil Record

FOSSILS IN TIME AND SPACE 33

3 boundary stratotype
for base of next stage

Time 2 stage X

biozone Y
XXXXXXXX
parastratotype
1 boundary stratotype
for base of stage
Space

Figure 2.6 Key concepts in the definition of stratotypes and parastratotypes applicable to all

stratigraphic units. The base of stage X is defined at an appropriate and suitable type section,
coincident with the base of biozone Y, which can be used to correlate the base of the stage. The type
section is usually conserved and further collecting across the boundary interval is restricted to the
parastratotype section. The base of the stage is indicated as XXX. (Based on Temple, J.T. 1988. J Geol.
Soc. Lond. 145.)

Chronostratigraphy Lithostratigraphy Biostratigraphy
Series or Stage Chronozone Formations and member Graptolite biozones
epoch or age
Much Wenlock
Limestone Formation ludensis
Gleedon
Homerian Farley Member
of Coalbrookdale Formation nassa

Whitwell lundgreni
Wenlock
Coalbrookdale ellesae
Formation
linnarssoni
rigidus
Sheinwoodian
riccartonensis
murchisoni
Buildwas
Formation
centrifugus
Figure 2.7 Stratigraphic case study: description and definition of the litho-, bio- and

chronostratigraphy of the stratotype section of the Wenlock Series, along Wenlock Edge in Shropshire,
UK. This is the internationally accepted standard for the Wenlock Epoch, the third time division of the
Silurian Period.

section must, of course, be satisfi ed. The the section and with sections elsewhere. Estab-
golden spike, which represents a point in the lishing stratotypes and golden spikes requires
rock section and an instant in geological time, international agreement, and that can some-
is then driven into the section, at least in times be hard to achieve (Box 2.3)! This
theory. In practice the spike is usually adjusted horizon will then be the global standard
to coincide with the first appearance (FAD) of section and point (GSSP) for this stratotype.

a distinctive, recognizable fossil within a well- The Wenlock Epoch (time) was one of the

documented lineage. The ranges of all fossils first intervals of geological time to be defi ned
occurring across the boundary are docu- with reference to a stratotype section for the
mented in detail as aids to correlating within Wenlock Series (rock) (Fig. 2.7). A lithostratig-