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

• Autorzy: Bello J. , Melendez G. , Page K. , Ramajo J.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

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).

Słowa kluczowe

EN

biostratigraphy; ammonites; taphonomy; Middle Oxfordian; Perisphinctinae

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 230--230

Twórcy

autor

Bello J.

autor

Melendez G.

autor

Page K.

autor

Ramajo J.

• Departamento de Geologia (Paleontologia), Universidad de Zaragoza, 50009 Zaragoza, Spa,