The Upper Cretaceous Niobrara Formation and the overlying Sharon Springs Member of the Pierre Shale are two of several organic-carbon (OC) rich units deposited in the Western interior seaway. A key to assessing the validity of models proposed to account for OC enrichment in these units is understanding the three-dimensional (3D) distribution of OC within these units. Within the study area abundant subsurface data in the form of geophysical well logs are available. These logs were used to divide the Niobrara and Sharon Springs into regionally correlatable chronostratigraphic horizons and to estimate OC-content. By combining these elements a 3D picture of the OC-distribution was obtained. This distribution was compared to changes in lithology, sedimentation rate, and tectonic activity. The Niobrara and Sharon Springs contain local and regional disconformities which indicate water depths were near an estimated storm-wave base depth of 100 m. Local disconformities in the Niobrara are indicative of basinal tectonic activity that is linked to Sevier thrusting to the west. Large-scale Niobrara chalk/marl cycles also appear to be linked to Sevier thrusting. There is a regular vertical pattern of OC enrichment in the Niobrara, but no pronounced regional patterns are evident. Estimated paleoproductivities are moderate, except to the southeast where higher productivities may have been a consequence of upwelling. Small-scale chalk/marl cycles result from alternation of high productivity during periods of fairly vigorous circulation (chalks) with low productivity during periods of more sluggish circulation (marls). The regional diachrony of the Sharon Springs facies was a result of clastic dilution associated with progradation from the west and the paleobathymetry. Paleoproductivities were moderately high during Sharon Springs deposition, but there is no conclusive evidence of upwelling. Both units were deposited beneath bottom waters that were on average dysoxic, but oxygenation levels varied intermittently from fully oxic to anoxic. These changes were climatically modulated. At short time scales they may have been seasonal and at longer time scales they may have been driven by Milankovitch cyclicity.

Impact events may have affected the evolution of life on Earth. The mass extinction event at the end of the Cretaceous Period, which includes the demise of the dinosaurs, has been linked to the large impact event that produced the Chicxulub structure located in the Yucatán Peninsula, Mexico. Unfortunately, the geologic record is too spotty to prove any causal relation between the impact event and the mass extinction event that occurred 65 Myr ago. However, the size and location of the impact structure have drawn attention to impact-related abrupt perturbations of the climate and their effects on the biota. My main approach to studying these impact-related perturbations is through hydrocode models of the impact event. Few simulations of the Chicxulub impact event have previously been done. In these simulations the event was modeled as an asteroid impact, using two-dimensional hydrocodes that permit modeling only vertical impacts (i.e. perpendicular to the surface). This work presents the results of a series of high-resolution two- and three-dimension hydrocode simulations of the Chicxulub impact event. The simulations span several different projectile sizes, cover asteroid as well as comet impacts, and explore the effects of impact angle on the impact event. The focus of the simulations is to obtain reliable estimates of the climatically active gases, namely S-bearing gases, CO₂ and water vapor, released to the atmosphere by the impact event. These estimates will be used in modeling the perturbation of the climate of the end of the Cretaceous, and, hopefully, will shed new light on the relation between the impact event and the mass extinction that occurred 65 Myr ago.

During the last deglaciation, 15,000 to 12,000 calendar years ago, global warming and wholesale shifts in regional precipitation patterns produced dramatic changes in vegetation worldwide. Paleobotanical records, namely pollen and macrofossils, have been used not only to reconstruct shifts in plant distributions and abundances, but also to quantify changes in temperature and precipitation amounts or seasonality. In addition to climatic change, during the full glacial period atmospheric CO₂ values had dropped 30% to 200 ppmv compared to the Holocene, preindustrial value of 280 ppmv. Hypothetically, variations in atmospheric CO₂ affect plant water-use efficiency (carbon gained to plant-water transpired) and thus may have modulated vegetation response as climates change. The studies incorporated in this dissertation focused upon carbon isotope and morphological changes in leaves of key functional groups. The studies concentrated on plant species that are abundant in the fossil record and comprise major floral components of past and present vegetation. Key findings include: (1) that shifts in δ¹³C in modern populations along steep environmental gradients seldom exceeds inter-plant variability at a given site, (2) inter-plant and intra-site variability in modern and historic herbarium collections of the C₄ halophytes Altriplex canescens and A. confertilfolia and packrat midden macrofossils of A. canescens excludes their use as a reliable proxy for atmospheric δ¹³C, (3) calcium-oxalate crystals are common component in plant tissue and can have a significantly different δ¹³C value that increases inter-plant variability, especially in C₄ plants such as Atriplex canescens and A. confertifolia, (4) carbon isotope and stomatal density/index measurements of macrofossils from packrat middens show species specific adaptation in ecophysiological processes as atmospheric CO₂ rose from the full glacial, and (5) the greatest adaptation to low atmospheric CO₂ during the last ice age was in the C₃ species and that C₄ and CAM plants showed few changes in their discrimination against ¹³C or in the number of stomata on their leaf surfaces.

Thirty eight piston cores and numerous seismic profiles collected by two R/V Marion Dufresne and several CSS Hudson cruises were examined and cores from other cruises reinterpreted in the course of this study of Late Pleistocene ice-rafting events (Heinrich events) in the Labrador Sea. / In the northwestern Labrador Sea, close to the margin of the former Laurentide Ice Sheet, Heinrich layers are unusually thick. Thicknesses of up to 4.8 m result from deposition from nepheloid-flows and low-density turbidity flows and from iceberg melting. Heinrich layers formed in three stages, explained by a proposed model that also attempts to explain ice-sheet dynamics, ice-stream behavior, and sediment transfer mechanisms from the ice-sheet to the deep sea. Nepheloid-flow deposits seem to result largely from fresh water buoyantly rising out of giant turbidity currents generated at the Hudson Strait outlet. / High-resolution stratigraphic records of oxygen isotopes, concentration of total carbonate, coarse-fraction content, and magnetic susceptibility, and 70 new 14C-AMS dates establish the presence of eight Heinrich events, H0 to H6 in the northwest Labrador Sea, including a new event, termed H5a (between H5 and H6). This refined chronology shows that the recurrence intervals between Heinrich events are fairly evenly spaced, with an average of ∼7 ka, as postulated by the binge and purge model for their origin. / High-resolution oxygen isotope, concentration of total carbonate, and coarse-fraction content data suggest that both meltwater and iceberg supply increased during Heinrich events. This is the first time that increased meltwater supply by direct discharge from a major ice outlet during Heinrich events has been documented, because ice-proximal areas tend to be barren of foraminifera. / The presence of H3 between 46° and ~63°N in the Labrador Sea, previously debated, has been proved. Thickness variations for H3 were compiled on an isopach map showing a maximum thickness of 4.8 m near Hudson Strait and thinning to 30 cm in the central Labrador Sea. / H0 is present in upper Labrador slope cores, compared to other Heinrich layers which were found widely on the slope, rise, and in the basin. These findings suggest that during or prior to H0, the Hudson Strait ice-stream had retreated landward, so that glaciomarine sediments were delivered to the shelf and iceberg trajectories were following the course of the already established Labrador Current.

Oxygen isotope analyses of corals from the Gulf of California and Gulf of Panama are calibrated with environmental parameters. Uncertainty in the isotopic composition of sea water in the Gulf of California prohibits strong correlation between temperature and $\delta\sp{18}$O. The marginal condition for coral growth in the Gulf of California prevents the construction of a long paleoclimate record. The Gulf of Panama record is strongly correlated with salinity (r$\sp2$ = 0.72) and indicates a trend toward drier conditions in Panama since 1950. Although El Nino is recorded in both records through a decrease in the annual maximum isotopic value, this signature is not unique to El Nino thereby minimizing the ability of corals to monitor this system. Strong coherence between the Gulf of Panama record and three other Panamanian records attests to the ability of corals to record regional climate variability.

A series of small mud mounds are exposed in the McConnell and Miette thrust sheets on the southern flank of the Miette reef complex. They occur on the southeastward inclined carbonate clinoforms of the late Frasnian Arcs Member. These mounds are rooted on marine, argillaceous lime mudstones and are surrounded by lime mudstones of several prograding clinoforms of the upper Arcs Member or dolomitic siltstones of the lower Ronde Member. / Mounds are approximately 17 to 36 m high and 32 to 81 m wide and columnar to domal in shape. The lower part of the mounds consists of sponge-rich wackestones and packstones, and locally laminar stromatoporoid boundstones. Calcareous green algae tend to predominate in the upper parts of the mounds. / Variable cavities occur and are filled with geopetal sediments, isopachous fibrous and blocky calcite cements. The most common cavity types, irregular and irregular stromatactoidal cavities, might be related to organic origins, possibly the decay of sponges in conjunction with submarine cementation. / Abrupt mound margins indicate that the mounds grew upwards more rapidly than the accumulation of the adjacent basin and clinoforming slope sediments. (Abstract shortened by UMI.)

<p> The mesic forests distributed within the Rocky Mountains of northern Idaho are unique because many species contained within the forest are separated from their main distribution along the Pacific Northwest coast. It remains unclear whether most species within the inland disjunction survived the glacial periods of the Pleistocene, or whether they were more recently dispersed from coastal populations. To see if the dominant tree taxa of the mesic forests today could have persisted in a refugium south of the large ice sheets, four sediment cores were used to reconstruct the vegetation and climate history of the region. A nearly continuous record of pollen and sediment composition (biogenic silica and inorganic and organic matter) over the last ca. 120,000 years provides evidence of a dynamic ecosystem. Over a long timescale, the slow shifts in vegetation are attributed to the changes in climate. During the last interglacial period, the region was warmer and drier with a <i> Pinus</i> dominated mixed conifer forest. Approximately 71,000 years ago, a <i>Pseudotsuga/Larix</i> forest became established in the area as a response to the increased available moisture. As climate cooled and glaciers expanded the <i>Pinus</i> and <i>Picea</i> forest was the dominant vegetation type until ca. 40,000 years ago. The environment during the Last Glacial Maximum (LGM) was so harsh that no vegetation record was recorded. After the LGM, climate warmed, enabling a Pinus and Picea forest to establish and persist until the Holocene.</p><p> The mesic taxa that dominate the modern forests did not arrive in northern Idaho until the mid- to late-Holocene. The recent arrival of the dominant tree species, <i>Thuja plicata</i> and <i>Tsuga mertensiana, </i> suggests that they likely did not persist in a refugium during the last glaciation. Instead, these species recently dispersed from coastal populations, but expansion into their interior distributions was likely limited by both climate and species competition in already established forests. During the late-Quaternary, the deposition of thick tephra layers (>20 cm) from the eruptions of Glacier Peak (ca. 13,400 years ago) and Mt. Mazama (ca. 7,600 years ago) also facilitated an abrupt and persistent change in vegetation in northern Idaho.</p>

Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: David Varricchio. Includes bibliographical references (leaves 86-96).

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains viii, 136 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 75-79).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.