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Low-permeability Ordovician shale and limestone formations of the Michigan Basin are a target of interest for a deep geological repository for the long-term isolation of low and intermediate-level radioactive waste. Porewater studies contribute to an understanding of the age and evolution of paleofluids as part of ongoing research. Sulfur and oxygen isotope data presented here add to the characterization of these formations. For this work, a method was developed and used to extract porewater sulfate from low permeability rocks for the analysis of sulfate concentration and its δ34S and δ18O values, using an elemental analyzer interfaced with an isotope ratio mass spectrometer (EA-IRMS). Porewater sulfate concentrations were very low, varying from 0.02 to 228.88 mmol/ kgw. Values for δ34S were all near or below those for Ordovician seawater. The earlier work examined the δ34S and the morphology of framboidal pyrite in the Ordovician formations provides strong evidence for diagenetic sulfate reduction (Jautzy et al. in prep.). The lack of enrichment for δ34S and δ18O in porewater sulfate suggests that diagenetic sulfate reduction was quantitative and that the porewater sulfate measured in these samples is not residual sulfate remaining from that time. The distribution of sulfur isotope values between that of Silurian seawater and those of the framboidal pyrite suggests an origin from the infiltration of Silurian brines with contributions from pyrite oxidation. The δ18O values are consistent with this, showing mixtures between Silurian seawater sulfate and sulfide oxidation without the involvement of atmospheric oxygen. This evidence for anoxic sulfide oxidation indicates that inadvertent exposure to atmospheric O2 during porewater leaching in the laboratory is unlikely and that in-situ oxidation involving electron acceptors with lower electromotive potential took place, possibly over geological time. The combination of sulfate mass and the stable isotopes of porewater sulfate, along with the presence of Fe (III) and Mn (IV) bearing minerals indicate potential evidence of in-situ sulfide oxidation in one third of twenty-six core samples. The relative timing of events is not clear as to whether sulfide oxidation could have occurred during the Ordovician and/or after the infiltration of evaporated Silurian seawater into the Ordovician strata. This study adds a new understanding of the redox evolution within this sedimentary system with implications for contaminant transport.

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The abundance and distribution of biogenic, terrigenous and volcanic particles in the Panama Basin are markedly dependent on bottom topography and dissolution of calcite in the deeper parts of the basin. Of the coarse fraction (>62μ), foraminiferal tests and acidic volcanic glass shards are concentrated on the Cocos and Carnegie Ridges as lag deposits. Foraminiferal fragments are found on these ridge flanks and on the Malpelo Ridge due to reworking by bottom currents accentuated by dissolution of calcite with increasing depth. The finest calcite, probably coccoliths with fine foraminiferal fragments, together with the hydrodynamically light radiolarian skeletons are concentrated by bottom currents in the basin adjacent to the ridges. The foraminiferal calcite compensation depth in the basin is 3400 m. This relatively shallow depth probably reflects the high surface water productivity over the basin, although the pattern of productivity is not reflected in the pattern of biogenic sediments. Acidic volcanic glass appears to have been carried into the basin from Costa Rica, Colombia and Ecuador by easterly winds at altitudes of 1500 to 6000 m. Basaltic shards from the Galapagos Islands have been dispersed only over short distances to the west. Terrigenous sand-sized material is found on the edge of the continental shelf, where associated glauconite points to a relict origin, and along the northern Cocos Ridge, where contour currents may act as the dispersal mechanism. / Graduation date: 1973

In order to quantitatively examine the crustal structure of the Panama Basin without the benefit of local seismic refraction data, the following assumptions were made: (1) No significant lateral changes in density take place below a depth of 50 km. (2) The densities of the crustal layers are those of a 50-km standard section derived by averaging the results of 11 seismic refraction stations located in normal oceanic crust 10 to 40 million years (m. y. ) in age. (3) The density of the upper mantle is constant to a depth of SO km. (4) The thickness of the oceanic layer is normal in that region of the basin undergoing active spreading, exclusive of aseismic ridges. (5) The thickness of the transition layer is 1. 1 kin everywhere in the basin. Subject to these assumptions, the following conclusions are drawn from the available gravity, bathymetry, and sediment-thickness data: (1) Structurally, the aseismic ridges are surprisingly similar, characterized by a blocky, horst-like profile, an average depth of less than 2 km, an average depth to the Mohorovicic discontinuity of 17 km, and an average free-air anomaly of greater than +20 mgal. The fact that their associated free-air anomalies increase from near zero at their seaward ends to greater than +40 mgal at their landward ends suggests that the Cocos and Carnegie ridges are uplifted at their landward ends by lithospheric bending. (2) The centers of sea-floor spreading and fracture zones are characterized by a shoaling of the bottom and an apparent deepening of the Mohorovicic discontinuity. The only exception to this generalization is the northern end of the Panama fracture zone between the Cocos and Coiba ridges. (3) The Panama fracture zone and the fracture zone at 85°20'W longitude divide the Panama Basin into three provinces of different crustal thickness. Between these two fracture zones the crustal thickness is normal; west of 85°20W longitude it is greater than normal; and east of the Panama fracture zone it is less than normal. (4) In that part of the Panama Basin east of the Panama fracture zone there is a major discontinuity at 3°N latitude between a smooth, isostatically compensated crust to the south and an extremely rugged, uplifted crust to the north. An explanation for this discontinuity is the effect of the inflection in the shape of the continental margin at 3°N latitude on the eastward subductiori of the Nazca plate. / Graduation date: 1974

Holocene bulk sediment and component accumulation rates were measured in twenty-eight piston and gravity cores taken from the floor of the western Panama Basin and on the surrounding ridges. Radiocarbon ages and oxygen isotope curves provided Holocene age control in nine cores. Time datums in nineteen other cores were inferred by correlation of calcium carbonate curves to the dated cores. Dry bulk densities were measured in ten cores and were estimated in the others by an empirical relationship between dry bulk density and the percentages of sand, clay, and calcium carbonate. Other studies of the textural, mineralogical and sand fraction composition of near surface sediments in these cores provided analyses which could be used to obtain accumulation rates for these components. A general similarity between the map pattern of surface productivity and the patterns of carbonate and opal accumulation rates suggests a first order control of biogenic sedimentation by fertility of surface waters. Accumulation rates of terrigenous components are highest near the continents; the map and depth patterns suggest dispersal by currents shallower than 2000 m or by winds. It is inferred from textural component accumulation rate patterns that no significant regional redistribution of sediment by winnowing occurred during the Holocene. Deposition from deep thermohaline circulation probably increased the accumulation rates of silt, clay, and opaline components in the gaps between the western and eastern troughs. Calcium carbonate accumulation rates at equal depths are generally lower within 250 km of the edge of the continental shelf. Below 2000 m in high productivity regions > 250 km from the shelf calcium carbonate accumulation rates decrease linearly with depth according to a gradient of -3.3 gm CaCO₃/cm²/1000 yrs/ km. From this gradient, two independent estimates of the lysocline in this region, and a model of calcium carbonate accumulation, the average Holocene rate of supply of calcite from the surface is calculated to be 5-10 gm/cm²/1000 yrs. / Graduation date: 1976

Windblown dust is a significant source of sediment and organic matter for many basins, but its influence on ancient basins can be difficult to detect and quantify. We quantified the biomarker content, including n-alkanes, hopanes, and steranes of the Brushy Canyon Formation sandstones and siltstones to evaluate the significance of windblown dust in delivery of sediment and terrestrial organic matter to the Middle Permian Delaware Basin. Ramp siltstones of the basin have been interpreted as representing deposits of unconfined low-density turbidity currents or "aeolo-marine" sediments. We analyzed the organic contents of five samples of channel-confined turbiditic sandstones and siltstones and five samples of ramp siltstones outcropping in the Guadalupe Mountains National Park, West Texas, to estimate the relative proportions of terrestrial and marine organic matter in the two types of host rocks. The total organic carbon content of all samples varied from 0.07 percent - 2.04 percent. The abundance of high molecular weight n-alkanes (n-C27 and greater) suggests that terrestrial organic matter was present in nearly all samples. Terrestrial organic matter input to the basin was characterized using a crossplot of pristane/n-C17 versus phytane/n-C18. Ramp siltstones showed ~10-fold greater variation in terrestrial content than did turbiditic sandstones and siltstones. This observation is more consistent with the aeolo-marine interpretation of ramp siltstones, and suggests that terrestrial organic matter was delivered to the Delaware Basin by wind transport during deposition of the Brushy Canyon Formation.

Thesis--Madras University. / Bibliography: p. [149]-157.

Thesis (M.S. in Physical Oceanography and Meteorology)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Bourke, Robert H. ; Paquette, Robert G. "September 1990." Description based on title screen viewed on December 16, 2009. DTIC Descriptor(s): Polar regions, *deep water, dynamics, water, rates, arrays, surfaces, fresh water, drift, ice, surveys, surface waters, high density, transport, patterns, thinness, barometric pressure, Atlantic ocean, sea water, height, basins(geographic), Eurasia, gradients, Greenland sea, Lagrangian functions, Greenland, cores, water analysis, temperature DTIC Identifier(s): Jan Mayen current, *ocean currents, *sea water, *water analysis, oceanographic data, electrical conductivity, temperature, density, transport properties, east Greenland current, Greenland sea, theses Includes bibliographical references (p. 137-139). Also available in print.

In the 1980s, USAID (US Agency for International Development) funded an environmental assessment of dams on the Gambia River, which determined that construction of the Balingho anti-salinity barrage would result in adverse unmitigative environmental and social consequences. Attempts by host country politicians, USAID and UNDP (United Nations Development Programme) to discredit this process made it necessary to take the matter to the Natural Resource Defense Council. A case study of the events surrounding these dams and their potential construction illustrates the ‘big dam’ paradigm and its potential harm to people, their livelihoods and the environment in Sub-Saharan Africa.