Page 45 - Introduction to Paleobiology and The Fossil Record

32 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

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

Carboniferous (“coal-bearing”), a unit of All the system boundaries have been or are
rock that early industrialists were keen to currently being reinvestigated by working
identify! In a mad rush in the 1830s, Roderick groups of the International Union of the Geo-
Murchison (1792–1871) and Adam Sedgwick logical Sciences (IUGS). The potential of each
(1785–1873) collaborated, and tussled, over base for international correlation must be
the Lower Paleozoic. Sedgwick named the maximized. Thus the traditional bases of these
Cambrian and Murchison named the Silurian, systems must be placed within intervals of
based on sections in Wales. Each claimed the continuous sedimentation, with diverse and
middle ground for his system, so what Mur- abundant faunas and fl oras in geographically
chison called the “Lower Silurian”, Sedgwick and politically accessible areas that can be
called “Upper Cambrian”. This territorial conserved and protected; ideally the sections
claim was resolved later by Charles Lapworth should have escaped metamorphism and tec-
(1842–1920) who agreed with neither of tonism (Fig. 2.6). You can read more about
them, and named the contentious rock succes- the work of the IUGS at http://www.black-
sions the Ordovician in 1879. Ironically the wellpublishing.com/paleobiology.
Ordovician is one of the longest and most Chronostratigraphy or global standard
lithologically diverse of the geological systems stratigraphy is one of the most fundamental
but it was only formally accepted by the inter- of all stratigraphic concepts. Everyday inter-
national community in 1960. vals of time, such as seconds, minutes and
A problem with many of the original defi ni- hours, are based on a universal time signal
tions of the geological systems was that they from an atomic clock. Units of geological
were separated from each other by unconfor- time, such as the epoch and period, are much
mities. For the early workers, unconformities longer and of uneven lengths. The only stan-
provided a convenient break between systems dards available for the defi nition of these
and, more importantly, it satisfied their view intervals are the rock successions themselves.

that the major divisions of Earth’s history Thus the rocks of the type section in the type
should be divided by global, catastrophic area for the Silurian System act as an interna-
events. Unfortunately, many of these uncon- tional standard for the Silurian Period, the
formities turned out to be only regional breaks time during which that system was deposited.
that occurred in Europe, but not elsewhere. The base of a chronostratigraphic interval is

The bases of most systems then were repre- defined in a unique stratotype section, in a
sented by stratigraphic gaps, and gaps provide type area using the concept of a “golden
a poor basis for the global correlation of sys- spike” or marker point (Holland 1986). All
temic boundaries. the usual criteria for a workable stratotype