Mineralogy micromorphology, and geochemistry at DSDP Site 89-585

At Site 585 of Deep Sea Drilling Project Leg 89 more than 500 m of volcaniclastic to argillaceous middle-Late Cretaceous sediments were recovered. Analyses by X-ray diffraction (bulk sediment and clay fraction), transmission electron microscopy, molecular and atomic absorption, and electron microprobe were done on Site 585 samples. We identify four successive stages and interpret them as the expression of environments evolving under successive influences: Stage 1, late Aptian to early Albian - subaerial and proximal volcanism, chiefly expressed by the presence of augite, analcite, olivine, celadonite, small and well-shaped transparent trioctahedral saponite, Al hydroxides, Na, Fe, Mg, and various trace elements (Mn, Ni, Cr, Co, Pb, V, Zn, Ti). Stage 2, early to middle Albian - submarine and less proximal volcanic influence, characterized by dioctahedral and hairy Mg-beidellites, a paucity of analcite and pyroxenes, the presence of Mg and K, and local alteration of Mg-smectites to Mg-chlorites. Stage 3, middle Albian to middle Campanian - early marine diagenesis, marked by the development of recrystallization from fleecy smectites to lathed ones (all of alkaline Si-rich Fe-beidellite types), by the development of opal CT and clinoptilolite, and by proximal to distal volcanic influences (Na parallel to Ti, K). Local events consist of the supply of reworked palygorskite during the Albian-Cenomanian, and the recurrence of proximal volcanic activity during the early Campanian. Stage 4, late Campanian to Maestrichtian - development of terrigenous supply resulting from the submersion of topographic barriers; this terrigenous supply is associated with minor diagenetic effects and is marked by a clay diversification (beidellite, illite, kaolinite, palygorskite), the rareness of clay recrystallizations, and the disappearance of volcanic markers.

Hydrography and biogeochemistry during S.A. Agulhas II cruise Agu011, in the SW Indian Ocean, April 2014

Several open-ocean mesoscale features, a "young" warm-core (or anti-cyclonic) eddy at 52°S, an "older" warm-core eddy at 57.5°S, as well as an adjacent cold-core (or cyclonic) eddy at 56°S, were surveyed during a R/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, that will be suitable for comparison and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards into the Southern Ocean. A total of 18 CTD stations were occupied in a sector south of the South-West Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise.