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.

Benthic foraminifera in surface sediments of the Persian Gulf

During "Meteor"cruise 1965 the author collected 134 samples of surface sediments from the Iranian part of the Persian Gulf. Benthic Foraminifera populations have been analysed for determining their depth zonation. These data are supposed to allow detailed depth interpretation of Pleistocene sediments found in cores. In addition, the ecological information might be usefull to reconstruct the depositional environment of fossil sediments in similar shallow epicontinental seas. The investigation is published in two parts: the present part 1 contains the catalogue of species with short discussions of taxonomic problems, notes on the distribution within the Persian Gulf and 11 plates, partly with scanning electron micrographs. The results of the statistical analysis are given in data tables which include number of species, percentages of 2 (and 5) ranked species, standing crop and foraminiferal numbers. The author used "species groups" to avoid ambiguities with species requiring additional taxonomic studies. However, species numbers within these units are estimated to yield applicable diversity information. - A total of 52 species and 7 "species groups" were separated, 2 new species were described.

Early Cretaceous planktonic foraminifera from the Tethys

Early Cretaceous planktonic foraminiferal assemblages include rare planispiral and pseudoplanispiral morphotypes with elongate chambers that BouDagher-Fadel et al. assigned to Schackoina or accommodated in the new genus Claviblowiella. New findings of well-preserved planktonic foraminiferal faunas from the Lesches en Diois (SE France) section, the Cismon core (NE Italy), the Calabianca (NW Sicily) section and the Upper Aptian of Deep Sea Drilling Project (DSDP) Site 545 drilled off Morocco, have allowed a better understanding of the morphological features of these rare, unevenly distributed taxa. Our data demonstrate that each small planispiral species with globular chambers has a corresponding "clavate" morphotype which (as the "normal" forms) exhibits a smooth, finely perforate wall. Consequently, the latter have been assigned here to the genus Globigerinelloides and treated as subspecies of the "non-clavate" taxa. The (clavate) subspecies belonging to the genus Globigerinelloides here retained are G. duboisi sigali Longoria, G. maridalensis elongatus subsp. nov., G. blowi lobatus subsp. nov. and G. paragottisi clavatus subsp. nov., while Globigerinelloides minai Obregòn de la Parra is not retained. In addition, a new genus, Pseudoschackoina, type species Planomalina saundersi Bolli (senior synonym of Hastigerinoides cepedai Obregòn de la Parra, has been formalised for individuals possessing elongate, pointed, laterally compressed chambers, bearing tubulospines arranged on a pseudoplanispiral (dysaxial) coiling mode. Stratigraphically, in the sections studied the first taxon to appear is Pseudoschackoina saundersi, in the uppermost part of the Selli Level (=OAE1a), immediately followed, just above the OAE1a, by all the "clavate" globigerinelloidids. Regarding the last occurrences, Pseudoschackoina saundersi and G. maridalensis elongatus disappear in the lower part of the Globigerinelloides algerianus Zone, Globigerinelloides paragottisi clavatus at the top of the same zone, while Globigerinelloides blowi lobatus and G. duboisi sigali range up to the lower part of the Ticinella bejaouaensis Zone.

Rhabdocline weirii; Hemiphacidiaceae

Rhabdocline weirii subsp. oblonga subsp. oblonga A.K.Parker & J.Reid, determined by G. D. Darker