Uppermost Jurassic to Lower Cretaceous benthic foraminiferal biostratigraphy at ODP Site 765 on the Argo Abyssal Plain.

Benthic foraminifers were studied in 99 samples collected from the lower 200 m of Hole 765C. The studied section ranges from the Tithonian to Aptian, and benthic foraminifers can be subdivided into five assemblages on the basis of faunal diversity and stratigraphic ranges of distinctive species. Compared with deep-water assemblages from Atlantic DSDP sites and Poland, assemblages from the Argo Abyssal Plain display a higher diversity of agglutinated forms, which comprise the autochthonous assemblages. Assemblages at the base of Hole 765C are wholly composed of agglutinated forms, reflecting deposition beneath the carbonate compensation depth (CCD). Most calcareous benthic species are found in turbidite layers, and the presence of an upper Valanginian Praedorothia praehauteriviana Assemblage may indicate deposition at or just below the CCD. The P. praehauteriviana Assemblage from Hole 765C is the temporal equivalent of similar assemblages from DSDP Holes 534A, 416A, 370, 105, and 101 in the Atlantic Ocean and Hole 306 in the Pacific Ocean. Stratigraphic ranges of cosmopolitan agglutinated species at Site 765 generally overlap with their reported ranges in the Atlantic and in the bathyal flysch sequences of the Carpathians; however, several species from Hole 765C have not been previously reported from Uppermost Jurassic to Lower Cretaceous abyssal sediments

Neogene benthic foraminiferal stratigraphy and deep water history of Sites 645, 646, and 647, Baffin Bay and Labrador Sea

Benthic foraminifers were examined from Neogene sediments of Ocean Drilling Program (ODP) Sites 645, 646, and 647 to determine their biostratigraphy and to place constraints on the paleoceanographic history of Baffin Bay, Eirik Ridge, and the Gloria Drift. At Site 645 in Baffin Bay, a Pleistocene Stetsonia assemblage is similar to the modern Baffin Bay assemblage, but an underlying Epistominella takayanagii assemblage has no modern analog. Miocene assemblages below a barren interval display low diversity and consist mainly of agglutinated species. At Site 646 in the Labrador Sea, benthic faunal turnovers occur near important seismic horizons. A Miocene Nuttallides umbonifera assemblage similar to assemblages at other North Atlantic sites occurs below reflector R3. Above reflector R3, a coarse agglutinated assemblage containing more diversified calcareous benthic foraminifers was found that displays affinity to assemblages in the Norwegian-Greenland Sea. The faunal turnover near reflector R3 was interpreted as reflecting the onset (or renewal) of significant Denmark Straits Overflow Water at Site 646 at ~7.5 Ma, Agglutinated species disappear between reflector R2 and the base of the sediment drift, indicating a change in deep-water properties that occurred at ~ 4.7 Ma. This turnover ultimately may be linked to the reopening of the Mediterranean. The beginning of drift sedimentation at the Eirik Ridge is dated at —4.5 Ma. Drift formation ceased at ~2.5 Ma, concomitant with the appearance of ice-rafted sediments. Pleistocene assemblages containing Stetsonia horvathi display affinity to deep assemblages in high-latitude ocean basins. Upper Pliocene and Pleistocene benthic assemblages at Site 647 contain N. umbonifera, which indicates a continued influence of corrosive deep water at the Gloria Drift

Quantitative foraminiferal and palynomorph biostratigraphy of the Paleogene in the southwestern Barents Sea

The stratigraphic distribution of both foraminifera and dinoflagellate cysts is recorded from the Paleocene to Eocene Torsk Formation in 12 petroleum exploration wells drilled in the southwestern Barents Sea. The foraminiferal assemblages are wholly agglutinated, and are referred to outer shelf to middle bathyal environments. A quantitative analysis of biostratigraphic events, mainly last occurrences (first downhole occurrences), is performed by means of the Ranking and Scaling (RASC) program. This procedure combined with conventional stratigraphic treatment has enabled us to establish the most likely order of microfossil events, and to propose a new quantitative zonal scheme for the southwestern Barents Sea. In the studied wells the following six zones and subzones are distinguished (in ascending order): BSP 1, Psmmosphaera fusca – Hyperammina rugosa, late early to early late Paleocene; BSP 2, Spiroplectammina spectabilis early late Paleocene; BSP 3A, Reticulophragmium pauperum, middle late Paleocene; BSP 3B, Haplophragmoides aff. eggeri, latest Paleocene; BSP 4, Spiroplectammina navarroana, earliest Eocene; BSP 5, Reticulophragmium amplectens, early to middle Eocene. Owing to the occurrence of cosmopolitan deep-water agglutinated foraminifera, the new zonal scheme compares well with previous zonations developed for the Paleogene of the mid-Norwegian shelf, the North Sea and Labrador Shelf

Paleogene Benthic Foraminifer Biostratigraphy and Paleoecology at Site 647, Southern Labrador Sea

Benthic foraminifers were examined from the Paleogene of Ocean Drilling Program (ODP) Site 647 and Deep Sea Drilling Program (DSDP) Site 112 in the southern Labrador Sea. The Paleogene sequence of the deep Labrador Sea can be subdivided into seven assemblages, based on the ranges and relative abundance of characteristic taxa. The first occurrences (FOs) and last occurrences (LOs) of important benthic taxa are calibrated to a standard biochronology, by interpolating from our age model for Site 647. The biostratigraphy of Site 647 is used to improve the age estimates of Site 112 cores. Fifteen microfossil events in Site 647 also are found in the sedimentary wedge along the Labrador Margin. A comparison of the probabilistic microfossil sequence from the Labrador Margin with that at Site 647 yields four isochronous benthic foraminifer LOs. Two new species are described from Sites 647 and 112: Hyperammina kennulleri, Kaminski n.sp., and Ammodiscus nagyi Kaminski n.sp. Significant faunal turnovers are observed at the Ypresian/Lutetian and Eocene/Oligocene boundaries. The Ypresian/Lutetian boundary is characterized by a Glomospira-facies and is attributed to a rise in the CCD (carbonate compensation depth) associated with the NP14 lowstand in sea level. The Eocene/Oligocene boundary is delimited by the LO of Spiroplectammina spectabilis and Reticulophragmium amplectens. The change from an Eocene agglutinated assemblage to a predominantly calcareous assemblage in the early Oligocene took place gradually, over a period of about 4 Ma, but the rate of change accelerated near the boundary. This faunal turnover is attributed to changes in the preservation of agglutinated foraminifers, as delicate species disappeared first. Increasingly poorer preservation of agglutinated foraminifers in the late Eocene to earliest Oligocene reflects the first appearance of coal, nutrient-poor deep water in the southern Labrador Sea. The approximately coeval disappearance of agglutinated assemblages along the Labrador Margin was caused by a regional trend from slope to shelf environments, accentuated by the "mid"-Oligocene lowstand in sea level

They are young, and they are many: dating freshwater lineages in unicellular dinophytes

Dinophytes are one of few protist groups that have an extensive fossil record and are therefore appropriate for time estimations. However, insufficient sequence data and strong rate heterogeneity have been hindering to put dinophyte evolution into a time frame until now. Marine‐to‐freshwater transitions within this group are considered geologically old and evolutionarily exceptional due to strong physiological constraints that prevent such processes. Phylogenies based on concatenated rRNA sequences (including 19 new GenBank entries) of two major dinophyte lineages, Gymnodiniaceae and Peridiniales, were carried out using an uncorrelated molecular clock and five calibration points based on fossils. Contrarily to previous assumptions, marine‐to‐freshwater transitions are more frequent in dinophytes (i.e. five marine‐freshwater transitions in Gymnodiniaceae, up to ten but seven strongly supported transitions in Peridiniales), and none of them occurred as early as 140 MYA. Furthermore, most marine‐to‐freshwater transitions, and the followed diversification, took place after the Cretaceous–Paleogene boundary. Not older than 40 MYA, the youngest transitions within Gymnodiniaceae and Peridiniales occurred under the influence of the Eocene climate shift. Our evolutionary scenario indicates a gradual diversification of dinophytes without noticeable impact of catastrophic events, and their freshwater lineages have originated several times independently at different points in time

Kimmeridgian-Tithonian sea-level fluctuations in the Uljanovsk-Saratov Basin (Russian Platform)

Abstract The Uljanovsk-Saratov Basin, located in the southeast of the Russian Platform, presents an intriguing record of the Kimmeridgian-Tithonian sea-level fluctuations. In the Late Jurassic, this basin was a trough within the Interior Russian Sea. The data available from both outcrops and boreholes have permitted outlining a number of lithostratigraphic units and regional hiatuses in the northeastern segment of the Uljanovsk-Saratov Basin, thus permitting a precise reconstruction of transgressions/regressions and deepenings/shallowings. In total, three transgressive-regressive cycles and two deepening pulses have been established. These regionally documented changes were both related in part to global eustatic changes, and they also corresponded in part to the regional sea-level changes in some basins of Western Europe and Northern Africa, but not to those of the Arabian Platform. Differences observed between the global and regional curves as well as rapid Tithonian sea-level oscillations are explained by the influences of tectonic activity. It is hypothesized that the regional Tithonian oxygen depletion might have been a consequence from the rapid flooding of a densely vegetated land

Mediterranean pliocene globorotalia : a biometrical approach

Globorotalia assemblages are studied from Pliocene deposits in Crete (Greece), Italy, the Gulf of Mexico region, and New Zealand. In each assemblage counts and measurements were performed on 10 test characters. The taxonomy is based on (1) biconvex or planoconvex shape, (2) "growth" patterns of size ratios, (3) frequency distributions of discrete characters on the test. Attention is given to the treatment of such quantitative data. The assemblages have been collected in five groups named after typologically defined species: (1) margaritae group, (2) crassaformis group, (3) puncticulata group, (4) bononiensis group, and (5) inflata group. Each group is illustrated by means of a number of scanning electron microscope photographs; some attention is drawn to wall structures. The puncticulata, bononiensis, and inflata groups occur in stratigraphic order; the ranges do not overlap. In Crete an incidental morphological transition was observed between the bononiensis group and the inflata group. In the Mediterranean the association of the margaritae group and the puncticulata group is restricted to the Lower Pliocene (Tabianian). The puncticulata group ranges slightly higher in the stratigraphic column than does the margaritae group. The upper part of the range of the puncticulata group, the total range of the bononiensis group, and the lower part of the range of the inflata group are indicative of the Middle-Upper Pliocene (Piacenzian). The crassaformis group occurs throughout the Pliocene. In the Gulf of Mexico region the puncticulata and bononiensis groups were not observed. The occurrence of the margaritae group and the beginning of the inflata group may be used for stratigraphic correlations. The crassaformis group displays trends, but it may be doubted if the zigzag path of this group is stratigraphically useful, except perhaps on a local scale. Assemblages of a New Zealand G. crassaformis bioseries show no resemblance to our crassaformis group