Geological Problems of Nepal, Himalaya and its solution

Geological Problems of Nepal, Himalaya and its solution

K. D. Bhattarai

Introduction
This paper deals mainly with the three aspects of geology of Nepal Himalaya, which are also the main objectives of the presentation, and they are:

To provide out line information on geology of Nepal Himalaya.
To draw attention of the concerned community about the existing geological problems of Nepal Himalaya
To provide certain suggestion on the types of works needed to solve the existing problems.

Location of Nepal Himalaya
Nepal is divided in to various morph tectonic zones as other parts of Himalaya. (fig. 2)

Fig.2 Generalised morphotectonic map

Out line information on geology of Nepal Himalaya.
Considerable knowledge on geology of Nepal Himalaya is now available due to the effort of foreign as well as local geologist. However due to various complication, lack of definite proof, personal jingoism of the workers, lack of cooperation among geologist working on Nepal Himalaya and also due to absence of regular communication and circulation of latest publication among active workers on Nepal Himalaya, a valid and acceptable to all model is still not ready.

Due to presence of fossils and fairly detail work especially on the neighboring part India, The Sivalik formation that is more or less continuous all along he entire foothill of the Himalaya is will understood to some extent.

Similarly due to considerable amount of work especially by foreign geologist on the Higher Himalaya and also due to presence of fossiliferous sequence ranging from comb rain to Miocene Higher Himalaya of Nepal are also to some extent better understood than the complex lesser Himalaya.

Due to presence of the Nappe, Klippe, over thrusting, Tectonic windows and many other problems along with the unfosailiferous nature of the sequence with few exception (5/28{ very little is understood about the geology of lesser Himalaya of Nepal. Systematic study detail investigation and logical explanation of the available geological data is absolutely necessary in this part of the country for better understanding. However it is not only the lesser Himalaya that requires the systematic study and logical explanation hut the sub Himalaya as well as Higher Himalaya also as mentioned earlier require in depth study of available information along with the support of the geological data that are available now.

Sivalik
It is commonly used for molasses type Neogene's sediments of Himalayan foot hill zone. The age range as indicated by mammalians fossils from middle Miocene to early Pliocene.

In Nepal the Siwalik system form 20-30 km foothill belt sand extend south into the subsurface of the genetics plain these terrestrial largely fluviatile deposits reach over 5 km in thickness. Not much detail study of Siwalik stratigraphy of Nepal has been done yet and is know n only in gross outline. However based on well studied area of neighboring India Krishnan, 1943, Wadia, Pilgrim 11910, 1913, Lewis 1937, Fatmi 1943, etc.) the three fold divisions of Siwalk which is well established in India is also widely accepted in principle for Nepal also. (22, 30) however Glennie and Ziegler (1964) divided the Siwalik group into lower Sandstone faces and upper conglomerate facies.

The three fold divisions of Siwalik into clayey sandy siwalik (Nahan by Lehner) the predominantly sandy middle Siwalik and he predominantly conglomeratic upper Siwalik is used in Nepal, but they are seen as a patchy outcrops North of MBT on the Surkhet area.

The top of the Upper Siwalik is always truncated by the MBT. The pebbles in he conglomerate appears to be strikingly different from the recent pebbles materials of the rivers. Specially in the section of central Nepal (27).

The different members of Siwalik are repeated several time due to folding and faulting (6) and the belt is characterized by broad gentle folds dying out towards the Genetic plain with minor sign thrust faulting nearer to MBT (Tony Hegen fig 83-9 pp 101-111).

Lesser Himalaya
The lesser Himalaya of Nepal is the complex zone both from point of view of stratigraphy and structure. Klippe, of metasedimentaries, with granitic elements physically overlie less metamorphosed or un metamorphosed un fossili ferrous sequence over great distance. The unfossiliferos sequence are seen through the over thrust metamorphic in 'window" and ' semi window". The paucity of fossili ferrous sediments and complex structure relationship of various proterozoic- paleo zole sequences is common feature of this belt.

These belt mainly consists of classic sediments with locally important carbonates zones. Some of these rocks are practically un metamorphosed but most arte converted low grade metamorphism to slate, Phyllites, quartzite's, and finely crystalline lime stones. It can be distinguished into a narrow outer tectonically more intense and a broad inner or midland tectonically less or undisturbed sedimentary belt, the two being separated by a discontinuous zones of schist's, gneisses, migmatites, and also minor granite known as the lesser Himalayan crystalline which seem to overlie the sediments in large synclinal cores. The Mahabharata range south of midlands comprises the outer sedimentary belts and parts of crystalline. However in the eastern lesser Himalaya the crystalline cover most of the midlands and merge with the central crystalline zone of high range.

The less metamorphosed piles f sedimentary rocks reaches 20 km or more. Weather this thickness resulted from mere sedimentation or tectonic repetition is a controversial matter and is one of foremost problem of Nepal Himalaya. Due o almost lack of fossils except in pulchouki (5) and Chandragiri (28) and reverse metamorphism the problem of lesser Himalaya becomes more complicated.

Far Western Sector
Geological exploration in far western Nepal has naturally been influenced by concepts previously developed in the adjoining Kumaun Himalaya (and vice versa). In the Kumaun sector the zonation of lesser Himalaya in to an outer and inner sedimentary belt and intervening crystalline zone is particularly clear.

Available literature shows that the strati raphical concept of pilgrim & West 91928) and Anden 91934) for Kumaun Himalaya is more or less applicable (with local variation ) in the west and far west part of Nepal Himalaya also.

The lesser Himalaya of far western Nepal, between MBT and MCT, is characterized by the presence of nappies and para-atochthonous zone, allochthnous zone, crystalline napes and autochthon zone.

The autochthonous Baitadi meta sedimentary unit is exposed in the teconic windows of the inner lesser Himalaya and forms the lowest structural unit. karnali sedimentary zone out crops to the north of MDT. higher up in the structural ladder, Budar meta sedimentary until forms the continuation of Nuwakot nappe of central west Nepal. The crystaalline nape and Klippens, the youngest structural unit, are confined in major synclinal structures advancing far to the south in outer lesser Himalaya.

Western Sector
Hagen (22) was the first one to point out the conspicuous krol affinities of the Puthyan-Tanshing zone, the outer sedimentary belt of western Nepal. However it was Fuchs and Frank (16) to compare the litho logic and stratigraphic similarities.

A par autochthonous schuppen structure has in principle been accepted by many authors, including Hagen for the outer sedimentary belt of western Nepal. in contrast the sedimentary pile of inner

Belt was interoperated by Hagen (220 as a succession of this extensive nappy sheets, thrusted over an autochthonous sedimentary floor which he thought to be exposed in the tectonic window of Pokhara.

However it is to mention here the separation of inner and outer belt is possible easily where lesser Himalayan crystalline covers the lesser Himalayan sedimentary rock-separating the outer belt in the sediments south of crystalline and inner belt to the sediments north of crystalline. in a area where such crystalline are not noticed, this separation of inner and outer belt becomes arbitrary.

The Strati graphy of western part is discussed by Frank and Fuchs (16) who divided the area into four tectonic units as following. Taushing unit, Rukum unit, Chail Nappe, and crystalline nappe. And used the lern krol unit and latter on the Tansen unit-to describe the stratigraphy of the area using the nomenclature of classical work of Aden in Krol area (Kumaun Himalaya).

Central Sector
This part was studied in detain by J. Stocklin and present author (K.D. Bhattarai) and a geological map covering the area was published along with report (27) by UNDP.

The whole sector is divided into Nuwakot complex and Katmandu complex. The essential difference between the two complexes lies in their differing litho stratigraphic sequences. Equally important are differences of metamorphic grade. The Katmandu Complex, except for some epi-metamorphic rocks occurring in its highest part, includes relatively high-grade metamorphic rocks such as biotitic quartzite's, two-mica schist's, garnet-schist's marbles, guises, migmastites, and also granite. The ensemble of these high-grade met sediments and crystalline rocks is also referred to as "Katmandu crystalline". That the bulk of its met sedimentary portion is older than the lower Paleozoic fossil beds on top of it is unquestioned. The Nowakot complex, on he contrary, contains no crystalline rocks but only met sediments of low metamorphic grade and, except for some scanty evidence of early Paleozoic age for part of it, its age is largely unknown.

Physically, the Katmandu Complex the Nawakot Complex along a contact that is in most places sleepily inclined. The nature of this contact, and therefore he nature of the superposition of the high-grade Katmandu on the low-grade Nawakot rocks, is much disputed.

Each Complex has been divided in to two Groups. The Nawakot Complex comprises the Lower Nawakot Group and the Upper Nawakot Group: the distinction has been made to indicate a possible major strati graphic unconformity between the two. The Katmandu Complex is divided into the (lower) Sahimphedi Group and the (upper) Phuchauki Group, the two being strati graphically continuous but distinguished by different grades of metamorphism.

In addition, the Katmandu Complex includes the granitic and migmatitic rocks, which do not lend themselves easily to stratigraphic treatment.

Eastern Sector
The present region can be divided into autochthonous and allochthonous masses. The autochthonous masses are the 1) Dudh Kosi Dome Zone 20 Tumlingtar window 3) Dhankuta Zone 4) Murghat Zone 5) South marginal Zone. The allochthonous masses are 1) Barun phullite schuppe, 2) Irkhua.

Higher Himalaya
The term Higher Himalaya is used in Himalayan geological literature as a broad stratigraphic division for the various types of rocks that occupy the spatial position between M.C.T. 9Main Central Thrust) which separate it from lesser Himalaya in the south and Tsangpo ophiliotic zone in the north. The rocks of this division are subdivided into the higher crystalline zone (Tibetan slab) and Tibetan sediments of tethys sediments which overlie he Tibetan Slab.

Correlation and discussion
During study of the geology of Nepal Himalaya: it is evident, as the author observed, that almost all the geological Maps of the country are interpreted in different ways, and practically all the author are speaking on different lines, and an attempt to correlate their views were further hardened by the discrepancy on the nomenclature adopted. It was not uncommon to find different litho logical name for the rocks of the same area by different authors, present situation is expressed by Vadiya (24) as a Tangled confusion, and by stocklin (25) as a hopeless confusion. I consider the present situation as a chaotic-which requires systematic approach, with imagination and wisdom and courage to synthesize he various available information and present it in as systematic way as possible.

The overall correlation put forward by some of the authors is mostly to long distance and much generalized type, which I feel will not be able to sole the geological problems of Nepal Himalaya. I believe in J.B. Auden, who as early as 19135 after his traverse to Himalaya said "It is realized that there is often danger in early generalization from incomplete observation such as are made on Traverses. The Himalaya are so vast, however, that years will elapse before they are mapped geologically in detail, and it seems desirable therefore to place such observation on record, so as to build scaffolding for latter formulation f geological structure, which will eventually emerge from detailed work. Such results may also have a bearing on the4 understanding of the geology of the small areas where mapping is at present in hand:" (22) and I think the type of correlation put forward by T. Hagen will not help to solve the geological problems of Nepal Himalaya. He correlates Nepal Himalaya with Alps- and suggests: in his own word p156 (22)" In general way we may say that the number of over thrust napes in particular sections is similar in the Alps and in the Nepal Himalaya', and correlates Katmandu and khumbu nappies with Austro-Alpine Nappes, Nawakot-Bajang napes with Helvetic Nappies etc. Further he correlates Her Massif with Dandeldhura massif, etc.

Other type of correlation put forward by V.A. Talalov (34) is the Time stratigraphic-in which he puts together the clearly separable units like coarse crystalline Massive 'Bhaise Dovan marble' 927) with a unit of mixed litho logy of carbonate, schist, and Quartzite. The 'Malekhu formation' (27) in one group of calcareous formation known as "Hilang suite". This type of time stratigraphy classification-based on very few absolute age determination-also is not going to help much to unfold the various geological problems of Nepal Himalaya.

The other correlation put forward by some authors is the litho logic correlation. However due to careless application of stratigraphic terminology to rocks of distant places based on easy correlation simply relying upon apparent litho logic similarities, and proposed of new unit-names without designation of type section and clear definitions of those unit, as correctly mentioned by Sakai (32), the litho logical correlation are also confusing and need many modification.

Some discussionn SOSN geological problems of Nepal Himalaya
The overall brief description about the present status of the geological study of Nepal Himalaya, and a modest attempt to correlate the various works clearly provide us the magnitude of problem that is face by any geologist who tries to understand it. Some of them are mentioned below.

The gaps in the knowledge and legitimate diverse attitudes and approaches (Fig. 11) of the individual's geologist in Nepal Himalaya.

The evolving of new concepts based on data which are available in one part of the country, but not noticeable in other parts of the country.

The un fossil ferrous nature of most of the litho stratigraphic units and the structural complexity of the mountain belt due to diverse indigenous process.

The similarly in litho logy of un fossil ferrous rocks in one band, provides basis for correlation in other band where the gap in distance between such litho strati graphical correlation is considerable such correlation are often misleading.

The low angle thrust sheets or nape versus the vertical tectonics and gravity slides.

The extent of the Southern extension of the Siwalik under the alluvium.

Is MBT really boundary between the southern foot of the mountains and the fans of the Siwalik material?

Is Siwalik a old crowded land surface on to which the advancing napes have been over thrusted?

Does the Siwalik continue further north below the napes, if so how far?

Is the entire Siwalik of 5-6 km thick belong to one single succession?

Is the division of the Siwalik into thrusted Siwalik, folded Siwalk and undisturbed Siwalik-as in Alps is acceptable?

What is the amount of horizontal displacement along M.B.T. ?

The wide spread stromatolites of lesser Himalaya is of short time interval or range for longer period ?

The Pandeldhura is a autochthonous massif or a Nape?

Similarly what is the number of window/semi window Klippe-nappe, schuppe zone of lesser Himalaya of Nepal.

How many sedimentary basins were there in Nepal Himalaya?

Was the lesser Himalaya the north ward extension of the peninsular feature or the south ward extension of Tibetan sediments?

What are the over all tectonic features of the Nepal Himalaya?

Is the separation of Mahabharat and midland tectonic unit valid for the whole country or this is a local phenomena ?

The arbitrary position of MCT in the Eastern sector?

Stratigraphy of the central crystalline zone ?

Is the "tectonic slab" i.e. tectonically one unit theory of LE Fort acceptable?

What is the age of the crystalline zone?

What is the origin of the gneisses-sedimentary, Remobilized old-or introduced young material? And so on.

Some Suggestion
The mentioned problem undoubtedly is a geological but requires along with geological work some organizational approach also.

The clear example can be seen from the systematic work of our neighboring countries, India and China-where the large number of geo-scientist and many organizations are involved to solve the problem of their part of the Himalaya.

Author's suggestions are listed below;

In this context, it is time for the concerned national authority to start some organizational set up whose prime responsibility will be to research-explore-interpret and solve the geological problems of Nepal Himalaya. At present, the thrust towards realization and solving the problems does not exist. Considering its size (bigger than Alps) and spatial occupation (75 % of the country's area), the number of persons really involved in the Nepal Himalayan geological problems and organization available is negligible.

At present Department of mines & Geology (DMG) is the only organization who look, after to some extent, the geological activity of the nation. However, due to it's various, considered of important activity like leasing the mines, petroleum exploration, mineral exploration geophysical activity-seismic activity etc. Not much attention to research oriented activity is possible.

Further, due to absence of such organization responsible for geological research, the development of the geological information center is totally lacking. The D.M.G. Library is limited books, from law to all most all faculty sciences, hardly fulfill the requirements of lacks latest information-journals on geology and associated activities.

As mentioned earlier in this paper, the number of work conducted and literature produced, who regard to Nepal Himalaya is vast but to collect and locate them for study is next to impossible for any researcher, without heavy organizational back up-which is totally lacking in Nepal.
The division of the country geologically should be made into 4 geological sectors. (Fig. 11) during the study and in the attempt to correlate, it was noticed that the long distances correlation is often misleading, so this type of national divisions will help to make detail study-correlation & etc.
Establishment of stratigraphy, succession etc. Of each sector with detail & in depth studies is needed.
Detail in depth studies of each sector, within will-defined parameters should be carried out. In over view of the work shows that there is no consistency on the depth of study-scene give weight age to structure, some to petrography some to litho logy, and some to magamatism etc. Any two of the DMG report, will not show any consistency on the methodology-requirement etc.
Mention of all the existing problems of each sector should be made and based on the requirement, selection of detail study section, for each of the sector should be carried out.
Systematic search of the fossil in the Nepalese Siwalik area and interpretation of all the fossil o enable to divide the Nepalese Siwalik into further subdivision should be done and attempt to find their variation should be made.
Change in pre-convinced idea hat each of the Siwalik formation is litho logically unique and identical everywhere and that a specific fossil assemblage comes from that single litho logy is needed.
Detail structural and other detail study to explain the various repetitions of the beds in the Siwalik is needed.
Detail study of Siwalik by drilling for academic interest only may not be feasible in Nepal due to its economic condition-however; the broad utilization of the drilling data is suggested. (In near future drilling of some Terai regions by petroleum companies are expected).
Correlation of the Kumaun Himalaya with far west sector and far west sector with west and west sector with central sector and central sector with eastern sector in first steep (see Fig. 11) should be made.
Further detail study of central Nepal, if required and modification based on the new knowledge o make the central part as a base of correlation with eastern as well as western sector can be done.
Completion of Geological maps of four sectors and Geological map of Nepal Himalaya with alternative if required is necessary.
Mention and identify overall problems of Nepal Himalaya in broad sense and select detail study area to solve the problems.
Based on available knowledge and new work build up, certain hypothesis about the geological history, number of basins, structure and age problem-if required more than one hypothesis should be made.
Find out shortcoming of each hypothesis and orient studies to solve the shortcomings.
Categories and start necessary research work to solve the noted problems.
Finally, establish the true and acceptable theories on geology of Nepal Himalaya.

Conclusion
After brief presentation of the present status of geological work in Nepal, an unsuccessful attempt of co-relation and mention of salient existing problems and few suggestion I feel, systematic and detail study is absolutely necessary to solve the geological problems of Nepal Himalaya.

It will be improper to think that geological problem of Nepal Himalaya will be solved by the detail study of adjoining Himalayas. Similarly it will be an over expectation to think that by the help of appreciable work of foreign researcher, geologist, all the problems of Nepal geology will be solved, simply because all most all foreign geologist, researcher, scientist, have certain limitation and some objective of their own. Indeed such studies, will help us tremendously and past history have shown that may of the important geological information of Nepal Himalaya has come from foreign geologist. Still, it will be native to expert, without proper and systematic work from the local geologist, to solve the problems of Nepal Himalaya.

Overall lack of detail study; on regional scale is one of the primary causes of all sort of misinterpretation. The detail study along with the supportive studies of thin sections, age determination, etc. I believe, will provide many necessary data to solve many of the problems mentioned above.

Acceptance of some disputable facts and temporary alternate interpretation if necessary; without any prejudice to any school of thought will be very helpful.

Nepal Himalaya is big enough with complex problems, so to solve all its problems by individual or group of people is not possible. A rational approach without influence of any school of thought, along with systematic studies (as suggested0 with the supporter of responsible organization with the help of dedicated work loving local geologist and regular with interested foreign geo-scientist, is the only solution in my opinion.

In absence of this, the prevailing personal Jingoism, lack of interaction among co-workers, legitimate individual interpretation and temptation to put forward new nomenclature and hypothesis of their own etc. will always be their and problems of Nepal Himalaya will be more complicated.