Terrestrial Palaeoecology and Global Change

70 Valentin A. Krassilov. Terrestrial Palaeoecology
stone marking a higher order erosion cycle and containing mass accumulations of
Phoenicopsis. Up the fining-upward sequences, Phoenicopsis is regularly joined
by osmundaceous ferns, nilssonias, ginkgophytes and Pityophyllum conifers of the
peatland mosaic. Ginkgo-like leaves are numerically subordinate but occur as allochthonous
material in a wide range of facies. Their dominance in a few Jurassic
and Cretaceous localities might have been due to a downslope shift of altitudinal
vegetation belts.
With accumulation of comparative data, habitats of extinct plants come out as clearly
as if they were growing before our eyes. Thus, over the Mesozoic periods, Nilssonia
and Podozamites formed willow-like riparian thickets while the narrow-leaved bennettite
Nilssoniopteris was a heath-like bog shrub. Certain woody plants commanded a
wider range of habitats, as Czekanowskia, a vigorous colonizer of delta-plains, or Elatides,
a dominant of coniferous bog forests. Their catenic/seral successors were, depending
on the climatic zone, either the deciduous Phoenicopsis forests or the brachyphyll–
cycadophyte shrublands that climbed upslope to the luxurious Ginkgo forests, a mesic
upland climax.
Laibin. A Palaeozoic example comes from the Permian of Laibin Province, South
China. In a series of outcrops on the banks of Hongshui River, the Upper Permian
(Lopingian) deposits are represented by two sedimentary megacycles corresponding to
the Heshan and Talung formations (Jin et al., 1998; Shen et al., 1999). Fossil plants
occur in the shallow water marine to paralic facies in the upper members of both megacycles.
In a black shale bed of Talung Formation, a few ullmannioid shoots, Steirophyllum,
were found in association with abundant ceratitid impressions. In the upper Talung
member above, the conifers Hermitia and Steirophyllum are preserved as moulds on
the bedding planes of tuffaceous shales with distinct ripple marks and trace fossils. The
lowest stand of the Talung Sea is marked by coal-bearing deposits on top of the marine
to paralic regressive sequence.
The fossil plant horizon is about 50 cm thick consisting, from base up, of a root
bed over a lenticular coal, with Paracalamites stems and abundant, though crumpled,
pecopterid leaves, overlain by a ferruginous shale with a gigantopterid Gigantonoclea
guizhouensis and the numerically subordinate marattialean fern leaves
Pectinangium accompanied by few coniferoids. Of these assemblages, the Paracalamo–Pecopteridetum
represents a widespread interzonal type of Permian wetlands
dominated by arthrophytes and pecopterids. Its replacing Gigantonoclietum
is typical of the Cathaysian gigantopterid province, where it occurs both in the coalbearing
and redbed facies. Their succession (Fig. 35) is here interpreted as a seral/
catenic sequence following the retreating sea. It started with a pioneer arthrophyte–
pecopterid coastal peatland community that was then invaded by a backswamp gigantopterid
community. The conifer remains are fragmentary suggesting a distant
source upslope.