Jurassic fine-grained limestone and radiolarian chert in the northern Limestone Alps of Austria contain evidence of bathyal to abyssal depositional sites. Evidence for a deep-water origin of the Alpine Jurassic sequence has been noted by a succession of European geologists including Fuchs (1887), Steinmann (1925), and Trumpy (1960), and has strongly influenced the European view of geosynclinal sedimentation. The major lines of evidence for deep-water deposition of this Jurassic section are:

1. Fauna and rock composition:
The fauna consists predominantly of planktonic and nektonic forms such as ammonites, radiolaria, and calpionellids. Electron microscopy reveals that much of the fine-grained limestone consists of nannoplankton.

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2. Very slow sediment accumulation rates:
This is apparent in several ways: occurrence of manganese nodules and crusts on bedding planes; very thin but complete stratigraphic sections representing long time intervals; and cosmic spherule abundances in the rocks. Average sediment accumulation rates on the order of 0.1 to 2.0 cm./10³ years are suggested by rough calculations; however, it is evident that the actual rates changed considerably within the time intervals considered.

3. Solution effect:
Solution of all or nearly all calcium carbonate minerals produced the radiolarian chert as an insoluble residue; this is believed to be analogous with certain areas of the present deep-sea floor below the depth of complete CaCO₃ dissolution. In other parts of the Jurassic section, aragonitic skeletal parts (ammonite shells) were dissolved; calcitic parts (ammonite aptychi) are well preserved. The latter situation is believed to be analogous with certain present deep-sea areas where dissolution of aragonitic pteropods occurs at shallower depths than calcite dissolution.

4. Subsidence rates:
This can be fairly well established for the Triassic Period in the Austrian Alps because the total thickness of the shallow-water Triassic deposits (reefs, evaporites, etc.) is indicative of total subsidence. If projected unchanged into the Jurassic Period, this rate establishes at least minimum depths during the Jurassic and indicates that subsidence rates greatly exceeded sedimentation rates. Other evidence suggests that the subsidence rate actually increased during Jurassic time, at least in the beginning.

Together these criteria suggest maximum water depths of 4,500-5,500 meters in the northern Limestone Alps during Jurassic time.

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