Geology of kerala .pptx

geology of kerala state
kerala geology for BSc students

1. Geology Of Kerala Sidharth C A 1 ST Year MSc Geology Central University Of Kerala

2. Introduction Kerala is wedged between the Arabian Sea to the west and the Western Ghats to the east. The topography consists of a hot and wet coastal plain gradually rising in elevation to the high hills and mountains of the Western Ghats. Total area of Kerala is 38,863 sq. km (1.18% of India’s landmass) Kerala lies between north latitude 8⁰17'30"N and 12⁰47'40"N and east longitudes 74⁰27'47"E and 77⁰37'12"E. The Kerala region is an important segment of the South Indian Precambrian terrain, where major units of the Archean continental crust such as granulites , granites, gneisses and greenstones are preserved. Total area of Kerala is 38,863 sq. km (1.18% of India’s landmass) The on land sedimentary formations are confined to late Tertiary (Neogene) period only. The absence of Palaeozoic and Mesozoic rocks may be due to the maximum erosion which might have led to non deposition

3. The rock types found in the Kerala region can be grouped into three as follows; a) The Precambrian crystalline rocks b) The Tertiary sedimentary rocks c) The Recent to Sub-Recent sediments Tertiary sedimentary formations of Kerala basin are unconformably overlaid on Precambrian rocks. The Tertiary sedimentary basin of Kerala extends from Cape Camorine to Manjeshwar . This Tertiary sedimentation basin extends as a narrow belt along a major part of Kerala coast. The bulk of the rocks of Kerala, especially the granulites and associated gneisses belong to Precambrian. Sporadic late Precambrian-early Palaeozoic granites and associated pegmatites, and Meso- Cenozic dykes intrude these rocks. The on land sedimentary formations are confined to Neogene period only. This indicates that the geologic column of the region is far from complete, with hardly any representation of rocks of the great periods belonging to Palaeozoic , Mesozoic and early Cenozoic eras of the Geologic Time Scale.

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5. THE PRECAMBRIAN ROCKS The Precambrian crystalline rocks form an important part of the Kerala region. These rocks are the oldest and form the basement for the later deposits. These complex crystalline rocks are of igneous and metamorphic in origin. The crystalline rocks can be broadly categorized as follows; a) The Khondalite group b) The Charnockite group c) The Sargur group d) The Dharwar group e) The basic and ultrabasic rocks f) Granites and related rocks

6. a) KHONDALITE GROUP Rock is known as Garnetiferous sillimanite gneiss, containing varying amounts of graphite and some quartz and orthoclase. Its occurrences are seen in various parts of the State. The largest patch is noticed in south Kerala in association with garnet-biotite gneiss and garnetiferousquartzo-felspathicgneiss . Another linear belt is observed in the northern flank of the PalghatGap , where it is seen in association with calc-granulite and crystalline limestone. Both these belt extend into Tamil Nadu. Minor occurrences have been reported from Idukki- Munnarregion and from southeast of Kasaragod

7. b) CHARNOCKITE GROUP The most widespread rocks in Kerala are charnockites and associated gneisses. These are pyroxene (Hypersthene)-bearing granulites and gneisses and occupy a major part of the Western Ghats and the midland regions of the State, especially in central and north Kerala. Large bands of charnockites are also observed within the south Kerala. Charnockite group consists of older massive charnockites and charnockite gneisses and younger incipient charnockites in various parts of the state. Thomas H Holland(1893) suggested the name ‘ charnockite ’ for hypersthene granite, in honour of Job Charnock, the founder of Calcutta, whose tombstone was made of this rock. Holland extended the term charnockite and introduced the term ‘ Charnockite series’. The minerals commonly present in the charnockite series of rocks are blue quartz, bluish green feldspar, hypersthenes , diopsides, garnet (rich in alamandineand pyrope), brownish hornblende, biotite, zircon, apatite, magnetite, illmenite , pyrite and pyrhotite .

8. c) SARGUR GROUP In Kerala, the greenstone sequence is represented by the high grade schists of Sargur and low grade schists of Dharwar , both being southward extension into Wayanad of the corresponding groups in southern Karnataka. In Wayanad, the Sargur group is represented by bands of quartz mica schists with kyanite, quartz sericite schists, quartz- magnetites , quartzites, and metamorphosed ultramafics . Several linear bands seen in parts of Thaliparambu , Kannur, Sultan’s Battery, Mananthavady , and in the eastern parts of the Kasaragod

9. d) DHARWAR GROUP The younger Dharwar schists overlying the Sargur schists, consisting of oligomictic conglomerate current bedded quartzites, garnet-mica-schists and biotite quartzites forming an inter-layered sequence. The polymictic conglomerates recorded in Kuthuparambu in Tellichery area occupy the basal portions of the quartz-mica schists and current bedded quartzites and unconformably overlie the older formation of charnockites gneisses and high grade schists of Wayanad Sargurs and consists of subrounded to subangular pebbles of granite few quartz, amphibolites and hornblende gneisses of varying sizes ranging from 1cm to 50cm.

10. e) BASIC AND ULTRABASIC ROCKS Basic and ultrabasic rocks are reported from a number of places in Kerala. Gabbro bodies are reported from Kartikulam , Adakathodu and Karrang , aligned along the Bavalifault zone in Cannanore district, which is the westward extension of the Moyar lineament. The gabbro body at Kartikulam occupies an area of 45 sq.km with a length of about 10km.

11. f) GRANITES AND RELATED ROCKS Two massifs of intrusive granite are recognized in Kalpatta and Tovarimalai in south-west Wayanad. These pink and granites and orthogneisses are intrusive into Dharwar schists. Another massif is located in Angadimogar in Kasaragod district. The granites are also seen in Munnar hills . Granite gneisses are reported from Achankovil . Intrusive granites occur in Idukki. Migmatites are reported from all over the crystalline rock territory

12. TERTIARIES OF KERALA The Tertiary sedimentary formations of Kerala basin unconfomably overlie the Precambrian. The name Kerala Basin denotes the southernmost part of a great sedimentary province spread over a major part of the western continental margin of the Peninsula. The Tertiary sedimentary basin extends from Cape Camorine to Manjeshwar and it is the southern-most one among the chain of Tertiary basins along the west coast of the Indian Peninsula. Based on the distribution of the Tertiary formations, Paulose and Narayanaswami(1968) recognized two major basins of deposition: Between Thiruvananthapuram and Ponnaniin the south and central Kerala with a maximum width of 16 km between Quilon and Kundara . Between Cannanore and Kasaragod in the north Kerala with a maximum width of 10 km at Cheruvathur

13. There are two important Tertiary formations of Neogene age . Warkalli formation (Mi-Pliocene): Comprising a series of vegetated sand stones and clays with lenticular seams of lignite. Quilon formation (Miocene): Below Warkalli , Characterized by more compact sands and clays with fragments and thin beds of limestone. The Warkallis with a thickness of nearly 80m are underlain by rocks of the Quilon formation, having a maximum thickness of 70m. These are underlain by a thick sequence of sediments called the Vaikom beds. Paulose and Narayanaswami (1968) have suggested the following general stratigraphic succession of these sedimentary rocks

14. a) VAIKOM FORMATION This consists of gravel, coarse to very coarse sand with greyish clay and carbonaceous clay with thin seams of lignite. The lowest unit of this sequence is exposed in the laterite quarries at Vaikom and hence they are called the Vaikom formation. They attain a thickness of 100m and overlie the weathered crystalline rocks.

15. b) QUILON FORMATION The Quilon formation consists of fossiliferous limestone, sand sandclays .At the type area, Padappakara ,a full succession of the Quilon Formation is revealed in a cliff section fringing the Ashtamudi estuary . These formations were earlier considered to be present only in the above locality, but later investigation have brought out similar ones at various localities like Chatannur , Nedungolam , Edava , Kidangayara , Pozhikkara . Similar formations are recognized in Jaffna ( NorthCeylon ). Menon(1967) has given the following sequence of the Quilon formationat Padappakara :

16. c) WARKALLI FORMATION The Quilon formation is conformably overlain by rocks of the Warkalli Formation which occurs as patches along the coast .The type section is located at Varkala , edging the seashore ,22km south of Quilon, where it attains a thickness of 60m and has the following succession:

17. This formation is nearly horizontal and has since been traced almost in the entire coastal stretch from near Cape Camorine in the south to Kottayam and Ernakulam in the north, bordering the backwater tract on the east, but obscured beneath the recent deposits of sand and silt. Total areal extent is over 2000 sq.km for this formation. Other occurrences of the Warkalli formation are at Vettur , Kundara , Thamarakulam and Puliyurin the south, and in the cliffs of Cheruvathur and china clay quarries at Pazhayangadi , Ramapuram , Nileshwar and Kalanadin . The carbonaceous clay and lignite are often impregnated with sticks and nodules of marcasite. These are present only towards the base of the succession. Menon(1967) reported the presence plant fossils in many places. The presence of marcasite indicates a reducing environment. The lithology and the spatial distribution of these suggest that the Warkalli sediments are shallow water shoreline littoral deposits. Warkalliis considered as equivalents of the Cuddalore sandstones

18. RECENT DEPOSITS (QUATERNARY FORMATIONS) The Quaternary formations include peat beds of both marine and fluvial environments, sand bars and sandy flats alternating with present day marshy lagoonal clays and shell deposits. These are found in the entire stretch of sedimentary basin. Mudflats along the Kerala coast especially in the central segment are also a part of the Quaternary formations. The Quaternary formations are separated from the underlying Tertiary rocks by a ferruginous clay/laterite layer. The Quaternary sediments were considered to be deposited in lagoonal brackish water environments, got filled up and were uplifted later.