The late Albian Mowry Shale of Wyoming and Montana, and the time equivalent Big River Formation of Saskatchewan, were studied to determine the cause of anoxia within the Mowry Seaway and the presence or absence of small scale (fourth order) cyclicity. The Mowry Shale is an important source rock, characterized by high total organic carbon content (TOC) (0.5-5.0%), abundant fish debris, numerous bentonites, and prolific radiolarians. Minimal bioturbation at distal sites from Wyoming to Canada indicates that the preservational quality of bottom water with respect to organic matter was high throughout the basinal area of the seaway. TOC values were highest at the southern end however, coincident with a high in radiolarian abundance. This correlation suggests an added input of planktonic organic carbon at the southern end of the seaway, due to higher levels of paleoproductivity. Therefore, anoxia within the Mowry Seaway may have resulted from two processes, stagnation in Canada, and elevated planktonic fertility in Wyoming and Montana. Seasonal upwelling has been predicted along the SE margin of the Albian seaway from independent climate models. Burial rates of Si and P in the Mowry Shale indicate paleoproductivity levels comparable to lower values reported from modern coastal upwelling zones. This fertility could have been supported entirely by nutrients derived from a (depleted) seawater source, even with limited renewal rates. Six locations in N. Wyoming were tied into an onshore - offshore resistivity well log transect. TOC, phosphorous content, and lithologic profiles from each section could then be correlated using numbered bentonite markers. Vertical sedimentation trends were divisible into three intervals. Within the context of sequence stratigraphy, these units may be interpreted as the Transgressive Systems Tract (decreasing sand, increasing TOC), the Condensed Interval (minimum sand, peak TOC), and the Highstand Systems Tract (increasing sand, decreasing TOC). Higher order cyclicity is present in the Mowry Shale, as 1-10m coarsening-up cycles near the western margin, and 5-30m fertility cycles in the basin. Correlation of marginal to basinal cycles indicate that during shallowing-up, decreases in TOC on the shelf coincide with minor increases in TOC in the basin.

The kinematic evolution of allochthonous salt sheets in the northeastern Gulf of Mexico proceeds in three stages. (1) Since its middle Jurassic deposition the Louann Salt was loaded by sediments causing episodic basinward movement and by the end of Lower Cretaceous concentration of salt masses in a slope environment. (2) A regime of starved sedimentation during Late Cretaceous and early Oligocene is responsible for the stabilization of these early salt accumulations. (3) Finally during Neogene-Pliocene, with renewed rapid accumulation of sediments, salt tongues and allochthonous salt sheets formed by gravity spreading within younger sediments on the slope. Autochthonous salt structures, salt tongues and allochthonous salt sheets represent the typical stages for the evolution of allochthonous salt sheets. The down-to-the-basin major growth faults separate allochthonous salt from its feeder stock.

Geological and geophysical data were interpreted to reconstruct the glacial history of Marguerite Bay. Antarctic Peninsula, since the Last Glacial Maximum. An extensive paleo-subglacial meltwater drainage system, which drained the lower Peninsula since at least the Last Glacial Maximum, was mapped on the inner-shelf. A distinct organization of flow is seen across the inner-shelf, as relatively small-scale randomly-oriented linked-cavities feed into larger, linear channels and tunnel valleys. Meltwater discharge estimates suggest that production from steady-state processes (geothermal heat and frictional heat dissipation) were enhanced locally by the sudden up-glacier release of subglacially-stored meltwater. Such large instantaneous meltwater releases may have led to periods of rapid sliding, or intermittent ice-bed separation, within the system. Evidence of glacial erosion on bedrock highs, in the form of striations and grooves, suggests that ice flow remained relatively slow outside the main troughs. As sediment accumulated on the mid-shelf, free meltwater became incorporated into the porous sedimentary strata, thus enabling the facilitation of sediment deformation and relatively rapid ice flow. The presence of mega-scale glacial lineations on the outer-shelf, which clearly extend to the shelf-break where gullies erode downslope, further supports a relatively rapid ice flow, and suggests that maximum ice extent during the Last Glacial Maximum was at the shelf-break. Therefore, ice flow behavior in the bay and trough was primarily controlled by subglacial substrate, the occurrence of subglacial meltwater and local topography. Sediment facies were interpreted as subglacial, proximal-grounding zone, sub-ice shelf, fjord and ice-distal/open marine, based primarily on lithologic attributes, shear strength and down-core magnetic susceptibility response. AMS dating of specific glaciomarine sediment facies implies that grounded ice retreated diachronously across the outer-shelf, retreating initially within the trough (approximately 12,000 years ago), and later in the inter-trough area (approximately 8,000 years ago). A high-resolution Holocene paleoclimate record, reconstructed from sediments in Neny Fjord, suggests that deglaciation had occurred by 8,000 years ago. Radiocarbon dates suggest that glaciers had re-advanced by 4,500 years ago. Magnetic susceptibility response and sediment facies analyses suggest that climate appears to have remained relatively ice-proximal over the last 2,000 years, punctuated by at least three cool oscillations.

Because of its strategic location at the intersection of three regional trends, a kinematic study of the deformation on Isla de Margarita was undertaken to provide additional constraints for Caribbean plate tectonic models. Previous work revealed a metamorphic nucleus composed of amphibolites, schists, marble, serpentinized ultramafics, and leucocratic intrusives. Studies on eclogite knockers provided quantitative estimates for the meta-morphic pressures and temperatures. In this study, five generations of deformational structures were identified on Isla de Margarita. The earliest structures (D$\sb{\rm 1a}$) are rarely preserved, occurring as the main foliation in the eclogite knockers and as a foliation within microlithons bounded by the S$\sb{\rm 1b}$ foliation. The D$\sb{\rm 1b}$ deformation is synchronous with epidote-amphibolite to greenschist facies metamorphism which overprints the eclogite assemblage. It forms the dominant metamorphic foliation on the island and is axial planar to associated isoclinal folds. Quartz c-axis and S-C fabrics developed under greenschist facies conditions and characterize the D$\sb{\rm 1c}$ extensional deformation. In the Miocene, the non-metamorphic D$\sb2$ deformation folded the D$\sb{\rm 1b}$ foliation into a southwest-plunging anticlinorium. The latest brittle deformation (D$\sb3$) shows northeast-southwest extension, aligned with the fold axes and extensions of all earlier deformations. Analysis of the relative motions between North and South America shows there is insufficient Mesozoic convergence to form in situ the metamorphic belts of northern South America. These metamorphic belts must therefore have formed far to the west along the Farallon/South American plate boundary. A proposed model relates the Cretaceous synmetamorphic D$\sb{\rm 1a}$, D$\sb{\rm 1b}$ and D$\sb{\rm 1c}$ progressive deformations to arc-parallel extension in the Aves Ridge subduction complex. The remains of the Cretaceous arc have since been disrupted by the strike-slip boundaries of the northern and southern Caribbean, as well as by the opening of the Grenada Basin. The associated metamorphic rocks have also been disrupted and progressively emplaced onto the continental margin of South America from west to east. The D$\sb2$ and D$\sb3$ deformations are associated with this dextral plate boundary deformation between the Caribbean and South America.

Outcrop studies of Eocene-Oligocene depositional sequences exposed in the Coastal Plain of Alabama and Mississippi disagree on the sea level history recorded across several stratigraphic intervals. The placement of depositional sequence boundaries (unconformities caused by sea level fall) and maximum flooding surfaces relative to the lithostratigraphy by various authors implies that relative sea level change was diachronous across the central Gulf Coast. In addition, the number of depositional sequences (i.e., the number of third-order sea level fluctuations) interpreted for these units commonly varies. These discrepancies are puzzling, given the short distances among study areas and the fact that most workers have based their interpretations on observations from the same outcrops. Regional subsurface studies of these generally marine units integrate several data sets to constrain the sea level history as recorded across three controversial stratigraphic intervals. Lithologic and chronostratigraphic data from two test cores located in southern Alabama provide facies information and age constraints. Thin sections from the cores were point-counted to obtain quantitative petrographic trends for detrital and authigenic sedimentary components; these trends define transgressive-regressive (T-R) cycles that record relative sea level change. Oxygen and carbon isotopic data from the cores test the hypothesis that chemical stratigraphic changes record eustatic sea level fluctuations. Finally, regional subsurface mapping of geologic units locally reveals stratigraphic truncation, which is interpreted to reflect erosion following a sea level fall. The revised sequence stratigraphic interpretations proposed herein result in part from the application of depositional models tailored to fit the central Gulf. Previous depositional models applied to the Alabama section do not account for variability in the basic parameters that control stratal architecture in depositional sequences, such as sediment flux and basin physiography. Due primarily to a low sediment supply, the Eocene-Oligocene section of the central Gulf Coastal Plain has little in common with traditional Exxonian "slug" models for deposition. Instead, a new model is proposed, whereby the majority of sediment progradation takes place in response to sea level fall. This model reinterprets some units previously referred to as highstand deposits as lowstand progradational/aggradational deposits, thus requiring a sequence boundary at their base.

The Clementine Mission acquired the first global compositional data for the Moon. Five discrete wavelengths (415, 750, 900, 950, 1000 nm) span the ultraviolet-visible spectrum. Using this data, I have performed a systematic study of the mare deposits on the far side of the Moon, between 80' east and 80' west longitude. The major study areas are the Australe, Marginis, Moscoviense, Orientale, Smythii, and South Pole-Aitken basins. Mare basalt deposits within these basins or regions around them are characterized by their volume, age, chemistry and geologic setting. The integration of this information yields information concerning the thermal history, lateral and vertical heterogeniety of the mantle, and conditions at the time of eruption for far side mare deposits. Furthermore, this information provides constraints for models that discribe lunar volcanism and the composition of the mantle. Volcanism on the Moon's far side was not as protracted or as voluminous as on the near side. However, multiple episodes of volcanism are recognized in each of the major basins studied. Brief periods of volcanism occurred in degraded basins such as Campbell, Compton, Freundlich-Sharnov and Mendel-Rydberg and the isolated deposit Kohlshutter. The average iron and titanium composition of far side basalt deposits is lower relative to basalt deposits on the near side. Impact mixing has more efficiently contaminated the lower volume mare deposits with highlands material. Very high-Ti basalts, like those at Apollo 11 and 17 landing sites, are absent. Late stage moderately high-Ti units (4-6 wt.% $\rm TiO\sb2)$ are located in the Moscoviense, South Pole-Aitken and Australe basins. My interpretation of these data is that the proposed thicker far side crust has prevented very high-Ti basalts from erupting onto the surface of the far side of the Moon. A simple stratified mantle with high-Ti late cumulates situated above low-Ti early cumulates does not explain the observed distribution of late stage, moderately high-Ti basalt units on the far side.

Volcanic passive margins are a major type of large igneous provinces, characterized by seaward dipping reflectors (SDRS), normally associated with subaerially emplaced basalt flows and intercalated at least in part with continental sediments. In the South Atlantic, volcanics extent laterally for hundreds of kilometers and can reach a thickness of about 15 kilometers. A number of questions related to their formation. Among them, the influence of hotspots, the timing of volcanic emplacement with respect to continental breakup and the nature of the crust associated with the volcanic wedge remain uncertain. The Walvis and Pelotas basins are particularly well imaged examples of volcanic passive margins, providing an unique opportunity to investigate the evolution of volcanic margins. The sedimentary infill of the Pelotas and Walvis basins directly resulted from the Jurassic to lower Cretaceous breakup of Pangea. In the Pelotas Basin along the Brazilian margin, forty eight sequence boundaries were identified based upon the analysis of 1,500 km of 2D reflection seismic profiles and four hydrocarbon exploration wells. These sequences form the sequence stratigraphic framework for the lower Cretaceous (Albian) to Cenozoic sedimentary succession and their age control is based upon calcareous nannofossils and planktonic foraminifera biostratigraphies. This local sequence stratigraphic framework is compared with the global chart (Haq et al., 1987) and the new cycle chart of Hardenbol et al. (in press). Positive oxygen isotope events defined in several deep-water DSDP/ODP sites are compared with the sequence boundaries defined in the Pelotas Basin, Exxon record (Haq et al., 1987), and new cycle chart (Hardenbol et al., in press). From the sequence stratigraphic analyses, a chronostratigraphic chart and an onlap curve were built. A relative sea-level curve for the upper Cretaceous and Cenozoic records was developed in the Pelotas Basin based on the variations in the coastal onlap. Magnitude of sea-level fluctuations were estimated in measuring the downward shift of coastal onlap in seismic profiles for each sequence boundary. A composite oxygen isotope record were built based upon benthonic foraminifera from DSDP/ODP sites and compared with the Antarctica glacial history, the eustatic curve of Haq et al. (1987), and the relative sea-level curve of the Pelotas Basin. A reasonable correlation results from the comparison between the relative sea-level curve derived from sequence stratigraphic studies and the composite oxygen isotope record. At least since the middle Eocene, positive isotope events correlate well with sequence boundaries. These correlation indicate that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since at least the middle Eocene. Oxygen isotope values for deep-water benthonic foraminifera during the Aptian to lower Albian stages and Campanian to Maastrichtian stages are similar to those observed during the middle Eocene. Due to the evidence for Antarctic glaciation during the middle Eocene, similarity between Cretaceous and Eocene isotope values could indicate the presence of polar ice as early as the Aptian.

This study presents a new conceptual tectonic model for the exhumation and emplacement of the Villa de Cura blueschist belt, which places specific constraints on the development of the Caribbean-South American plate boundary zone. New structural and fluid inclusion microthermometric analyses constrain the evolution of the western and central parts of the Villa de Cura blueschist belt, Venezuela. The structural evolution is represented by seven generations of deformation structures. Three ductile generations are associated with Late Cretaceous subduction zone deformation, and Paleocene-Eocene exhumation of the belt from the fore arc of the Great Arc of the Caribbean. Two brittle-ductile generations record the Eocene-Miocene emplacement of the belt onto the South American continental margin; during this deformation early aqueous fluid inclusion assemblages are reequilibrated. Two brittle generations result from plate boundary deformation similar to that occurring at present; methane-rich fluid inclusion assemblages are associated with hydrocarbon entrapment during these deformations.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.

Marine geological evidence supports rapid retreat of the West Antarctic Ice Sheet in the eastern Ross Sea before the last glacial maximum. As the only accessible marine record of a major drainage outlet of the West Antarctic Ice Sheet (WAIS), this central and eastern Ross Sea dataset provides a unique opportunity to test the hypothesis of WAIS instability, assess its regulating role in eustasy, and explore the geological record of paleo-ice stream behavior. As the last vast marine-based ice sheet on the planet, the WAIS is seen as a key source of potentially rapid sea level rise. The collapse and disintegration of the WAIS would raise sea level by 5--6 m, a major threat to the world's coastal cities. Marine geological data were collected along the axis of large bathymetric troughs during a 1999 cruise of the R/V Nathanial B. Palmer. Thick till sheets, extensive lineations, and multiple grounding zone wedges imaged on seismic profiles and multibeam bathymetric records, indicate that troughs in the Ross Sea were occupied by paleo-ice streams during the last glacial maximum. Ice stream boundaries in the eastern Ross Sea are characterized by laterally accreting sedimentary strata indicating lateral migration of ice streams. The abrupt transition from lineated to non-lineated morphologies reflects sharp ice stream margins. Sediment cores recovered glacial-marine deposits overlying till, a facies succession that indicates an abrupt transition from subglacial to open marine deposition. High concentrations of ice rafted debris in the glacial-marine units and iceberg furrows suggest mass wasting of the ice sheet and iceberg calving from the grounding line during retreat. Corrected radiocarbon ages of samples taken above the contact between subglacial (till) and glacial-marine sediments range from 23.4 to 26.0 ka. B.P., indicating pre-LGM ice sheet withdrawal in the eastern Ross Sea. This was long before the ice sheet retreated from the western Ross Sea and is inconsistent with previous models for ice sheet retreat in the region.

Structural analysis of units astride the Motagua fault zone, the boundary between the North American and Caribbean plates in Guatemala, is critical to understanding the tectonic evolution of the northwestern Caribbean region. Existing models consider minimal geochronological data and are based on little structural data. Furthermore, published studies of the region predate concepts of microstructures and kinematic indicators. This study integrates classical structural analysis, contemporary techniques, and geochronological data to constrain a tectonic model for the Maya and Chords blocks. Four ductile phases in the Maya block and five in the Chortis block signal two separate tectonic collisions, as progression of structures and strain fields of Maya and Chortis is not correlative. Evidence is presented for collision of Chords and southwestern Mexico at ∼120Ma and for Maya and the Nicaraguan Rise at ∼70Ma. Four brittle phases in both blocks reflect recent deformation following translation of Chords to its current position.