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Notes on the evolution of the ammonite families Aulacostephanidae and Cardioceratidae and the stratigraphy of the uppermost Oxfordian and lowermost Kimmeridgian in the Staffin Bay sections (Isle of Skye, Northern Scotland)

Wierzbowski A., Matyja B. A., Wright J. K

Volumina Jurassica

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2018

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Vol. 16, no 1

27--50

EN

Detailed study of all the ammonite collections gathered by the authors in the Staffin Bay sections has resulted in minor changes in the distribution of ammonite taxa, and slight modification of the position of the Oxfordian/Kimmeridgian boundary. Most significant is the discovery of Pictonia (Triozites) cf. seminudata which results in the placing of the stage boundary 0.16 m below the level formerly proposed. This study discusses the evolution of the Subboreal family Aulacostephanidae, and the Boreal family Cardioceratidae, indicating changes in the patterns of individual development in the evolution of both families in terms of heterochrony. The Oxfordian/ Kimmeridgian boundary interval shows major morphological changes in both ammonite families which were released from phylogenetic constraints by heterochrony, closely related to changes in environmental conditions.

2

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.

3

On the typological basis of Perisphinctes Waagen, 1869 and the leading modern ammonite superfamily Perisphinctoidea Steinmann, 1890

Callomon J. H., Wright J. K.

Volumina Jurassica

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2016

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Vol. 14, no. 1

1--14

EN

A re-examination of the type specimen of Ammonites biplex Sowerby, 1821 shows that the reasons previously given for rejecting this species as the type species of Perisphinctes, to be replaced by Amm. variocostatus Buckland, 1836 (Hemming, 1954), were unfounded. Fortunately, the replacement, based on a macroconch type, is a better representative of the genus than its originally validly designated microconch, Ammonites biplex. The decision in Opinion 303 (Hemming, 1954) is therefore a good one but arrived at for the wrong reasons. It should be left unchanged.