The nannofossil assemblages in the studied area are characterized by low species diversity and by the dominance of cold-water forms or cosmopolitan species.
A detailed biochronology for Quaternary sediments on the eastern flank of the Juan de Fuca Ridge was obtained, providing basic knowledge for various studies related to Leg 168 and to the area of the Juan de Fuca Ridge. The upper Pliocene sequences at Site 1027 do not contain any upper Pliocene marker species, such as Discoaster species. An age of 3.2 Ma or younger was estimated for these sediments based on results from analyzing nannofossil assemblages. Based on the resolved biochronology, sedimentation rates of sediment sequences at these 10 sites and their variations were determined. A sedimentation hiatus between basal sediments and basements in this young seafloor region was observed.
A number of results suggest that variations in nannofossil RGA in the Juan de Fuca Ridge, affected by dilution of turbiditic materials, do not reflect the real variation in production of this group of microfossils.
This study found that calcite overgrowth of nannofossils is controlled by temperature, heat flow, thermal gradient in sediments, and the variation in composition of pore water, as well as the supply of calcite materials in sediments. These results provide a detailed knowledge about the effects of low-temperature hydrothermal alteration on diagenesis of nannofossils.
Nannofossils are very sensitive to variations of pore-water pH in sediments: a reduction in pH resulted in the dissolution of nannofossils. The dissolution of nannofossils at Sites 1031 and 1032 were also directly affected by the pore-water upward flows at these two sites.
A few records of nannofossil preservation suggest that the effects of hydrothermal activity on diagenesis of nannofossils might involve more complicated processes and mechanisms that we do not yet understand.