Calcareous nannofossil abundances in Mesozoic sediments of ODP Leg 129 holes

Calcareous nannofossils were studied from Jurassic and Cretaceous sediments drilled in the western Pacific during Ocean Drilling Program Leg 129. Mesozoic sediments at Sites 800, 801, and 802 are dominated by volcaniclastic turbidites, claystones, porcellanites, and radiolarites. Pelagic limestones are limited to the middle Cretaceous, and a few calcareous claystones were recovered in the Upper Jurassic section at Site 801. We documented the distribution of nannofossils, their total abundance, preservation, and relative species abundance based on semiquantitative and qualitative studies. Preservation of the calcareous nannofloras is poor to moderate, and the total abundance fluctuates from rare to very abundant. Marker species proposed for the middle and Late Cretaceous were recognized, allowing the application of standard nannofossil biozonations. At Site 800 calcareous nannofloras are abundant and moderately preserved in the Aptian-Cenomanian, and nannofossil biostratigraphy constitutes the basic stratigraphic framework for this interval. Radiolarians are the most abundant and persistent group throughout the sequence drilled at Site 801. Long intervals are barren of nannofloras and assemblages are usually characterized by low abundance and poor preservation. Nannofossil biostratigraphy was applied to the upper Aptian-Cenomanian interval and a few marker species were recognized for the late Tithonian. At Site 802 Cretaceous biostratigraphy is mainly based on calcareous nannofossil biozones corroborated by radiolarian and palynomorph events in the late Aptian-Coniacian age interval. A hiatus was indicated between the Santonian and the late Campanian, and another is suspected in the interval between the Cenomanian and the Coniacian.

Distribution and abundance of nannofossils in DSDP Site 89-585

Late Aptian through middle Eocene nannofossil assemblages were recovered from a continuously cored section at Site 585. Poorly preserved assemblages of low diversity were observed in samples taken throughout both upper Aptian and/or lower Albian sandstone and mudstone and middle Cenomanian to lower Turonian claystone at the base of this section. A 70-m interval barren of nannofossils separates these poorly preserved assemblages from those recovered from an upper Campanian chalk farther uphole. This chalk marks the most significant change in carbonate deposition at this site, and deposition of interbedded zeolitic claystone and sediment of varied nannofossil content proceeded without major interruption until the early Paleocene (Fasciculithus tympaniformis Zone, CP4). A middle Eocene chalk (dated by nannofossils) unconformably overlies lower Paleocene sediment in both Holes 585 and 585A. Only a few interbeds of zeolitic claystone are present within 100 m of nannofossil-rich sediment above this unconformity. This entire interval is cautiously assigned to the Discoaster sublodoensis Zone (CP 12), which indicates a sedimentation rate almost an order of magnitude higher than expected from normal pelagic sedimentation. The most obvious feature of the assemblages examined from these cores is the amount of reworked material. Rare Nannoconus elongatus and Braarudosphaera sp. in several upper Campanian to middle Eocene samples demonstrate the contribution of pelagic material from upslope and, along with other reworked species throughout the Upper Cretaceous samples examined, provide evidence contradictory to an excursion of the calcium compensation depth to deep basinal settings in the western Pacific during the Campanian-Maestrichtian time (Thierstein, 1979). The overwhelming dominance of reworked species in all middle Eocene samples examined and the persistence of these assemblages throughout such a large thickness of sediment suggest that currents that redeposited material intensified at this time and may be associated with the formation of the lower Paleocene/middle Eocene unconformity at this site. A single surface core of calcareous ooze taken from Hole 585A dated as early Pleistocene contains abundant and well-preserved late Miocene and Pliocene species.

Ichthyoplankton density and zooplankton biomass in the Benguela upwelling system during AFR258 in December 2009

IIchthyoplankton density (fish eggs and larvae) and bulk zooplankton biomass in December 2009 were determined for 22 stations in the Benguela upwelling system, based on oblique Multinet hauls during the FRS Africana cruise AFR258. A HYDROBIOS Multinet, type Midi (0.25 m**2 mouth area) was equipped with five nets of 500 µm-mesh size, temperature and oxygen probes, and an inner and outer flow meter to monitor the net's trajectory (for volume filtered calculations) as well as net clogging. The Multinet was handled over the side, towed horizontally at 2 knots. Winch speed when fearing was 0.5 or 0.3 m/s, heaving velocity 0.2 - 0.3 m/s. The Multinet was towed obliquely at 22 stations sampling the upper 200 m of the water column, which were divided into five different depth strata after inspection of temperature and oxygen concentration depth profiles. Ichthyoplankton densities and zooplankton biomass were calculated for each depth stratum (=single net) from total abundance and the volume of water filtered [individuals per m**3 and g wet weight per m**3, respectively]. Densities and biomass were integrated over the area for each station [individuals per m**2], as sum of calculations for each net: Sum ([individuals per m**3]*Delta (depth bot[m]-depth top [m]).