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Removed overburden, burial, maturation, and petroleum generation analysis indicates that maturity in the Arkoma Basin and the Ouachita Foldbelt is explained effectively using simple burial models that account for the significant surface erosion that has occurred and assuming geothermal gradients similar to present-day gradients have been approximately constant through geologic time. Regional models, based on analysis at 115 well locations, indicate that from 5,000 to 15,000 ft (1.5–4.5 km) of section, differing with location from north to south and west to east, has been removed from the Arkoma Basin region, and as much as 25,000–40,000 ft (7.5–12 km) have been removed from areas of the Ouachita Foldbelt. Based on burial and thermal history reconstruction, increasing maturation from west to east across the basin is primarily the result of increasing overburden and subsequent surface erosion from west to east. The models predict most publicly available vitrinite reflectance data within a factor of 1.5 at two standard deviations. Comparison of model and measured reflectance-depth trends in six wells indicates that hydrothermal fluid movement should not have modified reflectance by more than approximately 20% in the center of the basin. Analysis indicates that most of the basin is overmature for oil production from intervals below the Spiro Sandstone, except to the north and northwest. Although thermal maturities are high, methane is stable throughout the basin. Except for the basal Arbuckle Group, all formations were thermally immature for oil generation prior to burial by the Mississippian and Morrowan in the Ouachita Foldbelt of Oklahoma and by the Atokan and Desmoinesian over most of the basin and study area. In the deeper part of the present basin, all strata entered and passed through the oil window during or within 10 My after Atokan time. Because no additional major quantities of hydrocarbons were generated after Atokan time, the hydrocarbons must have been emplaced and trapped during this brief time interval. 相似文献
2.
The problem of cost shifting from higher tiers of government to local councils in Australia is widely recognised and has been investigated by several official inquiries. However, it has thus far been difficult to gather reliable estimates of the magnitude of the problem. Quite apart from the taxing definitional and data problems associated with the phenomenon, these difficulties have been compounded by the fact that very few attempts have been made to measure the impact of specific instances of cost shifting in Australian local government, especially its spatial impact. In an attempt to remedy this neglect, this paper seeks to measure the spatial effects of pensioner rate concession rebates on local councils in New South Wales. 相似文献
3.
Mark E. Byrnes R. Wayne Nelson Robert G. La Poe Dennis E. Lundquist William McNeill 《Ground Water Monitoring & Remediation》1990,10(4):90-95
A remedial investigation (RI) was performed in an area downgradient from an abandoned missile silo at Vandenberg Air Force Base, California, as part of the United States Air Force Installation Restoration Program (IRP). A number of complementary investigative techniques were used to assure a reliable assessment of site contamination. These included the review of aerial photographs, the use of an organic vapor analyzer (OVA) and carbon adsorption/mass spectrometer (MS) method to conduct a soil-gas survey; magnetic and electromagnetic geophysical surveys; bedrock permeability testing; and the chemical analysis of soil, sediment, surface water, and ground water samples. The results from this investigation revealed the presence of an undocumented landfill and a small trichloroethylene plume in ground water at concentrations ranging from 6.7 ppb to 31 ppb. The investigation also identified local ground water flow direction, provided strong evidence of the location of potential sources of contamination, and defined the downgradient extent of ground water contamination. Because the identified contaminants have not as yet reached the environmentally sensitive wetland at the base of the slope below this facility, there is still time to propose remedial alternatives that would serve to protect this environmentally sensitive area. 相似文献
4.
Coastal morphodynamics and Chenier-Plain evolution in southwestern Louisiana, USA: A geomorphic model 总被引：1，自引：0，他引：1
Using 28 topographic profiles, air-photo interpretation, and historical shoreline-change data, coastal processes were evaluated along the Chenier Plain to explain the occurrence, distribution, and geomorphic hierarchy of primary landforms, and existing hypotheses regarding Chenier-Plain evolution were reconsidered. The Chenier Plain of SW Louisiana, classified as a low-profile, microtidal, storm-dominated coast, is located west and downdrift of the Mississippi River deltaic plain. This Late-Holocene, marginal-deltaic environment is 200 km long and up to 30 km wide, and is composed primarily of mud deposits capped by marsh interspersed with thin sand- and shell-rich ridges (“cheniers”) that have elevations of up to 4 m.In this study, the term “ridge” is used as a morphologic term for a narrow, linear or curvilinear topographic high that consists of sand and shelly material accumulated by waves and other physical coastal processes. Thus, most ridges in the Chenier Plain represent relict open-Gulf shorelines. On the basis of past movement trends of individual shorelines, ridges may be further classified as transgressive, regressive, or laterally accreted. Geomorphic zones that contain two or more regressive, transgressive, or laterally accreted ridges are termed complexes. Consequently, we further refine the Chenier-Plain definition by Otvos and Price [Otvos, E.G. and Price, W.A., 1979. Problems of chenier genesis and terminology—an overview. Marine Geology, 31: 251–263] and define Chenier Plain as containing at least two or more chenier complexes. Based on these definitions, a geomorphic hierarchy of landforms was refined relative to dominant process for the Louisiana Chenier Plain. The Chenier Plain is defined as a first-order feature (5000 km2) composed of three second-order features (30 to 300 km2): chenier complex, beach-ridge complex, and spit complex. Individual ridges of each complex type were further separated into third-order features: chenier, beach ridge, and spit.To understand the long-term evolution of a coastal depositional system, primary process–response mechanisms and patterns found along the modern Chenier-Plain coast were first identified, especially tidal-inlet processes associated with the Sabine, Calcasieu, and Mermentau Rivers. Tidal prism (Ω) and quantity of littoral transport (Mtotal) are the most important factors controlling inlet stability. Greater discharge and/or tidal prism increase the ability of river and estuarine systems to interrupt longshore sediment transport, maintain and naturally stabilize tidal entrances, and promote updrift deposition. Thus, prior to human modification and stabilization efforts, the Mermentau River entrance would be classified as wave-dominated, Sabine Pass as tide-dominated, and Calcasieu Pass as tide-dominated to occasionally mixed.Hoyt [Hoyt, J.H., 1969. Chenier versus barrier, genetic and stratigraphic distinction. Am. Assoc. Petrol. Geol. Bull., 53: 299–306] presented the first detailed depositional model for chenier genesis and mudflat progradation, which he attributed to changes in Mississippi River flow direction (i.e., delta switching) caused by upstream channel avulsion. However, Hoyt's model oversimplifies Chenier-Plain evolution because it omits ridges created by other means. Thus, the geologic evolution of the Chenier Plain is more complicated than channel avulsions of the Mississippi River, and it involved not only chenier ridges (i.e., transgressive), but also ridges that are genetically tied to regression (beach ridges) and lateral accretion (recurved spits).A six-stage geomorphic process-response model was developed to describe Chenier-Plain evolution primarily as a function of: (i) the balance between sediment supply and energy dissipation associated with Mississippi River channel avulsions, (ii) local sediment reworking and lateral transport, (iii) tidal-entrance dynamics, and (iv) possibly higher-than-present stands of Holocene sea level. Consequently, the geneses of three different ridge types (transgressive, regressive, and laterally accreted) typically occur contemporaneously along the same shoreline at different locations. 相似文献
5.
Ischadites lindstroemi Hinde 1884 is described from the Ordovician Daylesford Formation (lower part of the Bowan Park Group) of central western New South Wales. The species characterises a distinctive unit in the formation, occurring in bands throughout the unit. From a study of the associated lithofacies and their stratigraphic distribution in the limestones, an interpretation of the environment in which the species lived is presented. The species is considered to have inhabited a shallow‐water, lime‐mud environment, which was off‐shore and marginal to calcarenite shoals. 相似文献
6.
Kimette Radtke Robert W. Byrnes Pamela Kerrigan William E. Antholine David H. Petering 《Marine environmental research》1992,34(1-4)
It is widely thought that redox-active metals in cells such as iron or copper catalyze the reduction of hydrogen peroxide to toxic hydroxyl radicals or their equivalent. However, this has not been directly demonstrated in vivo. To probe this requirement, the freshwater microorganism Euglena gracilis was used. Its intracellular iron content can be modulated by the concentration of iron in the defined growth medium without effect on the proliferation rate of the cells. E. gracilis contains two large storage pools of cytosolic iron which can be monitored to assess cellular iron status. The toxicity of H2O2 in E. gracilis was inversely related to the amount of iron in the extracellular medium. At high levels of external iron, the metal carried out the Fenton reaction with H2O2 outside the cell, producing hydroxyl radicals as detected by electron-spin resonance spin-trapping experiments. This reaction reduced the amount of H2O2 that could diffuse into cells to cause toxicity. When cells with different intracellular iron content were placed in iron-deficient media, the the toxicity of H2O2, measured by inhibition of proliferation, was directly related to the concentration of internal iron. Using cells deficient in iron, this oxidant did not inhibit proliferation at low concentration but was somewhat effective at higher concentrations. Although the iron chelating agents, 1,10-phenanthroline and desferrioxamine, also depressed cytosolic iron, they were cytotoxic to E. gracilis and so could not be used unambiguously to examine the role of intracellular iron in the toxic effects of hydrogen peroxide. 相似文献
7.
Yan Lavallée Shanaka L. de Silva Guido Salas Jeffrey M. Byrnes 《Bulletin of Volcanology》2006,68(4):333-348
Through examination of the vent region of Volcán Huaynaputina, Peru, we address why some major explosive eruptions do not
produce an equivalent caldera at the eruption site. Here, in 1600, more than 11 km3 DRE (VEI 6) were erupted in three stages without developing a volumetrically equivalent caldera. Fieldwork and analysis of
aerial photographs reveal evidence for cryptic collapse in the form of two small subsidence structures. The first is a small
non-coherent collapse that is superimposed on a cored-out vent. This structure is delimited by a partial ring of steep faults
estimated at 0.85 by 0.95 km. Collapse was non-coherent with an inwardly tilted terrace in the north and a southern sector
broken up along a pre-existing local fault. Displacement was variable along this fault, but subsidence of approximately 70 m
was found and caused the formation of restricted extensional gashes in the periphery. The second subsidence structure developed
at the margin of a dome; the structure has a diameter of 0.56 km and crosscuts the non-coherent collapse structure. Subsidence
of the dome occurred along a series of up to seven concentric listric faults that together accommodate approximately 14 m
of subsidence. Both subsidence structures total 0.043 km3 in volume, and are much smaller than the 11 km3 of erupted magma. Crosscutting relationships show that subsidence occurred during stages II and III when ∼2 km3 was erupted and not during the main plinian eruption of stage I (8.8 km3).
The mismatch in erupted volume vs. subsidence volume is the result of a complex plumbing system. The stage I magma that constitutes
the bulk of the erupted volume is thought to originate from a ∼20-km-deep regional reservoir based on petrological constraints
supported by seismic data. The underpressure resulting from the extraction of a relatively small fraction of magma from the
deep reservoir was not sufficient enough to trigger collapse at the surface, but the eruption left a 0.56-km diameter cored-out
vent in which a dome was emplaced at the end of stage II. Petrologic evidence suggests that the stage I magma interacted with
and remobilized a shallow crystal mush (∼4–6 km) that erupted during stage II and III. As the crystal mush erupted from the
shallow reservoir, depressurization led to incremental subsidence of the non-coherent collapse structure. As the stage III
eruption waned, local pressure release caused subsidence of the dome. Our findings highlight the importance of a connected
magma reservoir, the complexity of the plumbing system, and the pattern of underpressure in controlling the nature of collapse
during explosive eruptions. Huaynaputina shows that some major explosive eruptions are not always associated with caldera
collapse.
Editorial responsibility: J Stix 相似文献
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Mixtures of pure dry CaCO3 and MgCO3 were reacted at 10 kbar in a piston-cylinder apparatus. Solidus and liquidus boundaries were delineated by interpretation of quenched textures. X-ray determined compositions of quenched carbonates are not a reliable guide to the phase relations. The binary melting loop for CaCO3-MgCO3 extends from CaCO3 at 1460°C through a liquidus minimum near 30 wt% MgCO3 and 1075°C, and it is terminated at the incongruent melting reaction for dolomite solid solution at 1125° C (liquid with 32 wt% MgCO3) Magnesite solid solution dissociates at 1090°C to produce dolomite + periclase + CO2, truncating the dolomite-magnesite solvus. The 10 kb liquidus minimum at 1075°C and 30 wt% MgCO3 occurs at lower temperature and higher ratio than the 27 kbar liquidus minimum at 1290°C and 38 wt% MgCO3. This relationship suggests that the first liquid produced by melting of a carbonate-bearing peridotite has increasing ratio with increasing pressure. These phase relations provide part of the framework required to trace paths of crystallization of kimberlite and carbonatite magmas. 相似文献
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