UTRECHT MICROPALEONTOLOGICAL BUllETINS

II.2.4.15. The Prioniodus
crassulus Assemblage Zone
Diagnosis: A conodont assemblage zone characterized by the occurrence of
Prioniodus crassulus prior to the first appearance of Prioniodus navis (charts
II, III and IV, fig. 15).
Description: The addition of Prioniodus crassulus, often in small numbers, is
the only difference with the faunal composition of the Oistodus lanceolatus
Assemblage Zone.
Type-locality: Kopingsklint, section 1.
Type-stratum: The basal limestone bed of the Bruddesta Formation in
section 1.
Remarks: In sections 1 and 14 the first appearance of Prioniodus crassulus
coincides with maxima in the occurrence of Oepikodus evae in the basal
portions of the Bruddesta Formation. It is possible, that in section 6 the
appearance of Prioniodus crassulus coincides with the acme of Oepikodus
evae in the basal part of the Bruddesta Formation as well. This would make
the lower boundary of the Prioniodus crassulus Zone coincide with the lower
boundary of the Bruddesta Formation throughout the area (chart V). Oistodus
papiliosus was not actually found in this zone, but it might occur
according to its deduced regional range. See also the remarks of chapters
II.2.4.14 and II.2.4.16.
11.2.4.16. The Prioniodus navis/Prioniodus crassulus Assemblage Zone
Diagnosis: A conodont assemblage zone defined by the concurrence of the
ranges of Prioniodus crassulus and Prioniodus navis (charts II, III and IV,
fig. 15).
Description: In the rock-sequence of N.W. bland the overlap zone of
Prioniodus navis and P.crassulus contains in addition: Scolopodus peselephantis,
Protopanderodus longibasis, P.rectus, Drepanoistodus forceps,
Stolodus stoia and Oistodus lanceolatus, throughout. Oepikodus evae seems
to end its range in the lower portion of this zone. Paroistodus parallelus,
Scolopodus rex, Drepanodus arcuatus, Dreparroi-stodu-s -eonulatu-s and Periodon
flabellum were discontinuously encountered in this zone.
Type-locality: Kopingsklint, section 1.
Type-strata: Some 35 cm. of limestone beds in the lower portion of the
Bruddesta Formation, samples 17 to 22, section 1 (chart II).
Remarks: Oistodus papiliosus was not found in this zone, but it might form
part of the assemblage according to its deduced regional range.
The boundary between this zone and the underlying Prioniodus crassulus
Zone is of dubious character, because of the rareness of both marker species.