『Abstract
The intimate stratigraphical association between Lower Toarcian
manganese carbonates and carbon-rich shales in Austria, Czechoslovakia,
Germany, Hungary, Italy, and Switzerland is suggestive of a genetic
connection between the two, given the similar anoxic to euxinic
depositional environments in which both these distinctive sediments
form today. Ammonite biostratigraphy and carbon-isotope stratigraphy
suggest that these metalliferous deposits are everywhere of identical
age, namely tenuicostatum to early falciferum Zones.
Recognition of an early Toarcian anoxic event in the Alpine-Mediterranean
domain, characterized by the development of a well-developed oxygen-minimum
zone across the rifted proto-continental margins of the Tethys,
indicates that these metalliferous deposits can be related to
mid-water transport of manganese, possibly of continental derivation.
The fact that, in the majority of localities, formation of the
manganese carbonates immediately pre-dated deposition of the carbon-rich
shales suggests that their deposition was characteristic of conditions
immediately preceding the anoxic event itself: carbon-isotope
evidence suggests that regional carbon-burial rates, presumably
linked with concomitant deoxygenation of water masses, were beginning
to increase during this interval. In some areas fluctuating redox
conditions at the sediment-water interface during the anoxic event
itself led to the precipitation of manganese carbonates. Although
the early Toarcian event affected many parts of the Alpine-Mediterranean
region, including Greece, it is only in central Europe, particularly
Hungary, that economic manganese deposits were formed, and hydrothermal
sources cannot be excluded as a factor in their genesis.』
Introduction
Palaeontological dating of manganese shales
Austria-Germany-Switzerland
Czechoslovakia
Hungary
Italy
Regional summary
Carbon-isotope stratigraphy of Jurassic pelagic limestones
in Austria and Hungary
Rationale
Analytical methods
Scheibelberg section, Kammerker, Tirol, Austria
Kisgerecse, Hungary
Tuzkovesarok Bakonycsernye, Hungary
Significance of results
Discussion
Relationship with Jurassic iron-manganese oxy-hydroxide nodules
Conclusions
Acknowledgments
References cited