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The ammonite faunas of the Callovian-Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP

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Page K. , Melendez G. , Wright J.

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tom Vol. 7, no. 1

89-99

EN

At Moenkopi Wash along the Ward Terrace escarpment of northern Arizona strata of the upper Dinosaur Canyon Member of the Moenave Formation contain sedimentary structures we interpret as casts of tetrapod burrows. Sandstone casts and in situ burrows occur concentrated in two horizons that extend several hundred meters along the Ward Terrace escarpment. The structures, hosted in beds of eolian sandstone, form interconnecting networks of burrows that branch at right angles. Individual burrow casts have sub-circular cross sections and consist of nearvertical tunnels and horizontal to low-angle galleries that connect to larger chambers. Most burrow casts measure 5 to 15 cm in diameter, are filled by sandstone of similar grain size as the host rock, and have walls that are unlined and lack external ornamentation. Bedding plane exposure of the lower horizon reveals that the density of burrows exceeds 30 vertical tunnels per square meter. One exposure in the upper horizon reveals burrows concentrated in a mound-like structure with 1 m of relief. Rhizoliths, distinguished from burrows by their typical smaller diameters, calcareous infilling, and downward branching, co-occur with these burrows in the upper horizon. The fossil burrows in the Moenave Formation appear to have been constructed by a fossorial tetrapod with social behavior similar to the modern Mediterranean blind mole-rat. Although no skeletal remains are associated with the burrows, the fossil record suggests that the most likely producers of the Moenave burrows were tritylodontid cynodonts.

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The ammonite faunas of the Callovian/Oxfordian boundary interval in Europe and their relevance to the establishment of an Oxfordian GSSP

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Melendez G. , Page K. , Wright J. , Atrops F.

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tom Vol. 4, no. 1

185-185

EN

The latest Callovian and Early Oxfordian represent one of the most dynamic intervals in the history of Jurassic Ammonoidea and is characterized by one of the highest levels of mixing of Boreal, Submediterranean and even Mediterranean faunas. In particular the massive expansion of Boreal Cardioceratidae from their original “home” in Arctic areas as far south as South East France, brings them into contact with Mediterranean-style faunas rich in Phylloceratidae. This so-called “Boreal Spread” (after J. H. Callomon) provides the framework within which high-resolution inter-bioprovincial correlations are possible and hence the context for a sucessful GSSP designation for the base of the Oxfordian Stage within Europe (and hence the beginning of the Upper Jurassic). Associated with the Cardioceratidae, however, is a great variety of Perisphinctina, including Aspidoceratidae, Periphinctidae, Grossouvridae and rarer Pachyceratidae as well as frequent Hecticoceratidae and rarer Phylloceratidae. The latter groups are much more abundant in southern areas (Tethyan Realm), but the Aspidoceratidae do persist well into the Boreal Realm. Crucially, several groups of the Perisphinctina persist beyond Europe and therefore provide tantalising indications that a truly global correlation of any GSSP established in Europe will ultimately be possible. The current paper will review the stratigraphical, taxonomic and palaeobiogeographical context and significance of the trans Callovian/Oxfordian boundary faunas within Europe, building on recent results from the UK and France. Conclusions will be drawn concerning the appropriate – or convenient – level at which the place the Callovian-Oxfordian in Europe and its potential interpretation elsewhere. Such conclusions are highly relevant to the eventual establishment of an Oxfordian GSSP.

3

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

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

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tom Vol. 4, no. 1

144-144

EN

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.

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Integrated stratigraphical study of the candidate Oxfordian Global Stratotype Section and Point (GSSP) at Redcliff Point, Weymouth, Dorset, UK

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Page K. , Melendez G. , Hart M. , Price G. , Wright J. , Bown P. , Bello J.

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tom Vol. 7, no. 1

101-111

EN

Ham Cliff near Redcliff Point, Weymouth, Dorset (SW England) exposes one of Europe's most complete Callovian-Oxfordian boundary sequences and has consequently been identified as a potential candidate GSSP for the base of the Oxfordian Stage. The boundary sequence lies within the thick mudrock facies of the Oxford Clay Formation and is abundantly fossiliferous, cardioceratid ammonites in particular being conspicuous. By convention, the stage boundary is drawn at the first occurrence of the genus Cardioceras here represented by C. redcliffense Page, Melendez and Wright at the base of the Scarburgense Subchronozone of the Mariae Chronozone. Associated Perisphinctoidea (including Peltoceras, Alligaticeras and Euaspidoceras) provide additional biostratigraphical information. Other macrofossil groups show less discernible changes, although frequent belemnites (Hibolithes) provide new highresolution carbon and strontium isotope data which are consistent with global curves and continuous sedimentation across the boundary interval. Magnetostratigraphic information is also available. Foraminiferal assemblages are dominated by epistominids but include a flood of early planktonic forms, including ?Globuligerina oxfordiana (Grigelis) immediately above the boundary. Well-preserved nannofloras are dominated by Watznaueria with conspicuous Zeugrhabdotus, podorhabdids and Stephanolithion indicating the NJ14 Biozone. Ostracoda and holothurian spicules are also recorded. These results are synthesised to provide a multidisciplinary, integrated review of the suitability of Redcliff Point for the definition of an Oxfordian GSSP. Correlations with the French candidate site in Haute-Provence are discussed and proposals made for formally establishing a GSSP for the base of the Oxfordian Stage in Europe.

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Integrated stratigraphical study of the candidate Oxfordian Global Stratotype Section and Point (GSSP) at Redcliff Point, Weymouth, Dorset, UK

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Page K. , Melendez G. , Hart M. , Price G. , Wright J. , Bown P. , Bello J.

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tom Vol. 4, no. 1

200-201

EN

Redcliff Point near Weymouth, Dorset (SW England) exposes one of Europe’s most complete Callovian-Oxfordian boundary sequences and has been the subject of a rigorous multidisciplinary assessment. The boundary sequence lies entirely within the clay facies of the Oxford Clay Formation, the relatively high carbonate content of which facilitates the excellent preservation of both macro- and microfaunas (and floras) as well as geochemical information. Ammonites, in particular, are conspicuous, and partly retain an aragonitic shell. By convention, the stage boundary is drawn at the first occurrence of the genus Cardioceras, which has been interpreted as corresponding to the transition between “Quenstedtoceras” paucicostatum (Lang) and Cardioceras ex gr. scarburgense (Young and Bird), specifically at the first occurrence of C. woodhamense Arkell sensu Callomon (non Marchand). This transition is well seen at Redcliff and provides the primary means through which the boundary can be correlated. Associated Perisphinctina (including Peltoceras, Alligaticeras, Properisphinctes and Euaspidoceras) provide additional biostratigraphical information. Other macrofossil groups show less discernible changes, although the end of the Callovian in England marks the local, virtual disappearance of Boreal cylindroteuthid belemnites with the persistence of Tethyan hibolithids into the Early Oxfordian. Isotopic studies of recovered belemnites record important information on carbon and strontium isotopes and provide new, high resolution data for the refinement of the global curves. The isotope data are also consistent with continuous sedimentation across the boundary. Foraminiferal assemblages are dominated by poorly preserved epistominids. Planktonic Foraminifera are recorded, mainly as pyrite steinkerns. This makes identification difficult although a flood close to the boundary appears to be Globuligerina oxfordiana. Other planktonic taxa are present, including one species that may be new. Nannofloras are well preserved, common to abundant and dominated by Watznaueria britannica with conspicuous Zeugrhabdotus erectus, podorhabdids and Stephanolithion bigotii. The presence of Stephanolithion bigotii maximum throughout, places the samples within the NJ14 biozone. Ostrocoda and holothurian spicules are also recorded. These results are synthesised to provide a multidisciplinary, integrated review of the suitability of Redcliff Point for the definition of an Oxfordian GSSP. Correlations with the French candidate site in Savournon, Haute-Provence are discussed and proposals made for formally establishing a GSSP for the base of the Oxfordian Stage in Europe.