Terrestrial Palaeoecology and Global Change

Chapter 9. Crises
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IX. CRISES
The geological record is punctuated by biotic turnovers that coincide with the major
tectonic, eustatic and climatic events (Krassilov, 1969, 1973a, 1978b, 1995a, etc.; Wethey,
1985; Erwin, 1990; Stanley & Yang, 1994; Retallack, 1995). Evolutionary significance
of such biospheric events, discarded by the traditional evolutionary theory, presently
attracts more attention in view of the nascent environmental hazards.
Etymologically, crisis means a turning point. The major geochronological boundaries,
such as the Permian/Triassic (PTB) ca. 290 Ma or the Cretaceous/Tertiary (KTB) ca.
65 Ma, are marked by the conspicuous diversity lows, hence they are turning points in
respect to the manistream build-up of biological diversity.
In historic sciences, patterns emerge from repetition. To arrive at regularities of biospheric
crises we have to compare the sequences of geological and biological events
across the critical boundaries. As will be shown later in the chapter, the similarities of
transboundary sequences involve the geomagnetic, sea-level and magmatic events, the
lithological, geochemical and isotopic anomalies, and the turnovers of biotic communities.
The Permian/Triassic and the Cretaceous/Tertiary crises, whatever the causes, are
generally held to have been the most severe in the history of the Earth. As such they
provide a testing ground for evolutionary models, as well as for stratigraphic practices.
It must be reminded here that chronostratigraphic boundaries are currently conceived
of as time levels defined by selected points (spikes) in their type sections.
Conventionality of the boundary choice is rooted in the Lyellian–Darwinian gradualistic
interpretation of the fossil record and, at a deeper philosophical level, in the principle
of continuity denying natural boundaries as such. Stratigraphic methodology (e.g.
Remane et al., 1996) light-heartedly confuses time with history, disregarding the developmental
discontinuity of geobiological systems that confer a distinctness on chronostratigraphic
divisions.
In recent years, the conventional golden spikes have been substantiated, first, by the
iridium spike at the KTB and, later, by the isotopic δ 13 C spikes at this and other major
boundaries. Their interpretation as the signatures of occasional events (e.g., impacts of
extraterrestrial bodies) inflicting a radical turn upon the course of the earth’s history
implies no regularities of evolutionary developments. It remains to be learned if such
indeterministic attitudes agree with what is actually known about the turning points.
IX.1. Transboundary trends
In both the PTB and KTB examples, geomagnetic signatures indicate a major event
before the boundary, following a long quiescent period (Fig. 137). In the Permian, a
period of constant polarity lasted from the Sakmarian, ca. 285 Ma, to mid-Tatarian (Capitanian),
ca. 260 Ma (Jin et al., 1997, 1998). Starting from the latter date, constant polar-