MILIOLIDAE - Acta Palaeontologica Polonica

18
EWA
LUCZKOWSKA
Sarmatian
Tortonian-Sarmatian boundary and zone with Anomalinoides dividens.
- A new miliolid species, Cycloforina stomata, appears directly
after the numerous Tortonian species have vanished completely, which
level may be recognized as the boundary between the Tortonian and
Sarmatian. The period between the rapid extinction of the Upper Tortonian
microfauna and the gradual development of the new Sarmatian one
is characterized by this single species. The bottom layers of the Sarmatian
are at first poor in fauna in general. The fauna consists chiefly of single
specimens of redeposited Tortonian foraminifera, otoliths, fish remains,
sometimes ostracods, numerous Cycloforina stomata and single specimens
of Anomalinoides dividens. There is also a large amount of pyrite and
many small, often pyritized, pelecypods and snails. These layers belong
to the lower portion of the zone with Anomalinoides dividens and range
in thickness from hardly several dozen centimetres to several metres in
the coastal zone (Luczkowska, 1964 and 1967), whereas in the foredeep
zone they reach as many as several dozen or even several hundred metres.
In this connection the mass occurrence of the species typical of this zone
is observed either in the bottom layers of the Sarmatian, almost in contact
with the Tortonian microfauna, or higher, above the bottom layer poor
in fauna.
In the clay facies of the coastal zone there is a sharp boundary
between the range of the Tortonian miliolids and that of the Sarmatian
ones. For example, in bore-hole Wolica 107 near Szydl6w there occurs
a typical assemblage of the zone with Hanzawaia crassiseptata at a depth
of 57-58 m, and directly above it, at depth of 56-57 m, Cycloforina
stomata and single redeposited Tortonian forms. From a depth of 56 m
upwards, Anomalinoides dividens, the typical species of this zone, occurs
in very large numbers already. A similar situation is observed at other
bore holes in the Szydl6w region, e.g. Solec 105, where the bottom layers
of the Sarmatian, bearing a poor assemblage with single specimens of
Anomalinoides dividens, otoliths, fish remains, pyrite and Cycloforina
stomata occur at a depth of 17.20-21.0 m and directly overlie lithologically
identical strata with a rich Upper Tortonian microfauna. In
bore-hole Wolica 101 near Szydl6w an abundant assemblage with Anomalinoides
dividens, Varidentella rotunda and Articulina sarmatica appears
above the rich Upper Tortonian assemblage at a depth of 18.7 m,
without any intermediate layers with a scanty microfauna.
An analogous situation is observed in the deeper zone of the Precarpatian
Foredeep, e.g. in the central part. In bore-hole Niwka-1 the
rich assemblages of the Upper Tortonian foraminifera including Quinqueloculina
regularis and agglutinating species (constituting a facial
equivalent of the assemblages with calcareous foraminifera from the zone