Magnetostratigraphy of the Miocene-Pleistocene Surai Khola Siwaliks in West Nepal

Abstract

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).

Depositional chronology and fabric of Siwalik group sediments in Central Nepal from magnetostratigraphy and magnetic anisotropy

“…The experiments conducted are: NRM measurements with stepwise alternating field demagnetization (AFD: up to 150 mT) and thermal demagnetization (ThD: up to 700C), measurements of the initial magnetic susceptibility and its changes during stepwise heating, isothermal remanent magnetization (IRM) acquisition and demagnetization, and study of opaque minerals in polished thin sections (Appel et al 1991, Gautam and Appel 1994, and Rösler et al, 1997. Figure 5 shows the NRM data plotted against magnetic susceptibility for 3 sections.…”

“…Data from the four sections belonging to this area are treated in detail in Appel et al (1991), Rösler et al (1997) and Rösler (1998). The sections are briefly described here.…”

“…The next generous effort was made by M. Yoshida in Arung Khola-Binai Khola where over 12 sections distributed over an area of 5,000 km 2 were measured for the polarity record and the finer lithostratigraphic divisions were dated using magnetostratigraphy (Tokuoka et al, 1986). With the development of cryogenic magnetometers and sophisticated laboratory procedures capable of extracting the weak primary magnetization, relatively continuous sequences of the Nepalese Siwaliks have been important targets for the world"s paleomagnetic community (Appel et al, 1991;Harrison et al, 1993;Gautam and Appel, 1994;and Rösler et al, 1997).…”

The Cenozoic Vertebrate Fossils from the Nepal Himalaya: A Review

“…On the basis of lithological character she divided the stratigraphy of the Siwalik Group along the Surai Khola section into fi ve units namely the Bankas Formation, Chor Khola Formation, Surai Khola Formation, Dobatta Formation and Dhan Khola Formation. Palaeomagnetic dating of the Surai Khola sequence indicated a time scale from 13 to 1 Ma (Appel et al 1991, Appel andRoesler 1994 (West et al1991). …”

Magnetic minerals and magnetic properties of the Siwalik Group sediments of the Karnali river section in Nepal

“…During the last two decades, it has been demonstrated that the chronology of the Mio-Pliocene fluvial sediments of the Siwalik Group from Pakistan, India and Nepal can be deciphered through correlation of magnetic polarity reversal patterns to the geomagnetic polarity time scale (GPTS) (Barndt et al, 1978;Opdyke et al, 1979;Tauxe and Opdyke, 1982;Johnson et al, 1982Johnson et al, , 1983Tokuoka et al, 1986;Ranga Rao et al, 1988;Opdyke, 1990;Appel et al, 1991;Harrison et al, 1993;Gautam and Appel, 1994;Burbank et al, 1996;Rösler et al, 1997). These data are invaluable for regional chronological correlation throughout the Sub-Himalayan belt.…”