Terrestrial Palaeoecology and Global Change

8 Valentin A. Krassilov. Terrestrial Palaeoecology
restrial remains (also shallow-water benthic remains indicating a quasipelagic, rather
than pelagic, origin).
Fluctuations of carbonate dissolution depths and the concomitant divergence of calcite/aragonite
lysoclines are reflected in a selective preservation of carbonate fossils (an
alternation of ferruginous cephalopod limestones, amonitico rosso, and Aptichus facies
with calcitic cephalopod mandibles in the absence of aragonitic shells: Bosellini & Winterer,
1975 and a Cretaceous example in II.7.4).
Continental runoff stimulates oceanic dead mass deposition in the form of organicrich
black shales marking widespread oceanic anoxic events (OAE). The well-known
Mesozoic OAEs correlate with transgressions, global warming, positive δ 13 C carb
anomalies,
lacustrine black shale events (in the Mongolo-Okhotsk rift system: II.7.3) and thick
coal deposition (the Aptian and Late Albian to Cenomanian coals of eastern Asia, Alaska,
Fort St. John Group of western Canada, etc., reviewed in Krassilov, 1985, 1992b).
The latter is evidence of a high rate terrestrial dead mass production that depletes 12 C
content of atmospheric carbon and an equilibrated carbonate reservoir.
Prominent δ 13 C fluctuations, mostly negative, correlate with prominent orogenic
events, high rate sea-level fluctuations and climate change (VII.1.2). This is what to be
expected since both the ecological and taphonomic variables of dead mass production,
export and deposition are affected by disruption of terrestrial ecosystems.
II.2. Self-fossilization and taphonomic enrichment
Whatever the source of organic material, it is not just passively buried and fossilized
but constitutes instead an active component of taphonomic environment. Thus, microbial
mats are self-fossilizing in the sense that they lithify their own production. The rhizosphere
– a community of underground plant organs, their fungal and animal symbionts –
is self-fossilized by pedogenic mineralization. Submerged parts of wetland plants are
protected from poisonous substances produced by anaerobic microorganisms by oxygen
emitted from their aerenchyma to the anoxic environment. Such local oxydation induces
precipitation of ferric oxydes as casts on roots and buried stems, hence ferruginous
“fossil forests” (such as described in Nessov & Golovneva, 1995).
Conversely, a reduction gradient over decaying plant material induces transport of
silica, ferric compounds, carbonates and other fossilizing substances accumulating in the
organic-rich zone. Coal-balls are familiar example of fine preservation owing to impregnation
of cell walls by carbonates migrating from saline soil solutions to the rheotrophic
peat. Fungal degradation is a common feature of coal-ball material (Stubblefield & Taylor,
1988), perhaps facilitating the mineralization by splitting cell walls.
Bedding planes in organic-rich deposits are covered with electronically distinct microbial
films that coat sedimentary grains (Noffke et al., 2001). The so-called plant
impressions are, in fact, microbial films coloured with ferric precipitates mixed with