Himalayan Geology, Vol.21 (1), 2000, pp.1-11, Printed in India

 

 

Influence of Delhi-Hardwar-Harsil Ridge (DHHR) on Basin Configuration in Himalayan Foothills Belt during Tertiary

 

DEVENDRA PAL,  R.A.K. SRIVAST AVA  AND  N.S. MATHUR

Wadia Institute of Himalayan Geology. Dehradun 248001, India

 

 

Abstract: The lower Tertiary successions extend from northwest to southeast along the Sub Himalaya, the Lesser Himalaya, the Zanskar and the Indus belts. However, in the Sub Himalaya these successions are not exposed east of thc Delhi-Hardwar-Harsil Ridge (DHHR), which is a NNE-SSW trending basement ridge of the Aravallis and Delhis.  In the Sub Himalaya, the lower Tertiary successions were deposited in a linear foredeep that was formed to the south of the Himalaya during the late Mesozoic Orogeny and was restricted by the DHHR to its west.

 

Taking all the facts and field relations into account the authors have interpreted that: (a) the Main Boundary Thrust (MBT) of the western Sub Himalaya cannot be equated with the MBT of central parts; (b) the DHHR controllcd the Maastrichtian-lower Tertiary sedimentation and restricted it to the west of the DHHR in the Sub Himalaya; (c) the lower horizons of the Siwalik succession (the Kamlial) are not exposed east of Nahan; and (d) the Paleocene-Eocene successions of Rajpur (the Tethyan sequence towards north of the Pir Panjal Range) and Garhwal (the Lesser Himalayan sequence) are parts of totally different setups which are neither in continuity of the Sub Himalaya. nor are parts of these setups. In fact, these are only time equivalents.

 

Palaeogeographic reconstruction, based on faunal and sedimentological studies and geomorphic controls besides the tectonic set up, has led the authors to redefine the existing model pertaining to basin development of the Sub Himalaya.  In the first part only basement rocks of the Vaishnodevi Limestone and the Aravalli of the DHHR existed.  Marine transgression from west to east took place immediately after the late Mesozoic orogeny. The sea was nearly 80-100 km wide in the western part and 10-15 km in the Sataun-Nahan peripheral area, where the Kakara-Subathu Sea was deposited. Thc Lower Murree (= Dagshai/Lower Dharmsala) was deposited when the Subathu Sea regressed. Monsoon conditions commenced with deposition of the Kasauli (Upper Murree/Upper Dharmsala). At this stage another basin came into existence south of Vaishnodevi and Bilaspur where fluvial conditions led to deposition of the Lower Siwalik to north of Ramnagar and Jogindernagar. Next stage was marked by deposition of the Middle and Upper Siwalik not only to the west of the DHHR (the Delhi-Aravalli and Vindhyan) but also to the east in the central part of Himalaya.  The Middle and Upper Siwalik successions arc much richer in mammalian fossils in the western part than in the east.

 

 


 

Introduction

 

The Himalayan mountain chain runs from Nanga Parbat in the northwest to Namche Barwa in the east along the northern region of India and passes through Pakistan, India. Nepal, Bhutan and Tibet. This chain runs in a NNW-SSE direction from Poonch to Paonta Sahib and then abruptly swings in a WNW-ESE direction in Uttar Pradesh (U.P.) and becomes E-W in eastern Nepal. It is generally believed that various geological formations are continuous, running as linear belts from west to east all through the length of the Himalaya.  Gansser (1964) recognised five lithotectonic units (from south to north) in the Himalayan orogenic belt that runs for a strike length of over 2400 km and has a width varying from 230 to 320 km; these units from south to north are: Sub Himalaya (zone I), Lesser Himalaya (zone 2), Higher Himalaya (Zone 3). Tethys Himalaya (zonc 4) and Indus Suture (= ophnolite zone; zone 5).

 

Out of these five lithotectonic units the Sub Himalaya, which is constituted by the Siwalik Hills all along the foothills belt of the Himalaya, stands abruptly in the backdrop of the Indo-Gangetic Plains towards the south. This belt comprises rocks of Tertiary and Quaternary ages with a few inliers of older sedimentaries. However, no crystallines or their nappes occur in this belt which are otherwise common in the Lesser Himalaya. The thrusts recognised by several workers in this belt arc basically high angle reverse faults. Normal faults that occasionally occur on dip slopes are of no regional importance as compared to reverse faults.

 

In the Sub Himalayan belt of Jammu and Himachal Pradesh, the Paleogene successions are better developed than those of Uttar Pradesh and Nepal, where only the Maastrichtian to lower Paleogene sediments were deposited. It has also been observed that the upper Paleogcne and lower Neogene successions, which are best developed in this zone in Jammu and Himachal Pradesh gradually pinch out at Kalsi (cast of Paonta Sahib) and are not observed east of this place (Figs. 1 and 2).  It is, therefore, interpreted that there must have been a physical barrier at Kalsi which restricted the basin to the west. This physical barrier is recognised as the Delhi-Hardwar-Harsil Ridgce(DHHR), which trends in a NNE-SSW direction (Pal, 1993; Pal et al., 1998).


 

Delhi-Hardwar-Harsil Ridgc (DHHR)

 

The DHHR is a northerly extension of the Aravalli Mountain Belt, which also trends in a NNE-SSW direction and stretches from Amba Mata-Deri (Gujarat-Rajasthan) to Delhi via Ajmer and Jaipur. Its northernmost outcrop is exposed on the right bank of the river Yamuna at Wazirabad Bridge in Delhi. Its further northward extension below the Indo-Gangetic Plains at Panipat and Saharanpur has been confirmed by the ONGC. The DHHR comprises quartzite, slate and basic rocks, which belong to the Delhi Group. From Delhi this ridge gradually slopes down in northerly direction below the Indo-Gangetic Plains. Therefore, it deepens northwards. This ridge occurs in the form of scattered outcrops in the southern, middle and northern parts of the Aravalli. The discontinuous nature of exposures of the Aravalli Mountain Belt in Rajasthan can be attributed to either denudation or structural complexities.

 

Supporting facts

 

A DHHR-like feature was also noticed by Arora et al. (1993  who described a Trans-Himalayan conductor right through Mohand and Dehra Dun which almost overlaps the DHHR an d may be synonymous with the DHHR. The authors have described two different crusts on either side of this conductor, their density, conductivity and rigidity being totally contrasting.  Raiverman (1992) worked out sedimentation history during the Cenozoic times and showed several trans-Asiatic lineaments including the Astin Tagh-Yamuna-Aravalli curved lineament, which runs across the ". Himalaya. Misra (1996) brought out a geological map showing localities of tin, tungsten and lead mineralisation in Debari, Khetri, Degana (Rajasthan), Tosham (Haryana) and Purbani (Kinnaur), which fall in a straight line and almost coincide with the western flank of the DHHR.

 

Physical extensions of the DHHR

 

The DHHR is 65-70 km wide between Kalsi (Paonta Sahib) and Chilla (Hardwar). It is estimated to exist at a depth of 2 km at Dehra Dun and becomes gradually deeper when followed northward in Mussoorie and Uttarkashi. The DHHR is bounded by faults on its western and eastern sides, which are known as the Yamuna Tear Fault and Ganga Tear Fault, respectively.  The Yamuna and Ganga rivers follow traces of these faults while flowing down from the Lesser Himalaya into the Indo-Gangetic Plains. The existence of the DHHR is supported by the presence of a 1600 Ma old volcano-sedimentary sequence, which is supposed to be continuation of Bijawar (Vindhyan) below it (Qureshy, 1998).

 

The DHHR has attained a primary importance as far as sedimentation control of the Sub Himalaya is concerned. This ridge also controlled the basin configuration in the Lesser and Tethys Himalayas marked by pinching out of various geological formations on either side of it. The regions lying to the east and west of the DHHR have been grouped under segments I and 2, respectively.

 

 

Main Boundary Thrust (MBT) and Main Boundary Fault (MBF)

 

The Main Boundary Thrust (MBT)… separates the Sub Himalaya from the Lesser Himalaya. It is believed that large scale movement took place along the MBT Main Boundary Thrust bringing the Lesser Himalayan metasedimentaries over the Sub Himalayan successions. In Uttar Pradesh (eastern part of DHHR), the MBT is known as the Krol Thrust as it has brought the Krol belt of the Lesser Himalaya over the Siwalik (Auden,1934,1937). This means that the Krol Thrust in segment I overlaps the MHT. In segment 2 further to the west in Jammu, the 'MBF' is equated with the Murree Thrust (MT) which brings the Tethyan succession (Baila-(Gamir-Panjal Traps-Mandi-Rajpur) over the Murree Group (late Paleogene-Early Miocene) of the Sub Himalaya. It may be pointed out that this thrust has erroneously been named as the 'Main Boundary Fault' by some workers. The MHF Was originally defined as a tectonic contact separating the upper Tertiaries (Neogene) from the lower Tertiaries (Paleogene), a definition followed by Wadia ( 1928, 1931, 1966 ). In the Jammu region the MBF is much to the south of the MBT, the latter being manifested at Peeda (Nasri Nala) and slightly north of  Poonch in the western part, whi1e the former is observed to the south of Rajauri, Kalakot, Riasi, Katra and to north of Udhampur, where Kishanpur Thrust (Karunakaran and RangaRao, 1979) merges with the MBF.  As the KT(=MHT) has brought Krol Thrust sheet over the Siwalik in segment 1, the age of thrusting has to be younger than the Upper Siwalik, i.e -0.20 Ma (Late Pleistocene), while the MBF (='Riasi Thrust') in segment 2 is a fault plane that developed after deposition of the Upper Murree (=Upper Dharmsala/ Kasauli) sediments, which were uplifted and southern margin of the sediments was faulted and became the MBF. Therefore, the age of MBF has to be early Miocene, i.e. ~18 Ma (before deposition of the Lower Siwalik to the south of this fault). So, it is clear that the MBF is much older than the Krol Thrust/Murree Thrust/MBT.

 

 

Contrasting Geological setting on either side of the DHHR

 

The geological setups (Table 1) in the Sub Himalaya, Lesser Himalaya and Tethys Himalaya of segments I and 2 are different (Fig. 3). In the following paragraphs, the geographical extent of various formations in these lithotectonic zones on the eastern (segment 1) and western (segment 2) sides of the DHHR is discussed briefly.

 

Table 1. Tectonostratigraphic sequence in the two segments (west and east of the DHHR) of the  Himalaya

 

 


SEGMENT 2                                                             SEGMENT I

(west of  DHHR in J & K,                             (east or DHHR in Garhwal)

H.P. and Haryana)

                       

TETHYS HIMALAYA                                              LESSER HIMALAYA

 

Rajpur Fm. (Hazara facies)                                           Subathu Fm.

 

     (Subathu facies)      

Kakara Fm.

 

Mandi Fm.                                                                   ______Unconformity______

Panjal Volcanics                                                           Tal Fm

Agglomeratic Slates Fm.                                               Krol Fm.

Blaini Fm.

 

Gamir Fm.                                                                    ______Unconformity______

Baila Fm.                                                                      Nagthat  Fm.                                                                                                                                                                                                   Chandpur Fm.

Mandhali Fm.

 

 

 Krol Thrust in south______Unconformity in north______

Deoban Gr. ---

 

__________________Murree Thrust_________________

 

 

 

SUB HIMALAYA

 

Inner Belt

 

Upper Murree Fm. (Upper Dharmsala Fm.= Kasauli Fm.)

Lower Murree Fm. (Lower Dharmsala Fm.= Dagshai Fm.)

Subathu Fm.

(Subathu facies)

Kakara Fm.

 

____________Unconformity____________

Vaishnodevi Limestone (=Sirban/Riasi/Great/

Jammu/Dharamkot/Bandla/Tundapathar Lime-stone)

 

Outer Belt                                                                  Outer Belt

 

Upper Siwalik Subgroup                                               Upper Siwalik Subgroup

Middle Siwalik Subgroup                                              Lower /Middle Siwalik

Lowcr Siwalik Subgroup                                              transition and

 

Middle Siwalik Subgroup

 

 

 


Sub Himalaya

 

There are two linear belts of sedimentary successions within the Sub Himalaya: the Inner and Outer (Fig.4}. The Inner Belt comprises the Kakara-Subathu-Murree/Dharmsala/Dagshai-Kasauli succession overlying the Vaishnodevi (Riasi/Sirban) Limestone and the Outer Belt consists of the Neogene (Siwalik Group) sediments. The two are separated by the MBF.

 

Inner Belt or Sub Himalaya

 

In segment 2, within the inner belt of the Sub Himalaya, there are several exposures of older basement rocks in thc Jammu area represented by the Vaishnodevi Limestone (= Sirban Limestone/Great Limestone/Riasi Limestone/Jammu Limestone), and its equivalents (Dharamkot Limestone in Dharmsala area, Bandla Limestone in Bi1a.spur area and Tundapathar Limestone in Shimla area) in Himachal Pradesh and Haryana. These lithounits occur in the form of inliers in this belt.

 

Thc Vaishnodevi Limestone is made up of thickly bedded, highly jointed, hard, siliceous, dark grey commonly oolitic limestone showing algal mats and stromatolites (Rao and Rao, 1979). Due to hardness of the rock type, it is quite resistant to erosion and physical weathering, and therefore stands out in relief to the low-lying topography. This unit has yielded a rich microbiota indicative of late Proterozoic to Vendian age (Venkatachala and Kumar, 1996) thereby corroborating the age assigned by Raha et al. (1978) and Raha (1980). The Vaishnodevi Limestone is autochthonous and is exposed south of the Main Boundary Thrust and forms the base of the Sub Himalayan rocks. As a result of it, its geological equivalents are situated in the southern parts.  Therefore, the only possibility is that the Precambrian-Cambrian limestone of the Salt Range (Hazara/Abbottabad Formation) could be continuing north-eastwards in Muzaffarabad-Poonch, Kalakot-Metka-Mohgala, Vaishnodevi-Trikuta Hills (Riasi inlier), Dhansal-Sawalkot, Dharamkot-(Dharmsala)-Bandla (Bilaspur)-Kakarhatti-Tundapathar upto the western flank of the DHHR.  Out of these, the Riasi inlier is thr largest in its extent and Dhansal-Sawalkot inlier is the second largest. Though the Vaishnodevi Limestone belt is in juxtaposition with the calcareous sequences of the Himalaya, the former cannot be in strike continuity of Himalayan sequence.   They represent extrabasinal sediments in the Himalaya and obviously are part of basement of the Peninsular India and could be extending in Himalaya also as MBT and MBF are post- depositional. The landforms in the Vaishnodevi Limestone were partially submerged in the Subathu Sea of the Sub Himalaya (Inner Belt) and partially remained above water (positive areas). This is evident from the unconformity exposed between the limestone and the Kakara-Subathu succession. A rich fauna has been recorded from the Subathu sediments of the Jammu region (Singh, 1980a; Kumar and Sahni, 1985; Juyal and Mathur, 1992).  Higher peaks of Vaishnodevi Limestone have remained positive area during

 

Cretaceous and Cenozoic times. In segment 2, the Late Cretaceous to Palaeocene (Quaker-Sabbath/Murray/ Dharmsala/Dagshai-Kasauli) succession was deposited unconformably over various Precambrian lithounits and is more than 200 km wide in Jammu, but becomes narrower eastwards in the Kalka-Subathu section with its width varying from 100-120 km before the succession finally pinches out at Kalsi (west of DHHR). In Himachal Pradesh, the Subathu Formation has yielded a rich foraminiferal assemblage indicative of Ypresian-Early Lutetian age. The assemblage comprises Nummulites burd. burdigalensis de la Harpe, N. beaumonti d' Archiac and Haime, N. . praediscorbinus Schaub, N. discorbinus (Schlotheim), N. subramondi de la Harpe. Assilina plana Schaub, A. placentula grande Schaub, A. laxispira de la Harpe and A. spira abrardi Schaub (Mathur, 1997; Juyal, 1997). The Inner Belt of the Sub Himalaya does not continue to the east of the DHHR in segment 1.

 

Outer Belt of Sub Himalaya

The Murree/Dharmsala/Dagshai-Kasauli succession so well developed in Jammu (3500 m) and Himachal Pradcsh (3000 m) (segment 2) was not deposited in Garhwal (east of the DHHR i.e. segment 1) (Agarwal et al., 1994). Similarly the Siwalik succession is well devclopcd in Outer Belt of segment 2 and is represented by the Lower, Middle and Upper Siwalik. The Lower Siwalik comprises red clay and sandstone with reddish brown marl and siltstone, whereas the Middle Siwalik consists of sandstone and variegated clay with conglomerate towards the top, and the Upper Siwalik is composed of sandstone and conglomerate with reddish brown silt and clay. From the Lower Siwalik of Ramnagar (Jammu). Sehgal (1998) has reported charophytes, gastropods, pisces, crocodiles, turtles, primates, carnivores, proboscideans, suids, anthracotheres, tragulids, giraffids and bovids. Based on this biota, he assigned a middle Miocene age to the Lower Siwalik. The fossil assemblages of Ramnagar are referred to three ecological communities, namely aquatic and semiaquatic community represented by stream, stream bank and pond populations; the abroreal by primates; and the terrestrial by other mammals (Sehgal, 1998). According to Sehgal (1998), the bulk of the mammalian assemblage is indicative of tropical rain forest environment with swampy conditions. The Middle Siwalik in Himachal Pradcsh is characterised by thickly bedded multi-storeyed, grey sheet sandstone showing salt and pepper texture with minor mudstone deposited by erstwhile south-easterly flowing axial drainage (Ghosh et al., 1998). According to Ghosh et al. ( 1998) the Upper Siwalik has varied lithofacies association. It comprises buff, ribbon shaped, fine grained. matrix-rich sandstone within the grey sandy domain. These sandstone bodies, which are bound by overbank deposits and without any lateral accretionary features, represent laterally fixed channel of south-south-east flowing piedmont drainage originating from the proximal part of the foreland basin. The Middle and Upper Siwalik have yielded a rich vertebrate fauna (Nanda. 1976, 1978. J 998). In Jammu and western Himachal Pradesh regions, the Kamlial and Chinji formations of the Lower Siwalik can be recognised. There is so much difference in lithology of the Lower Siwalik of these regions from eastern Himachal Pradesh that their equivalent in the latter region has been named as the Nahan.

In segment I, the extent of the Siwalik exposures is much reduced and is not more than 30 km in Mohand-Rajpur (Mussoorie) section of the Doon Valley and is minimum (3- 4 km) at Kotdwar in the Khoh Valley between Sidhbali temple and Haldwani Bridge (south of Dugadda). In Garhwal region (segment I ), only the upper part of Lower Siwalik, and the Middle and Upper Siwalik have been reported (Ranga Rao et al., 1979; Tiwari, 1981 ). In this region, repetition of beds is due to Mohand Anticline, Doon Syncline and Malsi Anticline (from S to N). The total thickness of the Siwalik succession is around 4000 m in the Mohand-Rajpur section. The Middle Siwalik near Mohand consists of micaceous, fine to medium grained, grey, multistoried sandbodies and grey mudstone which changes to red in the younger horizons. According to Tandon et al. ( 1988), the occurrence of red mudstone in the top part of the Middle Siwalik suggests oxidising conditions and relatively well drained flood plains. The Upper Siwalik comprises conglomerate (cobbles and pebbles), its provenance being from the Himalayan metamorphics like granites, gneisses, schists, quartzites, slates, etc. (Kumar and Srivastava, 1995). It is very important to note that rich and well preserved vertebrate fauna recorded from the Middle and Upper Siwalik of segment 2 (Jammu and western Himachal Pradesh) has not been found in segment I (Garhwal region), or its presence is negligible (Sahni and Tiwari, 1979; Tandon et al., 1988). It has, therefore, been inferred that the DHHR hindered the movement of vertebrates from west to east. The richer yield of Tertiary vertebrate fauna in the areas to the west of the DHHR is a consequence of role played by the manifestation of the DHHR in controlling the configuration of the foreland basin on either side of it. For smaller vertebrate fauna, it might have acted as a physical barrier, which seems to be well reflected in the composition of larger vertebrates and in their food- , web. It further supports the contention that the DHHR, which formed a physical barrier, not only limited the sedimentary basins but also controlled the physical movement of vertebrates. Therefore, the lithologies of the Middle and Upper Siwalik are also markedly different on either side of the DHHR.

 

 

Lesser Himalaya

 

Almost all the workers took it for granted that the Krol Belt extending from the Krol Hill in Solan to Nainital in Kumaun is a single belt ignoring completely the absence of Krol Sandstone  and Tal Phosphorite (two economic deposits) on eastern  and western sides of the DHHR. The Krol Sandstone (50-60m) is remarkably uniform and occurs persistently at the base of the Krol Limestone (Member A) in the Outer Krol Belt. It comprises compact orthoquartzite and friable sandstone. It has highly rounded, coarse grained and well sorted quartz grains with little or no matrix. This unit is completely missing in the Inner Krol Belt of Mussoorie, Garhwal and Nainital. It was Bhargava (1972), who clearly established that the two successions in the Krol Hill and Nainital areas are neither in strike continuity nor were deposited in a single basin. He grouped the Krol succession of the Simla and Nainital areas under the Outer and Inner Krol belts, respectively. The Nainital, Garhwal and Mussoorie synclines fall In the Inner Krol Belt, whereas the Krol, Pachmunda and Sain Dhar Synclines are in the Outer Krol Belt. The Krol Sandstone is found in the Outer Krol Belt while the Tal Phosphorite is restricted to the Inner Krol Belt. Similarly, the volcanic rocks are quite common in the Inner Krol Belt, whereas basic volcanic rocks are absent in the Outer Krol Belt.

 

To the north of the MBT (=Krol Thrust), which is a sharp line from Kalsi to Rajpur, Rishikesh, Dugadda and Rathwadhab, a prominent and well marked sequence of the Krol Belt is exposed in a linear form almost parallel to the Sub Himalayan trend. This is in sharp contrast to what is observed in the west (Outer Krol Belt). East of the DHHR, the Lesser Himalayan sequence comprising Jaunsar and Krol groups is thrust over the Siwalik. The Kakara (= Bansi)- Subathu Dagshai succession lies unconformably over the Krol- Tal succession and occupies the youngest position in the Inner Krol Belt. The Jaunsar Group, represented by the Mandhali, Chandler and Nagthat formations, forms the base of this sedimentary belt and is overlain by rocks of the Krol Group. The Blaini Formation is the oldest unit of the Krol Group and is represented by pebbly quartzite and turbidites (Blaini Member) grading upwards into the Infra-Krol Member. The latter unit is overlain by the Krol Formation, which contains limestone in great abundance and forms higher ranges in the Lesser Himalaya due to its resistence to physical weathering. The overlying Tal Formation comprises carbonaceous shale, phosphorite and chert at its base followed upwards by shale and quartzite. This unit has yielded Cambrian fauna (Azmi et al., 1981; Rai and Singh, 1983; Kumar et al.. 1983 ). The Kakara Formation lies unconformably over the Tal Formation. It comprises hard grey, massive, oolitic shelly limestone. It has been assigned varying ages in the Maastrichtian-Thanetian interval based on various taxa: a Maastrichtian-Danian age by Mathur (1977) (cerioporids and molluscs) and Bhatia (1980) (cerioporid bryozoan -Diplocavae calcareous algae and hydrozoan); a late Cretaceous age (Coniacian) by Singh (1980b) ( Globotruncana); and a Maastrichtian- Thanetian age by Juyal and Mathur (1990) ( Diplocava nilkanthi (Singh) and Phafcocythere rete Siddiqui - a Thanetian ostracode species and several other long ranging nlanetian-Lutetian ostracode taxa recovered from the upper part of this unit). This shelly limestone of Garhwal region (=Nilkanth Formation of Singh, 1979/Bansi Formation of Valdiya, 1980) has been equated with the Kakara Formation of the Shimla region based on lithology and sedimentology, thereby supporting the views held by Valdiya ( 1980). The succeeding Subathu Formation consists mainly of grey, green to red shalc with subordinate siltstone, sandstonc and limcstone which is frequcntly fossiliferous. The Subathu Formation has been assigned a Ypresian to an Early Lutetian age based on the occurrcnce of a rich fauna (Mathur, 1997; Juyal, 1997). The Dagshai Formation is the youngest unit in this belt of which only the basal part, comprising green sandstone and red shale, is present at Dugadda (segment ] ).In segment 2, the Subathu Formation occurs in the form of tectonic windows north of the Krol Thrust at SoJan. In this segment in the Shali area, north of Solan, the Subathu Formation rests unconformably over the Shali-Madhan succession. Further in Mussoorie-Chakrata area the KroJ- Tal succession along with the Deoban is exposed right from the MBTto the Main Central Thrust (MCT). This itself is a unique setting confirming existence of the DHHR. Further the rocks of the Krol- Tal succession show very gentle dips and beds are even horizontal at Chakrata. Auden ( 1933) had interpreted strike continuity of the Aravallies across the Himalaya in the Chakrata area. In a later work, Rupke ( 1974) gave a detailed account of rocks of the Damta Group in western Garhwal, whcre he proposed a new name -Damta High -a basinal high which effectively controlled sedimentation on its peripheries in the Chakrata-Nagthat area. This almost coincides with the DHHR, which passes through this area and has controlled the sedimentation.

 

 

Tethys Himalaya

The succession to the north of the MBT ('Murree Thrust') in the Poonch area has been considered by some workers to fall in the Lesser Himalaya. The authors interpret that this succession represented by the Gamir-Baila-Panjal Trap-Mandi-Rajpur succession is a part and parcel of the Tethys Himalaya. The litho-and biostratigraphy of this succession has been outlined by Verma et al. ( 1981 ). The Rajpur Formation, the youngest unit of the succession, is best exposed at Rajpur village, north of Poonch. It is divisible into two distinct members, the lower Nummulitic Limestone Member and the upper Variegated Shale Member. The lower member has yielded several species of Daviesina. Nummulites and Assilina indicative of Thanetian-Ypresian age. The Rajpur Formation which is exposed in the western part of Kashmir has earlier been designated as' Hazara facies’ (Wadia, 1966).

 

The above Tethyan sequence continues eastwards in the Zanskar and Spiti regions. The Permo-Triassic limestone and Chikkim Formation pinches out to the west of the river Satluj near where a Trans-Himalayan granite (Leopargil Granite) is emplaced along the DHHR which is almost perpendicular to the Himalayan strike, as if it restricted basins on either side of it, as the Malla Johar Basin of Kumaun does not cross this granite mass.

 

 

Basin Development history during Cenozoic

A model of basin development for the Sub Himalaya based on physical discontinuity across the DHHR and geological setting of various successions to the east and west of this ridge (segments I and 2) is given in Figure 5. In the first stage of basin development, the Sub Himalayan basin extended from Poonch in the west to Paonta Sahib in the east, where the DHHR formed  its eastern limit and the Panjal Traps formed the northern limit. It has many exposures probably in geological continuity of the Vaishnodevi Limestone at Kalakot, Metka, Mohgala, Riasi, Dhansal- Sawalkot, Dharamsala, Bilaspur, Kakarhatti and Tundapathar  areas. This basin was formed during the Late Cretaceous times (Mathur, 1990, 1997; Mathur and Juyal, 1996). The Maastrichtian-lower Paleogene  marine sediments, represented by the Kakara-Subathu succession, were deposited in this basin. The marine sedimentation was replaced by fluviodeltaic system as the basin was partially filled up and partly became positive. The rivers started flowing down from higher areas ill the north and the rock.-; of the overlying Murree were deposited in the Inner Belt, their provenance was both from north and south.

In the second stage, the basin got uplifted and a newer landscape in the Paleogene-Early Miocene sediments also came into existence. The southern border of this landscape became the MBT and the Lower Siwalik \vas deposited to south of it in the Outer Belt. An estuary of brackish water stretched towards north from Ramnagar to Udhampur, and another from Sundarnagar to Jogindernagar. The eastern limit was restricted to the DHHR. Nahan lying on the peripheral area of the ridge gave rise to slightly different lithology due to its location on the edge of the ridge.

In the third stage, the DHHR got partly submerged due to some tectonic movement. As a result of it two different lithofacics developed on either side of the DHHR. It can be assumed that a single basin existed from the Middle Siwalik onwards and finally the entire succession got uplifted in the Early Quaternary and gave rise to landscape of present day. A situation similar to original MBF is further developing in the form of Himalayan Frontal Fault (HFF) in the Indus and Gangetic Plains.

 

Acknowledgements: The authors are grateful to the Director of the Wadia Institute of Himalayan Geology, Dehradun for providing various facilities.

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