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Modeling results (general circulation model combined with oceanic biogeo-
chemistry, specifically nutrient transport) suggest sluggish ocean circulation
and the development of widespread anoxia in the deep ocean as a consequence
of a low equator to pole temperature gradient and the enhanced export of phos-
phate to the deeper ocean [31]. However, nutrient limitation causing a reduced
primary productivity prevents prolonged sulphidic deep water conditions.
In contrast, numerous sedimentary basins comprising pyritic black shale
successions exhibit petrographic, geochemical and sulphur isotopic data in
favor of sulphidic deep water during the late Permian and its transition into the
Triassic (e.g. [50]). In fact, a significant drop in the atmospheric O 2 abundance
has been attributed as a cause for a collapse of the marine ecosystem at this
time boundary with an emphasis on reef communities [89].
Finally, perturbations of the global carbon cycle suggest a combination of
a shift in magnitude and locality of organic carbon burial, from high burial
of terrestrial and marine organic matter during late Paleozoic time to low and
primarily marine organic carbon burial in the Triassic and thereafter [10].
A reduced level in atmospheric oxygen would be the predicted consequence.
Superimposed on this is a proposed sudden release of methane [71], as indicated
by a short-term, high-magnitude shift towards negative δ
13 C values (e.g. [42]).
4.4 Jurassic and Cretaceous Black Shales (OAEs)
The widespread deposition of organic-rich black shales characterizes early
Jurassic and Mid-Cretaceous times (Fig. 1), with numerous examples from
present-day continental areas and in DSDP/ODP cores. The observation of an
apparently time-equivalent deposition of this distinctive lithology during rel-
atively short-term intervals on several continents suggested a global phenom-
enon and, hence, a common cause. Initially coined for the Mid-Cretaceous,
these globally correlative short-term (less than 1 million years) levels of black
shale deposition were termed “Oceanic Anoxic Event (OAE)” [73]. Extensive
research over the past decades produced a wealth of information which centered
on the following issues (e.g. [27, 33])::
Paleoceanography, Sea level changes, Paleoclimate
Organic and inorganic geochemistry
Implications for global geochemical cycles
A generally warm climate, relatively high sea level, a proposed high abun-
dance of atmospheric carbon dioxide and climate induced oscillations in pre-
cipitation and continental run-off causing salinity stratification resulted in ex-
tended epicontinental seas characterized by sluggish deep water circulation and
persistent deep water anoxia. One of the consequences was the enhanced de-
position and preservation of organic matter, the latter visible on a global scale
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