The middle and upper Miocene sediments of the Humboldt Basin, northern California, have been investigated for the presence of radiolarian fauna. The vast majority of the radiolaria found are cold water indicators, however there are four distinct periods of invasion of warm water fauna. Two minor ones occurring at 11.5ma and approximately 8.0ma and two major events at 5.0ma and approximately 5.5ma. Occurrences of radiolaria indicative of low oxygen conditions, cold deep forms, and radiolarians associated with the California Current indicate that Paleoceanic circulation in the Humboldt Basin region at 6.5ma was similar to "normal" (anti-El Nino-like) circulation of Recent time. Depositional environments and paleoceanographic circulation are modeled from information obtained from 192 Miocene to Pliocene samples of five stratigraphic sections across the subaerially exposed southern margin of the paleo-basin. Radiolarian fauna indicate that initial deposition was in a basin open to deep marine waters. Through time and in a west to east direction, the radiolarian populations exhibit increasingly shelfal characteristics as shallow water sediments prograded to the west. Total organic carbon data from key chronozones support the models of oceanic circulation developed for the key time planes. The fluctuations in the California Current System are the dominant controls on faunal distribution and organic carbon preservation. An example of doming of deep water masses (Weinheimer et al., 1986) indicating analogous El Nino-like circulation is detected and differentiated from other similar appearing events of a different nature (normal, anti-El Nino circulation).

Paleoecological and geochemical methods were used to study changes in Galveston Bay for the period 1850-1988. The purpose of the study was to: (1) examine foraminiferal species distribution in space and time, (2) measure changes in sediment geochemistry, and (3) determine if human actions have measurably affected the distribution of foraminifera. During 1987-1988, gravity cores were collected, examined by x-radiography for evidence of disturbance, and subsampled at various depths. Sediment accumulation rates were determined by lead-210 analysis. Subsamples were analyzed for particle size, TOC, foraminifera, and selected chemical elements including Al, Ba, Ca, Cd, Cr, Cu, Fe, Mg, Na, Ni, Sn, Sr, V, and Zn. Foraminifera were identified to species and enumerated as percent relative abundance. Barium concentration was depth-dependent for a number of cores. A regression of year before present against Log10 of barium was used to establish the chronology of additional cores. There were two significant geochemical trends: (1) a high correlation of the metals, including Al, Cr, Cu, Fe, Mg, Na, and V, to percent silt and clay, and (2) high intercorrelations between metals, especially to Al and Fe. Barium was poorly correlated to percent silt and clay and to metals. Thus, adsorption onto silt and clay particles and co-precipitation of metals with iron and aluminum hydrous oxides are apparently two of the dominant processes controlling the fate of metals in Galveston Bay. Dominant foraminifera in Galveston Bay were Miliammina fusca, Ammotium salsum, Ammonia parkinsoniana, and Elphidium spp. The species composition of individual subsamples generally fit into one of two biofacies described for Gulf of Mexico estuaries: (1) the Miliammina-Ammotium biofacies, generally confined to low salinity and (2) the Ammonia-Elphidium biofacies, dominant in the middle and lower estuary. Results showed a temporal shift from Miliammina-Ammotium to the Ammonia-Elphidium. These shifts occurred in the late 1800s in lower and middle Galveston Bay and as recently as the 1970s in Trinity Bay. This stepwise progression of a high-salinity biofacies further into the estuary coincides with dredging in the Houston Ship Channel. The pattern and timing of the species shift supports the hypothesis that dredging of the Houston Ship Channel has been a major contributing factor to salinity intrusion in Galveston Bay.

No description available.

Using four periplatform sediment cores of intermediate water depth (900 to 1400 m) from the western Caribbean Sea, an investigation was conducted to ascertain the difference in cyclicity between the late-Brunhes Mode and the mid-Brunhes Mode. The past 185 ky define the late-Brunhes Mode, which records extreme changes between glacial and interglacial conditions, and consistent behavior within isotopic stages. Defined as 525 to 185 ky for the purposes of this study, the mid-Brunhes Mode represents a time of mild changes between and within glacial and interglacial stages, much like an extended late-Brunhes interglacial stage. Changes between the two modes were monitored using proxies for dissolution, AAIW influx (influence of the Southern Ocean on intermediate Caribbean waters), nutrients, migration of the North Atlantic Gyre, sea level and strength of the Caribbean Current.

A marine sedimentologic investigation was conducted on the northern Antarctic Peninsula continental margin. The data base included piston cores, surficial sediments, and high resolution seismic reflection profiles. The objectives of this study were three-fold: examine sedimentation patterns in the Bransfield Basin, a high-latitude, actively spreading back-arc basin; relate sedimentation processes to lithofacies patterns in bays and fjords of the South Shetland Islands, Palmer Archipelago, and Danco Coast; and interpret the recent glacial-climatic history of this region. As a back-arc basin in a polar latitude, the Bransfield Basin represents a unique sedimentary environment. Fluvial discharge systems are lacking and the Bransfield Basin receives only minor amounts of continentally-derived sediment. The South Shetland arc is inactive, and the locus of recent volcanic activity is the axis of back-arc spreading. The sediments accumulating in the Bransfield Basin represent the input of terrigenous, biogenic, and volcaniclastic phases. Sediment distribution reflects the interplay of marine currents, primary production, and volcanic activity. At water depths $<$250 m, marine currents actively redistribute sediment, and residual deposits blanket the shelf between the northern tip of the Antarctic Peninsula and Tower Island. A transition from residual deposits to deposits with increased mud content west of Tower Island indicates a decrease in the intensity of marine currents as they flow east to west along the shelf. Lower energy conditions characterize the Bransfield Basin, permitting the suspension settling of fine terrigenous and biogenic phases. These predominantly fine-grained deposits record episodic pulses of increased volcaniclastic input. The normally graded volcanic ash layers represent both air fall deposits and sediment gravity flow deposits (turbidites). The distribution and composition of lithofacies recovered in bays and fjords appear to be regulated by the proximity to ice margins and to discharging meltwater systems. Where terrigenous sediment input is less pronounced, a biogenic lithofacies is present. Seismic records show that the thickness of the meltwater facies increases from south to north in the study area. It appears that initiation of meltwater production occurred relatively recently in bays of the Danco Coast. In contrast, sedimentation in bays of the Palmer Archipelago and South Shetland Islands is meltwater-dominated, and terrigenous sediments are rapidly accumulating. (Abstract shortened with permission of author.)

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 46-49).

Pollen, spores, and dinoflagellate cysts are used with the modern analog technique (MAT) to provide paleoclimate reconstructions for terrestrial and marine environments in northeastern North America. Multivariate analysis of marine and nearby terrestrial pollen sequences from Hudson Bay, Labrador and the St. Lawrence, differentiate tundra, boreal and deciduous forest assemblages in time and space. These three regions had differing climate histories with respect to deglaciation and air mass boundaries. Prior to 6000 14C yr BP, cooler temperatures reconstructed along the Labrador margins agree with climate simulations indicating a persistent anticyclone over the Quebec-Labrador ice sheet. A late Holocene cooling at forest-tundra sites suggests a recent southern movement in the mean position of the polar front. The degree to which those critical thresholds of dissimilarity, that are used to identify non-analog pollen assemblages, are due to limitations of the modern pollen database or critical decisions within the MAT are explored by means of stochastic simulation, spatial statistics and graphical techniques. Critical thresholds of SQD, as derived by the expected value under randomization, become greater as the number of taxa in the pollen set increases. Larger pollen sets, with continentally infrequent but regionally abundant taxa, better distinguish between continental vegetation zones. Global and local spatial autocorrelation within climate anomalies indicate where the modern sample network induces biases in the climate reconstruction using the MAT. The spatial scale of terrestrial climate or vegetation reconstructions from pollen in lake-sediments is investigated through the study of pollen source area in southern Quebec. Despite the different regional vegetation, estimated pollen source areas and relevant pollen productivity for Pinus, Picea, Abies, Fagus, Quercus and Tsuga are consistent with studies from Michigan, Wisconsin and Sweden. These estimates are robust with respect to various plant abundance distance-weighting schemes and imply that the same inferences can be made regarding plant abundance from pollen throughout a lake-derived fossil pollen sequence. Stochastic simulations illustrate that the definition of relevant pollen source area requires consistent within-site vegetation heterogeneity within a network of pollen sites. Underutilized proxy-climate data from wetland taxa are demonstrated to contain climate signals at the continental scale and have the potential to further our climatic and biogeographic picture of North America over the past 21,000 years. Pollen and spores from modern wetland taxa conform to their geographic ranges and allow interpretations of their past range changes. The climatic tolerances that govern their geographic distributions are used to interpret past range changes in climatic terns. Sphagnum spore distributions suggest major peatland developments after 9 ka and 5 ka. Sphagnum, Potamogeton, Isoetes, Myriophyllum Typha/Sparganium, and Menyanthes trifoliata were in Alaska during the last glacial maximum (LGM) and moved into the ice-free corridor by 13 ka. Since the LGM, four migration routes for aquatic taxa are identified in response to the climate changes of the late Quaternary.

The aim of this study is to analyse a mammalian terrestrial fossil fauna in order to assess the early Holocene fauna of the St. Lawrence-Ottawa valley region. The fossils were excavated from Caverne de la Mine located on the Eardley Escarpment in Gatineau Park, western Quebec, near the city of Ottawa (45&deg;28'18"N, 75&deg;51'01"W). The fossil deposit dated between 5 020 +/- 70 and 8 230 +/- 80 B.P. yielded twenty-three taxa among ten mammalian families. Two species, Dicrostonyx hudsonius and Microtus pinetorum, are not part of the modern local fauna. Analysis of the fossil assemblage has shown that most species constituting the local fauna were established in the region soon after deglaciation. However, shifting community structure and the presence of extirpated taxa suggest that the local fauna underwent some adjustments since the beginning of the Holocene. The faunal adjustments mirror evolving vegetation cover in the area. (Abstract shortened by UMI.)

The biogeography of diatoms in 62 lakes across the Canadian Arctic Archipelago was studied. A total of 326 taxa was found, with up to 85 and as low as 8 taxa identified in any one lake. Rarefaction-estimated richness correlated with lake size. Although diatom assemblages showed regional patterns, between-lake variability in any region was high, indicating that local factors are important in determining the assemblages. Newly delineated genera showed interpretable geographic patterns and could be related to environmental factors, suggesting that this more natural grouping may enhance our understanding of diatom ecology. Some taxa showed southern and regionally limited distributions. Many taxa prefer colder temperatures while others were more influenced by lake water parameters. Assemblages with zero or low abundance of fragilaroid taxa tended to occur in larger lakes with higher silica. These lakes had more diverse assemblages including Gomphonema, Encyonema , and Encyonopsis taxa, suggesting a possible relationship between non-fragilaroid taxa and lake size and silica. Geographic, physical, and chemical factors are needed to explain diatom distributions in the Arctic.