Tripura, the land of fourteen gods and million statues

Physiography:
The major geomorphic features observed in the state are topographic highs (hills) and depressions, valleys, flats and slopes sculptured on the surface in a linear fashion. In Tripura the topographic highs and depressions are in all cases coincident, respectively, with the anticlinal and synclinal structures of the rock formation. A number of broad and elongated valleys, as for example, Agartala-Udaipur-Sabrum, Khowai-Teliamura-Amarpur-Silachari etc. are located between the north-south trending, parallel to sub- parallel high ranges (topographic highs) such as the Baramura-Deotamura ranges, Atharamura ranges, Langtari ranges, Shakan ranges, and the Jampui hill ranges. The main rivers are the Khowai, Doloi, Manu, Jun and Langai flowing towards the north, and those flowing towards west are the Gomati, Muhuri and Feni. The drainage patterns are of dendnitic, parallel to sub-parallel and rectangular types.

Geology:
The study of rocks of Tripura dates back to 1908 when H.C. Dasgupta first classified the folded sedimentary rocks into 'Coal measures' and 'Tripura Group'. The rocks encountered in Tripura State range in age from Lower Tertiary (40 million years old) to Recent (less than 1 million years old). These sedimentary rocks are derived from the sediments that were deposited in a mobile trough known as the Barail geosyncline. The shallowing of this large basin was followed by the deposition of sediments in the continental slope-rise segments and then by the deposition in unstable foredeep. The deposition in each type of basin and environment is beautifully reflected in the rocks showing distinctive characteristics. The continuity of deposition of the sediments is marked by breaks known as unconformity, and deformational disturbances have been beautifully recorded in the rocks and carefully demarcated by the geologists. This geotectonic cycle finally ended by regional elevation of the platform and uplift of the basin to give rise to the present geomorphic features.

Thus, the sedimentary rocks of Tripura can be divided into 'Formations', 'Sub-Group' and 'Group' on the basis of their lithological composition, depositional characteristic and structural features.

The oldest rocks of Tripura, known as the Surma Group are characterised by repetitions of massive, well- bedded sandstone and gray and olive shale in equal proportion at the bottom followed upwards by repetitions of thinly laminated chiefly argillaceous rocks like siltstone shale, mudstone, etc. The presence of features like current bedding 'ripple-drift cross laminations', 'load-casts', 'turbidite structures', 'flame structures', etc. clearly indicate that the basin in which the sediments were deposited was highly disturbed by movements.

This group of rocks has been divided into the Bhuban and Boka Bill Sub-Groups, based on the lithological characters of the rocks. These rocks of the Surma Group are overlain by another group of sedimentary rocks known as the Tip am Group. Based on their lithological characters, the rocks of the Tipam sandstone Sub-Group can be further divided into smaller units known as the Manu Bazar formation at the bottom and the Champanagar formation on top of it. The Manu Bazar formation consists of fairly bedded, fine to medium grained sandstone with thin layers of sandy shale, siltstone and sandy mudstone. The upper part of Tipam known as the Champanagar formation consists of coarsegrained sandstone with occasional thin layers of sandy shale and abundant lumps of silicified wood. These rocks were deposited in near shone condition of deposition. The youngest rock group of Tripura is known as Dupi Tila Group. The rocks included are sandy clay, clayey sandstone, all coarse-grained ferruginous sandstone with thin layers of plastic clays, while silica sand and laterite. Towards the basal part of the Group, there is a conglomerate bed in which pebbles of clay-stone and siltstone are embedded in a matrix of sand and clay.

Overlying all the above rocks, are the unconsolidated sediments like coarse sand, sandy clay, silt, silt clay, clayey silt and clay, which were deposited by the recent fresh water channels and in back swamps. In Tripurã the sedimentary rock beds are elongated in a north-south direction and folded into compressed antidines alternating with broad very gently depressed syndines. The rock layers are displaced by sub-vertical faulting predominantly in E-W direction. the axial plane of folding is chiefly in a north-south direction and produced possibly due to compressional forces from the East-West direction.

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Mineral Resources of Tripura:
The most important mineral potential possibility of Tripura is oil and natural gas which are being explored by the Oil and Natural Gas Commission. Several gas seepages were reported by S.N. Sen of the Geological Survey of India in 1956, near Ampi Bazar, Saikhanbari headwaters of the Channel, Chara stream and about 2 km. W. N. W. of Kiphclapaaa village.

Glass Sand:
Deposits of white sand with an average silica content above 98 per cent and suitable for the manufacture at ordinary coloured glasswares occur along the bank of Bijai nadi stream in Bisramganj with an estimated reserve 1,60,000 tonnes, near old Agartala with an estimated reserve of 50,000 tonnes, and at Purba and Paschim Champ amura. The sand deposits occur below ito 2.5 thick overburden of soil or clay.

On the recommendations of the Geological Survey of India, a glass factory was set up at Arundhutinagar near Agartala with a capacity of 2 tonnes of glassware per day. Sand deposits located at Agartala may meet the demand of raw material for the production of soda ash for use in the existing soap factory in Tripura.

Clay:
White plastic clay suitable for the manufacture of coloured ceramic products occur at several places near Agartala, Dharmanagar and Bisramganj areas. Small deposits have been reported from the Teliamura-Ampi Bazar road cutting, and near Khowai and Jogindernagar.

Grey plastic clay has been located on the hill-sides near Paschim Champamura with a reserve of 914 tonnes, in Ranir Bazar with a reserve of 20,000 tonnes, at Sekerkot with an estimated reserve of 60,800 tonnes. Grey and white plastic clay occur at Tarkarjala village, Mohanpur, and Latiachhara areas. Most of the clay deposits are comparatively small in dimension but they are suitable for the manufacture of ordinary coloured potteries, roofing tiles, etc. Batch samples of some of these clays have been sent recently to Ceramic factories for Pilot plant tests.

Lignite:
Small occurrences of pyritiferous non-cacing variety of lignite occur in the rocks on the western flank of Unkoti Kalangshi hill, north of Kumarghat, at Betaga and Sabrum. The lignite bands are thin and under considerable rock cover and so cannot be worked economically.

Limestone:
Sporadic occurrences of occasionally fossiliferous siliccou limestone have been reported from the Sakhan and Jampui ranges. These occurrences however are of not much economic importance.

Building material:
In the state there is no hard and durable rock suitable for use as road metal and for building purpose except the moderately hard calcareous sandstone concretions. The shale deposits in the Atharamura range can be used for the manufacture of clay-cement-nodules to be used as road metal for which there is a great local demand.

The lateritised conglomerate moorum with quartz pebble is being extensively quarried for road metal. Grey-coloured, tough calcareous sandstone found in Gagrachara can be used as road metal.

Hydro Potential:
The Geological Survey of India is actively collaborating with the state Government for the construction of the Manu Earth Dam which is proposed to be constructed at the upper reaches of the Manu river, for flood control and irrigation. A gravity type of brick and stone concrete dam with a reservoir at the upper reaches of the Gomati river has been constructed for the generation of hydel power from two generators, each having a 5 MW capacity. The Geological Survey of India was actively associated with the construction of the hydel project. There is a proposal for construction of a dam in the upper reaches of the Khowai river to control seasonal floods and improve irrigation.

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