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Actinommids (spumellarian Radiolaria) are a group of microfossils in which taxonomy and phylogeny hitherto have been based on features of morphology that change with the growth of individuals. To make Miocene actinommids from the equatorial Pacific useful in biostratigraphy, paleocenography, and paleoecology, ontogenetically invariant morphological features can be analyzed by methods of numerical taxonomy to group the specimens into genera, which are further subdivided into species by visual comparison. According to these criteria, 31 species, 18 of which are new, are recognized in the Late Miocene section of DSDP Sites 77 and 289, and an informal revision of actinommid higher taxa is tentatively proposed.
Categories: Publication; Types: Citation; Tags: Micropaleontology
DOMES Site A, in the equatorial North Pacific, was surveyed in detail in an attempt to relate the distribution of nodules to sedimentation. The sea floor is characterized by a broad east-west-trending valley defined by strongly dissected highlands to the north and south. Sediment recovered from the highlands and from the north margin of the valley is late Quaternary. The associated nodules are small, often polynucleated, have smooth surface textures, and the dominant mineral is ??-MnO2. By contrast, cores along the south margin of the valley contain early Tertiary sediment; the nodules usually are large, discoidal in shape, all have a granular surface texture, and the dominant mineral is todorokite. Cores from the...
A box core taken at 11??50.3??? N and 137??28.2??? W in the Central Pacific manganese nodule province was studied to determine the pattern of diatom and radiolarian preservation with depth in the sediment, as well as to observe downcore variations in clay mineralogy. We observed marked deterioration of the siliceous microfossils within the upper 30 cm of this sediment; over this depth interval the Quaternary diatoms disappear first, followed deeper downcore by the dissolution of Quaternary radiolarians. Tertiary microfossils in general were the most corrosion resistant, and the residual microfossil assemblage in the lower part of the core consisted of fragmented, robust Tertiary forms. Consequently, the apparent...
Categories: Publication; Types: Citation; Tags: Nature
Radiolarians from the surface sediments of the Navarin Basin geologic province in the western part of the Bering Sea are more diverse and abundant than previous reports indicate. The shelf is dominated by two spongy radiolarian species groups (Stylochlamydium venustum and Spongotrochus glacialis groups), while the slope has more diversity. The distributions can in part be explained by present oceanographic conditions. Studies of five cores along the slope show that there is a faunal change within the top 5 m of sediment. The spongy radiolarians are more abundant in recent sediments but gradually decrease downcore as Cycladophora davisiana becomes the dominant species, which probably reflects an environmental change....