Page 290 - Carbonate Facies in Geologic History

Biological Content 277

9. Rare, deformed, slumped and brecciated layers (Krummelagen) are present.
Two of these are widespread over the Franconian area. Plate XXVII shows one of
these at Nusplingen in Schwabia. Very small-scale graded bedding is recognized
throughout. Rare groove casts occur. These sedimentary structures indicate depo-
sition in considerable depth with some slope to the sides of the basins.

Diagenesis of Strata

More compaction appears in the Solnhofen than is usual for many ancient lime-
stones.
1. Cohesiveness of the bottom sediment was sufficient for organisms such as
fish and ammonites, to leave marks as they settled upright on the bottom and
later fell over. A few arthropods left sharply preserved claw and telson tracks in
the mud.
2. Syneresis of the lime mud occurred at an early time, presumably by de-
watering in a subaquatic environment. This causes a rough top surface of the beds
and a smoother bottom surface. The roughened top surface was erased by move-
ment of a decaying fish carcass, indicating early formation of the rough surface
(De Buisonje, 1972).
3. Compaction occurred in the limestones away from fossils. Such beds traced
away from the fossil remains became 1/4 to 1/6 as thick compared to where
present with the fossil. The noncompacted fossil is often forced into the overlying
limestone Flinze bed and rests on a socle (pediment) of uncompacted, early ce-
mented limestone. On the other hand, flattening of ammonite and other shells is
observed in tops of marly layers just under overlying Flinze beds.
4. Microscopic study of the micrite reveals many planar and sutured grain
contacts, apparently the result of pressure solution.

Biological Content

1. The strata are actually poor in fossils but the biologic composition is varied
and unusual. Only the swimming crinoid Saccocoma is common.
2. Fossils generally occur along bedding planes in the Flinze and in the marly
(Faule) layers.
3. The soft parts are excellently preserved in some specimens showing very
slow decay, in an environment lacking currents and scavenging benthos. Periods
of very rapid burial may be responsible for the excellent preservation-the extent
to which this is true is not ascertainable.
4. In all, 750 species of animals and plants have been described. The original
list of Johannes Walther (1904) has been updated and revised-of this 99% of the
organisms are of marine nekton or pelagic environment. In order of diminishing
frequency these are Sacco coma (free swimming crinoid), ammonites, fish, crusta-