ROCK MAGNETISM AND PALEOMAGNETISM OF MIOCENE FLUVIAL SEDIMENTS IN NORTHERN PAKISTAN (HEMATITE)

The rock magnetism and paleomagnetism of the Siwalik Group rocks exposed on the northern rim of the Soan synclinorium (northern Pakistan) were investigated. The principal aims of the research were (1) to determine the age and fidelity of magnetic remanence in these Miocene red beds and (2) to construct the local magnetostratigraphy in order to facilitate precise temporal correlation on a local, regional and global scale.;The properties of DRM and p-DRM in hematite are determined by study of modern analogues. A hematite DRM is found to preserve a significant inclination error in non-horizontal or vertical fields. Since DRM and p-DRM can rarely be distinguished in the Siwalik specimens, the paleomagnetic directions isolated should not be used to determine a paleopole position. Magnetostratigraphic studies are, however, justified.;The magnetostratigraphy of the study area is presented. Based on the work presented here, a revised correlation of the magnetostratigraphy to the magnetic polarity time scale is warranted. Tracing of several polarity unit boundaries along strike allows the reconstruction of contemporaneous fluvial systems operating on the Siwalik flood plain.;The magnetic remanence of the Miocene Siwalik red beds is carried by two forms of hematite. Pigmentary hematite gives rise to a viscous remanent magnetization (VRM) in the present field direction and a chemical remanent magnetization (CRM) recording both normal and reversed field directions. Both the VRM and the CRM can be removed by thermal demagnetization techniques because the pigmentary phase has a lower blocking temperature than the specular phase of hematite in the Siwalik beds. The specular hematite is argued to be detrital and the remanence it carries is shown to be early acquired. The origin of the characteristic remanence, carried by the specular phase, is either depositional (DRM) or post-depositional (p-DRM).