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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

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2009

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Vol. 7, no. 1

113-134

EN

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.

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

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

Volumina Jurassica

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2009

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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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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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Palaeogeographic evolution of the eastern Iberian carbonate ramp during the Middle Oxfordian

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

Volumina Jurassica

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2006

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Vol. 4, no. 1

103-104

EN

Sedimentation on the East Iberian carbonate platform during the Middle and early Late Oxfordian represents the onset of subtidal marine conditions after a long period (Middle Callovian - Early Oxfordian) where extremely shallow to temporarily emerged environments predominated, favouring the development of condensed deposits. A progressive deepening during the Middle Oxfordian led to the development of sponge and microbiolite buildups alternating with biostromes. Levels with inverted or fragmented sponges and bioclastic storm deposits mark the most energetic events. Ammonite assemblages comprise mainly drifted shells from open-marine areas with only short-lived episodes of colonisation. Five stages are distinguished in this Middle Oxfordian sequence. 1. Parandieri Subchronozone - Middle Oxfordian deepening begins. In deeper areas to the NW, carbonate sediments contain abundant, well-preserved sponges occasionally in upright position. In shallower distal areas (SE) across a palaeogeographic swell, sedimentation is limited to thin, condensed levels of iron-oolite limestones and sponge spicules. 2. Luciaeformis-Schilli Subchronozone interval - a widespread deepening event leads to the development of sponge limestone facies throughout the platform. Sponge biostromes and buildups are developed in the NW, and in distal areas (SE) biostromic levels with inverted sponges and tempestite levels with broken sponges are common. A brief ammonite colonisation event took place in the NW during the middle Schilli Subchronozone. 3. Rotoides Subchronozone - lower part forms a condensed sequence (representing a storm deposit interval) formed by bioclastic limestones with sponge fragments and ammonite internal moulds. In the SE this interval is represented by a centrimetic level of bioclastic and ferruginous pelloids, which grade laterally into layers with fragmented sponges and pellets. The upper, Wartae Horizon, is represented in NW areas by a more expanded sequence of well-bedded micritic sponge limestones. 4. Stenocycloides Subchronozone - a micritic limestone sequence containing fragmented and broken sponges occasionally in upright position develops in the NW. In the SE more condensed, pelloidal, glauconitic limestones with packed, inverted sponge fossils are present. Ammonite assemblages comprise mainly reelaborated moulds. 5. Grossouvrei Subchronozone - the lower part in the NW forms a homogeneous interbedding of micritic limestones and marls with an increasing quartz content upwards; sponges are generally inverted or fragmented. In the SE, pelloidal and glauconitic limestones are dominant. Facies analysis and taphonomic features of ammonites indicate that maximum depths were reached at around the Grossouvrei-Hypselum zone boundary.

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On the origin and palaeobiogeographic spread of Oxfordian ammonite genus Passendorferia and Tethyan subfamily Passendorferiinae Melendez

Melendez G., Atrops F., Bello J., Brochowicz-Lewiński W., D'Arpa C., Fozy I., Perez-Urresti I., Sequeiros L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

240-241

EN

Oxfordian ammonite group Passendorferiinae (known as "Mediterranean Perisphinctids") form a lateral divergent branch of the main stem of Perisphinctidae, originating probably from Late Callovian Grossouvriinae (Alligaticeras) and spreading mainly in the Mediterranean (Tethyan) Province during the Early, Middle and Late Oxfordian. This morphologically homogeneous group is characterized by the evolute serpenticone coiling with sub-circular to subquadrate whorl section. Ribbing "simple" radial, is formed by mostly single and symmetrically bifurcate ribs, turning into thicker, straight, "columnar" ribs, slightly elevated on the ventral margin in adult stage of macroconchs. All these features make them strongly homoeomorphic with Tethyan Kimmeridgian Nebrodites, with which they have been often mistaken. The phyletic link might be represented by the genus Geyssantia Melendez, from Late Oxfordian Planula Chronozone. Microconchs, 80 to 120 mm Dm are isocostate, densely ribbed, lappeted and, show typically the development of parabolic nodes at the final part of adult phragmocone. Macroconchs 240 to over 320 mm Dm, slightly variocostate, show thick uniform columnar ribs in adult stage. Two main genera are so far recognized, evolving independently during Early and Middle Oxfordian: Passendorferia Brochwicz Lewiński, known from Lower Oxfordian early Cordatum Chronozone to Upper Oxfordian, Bimammatum-(?)Hauffianum Chronozone, characterized by extremely evolute serpenticone inner whorls with subcircular whorl section leading to subquadrate middle and outer whorls, and Sequeirosia Melendez, known mainly from the Middle Oxfordian characterized by more involute serpenticone coiling with subquadrate whorl section from early inner whorls. Passendorferiinae colonised and spread mainly on the southern margin of Tethys, being autochthonous in epioceanic carbonate platforms of western Tethys, from Hungary to southern Alps, Sicily, North Africa or Betic ranges, and reaching occasionally the external deeper areas of shallow epicontinental platforms at the northern margin of Tethys. This separate biogeographic distribution with respect to Perisphinctinae probably reflects a progressive extensional block differentiation of western Tethys at the Callovian-Oxfordian boundary and at the onset of Middle Oxfordian Transversarium Chronozone. Their rapid evolution provides them a biostratigraphic value similar to that of Perisphinctinae. At the turn of Middle-Late Oxfordian they gave rise to early Ataxioceratinae (Orthosphinctes), which would replace the Perisphinctinae and colonise the marginal epicontinental blocks of northern Tethys.

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

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

Volumina Jurassica

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2006

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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.