Southern Third Research Articles

Structure of the Alula‐Fartak Fracture Zone, Gulf of Aden

The Alula‐Fartak transform fault is associated with a broad, steep‐sided valley running NNE‐SSW across the mouth of the Gulf of Aden. A discussion of the tectonics of the fracture zone is based principally on GLORIA side scan sonar and gravity data. The transform valley is 180 km long and 25 km across, has 3.5 km of relief, and is bounded by transverse ridges. The northern two‐thirds is highly asymmetrical in cross section. The eastern wall dips 38° and appears to be a single scarp exposing a section of oceanic crust 3100 m thick. The western wall is much less steep and accommodates several normal faults oriented at about 15° to its general trend. A very fine, long sonar target running along part of the valley delineates the main active strike‐slip fault. The sonar data also reveal many fine faultlike targets between the main walls, running approximately at right angles to the trend of the valley, which may be anti‐Riedel shears. A 50‐km‐long, 7.5‐km‐wide, and 1.5‐km‐high median ridge runs along the southern third of the transform valley. Gravity data show that the valley is underlain by a significant mass deficiency thought to be a large serpentinite intrusion. The median ridge is suggested to be the surface manifestation of a large serpentinite diapir. The ridges flanking the transform valley are above a level compatible with isostatic equilibrium and are interpreted as flexural features raised in response to the upward loads imposed on the lithosphere by the fracture zone valley and its underlying mass deficiency. Very shallow crust is located close to the ridge‐transform intersections. This is considered to result from static flexure induced by the negative load of the transform valley superimposed on dynamic compensation of the spreading center valley. Evidence of a c. 3.5 m.y. B.P. change in spreading direction suggests the transform has experienced a recent component of opening, accounting for several aspects of its structure.

Regional geological investigations and 1:500 000 mapping in North-East Greenland

North-East Greenland is the last major area that remains to be geologicaIly mapped in the programme of regional mapping at a scale of 1:500000. In 1988 a three-year field mapping programme was initiated aimed at regional geological studies and geological mapping in the area between 75°N and 78°N. The southern third of this region (75°-76°N) is included on the map at a scale of 1:250000 by Koch & Haller (1971), and the n0rthern part forms part of a map at a scale of 1:1 000000 (Haller, 1983). However, the region as a whole has previously only been studied on a reconnaissance basis with limited ground control, and the published maps make extensive use of aerial photograph interpretation.

The Decoupling of Farm and Household: Differential Consequences of Capitalist Development on Southern Illinois and Third World Family Farms

The literature on women's role in economic development in the third world indicates that as agrarian societies industrialize, women tend to take on ever greater responsibility for agricultural production, in addition to their reproductive and household duties, as working age men and, in some cases, women seek wage labor to supplement insufficient farm production (Boserup 1970:80–81; Bossen 1984; Deere and León de Leal 1981; Ward 1984).

Use of Multivariate Discriminant Analysis of Male Wing Morphometrics to Delineate a Hybrid Zone for Papilio glaucus glaucus and P. g. canadensis in Wisconsin

The eastern tiger swallowtail butterfly Papilio glaucus L. is distributed throughout Canada and the eastern half of the United States. Two of the three purported subspecies (Papilio glaucus glaucus and Papilio glaucus canadensis) occur in Wisconsin. In order to determine the extent of hybridization between the two subspecies, 18 wing characters were measured or scored for three reference groups: canadensis (from Canada, northern Minnesota and the Upper Peninsula of Michigan), glaucus (from southern Ohio and central Illinois) and known laboratory F, hybrids. These data were subjected to multivariate discriminant analysis, and the resulting rule was then used to statistically analyze field-captured adults from various counties of Wisconsin. Individuals collected from Wisconsin were entered as unclassified data and analyzed with regard to the reference groups in two ways. First, general body size (as indicated by forewing length) was included because of long recognized size differences between the subspecies. Second, the data were reanalyzed after body size was removed statistically. The results of the second analysis parallel those of the first, indicating that useful, nonsize related taxonomic characters are included in the measured traits. Of 15 wing traits (and three ratios), three wing characters alone gave an overall classification accuracy of 84%, which is close to the 88.5 7O correct classification with all traits used. The southern third of Wisconsin is very different from the northern two-thirds in tiger swallowtail composition. No field-captured individuals (unknowns) were classified as Papilio glaucus glaucus in the northern two thirds of the state, while most of the field captures from the southern third of the state were classified as such. Computerclassified reached their greatest frequency in the S-central part of Wisconsin and support the evidence of a hybrid between these Papilio subspecies. INTRODUCTION Hybrid zones have been defined as narrow regions in which genetically distinct populations meet, mate, and produce hybrids (Barton and Hewitt, 1985). Hundreds of suspected hybrid zones have been identified and a recent review concludes that it is difficult to distinguish whether the distinct forms in zones of parapatry are maintained by hybrid unfitness or differential adaptation to environmental factors (Woodruff, 1981; Barton and Hewitt, 1985). Central Wisconsin is particularly interesting in that it represents a tension zone for plant communities (Curtis, 1959) and a of overlap and suspected hybridization for many insects (Remington, 1968; Platt and Brower, 1968; Scriber, 1982, 1983). There is great interest in understanding the causal mechanisms and processes promoting or preventing gene exchange among populations and hybrid zones offer a valuable natural laboratory in this regard (e.g, Littlejohn and Watson, 1985; Slatkin, 1985). 'Department of Entomology, University of Wisconsin, Madison 53706. 2Current address: Department of Entomology, Michigan State University, East Lansing, 48824. 3Departments of Horticulture and Statistics, University of Wisconsin, Madison 53706. 4Current address: Department of Medical Genetics, University of Wisconsin, Madison 53706.

Methodology for Woodfuel Development Planning in the Kenyan Highlands

The Kenya Woodfuel Development Programme (KWDP) has developed a three-tier approach to the study of rural woodfuel energy supplies. The methodology has evolved in the course of studying three districts (Kakamega, Kisii and Murang'a) in the densely-populated high- lands of Kenya between 1983 and 1986. The approach hinges on three elements: (1) district sub-regionalization based on low-level colour air- photography; (2) household questionnaire surveys based on a nested sample derived from the sub-regionalization; (3) a cultural survey through which prevailing attitudes to on-farm agroforestry and woodfuel issues are revealed. Additional aspects of the programme include a district-wide on-farm woody biomass survey based on the results of the air-photo survey and field work, and a farm typology which is being developed on the basis of all three surveys. Some of the more important conclusions which have emerged from this work include the following: (a) The integration of tree production into general farming activities is complex and deeply-rooted. Local farmers have an intimate knowledge of the benefits and weaknesses of the different trees growing in different situations on the farms. These are manifest in different ways among the sub-regions of the districts. (b) As a proportion of the total on-farm woody biomass, deliberately managed and planted woody biomass increases with increasing population density. (c) Contrary to expectations, as population density increases and farm size diminishes, the amount of land devoted to woody biomass production increases. In the southern third of Kakamega District, with rural population densities exceeding 700 per sq. km, more than 20% of the land is devoted to woody biomass. (d) Assuming an annual requirement of 1 m3 of wood per person, it is estimated that 31% of the district's farms experience a shortage of greater than 50% of needs. Only 21% have a surplus. Despite such a high proportion of land devoted to trees, the population densities are so high that these areas experience the greatest deficits.

THE ORINOCO OIL BELT, VENEZUELA

The Orinoco Oil Belt of Venezuela is a very extensive, non‐discrete, crude‐oil producing area located along the southern third of the Maturín (Eastern Venezuela) basin, north of the Orinoco River and the Guayana Shield. It extends due westwards from Puerto Ordaz for 460km; the main producing areas, defined on the basis of productivity and magnitude of crude oil in‐place, cover 13, 600 sq. km. There are no significant surface indications of petroleum anywhere in the Belt. The first well drilled was La Canoa‐1 in 1936, initiating a stage of exploration which ended in 1967 with publication of a preliminary evaluation of the potential reserves; the Ministry of Energy and Mines, then of Mines and Hydrocarbons, and the State oil company Corporación Venezolana del Petróleo (CVP) completed a second stage of exploration in 1977; Petróleos de Venezuela and its operating companies then drilled 669 wells in five years (1979–83) totalling 643,000 m with 5.5 MM** m of logs, and shot 15,000 km of seismic lines at a cost of $US 615 MM, an effort conservatively estimated as having taken 2,500 man‐years. The main producing areas are, from east to west, Cerro Negro, Pao, Hamaca, San Diego, Zuata, and Machete. Petroleum characterisation in the Belt is based on the study and analysis of 288 samples. Viscosity (dynamic) of the crude oils at reservoir conditions ranges from 2,000 to 7,000 m Pa.s (cp)†.Production rates average 25 cu. m/d(160 b/d), increasing fourfold after steam stimulation. At the end of 1985, production was 13,000 cu.m/d(80,000b/d)†, from the Cerro Negro and Hamaca main producing areas. Operating costs are similar to those in other heavy‐crude oilfields in the basin. The volume of crude oil in‐place is estimated to be 187.8 B cu. m (1,181 B brls), which makes the Orinoco Oil Belt the largest crude oil accumulation in the world. Proved reserves are 4.161 B cu. m (26.170 B brls). and unproved reserves 14.822 B cu. m (93.230 B brls). Investigative activities are underway, particularly in the Cerro Negro and San Diego producing areas. In subsequent papers of this thematic survey, A. Isea presents a geological synthesis of the Orinoco Oil Belt; G. Don Kiser discusses the exploration results of the Machete area; A. Santos and L. Frontado describes the reservoir geology of the Cerro Negro steam‐injection area; and A. Vega and I. de Rojas summarise exploration results from the Zuata area.

Structural framework of the Gulf of Elat (AQABA), Northern Red Sea

The Gulf of Elat (Aqaba) occupies the southern part of the Dead Sea rift. The rift is considered to be a plate boundary of the transform type (partially leaky) which connects seafloor spreading in the Red Sea with the Sagros‐Taurus zone of continental collision. The deep water in the Gulf of Elat, up to 1850 m, provides a rare opportunity to examine the process of continental rifting by marine geophysical techniques. The bathymetry alone provides much information about fault patterns in this area. The fragmentation of the once continuous Arabian‐African platform is a complicated process. It shapes the structure of the gulf which has developed through continuing tectonism, primarily consisting of faulting. Recent geophysical and geological studies of the Gulf of Elat including bathymetry, bottom photographs, continuous seismic profiles, seismic refraction, gravity, magnetics, heat flow, and coring provide new information about the shallow and deep crustal structure of this important segment of the world rift system. The shallow structure of the gulf is dominated by three elongated en echelon basins, which strike N20°–25°E. Undulations in the floors of the basins produce several distinct deeps. These basins are interpreted as pullaparts. The new data from the gulf suggest that classical models for the formation of these structures should be modified. Only one of the longitudinal faults of each depression is a strike‐slip fault, while the other is predominantly a normal fault. The situation with the other two sides of the basin which are supposed to be composed of normal faults may also be more complex than previously thought. At least in one case, one such boundary is composed of a strike‐slip fault while the other has no significant fault. Crustal models of the Gulf of Elat based on gravity data indicate that the basins are rather shallow and do not extend into the lower crust. The fill of the basins extends to about 5 km below the seafloor in. the northern and southern basins and less in the central basin. Most significant magnetic anomalies in the Gulf of Elat extend from land into the sea. None of them, however, extends from one coast to another across the gulf. This supports the geological evidence for a shear between the Arabia and Sinai plates. The magnetic field over the southern third of the gulf is rather smooth and markedly different from that of the other parts. The nature of the magnetics, the crustal structure of the western margin, and the heat flow values indicate a thinner crust and different tectonic processes in the southern part of the gulf. Overall, it seems that within the southern Gulf of Elat a transition occurs between crustal spreading that takes place in the Red Sea to a rifting without spreading that takes place along the Dead Sea transform. Spreading activity propagates from south to north. The most active place is the central basin which is being propagated northward into the shallow northern basin.

Modeling of the surface static displacements and fault plane slip for the 1979 Imperial Valley earthquake

Abstract Synthesis of geodetic and seismological results for the 1979 Imperial Valley earthquake is approached using three-dimensional finite element modeling techniques. The displacements and stresses are calculated elastically throughout the modeled region. The vertical elastic structure in the model is derived from compressional and shear wave velocities as used in the seismic data analysis (Fuis et al., 1981) combined with a sediment density profile. Two strategies for applying initial conditions are followed in this modeling. In the first strategy, a sample seismological estimate for fault plane slip is used to predict the resultant surface motions. We show that the geodetic strain results over distances of tens of kilometer from the fault (Snay et al., 1982) are basically consistent with the model seismic fault displacements. Geodetic results from within a few kilometers of the fault trace (Mason et al., 1981) seem to require more slip at shallow depths than appears at seismic time scales. This is consistent with the occurrence of aftercreep at shallow depths in less well-consolidated material, which would bring surface displacements into line with maximum slip at depth, but not greatly affect the net moment. In the second strategy, we consider stresses on the fault plane, rather than displacements, as model variables. To constrain this part of our numerical modeling, we assume that the fault driving stress is governed by ambient tectonic stress and an opposing Coulomb friction derived from experiment. The coseismic stress drop from point to point on the failed fault is given by the difference between the tectonic shear stress and the frictional stress. After arriving at such a uniform model which adequately represents the Snay et al. results, we further modify a small region near the seismic “asperity” to make the fault plane motions qualitatively and quantitatively resemble the model of coseismic motions used in the first strategy. The observed offset on the fault trace (Sharp et al., 1982) is approximated in this final stress-driven model by removing the driving stress on the southern third of the fault. Thus, the principal features of the coseismic slip pattern are explained by a stress-driven fault model in which: (a) a spatially unresolved asperity is found equivalent to a stress drop of 18 MPa averaged over an area of 15 km2, and (b) driving stress is essentially absent on the fault segment overlapping the 1940 earthquake rupture zone.

Chemical patterns of bulk atmospheric deposition in the state of Colorado

Samples of bulk deposition from the atmosphere were taken over a 1‐year interval between May 1982 and May 1983 at 42 sites distributed over the state of Colorado. Collections were complete for the entire year at 36 of these sites. The collections were made biweekly and were analyzed for major cations, major anions, total particulate material, and the hydrogen ion (pH). A pH below 5.6 was characteristic of the annual precipitation over two thirds of the state, including all of the high‐elevation areas in central Colorado as well as substantial portions of the plains. The lowest pH values (average below 5.0) were found near the Continental Divide in the northern third and southern third of the state. Emissions of NOx and SO2 from power plants within or near the borders of the state are of a magnitude similar to that of the total deposition of SO4 = and NO3− N within the state. Gradients of acidity within the state are to a large degree explained by three factors: (1) location of power plants and urban areas with respect to prevailing winds, (2) differential transport of strong acids and alkalis, and (3) amount of wet precipitation. At lower elevations, carbonates neutralize strong mineral acids, as shown by the distributions of strong acid anions and divalent cations. Because of their association with terrestrial particulate materials, alkalis are transported over shorter distances than the gaseous precursors of mineral acids. Thus air masses moving over the mountains, which lack large sources of either alkalis or acids, show an increasing bias toward acidifying substances at higher elevations. This causes a statewide negative relation between pH and elevation. Superimposed on the elevation effect is a moisture effect caused by a strong relationship between strong acid deposition and amount of wet precipitation.

Dieldrin, heptachlor, and chlordane residues in soybeans in Illinois 1974, 1980.

The Illinois soybean crop was monitored in 1974 and 1980 for dieldrin, heptachlor, and chlordane residues resulting from the use of these compounds for corn soil insect control in the years before extensive soybean cultivation. Residue levels were compared with past published amounts. Dieldrin residue levels in soybeans declined between 1974 and 1980. Heptachlor and heptachlor epoxide levels remained level between 1974 and 1980. Chlorinated hydrocarbon residues were lower in the southern third of Illinois than for the remainder of the state.

Egyptian Exploration: Background, Models, and Future Potential: ABSTRACT

Egypt has proven to be an area with excellent exploration End_Page 492------------------------------ potential. Recent discoveries in the Western Desert tilted fault blocks are leading to a reevaluation of new play concepts based on an east-west Tethyan rift structure model. Facies favorable to hydrocarbon accumulation are associated with shallow-water marine depositional environments. Production has not been great on a per-well basis, but fields have consistently outproduced the original recoverable reserve estimates. The Gulf of Suez lies within the rift between North Africa and Arabia-Sinai. It remains a major producing area with production from sandstones which range in age from Carboniferous to Cretaceous. The Upper Cretaceous and Lower Tertiary carbonates are potentially attractive zones, as are the Miocene clastics and carbonates. Miocene marls and Upper Cretaceous shales are source rocks, and thermal maturation can be directly related to continental rifting with the oil window most attractive in the southern third of the Gulf of Suez. Structural style is strongly rift-influenced with tilted and locally eroded hosts prevalent. The central gulf has a general eastern dip, whereas the northern and southern areas have a regional westward dip. This has had a direct influence in isolating some majo oil fields and has adversely affected reflection seismic surveys. Exploration has been difficult because of excessive Miocene and younger salt thicknesses. With increasingly refined technology, attractive targets now are being delineated in the hitherto unexplored lows between horsts within the gulf. End_of_Article - Last_Page 493------------

Hydrology of Okarito Lagoon and the inferred effects of selective logging in Okarito Forest

Okarito Lagoon (43° 11′S, 170° 14′E) is a small (20 km2) shore‐parallel, predominantly subtidal estuary, deepest near the landward end, and linked to the sea by two subtidal channels incised through shallow subtidal and intertidal flats which occupy the southern third of the lagoon. Tides at sea vary from 2.1m (spring) to 1.2 m (neap), but in the lagoon the tidal range is constant through the lunar cycle and varies from 0.80 m at the entrance to 0.17 m in the upper lagoon. Tidal water level and flow asymmetries in the subtidal channels are separated by a 1.7 h phase difference. Variations in the net discharge through the inlet result from changing flow cross‐sections rather than from variations in current velocities. Both the tidal‐averaged volume and the tidal compartment of the lagoon vary through the lunar cycle, from maxima at spring tides to minima at neap tides. Freshwater inflows vary from less than 11 m3.s‐1 to more than 750 m3.s‐1. During storms, water level in the lagoon rises rapidly by 2–3 m, then declines to normal over several days. Three water masses, two with salinity and turbidity largely controlled by antecedent rainfall, normally occur in the lagoon. Suspended sediment concentrations in both freshwater inflows and lagoon waters are normally low but increase during floods. Most sediment is supplied by the Waitangi‐taona River or by erosion of tidal channel margins. The lagoon is floored with organic‐rich mud and sandy mud, deposited predominantly from suspension. Surface sediment is consistently muddier than subsurface sediment, probably reflecting an increase in the mud supply since diversion of the Waitangi‐taona River in 1967. Comparisons of the estimated sediment yield and water inflow effects of the 1967 river diversion with short‐term observations during selective logging suggest that the effects of logging on sediment yield, water balance of the lagoon, and dissolved solids inputs will be small compared with changes caused by diversion of the Waitangi‐taona River.

A New Species of Haematopota (Diptera, Tabanidae) from Mali, West Africa1

Haematopota athlyna n. sp. is described from specimens collected in the southern third of Mali, West Africa.

Ecology of recurrent groups of pteropods, euphausiids, and chaetognaths in the Gulf of Thailand and the South China Sea

Seventy-five species of pteropods (20 species), euphausiids (26 spcies), and chaelognaths (29 species) occur in the Gulf of Thailand and the South China Sea. All but one of these species are present in the South China Sea, while only 17 species (7 pteropods, 1 euphausiid, and 9 chaetognaths) are consistently present in the Gulf of Thailand. Abundances of South China Sea species have significant positive rank correlations with depth of water, salinity, and dissolved oxygen and negative correlations with temperature. These species are most abundant in the northern, oceanic, two-thirds of the South China Sea and many of them are vertical migrators or live at depth. Species in the Gulf of Thailand may be divided into two subgroups based on their tolerance for the semi-estuarine environment. Species in the most tolerant subgroup are more abundant within the Gulf of Thailand than in the South China Sea and have significant negative rank correlations with depth of water, salinity, and dissolved oxygen and positive correlations with temperature. The shallow, low-salinity environment of the Gulf is not as favorable for the species of the second sub-group. Rank correlations with depth of water, salinity, temperature, and oxygen are the same in sign but lower in value than for the South China Sea species, and maxisium abundances occur in the 50 to 200 m water depths of the southern third of the South China Sea. Species inhabiting the Gulf of Thailand are mostly non-migrators which are epipelagic even in the open ocean. The proportion of tolerant species diffiers among the major taxonomic groups, reflecting differing adaptive strategies.

Temperature and Moisture Conditions on a Plowed Jack Pine Strip Cut in Southeastern Manitoba

Soil moisture, maximum surface temperatures, and duration of critical temperatures for jack pine (Pinusbanksiana Lamb.) seedlings were measured across a scarified east–west strip cut on a dry site in southeastern Manitoba. Temperature conditions were significantly less severe on the southern third of the strip and usually more favorable on the south side and in the trough of plowed furrows. Soil moisture remained within the available range [Formula: see text] at 3.8- and 7.6-cm depths under undisturbed and trough seedbeds throughout the growing season. Results indicate that moisture and temperature conditions lethal to germinants exist on all seedbeds of this site under weather conditons normally expected in the area. The more uniform moisture conditions under the trough seedbed suggest that it is most favorable for planting.

Tidlig-neolitiske anlæg ved Rustrup

Tidlig-neolitiske anlæg ved Rustrup

Geohydrology of the Buried Triassic Basin at the Savannah River Planta

ABSTRACTAt the Savannah River Plant near Aiken, South Carolina, as at other locations where there are chemical separations plants for the processing of nuclear fuels, the high‐level radioactive wastes are stored in concrete and steel tanks buried just beneath the surface of the ground. This waste is of such activity and longevity that it cannot be dispersed into the environment, but it must be contained for periods of time extending at least into hundreds and perhaps thousands of years. One concept for the terminal containment of this waste is to store it in excavated chambers within the bedrock, which is covered by about 1000 feet of Coastal Plain sediments at the plantsite. As part of the safety evaluation of this concept, the geology and hydrology of both the Coastal Plain sediments and the bedrock have been studied. However, intensive investigation of bedrock waste storage has now been deferred pending more detailed evaluation of alternative concepts of waste storage and management.In the studies completed, a buried Triassic basin that might have potential for waste storage was discovered beneath the southern third of the plantsite. Investigation into the characteristics of this basin was started in 1971. This was not an engineering or design study but was aimed at understanding the geohydrology of the Triassic basin to determine its compatibility with the safe storage of waste.Seismic surveys, gravity and magnetic surveys, and the drilling of several exploratory wells indicate that the Triassic basin is about 30 miles long, 6 or more miles wide, and perhaps 5300 feet thick. One well penetrated the Triassic border, a second was in the center of the basin, and a third investigated an inferred intrabasin fault. The rock is predominantly mudstone of very low permeability with a few lenses of poorly sorted gritty sand. The water yield of all the exploratory wells is extremely low, and water‐transmitting fractures are virtually nonexistent.In two wells within the basin, heads above land surface have been measured that cannot be explained by connection with a recharge area. Ten possible explanations have been evaluated: aquifer head, fossil head, tectonic compression, rapid loading and compaction of sediments, water derived from igneous intrusions, infiltration of gas, precipitation of minerals, phase changes, temperature increase, and osmotic membrane phenomena. Systematic evaluation, particularly of the time for dissipation of an elevated head to the head of its surroundings, eliminates most of these explanations. Those that remain as possible explanations are: tectonic compression, temperature increase, and osmotic membrane phenomena. It is not known at present whether the high head is general over the entire basin or only in segments of it.

Geohydrology of Buried Triassic Basin at Savannah River Plant, South Carolina

A buried Triassic basin with possible potential for storage of high-level radioactive wastes was discovered beneath the southern third of the Savannah River Plant site near Aiken, South Carolina. Investigation into the characteristics of the basin was aimed at understanding the geohydrology to determine its compatibility with the safe storage of waste. Before it was completed, the investigation was deferred pending more detailed evaluation of alternative concepts of waste storage and management. However, some of the geohydrologic results of the investigation are reported herein. Seismic surveys, gravity and magnetic surveys, and the drilling of several exploratory wells indicate that the Triassic basin is about 30 mi long, 6 or more mi wide, and perhaps 5,300 ft thick. One well penetrated the Triassic border, a second was in the center of the basin, and a third investigated an inferred intrabasin fault. The rock is predominantly mudstone of very low permeability with a few lenses of poorly sorted gritty sand. The water yield of all the exploratory wells is extremely low, and water-transmitting fractures are virtually nonexistent. In two wells within the basin, heads above land surface have been measured that cannot be explained by connection with a recharge area. Possible explanations are tectonic compression, temperature increase, and osmotic-membrane phenomena. Whether the high head is general over the entire basin or only in segments of it is unknown.

Geohydrology of Buried Triassic Basin at Savannah River Plant: ABSTRACT

At the Savannah River plant near Aiken, South Carolina, as at other locations where there are chemical-separation plants for the processing of nuclear fuels, the high-level radioactive wastes are stored in concrete-and-steel tanks buried just beneath the surface of the ground. This waste is of such activity and longevity that it cannot be dispersed into the environment, but it must be contained for periods of time extending at least into hundreds and perhaps thousands of years. One concept for the terminal containment of this waste is to store it in excavated chambers within the bedrock, which is covered by about 1,000 ft of coastal plain sediments at the plant site. As part of the safety evaluation of this concept, the geology and hydrology of both the coastal plain sedi ents and the bedrock have been studied. Intensive investigation of bedrock waste storage now has been postponed indefinitely while other concepts of waste storage and management are being investigated. A buried Triassic basin that might have potential for waste storage was discovered beneath the southern third of the plant site. Investigation into the characteristics of this basin was started in 1971. This was not an engineering on design study but was aimed at understanding the geohydrology of the Triassic basin to determine its compatibility with the safe storage of waste. Seismic surveys, gravity and magnetic surveys, and the drilling of several exploratory wells indicate that the Triassic basin is about 30 mi long, 6 or more mi wide, and perhaps 5,300 ft thick. One well penetrated the Triassic border, a second was in the center of the basin, and a third investigated an intrabasin fault. The rock is predominantly mudstone of very low permeability, with a few lenses of poorly sorted gritty sand. The water yield of all the exploratory wells is extremely low, and water-transmitting fractures are virtually nonexistent. In 2 wells within the basin, heads above land surface have been measured that cannot be explained by connection with a recharge area. Ten possible explanations have been evaluated: aquifer head, fossil head, tectonic compression, rapid loading and compaction of sediments, water derived from igneous intrusions, infiltration of gas, precipitation of minerals, phase changes, temperature increase, and osmotic membrane phenomena. Systematic evaluation, particularly of the time for dissipation of the elevated head to the head of its surroundings, eliminates most of these explanations. Those that remain as possible explanations are: tectonic compression, temperature increase, and osmotic membrane phenomena. It is not known at present whether the high head is general over the entire basin or nly in segments of it. End_of_Article - Last_Page 1601------------

ACETYLENE REDUCTION IN RELATION TO LEVELS OF PHOSPHATE AND FIXED NITROGEN IN GREEN BAY

The use of acetylene reduction as an index of N2 fixation (Dilworth, I966; Sch6llhorn and Burris, I966) has aided substantially in the assessment of biological N2 fixation in the field (Koch and Evans, I966; Sloger and Silver, I967; Stewart, Fitzgerald and Burris, I967; Hardy et al., I968). Despite deficiencies, e.g. its indirect nature and the lack of a consistent factor to convert acetylene reduction directly to N2 fixation, the method is valuable for field work because it is sensitive, rapid, and simple. This paper reports data collected during the summer of I97I on the southern third of Green Bay of Lake Michigan. The southern section of Green Bay shows eutrophication (Stewart et al., I97I), and the present study undertook to characterize acetylene reduction and nutrient levels throughout the summer. Acetylene reduction activity closely correlated with population increases of blue-green algae, primarily species of Aphanizomenon and Anabaena, and these population increases occurred at sites where the soluble phosphate concentration was high. Increases in the population of Anabaena and Aphanizomenon species (and in acetylene reduction activity) usually were preceded by increases in the soluble phosphate in the water.