Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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Growth increment (sclerite) patterns on fish scales are of a potential significance for
palaeoclimatology as a source of evidence on changing growth rates related to seasonal
trophic conditions (Krassilov, 1983b). Fish scales from the Mid-Cretaceous (Albian) of
Crimea within the redbed domain show a regular sclerite spacing interrupted by narrow
zones of constricted sclerites, but lacking distinct annual rings. Such pattern indicates
only a brief period of retarded growth related to seasonal draughts (Fig. 82).
In spite of their apparent utility for palaeoclimatology, the climatic constraints of laterite
pedogenesis, caliche, bauxites and related products of biochemical weathering, rather
than remaining constant over times, change with atmospheric CO 2
levels, relief, geological
substrates and vegetation. Most redbeds are volcanomictic molassoids confined to
post-orogenic phases of tectonomagmatic evolution (in particular, of the Hercynian and
Laramid orogenies). The direct sedimentological effects of tectonomagmatic activation
are topographic, creating new basinal morphologies, as well as geochemical, providing a
source of metallic enrichment (in particular, by iron from mafic minerals). The indirect
effects are owing to the associated sea level and climatic events (II.7.2).
Acidification of surface waters and rhizosphere by volcanic substrates enhances
biochemical weathering promoting redbeds and their related pedogenic lithotypes far
beyond their present-day climatic ranges. With peneplanation of volcanic plateaux, the
Cretaceous to Eocene bauxite deposition, traditionally taken as evidence of a tropical
climate, spread into the temperate vegetation zone over northern Kazakhstan and West
Fig. 82. Growth increments (sclerites) on a fish scale from the Albian of northern Crimea as a climatic
indicator (Krassilov, 1983a): the absence of annual rings indicates a round-year growth, with broad zones of
regular sclerites attesting to constant growth rates. The intervening zones of about 5-6 narrow irregular
sclerites (arrow) reflect a retarded growth over the relatively brief (four – seven weeks) periods of adverse
conditions, such as trophic lows during dry seasons.