Large-scale oblique features in an active transform fault,the Wilkes fracture zone near 9°S on the East Pacific Rise

The Wilkes fracture zone offsets the East Pacific Rise about 200 km right-laterally near 9°S. The bathymetric expression of the fracture zone ranges from a simple slope or step along its inactive extension to a 100 km wide zone of oblique structural features in the active portion. A low ridge 200 to 300 m high, 5 to 15 km wide and 185 km long is the dominant oblique structure; it trends 23° north of the main transform trend. A high-amplitude magnetic anomaly trends 097° along the southern part of the active portion and apparently marks the main transform direction. The structurally simple, inactive portions of the Wilkes fracture zone trend 105°. Plots of epicenter locations reveal two groupings of earthquakes, one along an 082° trend in the central part of the fracture zone, and a cluster near the southwestern fracture zone — spreading center intersection.Taken together the data suggest that some event, other than a shift in the Nazca-Pacific pole of rotation, occurred 0.9 m.y. ago to change the Wilkes fracture zone from a simple fault to a complex zone of shearing. Since that time the long oblique ridge, probably the surface expression of a Riedel shear, was formed. At present the entire 200 km long, 100 km wide region between the offset axes is seismically active, but transform motion may be largely confined to the southern margin of the active zone, coincident with the high-amplitude magnetic anomaly there.     

PCB resistance within phytoplankton populations in polluted and unpolluted marine environments

A comparison between clones of two species of diatoms, Asterionella japonica and Ditylum brightwellii, isolated from Sandy Hook, New Jersey (polluted site) and Montauk, New York (unpolluted site) indicated that some of the clones from Sandy Hook were more resistant to polychlorinated biphenyls (PCB). A japonica was less sensitive to PCB than D. brightwellii since seven clones of A. japonica from both sites were tolerant of 25 μg litre^?1 PCB whereas no clones from either site of D. brightwellii showed such resistance. Growth under high light intensity increased the sensitivity to PCB in all clones except one super-resistant clone from Sandy Hook which was not affected even by additions of 50 μg litre^?1 to the growth medium. This interactive effect of light on PCB sensitivity may relate to the photo-adaptive characteristics of each clone.     

Seabed measurements of modern corrosion rates on the Florida escarpment

A mooring containing diverse carbonate and anhydrite substrates was exposed to bottom waters for 9 months at the base of the Florida Escarpment to determine the influence of dissolution on the development of this continental margin. Weight loss was measured on all samples. Etching, pitting, and loss of the original framework components were observed on substrates with known characteristics. Extrapolations of modern dissolution rates predict only about 1.6 meters of corrosion per million years. However, more rapid anhydrite dissolution, up to 1 km per million years, would cause exposed anhydrite beds to undercut and destabilize intercalated limestones.     

Le zooplancton du lac de Bret en 1902/03, 1943 et 1951

Summary The Lac de Bret, formerly an “oligotrophic” lake, has by several artificial risings of its level become “eutrophic” with the drawbacks of that state during the summer stagnation. A plant of partial underwater aeration has improved the situation and has been described in this Review (11, 423 [1949]). The above study compares the zooplancton of this lake in the years 1902/03 when it was yet oligotrophic with its plancton in the year 1943 during the investigations in the lake become eutrophic and finally in the year 1951 when it had again grown sound after five seasons of estival acration.      

Geochemistry of fine-grained clastic sedimentary rocks of the Neoproterozoic Ikorongo Group, NE Tanzania: Implications for provenance and source rock weathering

The Neoproterozoic Ikorongo Group, which lies unconformably on the late Archaean Nyanzian Supergroup of the Tanzania Craton, is comprised of conglomerates, quartzites, shales, siltstones, red sandstones with rare flagstones and gritstones and is regionally subdivided into four litho-stratigraphic units namely the Makobo, Kinenge, Sumuji and Masati Formations.We report geochemical data for the mudrocks (i.e., shales and siltstones) from the Ikorongo basin in an attempt to constrain their provenance and source rock weathering. These mudrocks are compositionally similar to PAAS and PS indicating derivation from mixed mafic–felsic sources. However, the siltstones show depletion in the transition elements (Cr, Ni, Cu, Sc and V) and attest to a more felsic protolith than those for PAAS and PS. The Chemical Index of Alteration (CIA: 52–82) reveal a moderately weathered protolith for the mudrocks. The consistent REE patterns with LREE-enriched and HREE-depleted patterns ((La/Yb)_CN = 7.3–38.3) coupled with negative Eu anomalies (Eu/Eu* = 0.71 on average), which characteristics are similar to the average PAAS and PS, illustrate cratonic sources that formed by intra-crustal differentiation.Geochemical considerations and palaeocurrent indications suggest that the provenance of the Ikorongo Group include high-Mg basaltic-andesites, dacites, rhyolites and granitoids from the Neoarchaean Musoma-Mara Greenstone Belt to the north of the Ikorongo basin. Mass balance calculations suggest relative contributions of 47%, 42% and 11% from granitoids, high-magnesium basaltic-andesites and dacites, respectively to the detritus that formed the shales. Corresponding contributions to the siltstones detritus are 53%, 43% and 4%.     

Desiccation-induced Shrinkage in Compacted Lateritic Soils

Specimens prepared from three lateritic soil samples were subjected to drying under laboratory conditions. Volumetric shrinkage strains were measured at the end of the drying period. Results of this study indicate that, for the lateritic soils tested, volumetric shrinkage strains are influenced by soil composition and compaction conditions. Volumetric shrinkage strain increased with higher compaction water content. The influence of compaction water content on measured volumetric shrinkage strain was more pronounced in specimens with higher fines content. A regression equation was developed from the data to estimate volumetric shrinkage strain given the compaction water content relative to optimum, plasticity index, fines content and compactive effort.     

Using home buyers’ revealed preferences to define the urban–rural fringe

The location of new homes defines the urban–rural fringe and determines many facets of the urban–rural interaction set in motion by construction of new homes in previously rural areas. Home, neighborhood and school district characteristics play a crucial role in determining the spatial location of new residential construction, which in turn defines the boundary and spatial extent of the urban–rural fringe. We develop and apply a spatial hedonic variant of the Blinder (J Hum Resour 8:436–455, 1973) and Oaxaca (Int Econ Rev 9:693–709, 1973) price decomposition to newer versus older home sales in the Columbus, Ohio metropolitan area during the year 2000. The preferences of buyers of newer homes are compared to those who purchased the nearest neighboring older home located in the same census block group, during the same year. Use of the nearest older home purchased in the same location represents a methodology to control for various neighborhood, social–economic-demographic and school district characteristics that influence home prices. Since newer homes reflect current preferences for home characteristics while older homes reflect past preferences for these characteristics, we use the price differentials between newer and older home sales in the Blinder–Oaxaca decomposition to assess the relative significance of various house characteristics to home buyers.