SURVEY REPORT OF , TAMILNADU,

INTRODUCTION:

Karur District is a district located very centrally along the and Amaravathi rivers in the Indian state of . It is bounded by in the north, district in the south, Tiruchirapalli district on the east and Erode & on the west. It comprises six taluks viz. , Karur, Kadavur, , , with karur as headquarters. It encompasses an area of about 2856 sq km2.

GEOLOGY : Crystalline rocks of Archaean to late Proterozoic age occupy over 80% of the area of the state, while the rest is covered by Phanerozoic sedimentary rocks mainly along the coastal belt and in a few inland River valleys. The hard rock terrain comprises predominantly of Charnockite and Khondalite groups and their migmatitic derivatives, supracrustal sequences of Sathyamangalam and Kolar groups and Peninsular Gneissic Complex (Bhavani Group), intruded by ultramafic-mafic complexes, basic dykes, granites and syenites. The sedimentary rocks of the coastal belt include fluviatile, fluvio-marine and marine sequences, such as Gondwana Supergroup (Carboniferous to Permian and Upper Jurassic to Lower Cretaceous), marine sediments of Cauvery basin (Lower Cretaceous to Paleogene), Cuddalore / Panambarai Formation (Mio-Pliocene) and sediments of Quaternary and Recent age.

The metasedimentary rocks occur either as individual bands or as swathes of bands repeated several times with width varying from 10 m to 100 m and exposed length from 100 m to a few kilometers, within the Charnockites and Migmatites. These bands are repeated several times because of tectonic slicing.

The Charnockite Group comprises pyroxene granulite and charnockite. The pyroxene granulite is dark grey, medium grained granulitic rock with typical salt and pepper texture, seen on the weathered surface. It consists of diopside, hypersthene, plagioclase, hornblende, biotite and quartz. Charnockite is the predominant rock in the area. It is grey, medium to coarse grained, greasy looking with foliation seen prominently on the weathered surface. It is essentially made of smoky or grey quartz, pale grey microcline and hypersthene as major minerals with plagioclase, hornblende and biotite as accessories. It forms high hill ranges and also occupies the plains, covered by 1-2 m thick soil.

Migmatite Complex is represented by hornblende-biotite gneiss, granitic gneiss and pink migmatite. This Complex is a group of banded felsic rocks of varying mineralogical composition that are formed due to the influx of quartzofeldspathic material into high grade metamorphic rocks. Two types of migmatite are seen in the Karur district, one is grey and the other is pink. Next to charnockite, migmatite gneiss is the second most extensive rock. The migmatite gneiss consists of quartz, k- , plagioclase, hornblende and biotite in varying proportions.

Intrusive igneous rocks are seen in the area are meta-gabbro and anorthosites as for example around Kadavur and Aravakurichi. Meta gabbro is coarse grained, dark grey, mainly comprising pyroxene, amphibole and plagioclase. Anorthosite is pale pink to light brown, medium to coarse grained rock essentially made up of plagioclase with a small amount of pyroxene and amphibole. Quartz and pegmatite veins are of restricted areal extent. Minor bodies of younger granite are exposed in the area east of Aravakurichi.

Foliation/ gneissosity, the prominent planar structure seen in the metamorphic rocks is ENE-WSW in the west and near N-S in the central part of the district. The eastern part of the district shows complicated folded structures due to interference of two phases of folding, forming a series of domes and basins. Faults and shear zones trend N-S in the central part, and NW-SE in the southern part.

Minor bands of crystalline limestone occur at a few places. A few copper, molybdenum and mica occurrences are also noticed at places like Kadirayankulam and Ramanathapuram. Quarries for road metal and building stones are located at several places.

GEOMORPHOLOGY AND GEOHYDROLOGY:

The entire area of the district is a pediplain. The Rangamalai hills and Kadavur hills occurring in the southern side of the district constitutes the remnants of the much denuded Eastern Ghats and rise to heights of over 1031m above mean sea level. From these hills the district slopes gently towards north east and forms a vast stretch of plain country till the eastern boarder of the district. There are numerous small residual hills represented by Ayyarmalai, and Velayuthampalayam hills. The general elevation of the area is ranging between 100 m and 200m above mean sea level. The prominent geomorphic units identified in the district through interpretation of Satellite imagery are 1) Structural hill, 2) Pediments, 3) 128 Shallow Pediments, 4) Buried Pediments and 5) Alluvial plain. An overall appraisal of groundwater occurrence in each geomorphic unit and the significance of its hydrogeological characters.

LAND USE PATTERN

The land use pattern of the district depends mainly on topography, land form, soil cover etc. Out of the total geographical area of the district, only 2.14 percent is covered by forest and 11.6 percent of the area is put into non agricultural use. Cultivable waste accounts for 23.5 percentage.

SOIL TYPES

Soil types of the area are more important, since they are the main criteria for agricultural production and also for the recharge of groundwater. Different types of soil are derived from a wide range of geological formations. A soil map of Karur district based on the survey by the Tamil Nadu Agricultural Department indicates four different types of soils viz., Red Soil, Thin Red Soil, Red Loam and River Alluvium Soil. The red soils are predominantly seen in Kadavur, Kulithalai, Krishnarayapuram, Thanthoni and Thogamalai blocks. The thin red soils are seen in Aravakurichi and K.Paramathy blocks. Major portion of Karur block is covered by red loom.

GEOTECHNICAL CHARACTERISTICS AND NATURAL HAZARDS:

Based on permeability, bearing capacity / compressive strength and foundation characteristics, the area has been demarcated into two Engineering Geological Provinces. Permeability of the rock types ranges from low to cumulative high, bearing capacity / compressive strength ranges from Low (1-2 kg/cm2) to High (1000-2000 kg/cm2) and foundation characteristics from poor to very good. The area falls in Seismic Zone -II (ISI).