Terrestrial Palaeoecology and Global Change

286 Valentin A. Krassilov. Terrestrial Palaeoecology
with the Late Eocene and subsequent orogenic events in the Tethys belt and a consequential
stepwise expansion of the polar ice caps (VII.2.2). Notably, palynological data
suggest the appearance of rainforests both in southeastern Asia (Muller, 1970) and the
Guinea-Congo area (Maley, 1996) not earlier than the Oligocene.
The equatorial concentration of terrestrial biomass is owing, in the first place, to a
steep meridional temperature gradient imposed by mountain ranges in the path of tropical
air masses and the advancing polar atmospheric fronts that jointly reduce a heat
export from the tropical zone. In front of the mountains, the ascending air cools rapidly
shedding rain over the tropical zone. Beyond this, the vapour-starved descending air
masses inflict desiccation over a vast area of tropical deserts. At the same time, the nival
deserts and lowland tundras develop within the polar atmospheric cells, and the taiga
forests thrive within the reach of the polar fronts. Temperization of the mid-latitudes by
surges of polar air results in a spread of deciduous vegetation. The ensuing two-peak
distribution of terrestrial biomass is typical of a mildly glacial climate as at present.
A different pattern would appear with deglaciation and a decrease in climatic gradients.
The equatorial zone would secure less heat while precipitation would drop with a
decrease in the tropical monsoon intensities. Simultaneously, a warmer SST would stir
cyclogenesis at the middle to high latitudes thereby shifting the peak of terrestrial biomass
as in the Cretaceous example below.
Climate change also affects the latitudinal pattern of dead mass production. In the
tropical zone, peat accumulation is mostly confined to coastal wetlands, such as mangroves,
that also provide a major source of organic matter exported to oceanic basins,
whereas in the temperate zone more peat is deposited in the inland basins. Accordingly, the
paralic coals spread with tropical climates, as in the Early to Middle Carboniferous, whereas
the limnic (inland) coal basins gain in importance with temperization, as in the Late
Carboniferous to Early Permian Angarian and Gondwana basins, the mid-Jurassic Irkutsk
and Kansk-Atchinsk basins of Siberia or the Miocene browncoal basins of central Europe.
The distribution of terrestrial vertebrate biomass presently shows a single peak over
the xerothermic zone of tropical savannas and woodlands.. The extinct mammoth fauna
indicates a different distribution in the Pleistocene, with a secondary maximum in the
high-latitude savannoid zone. Likewise, the relatively frequent Cretaceous dinosaur occurrences
in the warm-temperate ecotonal zone about 50°N and over the circumpolar
zone (Nessov & Golovneva, 1990) seem to indicate a two-peak pattern.
VIII.2.3. Assessment of Cretaceous terrestrial biomass
The following operations are proposed (Krassilov, 1999a) for an approximate assessment
of terrestrial biomass over times:
(1) Reconstruction of palaeobiomes on the basis of plant morphologies and the relevant
taphonomic information (IV.3-4).