S U M M A R YMagnetostratigraphic age dating has been carried out on sandstones of a wellexposed continuous 5500 m thick Miocene-Pleistocene section in the Surai Khola area (West Nepal). The section is situated in the Siwalik Range which consists of molasse sediments from the Himalaya. Progressive demagnetization and isothermal remanence experiments prove that haematite is the carrier of the characteristic remanent magnetization (ChRM) throughout the entire section. The final polarity sequence is based on 436 samples, of which 233 have normal and 203 reverse polarity. Antiparallel mean directions of the normally and reversely polarized samples indicate that the ChRM is of primary origin. Comparison of the polarity sequence with a standard polarity time-scale yields a time period for the section between chron l r or chron 2r (Matuyama) and probably chron 5AB (between 1-2 Myr and about 13 Myr).

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Magnetostratigraphic research, undertaken within the past 15 years in the Siwaliks distributed along 400 km of the Sub-Himalaya in central Nepal, has proved that the sediments possess highly reliable hematite-based primary detrital remanent magnetization suitable to determine depositional chronology. In order to bring out the polarity sequences in a common chronological frame, all available data are newly correlated to the latest global magnetic polarity time scale of Cande and Kent (1995). Chronological data presented are referred in relation to the diverse lithological nomenclature to the formations whose ages are not constrained by isotopic or paleontologic ages. The age of the sections dated by magnetostratigraphy ranges between 14 and <2 Ma. Sediment accumulation rates average to 32-50 cm kyr -1 . Rock-magnetic parameters, e.g. initial susceptibility and isothermal remanent magnetization ratios, allow correlation with an accuracy of up to a few hundred meters among several kilometers thick adjacent sections.Anisotropy of magnetic susceptibility (AMS) data reveal a well-defined fabric contributed by paramagnetic (k = 10 -5 to 3x10 -4 SI) as well as ferromagnetic minerals (k = 3x10 -4 to 10 -2 SI). AMS ellipsoids are mainly oblate along with prolate ones and the degree of anisotropy is mostly low (P"<1.2). The magnetic fabric is of pre-folding origin with tiltcorrected sub-vertical magnetic foliation poles. The magnetic lineations do not show parallelism to the expected paleocurrent directions. Rather, sub-parallelism between the clusters of magnetic lineation and the fold axes/bedding strikes/thrust fronts is observed. A superimposed fabric consisting of a sedimentary-compactional and an overprint induced by mild deformation process is suggested. The latter process was active during and subsequent to the deposition in the compressive tectonic setting of the foreland basin. The magnetic lineations for Tinau Khola and Surai Khola sections cluster around N80W and N88W respectively, whereas N27W trend characterizes the Amiliya-Tui area south of Dang. The peak clusters in lineations are probably orthogonal to the true shortening axes. Their variation along the Sub-Himalaya, together with the fold axes or thrust front trends, may be used for accurate tectonic reconstruction. It is especially important when orthogonality of the latter to the shortening axes may not hold true in the sectors with imbricate fold-and-thrust structures.

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S U M M A R YThe magnetostratigraphy of five new sections through the Neogene Siwalik Group of Nepal is presented. Rock magnetic experiments and detailed thermal demagnetization experiments prove that haematite is the carrier of a primary DRM br a PDRM. After stepwise thermal demagnetization of specimens from all sections, directions of characteristic remanent magnetization were obtained. The results show a positive reversal test and exhibit inclination errors of about 20". Due to gaps in exposures and extremely variable demagnetization behaviour of the haematite-bearing sediments, the resulting polarity sequences are poorly defined for some parts of the sections. However, doublesampled parts of some sections yield similar results. A correlation with the Surai Khola section (Appel, Rosler & Corvinus 1991) is proposed, based on rock magnetic parameters. AMS results from three of the sections prove the existence of primary sedimentary magnetic fabrics in these sections with systematic orientations of minimum and maximum susceptibility axes. Correlation with a standard polarity timescale indicates that the ages of all new sections lie within the age limits of the Surai Khola section.