Terrestrial Palaeoecology and Global Change

344 Valentin A. Krassilov. Terrestrial Palaeoecology
Fig. 139. Tree-ferns in the understorey
of an upland Nothofagus
rainforest above the open lowland
vegetation, Victoria, Australia: an
altitudinal differentiation that
would render an increase in fern
spores with an upland–lowland
shift of vegetation belts.
PTB. In the well-studied Meishan sequence, South China, the Permian/Triassic transitional
interval between the latest Permian Paratirolites and the lowermost Triassic Otoceras
ammonoid zones contains an easily distinguishable layer (about 10 cm) of “white
(boundary) clay”, a hydrolysed ash with microspherules. According to Yang et al. (1995),
the “white clay” is traceable over 12 Chinese provinces covering more than one million
sq. kilometres. It is non-fossiliferous except a few latest Permian (Changhsingian) conodonts.
The overlying black clay, an organic-rich calcareous laminated claystone with
even more abundant metallic and glassy microspherules, is enriched with siderophile
elements and bears an iridium spike.
Mass extinctions of reefal macrobenthos occur well below the transitional interval,
within which the highest extinction rates (up to 94%) in foraminifers, ostracods and
cephalopods are recorded at the base of the “white clay” and immediately above it
(Jin et al., 2000). The conodonts and bivalves show a more gradual decline while a
few brachiopod relicts survive up to the secondary mass extinction level in the Early
Triassic.