Middle Siwalik Subgroup Research Articles

Durability of sandstones from Sub-Himalaya of central Nepal

The Sub-Himalaya of Nepal experiences sub-tropical climate where geologically young and delicate sedimentary rocks are prone to chemical and physical weathering and consequent erosion. The main aim of this study is to identify and evaluate the durability characteristics of some sandstones against slaking, freezing-thawing and abrasion. Lithosomes were characterized in the field. The following laboratory tests included measurements of dry density, specific gravity, water absorption, Slake Durability Index (SDI), Sulphate Soundness (SS), and Los Angles Abrasion (LAA). Sandstones from the Lower Siwalik Subgroup (LSS) are massive to cross-stratified, very fine- to medium-grained, and occasionally calcareous, whereas the sandstone from the Middle Siwalik Subgroup (MSS) are mostly cross-stratified to few massive, medium- to coarse-grained with salt-and-pepper appearance, and uncommonly calcareous. Sandstones have four different types of deterioration and had high to extremely high SDI. The majority of the sandstones have displayed similar slaking tendencies. Under the five-cycle SS test, the majority of sandstones from LSS and MSS have experienced low final weight loss (below 10%). However, two from LSS and three from MSS have experienced greater final weight loss. The LAA values range from 29.66% to 99.14%, and except two sandstones from LSS, rest of the samples have exceeded 45% abrasion showing they were incompetent in terms of abrasion test, and are highly susceptible to abrasion. The uniformity factor ranges from 0.21 to 0.44 indicating that all the sandstones were of non-uniform hardness. Correlation among physical parameter and durability indices was weak to moderate probably because of varied nature of sandstones.

Textural behaviour, facies, and depositional environments of the Middle Siwalik Subgroup of the Jammu area, Jammu & Kashmir State, NW Himalaya

Textural behaviour, facies, and depositional environments of the Middle Siwalik Subgroup of the Jammu area, Jammu & Kashmir State, NW Himalaya

Provenance of the Middle Siwalik sandstones of the Himalayan foreland basin (south central Kumaun, India): Implications for tectonics and paleoclimate of the source area

Thirty medium‐ to fine‐grained sandstone samples of the Middle Siwalik Subgroup of the south central Kumaun Himalaya have been subjected to detailed petrographic and petrofacies analyses. The sandstones are moderately to well‐sorted, lithic and sublithic arenites. They are quartzolithic, having abundance of metasedimentary and sedimentary lithic fragments, which characteristically derive from a recycled, collision orogen provenance of quartzose and mixed quartzose‐lithic terrains. The primary and accessory framework grains of the sandstones are of mixed igneous, sedimentary, and low‐ to high‐grade metamorphic affinity. The petrographic and petrofacies characters suggest derivation of the sandstones from a vast area extending across the nearby located Lesser and Great Himalayan terrains. A comparison of these sandstones' QtFL petrofacies and petrographic characters with the similar data from Middle Siwalik sandstones of other studied sections reveals that their compositions are comparable all across the entire expanse from Potwar Plateau in Pakistan to eastern Himalaya in India; the Middle Siwalik sandstones everywhere have been sourced from the Lesser and Great Himalayan terrains, albeit with varying proportions through space and time.

Engineering geological study of the Mai Khola Hyroelectric Project, Ilam, eastern Nepal

The Mai Khola Hydroelectric Project, a run-of-river scheme, has a capacity 15.6 MW. It has design discharge of 16 m3/s, design net head of 112.71 m and includes 2192 m long inverted-D shaped headrace tunnel with 4.3 m diameter, concrete dam of 10.6 m height and semi-surface powerhouse. The project area consists of rocks of the Middle Siwalik Subgroup, comprising of sandstone, siltstone and mudstone, inter bedded frequently. Sandstone is predominant in head works area, headrace tunnel and is completely absent in a surge tank, and penstock alignment. Siltstone alternating with thin layer of mudstone is predominant in powerhouse area. The headrace tunnel outlet portal and surge shaft lie on the hill slope characterized by colluvial deposits. The penstock alignment passes through highly weathered siltstone and mudstone. The semi-surface powerhouse and the tailrace canal lie on the lower alluvial terrace. The Main Boundary Thrust (MBT) is the major structure observed at about 90 m upstream from the weir axis. The average Q-value of rock mass along the headrace tunnel surface mapping was 0.062–1.33 and after excavation the value was 0.004–0.23. An extremely poor to poor relation was observed between the rock mass class on surface mapping and exceptionally poor to very poor on excavation. Analysing the results of the surface and underground study of the rock mass, the excess support is required during construction.

Petrography and geochemistry of the Middle Siwalik sandstones (tertiary) in understanding the provenance of sub-Himalayan sediments in the Lish River Valley, West Bengal, India

A petrography–geochemistry-based evaluation of the provenance of the sandstones of the Tertiary Middle Siwalik Subgroup in the Lish River Valley, West Bengal, is presented. The framework grains in the sandstones suggest mixing of sediments from spatially separated gneissic, quartzitic and phyllitic source rocks. Modal values of different framework minerals suggest that recycled sediments in an orogenic setting were deposited in the Middle Siwalik basin in the area. The major and trace element ratios suggest dominantly felsic input and mixing with subordinate basic material in an upper continental crustal setup. The major and trace element data also indicate that rocks of a passive margin setting acted as the source to the sediments. The present paper postulates that the Middle Siwalik sediments were derived from pre-Himalayan gneissic and metabasic rocks of an erstwhile passive margin setting and presently forming the Higher and Lesser Himalaya, respectively.

Gazella (Bovidae, Ruminantia) remains from the Siwalik Group of Pakistan

Khan, M.A., Babar, M.A., Akhtar, M., Iliopoulos, G., Rakha, A. & Noor, T., November 2015. Gazella (Bovidae, Ruminantia) remains from the Siwalik Group of Pakistan. Alcheringa 40, xxx–xxx. ISSN 0311-5518.New gazelle fossils are described from the Siwalik Group of Pakistan. The material includes horncores, maxilla and mandible fragments, and isolated teeth. The available samples are assigned to three Gazella species: Gazella sp. in the Lower Siwalik Subgroup (ca 14.2–11.2 Ma), and G. lydekkeri and G. superba in the Middle Siwalik Subgroup (ca 10.2–3.4 Ma). Based on a review of the Siwalik Group gazelles, G. padriensis is synonymized with G. lydekkeri. Gazella superba Pilgrim, 1939 sensu stricto is a large form and is a valid species of the genus in the Siwalik Group.Muhammad Akbar Khan [akbaar111@yahoo.ca], Muhammad Adeeb Babar [babar_fcc2005@yahoo.com], Muhammad Akhtar [drakhtarfdrc@hotmail.com], Allah Rakha [babar.441@googlemail.com], Tuba Noor [akbar.zool@pu.edu.pk], Abu Bakr Fossil Display & Research Centre, Department of Zoology, Quid-e-Azam Campus, Punjab University (54590), Lahore, Pakistan; George Iliopoulos [borelakias@gmail.com], Geology Department of the University of Patras, Patras, Greece.

Soft-sediment deformation structures in the sub-Himalayan Middle Siwalik Subgroup, Lish River section, India

The Mio-Pliocene Middle Siwalik Subgroup, in the Lish River Section in the Darjiling District of the Eastern Himalaya, consists of sandstone, mudrocks, heterolithic units and conglomerates preserving six distinct associations of soft-sediment deformation structures at different stratigraphic levels. The foreland basin sediments of the Himalayan orogen were deposited in alluvial fan settings. Deformation structures present are: folds of variable geometry, pseudonodules, water escape features, flame structures and chaotic laminae. Liquefaction and/or fluidization of sediments in the soft state are inferred to have been responsible for the origin of these structures. Both the depositional palaeoenvironment and seismic tremors generated due to thrusting activities in the hinterland situated to the north of the then Middle Siwalik basin contributed to triggering the liquefaction/fluidization and creation of the softsediment deformation structures within the Middle Siwalik sediments.

Paleocurrents, Paleohydraulics, and Palaegeography of Miocene-Pliocene Siwalik Foreland Basin of India

Early Miocene-Pliocene Middle Siwalik Subgroup of Kuluchaur area, Uttarakhand, North India, comprises sheet-like, coarse to medium grained, cross bedded sandstone bodies and multistoreyed variegated mudstones. Paleocurrent study shows commonly unimodal and locally bimodal distribution and displays a high magnitude of resultant (R*=0.7337) oriented towards south-southwest (206° ± 42.27°). Palaeochannel morphological attributes suggest that the depositing river system was about 230 m wide and 4.5 m deep. These broad, shallow, and low sinuous channels with extensive flood plain flowed on a steeper slope (0.00043 degrees) with flow velocity of 60–140 cm/sec. It is visualized that the immature Middle Siwalik rocks were deposited by southward flowing braided rivers transverse to the Himalayas, predominantly in the form of overlapping alluvial fans similar to those depositing sediments at present in the Indo-Gangetic plains. Fairly consistent fluvial palaeoslopes, together with enormous thickness of sediments, are evidences of rapid subsidence of the basin. We conclude that the paleogeography of Indian subcontinent established at the onset of Miocene-Pliocene Siwalik sedimentation is continuing till today.

Depositional environment and provenance of Middle Siwalik sediments in Tista valley, Darjiling District, Eastern Himalaya, India

The frontal part of the active, wedge-shaped Indo-Eurasian collision boundary is defined by the Himalayan fold-and-thrust belt whose foreland basin accumulated sediments that eventually became part of the thrust belt and is presently exposed as the sedimentary rocks of the Siwalik Group. The rocks of the Siwalik Group have been extensively studied in the western and Nepal Himalaya and have been divided into the Lower, Middle and Upper Subgroups. In the Darjiling–Sikkim Himalaya, the Upper Siwalik sequence is not exposed and the Middle Siwalik Subgroup exposed in the Tista river valley of Darjiling Himalaya preserves a ~325 m thick sequence of sandstone, conglomerate and shale. The Middle Siwalik section has been repeated by a number of north dipping thrusts. The sedimentary facies and facies associations within the lithostratigraphic column of the Middle Siwalik rocks show temporal repetition of sedimentary facies associations suggesting oscillation between proximal-, mid- and distal fan setups within a palaeo-alluvial fan depositional environment similar to the depositional setup of the Siwalik sediments in other parts of the Himalaya. These oscillations are probably due to a combination of foreland-ward movement of Himalayan thrusts, climatic variations and mountain-ward shift of fan-apex due to erosion. The Middle Siwalik sediments were derived from Higher- and Lesser Himalayan rocks. Mineral characteristics and modal analysis suggest that sedimentation occurred in humid climatic conditions similar to the moist humid climate of the present day Eastern Himalaya.

Sedimentary facies and soft-sediment deformation structures in the late miocene-pliocene Middle Siwalik subgroup, eastern Himalaya, Darjiling District, India

The Himalayan fold-and-thrust belt has propagated from its Tibetan hinterland to the southern foreland since ∼55 Ma. The Siwalik sediments (∼20 - 2 Ma) were deposited in the frontal Himalayan foreland basin and subsequently became part of the thrust belt since ∼ 12 Ma. Restoration of the deformed section of the Middle Siwalik sequence reveals that the sequence is ∼325 m thick. Sedimentary facies analysis of the Middle Siwalik rocks points to the deposition of the Middle Siwalik sediments in an alluvial fan setup that was affected by uplift and foreland-ward propagation of Greater and Lesser Himalayan thrusts. Soft-sediment deformation structures preserved in the Middle Siwalik sequence in the Darjiling Himalaya are interpreted to have formed by sediment liquefaction resulting from increased pore-water pressure probably due to strong seismic shaking. Soft-sediment structures such as convolute lamination, flame structures, and various kinds of deformed cross-stratification are thus recognized as palaeoseismic in origin. This is the first report of seismites from the Siwalik succession of Darjiling Himalaya which indicates just like other sectors of Siwalik foreland basin and the present-day Gangetic foreland basin that the Siwalik sediments of this sector responded to seismicity.

Paleochannel and paleohydrology of a Middle Siwalik (Pliocene) fluvial system, northern India

Late Cenozoic fresh water molasses sediments (+6000 m thick) deposited all along the length of the Himalayan fore deep, form the Siwalik Supergroup. This paper reports the results of the paleodrainage and paleohydrology of the Middle Siwalik subgroup of rocks, deposited in non-marine basins adjacent to a rising mountain chain during Pliocene. Well-exposed sections of these rocks have provided adequate paleodrainage data for the reconstruction of paleochannel morphology and paleohydrological attributes of the Pliocene fluvial system. Cross-bedding data has been used as inputs to estimate bankfull channel depth and channel sinuosity of Pliocene rivers. Various empirical relationships of modern rivers were used to estimate other paleohydrological attributes such as channel width, sediment load parameter, annual discharge, and channel slope and flow velocity. Computed channel depth, channel slope and flow velocity are supported independently by recorded data of scour depth, cross-bedding variability and Chezy’s equation. The estimates indicate that the Middle Siwalik sequence corresponds to a system of rivers, whose individual channels were about 400 m wide and 5.2–7.3 m deep; the river on an average had a low sinuous channel and flowed over a depositional surface sloping at the rate of 53 cm/km. The 700-km long Middle Siwalik (Pliocene) river drained an area of 42925 km 2 to the north–northeast, with a flow velocity of 164–284 cm/s, as it flowed generally south–southwest of the Himalayan Orogen. Bed-load was about 15% of the total load of this river, whose annual discharge was about 346–1170 m 3 /s normally and rose to approximately 1854 m 3 /s during periodic floods. The Froude number of 0.22 suggests that the water flows in the Pliocene river channels were tranquil, which in turn account for the profuse development of cross-bedded units in the sandstone. The estimated paleochannel parameters, bedding characteristics and the abundance of coarse clastics in the lithic fill are rather similar to the modern braided rivers of Canada and India such as South Saskatchewan and Gomti, respectively.

A multistorey sandstone complex in the Himalayan Foreland Basin, NW Himalaya, India

Ten parallel stratigraphic sections (1500–1800 m thick) spread over an area of >400 km 2 in Dehra Dun sub-basin (DSB) of the Himalayan Foreland Belt (HFB) were studied to understand the anatomy of one of the largest (900–1200 m thick) fluviatile Multistorey Sandstone Complexes (MSC) of the world using fluvial geometry, compositional data and magnetic fabrics over a magnetostratigraphically controlled master section. The multistorey sandstone complex, between 10–5 Ma representing the Middle Siwalik sub-Group, comprises of grey, medium- to fine-grained lithic arenites to lithic greywacke and records tectonic and/or climatic episodes. Three main facies associations are recognised: sandstone–mudstone, sandstone, and conglomerate-sandstone that represent fluvial fan deposit. Palaeocurrent data show radial palaeoflow pattern with major palaeodrainage towards the southern quadrant. The magnetic fabric studies suggest three major tectonic pulses. The first pulse at ∼8.7 Ma resulted in the development of major depocenter for the MSC, the second pulse at ∼7.65 Ma enhanced the sedimentation and progradation, while the third pulse at ∼6.5 Ma records overlapping earlier fluvial fan by another coarse grained piedmont alluvial fan. Thrust movement in the northern fold belt, basement lineaments and rate of basin subsidence controlled the lateral and vertical facies distribution and palaeodrainage. The sedimentation pattern of the multistorey complex is characterised by mainly sheet flood deposits of laterally avulsing unconfined braided rivers and resembles to the modern megafan sedimentation in the Ganga Basin to the south.

Coalescence megafan: multistorey sandstone complex of the late-orogenic (Mio-Pliocene) sub-Himalayan belt, Dehra Dun, India

In the Himalayan foreland basin, a prominent multistorey sandstone complex, in the Middle Siwalik Subgroup, is exposed along the southern flank of the Dehra Dun valley in the Mohand anticline. Extending laterally for ∼ 40 km, the Middle Siwalik Subgroup consists of sandstone-mudstone couplets (300–450 m thick) in the lower part and the multistorey sandstone complex (900–1200 m thick) in the upper which forms a gross coarsening upward sequence. The major lithofacies are trough cross-stratified sandstone, planar cross-stratified sandstone, ripple drift laminated sandstone, horizontal laminated sandstone and massive sandstone with subordinate amounts (<20%) of mudstone and conglomerate. The multistorey sandstone complex is punctuated by several erosional surfaces over which abundant mud clasts are present. The trough cross-stratification exhibits a dominantly southward palaeoflow with much variation in the southeast and southwest quadrants. However, at outcrop level the palaeoflow data reveal internal consistency. This spatial and temporal variability in palaeoflow direction indicates the existence of two major drainage systems of coalescing alluvial megafan type. The estimated palaeochannel sinuosity is of the order of 1.04 to 1.23 with a return period of 4 to 8 × 103 years.Palaeoflow variability, facies distribution, frequent avulsion and the coarsening upward sequence collectively suggest the progradation of coalescing alluvial fans towards the south and southwest. This was principally controlled by thrust movements and differential basin subsidence at the margin of the Himalayan orogen.