La biochronologie des Mammifères néogènes d'Europe. L'échelle MN, son application à la succession des faunes du Portugal

Similarly to other organisms, Vertebrates changed during the Cenozoic Era. Mammals are the only ones to change quickly; their well mineralised bones and teeth are often fossilised. They are highly diverse and even isolated teeth can be identified. They are thus a good tool for establishing a biochronological framewoork. Among Mammals, Rodents with a short lifetime evolve more quickly than the large Mammals. In Europe, the first elaborated zonation was investigated by the Regional Committee on Neogene Stratigraphy and issued as the MN Zonation (Mammals Neogene) by Mein, 1976. During the following years, progress in knowledge lead to new charts. The latest one resulted from collective work (de Bruijn et al., 1992). Bîochronology gives relative data; if we desire to have numerical age estimates, we must correlate these results with radiometrie data, marine biostratigraphîcal units or the Geomagnetic Polarity Time Scale. For Europe, these results are summarised by Steininger et al. (1989-1996) and Steininger (1999). After some recents developments on MN Zonation, here is discussed the succession of Neogene small mammals Portuguese localities. Fortunately these localities are in majority inbedded in marine context. Their assigment to MN Zones is proposed and correlations with the spanish Aragonian Scale (Daams el al., 1999) are also suggested. In fact, some differences appear between Portugal and Aragonian assemblages, probably for ecological reasons. Therefore, the MN zonation is always useful for short and long distance biochronological correlations.

The Cenomanian-Turonian transition in West Central Portugal: ammonites and biostratigraphy

The Upper Cenomanian and Lower Turonian ammonite assemblages from the onshore sectors of the West Portuguese Margin are reviewed after new studies on the type section of Figueira da Foz, and correlative sections of Baixo Mondego. The faunal succession shows a strong contribution of vascoceratids and other ammonites with North African and Tethyan affinities. Euomphaloceras septemseriatum (Cragin, 1893), Kamerunoceras douvillei (Pervinquere, 1907), Fagesia catinus (Mantell, 1822), Neoptychites cephalotus (Courtiller, 1860), and Thomasites rollandi (Thomas & Peron, 1889) are for the first time mentioned to Portugal. The Upper Cenomanian is recognised after a set of 3 assemblage zones: Neolobites vibrayeanus z., Euomphaloceras septemseriatum z ., and Pseudaspidoceras pseudonodosoides z. The carbonate succession shows an important unconformity across the Cenomanian-Turonian boundary, associated to subaerial exposure, and to the development of a palaeokarst over Upper Cenomanian units. The first Lower Turonian carbonates are yielded a single but diverse ammonite assemblage of middle Lower Turonian age (Thomasites rollandi z.). This biozone was previously recognised in Central Tunisia by G. Chancellor et al. (1994).

Toarcian GSSP candidate: the Peniche section at Ponta do Trovão

The Peniche section (Ponta do Trovão) in Portugal is presented as potential stratotype (GSSP) for the Pliensbachian/Toarcian boundary. The lithostratigraphic succession is described and the chronostratigraphy, based on ammonite assemblages, is presented; the change in foraminifera assemblages occurs later, only at the base of beds 16 (base of Semicelatum Subzone, Crosbeyi ? Horizon). An extensive bibliographical list of all scientific articles containing specific reference to this stratigraphic boundary, whether from the Lusitanian or Algarve basins, is also presented.

Caracterização mineralógica da sequência sedimentar Ha7 do Cretácico Inferior do Guincho (Bacia Lusitaniana) (*)

Mineralogical assemblages, specially clay mineral assemblages, have been widely used in multidisciplinary stratigraphical studies. This paper presents the results obtained in the study of a Lower Cretaceous depositional sequence from the Lusitanian Basin (Portugal). The Upper Hauterivian – Lower Barremian section at Guincho Fort pertains mostly to the Ha7 3rd order depositional sequence defined by J. REY & al. (2003) and has been studied in a detailed bed-by-bed sampling corresponding to a total of 85 samples. The analysis of the obtained clay mineral assemblages has contributed to the paleoenvironmental and paleogeographical reconstruction of the studied interval and has improved the sequence stratigraphic interpretation and positioning of sequence boundaries and other sequential surfaces (transgressive and flooding surfaces).