32 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD
Carboniferous (“coal-bearing”), a unit of
rock that early industrialists were keen to
identify! In a mad rush in the 1830s, Roderick
Murchison (1792–1871) and Adam Sedgwick
(1785–1873) collaborated, and tussled, over
the Lower Paleozoic. Sedgwick named the
Cambrian and Murchison named the Silurian,
based on sections in Wales. Each claimed the
middle ground for his system, so what Mur-
chison called the “Lower Silurian”, Sedgwick
called “Upper Cambrian”. This territorial
claim was resolved later by Charles Lapworth
(1842–1920) who agreed with neither of
them, and named the contentious rock succes-
sions the Ordovician in 1879. Ironically the
Ordovician is one of the longest and most
lithologically diverse of the geological systems
but it was only formally accepted by the inter-
national community in 1960.
A problem with many of the original defi ni-
tions of the geological systems was that they
were separated from each other by unconfor-
mities. For the early workers, unconformities
provided a convenient break between systems
and, more importantly, it satisfi ed their view
that the major divisions of Earth’s history
should be divided by global, catastrophic
events. Unfortunately, many of these uncon-
formities turned out to be only regional breaks
that occurred in Europe, but not elsewhere.
The bases of most systems then were repre-
sented by stratigraphic gaps, and gaps provide
a poor basis for the global correlation of sys-
temic boundaries.
All the system boundaries have been or are
currently being reinvestigated by working
groups of the International Union of the Geo-
logical Sciences (IUGS). The potential of each
base for international correlation must be
maximized. Thus the traditional bases of these
systems must be placed within intervals of
continuous sedimentation, with diverse and
abundant faunas and fl oras in geographically
and politically accessible areas that can be
conserved and protected; ideally the sections
should have escaped metamorphism and tec-
tonism (Fig. 2.6). You can read more about
the work of the IUGS at http://www.black-
wellpublishing.com/paleobiology.
Chronostratigraphy or global standard
stratigraphy is one of the most fundamental
of all stratigraphic concepts. Everyday inter-
vals of time, such as seconds, minutes and
hours, are based on a universal time signal
from an atomic clock. Units of geological
time, such as the epoch and period, are much
longer and of uneven lengths. The only stan-
dards available for the defi nition of these
intervals are the rock successions themselves.
Thus the rocks of the type section in the type
area for the Silurian System act as an interna-
tional standard for the Silurian Period, the
time during which that system was deposited.
The base of a chronostratigraphic interval is
defi ned in a unique stratotype section, in a
type area using the concept of a “golden
spike” or marker point (Holland 1986). All
the usual criteria for a workable stratotype
Table 2.1 Founding of the geological systems: systems, founders and the original type areas. In
addition the Mississippian and Pensylvanian that equate with the Lower and Upper Carboniferous,
respectively, were founded by Alexander Winchell (in 1870) and Henry Shaler Winchell (in 1891) based
on rocks exposed in the Mississippi Valley and state of Pensylvania. The Paleogene and Neogene
broadly correspond to the Lower and Upper Tertiary.
System Founder, date Original type area
Cambrian Sedgwick, 1835 North Wales
Ordovician Lapworth, 1879 Central Wales
Silurian Murchison, 1835 South Wales and Welsh borders
Devonian Murchison and Sedgwick, 1840 South England
Carboniferous Coneybeare and Phillips, 1822 North England
Permian Murchison, 1841 Western Russia
Triassic Von Alberti, 1834 Germany
Jurassic Von Humboldt, 1795 Switzerland
Cretaceous D’Halloy, 1822 France
Tertiary Arduino, 1760 Italy
Quaternary Desnoyers, 1829 France