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CHAPTER-2

GEOLOGY, GEOMORPHOLOGY AND TOPOGRAPHY

2.1 Geology

Geological, geochemical and structural aspects influence quality, occurrence and

movement of groundwater. Geological structures control surface and subsurface

hydrology. The nature and composition of the rocks and the structure in them such as

joints, fractures, fissures etc., are important in understanding the behavior and quality of

water.

2.2 Geology of Palakkad District

The area forms a part of the Precambrian metamorphic shield having a complex

geological setup. Wynad group is represented by rock of upper amphibolites to lower

granulite facies metamorphism. This complex divides the ultramafic-dominant upper

group and amphibolites-dominant lower group. The ultramafic group comprises talc-

chlorite schist, talc-pyroxene-garnet schist. The amphibolite group consists of

hornblende-biotite schist and gneiss with amphibolites bands garnet. These rocks are

exposed in the Attapady area. Hornblende-biotite gneiss and pink granite-gneiss of

peninsular gneissic complex are exposed in the north, especially north of Bharathapuzha

River. The Khondalite group, with outcrops NE of Malampuzha reservoir, comprises

garnet-sillimanite gneiss and calc-granulite. Narrow bands of calc-granulite are exposed

along the Walayar riverbed. Numerous thin bands of cal-granulite associated with

crystalline limestone have been observed in the area. Charnockite group is predominant

in the west. This group comprises massive Charnockite/gneissic Charnockite, pyroxene

granulite, pyroxenite, norite, and magnetite quartzite amongst which massive

Charnockite/gneissic charnockite is the most widely distributed. Pyroxene granulite and

magnetite quartzite occur as narrow bands. Thin segregations of pyroxenite and norite

occur in „the Palghat gap‟ the charnockite group is succeeded by the migmatite complex.

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represented by hornblende-biotite gneiss, garnet-biotite gneiss and quart-feldspar gneiss.

These rocks occupy the eastern part and the Palghat gap, they are melanocratic and

foliated and these rocks are intruded by pegmatite, quartz veins and gabbro and dolerite

dykes. Basic intrusives, especially dolerite, have two distinct trends in the district. One

being NW-SW which is common throughout the state and the other NE-SW, seen in the

northeast north Attapady. In the western part and south of Bharathapuzha, a few isolated

occurrences of Warkalli sediments are capping small mounds. The valleys are occupied

by fluvial alluvium of quaternary age. Laterisation is widespread in the west (Source:

GSI, 2005).

2.2.1 The Palghat Gap

The Palakkad gap is a big valley that crosses the western ghats. This is the most

accessible way of crossing the western ghats and thus the area has always been a

commercial centre. The area is densely populated and it is very productive as most of the

rice in Kerala comes from this region (Arya 2004). Palghat gap is a 30 km wide E-W-

trending plain of low mean altitude within the southern granulite terrain which is the only

major break in the otherwise continuous western ghats, a chain of lofty mountains (mean

altitude ca. 1000m), running for about 1600km parallel to the NNW-SSE-trending west

coast of India. While Jacob and Narayanaswami (1954) ascribed its formation to

fluviatile action, Arogyaswami (1962) favored structurally controlled marine and

fluviatile erosion. Block faulting (Vaidyanadhan, 1977); repeated uplift (Nageswara Rao

and Srinivasan, 1980) and crustal up warping (Subramanian and Muraleedharan, 1985)

have been invoked to explain its origin. More recently, the gap has been treated as a shear

zone by Drury and Holt (1980), and suture zone by Radhakrishna (1989) and

Ramakrishnan (1993). Many workers have considered the gap as forming a part of the

Palghat- Cauvery shear system. However, the presence of a shear zone has been

questioned (Naha and Srinivasan, 1996). An E-W-trending gravity high coincides with

the gap (Mishra, 1988), while the charnockite hills on either side are characterized by a

strong negative anomaly (Subrahmanyam and Verma, 1986). Seismic reflection and

electrical resistivity surveys have suggested a sheared weak zone at depth within the gap

(Bose and Kartha, 1977). Aeromagnetic studies by Reddi et al. (1988) have demarcated

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an E-W-trending down-faulted zone extending from the west of the Gap towards the east

coast of India. Thermo-barometric studies point to tectonic exhumation (Ravindrakumar

and Chacko, 1994). Earthquakes/tremors from the gap indicate its seismogenic potential.

The Geological succession of the palakkad region (Raju et al. 1979, Soman 1997) given

below Table.2.1.

Table 2.1 Geological Succession of Palakkad District.

Age Group Lithology

Cenozoic

Quaternary Periyar Formation (fluvial)

Neogene (tertiary) Laterite

Warkalli beds

Meso to Cenozoic Basic intrusives Dolerite

Gabbro

Proterozoic Acid intrusives Quartz and pegmatite veins

Archaean

Migmatites Complex

Hornblende-biotite gneiss

Garnet-biotite gneiss

Quartz-feldspathic gneiss

Charnockite Group

Magnetite quartzite

Pyroxinite/norite

Pyroxene granulite

Charnockite/Charnockite gneiss

Hornblende granulite

Khondalite Group

Calc-silicate, calc granulite with

crystalline limestone

Garnet-sillimanite gneiss

Peninsular Gneissic

Complex

Hornblende-biotite gneiss

Granite gneiss

Wynad Group Metaultramafite (talc-chlorite-schist)

Hornblende-biotite schist and gneiss

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2.3 Geology of the study area

In the study area rocks of Archaean, Proterozoic, Mesozoic and Cenozoic age are

present. The western portion of the area covered with charnockite rocks of archaean age

belonging to charnockite group. The remaining North, South and Eastern parts are

covered with the hornblende-biotite gneiss rocks of Migmatite complex. Proterozoic age

pegmatite and quartz vein, which are acidic intrusives, are also common in the NE part of

the study area. Hornblende- biotite gneiss rocks are widely distributed and intruded by

pegmatite and quartz veins in the study area. The valleys are occupied by fluvial alluvium

of quaternary age. Geological succession of the study area is given blow the figure 2.1.

Figure 2.1 Geology map of pudunagaram study area.

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Table 2.2 Geological succession of the study area.

Age Group Lithology

Cenozoic Quaternary Periyar Formation (fluvial)

Proterozoic Acid intrusives Quartz and pegmatite veins

Archaean Migmatites Complex Hornblende-biotite gneiss

Charnockite Group Charnockite/Charnockite

gneiss

2.3.1 Charnockite/Charnockite gneiss

Charnockites are encountered in the western part of the study area. These rocks

are occupied with hillocks and ridges in the southwest. In-situ charnockitisation of

gneisses (Ravindrakumar and Venkatesh Raghavan, 1992) is also noticed. These rocks

are products of migmatisation of pyroxene granulite (Vidyadharan and Sukumaran,

1978). The massive charnockites in majority of the cases are acid to intermediate in

composition and dark grayish green in colour. Charnockite/charnockitic gneiss consists

of quartz, feldspar and biotite. Garnet-bearing variants are also observed in the area. The

basic charnockite is more granulitic and contains clino- and ortho- pyroxenes

(hypersthene), feldspar, biotite and garnet. Whereas the acid variety (alaskite/enderbite)

is greenish, black, coarse-grained, massive to poorly foliated rock consisting of quartz,

feldspar and pyroxenes.

2.3.2 Hornblende-Biotite Gneiss

The Hornblende-Biotite Gneiss rock covers almost half of the study area. These

rock types occur within the Migmatites and associated with retrograded charnockites. The

naming is purely based on the preponderance of the minerals. These melanocratic,

medium-grained, foliated, banded rocks consist of alternate layers rich in hornblende or

biotite. Hornblende- biotite gneiss rocks are intruded by pegmatite, quartz veins and these

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are highly deformed in the study area. In the palakkad gap area, these gneisses occur over

a large area, showing migmatitic structures such as nebulites, schlierens, ptygmatic folds,

quartzo-feldspathic neosomes and ferromagnesian palaeosomes (Muraleedharan and

Raman, 1989).

2.4 Geomorphology

Geomorphology means a "discourse of earth landforms" and it is generally defined

as a Science of Landforms" which are the products of various exogenetic and endogenetic

forces it is a systematic study of landforms in relation to the climatological, geological

and structural aspects. Landforms play vital role in land resource mapping, terrain

evaluation and soil classification in addition to groundwater studies. The groundwater

conditions vary from terrain to terrain. Study of geomorphology is of particular

importance to aerial photo-interpretation as it forms major criteria in deciphering

lithology and structure. Physiographically the district can be divided into two parts viz,

the high land and mid land. The district is not blessed with coastal tract. The elevation of

the landforms varies from 20 to 2386m msl. The most important physiographic feature of

the district is the Palakkad gap. The train and road link between Kerala and rest of the

country mainly passes through the 32-40 km wide gap. The important peaks are Anginda

(2386 m), Padagiri (1585 m) and Karimala Gopuram (1440 m) (CGWB, 2005).

The geomorphological map of the area has been prepared by using Indian remote

sensing satellite Liss-4 data with 1:250000 scales merged satellite imagery and SOI

Toposheet no: 58B/1 with 1:50,000 scale have been used to map various geomorphic

features (Figure.2.2). Based on the interpretation of the satellite imagery and SOI

Toposheet the following hydrogeomorphic units have been delineated. Such as Alluvial

fills, Bajada, Dissected Plateau, Pediment, Residual hills and water bodies.

2.4.1 Alluvial fills and Bajada

Alluvial soil is found along the banks of streams. These valley fills are covering

the entire study area. In addition, this Valley fills deposits composed by talus and screen

material. A Bajada consists of a series of coalescing alluvial fans along a mountain front.

These fan-shaped deposits form from the deposition of sediment within a stream onto flat

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land at the base of a mountain. This geomorphic units are present in the southern part of

the study area that includes Tachankad, Vakkaod village.

2.4.2 Dissected Plateau

It is a plateau region of Hornblende-Biotite Gneiss associated with shallow

valleys/gullies with gently sloping land developed due to stream erosion. It is the most

prominent geomorphic unit occurring in study area. These formations are generally

located between weathered valleys and highly dissected plateaus. Most of the study area

is covered with this type of landform.

Figure 2.2 Geomorphology map of the study area.

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Figure 2.3 Land use land cover map of the study area.

2.4.3 Pediment and Residual hills

A pediment is a gently sloping erosion surface or plain of low relief formed by

running water in arid or semiarid region at the base of a receding mountain front, and it is

underlain by bedrock that is typically covered by a thin, discontinuous veneer of soil and

alluvium derived from upland areas. These types of geomorphic units are present in SE

part of the study area. Residual Hills are the hard rock is left behind after erosion has

occurred. These land forms occupy south and SE part of the study area.

2.5 Soils

Based on field observation the study area is classified in to 3 types

1. Alluvium sandy soil

2. Loamy soil

3. Clayey soil

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2.5.1 Alluvium sandy soil

It is the most predominant soil type in the study area. Alluvial soil is rich in sand

grayish to whitish in color occasionally brownish to yellowish in color and grain size

ranges from medium to course. Quartz particles are found in the alluvial dominated areas.

Pudunagaram, Pilappull, Karuppod, Koduvayar, Tachanted and Pallasena villages are

established along the alluvial area.

2.5.2 Loamy soil

Loamy soil is observed in eastern portion and southeast portion of the study area.

The types of loamy soil are

Sandy loam

Loamy clay

lateritic soil

The loamy soil is in reddish, brownish and yellowish colors with quartz particles.

They are rich in humus and organic matter. Major crops being cultivated in this area are

Ginger, Paddy & Cashew nut.

2.5.3 Clayey soil

The western part of study area is rich in clayey soil and pure clay is found in

middle southern part of the study area with grayish to whitish and brownish color. The

major crop cultivated in the area is Paddy (figure 2.3).

2.6 Topography

Topographic survey was carried out at 50 locations with grid pattern for more

precise measurement of surface elevation using advance Differential Global Positioning

System (DGPS) surveying technology. This instrument (Trimble R3 GPS) is equipped

with a GPS receiver, antenna and rugged handheld controller. The 25 Trimble R3

systems bring precise sub centimetre control of elevation which has been reduced to the

mean sea level.

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Figure 2.4 Residual Level contour of the study area.

Reduced level of the study area was measured using DGPS instrument and also

connected to the known bench mark. Topographically the study area is a midland. The

entire topography is flat, except 1 or 2 hillocks. Variation of the topographic contours is

prepared with the help of Golden Software Surfer (version 9.2) using kriging method and

observed that the elevation is varying from 78 to 128 m (above mean sea level). Elevation

is gradually increasing from west to east in the study area (Figure.2.4). The lowest

topography ranging from 78m (amsl) is observed in the western part of the study area and

the highest elevation of 128m (amsl) is noted in the eastern part.

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2.7 Summary

The study area is covered with Archaean, Proterozoic, Mesozoic and Cenozoic

age rocks. About 70% of the area is underlain by hornblende-biotite gneiss of

archaean metamorphic complex, and remaining area is covered with the

charnockite of archaean charnockite group and alluvial of quaternary age.

In the NE part of the study area hornblende-biotite-gneiss rocks are intruded by

proterozoic age pegmatite and quartz acidic vein intrusives.

Entire study area is falls in the palakkad gap. Palakkad gap is a big valley of 30

km wide E-W-trending plain of low mean altitude in western ghats. This is the

most accessible way of crossing the western ghats and it is densely populated and

very productive as most of the rice in kerala comes from this region.

Geomorphologically the area is classified as Alluvial fills, Bajadas, Dissected

Plateau, Pediments, Residual hills and water bodies.

Dissected plateau and alluvial fills are the most prominent geomorphic units

occurring in study area.

Study area covered with alluvial sandy soil, loamy soil and clayey soils. Alluvial

sandy soil is the most predominant soil type in the study area.

The entire topography is flat except 1 or 2 hillocks and elevation is gradually

increasing from west to east in the study area.

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Plate 2.1 Denudational hill in the study area.

Plate 2.2 Outcrop of the Hornblende-Biotite Gneiss in the study area.

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Plate 2.3 Hornblende-Biotite Gneiss rock with Pegmatite veins.

Plate 2.4 Paddy cultivation in the study area.

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Plate 2.5 Coconut cultivation in the study area.

Plate 2.6 Fresh water lakes in the study area.

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Plate 2.7 Soil types in the study area.

Plate 2.8 Topographic survey by Differential Global Positioning System.