A textbook case of bow shock entrainment in a YSO outflow

Near-infrared images in H₂ line emission and submillimetre maps in CO J  = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars.   The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H₂ bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H₂ luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H₂ luminosity ratio.     

Two-phase evolution of the Shadow Valley Basin, south-eastern California: a possible record of footwall uplift during extensional detachment faulting

Miocene strata of the Shadow Valley Basin rest unconformably on the upper plate of the Kingston Range - Halloran Hills detachment fault system in the eastern Mojave desert, California. Basin development occurred in two broad phases that we interpret as a response to changes in footwall geometry. In southern portions of the basin, south of the Kingston Range, phase one began with near synchronous initiation of detachment faulting, volcanism and basin sedimentation shortly after 13.4 Ma. Between c. 13.4 and c. 10 Ma, concordantly bedded phase one strata were deposited onto the subsiding hangingwall of the detachment fault as it was translated 5–9 km south-westward with only limited internal deformation. Phase two (c. 10 to 8–5 Ma) is marked by extensional dismemberment of the detachment fault's upper plate along predominantly west-dipping normal faults. Phase two sediments were deposited synchronously with upper-plate normal faulting and unconformably overlie phase one deposits, displaying progressive shallowing in dip and intraformational onlap. Northern portions of the basin, in the Kingston Range, experienced a similar two-phase development compressed into a shorter interval of time. Here, phase one occurred between c. 13.4 and 12.8–12.5 (?) Ma, whereas phase two probably lasted for no more than a few 100000 years immediately prior to c. 12.4 Ma. Differences in the duration of basin development in and south of the Kingston Range apparently relate to position with respect to the detachment fault's breakaway; northern basin exposures overlie the upper plate adjacent to the breakaway (0–15 km) whereas southern basin exposures occur far from the breakaway (20–40 km). We interpret the phase one to phase two transition as recording breakup of the detachment fault's hangingwall during footwall uplift. We propose a model for supradetachment basin evolution in which early, concordantly bedded basin strata are deposited on the hangingwall as it translates intact above a weakly deforming footwall. With continuing extension, tectonic denudation along the detachment fault leads to an increasing flexural isostatic footwall response. We suggest that isostatic footwall uplift may drive internal breakup of the upper plate as the detachment fault is rotated to a shallow dip, mechanically unfavourable for simple upper-plate translation. Additionally, we argue that continuing hangingwall thinning during phase two places geometrical constraints on the timing, amount and, thus, rate of footwall uplift. Kinematically determined footwall uplift rates (0.5–4.5 mm/yr) are comparable with rates determined independently by thermochronological and geobarometric methods.     

Dispersion into pisolitic laterite from the greenbushes mineralized Sn-Ta pegmatite system, Western Australia

A study of dispersion into pisolitic laterite duricrust in the Archaean Greeenbushes mineralized pegmatite district reveals a geochemical anomaly that measures some 20 km by 12 km centred on the ore deposits that, prior to commencement of mining operations, were concealed. The anomaly is broadest for As, Sn, Be and Sb, all of which show well-defined centres over the swarm of mineralized pegmatites. Coincident highs of Nb, Ta and B also define the 5 km by 1 km anomaly centre. Over the strongest part of the multi-element anomaly, the following levels in ppm are reached in the pisolitic laterite: As 1150, Sb 75, Sn 4200, Nb 75, Ta 75, W 30, Li 100, B 500 and Be 60.The immediate source for the dispersion anomaly is the swarm of soft, weathered pegmatites and their wall rocks, most of which occur within a 5 km by 1 km area, elongated along strike. The source, as judged from past production plus soft pegmatite reserves, was a mass of some 30–40 million tonnes with an approximate average grade of 220 ppm Sn, 25 ppm Nb and 30 ppm Ta.The geochemical expression of the multi-element anomaly can conveniently be expressed in a map of pegmatite-associated elements. For example, the index PEG-4*X which uses an empirically derived weighted linear combination 0.09As + 1.33Sb + Sn + 0.6Nb + Ta (where values for each element are in ppm) gives a broad consistent anomaly.Investigation of dispersion processes shows that mechanical dispersion of cassiterite and columbo-tantalite took place for distances of at least 5 km during laterite formation along gradients ranging from 5 m to 20 m per km. The occurrence of anomalous As in the skins of pisolites indicates hydromorphic dispersion during laterite formation, but mechanical dispersion of goethitic material with scavenged As has also taken place.The size of the geochemical dispersion anomaly, together with its contrast and consistency, shows that it is feasible in the Australian environment to explore for concealed mineral deposits using low-density surface sampling. Sample spacings of 3 km are being tested in an extension of this approach to exploration.     

Generating large stochastic simulations—The matrix polynomial approximation method

An algorithm for producing a nonconditional simulation by multiplying the square root of the covariance matrix by a random vector is described. First, the square root of a matrix (or a function of a matrix in general) is defined. The square root of the matrix can be approximated by a minimax matrix polynomial. The block Toeplitz structure of the covariance matrix is used to minimize storage. Finally, multiplication of the block Toeplitz matrix by the random vector can be evaluated as a convolution using the fast Fourier transform. This results in an algorithm which is not only efficient in terms of storage and computation but also easy to implement.     

Lags in vegetation response to greenhouse warming

Fossil pollen in sediments documents vegetation responses to climatic changes in the past. Beech (Fagus grandifolia), with animal-dispersed seeds, moved across Lake Michigan or around its southern margin, becoming established in Wisconsin about 1000 years after populations were established in Michigan. Hemlock (Tsuga canadensis), with wind-dispersed seeds, colonized a 50,000 km² area in northern Michigan between 6000 and 5000 years ago. These tree species extended ranges northward at average rates of 20–25 km per century. To track climatic changes in the future, caused by the greenhouse effect, however, their range limit would need to move northward 100 km per °C warming, or about 300 km per century, an order of magnitude faster than range extension in the past. Yet range extension in the future would be less efficient than in the past, because advance disjunct colonies have been extirpated by human disturbance, and because the seed source is reduced due to reductions in tree populations following logging. Many species of trees may not be able to disperse rapidly enough to track climate, and woodland herbs, which have less efficient seed dispersal mechanisms, may be in danger of extinction.     

Beneficial use of municipal sludge in the ocean

The micronutrients in municipal sludge enhance ocean productivity in much the same way as they enhance plant productivity when applied to the land. The organic solids of municipal sludge can also directly enhance production of valuable biomass in the ocean, particularly benthic biomass. Studies of municipal sludge and wastewater discharge into marine waters throughout the world have demonstrated that, if the application rate of municipal sludge or wasterwater was optimized by utilizing larger sites, beneficial enhancement of marine production could be achieved without the adverse effects associated with excessive application rates and overfertilization. Existing evidence indicates that, although not risk- or disadvantage-free, beneficial use of municipal sludges in the ocean is a viable management option which, in some instances, is likely to have fewer negative environmental side effects than other feasible beneficial use options.     

Massive sulfides in a sedimented rift valley, northern Juan de Fuca Ridge

A number of mounds each several hundred meters across and up to sixty meters high have been observed with SeaMARC II acoustic imagery and Seabeam bathymetry in the sediment-filled axial valley at the northern end of the Juan de Fuca Ridge. The mounds are located a few kilometers west of the eastern valley-bounding normal fault scarp where the local sediment fill is approximately 300 m thick. All of the mounds are believed to be of hydrothermal origin, and one is associated with anomalously high heat flow in excess of 1 W m⁻². A piston core collected from that mound comprises coarse clastic sulfide units interbedded with sulfidic muds. Hydrothermal minerals present in the 2.3 m section include pyrrhotite, pyrite, marcasite, sphalerite, chalcopyrite, iss (intermediate solid solution in the CuFeZnS system), chalcopyrrhotite, galena, talc, barite, and amorphous silica. Mineral fabrics of the clasts indicate that the material was precipitated at or near the sea floor by mixing of hot hydrothermal fluids with cold seawater. Low concentrations of Zn, Cu, Cd, and Ag relative to those found in unsedimented ridge hydrothermal deposits, and the presence of pyrrhotite as an early phase mineral indicates that the vent fluids have been modified by reaction with sediments beneath the mound. Rapid sedimentation in a rift valley is clearly conducive to the formation of large hydrothermal mineral deposits like those believed to be present within and beneath these mounds. The relatively impermeable sediment cover insulates the crust, inhibits groundwater recharge, promotes long-lived discharge at a restricted number of sites, provides a substrate for the efficient subsurface precipitation of minerals, and through continued sedimentation, protects surficial deposits from the corrosive effects of seawater. No reliable estimate of the bulk composition of the mounds can be made with existing data, but their size is comparable to major hydrothermal mineral deposits found on land; ancient settings in which many land deposits formed are in many ways similar to the one in which the features described here are currently forming.     

Chemical and biological processes in coquina of Castillo de San Marcos National Monument

Analyses of water flowing through coquina showed exclusion of atmospheric CO₂ and supersaturation in respect to calcite and hydroxyapatite. Extensive populations growing on the walls and benefiting from these nutrients included mainly blue-green algae, green algae and diatoms.     

A regional analysis of the meteorological aspects of the spread and development of blue mold on tobacco

Tobacco blue mold caused by Peronospora tabacina is a highly weather sensitive disease which occurred in the major tobacco production areas of North Carolina in 1980. Dates of first reported occurrence of blue mold by county units in eastern North Carolina progressed in a northeastward direction from the South Carolina border to the Virginia border between 1 May and 6 June. In the central piedmont region of the state, blue mold was first reported in mid-May while in the western mountains, blue mold was recorded in early June. Temperatures and total weekly rainfall data were analyzed for 18 weeks from late March to early August from 102 weather stations across North Carolina and from the bordering regions of surrounding states. An analysis of first occurrence dates and the temporal and spatial properties of temperature and precipitation indicated that the epidemic continued to spread despite temperatures outside the range previously considered favorable for the disease. Availability of moisture on the tobacco leaves for spore germination appeared to be the predominant factor in all parts of the state. Trajectory analysis was used to identify possible source regions for the spores which arrived over North Carolina tobacco fields. The analysis indicated that there were many days in April, May, and June 1980 when conditions were considered favorable for spore transport to North Carolina from the infected fields located to the south. Taking into account epidemiological latent periods, certain of these trajectory dates were selected as representing the most probable periods of spore transport.Paper No. 9019 of the Journal Series of the North Carolina Agricultural Research Series, Raleigh, NC 27650, U.S.A.This research was supported in part by the North Carolina Tobacco Foundation, Inc., and the R. J. Reynolds Tobacco Company, Inc.     

Solid state C NMR studies of selected oil shales from Queensland, Australia

Solid state ¹³C NMR techniques of cross polarization with magic-angle spinning, and interrupted decoupling have been employed to examine the nature of the organic matter in eight kerogen concentrates representing five Tertiary deposits in Queensland, Australia. The NMR results show that five of the kerogens have high proportions of aliphatic carbon in their organic matter and correspond to Type I–II algal kerogens. Three of the kerogens, derived from carbonaceous shales, have a high proportion of aromatic carbon in their organic matter and correspond to Type III kerogens. The fractions of aliphatic carbon in all the kerogens, regardless of type, are shown to correlate with the conversion characteristics of the corresponding raw shales during Fischer assay. Interrupted decoupling NMR results show the presence of more oxygen-substituted carbon in the carbonaceous shales, which may account for the greater CO₂ evolution and phenolic materials found in the pyrolysis products of the carbonaceous shales.