16 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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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