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1

Towards a consistent Oxfordian/Kimmeridgian global boundary: current state of knowledge

Wierzbowski A., Atrops F., Grabowski J., Hounslow M., Matyja B. A., Olóriz F., Page K., Parent H., Rogov M. A., Schweigert G., Villaseñor A. B., Wierzbowski H., Wright J. K.

Volumina Jurassica

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2016

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Vol. 14, no. 1

15--49

EN

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/ Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r). The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.

2

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

Page K., Melendez G., Wright J.

Volumina Jurassica

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2009

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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.

3

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.

4

High resolution ammonite stratigraphy of the Charmouth Mudstone Formation (Lower Jurassic: Sinemurian-Lower Pliensbachian) in south-west England, UK

Page K.

Volumina Jurassica

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2009

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Vol. 7, no. 1

19-29

EN

The "Lower Lias" mudrocks of the Charmouth Mudstone Formation inWest Dorset coast are world famous for their ammonite faunas, which range from mid Lower Sinemurian (Semicostatum Chronozone) to Lower Pliensbachian (topmost Davoei Chronozone) in age. The succession includes significant non-sequences, however, and as certain other intervals yield only crushed and relatively poorly preserved material, much of the sequence of ammonite faunas of this interval in south-west England has remained poorly understood. Inland, however, although it has been realised for many years that some of the missing horizons reappear, the Formation is very poorly exposed and as a consequence little has been known about its detailed stratigraphy and palaeontology. The systematic recording over 40 years by Mr H.C. Prudden (Montacute) of temporary excavations in East Somerset (around 20 km north of the Dorset coast), combined with material collected by others from similar exposures has now, however, revealed a virtually complete sequence of ammonite faunas through the interval represented by the Formation including from many of the which are missing on the Dorset coast. In particular, only one subchronozone remains to be conclusively proven in the region, the terminal Sinemurian, Aplanatum Subchronozone (Raricostatum Chronozone). This faunal succession is correlated with that on the coast to provide a detailed synthesis of the sequence of ammonite biohorizons in the region, which is correlated with a contemporary Standard Zonation and high-resolution biohorizonal/ zonule scheme for interval in North-West Europe. The significance for regional and international correlations of the Lower Lias is also discussed.

5

The conservation of Jurassic heritage in the UK – a critical review of the role of governmental organisations and their effectiveness

Page K., Wimbledon W.

Volumina Jurassica

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2008

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Vol. 6, no. 1

163-173

EN

In 1949 the concept of protected geological sites was first established in UK law by Nature Conservancy (NC) as ‘Sites of Special Scientific Interest’ (SSSIs). In 1977 a systematic site selection process - the Geological Conservation Review (GCR) was established by the UK-wide Nature Conservancy Council (NCC) which identified over 3000 features of geological interest nationally (excluding Northern Ireland), including around 275 representing aspects of Jurassic stratigraphy and palaeontology. These GCR sites formed the basis for all subsequent geoconservation SSSI designation including under strengthened legislation in 1981 and 2002. The fragmentation of the NCC in 1991 established separate country conservation bodies in Scotland (Scottish Natural Heritage), Wales (Countryside Council for Wales), and England (English Nature) with a fourth, the Joint Nature Conservation Committee (JNCC) to oversee certain national and international activities. In Northern Ireland, however, nature conservation remained the responsibility of the Environment and Heritage Service of the Department of the Environment. With the establishment of these five separate organisations, policy and practice began to diverge. The consequences of this divergence are discussed with particular reference to its effects on the conservation of sites of Jurassic palaeontological and stratigraphical importance. Recommendations for future conservation strategies and procedures are proposed.

6

Jurassic Global Stratotype Section and Points (GSSPs)-a potential serial World Heritage Site?

Page K., Melendez G., Henriques M.

Volumina Jurassica

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2008

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Vol. 6, no. 1

155-162

EN

The Operation Guidelines for the UNESCO World Heritage Convention state that proposed areas should: “..be outstanding examples representing major stages of Earth’s history, including the record of life”, “..contain all or most of the key interrelated and interdependent elements in their natural relationships”, “..have a management plan…” and “..have adequate long-term legislative, regulatory, institutional or traditional protection..”. By definition, Global Stratotype Sections and Points (GSSPs) should satisfy all these criteria, although in isolation, the proposal of any single GSSP is unlikely to succeed, however, as an individual site may lack a broader context. Nevertheless, combining a suite of GSSPs sites for a System within a ‘serial’ World Heritage site proposal would satisfy such a concern and could be an ultimate goal for the International Subcommission on Jurassic Stratigraphy.

7

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).

8

The conservation of Jurassic heritage in the UK – a critical review of current practice and effectiveness

Page K., Wimbledon W.

Volumina Jurassica

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2006

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Vol. 4, no. 1

254-254

EN

In 1949 the first concept of a protected geological site was introduced into UK law and within a few years the country had a network of such, now known as "Sites of Special Scientific Interest" (SSSIs). This initial law was strengthened in 1981, but in the meantime a systematic site selection process had also been established by the GB-wide Nature Conservancy Council (NCC) known as the Geological Conservation Review. This process led to the identification of over 3000 features of geological interest nationally (excluding Northern Ireland), including around 275 representing aspects of Jurassic stratigraphy and palaeontology. These "GCR" sites formed the basis for all subsequent geoconservation SSSI designation. Site conservation activity by the NCC was on a learning curve in the earlier days with the legal possibilities of the 1981 act being explored and techniques and philosophies being developed. Political moves, however, led to the fragmentation of the NCC in 1991 to established separate country conservation bodies in Scotland, Wales and England with a fourth to co-ordinate certain national and international activities. In Northern Ireland, however, nature conservation remained the responsibility of the Department of the Environment. With the establishment of these five separate organisations, policy and practice inevitably began to diverge. Wales established a regionalised distribution of geological advisors who take responsibility for much site-based casework. In Scotland, a small group of centrally based geologists provides advice, although in practice most casework is carried out by local, ecological, conservation officers. In England, however, a trend established towards the end of the NCC continued, with more and more key decisions being made by a centrally based group of geological advisors, with limited external scientific input. In addition, local, ecological conservation officers have increasingly been expected to not only give day to day advice on the management of geological sites, but also to set conservation objectives and monitor the same sites. These approaches have not only contributed to significant losses of key parts of several protected Jurassic sites and their contained palaeontological heritage, but also to a high level of under-recording of such damage. In October 2006, however, as a new organisation will take over nature conservation administration in England - "Natural England" - and the time is therefore right to rethink such approaches. Several proposed aims and objectives for the future will therefore be presented, which are not only of relevance to the UK as a whole, but also to the rest of Europe. It is ironic that in the 21st century in one of the countries that first established a systematic approach to geological conservation, especially site selection, significant damage to and losses of Jurassic heritage continue to be observed - a re-assessment of conservation strategies is therefore much needed.

9

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

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

Volumina Jurassica

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2006

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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.

10

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.

11

Jurassic Global Stratotype Section and Points (GSSPs) – a potential serial World Heritage Site?

Page K., Melendez G., Henriques M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

253-253

EN

The Operation Guidelines for the World Heritage Convention include the following criteria for the selection of natural heritage sites, which states that they should: "…be outstanding examples representing major stages of Earth's history, including the record of life, significant ongoing geological processes in the development of land forms, or significant geomorphic or physiographic features" [Criteria a (i)]; "The sites listed in a (i) should contain all or most of the key interrelated and interdependent elements in their natural relationships…" [Criteria b (i)]; "The site described in paragraph (a) should have a management plan…" [Criteria b (v)]; "A site described in paragraph (a) should have adequate long-term legislative, regulatory, institutional or traditional protection..." [Criteria b (vi)]. Global Stratotype Sections and Points (GSSPs) represent, by definition, the most stratigraphically complete and globally important stage-boundary sections known. They therefore fully satisfy the World Heritage criterion a (i). Crucially, their identification and ratification is regulated globally by the International Union of Geological Sciences (IUGS) which also advises UNESCO on the selection of World Heritage Sites for geological features - such a ratification can be taken as confirmation of global significance in more than just a technical or scientific sense. In addition, as part of the GSSP selection process aspects of the site's conservation status and safeguard for future study are also taken into consideration, Criterion b (vi) and be satisfied, if not b (v) as well. The proposal of any single GSSP in isolation as a World Heritage site is unlikely succeed, however, as individually such sites may lack a broader context. Combining a suite of GSSPs sites in a "serial" World Heritage site proposal - a well established approach in other contexts - is however, conceptually much more likely to succeed. In particular a proposal incorporating all the applicable GSSPs for a single system could certainly satisfy Criterion b (i), especially as all key interrelated and interdependent elements would then be included, i.e. all component stages of that system. Such a proposal could be an ultimately goal for the ISJS, as a celebration of decades of intensive work by many colleagues from many countries. Such a project would require a high degree of international agreement and already five countries are implicated in the process: Portugal, Spain, England, Scotland and France. Nevertheless, the close working relationships between specialists in different nations established through the Working Groups of the Subcommission can offer a marvellous opportunity for such collaboration.

12

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.

13

High resolution ammonite stratigraphy of the Charmouth Mudstone Formation (Lower Jurassic: Sinemurian – Lower Pliensbachian) in South West England (UK)

Page K.

Volumina Jurassica

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2006

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Vol. 4, no. 1

200-200

EN

The “Lower Lias” mudrocks of the Charmouth Mudstone Formation in West Dorset coast are world famous for their ammonite faunas, which range from mid Early Sinemurian (Semicostatum Chronozone) to Early Pliensbachian (topmost Davoei Chronozone) in age. The succession includes significant non-sequences, however, and as certain other intervals yield only crushed and relatively poorly preserved material, much of the sequence of ammonite faunas of this interval in South West England has remained poorly understood. Inland, however, although it has been realized for many years that some of the missing horizons reappear, the Formation is very poorly exposed and as a consequence little has been known about its detailed stratigraphy and palaeontology. The systematic recording over 40 years by Mr H. C. Prudden (Somerset Geology Group) of temporary excavations in East Somerset (around 20 km north of the Dorset coast) has now, however, revealed a virtually complete sequence of ammonite faunas through the interval represented by the Formation. In particular, many levels have now been identified which are missing in the major non-sequences on the Dorset coast, thereby revealing a much more complete stratigraphical sequence in the region than previously realized. In particular, only one subchronozone remains to be conclusively proven – the Aplanatum Subchronozone of the Raricostatum Chronozone – although this could still be due to collection failure as nodular facies do not appear to be present at this level and near-surface clay exposures are often too degraded to yield determinable specimens. This faunal succession is correlated with that on the coast to provide a detailed synthesis of the sequence of ammonite biohorizons in the region, which is correlated with a contemporary Standard Zonation and high-resolution biohorizonal/zonule scheme for interval in North West Europe. The significance for regional and international correlations of the Lower Lias is also discussed.

14

A potential stratotype for the Oxfordian/Kimmeridgian boundary: Staffin Bay, Isle of Skye, UK

Wierzbowski A., Coe A., Hounslow M., Matyja B., Ogg J., Page K., Wierzbowski H., Wright J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

17-33

EN

A coastal exposure of the Staffin Shale Formation at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK fulfils the criteria for definition as the Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Upper Jurassic). This marine shale succession was deposited during a long-term transgression, and is part of a complete, relatively well-expanded stratigraphic succession. A rich fauna of ammonites above and below the Oxfordian/Kimmeridgian boundary allows recognition of the Evoluta Subzone (Pseudocordata Zone) and Rosenkrantzi Subzone (Rosenkrantzi Zone) of the Subboreal and Boreal uppermost Oxfordian, and the Densicostata Subzone (Baylei Zone) and the Bauhini Zone of the Subboreal and Boreal lowermost Kimmeridgian). A suitable level for the boundary is thus marked by the replacement of the Subboreal Ringsteadia (M)/Microbiplices (m) by Pictonia (M)/Prorasenia (m), and by the first appearance of Boreal Amoeboceras (Plasmatites). Detailed study of the microfossils reveals an excellent dinoflagellate succession. A variety of stratigraphically important dinoflagellates are found, the assemblages being intermediate in character between Boreal and Subboreal ones. The magnetostratigraphic data, though rather troublesome to extract, shows a polarity pattern which can be confidently correlated to other UK boundary sections. The upper boundary of a normal magnetozone falls at, or very near, the proposed Oxfordian/Kimmeridgian boundary. The 87Sr/86Sr ratio at the boundary, based on an analysis of belemnites, lies between 0,70689 and 0,70697, averaging 0.70693. Matching worldwide trends, no distinct change in the ratio is seen across the boundary. A lack of variations in the carbon isotope composition of belemnites across the Oxfordian/Kimmeridgian boundary does not indicate perturbation in the global carbon cycle. However, high ?13C values and their scatter suggest the influence of local fractionation affecting isotope composition of dissolved inorganic carbon (DIC) in the partly isolated Boreal sea. A fall in the belemnite ?18O values in the Upper Oxfordian and Lower Kimmeridgian compared to the Mid Oxfordian suggests a slight rise in seawater temperature.

15

A Callovian-Kimmeridgian stable isotope record from Staffin Bay, Isle of Skye, UK: implications for the ocean-atmosphere system

Nunn E., Price G., Hart M., Page K., Leng M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

198-198

EN

The Staffin Bay section in the Isle of Skye, UK is one of the most stratigraphically complete Oxfordian sections in Europe. This contribution presents the first high-resolution stable isotope record of this Middle Callovian to Early Kimmeridgian succession. The isotope record includes both terrestrial and marine data that were obtained from microscopic wood debris and belemnites respectively. The organic carbon-isotope record was derived from organic rich sediment samples taken almost entirely from the Staffin Shale Formation. This formation is largely represented by a series of isolated foreshore exposures dominated by mudrocks that were deposited in a predominantly offshore marine environment. Over 200 sediment samples were analysed from the 150 m section. The concurrent ä13C marine carbonate curve was produced using belemnites collected from the same formation. Approximately 200 belemnite horizons were sampled. The organic carbon-isotope data show a broad Lower to Middle Oxfordian positive carbon isotope excursion from the Mariae to Tenuiserratum Zone, with maximum values occurring in the Cordatum Zone. This is followed by a return to pre-excursion values continuing into the Early Kimmeridgian Cymodoce Zone. A brief negative excursion (of ~2‰) is also identified near the Densiplicatum-Tenuiserratum zones boundary. Rock-eval analysis confirms that the organic matter is predominantly terrestrial in origin. The concurrent ä13C marine carbonate curve derived from belemnites shows a broadly similar trend. This suggests that the positive carbon-isotope excursion recorded here may have affected the global carbon reservoir (i.e. the whole ocean-atmosphere system). The carbon-isotope record derived from this section appears to be generally consistent with Oxfordian Tethyan records (e.g. Wierzbowski 2002, 2004) and a preliminary study of the Staffin Bay area by Pearce et al. (2005).