Great Geologists | 47
et de géologie stratigraphiques,” a series of introductory texts
on paleontology and stratigraphy. It is within these volumes
that d’Orbigny outlined his views on stratigraphic organization,
including the introduction of stages (étages) as a fundamental
concept – bodies of rock characterized by a particular set of
fossils and typified by a particular location (a stratotype). In
this respect he was building on the ideas of William Smith,
but more particularly Baron Georges Cuvier, who explained
the extinction of fossil organisms by means of catastrophes.
To d’Orbigny each stage (he recognized 27 comprising all of
geological history – of course we recognize many more today)
was separated by an upper and lower line of demarcation or
“discordance” representing an episode of natural upheaval.
The preserved rocks representing the stages were, in his
view, the result of transgression. Thus he viewed stages as
transgression separated by unconformities – a forerunner of
sequence stratigraphic concepts. We would have to disagree
with d’Orbigny in his view that the catastrophes separating each
stage were near-absolute – effectively each stage represented,
to him, a new creation. contributions have become recognized; both as the initiator
of the science of stratigraphical micropaleontology and as the
architect of the cornerstone of chronostratigraphy; the concept
of the stage. Moreover, his ideas are now in tune with what we
today term event stratigraphy, mass extinctions and sequence
stratigraphy. Earth history can indeed be subdivided by global
events. As the international stratigraphic community strives
to formally define stages as the basic nomenclature of our
science, perhaps we will eventually see a harmonization of
event stratigraphy, sequence stratigraphy, biostratigraphy and
chronostratigraphy – something that no doubt d’Orbigny would
approve of.
Nonetheless his view of successive transgressions separated by
unconformities can be considered the first step on the journey
to the sequence stratigraphic models that have been developed
and applied in the last few decades. Because d’Orbigny was
working mainly on outcrops in platform locations (his stratotypes
were “up-systems tract” in a sequence stratigraphic sense) we
would anticipate them being bounded by unconformities (i.e.
sequence boundaries) with associated faunal turnover. Legré-Zaidline, F. 2002. Alcide Dessalines d’Orbigny (1802-1857).
L’Harmattan. 249pp.
Posterity has not always been kind to the memory of
d’Orbigny’s contributions to our science. For many years after
his death his proliferation of species names for very similar taxa
(“this wild orgy of nomenclature” to quote Edward Heron-Allen)
and his ultra-catastrophist stratigraphic stance led to a critical
view of his work being adopted by zoologists, paleontologists
and geologists alike. Subsequently, however, his immense Torrens, H.S. 2002. From d’Orbigny to the Devonian: some
thoughts on the history of the stratotype concept. Compte
Rendus Palevol, 1, 335-345.
REFERENCES
This essay has drawn upon information from the following
sources:
Gohau, G. 1990. A History of Geology. Rutgers University Press.
259pp.
Monty, C.L.V. 1968. d’Orbigny’s concepts of stage and zone.
Journal of Paleontology, 42, 689-701.
Rioult, M. 1969. Alcide d’Orbigny and the stages of the Jurassic.
The Mercian Geologist, 3, 1-30.