Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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peak is only about 1.5°C lower than the Devonian. The mid-Jurassic (Bathonian) trough
is about 1°C lower than the Late Permian and of the same magnitude as the mid-Miocene,
which is consistent with the glacial mid-Jurassic deposits in northern Asia (Epstein,
1978), as well as a low taxonomic diversity of mid-Jurassic macrofossil assemblages
and a drop of thermophilic elements documented by palynological data (Hubbard
& Boulter, 1987).
The recurrent positions of the boundary at about 50°N (Devonian, Cretaceous, mid-
Eocene), 40°N (Permian, Late Triassic, Palaeocene) and 35°N (mid-Jurassic, mid-Miocene,
present) correspond to “warm”, “temperate” and “cool” climates respectively.
Open peaks in Fig.100 convey the intervals of obscure zonation in the Early Carboniferous
(Visean), Early Triassic (Olenekian), Late Cretaceous (Campanian), and Early to
early Middle Eocene (Sparnacian – Lutetian), with thermophilic arboreal lycopsids, semiarboreal
Pleuromeia, palms and the broadleaved evergreens sequentially spreading over
the Arctic Circle. If facilitated by a decrease of water uptake, these anomalous occurrences
may suggest a greenhouse climate.
VII. 5. Early Tertiary climates and afforestation–deforestation cycles
A culmination of temperization trend at about the Cretaceous/Tertiary boundary (KTB)
is indicated by the prevalence of leaf-mat taphonomy and serrate leaf morphology. The
northern nemoral zone extended to the southern Gobi (VII.4). Thick conglomeratic sequences,
as in the Tsagajan Formation (Krassilov, 1976a), reflect a major erosion cycle
driven by a drop of sea level. The poorly sorted coarse-grained deposits, with clay inclusions,
suggest slumping of waterlogged debris transported by melt water from a highland
snow cover. A steep altitudinal temperature gradient is also indicated by differentiation
of vegetation belts upslope, with a succession of polydominant conifer forest to monodominant
birch woodland as in the present-day cool-temperate zone. A downslope
migration of the birch belt in the Early Palaeocene of Sikhote Alin (Krassilov, 1989c;
VII.6) is evidence of an upland cooling ahead of the lowland temperization.
Vegetation change had commenced in the Maastrichtian already with the entries of
numerically subordinate Palaeocene newcomers, such as the small-leaved Trochodendroides,
the biserrate Corylites and other betuloid morphotypes (Krassilov, 1979; Golovneva,
1996; Herman, 1999), supposedly invading the pioneer to early successional stages
of disturbed riparian vegetation. These vegetation events coincided with an increase in
tectonic/volcanic activity. In eastern Asia, elevation of the marginal volcanic belt in conjunction
with ignimbritic eruptions and the emergence of volcanic island arcs might have
contributed to the climate change. However, a coeval spread of Nothofagus (Nothofagidites
pollen grains) to the southern mid-latitudes (Doktor et al., 1996) indicates the
global extent of temperization toward the end of Cretaceous. The early Palaeocene
assemblages reflect a taxonomically poor monodominant vegetation (Krassilov, 1976).