Updated biostratigraphy of Jurassic (lower Kimmeridgian) deposits containing the ammonite Ataxioceras from the eastern Iberian Range, northeastern Spain

Abstract

Ammonite biostratigraphy and its correlation potential are evaluated for Ataxioceras-bearing deposits in the eastern Iberian Range, E–NE Spain. The Chronostratigraphic Standard Hypselocyclum Zone of sub-Mediterranean areas is analysed. Correlation of the new Ataxioceras lothari Biozone is proposed utilising first appearance datum (FAD)-based biostratigraphy, resulting from a review of ammonite (Ataxioceratinae) systematics. The lower boundary of the A. lothari Biozone and its chronostratigraphic equivalent Lothari Chronozone are defined by the FAD of Ataxioceras Fontannes s.s., and their upper boundaries by the FAD of Crussoliceras Enay. Distinction of the sub-biozones (subzones) A. hippolytense and A. lothari is confirmed, but these units are slightly reinterpreted. No ammonite subdivisions are defined for the A. hippolytense subzone, although two informal “intra-subzone biodivisions” (A. lothari and Geyericeras aragoniense) are recognised within the A. lothari subzone, the latter defined for the first time. The correlation potential of the proposed biostratigraphic scheme (zone and intra-zone levels using Ataxioceratinae) is high for marine successions from both epicontinental and oceanic-fringe environments under Tethyan influence (southern Europe and north-western Africa). The potential for correlation at the intra-zone level is higher for epicontinental than for oceanic-fringe areas; yet the precise correlation of some biostratigraphic boundaries is difficult at the “intra-subzone biodivision” level between the eastern Iberian Range and SE France. Updated identification and subdivision of the equivalent Metahaploceras strombecki Biozone in oceanic-fringe sections are presented, together with this unit's correlation potential with respect to the proposed A. lothari Biozone.