Geographical Location (of Orissa)

Orissa’s geographical location is specified by its extension from 81 27’ E to 87 29’ E longititudes and 17 45’ N to 22 30’ N latitudes. Orissa is as big as Ireland in size and it covers an area of 60,135 sq miles, coastal tracts itself covers an area of about 500 Km. It is situated on the south-eastern coast of India and is a part of Peninsular India that shows rocks of the Pre-Cambrian age. Orissa is bounded by the states of West-Bengal on the north-east, Bihar on the north, Chattisgarh on the west, Andhra Pradesh in the south and the Bay of Bengal on the east. The description of geological and geographical features has given in brief to facilitate our understanding of the availability of raw material, associated landscape and impact on the socioeconomic conditions.

The state is divided into four geographical regions:

1. Northern plateau,
2. Central river basin,
3. Coastal plains,
4. Eastern Ghats.

Northern Plateau: Is an undulating upland intersected by rivers. It is a continuation of the Chhotanagpur plateau of Jharkhand. It consists of Mayurbhanj, Keonjhar, Sundargarh and Pallahara sub-division of Dhenkanal district.

Central River Basin: Comprises of the important rivers of the state i.e. The Mahanadi, Brahmani and Baitarini. It falls between the northern plateau and eastern hills.

Coastal Plains: It stretches from the Subarnarekha in the north to the Rushikulya in the south. The coastal region is formed by Subarnarekha, Budhabalanga, Baitarini, Brahmani, Mahanadi and Rushikulya rivers. It covers districts of Balasore, Ganjam, Puri which are sandy and on the other hand Cuttack district which is swampy and marshy.

Eastern Ghats: These are a series of hill ranges which stretches from the northern border of Orissa through the coastal region of Andhra Pradesh to Nilgiri in the western part of Tamil Nadu. This region comprises of Ganjam, Kalahandi, Khondamal and Koraput districts. (Nanda 1983: 5-8).

The physiographic evolution of the region has been controlled by diastrophism experienced by the region. Certain intervals in the rejuvenation resulting in chemical erosion (with little mechanical erosion) with the formation of laterite and bauxite, Orissa has the biggest bauxite deposit of India. Due to two more periods of rejuvenation, plateau level is stream dissected. These stages of upliftment have affected the entire state and beyond.

The Koraput plateau is disconnected from Ganjam plateau possibly by a couple of grabens (depression of earth’s surface between faults) along which Nagavali and Vamsadhara rivers flow. Sabari and sileru rivers and many smaller ones are captured; same is the case with some of the tributaries of Mahanadi above Tel’s

Grabens have been responsible for the deposition of Gondwana rocks along the east-west axis from Mahanadi up to Brahmani River. Monadnocks of Khondalites are seen between north of Chilika and Baitarini River and the eastern most exposure is at Assia hills where a regional closure of Eastern Ghats rock is found. Here important Buddhist monuments are located.

North of these rift regions are areas of older metamorphites. In the entire state, river piracy, antecedent drainage (in Gondwana areas), superimposed drainage, entrenchments along meanders and all such fluviatite features including erosion surfaces are well developed.

A broad stratigraphy of the region may be summed up as follows:-

Laterite

Younger alluvium

Older alluvium

Baripada beds

Unconformity

Gondwana rocks

Eparchean unconformity

Vindhyan rocks

Unconformity

Kolhan group

Unconformity

Gangpur group and their equivalents

Basic intrusives and traps

Ultra basici intrusion

Granitic intrusions

Iron ore super group and its equivalents

Older Metamorphics and their equivalents (?) position not definite

Unconformity

Other intrusive (Nepheline syenite, Anorthosite, Carbonite, Granite, Pegmatite etc.)

Intrusions of granites (more than one at different times)

Unconformity

Eastern Ghats super group (khondalite-charnockite super group)

Older granite gneisses (basement, later granitised)

(The terms of super group, group, formation etc as per stratigraphic nomenclature is being used to suggest the trend along which the new concepts on stratigraphic classification is seen. These have strict stratigraphic meaning only) (Behuria 1988:62).

The older rocks of Pre-Cambrian time have occupied most of the areas where compact rocks are exposed. The oldest one are supposed to be the granite ones below the Eastern Ghats rock that occupy almost the entire southern part of Orissa up to Brahmani River. These rocks represented by khondalite, charnockite, granite gneisses and migmatite forms a part of the sedimentary-volcanic intrusive complex resting probably on older gneisses which should be regarded as part of the primordial crust of the earth. The khondalite-charnockite sequence is in all probability younger to this as no evidence of the former being younger is available. It is interesting to note that the term ‘khondalite’ was first used by Walker in the beginning of twentieth century after the hill tribe ‘Khond’ of Kalahandi where this rock was exposed.

The word charnockite was used by Holland in 1900 after Charnock, the founder of Calcutta whose tombstone was built of this rock, brought from Mt. Thomas hill of Madras city. Both these rocks are highly metamorphosed and have their own peculiar uncommon characters. Khondalite has mainly quartz, fellspar, silimanite, garnet in variable proportions with or without graphite. Occurrence of khondalite stretches from the Brahmini River discontinuously up to Sri Lanka. It is usually a rusty brown rock due to decomposition of garnets and always wears a much decomposed appearance. Usually they occupy the hill tops and fringed by charnockite on both sides. Its nearest relative is leptynite which is known to be a migmatised khondalite or even migmatised basic granutite free of basics.Charnockite is much more massive and dark coloured. Although khondalite and charnockite were known to be sedimentary and igneous in origin respectively; a greater part of each of them may ultimately be considered to be metamorphosed igneo-sedimentary ones later migmatised.

Exposure of Gondwanas was discovered in Phulbani district in a narrow basin. The Gondwanas indicate glaciations conditions which gave place to humid conditions with prolific vegetation and gradually changing over to an arid climate during Triassic period. The PremianTriassic boundary is a climatologically one which shows evidences of a change from wet climate to dry. There has been a great hiatus in depositional history in Orissa up to the period of Mio-Pliocene in the tertiary time when Baripada Beds were deposited under marine conditions of deposition.

Sediments younger to these rocks are known to be the older and younger alluvium that stretches from north Balasore up to the northern part of Ganjam district where it thins out due to advent of khondalite rocks on the shore-line. While the older alluvium is cut by the river channels in which the younger one is sediment. Certain areas of khondalite out crops i.e. Assia hill, occur as inliers in the alluvium.

In this tropical region laterite is one of the most important rocks. This rock can change any other rock into its own by the process of lateritisation and any rock i.e. clay, shale, sand-stone, khondalite or granite all will fall to this process and change their appearance to laterite with or without having any ghost structure reminiscent of its past parentage. Laterite is soft when freshly cut from quarry, faces hardness on exposure. On the hill tops of Eastern Ghats it has produced bauxite. It is a typical rock that helps in the identification of erosion surface and thus hill tops with laterite as the cover and with accordance of summit levels are a good combination to support the idea of past erosion surface at a lower level which has later been uplifted and dissected by the rivers and other eroding agencies. The mosaic of laterite usually indicated the rock that has been transformed. Around Bhubaneswar changeover of sand-stone, shale and khondalite to laterite is a very common sight. In all the early monuments of Orissa laterites and locally available stones has been used extensively.