© 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) NEOTECTONIC IMPRINTS ALONG THE COURSE OF RIVER KALIJHORA, WEST BENGAL WITH SPECIAL REFERENCE TO TERRACE DEVELOPMENT 1Soumya Kanti Pramanik, 2Samrat Pal 1 PhD Research Scholar Sri Satya Sai University of Technology and Medical Science, Bhopal 2 Guest Lecturer, Chapra College, West Bengal Abstract: This paper is concerned about the issue of neotectonics and its imprints in topography, drainage along the course of river kalijhora in Darjeeling Himalaya in Darjeeling district in West Bengal. This is a detailed and micro level study. The present study area is situated in one of the most tectonically active regions of eastern Himalaya having three fault lines MBT (Main Boundary Thrust), SKT (South Kalijhora Thrust) and NKT (North Kalijhora Thrust). In the vicinity of this region there is MFT (Main Frontal Thrust) as well. Faults and thrusts are predominantly controlling the geomorphology of this area. Complex terrace structure, straight river course along the fault line, terraces converging down streams, unpaired terraces, polycyclic landscapes are the imprints of neotectonism present in this area. Index Terms: MBT, Neotectonism, SKT, NKT, MFT I. INTRODUCTION Over the past two decades lots of papers has been published on the effect of neotectonism on landform development. This is a new trend in geomorphological studies. The term neotectonics was first introduced by Obruchev to summarize active tectonic process. The geomorphological and geological significance can be better expressed if there is a proper assessment of the relationship of tectonics and related landforms. This assessment can be made by finding the imprints of tectonics and the interpretation of resulted landforms. The present study works focus on finding imprints of tectonics and the interpretation of resulted landforms. River Kalijhora is a tributary of river Teesta. The kalijhora originates from the hilly tracts of Sitong (1694m) peak of Karshiong of Darjeeling Himalaya (Fig-1). There are two main distributaries. One is kalikhola and another one is Karmathkhola. They unified together as Kalijhora towards east forming its confluence with Teesta near Kalijhora P.W.D Bungalow. There are several rivers of this area and adjacent areas have been studied. Those rivers are flowing transverse to the directions of fault lines like Teesta, Kurti, Mal, Chel, Lish, Ghish etc. River kalijhora is flowing mainly along the different fault lines. But sometimes it is flowing across the fault lines also. Fig-1. Location of the study area JETIR1810535 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 872 © 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) II. OBJECTIVES The main objectives of this study are: [1] Identification of Neotectonic activities [2] Geomorphological analysis [3] Detail terrace study III. PREVIOUS LITERATURE Sevoke-Kalijhora region has been considered as an area of attraction for several years. Much remarkable works have been done on this area. Prof. Malay Mukul has worked on the geometry and kinematics of MBT of this area. Prof. Lukram .I. Meetei has done a research works on Terrace Stratigraphy and sedimentary facies of a part of the Teesta river near kalijhora region. Prof. Subir Sarkar, Dhruba Mukhopadhyay et al (2012), have done remarkable works on neotectonism on Chel River of eastern Himalaya. E Anderson (2003) has done an impressive work on Late Quaternary river terrace development on Gaddagh river basin area, Ireland. The present researcher has taken valuable information from the works Mukhopadhyay (1982), C Chakrabartigoswami, Atul K Singh also. IV. METHODOLOGY ADOPTED For this work the present researcher had adopted - [1] Pre-Field- In the pre-field work river related data and topo map (73 B/5, 1:50000) has been collected from NATMO and geological map (50k) from GSI. High resolution 1.5-arc-sec ASTER-DEM and Google Earth images have also been used in this research work. [2] Field -In the field work the present author has done different measurements using GPS, clinometers etc. [3] Post-Field-Data computation and presentation has been done using Arc GIS 10.3 and Adobe Illustrator. V. GEOLOGICAL BACKGROUND This tectonically active region consists of four rocktypes.They are middle siwalik, lower Siwalik, Gondwana and Daling rocks. Here the Daling is the oldest one belongs to the Proterozoic periods. (Fig-2) On the other hand there are three thrust faults. They are MBT, NKT, and SKT. Among them the MBT is exposed on the northern and southern bank of the Kalikhola River. The Footwall of MBT consists of lower siwalik sandstone that is gently folded. The hanging wall is composed of coarse grained Gondwana. It dips gently to the north. The hanging wall Gondwana Sandstone and the fault contact have been folded into an antiform around north-easterly and the kalikhola stream flows across this antiformal hinge zone. (Mukul, 2000) Fig-2. Geological map of the study area JETIR1810535 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 873 © 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) VI. EVIDENCES OF NEOTECTONIC ACTIVITY 6.1 Drainage Network Analysis The overall drainage pattern dendritic in nature but in different places it is parallel and sub-parallel. One the other hand the river is almost straight in two areas. (Fig-3)The first one is situated between two NKT lines .The second one is near the river mouth along the MBT(Fig-4). This kind of river course is a clear cut example of fault guidance over streams. Fig-3. Here two boxes showing the straight river course Fig–4. River kalijhora is flowing along and across the MBT Fallowing the drainage density map (fig-5), values of DD has been increased in two areas. The first one is between the NKT lines .This may be because of the strong tectonic control .The area beside the NKT lines has low drainage density (DD) having greater altitudes .The second one is on the south western part of this basin .The the altitude is not so high and the areas consists of dense vegetation DD attains higher values .Of course the highest density found in the previously said region (between the NKT) .The JETIR1810535 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 874 © 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) drainage density is low in the eastern part and near the river mouth. There is an antiformal hinge zone in this area (MUKUL, 2000). But such drainage anomaly may be because of the less amount of slope. Fig-5. Drainage density map of the study area 6.2 Longitudinal Profile: A change in elevation along a stream longitudinal profile will cause an increase or decrease in stream gradient which in turn impacts the amount of geomorphic work the river is capable of accomplishing. Change in Elevation can occur within the river basin due to tectonic uplift or depression. There may be some external reasons too. The longitudinal profile of this river kalijhora is not quite smooth. A sudden change in elevation in the river longitudinal profile has been encountered. Such sudden jump in elevation not may be always because of the tectonic upliftments. There may be other reasons like topography etc. But this region is highly tectonically unstable. This sudden change in elevation is located in the MBT line (fig-6). Waterfalls, Terraces present in this area prove that this river is not in graded condition and has been gone through rejuvenation. So this change in elevation may be the indication of a Knick Point. Fig-6 Longitudinal profile of river kalijhora 6.3 Terrace Analysis River terraces are the remnants of former valley floor lying as an elevated platform on the either side of the rejuvenated river (Chorley et .al, 1984) .To understand the terrace eight cross profiles has been drawn with the help of GPS and Clinometers survey. Three distinctive terrace levels has been identified which are referred as TL -1, TL -2, and TL -3. (Fig-7a and 7b). JETIR1810535 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 875 © 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) Fig-7a and 7b: Eight cross profiles showing different terrace levels Fig- 8 Showing the location of the profiles 6.3.1 Terrace Morphology 6.3.1.1 Terrace level (TL) -1 This is the erosional (strath) terraces composed of unconsolidated gravels. This terrace level is quite vegetated. It is the highest and most prominent terrace surface. It rises 30-40 m from the channel floor. But sometimes it is more than that due to deep incision of the river. 6.3.1.2 Terrace level (TL) -2 and 3 Terrace level (TL) -2 and 3 appear as unpaired .TL -2 is composed of alluvial sand, cobbles, pebbles and boulders. TL-3 consists of dissected flood deposits also (Plate – 1) .The elevation of terrace level -2 is 5-10 m from the channel floor where as TL -3 rises 5 m approximately. 6.3.2 Identification of types of Terraces Three types of terraces have been identified. They are as follows: 6.3.2.1 Strath Terraces Presence of Strath Terraces is very clear from the profiles drawn. This terrace are composed of quaternary unconsolidated gravels are overlain by soil and are densely vegetated by trees and grasses. this unconsolidated gravels on the northern and southern bank have been uplifted about 4 m relative to the present channel bottom in some areas .(Mukul ,2000) JETIR1810535 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 876 © 2018 JETIR October 2018, Volume 5, Issue 10 www.jetir.org (ISSN-2349-5162) 6.3.2.2 Unpaired Terraces The terrace level 1 is very consistent but TL -2 and TL-3 appear as unpaired terraces.