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The Oxfordian ammonite genus Passendorferia Brochwicz Lewiński and the Tethyan subfamily Passendorferiinae Meléndez: origin and palaeobiogeography

Mendez G., Atrops F., Bello J., Brochwicz-Lewiński W., Darpa C., Fozy I., Perez-Urresti I., Ramajo J., Sequeiros L.

Volumina Jurassica

2009

Vol. 7, no. 1

113-134

The Oxfordian ammonite group Passendorferiinae (known as "Mediterranean perisphinctids") forms a group of perisphinctids characterized by strongly evolute serpenticone coiling and subcircular to subquadrate whorl section, and forms a lateral divergent branch of the main stem Perisphinctidae. They originated probably from Late Callovian Grossouvriinae (Alligaticeras) and spread mainly in the Mediterranean (Tethyan) Province along the southern margin of Tethys, occasionally reaching the outer areas of epicontinental platforms. Their particular morphological features make them somewhat homoeomorphic with Tethyan Kimmeridgian Nebrodites. The phyletic link might be represented by the genus Geyssantia Meléndez, known from the Late Oxfordian Planula Chronozone. Separate biogeographic distribution in relation to the Perisphinctinae might reflect a progressive differentiation of western Tethyan faunas at the Callovian-Oxfordian boundary and at the onset of the Middle Oxfordian Transversarium Chronozone. Their rapid evolution gives them a biostratigraphic value similar to that of the Perisphinctinae. At the turn of the Middle-Late Oxfordian they gave rise to early Ataxioceratinae (Orthosphinctes), which replaced the Perisphinctinae in epicontinental areas, and colonised the marginal epicontinental blocks of northern Tethys. The taxonomy of this group is based upon the recognition of sexual dimorphism, using a single generic and specific name for both (M) and (m), and hence rejecting the use of former subgeneric ames for both dimorphs. A new species within this line: Passendorferia nodicostata sp. nov. from the Plicatilis Biozone (Paturattensis Subbiozone) is defined and described for the first time.

New biostratigraphic data on the Oxfordian from Roccapalumba (Western Sicily)

D'arpa C., Melendez G., Di Stefano P.

Volumina Jurassica

2006

Vol. 4, no. 1

144-144

The small locality of Roccapalumba, in western central Sicily, is one of the most classical Jurassic localities described by G. G. Gemmellaro in his numerous monographs on the Jurassic faunas of Sicily. The Jurassic sequence by the village, crops out along an overturned carbonate succession overthrusting clastic deposits of Neogene age. Within this sequence the white massive limestones of Tithonian age form a characteristic escarpment on the landscape, which gives the name (“The Rock”) to the village. The earliest deposits cropping out at this point are Middle Jurassic, Bajocian to Early Callovian in age. Bathonian to Lower Callovian deposits are represented by light grey, micritic massive limestones. A sharp irregular surface marks the Middle/Upper Jurassic boundary level: a centimetric irregular limestone bed contains scarce Callovian ammonites, preserved as fragmented internal moulds showing evidence of taphonomic reelaboration (Paralcidia, Hecticoceras, Grossouvria). The Upper Jurassic sequence above this level comprises a first, lower succession of well defined grey-brownish, somewhat nodular limestone intervals (c. 20 m) of Oxfordian-Kimmeridgian age, and a second, upper succession of light grey massive micritic limestones (over 30 m) of presumably Tithonian age. A first lithological interval 7 to 7.5 m thick may be assigned to the Middle Oxfordian Transversarium Chronozone, Luciaeformis Subchronozone: some 1.5 to 2 m above the Middle/Upper Jurassic boundary level, the age of the deposits is evidenced by the presence of several specimens (fragmented shells) of Gregoryceras close to the G. riazi (Grossouvre) group. This first recorded association is followed by a second one including few specimens of Gregoryceras closer to G. transversarium (Quenstedt) group. This interval is topped by a clear discontinuity surface underlined by a yellow limestone level. The next interval, 3 m thick, may represent the middle-upper Transversarium Chronozone Schilli Subchronozone, by the record just above this level of a well preserved, resedimented (i.e. non-reelaborated) incomplete specimen of Sequeirosia (M) cf. brochwiczi (Sequeiros) and several fragmentary specimens of Passendorferia (m) erycensis Meléndez. Phylloceratina (Holcophylloceras, Sowerbyceras) are also common, whilst Lytoceratina are slightly scarcer. Above a new discontinuity marked by a second yellow limestone level, the next interval (about 3 m thick) has yielded few incomplete specimens of early Ataxioceratinae (Orthosphinctes) and Epipeltoceras gr. bimammatum (Quenstedt) that indicate Late Oxfordian, Bimammatum Chronozone age. Above a sharp, irregular truncational discontinuity surface, the sequence forms a 10-12 m thick interval of grey-brownish bioclastic, slightly nodular, well bedded limestones stratified in massive banks 40 to 50 cm thick. The Early Kimmeridgian age of this interval is evidenced by the frequent record of Ataxioceratinae (Lithacosphinctes spp.), “Aspidoceras” and a well preserved specimen of Nebrodites (M) close to the N. peltoideus (Quenstedt) group.