Sedimentary facies analysis of the fluvial environment in the Siwalik Group of eastern Nepal: deciphering its relation to contemporary Himalayan tectonics, climate and sea-level change

The Siwalik Group, ranging from the Early Miocene to Pleistocene, is believed to be deposited in the fluvial environment and controlled by contemporary Himalayan tectonics and climate. In this study, we established the fluvial environment and its controlling factors responsible for the deposition of the Siwalik succession along the Muksar Khola section in the eastern Nepal Himalaya. Five sedimentary facies associations are identified; these are interpreted as the deposits of flood plain-dominated fine-grained meandering river (FA1), flood-dominated overbank environment (FA2), sandy meandering river (FA3), anastomosing river (FA4), and debris flow-dominated gravelly braided river (FA5). These changes in the fluvial system occurred around 10.5 Ma, 10.0 Ma, 5.9 Ma and 3.5 Ma, defined by existing magnetostratigraphy constraints, due to the effects of hinterland tectonics, climate and sea-level change and continuous drifting of the foreland basin towards the hinterland concerning depositional age. The thick succession of an intraformational conglomerate reveals intensification of the monsoon started around 10.5 Ma in the eastern Nepal Himalaya. The present study also shows asynchronous exhumation of the Himalaya from east to west brought a significant difference in the fluvial environment of the Neogene foreland basin.

Sedimentary Facies Analysis of the Fluvial Environment in the Siwalik Group of Eastern Nepal: Deciphering its Relation to Contemporary Himalayan Tectonics, Climate and Sea-Level Change.

The Siwalik Group, ranging from the Early Miocene to Pleistocene, is believed to be controlled by contemporary Himalayan tectonics and climate. In this study, we established the fluvial system responsible for the deposition of the Siwalik succession along the Muksar Khola section and its controlling factors. Five sedimentary facies associations are identified which are interpreted as the deposits of flood plain dominated fine-grained meandering river (FA1), flood dominated overbank environment (FA2), sandy meandering river (FA3), anastomosing river (FA4), and debris flow dominated gravelly braided river (FA5). These change in fluvial style occurred around 10.5 Ma, 10.0 Ma, 5.9 Ma and 3.5 Ma due to the effects of hinterland tectonics, climate and sea-level change. The thick succession of intraformational conglomerate reveals the intensification of monsoon started around 10.5 Ma in the eastern Nepal Himalaya. The present study show asynchronous exhumation of the Himalaya east to west brought significant difference on the fluvial environment of the Neogene foreland basin. Moreover, this study also reveals continuous drifting of the foreland basin towards the hinterland concerning depositional age.

MORPHOMETRIC ANALYSIS OF BAUR CATCHMENT IN LESSER HIMALAYA: USING GEO-SPATIALTECHNIQUES

The current assessment is an undertaking to evaluateand compare variousmorphometric parameters of the Baur catchment. Morphometric analysis of the river basin provides a quantitative description of the drainage system, which is an important aspect of the categorization of the basin (Strahler, 1964).The Baur catchment is located in the outer part of the Lesser Himalaya in the Kumaun region, which is a major part of Western Himalaya.The geographical area of Baur Catchment is 106.233Km2.Morphometric analysis of Baur Catchment includes linear, areal, and relief aspects.The calculation of the morphometric parameter, along with map preparation, was performed with the help of GIS techniques and ancillary material.Most of the area of Baur Catchment is occupied by Siwalik Group (sandstone and clay intercalation with pseudo-conglomerate) of rocks.The entire Baur Catchment has found 6th order drainage, which reveals sub-dendritic to a dendritic type of drainage pattern. It is observed that the drainage density of the Baur Catchment is 3.525 km/halfkm2.

Balanced cross-section across the Siwaliks of the Trijuga Valley, eastern Nepal

The strata of the Siwalik Group in the Trijuga valley is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. The total thickness of the Siwalik strata exceeds 5000 m in the area. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­Khola Thrust (MKT) and Main Boundary Thrust (MBT) ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.

Lithostratigraphy of the Siwalik Group along the Muksar Khola section, Siraha-Udayapur District, Eastern Nepal Himalaya

The Siwalik Group extending east to west co-linear to the main Himalayan range is well exposed along the Muksar Khola section, Siraha-Udayapur district, eastern Nepal Himalaya. Siwalik Group in the present study area is divided into the Lower, Middle, and Upper Siwaliks based on grain size and sandstone-mudstone proportion. The Lower Siwaliks is characterized by very fine- to fine-grained, light grey sandstone interbedded with dark grey to olive black mudstone. The Middle Siwaliks, is characterized by the domination of fine- to coarse-grained sandstone, and based on the lithology and bed thickness it is divided into two members. The lower member is dominated by fine- to medium-grained “salt and pepper” sandstone with dark greenish to olive-grey mudstone while, the upper member is dominated by light grey to white medium- to coarse-grained sandstone with grey, dark grey to black mudstone. Increase in the grain size and thickness of sandstone beds, increase in the proportion of mudstone, decrease in induration of sandstone and decrease in the proportion of biotite grain in sandstone makes upper member different from lower member of the Middle Siwaliks. The Upper Siwaliks is characterized by very thick beds of clast supported conglomerate associated with coarse- to very coarse-grained, very thick bedded sandstone and dull yellowish-grey to grey mudstone. The boundary between the Lower Siwaliks and the Middle Siwaliks, lower member and upper member of the Middle Siwaliks, and the Upper Siwaliks are 10.0 Ma, 5.7 Ma, and 3.5 Ma, respectively. The present study records the presence of a large succession of intra-formational conglomerate succession in the Lower Siwaliks.

Uranium Traps in Phreatic Sandstone-type Prospect, Taunsa Area, Dera Ghazi Khan, Eastern Sulaiman Range, Pakistan: Evidences from Autoradiography and Optical Microscopy

Taunsa uranium occurrence like other uranium resources in Pakistan is hosted by the Late Miocene-Pliocene age Litra Formation of the Siwalik Group molasse sediments. Taunsa uranium prospect is a unique phreatic-type uranium resource in terms of its disturbed geological setting of the eastern limb of the Zindapir anticline in the eastern Sulaiman range. Autoradiography technique was used to locate the spots of anomalous uranium concentration in thin sections from ore of Taunsa prospect. Twenty polished thin sections from uranium ore ranging from 200 ppm-600 ppm were attached to detectors for a month which produced prominent alpha track which were used to find the traps of uranium. Subsequently, these spots were studied under SEM and EPMA for further investigations of uranium phases. Autoradiography revealed that Taunsa uranium ore is mostly associated with organic matter (probably petroleum), black shale clasts, biotite, fougerite (a green colour rusty mineral) and with micritic clasts. This study suggests that prospective facies of the host sandstone containing relatively abundant black shale clasts, organic matter and biotite may be targeted during exploratory drilling in Taunsa uranium deposit and its extensions in the eastern limb of Zindapir anticline