Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain

This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275?m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north?Csouth current is deflected into an east?Cwest flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2?Ma), the upper Pliocene revolution (2.4?Ma) and the mid-Pleistocene revolution (0.9?Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150?m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time.     

Precambrian history of the Zona Transversal of the Borborema Province,NE Brazil: Insights from Sm–Nd and U–Pb geochronology

The Borborema Province has three major subprovinces. The northern subprovince lies north of the Patos shear zone and is comprised of Paleoproterozoic cratonic basement with Archean nuclei, plus overlying Neoproterozoic supracrustal rocks and Brasiliano plutonic rocks. The central subprovince occurs between the Patos and Pernambuco shear zones and is mainly comprised of the Zona Transversal. The southern subprovince occurs between the Pernamabuco shear zone and the São Francisco craton and is comprised of a tectonic collage of various blocks, terranes, or domains ranging in age from Archean to Neoproterozoic. This report focuses on the Zona Transversal, especially on Brasiliano rocks for which we have the most new information.Paleoproterozoic gneisses with ages of 2.0–2.2 Ga occur discontinuously throughout the Zona Transversal. The Cariris Velhos suite consists of metavolcanic, metasedimentary, and metaplutonic rocks yielding U–Pb zircon ages of 995–960 Ma. This suite is mainly confined to a 100 km wide belt that extends for more than 700 km within the Alto Pajeú terrane. Sm–Nd model ages in metaigneous rocks cluster about 1.3–1.6 Ga, indicating that older crust was involved in genesis of their magmas. Brasiliano supracrustal rocks dominate the Piancó-Alto Brígida terrane, and they probably also constitute significant parts of the Alto Pajeú and Rio Capibaribe terranes. They are only slightly older than early stages of Brasiliano plutonism, with detrital zircon ages at least as young as 620 Ma; most T_DM ages range from 1.2 to 1.6 Ga.Brasiliano plutons range from ca. 640 to 540 Ma, and their T_DM ages range from 1.2 to 2.5 Ga. Previous workers have shown significant correlations among U–Pb ages, Sm–Nd model ages, petrology, and geochemistry, and we are able to reinforce and extend these correlations. Stage I plutons formed 640–610 Ma and have T_DM ages less than 1.5 Ga. Stage II (610–590 Ma) contains few plutons, but coincides with the peak of compressional deformation, metamorphism, and formation of migmatites. Stage III plutons (590 to ca. 575 Ma) have older T_DM ages (ca. 1.8–2.0 Ga), as do Stage IV plutons (575 to ca. 550 Ma; T_DM from 1.9 to 2.4 Ga). Stage III plutons formed during the transition from compressional to transcurrent deformation, while Stage IV plutons are mainly post-tectonic. Stage V plutons (550–530 Ma) are commonly undeformed (except along younger shear zones) and have A-type geochemistry. The five stages have distinct geochemical properties, which suggest that the tectonic settings evolved from early, arc-related magma-genesis (Stage I) to within-plate magma-genesis (Stage V), with perhaps some intermediate phases of extensional environments.     

Production scenarios and the effect of soil degradation on long-term food security in China

Food security in China underlies the foundation of the livelihood and welfare for over one-fifth of the world's population. Soil degradation has an immense negative impact on the productive capacity of soils. We simulated the effect of soil degradation, which occurs in combination with increases in population size, urbanization rate, cropping intensity and decrease in cropland area, on long-term food security in China using a web-based land evaluation system. Our results predict that food crops may experience a 9% loss in productivity by 2030 if the soil continues to be degraded at the current rate (business-as-usual scenario, BAU). Productivity losses will increase to the unbearable level of 30% by 2050 should the soil be degraded at twice the present rate (double-degradation scenario, 2× SD). China's capacity for producing food from agricultural crops will be either adversely affected by the loss of cropland area (130, 113 and 107 million ha in 2005, 2030 and 2050, respectively) or favorably affected by agricultural intensification (in terms of the multi-cropping index at 120, 133 and 147% in 2005, 2030 and 2050, respectively). The loss of cropland is predicted to cause a 13–18% decrease in China's food production capacity by 2030–2050 relative to its 2005 level of 482 Mt, while agricultural intensification is predicted to cause an 11–23% increase. In total, China will be able to achieve a production level of 424 and 412 Mt by 2030 and 2050, respectively, under BAU, while this production will be only 386 and 339 Mt under 2× SD, respectively. In per capita terms, the relationship between food supply and demand will turn from an 18% surplus in 2005 to 3–5%, 14–18% and 22–32% deficits by 2030–2050 under the zero-degradation (0× SD), BAU and 2× SD scenarios, respectively. Our results show that the present-day production capacity will not sustain the long-term needs of a growing population under the current management level. Technical countermeasures and policy interventions need to be enacted today in order to avoid food insecurity tomorrow.     

Geochemistry of surface waters in the vicinity of open pit mines at the Cay Cham deposit, Thai Nguyen province, northern Vietnam

This study provides an assessment of the environmental impact of open pit mining operations at the Cay Cham titanomagnetite-ilmenite deposit (northern Vietnam). The results of surface water sampling indicate the formation of acid mine drainage and contamination of adjacent areas by heavy metals (Cu, Zn, Ni, and Mn). The acid mine drainage is produced by oxidation leaching of sulfide minerals associated with primary mineralization owing to the low neutralization potential of the natural waters in the humid environment of tropical rainforest. The study showed that alternating dry and wet seasons typical of this climatic region promote the generation of stored acidity leading to a sharp decrease in pH of drainage water during the wet season and result in the negative impacts of this mine on both flowing and stagnant surface waters.     

Biogeochemical exploration for massive sulphide deposits in areas of dense vegetation: an orientation survey around the Kanköy Deposit (Trabzon, northeastern Turkey)

The eastern Pontides region is a mountainous terrain favourable for massive sulphide deposits. Besides the known deposits, it is highly likely that there are others to be discovered. This paper, therefore, describes the results of a soil and biogeochemical sampling program to assess the suitability of biogeochemical methods for the exploration of hidden deposits in temperate terrains. Soil sampling in the Pontides is shown to be a reliable follow-up method. It produced a significant geochemical response characterised by extensive Cu and Zn but localised Pb anomalies. Lead therefore is the element which can be used to pinpoint the mineralisation due to its relatively less mobile character. Hydromorphic dispersion enhanced the anomalies indicating that base of slope samples would produce reliable results. Of the plant species sampled, Corylus avellana (hazelnut tree) with deep penetrating roots shows comparable results to soil sampling and could be used to delineate the mineralisation. Rhododendron luteum may also be of help. In both species Pb shows limited dispersion and accumulates in the plants near the mineralised site whereas Cu and Zn tend to move away downslope. This shows that biogeochemical sampling could, with proper attention to species selection, be successfully used as an alternative method in the search of massive sulphide deposits in mountainous terrains with a high rainfall such as the eastern Pontides.     

Performance evaluation of active wireline heave compensation systems in marine well logging environments

The basic functionality and performance of a new Schlumberger active wireline heave compensation system on the JOIDES Resolution was evaluated during the sea trial and a 3-year period of the IODP Phase II operations. A suite of software programs was developed to enable real-time monitoring of the dynamics of logging tools, and assess the efficiency of wireline heave compensation during downhole operations. The evaluation of the system effectiveness was performed under normal logging conditions as well as during stationary tests. Logging data were analyzed for their overall quality and repeatability, and to assess the reliability of high-resolution data such as formation microscanner (FMS) electrical images. This revealed that the system reduces 65–80 % of displacement or 88–98 % variance of downhole tool motion in stationary mode under heave conditions of ±0.2–1.5 m and water depths of 300–4,500 m in open holes. Under similar water/heave conditions, the compensator system reduces tool displacement by 50–60 %, or 75–84 % variance in downhole tool motion during normal logging operations. Such compensation efficiency (CE) is comparable to previous compensation systems, but using advanced and upgradeable technologies, and provides 50–85 % heave motion and heave variance attenuation. Moreover, logging down/up at low speeds (300–600 m/h) reduces the system’s CE values by 15–20 %, and logging down at higher speeds (1,000–1,200 m/h) eliminates CE values by 55–65 %. Considering the high quality of the logging data collected, it is concluded that the new system can provide an improved level of compensation over previous systems. Also, if practically feasible, future integration of downhole cable dynamics as an input feedback into the current system could further improve its compensation efficiency during logging operations.     

Chromium(III) — chromium(VI) interconversions in seawater

The stable form of dissolved chromium in oxygenated seawater is Cr(VI). But Cr(III)-species are also present at an analytically significant level. It is shown that Cr(III) is oxidized only slowly by dissolved oxygen, and that manganese oxide is a strong catalyst for such oxidation. However, the low oceanic concentration of suspended MnO₂ impedes the conclusion that the former process is quantitatively less important than the latter one. The distribution of dissolved chromium among Cr(VI)- and Cr(III)-species is probably kinetically controlled.     

Higher-degree reference field in the generalized Stokes-Helmert scheme for geoid computation

In this paper we formulate two corrections that have to be applied to the higher-degree reference spheroid if one wants to use it in conjunction with the Stokes-Helmert scheme for geoid determination. We show that in a precise geoid determination one has to apply the correction for the residual topographical potential and the correction for the earth ellipticity. Both these corrections may reach several decimetres; we show how their magnitudes vary within Canada and we give their global ranges.     

Observed Lα profiles for two solar flares: 14∶12 UT 15 June, 1973 and 23∶16 UT 21 January, 1974

Photographic observations of the time development of the profile of the L line of hydrogen during flares were obtained with the NRL spectrograph on ATM. The profiles for the 15 June, 1973 and 21 January, 1974 flares reported here cover both core and wings of the line. The time sequences begin before flare maximum, and continue well into the decay phase. Careful attention has been given to photometry and absolute calibration. In the case of the 15 June, 1973 flare, data are presented both first-order corrected and uncorrected for incomplete filling of the spectrograph slit by flaring material. Correction of the 21 January, 1974 flare was not possible. We discuss core symmetry and shift, and show that our observations imply integrated flare L/H intensity ratios within a factor of two of unity for these two flares.