Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun Sub-Himalaya, India

Abstract

The shape of the frontal part of the Himalaya around the northeastern corner of the Kumaun Sub-Himalaya, along the Kali River valley, is defined by folded hanging wall rocks of the Himalayan Frontal Thrust (HFT). Two parallel faults (Kalaunia and Tanakpur faults) trace along the axial zone of the folded HFT. Between these faults, the hinge zone of this transverse fold is relatively straight and along these faults, the beds abruptly change their attitudes and their widths are tectonically attenuated across two hinge lines of fold. The area is constituted of various surfaces of coalescing fans and terraces. Fans comprise predominantly of sandstone clasts laid down by the steep-gradient streams originating from the Siwalik range. The alluvial fans are characterised by compound and superimposed fans with high relief, which are generated by the tectonic activities associated with the thrusting along the HFT. The truncated fan along the HFT has formed a 100 m high-escarpment running E-W for ∼5 km. Quaternary terrace deposits suggest two phases of tectonic uplift in the basal part of the hanging wall block of the HFT dipping towards the north. The first phase is represented by tilting of the terrace sediments by ∼30 • towards the NW; while the second phase is evident from deformed structures in the terrace deposit comprising mainly of reverse faults, fault propagation folds, convolute laminations, flower structures and back thrust faults. The second phase produced ∼1.0 m offset of stratification of the terrace along a thrust fault. Tectonic escarpments are recognised across the splay thrust near south of the HFT trace. The south facing hill slopes exhibit numerous landslides along active channels incising the hanging wall rocks of the HFT. The study area shows weak seismicity. The major Moradabad Fault crosses near the study area. This transverse fault may have suppressed the seismicity in the Tanakpur area, and the movement along the Moradabad and Kasganj-Tanakpur faults cause the neotectonic activities as observed. The role of transverse fault tectonics in the formation of the curvature cannot be ruled out.

Evaluation of neotectonic variability along major Himalayan thrusts within the Kali River basin using geomorphic markers, Central Kumaun Himalaya, India

“…The Bastiya is located in the foreland region of eastern Kumaun Himalaya. Near Bastiya, two major E‐W and NE‐SW trending faults have been previously reported by Valdiya (); Kotlia, Phartiyal, Kosaka, and Bohra (); and Luirei et al (). The Bastiya Fault is almost parallel to the HFT, which is a high‐angle northeast‐dipping reverse fault (Goswami, ; Goswami & Yhokha, ).…”

“…In other words, the alluvial fans in mountainous regions were formed because of the huge amount of sediment supply from the adjacent hill slopes towards the hinterland and deposited by locally truncated streams towards the foreland. Two major alluvial fans (Bastiya and Uchoual Gooth) have been reported in this area (Luirei et al, ; Valdiya, ; Valdiya, Rana, Sharma, & Dey, ). The Bastiya fan is the largest alluvial fan developed in this area, whose frontal part is truncated by the Himalayan Frontal Thrust (HFT) and Bastiya Fault (BF; Figure ).…”

“…However, towards the Himalayan front, the river flows across the Himalayan Frontal Thrust (HFT), which defines the southern limit of the Himalaya against the Indo‐Gangetic Plains of Quaternary age. The alluvial fans (Bastiya Fan) at the mouths of entrenched streams breaking through the raised hill front are uplifted and deformed into pressure ridges and depressions adjacent to the Himalayan Frontal Fault (HFF) (Luirei, Bhakuni, & Negi, ; Valdiya, ).…”

“…Towards the frontal part, the Kali River flows across the folded hanging‐wall rocks of the Himalayan Frontal Thrust (HFT). Goswami and Yhokha (), Goswami (), and Luirei et al () identified two parallel fault traces along the axial zone of the folded HFT. The river crossing the HFT zone suddenly changes the valley floor relief.…”

“…(a) Geomorphological map of Tanakpur area (modified after Luirei et al, and Goswami, ) shows (1) Siwalik, (2) North Bastia Surface, (3) Batna Gad Fan, (4) Bastai Fan, (5) BabatGad Fan, (6) Kudal Fan, (7) Recent Fan, (8) Unclassified Fan, (9) Terrace T2, (10) Terrace T1, (11) Unclassified Quaternary deposit, and (12) Escarpment. BF‐1: Bastiya Fault‐1; BF‐2: Basytia Fault‐2; HFT: Himalayan Frontal Thrust; and SBT: South Bastiya Fault.…”