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Updated Middle Oxfordian biostratigraphy in the Central Iberian Chain (Spain) and state of progress of perisphinctid systematics

Bello J., Melendez G., Page K., Ramajo J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

230-230

EN

Middle Oxfordian deposits in the Central Iberian Range (E Spain) are generally developed in biohermal to biostromal sponge limestones (Yatova Fm.). A major stratigraphic gap at the Callovian/Oxfordian boundary typically omits most of the Lower Oxfordian - excepting a few ephemeral sedimentary episodes - and the basal Middle Oxfordian Plicatilis Biozone. Despite being locally incomplete, however, the Transversarium and Bifurcatus biozones are well developed throughout the basin and display a remarkably complete ammonite succession. Perisphinctids are the key-group for biostratigraphic purposes and research carried out over the last 25 years has significantly contributed to refining the zonal scale for this interval. New information on this sequence indicates the following key points: 1. Recent progress includes the widespread recognition and correlation, including outside of Iberia, of the Rotoides Subbiozone at the top of the Transversarium Biozone and its further subdivision into two well-defined biohorizons: a lower, Universalis Biohorizon (Index: Per. universalis Bello, sp. nov. =Per. jelskii Siemiradzki, 1899, non 1891) and an upper Wartae Biohorizon. The latter is important as the direct forerunner of true representatives of Per. (Dichotomoceras) of the stenocycloidesbifurcatoides group. In addition, the identification of a Malinowskae Biohorizon with Per. malinowskae Br-Lewifski at the top of Bifurcatus Biozone (=Upper Grossouvrei Subbiozone) provides a valid name and level for specimens long misinterpreted as Per. bifurcatus (Quenstedt). 2. Taphonomic analysis of ammonite associations has provided an important tool for interpreting the sedimentary processes and the palaeogeographic evolution of the basin, including establishing the duration and reconstructing the processes associated with stratigraphic gaps. Similarly, taphonomic features shown by ammonite internal moulds across the Middle-Upper Oxfordian boundary (Bifurcatus-Hypselum chronozones) has facilitated the interpretation of this interval as a deepening stage on the platform, and therefore highly relevant for sequence and palaeogeographic analysis. 3. Finally, substantial progress achieved on the Perisphinctinae indicates the benefits of "re-shapeing" the systematics of the group in terms of modern, biological nomenclature. An open proposal is made considering the possibility of a unified taxonomy combining dimorphic pairs and a classification of the subfamily at the genus level, either a succession of genera as evolutionary links or perhaps a succession of species under a unique genus Perisphinctes (M & m).

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The Middle Oxfordian Platysphinctes event-horizon – an integrated tool in the correlations around the boundary of the Plicatilis and Transversarium zones in Europe

Glowniak E., Wierzbowski H.

Volumina Jurassica

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2006

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Vol. 4, no. 1

162-163

EN

Palaeobiogeographic differentiation of the Late Jurassic faunas of the northern hemisphere was connected with temporal excursions and mixing of the Boreal-Subboreal and Mediterranean ammonites in the area of the Submediterranean epicratonic seas of the northern Tethyan shelf. These excursions are well recognized from the Late Oxfordian onwards (e.g. Atrops et al. 1993) but are less well-known in the Middle Oxfordian. However, the lower Mid-Oxfordian Platysphinctes event-horizon first recognized in central Poland (GĐowniak 2000), has been recently evidenced also in southern Poland and NW Germany. According to the new study (GĐowniak 2006b, in press) it appears in central Europe within the Arkelli Horizon of the Arkelli Subzone (Mid-Oxfordian Plicatilis Zone in the usage of the Submediterranean zonal scheme based on perisphinctid lineage, GĐowniak 2002, 2006a) and was a proxy for a biogeographical phenomenon referred to as the “Mediterranean Spread”. At that time, geographical barriers did not hinder communication between the Submediterranean and Tethys basins, which may point to the occurrence of the “Mediterranean Spread” in conditions of a sea-level rise. In accordance with the previous opinion remain geochemical isotope data based on stratigraphically well-dated belemnite rostra derived from the Mid-Oxfordian sections of central Poland (Wierzbowski 2002). A gradual positive shift in ä13C values, which starts at the Lower/Middle Oxfordian boundary, reaches its maximum in the Platysphinctes event-horizon. According to Wierzbowski (2002) the early Middle Oxfordian carbon isotope excursion may have been linked to transgression, which occurred during a longer period of the crisis in oceanic carbonate sedimentation. The early Middle Oxfordian positive carbon isotope shift was subsequently recognized in the sections of Scotland (Wierzbowski 2004, Pearce et al. 2005). The geochemical events from Poland and Scotland are simultaneous and should be correlated with the Platysphinctes event-horizon (cf. Wierzbowski 2002, 2004). As a consequence, the latter becomes a precise marker for the stratigraphic correlations of the Mid-Oxfordian zonal schemes in the upper Plicatilis Zone between the Submediterranean and Boreal-Subboreal Europe.

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Problems on the Middle Oxfordian biostratigraphy of Western Siberia

Podobina V., Polkovnikova E., Tatyanin G.

Volumina Jurassica

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2006

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Vol. 4, no. 1

206-207

EN

The knowledge of biostratigraphy of the Middle Oxfordian part of the section of the Verkhnevasyuganskiy Subhorizon although quite good is insufficient for solving all the problems of dating, detailed correlation, and identification of sandy beds of the substantial oil-and-gas bearing deposits complex in the new borehole sections. Another cluster of problems includes the detailed subdivision of two Middle Oxfordian ammonite zones (a-zones) of Western Siberia and their correlation with the coeval Plicatilis Zone of the Submediterranean zonal scheme. At present, two a-zones are distinguished in the Middle Oxfordian of Western Siberia: the lower zone with the Cardioceras densiplicatum and the upper zone with Cardioceras tenuiserratum. Two parts are distinguished in the Cardioceras densiplicatum Zone corresponding to the Cardioceras vertebrale and Cardioceras maltonense subzones. The upper zone is not subdivided, and it is based on the appearance of ammonites of the subgenus Cawtoniceras. Foraminifera are of exceptional biostratigraphical importance when the material from cores is considered where ammonoid finds are generally rare. The Middle Oxfordian sedimentary complex of Western Siberia contains foraminiferal assemblages of two f-zones: Ammodiscus thomsi-Tolypammina svetlanae and Trochammina oxfordiana. The former includes several isochronous beds recognized in different areas of the region. In the circum-polar Urals, L. G. Dain distinguished beds with Ammodiscus thomsi, Tolypammina svetlanae. In western areas, V. I. Levina distinguished beds with Ammodiscus cheradospira (=Ammodiscus aff. pseudoinfimus (=Ammodiscus thomsi) and Eomarssonella paraconica. In the southern area, V. F. Kozyreva recognized beds with Ammodiscus ex gr. pseudoinfimus (=Ammodiscus thomsi) and Trochammina oxfordiana. In the central and southern districts, beds with Trochammina oxfordiana and with Glomospirella galinae were established by G. M. Tatyanin. The geographical range of the Ammodiscus thomsi-Tolypammina svetlanae Zone covers: Western Siberia, the Preuralian, Yamal-Tyumen, Kazym-Konda, Froly-Tambey, Pur-Vasyugan facies districts (the Danilovskoye, Abalak, Vasyugan, Maurynya formations). In the Yenisey-Khatanga depression N. V. Sharovskaya distinguished beds with Trochammina oxfordiana, Lenticulina memorabilissima, now this is the Trochammina oxfordiana Zone (its top correspond to the Ammodiscus thomsi - Tolypammina svetlanae Zone). The range of the Trochammina oxfordiana Zone covers: Western Siberia, the Khatanga and Taz-Kheta facies districts, Central Siberia, the Paksa facies district (Sigovoe Formation). The analysis on the available findings of the Middle Oxfordian ammonites in the south-east of Western Siberia may offer a key to reconciling the combined macro- and microfauna finds with the ammonite scale, and refining the lower and upper boundaries of the Middle Oxfordian foraminiferal associations. This could make possible tracing and comparing the changes in the systematic composition of the foraminiferal assemblages within two Middle Oxfordian ammonite zones which include the sections of the oil-and-gas bearing horizons.

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Następstwo amonitów dolnego i środkowego oksfordu w profilu kamieniołomu w Ogrodzieńcu i ich znaczenie biogeograficzne

Matyja B., Głowniak E.

Volumina Jurassica

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2003

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Vol. 1, no. 1

53-58

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Makroskamieniałości oksfordu dolnego i środkowego z Zalasu koło Krakowa; ich wartość paleontologiczna, biostratygraficzna i paleogeograficzna

Tarkowski R.

Technika Poszukiwań Geologicznych

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2001

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R. 40, nr 4

15-22

PL

W pracy przedstawiono rezultaty badań skamieniałości oksfordu dolnego i środkowego z Zalasu koło Krakowa. Odsłonięte powyżej permskich porfirów skały osadowe oksfordu dolnego i środkowego umożliwiły opisanie profilu oraz oznaczenie bogatego zespołu makroskamieniałości (gąbki, ramienionogi, małże, ślimaki, amonity, belemnity, jeżowce) obejmującego przeszło 250 gatunków, w tym 17 nowych. Profil utworów oksfordu dolnego i środkowego w Zalasie należy zaliczyć do klasycznych w skali europejskiej.

EN

The paper presents results of research of the Lower and Middle Oxfordian fossils from Zalas, Cracow area. The Lower and Middle Oxfordian sediments cropping out above the Permian porphires enabled to describe profiles and to determine rich assemblage of macrofossils (Sponges, Brachiopods, Lamellibranches, Gasteropods, Ammonites, Belemnites, and Echinids) representing over 250 species, including 17 new ones. The profile of the Lower and Middle Oxfordian from Zalas should be regarded as the classical European profile.