Range chart of nannofossils in profile Serre Chaitieu, SE France

Range chart of nannofossils in profile Serre Chaitieu, SE France

Calcareous nannofossils of ODP Sites 149-897 and 149-901

Mesozoic calcareous nannofossil assemblages recovered during Ocean Drilling Program Leg 149 from the Iberia Abyssal Plain off the coast of Portugal were examined to determine the age of the rifting processes that affected the western Iberia Margin. Dark carbonaceous claystones (black shales) recovered from Site 901 contain highly diverse and abundant Tithonian calcareous nannofossil assemblages. Careful examination and documentation of this material has extended the ranges of numerous Jurassic and Cretaceous species and detailed a significant Late Jurassic assemblage turnover observed in the calcareous nannofossil record. The Lower Cretaceous sequence consists of intervals of serpentinized peridotite intercalated between various breccias and dark claystones. With the exception of a few samples, calcareous nannofossils are few and moderately preserved. The age of nannofossils within these varied sedimentary lithologies ranges from the late Barremian to the late Aptian. Eight new species are described: Ansulasphaera covingtonii, Clepsilithus meniscus, Conusphaera sinespina, Crepidolithus parvulus, Diazomatholithus galicianus, Percivalia arata, Rotelapillus pleoseptatus, and Tranolithus incus. Also proposed are five new combinations.

Absolute abundances of benthic foraminifers and stable isotopes from the Alvin dives 3709-3712

The presence of gas hydrates on the Blake Ridge diapir, northeastern Atlantic Ocean, offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late Holocene. Three push cores, covering a time span of ~ 1000 yrs, were retrieved from three distinct microhabitats at the top of the diapir at a water depth of ~ 2150 m: (i) sediments away from seepage (control core), (ii) sediments overlain by clusters of methanotrophic and thiotrophic bivalves, and (iii) chemoautotrophic microbial mats. The foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity, coupled with a near-absence of agglutinated species. However, an opportunistic population rise in CH4- or H2S-tolerant calcareous species (e.g., Globocassidulina subglobosa and Cassidulina laevigata) that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there. The delta18O and delta13C values of three species of benthic foraminifera - Gyroidinoides laevigatus, Globocassidulina subglobosa, and Uvigerina peregrina - and the planktonic species Globorotalia menardii were acquired from all three cores. The benthic species from methane seeps yield delta13C values of 0.1 to - 4.2 (per mil VPDB), that are distinctly more 13C-depleted relative to the delta13C of 0.4 to - 1.0 (per mil VPDB) at the control (off seep) site. The species from a mussel-bed site exhibit more negative delta13C values than those from microbial mats, possibly reflecting different food sources and higher rate of anaerobic oxidation of methane. The positive delta13C values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13C depletions. Hence the probable cause of negative delta13C of benthic foraminifera is primary calcification from Dissolved Inorganic Carbon (DIC) containing mixed carbon fractions from (a) highly 13C-depleted, microbially-oxidized methane and (b) a seawater source.

(Table 1) Distribution of Lower Cretaceous calcareous nannofossils at DSDP Hole 93-603B

Upper Berriasian to lower Aptian calcareous nannofossil assemblages have been studied from a siliciclastic deep-sea fan complex and a subjacent limestone sequence drilled beneath the lower continental rise in the western North American Basin, 270 miles (435 km) off Cape Hatteras, North Carolina (USA). Sharp lithologic facies changes and reworking by turbidites complicate the biostratigraphic interpretation, but provide an excellent opportunity to better distinguish "nearshore" from open-ocean nannofossil species, and to investigate the introduction of neritic taxa into the deep-see environment, a phenomenon that appears to have been widespread within the circum-North Atlantic during Neocomian times. Well-preserved assemblages in dark, carbonaceous claystones were probably displaced from the oxygen minimum zone along the upper slope or outer shelf. Neritic, continental margin species prevalent in this facies include the holococcolith Zebrashapka vanhintei n. gen., n. sp., Lithraphidites alatus magnus n. spp., Pickelhaube furtiva n. gen., and a host of nannoconids and micrantholiths. A qualitative evaluation of widely used guide fossils suggests that the triad of proposed markers for the base of Roth's Zone NC3 make their first appearances in the following (ascending) order: Diadorhombus rectus, TUbodiscus verenae, Calcicalathina oblongata. Of these, we chose the nominative species for the zone, T. verenae, to mark its base and to approximate the Berriasian/Valangian boundary. Cyclagelosphaera deflandrei is strongly affected by diagenesis and is therefore not a reliable index species for the base of Zone NC4 near the Valanginian/Hauterivian boundary (the last occurrence of T. verenae is also not suitable there). In addition, Lithraphidites bollii, a form apparently confined to the low latitudes of the Tethyan region, was absent at the more temperate Site 603 and not available as a subzonal marker for the upper Hautervian-lower Barremian (mid-NC4 and mid-NC5, respectively). Cruciellipsis cuvillieri, however, provides a reliable datum just below the Hauterivian/Barremian boundary (base of NC5), despite the potential for reworking in this section. Nannoconids tend to be reworked in this section, and do not provide trustworthy forms to mark the Barremian/Aptian boundary (base of NC6). Hayesites irregularis n. comb, probably does provide a useful first appearance datum within the lower Aptian, if it is not confused with a more birefringent and globular form, Rucinolithus terebrodentarius n. sp. Rhagodiscus angustus is mimicked by a similar form (Zeughrabdotusl pseudoangustus n. sp.), which apparently ranges down to the Hauterivian, thus Lithastrinus floralis provides a more useful first appearance datum for the base of the middle-upper Aptian Rhagodiscus angustus Zone (NC7). Aside from the new taxa mentioned above, the following are also described: Cretarhabdusl delicatus n. sp. and Cyclagelosphaera jiangii n. sp.

Cretaceous nannofossils from the Northwest African Margin

Deep Sea Drilling Project Leg 79 recovered Cretaceous nannofossils at two localities, Sites 545 and 547. Species diversity of the Cretaceous coccoliths is high, and the assemblages range in age from early Valanginian-early Hauterivian to latest Maestrichtian. Site 545 and portions of Site 547 can be combined to form a composite section ranging from the upper Aptian-lower Albian to the middle to upper Cenomanian. As defined by nannofossil events, this section represents a complete record of sedimentary deposition. The interval appears to be the most extensive and complete Cretaceous section yet drilled off the Northwest African margin. The Campanian and Maestrichtian sediments found at Site 547 (Hole 547A) are the youngest Cretaceous strata found on the Northwest African margin. Like the middle Cretaceous sections, the uppermost Maestrichtian of this interval also represents a complete record of sedimentation.