Magnetostratigraphy of the Late Cretaceous to Early Eocene sediments from the Tulsipur section, western Nepal: Tectonic implications for the Indian northern passive margin

Abstract

The sedimentary strata from the Late Cretaceous to Early Eocene in the Himalayan foothills offer detailed insights into land collision processes. Unfortunately, a comprehensive dating study on these strata has been lacking, limiting our understanding of the collision and splicing history of the Indian and Lhasa plates. To address this question, we conducted a paleomagnetic study on the Late Cretaceous to Early Eocene succession in the Tulsipur area, western Nepal. The paleomagnetic data obtained from a 357 m thick succession were used to establish a new magnetostratigraphic framework for this region. The observed magnetic polarity sequence contains six normal and six reversed polarity zones, spanning the age range of 68–54 Ma (Maastrichtian to Early Eocene). In addition, two major and two stable sediment accumulation rates (SARs) were identified which were likely controlled by tectonics. The rifting and subsidence events caused by continuous northward movement of the Indian plate might have modulated the shifting of distal offshore to tidal flat settings in this region. We document fifteen (Unit I) and seven (Unit II) transgressive-regressive cycles, indicative of passive margin instability influenced by near-field effects of the India-Asian convergence. This new magnetostratigraphic result is expected to serve as a basic age framework in reconstructing the Late Mesozoic and Early Cenozoic tectonic evolution. Furthermore, it will also facilitate reliable cross-regional correlation between lithostratigraphic units across passive margins in the southern Himalaya and similar strata in the Tethyan Himalaya and active continental margins of the southern Tibetan Plateau.