Terrestrial Palaeoecology and Global Change

Chapter 2. Taphonomy
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II.6. Tectonic style
Insofar as taphonomic environments are defined by tectonism, deposition of organic
material reflects tectonic style of the epoch. Thus, at the Jurassic/Cretaceous boundary,
most of terrestrial runoff went to the downfaulted marginal basins of the Atlantic, Pacific,
Indian and Arctic oceans, with depocentres in the pull-apart trancurrent fault zones.
Their thick estuarine to deltaic Wealden-type deposits accumulated organic material
preserved as structural fossils or kerogens (Batten, 1982). Rich Early Cretaceous plant
localities including the British Wealden flora, the Potomac flora of North American Atlantic
coast, the Nican flora of Partisansk Basin, Russian Far East, the Coonwarra flora
of Gippsland Basin, southeastern Australia, etc.(Fontaine, 1889; Krassilov 1967a: Douglas
1969; Watson & Sincock. 1992; Watson 2001) occur in the marginal transcurrent
basins.
Thick organic-rich deposits also accumulated in the concomitantly developing transcontinental
rift basins of central-eastern Asia, with lacustrine black shales and associated
fossil plant localities of Transbaikalia, Mongolia and northeastern China (II.7.2).
Subsidence of continental crust in the Late Cretaceous was accompanied by a nearly
four-fold decrease in sedimentation rates. Coal deposition was insignificant in comparison
with the Lower Cretaceous reserves while marine accumulations of hydrocarbons
were considerably reduced, mainly at the expense of gas source rocks with kerogens of
terrestrial origin. Both the marginal transcurrent basins and transcontinental rift zones
lost their significance as major traps of terrestrial dead mass. With transgression of
epeiric seas over cratonic areas, terrestrial runoff was channelled to the slowly sagging
epirift basins. The Late Cretaceous coal and the bulk of fossil plant material came from
the marginal clastic facies of epirift basins in northern Siberia, Kazakhstan, northerncentral
Europe and North America (reviewed in Vakhrameev, 1991).
The mid-Cretaceous is generally considered as the time of high-rate evolution in
many terrestrial groups of plants and animals changing the general aspect of land biota.
Angiosperms, rare before the Albian, spread over all landmasses forming new types of
plant communuties as well as enhancing innovations in the co-evolving groups of arthropods
and tetrapods. Yet the abruptness of the mid-Cretaceous biotic turnover is partly
owing to the change in tectonic style and taphonomy, with the major part of terrestrial
runoff redirected from marginal to intracratonal basins.
II.7. Taphonomic cycles
Since fossilization depends on taphonomic variables, such as deposition rates, mineral
composition, pH, etc., and since these variables undergo either directional or fluctuant
changes in the course of sedimentation, fossils of various dimensions, weight and durability
are unevenly distributed over sedimentary sequences. In situ burial of dead mass