Michèle Caron

Evolution of early planktic foraminifers

Abstract The evolution of Mesozoic species of planktic foraminifers, particularly the succession of their morphotypes and the variation in their diversity and their abundance, is shown to be related to the adaptation of evolutionary strategy to fluctuations in the oceanic environment. During periods of stress (“oligotaxic period”) the more primitive species tend to invade the oceanic surface waters by means of r-selection. During stable “polytaxic” conditions, the same species engage in an adaptive radiation colonizing progressively deeper water through K-selection. The succession of morphotypes from the middle Jurassic to the end of the Cretaceous is compared with living planktic foraminifers and related to the biogeographic (cold arctic, warm equatorial faunas) and bathymetric distribution. A general model for the evolution of early planktic foraminifers is made with reference to the preceding observations, and in relation to the pattern of variation of trophic resources.

Turonian Radiolarians from Karnezeika, Argolis Peninsula, Peloponnesus (Greece)

Near Karnezeika a roughly 140 m thick Upper Cretaceous section consists of interbedded pelagic limestones, cherts and coarse polymict breccias including ophiolites and shallow water limestones. At the base, pink pelagic limestones rest on deeply altered and fractured Lower Jurassic Pantokrator Limestone. This first pelagic facies is dated as middle Turonian, based on planktonic Foraminifera. Over 100 m of coarse ophiolite-carbonate breccias, interpreted as a channel or canyon fill in a pelagic environment, document the erosion of the Late Jurassic nappe edifice along the Cretaceous Pelagonian margin. Above these breccias, we mesured 16 m of principally pink and red pelagic limestones and radiolarian cherts, in which we recovered well-preserved radiolarians discussed here. In this interval, the presence of planktonic Foraminfera allows to state a late Turonian to Coniacian age. More than 40 radiolarian species are described and figured in this work. The radiolarian chronostratigraphy established by 10 different authors in 11 publications was compared for this study and used to establish radiolarian ranges. This exercise shows major discrepancies between authors for the radiolarian ranges of the studied assemblage. Nevertheless, a Turonian age can be stated based on a synthesis of cited radiolarian ranges. This age is consistent with the age based on planktonic foraminifera. In combining the ages of both Radiolaria and planktonic Foraminifera, the studied samples can be restricted to the late Turonian. However, the discrepancies of published radiolarian ranges call for an urgent, major revision of the Late Cretaceous radiolarian biochronology. The integration of planktonic foraminifera with radiolarians may greatly enhance biochronologic resolution in sections where both groups occur.

Remarks on the identification of the Albian/Cenomanian boundary and taxonomic clarification of the planktonic foraminifera index species globotruncanoides, brotzeni and tehamaensis

The planktonic foraminifera assemblage across the Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage defined at Mont Risou (Haute-Alpes in France) is here restudied to clarify the identification and stratigraphic distribution of Thalmanninella globotruncanoides ( = Rotalipora globotruncanoides Sigal, 1948) and Pseudothalmanninella tehamaensis ( = Rotalipora tehamaensis Marianos & Zingula, 1966) whose appearance levels are primary and secondary criteria for placing the Albian/Cenomanian boundary. Since the ratification of the GSSP in 2002, the identification of the foraminifera index species across the Albian/Cenomanian boundary has been reported to be sometimes difficult either because of their rarity or uncertainty in the taxonomic identifications. We discuss the taxonomic status of Thalmanninella brotzeni Sigal 1948, a species regarded for a long time to be a junior synonym of Th. globotruncanoides , through images of Sigal9s type materials deposited at the Musee National d’Histoire Naturelle (Paris), and elucidate the taxonomically important characters that enable unequivocal identification of Th. brotzeni, Th. globotruncanoides and Ps. tehamaensis . Planktonic foraminifera marker species from Mont Risou are compared with well-preserved specimens from Blake Nose Plateau (ODP 171B, North Western Atlantic Ocean) to verify the reliability and stratigraphic distribution of these marker taxa outside the Mediterranean Tethyan area.

Calibrage par ammonites des zones à foraminifères planctoniques de l'Albien supérieur du bassin du Sud-Est de la France

The Upper Albian series of the South-East Basin in France is certainly the most continuous and the thickest series of the Upper Albian age in the whole of western Europe. Numerous ammonites, characteristic of the dispar zone, are found in the subticinensis zone. This fact profoundly modifies the stratigraphic and regional sedimentological framework as well as comparative biozonation between planktonic foraminifera and ammonites, which was initially established in this basin (Moullade, 1966; Sigal, 1977).

NEW DESCRIPTION OF THE ROTALIPORID SPECIES BROTZENI AND GLOBOTRUNCANOIDES SIGAL, 1948 BASED ON RE-EXAMINATION OF TYPE MATERIAL

This short notes deals with the re-description and re-illustration of the holotypes of Thalmanninella brotzeni Sigal, 1948 and Rotalipora globotruncanoides Sigal, 1948, from Sidi Aissa, Algeria, middle Cenomanian. Both species are attributed to the genus Thalmanninella .