Magnetostratigraphy, Topography and Geology of the Nepal Himalaya: A GIS and Paleomagnetic Approach

Abstract

The ongoing collision between India and Asia is producing the world's highest mountain belt on earth. Since collision started several post tectonic events took place to shape the present day Himalayas. Early Miocene Dumri Formation and middle Miocene-Pliocene Siwalik Group fluvial sediments were deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt, preserving a record of tectonic events since early Miocene time. Detailed chronostratigraphy of Siwalik Groups and Dumri Formation is required to understand tectonic events in Himalayas. Owing to the lack of chronostratigraphically significant fossils and tuffaceous beds, paleomagnetic work is the only option to establish the chronostratigraphy of these sediments. Sparse paleomagnetic work done by previous authors remains controversial, mainly because of inappropriate sampling practices.Over the past three decades many geologists have mapped the Nepal Himalayan fold-thrust belt and published various geological maps and reports. However there is no uniformity among them in terms of interpretation of major structures and stratigraphic boundaries, lithological nomenclature and structural systems. To synthesize all this valuable information there is need of a scientific database development utilizing GIS computer software.This dissertation focuses on systematic paleomagnetic work in sub-Himalayan region and GIS database development for the Himalayan fold-thrust belt of Nepal to address the above problems.Systematic paleomagnetic work along major sections covering the entire NW-SE length of the Nepal Himalayas allowed for regional magnetostratigraphic correlation and demonstrates that major lithostratigraphic units in the Siwalik Group are diachronous by 2 Myr of variability. Sediment accumulation rates systematically increase from west to east over the time span ~11.1 to ~5.3 Ma; this could be the result of eastward propagation of a major thrust system in the Lesser Himalaya, such as the Main Boundary Thrust.GIS based geological and topographical database developed for the Nepal Himalaya allowed geological map compilation, query, visualization, and analysis of geological data for several geospatial analyses.