Upper Cretaceous of the Barranca (Navarra, northern Spain); integrated 1itho-, bioand event stratigraphy. Part I: Cenomanian through Santonian

Abstract

Fossiliferous Upper Cenomanian to Lower Maastrichtian strata in Navarra, northern Spain, particularly in the eastern Barranca, were investigated in terms of litostratigraphy, macrofossil biostratigraphy and event stratigraphy. Extensive bed-by bed-collections of ammonites, inoceramids, and echinoids allow the establishment of combined standard zonal schemes of inter-regional significance. Data on geochronological boundaries, macrofossil distribution, the succession of events and the inter-relations between bioevents, eustato-events and tectonic movements in northern Spain are presented. The Upper Cenomanian - Turonian successions of the Barranca sections (Arardi, Izurdiaga, Satrustegui) and of the Estella area (Ganuza, Ollogoyen), differ considerably in both lithofacies and thickness and periodically, in faunal composition, as a result of their palaeogeographical positions within an stable outer shelf and an unstable mit-shelf, respectively. The Ganuza/Ollogoyen standard section is revised. In the context of the established event stratigraphical scheme, discrepancies in previously applied ammonite zonation are pointed out and discussed in terms of their regional relevance. The expanded and relatively complete Turonian of the Estella area is subdivided into an unnamed interval devoid of ammonites (Upper Cenomanian Metoicoceras geslinianum Zone to the mid-Lower Turonian), six ammonite zones and an inoceramid/ammonite assemblage zone. The upper Lower Turonian Kamerunoceras ganuzai/Mammites nodosoides Zone is succeeded by the Middle Turonian zones of K. turoniense, Romaniceras kallesi, R. ornatissimum and R. deverianum; and the Upper Turonian Subprionocyclus neptuni and Cremnoceramus waltersdorfensis/ Prionocyclus germari zones. The Lower Turonian zonal scheme given by WIEDMANN (1979a) for the Estella area is shown to be impracticable, and neither Lower Turonian Choffaticeras quaasi Zone sensu SANTAMARIA (1992) nor a Watinoceras coloradoense Zone sensu LAMOLDA & al. (1989) can be recognized. On the other hand, the refined French Middle Turonian ammonite zonation of AMEDRO & al. (1982) is readily applicable, while the application of a Collignoniceras woollgari Zone is hardly possible. The base of the Middle Turonian has been placed at the FAD of K. turoniense, at a level stratigraphically lower (upper Lower Turonian) than the one recently accepted. C. woollgari is rare and appears no lower than the ornatissimum Zone. The base of the Upper Turonian is placed at the FAD of Subprionocyclus neptuni. Romaniceras deverianum appears considerably lower than the former, but has its main occurrence in the neptuni Zone, ranging up to overlap with Prionocyclus germari. The Barranca succession is condensed and includes hiati from the Upper Cenomanian Neocardioceras juddii Zone to the upper ganuzai/ nodosoides Zone; between the Middle Turonian kallesi and ornatissimum zones; and in the lower Upper Turonian neptuni Zone. Twelve bio-events that are significant for regional and inter-regional correlations are differentiated and dated: the Mytiloides kossmati, ganuzai, reveliereanus, turoniense/hercynicus, kallesi/ornatissimum, Scaphites geinitzii, Subprionocyclus I, Micraster ex gr. normanniaecortestudinarium, Subprionocyclus II events. Most of these events are time-equivalents of events already recognised by ERNST & al. (1983) in Germany. The biostratigraphic framework permits a dating and correlation of the major tectono-sedimentary and eustato-events, namely the Cenomanian-Turonian Boundary Event (CTBE), the Middle Turonian Event (MTE) and Lower Upper Turonian Event (LUTE). The calcareous Coniacian - Santonian succession of the eastern Barranca (Izurdiaga, Ecay and Zuazu sections), is divided into Lower Izurdiaga, Zuazu and Upper Izurdiaga formations, and into numerous component members. The succession is rich in echinoids, and is biostratigraphically important because of the co-occurrence of inoceramids and ammonites. The Coniacian ammonite assemblages show affinities to those of the French type region and to the largely endemic ones of the Spanish standard sections in Burgos. The data obtained permit a confident correlation of the biostratigraphic frameworks of these two areas for the first time. In contrast to the widespread basal Coniacian hiatus, the Barranca succession at this level is locally relatively complete. The lower Coniacian Cremnoceramus rotundatus, Forresteria petrocoriensis and Peroniceras subtricarinatum zones, the Middle Coniacian Gauthiericeras margae Zone and the lower Upper Coniacian Protexanites bourgeoisi Zone are recognized. In marginal sections, the bourgeoisi Zone is followed by an hiatus which comprises the late Upper Coniacian Magadiceramus subquadratus and the Lower Santonian Cladoceramus undulatoplicatus inoceramid zones recognized in the continuous section of the western Barranca. By means of ammonites, the Santonian at Olazagutia is divided into an unnamed interval devoid of ammonites; the middle Coniacian Texanites quiquenodosus and the Upper Santonian Jouaniceras hispanicum/Scalarites cingulatum Zone. This scheme has affinities with the zonation applied by KENNEDY & al. (1995) in the Corbieres, France. In addition to a sequence of regionally important events and marker-beds, some events, namely the Didymotis II, Micraster ex gr. cortestudinarium and Cladoceramus undulatoplicatus events, are of inter-basinal importance.