Terrestrial Palaeoecology and Global Change

Chapter 3. Palaeoecology
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etum, a pioneer stream-side growths fringing distributary channels, represented by allochthonous
material alone, replaced toward the delta interior by (5) Elatididetum expansae,
a back-marsh bog forest, of the widest facies range, merging on (6) Elatidi-
Pityophylletum, a coniferous peat-bog assemblage, and (6) Elatidi-Nilssoniopteridetum,
a bennettitalean peat-bog shrubland. The allochthonous Phoenicopsis and Ginkgoites
represent dryland vegetation.
Of special interest is the succession of osmundaceous ferns: Cladophlebis kamenkensis
– C. denticulata – Todites (Cladophlebis) williamsonii – Todites (Cladophlebis)
haiburnensis, perhaps reflecting a zonation of the fern-marh community partly
extending over the horsetail mire and ascending as understorey to the Elatidion.
Many uncertainties remained that could only be resolved by comparison with analogous
successions in other sedimentary basins.
Umalta. In the mid-Jurassic (Callovian) regressive sequence of Umalta, Bureya Basin,
Russian Far East, Dicksonia (Coniopteris) burejensis and Osmunda diamensis are
dominant in the basal deltaic facies that rest conformably on shallow marine sandstones
with ammonite shells and still contain marine phytoplankton, as well as occasional limulid
remains. The catenic position of the fern assemblage might have been as at Kamenka
(above). Horsetails, much smaller than at Kamenka, patchily occur as an edaphic variant
of the coastal marshland. Bulk maceration of a fern bed soil brought fossil mites,
diverse bryophytes of the ground cover (Krassilov, 1973c), fern sporangia, as well as
scattered scale-leaves and shoot fragments of Elatides ovalis, the latter dominant in the
next catenic assemblage upsection, the back-marsh Elatidion.
This, however, is less prominent than at Kamenka. Conversely, Czekanowskia (with
Leptostrobus-type cupules) is more abundant in the flood-plain deposits. Leaf-mats grading
on leaf-coals consist of Czekanowskia accompanied, or locally replaced, by a needleleaved
conifer Pityophyllum or a narrow-leaved ginkgophyte Pseudotorellia. Their
frequent associates are Osmunda diamensis and Sphenobaiera, a ginkgophyte with
deeply dissected leaves. Nilssonia, Podozamites and their reproductive remains cooccur
with Czekanowskia in the coarser levee facies.
The peatland vegetation is thereby reconstructed as a Pityo-Pseudotorellietum (Sphenobaieretum)
mosaic marginally admixed with a riparian Czekanowskietum and with a
fern growth as understorey or over the gaps. All plant assemblages of this stage contain
allochthonous remains of Phoenicopsis, which comes to dominance over a sequence of
the fluvial sandstone/siltstone cyclothems above.
Seral links between Czekanowskia, a pioneer form of the delta-plain to flood-plain
alluvium, and Phoenicopsis, a lowland climax dominant, are confirmed by repeated
observations of their stratigraphic successions and concurrent facies changes in a large
number of Siberian localities (II.7.1). Over the Umalta Section, their succession is catenic,
as well as seral.
The regressive sequence is overlain by a series of coal-bearing cyclothems, in
which an avulsion autocyclicity is periodically truncated by a thick lamellate sand-