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About 100 vertical electrical soundings (VES) were made at Tel-Halawi hill on the left bank of the Euphrates just before it flows into the Assad Lake in northern Syria. The VES stations were distributed, at 2 m spacing, along nine profiles (10 m apart), covering the southern part of the site. The electrode array adopted was a modified Schlumberger configuration (pole–dipole array with the B-electrode placed far enough to be of negligible effect). During every sounding potential electrodes (MN) were fixed symmetrically on both sides of VES point location O (MO = ON = 0.25 m), whereas the current electrode A was moved away with the following distances from the MN midpoint: OA = 1, 1.5, 2, 3, 4, 5, 7 and 10 m. The resistivity data measured were then treated and plotted in the field as resistivity cross-sections of different pseudodepths, showing the specific influence of the buried targets at different depths. This procedure, although time consuming, looks a very promising technique for discovering near-surface targets through resistivity survey. This method reflects successively the resistivity contribution of the buried targets according to their depth, separating them with regard to the depth of burial. It offers also higher reliability of results, owing to the confirmed response of buried targets as related multiple anomalies on several resistivity cross-sections with gradually increasing depths. Many of these anomalies measured along the resistivity profiles were verified through excavation work. Copyright © 2001 John Wiley & Sons, Ltd.

SUMMARY Iron and sulphur in proportions appropriate to Fe 7 S 8 were reacted in evacuated quartz tubes for 24 hr at 500°C. Quenching produces predominantly hexagonal pyrrhotite, whereas further prolonged annealing at 250°C produces monoclinic pyrrhotite. We mainly report the properties of material cooled from 500° Ca t 10°C min'1, which is predominantly monoclinic but probably contains hexagonal pyrrhotite together with pyrite, FeS 2 . This material, which we refer to as 'non-ideal' pyrrhotite, may be a better analogue of pyrrhotite ore than ideal synthetic monoclinic pyrrhotite. The samples were characterized by X-ray, Mossbauer eVect and thermomagnetic analyses. The slow- cooled non-ideal monoclinic pyrrhotite exhibits thermal stability intermediate between monoclinic and hexagonal pyrrhotites. One striking observation is that the deviation from ideal monoclinic pyrrhotite increases with decreasing particle size. Particles about 1 mm in size have a low saturation magnetization value of about 6 Am2 kg'1, indicating a lower concentration of ferrimagnetic monoclinic pyrrhotite (saturation magnetization 18 Am2 kg'1) than particles of about 6 mm and above (saturation magnetization 12 Am2 kg'1). On the other hand, magnetization process parameters—coercive force, ratio of saturation remanence to saturation magnetization, coercive force of remanence, median destructive and inductive fields, the magnetic susceptibility—follow well-behaved power law dependences on particle size, similar to monoclinic pyrrhotite. Magnetic domain patterns in the slow-cooled non-ideal pyrrhotite are similar in type and style to those observed in synthetic monoclinic pyrrhotite and in natural pyrrhotite particles in rocks. Dynamic observations of domain walls in changing external alternating and direct magnetic fields are consistent with macroscopic obser- vations of magnetization change with field. The critical size for the monodomain/ multidomain transition in synthetic monoclinic pyrrhotite, at about 1 mm, is essentially the same as that previously determined for natural pyrrhotite grains in rocks. The observations suggest that the domain walls lie normal to the c-axis of the structure, consistent with the known magnetocrystalline anisotropy symmetry of monoclinic pyrrhotite. The type and style of the magnetic microstructures of hexagonal pyrrhotite are quite diVerent from those of monoclinic pyrrhotite. The domain patterns are on a much smaller scale, wavy, and sometimes resemble those of a hexagonal material such as magnetoplumbite or cobalt.

SUMMARY Palaeomagnetic investigations have been carried out on Tethyan sediments from the NW Zanskar Range (33.9°N, 76.5°E). A total of 455 oriented samples from 41 sites were drilled from four stratigraphic units of Middle Cretaceous to Early Eocene age (Shillakong Formation, Marpo Limestone/Spanboth Formation, Stumpata Quartzarenite/Spanboth Formation, Kong Formation). A characteristic remanence (ChRM) could be isolated for 27 sites (254 specimens) through detailed thermal and alternating field demagnetization and multicomponent analysis. All the ChRM directions identified are similar, irrespective of geological age. They fail the fold test and yield an overall in situ mean direction of D= 336.6°/I=+39.6° with α95= 5.9° and k= 22.9. This corresponds to a palaeopole position at 66.5°N, 323.5°E (N-pole). Isothermal remanence (IRM) acquisition and thermal demagnetization of a saturation IRM identify pyrrhotite as the dominant ferrimagnetic mineral and carrier of the ChRM. The pyrrhotite remanence is probably a thermoremanent magnetization acquired when the temperature of low-grade metamorphism decreased below about 300°C. The ChRM directions are thus clearly secondary in origin, and a negative conglomerate test carried out on the Kong Formation demonstrates that remanence acquisition post-dates the Early Eocene. The mean ChRM inclination suggests that the remanence was acquired at about 20°N. Cooling events in the higher Himalayan crystallines indicate an Oligocene age for this remanence acquisition. The mean ChRM declination shows a counterclockwise rotation of 23.4° since remanence acquisition. Assuming remanence acquisition at about 30 Myr ago, a slight counterclockwise rotation of about 10° relative to the stable Indian Plate can be concluded. This does not fit with the general pattern of palaeomagnetic results from neighbouring areas within the western syntaxis of the Himalaya, from which a clockwise rotation relative to the stable Indian Plate is expected for the Zanskar Range.

The IAGA global palaeomagnetic database, initiated in 1988, is supposed to contain directional and statistical palaeomagnetic data, and additional information on rock magnetic measurements for assessment of the reliability of the palaeomagnetic results. The rock magnetic information content of the database for 1969–1988 was analysed. As a main result, it could be shown that, at present, only about half of the palaeomagnetic results are supported by rock magnetic measurements; however, there is a tendency towards the improvement of this figure. The increase of investigations on sediments is clearly associated with the introduction of more sensitive magnetometers since the early 1970s. Trends could also be found for some rock magnetic techniques (e.g. isothermal remanent magnetization acquisition curves).

Since the introduction of the dipole shear sonic measurements a large number of compressional and shear data sets have been acquired, especially in shaly sands. Correlations between these measurements are now well established and used routinely. The Castagna mudrock and sandstone lines on the Vp and Vs crossplot are popular among geophysicists while trends of Vp/Vs versus Δt proposed by Brie et al. (1995) are popular among petrophysicists. As expected, a comparison of these correlations shows that they are quite similar in saturated and dry conditions. However, the Vp/Vs trends can simulate different pore fluid types or saturation conditions because the fluid effect is accounted for through the Gassmann equation. Using published correlations for adiabatic elastic moduli with temperature and pressure, we have generated slowness charts for water solutions and hydrocarbons and used them to refine the Vp/Vs trends. In particular we generated different trends for sands impregnated with fresh water, salt-saturated water and live oil. We show that the Vp/Vs trend for live oil is quite distinct from that in water. An application of these correlations is to convert shear to compressional. As shear slowness is little sensitive to fluid type, the obtained compressional slowness, Δtwet, simulates water-filled shaly sands. A comparison of Δtwet with measured Δt provides a quicklook indicator of hydrocarbons. Various examples are presented and discussed. We show that all correlations give good results in sands with porosity larger than 20%. Between 10 and 20% porosity, correlations must be adjusted to obtain reliable results. Below 10% porosity, the technique becomes unusable. The Δtwet estimate has other interesting applications in the domain of rock mechanics and stress evaluation because it is unaffected by fluid content. An example shows how the technique was applied to improve hydraulic-fracture design.