A diagenetic evaluation was performed on marine fossil shell material from Cretaceous sediments of North America, the Arctic, the Antarctic and several localities in Europe. Trace element chemistry, XRD, SEM and stable isotope geochemistry were consistent in their results. Preservation of the original shell material of the low-Mg calcite organisms, brachiopods and belemnites, and the numerous aragonitic organisms was slightly variable with the majority of samples well preserved. Those samples that were altered underwent diagenetic stabilization in both reducing and oxic environments. Using the chemical data from only well preserved fossil shell material, basin paleo-reconstructions showed that from Aptian to Maastrichtian time, the Cretaceous seas were generally aerobic with some dysaerobia evident at the sediment/water interface and in the shallow sediment column. Paleosalinities fluctuated from brackish to normal marine, especially in the Western Interior Seaway of North America and the Paris Basin. The Lower Saxony basin, the Arctic and Antarctic were mainly normal marine with brackish conditions developing on occasion. Paleotemperatures determined from $\partial\sp $O data of preserved aragonite and low-Mg calcite shell material, also showed some variance. The Arctic and Antarctic were coolest, with Campanian/Maastrichtian temperatures about 12 or 13$\sp\circ$C, whereas the Lower Saxony basin and the Western Interior Seaway were slightly warmer, ranging from 11 to 20$\sp\circ$C. The Barremian/Aptian appeared to be the warmest time and a cooling trend was fairly consistent from then on.

A lake sediment core spanning 9900 years, collected from a small lake on western Victoria Island, provides a high-resolution record of diatom community dynamics over the Holocene. Ten radiocarbon dates and 210Pb dating provided the core chronology. Loss-on-ignition (LOI) gradually increased over the Holocene whereas carbonate content and magnetic susceptibility showed an inverse trend. Biogenic silica content had apparent cyclicity over ~1500 year periods. Major shifts in diatom assemblages at 8100-8000 calendar years before present (cal yrs BP), 5800-5700 cal yrs BP, and 3800-3500 cal yrs BP occurred simultaneously with millennial-scale climate changes reported from the region. There is evidence of diatom community response to centennial scale variations such as the 'Medieval Warm Period' (~1000-700 calendar years before present, cal yrs BP), 'Little Ice Age' (~800-150 cal yrs BP) and recent warming. Variations of the taxa within the genera Staurosira, Pseudostaurosira, Fragilaria, and Staurosirella, usually combined into one genus in Arctic lake sediment studies, suggest these taxa may be more useful in paleolimnological studies than previously believed. Although recent changes in diatom community composition, production and species richness were apparent they were surpassed at other periods throughout the Holocene. The rate of community compositional change in the last few centuries was rapid, however it was not exceptional in the lake history.

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No description available.

Spatially continuous patterns of heavy mineral distributions in three dimensions characterized the sandy Holocene sediments of the lower Chesapeake Bay. A pilot study using Q-mode factor analysis on data from an earlier study determined mineral assemblages and mineral composition gradients; the gradients suggested that surficial sediments entered the Bay from offshore and from older deposits to the west. Principal components analysis of the same data indicated that the abundances of only 5 out of 21 minerals were adequate to explain most of the mineral variance. The mineralogy of 87 samples from cores defining two geologic cross-sections was added to the pilot study data and formed a new data set of 173 samples and 5 minerals. Q-mode factor analysis gave similar end-member compositions and mineral gradients as compared to the pilot study. Mineral gradients in the cross-sections show offshore sediment rich in amphibole, garnet, and pyroxene has entered the Bay mouth and presently overlies landward-derived sediment rich in zircon and epidote. The gradients depict tube- and tongue-shaped pathways located above paleodrainages. Surficial gradients support the notion of mutually evasive ebb and flood channels in the Bay entrance. Most of the Holocene sediment in the lower Bay appears to have originated from outside the Bay mouth, to include littoral drift from the north. The techniques used in this study may be useful in an attempt to subdivide a massive sandy lithosome by recognizing distinct stratigraphic units of different age or origin. A magnetohydrostatic mineral separator was constructed and tested.

An understanding of the relationships and lineage ranges among Early Tertiary mammals is established, but a quantitative characterization of community-level changes as been slower to develop. I focused on the dietary ecology of mammals as the major criterion to describe their communities. Dietary hypotheses were proposed using stereoscopic observation of enamel microwear. I applied this method to 23 species of living carnivorans in order to relate those diets to their microwear. I recognized diets in microwear state space that are different from those known for herbivores. This method reliably discriminates diets of larger species. Microwear of the slicing carnassial teeth has to be evaluated in the light of masticatory differences among species. Styles of "omnivory" can also be identified with microwear. I next applied this microwear method to a group of almost 90 species of Paleogene mammals. Most were browsers or mixed feeders, but some show divergence toward grazing. Microwear indicators of durophagy was recovered in some groups. Most archaic groups described were omnivorous, but their microwear reflects different types of omnivory. The Eocene-Oligocene transition (37-30 Mya) was a critical period in mammalian history characterized by climatic cooling and drying. The White River Group (WRG) in North America is a long-term record of this transition. I combined my dietary characterizations with body size to establish feeding guilds Eo-Oligocene faunas. I found that the early Eocene faunas were dominated by browsing guilds with only a few species apparently specializing on grass. By the Chadronian, both grazing and browsing guilds were established, but both were dominated by a large mixed feeder group, in keeping with the open woodland of the time. This basic structure was sustained through the Orellan and Whitneyan of the WRG in a surprisingly consistent form. However, a contemporaneous Chadronian fauna in southwestern Montana is known to contain very different proportions of herbivores; I found that this fauna was dominated by browsers. The surprising degree of stasis in the WRG though this substantial climate change interval is probably the result of the fauna's initial assembly from the survivors of pre-Chadronian extinctions.

No description available.

No description available.

No description available.

No description available.