Component composition and benthic foraminifera in sediments of ODP Leg 112

Indicators of surface-water productivity and bottom-water oxygenation have been studied for the age interval from the latest Pleistocene to the Holocene at three holes (679D, 680B, and 68IB) located in the center and at the edges of an upwelling cell at approximately 11°S on the Peruvian continental margin. Upwelling activity was maximal at this latitude during d18O Stages 1 (lower part), 3, the upper part of 5, the lower part of 6, and 7, as documented by high diatom abundance. During these time intervals, the bottom water was poorly oxygenated, as documented by low diversity benthic foraminiferal assemblages that are dominated by B. seminuda s.l. Both surface- and bottom-water-circulation patterns appear to have changed rapidly over short time intervals. Due to changes in surface circulation, the intensity of upwelling decreased, thereby decreasing the concentration of nutrients, and reducing the supply of organic matter to the bottom. Radiolarians became more abundant in the surface waters, and the bottom-water environment was less depleted in oxygen, allowing for the establishment of more diverse benthic foraminiferal assemblages. Surface-water productivity was probably minimal during the early part of d18O Stages 5 and 9, as indicated by the increased abundance of planktonic foraminifers and pteropods and their subsequent preservation.

Neogene diatoms of the Japan Sea

A series of excellent upper Miocene through Quaternary diatomaceous sequences recovered at four sites during Leg 127 was examined for diatoms. The diagenetic transition from opal-A to opal-CT is a diachronic horizon from the uppermost part of the Denticulopsis katayamae Zone (8.5 Ma) at Hole 797B to the uppermost part of the Neodenticula kamtschatica Zone (5.73 Ma) at Hole 795A. The diatom zonation of Koizumi (1985) best divides the upper Miocene to Quaternary sequences above the opal-A/opal-CT boundary and also is useful to date carbonate concretions including diatoms below the boundary. Forty diatom datum levels were evaluated biostratigraphically based on the sediment accumulation rate curve, and several isochronous datum levels are newly proposed for the Japan Sea area. A warm-water current did not penetrated into the Japan Sea through the Tsushima strait during the late Miocene and Pliocene time, because subtropical warm-water diatoms are essentially not present in such sediment samples. The occurrences of diatom are cyclic throughout the Quaternary sediments and are affected by eustatic sea level changes.

Miocene radiolarians of the Sulu Sea

Radiolarians are sporadic in sediments collected in the Sulu Sea during ODP Leg 124. Due to the generally poor preservation and low abundance of radiolarians in Sulu Sea sediments, no biostratigraphic datums are well defined, although three radiolarian zones are identified. Most samples containing radiolarians are pelagic or hemipelagic clays with varying proportions of volcanic ash. Detailed analysis of Sulu Sea radiolarians was limited to Miocene successions. Pliocene and Quaternary occurrences of radiolarians were noted but have not been zoned. The late middle Miocene of Sites 769 and 771 is represented by an assemblage of radiolarians (Diartus petterssoni Zone) that is entirely replaced by massive pyrite. This type of preservation develops only under anoxic conditions. The development of widespread anoxia in Sulu Sea waters in the late middle Miocene was probably the result of hydrologic isolation of basin waters, and may be associated with eustatic sea level fall over the silled basin. Upper lower Miocene pelagic and hemipelagic sediments that overlie pyroclastics and basalt flows in the Sulu Sea sites contain moderately to very poorly preserved radiolarians of the Calocycletta costata Zone. A thin unit of marine claystone was recovered from between the thick pyroclastics and basement rocks at Site 768. Radiolarians present in these claystones are rare and very poorly preserved. This radiolarian assemblage probably represents the C. costata Zone, although very poor preservation and low abundance make this interpretation equivocal. The radiolarian zones identified constrain the age of basin formation to late early Miocene or earlier.

Neogene and Quaternary radiolarians from the Izu-Bonin Forearc in the western Pacific Ocean

Radiolarians were recovered from three of the five holes investigated during Leg 125. Relative abundances are estimated at Holes 782A and 784A, where preservation is poor to good. Rare, poorly preserved radiolarians are present in Hole 786A. Seven radiolarian zones are recognized in the latest early- middle Miocene to early Pleistocene of Holes 782A and 784A. These zones are approximately correlated to the zones of Sanfilippo and others published in 1985.

Abiotic characteristics and diatom abundance and biomass in different sectors of the Argentinien Shelf and antartic waters

A large spatial scale study of the diatom species inhabiting waters from the subantarctic (Argentine shelf) to antarctic was made for the first time in order to understand the relationships between these two regions with regard to the fluctuations in diatom abundances in relation with environmental features, their floristic associations and the effect of the Polar Front as a biogeographic barrier. Species-specific diatom abundance, nutrient and chlorophyll-a concentration were assessed from 64 subsurface oceanographic stations carried out during the austral summer 2002, a period characterized by an anomalous sea-ice coverage corresponding to a ''warm year". Significant relationships of both diatom density and biomass with chlorophyll-a (positive) and water temperature (negative) were found for the study area as a whole. Within the Subantarctic region, diatom density and biomass values were more uniform and significantly (in average: 35 and 11 times) lower than those of the Antarctic region, and did not correlate with chlorophyll-a. In antarctic waters, instead, biomass was directly related with chlorophyll-a, thus confirming the important contribution of diatoms to the Antarctic phytoplanktonic stock. A total of 167 taxa were recorded for the entire study area, with Chaetoceros and Thalassiosira being the best represented genera. Species richness was maximum in subantarctic waters (46; Argentine shelf) and minimum in the Antarctic region (21; Antarctic Peninsula), and showed a significant decrease with latitude. Floristic associations were examined both qualitatively (Jaccard Index) and quantitatively (correlation) by cluster analyses and results allowed differentiating a similar number of associations (12 vs. 13, respectively) and two main groups of stations. In the Drake Passage, the former revealed that the main floristic change was found at the Polar Front, while the latter reflected the Southern ACC Front as a main boundary, and yielded a higher number of isolated sites, most of them located next to different Antarctic islands. Such differences are attributed to the high relative density of Fragilariopsis kerguelensis in Argentine shelf and Drake Passage waters and of Porosira glacialis and species of Chaetoceros and Thalasiosira in the Weddell Sea and near the Antarctic Peninsula. From a total of 84 taxa recorded in antarctic waters, only 17 were found exclusively in this region, and the great majority (67) was also present in subantarctic waters but in extremely low (< 1 cell/l) concentrations, probably as a result of expatriation processes via the ACC-Malvinas Current system. The present results were compared with those of previous studies on the Antarctic region with respect to both diatom associations in regular vs. atypically warm years, and the distribution and abundance of some selected planktonic species reported for surface sediments.

Radiolarians at DSDP Leg 58 Holes

Radiolarians were observed at all five sites drilled during DSDP Leg 58. Three sites (442, 443, 444) are south of Japan in the Shikoku Basin. The remaining two sites (445, 446) are east of Okinawa, in the Daito Ridge and Basin areas. The observations made on radiolarians during Leg 58 are understood best by considering these two areas separately. The basement ages, preservation, diagenesis, and paleoecology are similar within each area, but different between the two areas. The radiolarian zones of Riedel and Sanfilippo (1978) were used to determine the sediment age. Because of the mixed nature of the fauna, there was an opportunity to test the tropical zonation in middlelatitude sediments. A middle- to high-latitude biostratigraphy for the Pliocene and Pleistocene has been formulated (Hays, 1970; Kling, 1973; Foreman, 1975), but there is no Miocene radiolarian zonation for these latitudes. The tropical elements of the present fauna are sufficient to use the low-latitude zonation, although there is a loss of resolution in the Pleistocene. Because of poor preservation, zone boundaries are indistinct in much of the cored sediment. Determination of abundance in any sample is always subjective and varies among investigators. This work was in its final stages at the publication of Westberg and Riedel (1978), and the guidelines outlined therein are not closely followed. The abundances recorded in Tables 1 through 5 are based on strewn slides which were searched entirely if an individual of a species was found, or for 8 to 10 minutes if the species was not found.

Presence-absence species/sample matrix for the measured sections at the area of Maghara, North Sinai, Egypt

As age-diagnostic fossils are rare in the Middle to Upper Jurassic sedimentary succession of Gebel Maghara, North Sinai, Egypt, and in order to ensure maximal stratigraphic resolution, chronostratigraphic boundaries were determined based on quantitative biostratigraphy. A data matrix comprising 231 macrofaunal taxa in 93 samples from four sections has been processed with the Unitary Association (UA) Method. This led to construction of a sequence of 29 UAs (maximal sets of actually or virtually coexisting taxa), which have been grouped into 14 laterally reproducible association zones. The UA method allowed an in-depth analysis of the stratigraphically conflicting taxa, enabled the biostratigraphic subdivision of the studied interval, and also provided stratigraphic correlation among the measured sections and with the Tethyan ammonite zones.