Open AccessFidelity and time resolution of the magnetostratigraphic record in Siwalik sediments: high‐resolution study of a complete polarity transition and evidence for cryptochrons in a Miocene fluviatile section
Author(s) -
Rösler Wolfgang,
Appel Erwin
Publication year - 1998
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1046/j.1365-246x.1998.00677.x
Subject(s) - magnetostratigraphy , geology , paleontology , polarity (international relations) , earth's magnetic field , paleomagnetism , natural remanent magnetization , remanence , demagnetizing field , sedimentary rock , rock magnetism , geophysics , facies , magnetization , magnetic field , physics , structural basin , biology , cell , genetics , quantum mechanics
The Surai Khola section in southwest Nepal, a 5000 m continuously exposed record of fluvial sedimentation since Middle Miocene, was revisited for high‐resolution magnetostratigraphy in sequences with expected cryptochrons and reversals of the geomagnetic field. Polarity intervals with durations of a few tens of thousands of years are recorded as zones of stable palaeomagnetic directions. Polarity transitions are recorded as zones with complex demagnetization behaviour of specimens in the sedimentary column. Almost antiparallel palaeoremanence directions, residing in different haematite phases in the same specimens, could generally not be separated properly by thermal demagnetization. Differing demagnetization paths for neighbouring specimens during a reversal suggest that measured transitional directions are not true geomagnetic field directions, but rather are generated by the superposition of variable amounts of at least two almost antiparallel components of magnetization. Accompanying studies of recent river sand deposits demonstrate that these sediments acquire a true depositional remanent magnetization (DRM) with considerable inclination errors and scattered directions for individual specimens.