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This siltstone unit lies upon a conspicuous erosion surface highlighted by angular chips of phosphatized pebbles and ammonites.
The central part begins with ammonite-bearing crinoidal limestones and black pillow basalts.
Cladistic techniques have been applied to many fossil groups but ammonites remain largely understudied in this way.
Detailed collecting through 15 sections across the basin has facilitated a major revision of the ammonite zonation.
The fauna is limited to ammonites and a species of epifaunal bivalve.
This method can therefore be used to compare the morphological signal of ammonites with other physical or chemical signals.
We note, however, that ammonites have not been recorded from the 1.8 m of strata below the proposed boundary level.
The sudden appearance of these genera represents a major reinvasion of the basin by neocomitid ammonites.
Apart from ammonites and dinoflagellates, very little other stratigraphic data is discussed in detail.
Dashed ammonite-zone and bed boundaries reflect some uncertainty of their precise position in the core.
Most of the ammonites studied have ribs, tubercles, keels and other ornaments.
Nektonic taxa such as belemnites and ammonites dominate the fauna, with lesser bivalves and brittle stars found almost exclusively in the coarser units.
No ammonites have been recorded from between -1.8 m to 0 m in the section.
