Verteilungsmuster der Mesofauna im hohen Ober-Hauterive Nordwestdeutschlands

The vertical distribution pattem of mesofaunal elements is described from clay-marl bedding rhythms from the Frielingen section (Hannover, NW Germany), which exposes latest Hau- terivian sediments (early Cretaceous). Some mesofaunal groups show a correlation with the pale- dark bedding rhythms. The pale, marly beds are chracterised by bryozoans. In addition remnants of crinoids, echinoids, asteroids, ophiuroids and holothuroids are more common in pale layers than in dark ones. Converseley, the relative abundance of serpulids, fish remains, bivalves and gastropods shows no relationship to the bedding rhythms.Aus dem Tagesaufschluß Frielingen (Hannover, NW-Deutschland), in dem rhythmisch gebankte Ton-/Mergelsteinwechselfolgen des höheren Hauterive (Unterkreide) anstehen, wird die Vertikalverteilung der Mesofauna beschrieben. Es wird eine Abhängigkeit einzelner Elemente der Mesofauna von der Hell-Dunkelbankung nachgewiesen. Für die hellen, mergeligen Bänke sind Bryozoen typisch. Weiterhin treten Crinoiden-, Echiniden-, Asteroiden-, Ophiuren- und Ho- lothurienreste stets häufiger in den hellen Bänken auf. Serpuliden, Fische, Krebse, Bivalven und Gastropoden zeigen andererseits keine Beziehung zur Hell-Dunkelbankung

Biometry of Upper Cretaceous (Cenomanian-Maastrichtian) coccoliths - a record of long-term stability and interspecies size shifts

Biometric measurements of Mesozoic coccoliths (coccolith length and width) have been used in short-term biostratigraphic, taxonomic and palaeoecologic studies, but until now, not over longer time scales. Here, we present a long time-series study (∼ 30 million years) for the Upper Cretaceous, which aims to identify broad trends in coccolith size and to understand the factors governing coccolith size change over long time scales. We have generated biometric data for the dominant Upper Cretaceous coccolith groups, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa and Watznaueria, from 36 Cenomanian–Maastrichtian (100.5–66 Ma) samples from Goban Spur in the northeast Atlantic (DSDP Site 549). These data show that the coccolith sizes within Prediscosphaera, Retecapsa and Watznaueria were relatively stable through the Late Cretaceous, with mean size variation less than 0.7 μm. Within the Broinsonia/Arkhangelskiella group there was more pronounced variation, with a mean size increase from ∼ 6 μm in the Cenomanian to ∼ 10 μm in the Campanian. This significant change in mean size was largely driven by evolutionary turnover (species origination and extinctions), and, in particular, the appearance of larger species/subspecies (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) in the early Campanian, replacing smaller species, such as Broinsonia signata and Broinsonia enormis. Shorter-term size fluctuations within Broinsonia/Arkhangelskiella, observed across the Late Cenomanian–Turonian and Late Campanian–Maastrichtian intervals, may, however, reflect changing palaeoenvironmental conditions, such as sea surface temperature and nutrient availability. / Les dimensions des coccolithes du Mésozoïque (longueur et largeur) ont été utilisées dans des études biostratigraphiques, taxonomiques et paléoécologiques sur le court-terme mais jusqu’à présent, jamais sur le long-terme. Ici, nous présentons l’étude d’une série chronologique à échelle de temps longue (∼ 30 millions d’années) du Crétacé supérieur, visant à identifier les tendances générales de leur taille et de comprendre les facteurs gouvernant les changements de taille des coccolithes sur une échelle de temps longue. Nous avons généré des données biométriques pour les groupes de coccolithes dominants au Crétacé supérieur, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa et Watznaueria, sur 36 échantillons du Cénomanien–Maastrichtien (100,5–66 Ma) provenant du Goban Spur dans l’Atlantique Nord-Est (DSDP Site 549). Ces données montrent que la taille des coccolithes appartenant aux groupes Prediscosphaera, Retecapsa et Watznaueria fut relativement stable durant tout le Crétacé supérieur, avec une variation de la taille moyenne inférieure à 0,7 μm. Au sein du groupe Broinsonia/Arkhangelskiella, les variations furent plus prononcées, avec une augmentation de la taille moyenne de ∼ 6 μm au Cénomanien jusqu’à ∼ 10 μm au Campanien. Ce changement significatif de la taille moyenne fut largement dû aux processus évolutifs (spéciations et extinctions), et en particulier à l’apparition d’espèces/sous-espèces plus larges (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) au Campanien inférieur, remplaçant des espèces plus petites, telles que Broinsonia signata et Broinsonia enormis. Cependant, les fluctuations à court-terme au sein du groupe Broinsonia/Arkhangelskiella, observées aux transitions Cénomanien–Turonien et Campanien–Maastrichtien, pourraient refléter un changement des conditions paléoenvironnementales, telles que la température superficielle des eaux océaniques et la disponibilité en nutriment

Early Cretaceous biogeographic and oceanographic synthesis of Leg 123 (off Northwestern Australia)

Biogeographic observations made by Leg 123 shipboard paleontologists for Lower Cretaceous nannofossils, foraminifers, radiolarians, belemnites, and inoceramids are combined in this chapter to evaluate the paleoceanographic history of the northwestern Australian margin and adjacent basins. Each fossil group is characterized at specific intervals of Cretaceous time and compared with data from Tethyan and Southern Hemisphere high-latitude localities. Special attention is given to the biogeographic observations made for the Falkland Plateau (DSDP Legs 36 and 71) and the Weddell Sea (ODP Leg 113). Both areas have yielded valuable Lower Cretaceous fossil records of the circumantarctic high latitudes. In general, the Neocomian fossil record from DSDP and ODP sites off northwestern Australia has important southern high-latitude affinities and weak Tethyan influence. The same is true for the pelagic lithofacies: radiolarian chert and/or nannofossil limestone, dominant in the Tethyan Lower Cretaceous, are minor lithologies in the Exmouth-Argo sites. These observations, together with the young age of the Argo crust and plate tectonic considerations, suggest that the Argo Basin was not part of the Tethys Realm. The biogeography of the Neocomian radiolarian and nannofossil assemblages suggests opening of a seaway during the Berriasian that connected the circumantarctic area with the Argo Basin, which resulted in the influx of southern high-latitude waters. This conclusion constrains the initial fit and break-up history of Gondwana. Our results favor the loose fit of the western Australian margin with southeast India by Ricou et al. (1990), which accounts for a deeper water connection with the Weddell-Mozambique basins via drowned marginal plateaus as early as the Berriasian. In fits of the du Toit-type (1937), India would remain attached to Antarctica, at least until the late Valanginian, making such a connection impossible. After the Barremian, increasing Tethyan influence is evident in all fossil groups, although southern high-latitude taxa are still present. Biogeographic domains, such as the southern extension of Nannoconus and Ticinella suggest paleolatitudes of about 50°S for the Exmouth-Argo area. Alternatively, if paleolatitudes of about 35° are accepted, these biogeographic limits were displaced northward at least 15° along Australia in comparison to the southern Atlantic. In this case, the proto-circumantarctic current was deflected northward into an eastern boundary current off Australia and carried circumantarctic cold water into the middle latitudes. Late Aptian/early Albian time is characterized by mixing of Tethyan and southern faunal elements and a significant gradient in Albian surface-water temperatures over 10° latitude along the Australian margin, as indicated by planktonic foraminifers. Both phenomena may be indicative of convergence of temperate and antarctic waters near the Australian margin. High fertility conditions, reflected by radiolarian cherts, are suggestive of coastal upwelling during that time

Stable isotope (δ18O and δ13C) sclerochronology of Callovian (Middle Jurassic) bivalves (Gryphaea (Bilobissa) dilobotes) and belemnites (Cylindroteuthis puzosiana) from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England): Evidence of palaeoclimate, water depth and belemnite behaviour

Incremental δ18O and δ13C signals were obtained from three well-preserved specimens of Cylindroteuthis puzosiana and from three well-preserved specimens of Gryphaea (Bilobissa) dilobotes from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England). Through-ontogeny (sclerochronological) δ18O data from G. (B.) dilobotes appear to faithfully record seasonal temperature variations in benthic Callovian waters of the study area, which range from c. 14 °C to c. 17 °C (arithmetic mean temperature c. 15 °C). Water depth is estimated to have been in the region of c. 50 m, based upon comparisons between these data, previously published non-incremental sea surface δ18O values, and a modern analogue situation. Productivity in Callovian waters was comparable with that in modern seas, based upon δ13C data from G. (B.)dilobotes, with 13C depletion occurring during warmer periods, possibly related to an interaction between plankton blooms and intra-annual variations in mixing across a thermocline. Incremental δ18O data from C.puzosiana provide temperature minima of c.11 °C for all specimens but with maxima varying between c.14 °C and c.16 °C for different individuals (arithmetic mean values c. 13 °C). Temperatures for late ontogeny, when the C. puzosiana individuals must have been living close to the study site and hence the analysed specimens of G. (B.) dilobotes, are closely comparable to those indicated by the latter. However, for significant portions of ontogeny C. puzosiana experienced temperatures between c. 2 °C and c. 3 °C cooler than the winter minimum as recorded by co-occurring G. (B.) dilobotes. Comparisons with modern seas suggest that descent to a depth of c. 1000 m would be necessary to explain such cool minimum temperatures. This can be discounted due to the lack of deep waters locally and due to estimates of the depth tolerance of belemnites. The most likely cause of cool δ18O signals from C. puzosiana is a cosmopolitan lifestyle including migration to more northerly latitudes. Mean δ13C values from C. puzosiana are comparable with those from G.(B.)dilobotes. However, the incrementally acquired data are highly variable and probably influenced by metabolic effects.The probable identification of migratory behaviour in C. puzosiana calls into question the reliability of some belemnite species as place-specific palaeoenvironmental archives and highlights the benefits of adopting a sclerochronological approach

Filling the Gap: New Precise Early Cretaceous Radioisotopic Ages from the Andes

Two tuffs in the Lower Cretaceous Agrio Formation, Neuquén Basin, provided U–Pb zircon radioisotopic ages of 129.09 ± 0.16 Ma and 127.42 ± 0.15 Ma. Both horizons are well constrained biostratigraphically by ammonites and nannofossils and can be correlated with the ‘standard’ sequence of the Mediterranean Province. The lower horizon is very close to the base of the Upper Hauterivian and the upper horizon to the Hauterivian/Barremian boundary, indicating that the former lies at c. 129.5 Ma and the latter at c. 127 Ma. These new radioisotopic ages fill a gap of over 8 million years in the numerical calibration of the current global Early Cretaceous geological time scale

Bio- and chemostratigraphy of the Posidonia Shale: a new database for the Toarcian Oceanic Anoxic Event from northern Germany

We present calcareous nannofossil biostratigraphy, calcium carbonate and organic carbon isotope data of two cores drilled in the North German Basin (northern Germany) covering the upper part of the Amaltheenton-Formation (Fm) (upper Pliensbachian) and the Posidonienschiefer-Fm. (Toarcian). Fourteen bioevents spanning the latest Pliensbachian to late Toarcian time interval allowed the identification of the NJ5, NJ6 and NJ7 Zones of the Boreal biozonation. The early Toarcian Oceanic Anoxic Event (T-OAE), identified by the organic carbon isotopic excursion within the Posidonienschiefer-Fm., is constrained by the first occurrences (FOs) of Carinolithus superbus crassus and Diductius constans at the onset of the δ13C anomaly. The last occurrences (LOs) of the nannofossil species Crepidolithus granulatus, Parhabdolithus liasicus distinctus, Biscutum finchii and Biscutum grande are detected within the δ13C isotopic anomaly. The new biostratigraphic data acquired in the North German Basin are compared to data from sections at higher and lower latitudes to evaluate event reproducibility relative to the δ13Corg isotope curve. The FO of C. superbus crassus is an excellent datum to constrain the onset of the T-OAE at supraregional – global scale. Our finding indicates further nannofossil biohorizons within the T-OAE that might be useful at regional scale

Cenomanian/Turonian benthic foraminiferal faunas of the Demerara Rise depth transect (ODP Leg 207)

Abstrac

Die Unterkreide-Aufschlüsse (Valangin-Alb) im Raum Hannover-Braunschweig

14 outcrops of marine Lower Cretaceous (Valanginian-Albian) Sediments are described from the Hannover-Braunschweig area. The bio- and lithostratigraphy, flora, fauna, sedimentology, environments of deposition and geological Situation of these exposures arediscussed and illustrated. Where possible the sections were measured and examined with respect to their biostratigraphy. Finally an ecostratigraphical subdivision of the faunal assemblages is proposed for some of the sections from which conclusions are drawn regarding the conditions and environ- ment of Sedimentation.Ausgehend von 14 Tagesaufschlüssen aus dem Raum Hannover- Braunschweig, in denen Sedimente der marinen Unterkreide (Valangin-Alb) anstehen, werden Bio-Lithostratigraphie, Flora, Fauna, Sedimentologie, Ablagerungsmilieu und regionalgeologische Position dieser Aufschlüsse beschrieben und illustriert. Soweit diese noch zugänglich waren, wurden sie einer im wesentlichen biostratigraphisch orientierten Geländeaufnahme unterzogen. Weiterhin wird der Versuch unternommen, für einige dieser Profile eine ökostratigraphische Gliederung in Faunenabschnitte vorzunehmen, die ihrerseits Rückschlüsse auf die Sedimentationsbedingungen und das Milieu zulassen