134 9'h International Congress on the Jurassic System - Abstracts Parkinsoniids and garantianids (Late Bajocian Ammonoidea) as guide fossils and biostratigraphic indices GIULIO PAVIA1 * & SIXTO R. FERNANDEZ-LOPEZ 2 1Dipartimento di Scienze de/la Terra, Universita degli Studi di Torino, 10125 Torino, Italy; E-mail: [email protected] 2Departamento Paleontologfa, Facultad Ciencias Geol6gicas, ea/le Jose Antonio Novais,2, Universidad Complutense de Madrid, 28040-Madrid, Spain; E-mail: [email protected] Taphonomic, palaeobiological and appearances of innovative biota in several areas biochronological data are relevant in (then fossils in the stratigraphic record) may be interpreting time-space relationships of interpreted as synchronous events if they are the fossiliferous rock bodies, and in understanding effects of synchronous geographic dispersions the palaeoenvironmental changes taking from a common external source area. However, place on Earth' surface. It is assumed that the they are diachronous towards the source bed-by-bed order of succession shown by area. The appearances of innovative biota can fossils in the stratigraphic record represents be complementarily calibrated through the the chronological order of the producer taxa. synchroneity of the transgressive/regressive However, a particular feature of the fossil record changes analysed in sequence stratigraphy, too can condition the validity of the palaeontological (SANDOVAL et al. 2001). interpretations. In diverse cases it cannot be Since the latest decades of the past century, assured that fossils and rocks of the same the International Subcommission on Jurassic stratigraphic interval represent the same time Stratigraphy (ISJS) promoted activities to get interval or the same palaeoenvironment. In this definitions for the Global Boundary Stratotype sense, it must be stressed that the fossil record Section and Point (GSSP) of each stage of the can supply information on palaeoenvironments Jurassic System, and more recently (MORTON and processes that have left no traces in the 2003) asserted the opportunity to locate stratigraphic record (FERNANDEZ-LOPEZ 2000). sections that could be proposed as reference Consequently, palaeontological successions for the basal boundary of substages. The can display higher biochronological and definition of the base of each chronozone is geochronological completeness than also an aspect to be pursued. Such formal lithostratigraphic and biostratigraphic definitions are feasible where successions successions. Taphonomic analyses are display high chronostratigraphic completeness fundamental,astheirresultscanfurnishevidence and stratigraphic parameters do permit this of diachroneity within the facies and the fossil (FERNANDEZ-LOPEZ et al. 2009; PAVIA & ZUNINO assemblages of the studied stratigraphic unit. 2012). It becomes hard if the succession is The characterization of palaeontological units affected by stratigraphic and/ or taphonomic (such as the taphorecords) in a stratigraphic condensation (FERNANDEZ-LOPEZ 2011). That succession and their arrangement according is a common case in the Parkinsoni Zone, which to the time interval of the palaeobiological represents the latest Chron of the Bajocian entities, which produced the recorded fossils, Stage. The ammonite groups involved in the allow defining the palaeontological successions. togic_are basically: the microconch Parkinsonia The palaeontological succession can show /\·~ith t~acroconch partner Durotrigensia, a higher number of palaeoenvironmental, and the m~roconch Garantiana with many \ depositional, and palaeobiological events than allied taxa among them the microconch the stratigraphic succession (PAVIA & MARTIRE Pseudogarantiana. 1997; PAVIA et al. 2013). Parkinsonia Ls. - The first occurrence of Also the palaeobiogeographic parkinsoniids in the West Tethyan areas looks constrains have an effect on the potential as sudden, and it is the diagnostic criterion to of biochronostratigraphic interpretations:, define the base of the Parkinsoni Zone (RIOULT 9th International Congress on -the Jurassic System - Abstracts 135 et al. 1997) according to the record of the gradients between the Submediterranean group of Parkinsonia acris as the index of the and NW European provinces. New continuous basal subzone. Citations of "parkinsoniids" biostratigraphic and palaeontological recur in the literature (e.g., SCHWEIGERT et al. successions are needed to define the subzonal 2002) but their meaning need to be clarified and zonal Garantiana-Parkinsoni boundary. for effective taxonomic relationships and Garantiana l.s. - This early and middle biostratigraphic pertinence, as they commonly Late Bajocian taxon developed in the derive from condensed stratigraphic sections Submediterranean Province and repeatedly affected by taphonomic condensation with diversified during the Garantiana Chron re-elaborated fossils. Personal data from the"'-. with largest dispersion in the NW European Basque-Cantabrian Basin assure the presence Province. Taxa of the dimorphic couple of re-sedimented specimens (contemporaneous Garantiana-Pseudogarantiana are zonal and to the encasing sediments) in the middle part subzonal indexes for the Garantiana Zone of the Garantiana Zone (FERNANDEZ-LOPEZ throughout most of the Mediterranean­ 1988). Such specimens show intermediate Caucasian Subrealm. Garantianids developed morphological features between the genus through evolutionary lineages according to Caumontisphinctes of the uppermost Niortense palingenetic processes and peramorphic Zone, and the Parkinsonia of the basal Parkinsoni modifications, interrupted by paedomorphic Zone. This new biochronostratigraphic changes. This iterative evolutionary pattern information means thatthe origin of Parkinsonia produced numerous and brief phyletic has to be found in a still unknown place within lineages with common homeomorphs that the Submediterranean Province, and that the make it difficult to unravel their taxonomic first occurrence of Parkinsonia is not a valid "strapwork". Moreover, the type specimens criterion to recognize the basal boundary of of most garantianids were elected on fossils the Acris Subzone as it may be affected by deriving from the condensed sections of the diachroneity in terms of palaeobiogeographic NW European Province (e.g., DIETZE et al. 2002, Biochronostratigraphy Biostratigraphy Biochronology BATHONIAN stratigraphic registratic succession of intervals ammonite taphorecords BOMFORDI PARKINSON I DENSICOSTA Haed 12:-, RS-12/61 '' ------IRL-12/161 ACRIS --IBed 11 -- - - -- - --IRL-11/151 z <( TETRAGONA --IBed 10 ' ...... ______ 0 - IRL-10/141 0 Hsed9L, ....., GARAN TIANA SUBGARANTI ,, .... <( I\ .... co I \ ' - - - - - -IRL-9/131 I \ w DIC HO TOMA \ I \ I ~ I -- - - --IRL-9/121 BACULATA --1Bed8 , -1 ',- - - - - - - - I RL-8/10 I 'I , NIORTENSE POLYGYRALIS I - - -- - -I Rl-8/9 I I --1 Bed 7 : ,- _ ~ I RS-7/5 I - - --- - I Rl-7/8 I BANS Kl ' ' ~Bed 6 I ' -- --- - Rl-9/11 HUMPHRIE- BLAGDENI ' - - - - - - RL-717 SIANUM Fig. 1. The biochronological and palaeontologic succession of the Upper Bajocian of Mai zet. The left column lists the geochronological divisions and the standard (sub)chronozones for the Bajocian Stage of the West Tethyan Subrealm (modified from PAVIA et aL 2013: fig. 7). 136 9th International Congress on the Jurassic System - Abstracts and references therein). Only the latest genus FERNANDEZ-LOPEZ, s. 1988. El Bajociense superior y Paragarantiana is unambiguously recorded, as Bathoniense inferior en Mataporquera (Santander). Ciencias de la Tierra. - Geologfa 11: 73-84. contemporaneous with the sedimentary rock FERNANDEZ-LOPEZ, s. 2000. Ammonite taphocycles in bodies, from the lowermost Parkinsoni Zone carbonate epicontinental platforms. In: HALL, R.L. & Paragarantiana is largely documented in SMITH, P.L. (eds.), Advances in Jurassic Research 2000. the central sector of the Jurassic Anglo-Paris - GeoResearch Forum 6: 293-300. Basin, and on it we concentrated our research. FERNANDEZ-LOPEZ, S.R. 2011. Taphonomic analysis and sequence stratigraphy of the Albarracinites beds Although the Bajocian sections of Calvados (lower Bajocian, Iberian Range, Spain). An example are condensed, repeated taphonomic analyses of shallow condensed section. - Bulletin de la Societe (PAVIA et al. 2013, and references therein) Geologique de France 182: 405-415. allowed aligning successive palaeontological FERNANDEZ-LOPEZ, S.R., PAVIA, G., ERBA, E., GUIOMAR, M, HENRIQUES M.H., LANZA, R., MANGOLD, MORTON, N., units with biochronological meaning (Fig. 1). OLIVERO, D. & TIRABOSCHI, D. 2009. Formal proposal Our study delineates the following conclusions: for the Bathonian GSSP (Middle Jurassic) in the Ravin (1) Paragarantiana derived by a proterogenetic du Bes Section (Bas-Au ran, SE France). - Swiss journal process with paedomorphic result from ofGeosciences 102: 271-295. garantianids, during the transition between the MORTON, N. 2003. Meeting of Jurassic Subcommission Mondello, Sicily. 19th September 2002. - International Garantiana and Parkinsoni zones, displaying Subcommission on Jurassic Stratigraphy, Newsletter the first occurrence in layers of the first record 30: 3-4. of Parkinsonia gr. acris; (2) such a new phyletic PAVIA, G. & MARTIRE, L. 1997. The importance of lineage seems to be driven by a sea-level change taphonomic studies on biochronology: examples from the European Middle Jurassic. - Cuadernos de at the passage between the Garantiana and Geologia Iberica: 153-181 Parkinsoni biochrons; (3) this evolutionary