Palynology and dinoflagellate counts of surface sediments, and sea surface conditions, of sites in the North Pacific

Palynological analyses were performed on 53 surface sediment samples from the North Pacific Ocean, including the Bering and Okhotsk Seas (37-64°N, 144°E-148°W), in order to document the relationships between the dinocyst distribution and sea-surface conditions (temperatures, salinities, primary productivity and sea-ice cover). Samples are characterized by concentrations ranging from 18 to 143816 cysts/cm**3 and the occurrence of 32 species. A canonical correspondence analysis (CCA) was carried out to determine the relationship between environmental variables and the distribution of dinocyst taxa. The first and second axes represent, respectively, 47% and 17.8% of the canonical variance. Axis 1 is positively correlated with all parameters except to the sea-ice and primary productivity in August, which are on the negative side. Results indicate that the composition of dinocyst assemblages is mostly controlled by temperature and that all environmental variables are correlated together. The CCA distinguishes 3 groups of dinocysts: the heterotrophic taxa, the genera Impagidinium and Spiniferites as well as the cyst of Pentapharsodinium dalei and Operculodinium centrocarpum. Five assemblage zones can be distinguished: 1) the Okhotsk Sea zone, which is associated to temperate and eutrophic conditions, seasonal upwellings and Amur River discharges. It is characterized by the dominance of O. centrocarpum, Brigantedinium spp. and Islandinium minutum; 2) the Western Subarctic Gyre zone with subpolar and mesotrophic conditions due to the Kamchatka Current and Alaska Stream inflows. Assemblages are dominated by Nematosphaeropsis labyrinthus, Pyxidinopsis reticulata and Brigantedinium spp.; 3) the Bering Sea zone, depicting a subpolar environment, influenced by seasonal upwellings and inputs from the Anadyr and Yukon Rivers. It is characterized by the dominance of I. minutum and Brigantedinium spp.; 4) the Alaska Gyre zone with temperate conditions and nutrient-enriched surface waters, which is dominated by N. labyrinthus and Brigantedinium spp. and 5) the Kuroshio Extension-North Pacific-Subarctic Current zone characterized by a subtropical and oligotrophic environment, which is dominated by O. centrocarpum, N. labyrinthus and warm taxa of the genus Impagidinium. Transfer functions were tested using the modern analog technique (MAT) on the North Pacific Ocean (= 359 sites) and the entire Northern Hemisphere databases ( = 1419 sites). Results confirm that the updated Northern Hemisphere database is suitable for further paleoenvironmental reconstructions, and the best results are obtained for temperatures with an accuracy of +/-1.7 °C.

Lower Cretaceous dinoflagellate cysts of Exmouth Plateau, Nortwest Australia

Cores from Leg 122, Sites 762 and 763, were sampled at intervals of one sample per 1.5-m section in the Lower Cretaceous sequences. More than 400 samples were studied, most of which contained dinoflagellate cysts, spores, pollen, and various types of palynoclasts. From the entire palynomorph assemblage mainly dinoflagellate cysts were studied to give a stratigraphic outline for the Lower Cretaceous. Stratigraphic units were interpreted in terms of zones in use for the Jurassic and Cretaceous of Australia. At both sites a condensed Valanginian to Aptian sequence and an expanded middle to late Berriasian sequence containing a rich microplankton assemblage were recovered. Sites 762 and 763 can be correlated with each other and with the wells Eendracht-1 and Vinck-1.

Calcareous nannofossil biostratigraphy of ODP Leg 134 sites

Seven sites drilled in the central New Hebrides Island Arc during Ocean Drilling Program Leg 134 yielded varying quantities of upper Eocene through Pleistocene calcareous nannofossils. Most of the Miocene and Pliocene strata were absent from Sites 827-831 drilled along the collisional boundary between the Australia and Pacific plates where the North d'Entrecasteaux Ridge and Bougainville Guyot are being subducted. Sites 832 and 833, drilled in the intra-arc North Aoba Basin, contained upper Miocene through Pleistocene and early Pliocene through Pleistocene nannofossils, respectively. Detailed range charts displaying species abundances and age interpretations are presented for all of the sites. Despite problems of reworked assemblages, poor preservation, overgrowths and/or dilution from volcaniclastics, the nannofossil biostratigraphy delineates several repeated sections at Site 829 in the accretionary prism adjacent to Espiritu Santo Island. Paleogene pelagic sediments equivalent to those in a reference section at Site 828 appear to have been scraped from the downgoing North d'Entrecasteaux Ridge and accreted onto the forearc during the Pleistocene. Other sediments in the forearc include Pleistocene olistostromal trench-fill deposits containing clasts of various ages and compositions. Some of the clasts and olistoliths have affinities to rocks exposed on the neighboring islands and environs, whereas others are of uncertain origin. The matrix of the olistostromes is predominately Pleistocene, however, matrices of mixed nannofossil ages are frequently encountered. Comparisons of the mixed nannofossil ages in the matrices with sedimentological and structural data suggest that sediment mixing resulting from fault movement is subordinate to that occurring during deposition.

Calcareous nannofossil abundance and datums of sediments from ODP Leg 170 sites

Three Pleistocene, five Pliocene, and thirteen late and middle Miocene calcareous nannofossil datums have been identified in the Leg 170 cored sequences collected from a transect across the Middle America Trench off the Nicoya Peninsula. Although some nannofossil zones could not be delineated, particularly in the Pliocene and upper Miocene, there appears to be a complete or very nearly complete Pleistocene through lower Miocene section at Sites 1039 and 1040. The oldest assemblages, observed at Site 1039 and 1040, are latest early Miocene in age (nannofossil Zone NN4). These assemblages are associated with gabbro intrusions into the basal sediments (one contact metamorphic hornfels sample contains relict nannofossils), indicating an age for the intrusion event of between 15.6 and 18.2 Ma at both Sites 1039 and 1040. Reference Site 1039, located on the Cocos plate, provides the best-preserved sequence of sediments of late Pleistocene to latest early Miocene age. The sediments cored in the prism sections at Sites 1040, 1041, 1042, and 1043 all indicate that the age of nannofossil assemblages in the prism sediments, including the toe, wedge, and apron, are all Pleistocene with a considerable amount of upper Miocene reworking. A period of low sediment accumulation rates (~5.3 m/m.y.) is recorded for Pliocene and upper Miocene sediments at Sites 1039, 1040, and 1043. Pliocene calcareous nannofossil assemblages characteristic of the ~2.5- to 3.75-m.y. time interval (nannofossil Zones NN16 and equivalent nannofossil Subzones CN12b and CN12a) were not resolved at any site. Nannofossil Zones NN15, NN14, NN13, and NN12 (early late Pliocene to early Pliocene) could not be resolved at any site either because of the absence of marker species. Within the Miocene at Sites 1039 and 1040, nannofossil Zones NN10-NN6 were difficult to differentiate because of the absence of several species that define the zonal boundaries. These intervals, where the nannofossil zones have not been resolved or are partially resolved, are primarily composed of carbonate ooze deposited during an ~8.5-m.y. (2.5-11 Ma) low sediment accumulation rate time interval. The absence of many of the marker species is attributed to warmer water conditions during those periods. Many of the same marker species are absent in the sediments recovered from nearby Deep Sea Drilling Project Site 155 in the Panama Basin.

Dinoflagellate abundance and events of ODP Site 189-1172 sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Holes 1172A and 1172D (East Tasman Plateau; 2620 m water depth). Besides organic walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the dinocyst distribution from the Maastrichtian to lowermost Oligocene and Quaternary intervals and illustrate main trends in palynomorph distribution. The uppermost Cretaceous-lowermost Oligocene succession of Site 1172 has a confident biomagnetostratigraphy, enabling us to tie early Paleogene Southern Hemisphere dinocyst events to the geomagnetic polarity timescale for the first time. Dinocyst species from the Maastrichtian to earliest Oligocene at Site 1172 are largely endemic ("Transantarctic Flora") or bipolar; cosmopolitan taxa are present in the background as well. The Maastrichtian-early late Eocene dinocyst assemblages are indicative of shallow-marine to restricted marine, pro-deltaic conditions, closely tied to a massive siliciclastic sequence. By middle late Eocene times (~35.5 Ma), the siliciclastic sequence gave way to a thin glauconitic unit, considered to reflect the deepening of the Tasmanian Gateway. This transition coincides with the most prominent change in dinocyst associations of the Paleogene. The turnover is inferred to reflect a change from marginal marine to more offshore conditions, with increased winnowing and oxidation. Overlying pelagic carbonate ooze of middle early Oligocene and younger age is virtually barren of organic microfossils, although Quaternary assemblages have been recovered. This aspect is taken to reflect average low sedimentation rates and well-oxygenated water masses during most of the Oligocene and Neogene. The few palynologically productive samples from the Oligocene-Quaternary interval have a stronger cosmopolitan to subtropical signature, with warm-water species being common to abundant.