Chapter II GEOLOGICAL SETTING Chapter II

GEOLOGICAL SETTING

Introduction : The area covered by the present investigations exhibits a wide variety of geological formations, which in descending order of their antiquity are as below :

Coastal Sands, Soils, Alluvium Recent, Subrecent Laterite Pleistocene Deccan Trap Lower Eocene Quartzite-boulders-Infra-trappean ? Cretaceous ? Kaladgi Sandstones and quartzites Cuddapah Basic and Ultramafic intrusions g ranite-gneiss and pegmatites, Archaean aplites and quartz veins. Dharwars.

The distribution of different rock types enumerated above is shown in the modified lithological map (after Kelkar, 1956) (Fig.2.1) and their field characters are given in the following paragraphs.

Archaeans : Dharwars : Dharwars are exposed over the greater part of the area covered by the present study. These metasediments are represented by phyllites, crush conglomerates, quartzites, v 'y v v " v N v v ~ 0 2 4

HILES v y v v v v v v ~ v \' v 17 v v v ():) v v ....- v v v v v v 17 v v v v v -1-- v

laterite F 0 D \0 rar u\a ~.... " ' ' ; . 000 \ "'->~ .. . . . " Deccan Trap aF~·· -~ "'' U... "'" 0 \" '."-'''<' \ '" - \ D- - F . D . . Gran"ile gneiss VUi GUf

Quartz'de and crush~>d- r:rHl g Iom cralr.

Garnet zone Schistose ro cl1 } stau r ol.1te zone

Fig. 2·1: Regional u~SWlogt--~ ..u . .O ical map of ( atter K·V.Kelkar, 1 9 S6 l 12 banded-hematite quartzites, a variety of schists with variable proportions of garnet, staurolite and kyanite and composed largely of hornblende and mica and various g ranulites. These metasediments may be classified as

i) Psephitic and Psammitic rocks, ii) Pelitic schists and gneisses, iii) Amphibolites.

Psephitic and Psammitic rocks :

In the Sindhudurg district area, psephitic and psammitic rocks include crush conglomerates, quartzites and banded­ hematite quartzites. These rocks occur as narrow bands almost parallel to the coast, show steep easterly dips while the rocks little further inland show a northenly dip. Exposures of small bands of crushed conglomerates striking N-S are present in the bed of Gad river, west of , near Sindhudurg and along the shore near .

Fine to coarse grained quartzites composed almost entirely of quartz with wisps of accessory mica, possessing granoblastic texture occur as small bands almost all over the area. They are exposed at Banda, Pat, Coast of Malvan. Ferruginous quartzites are noticed below the laterite cap near Kochra, Pat, Otavane, Banda etc.

A few bands of banded-hematite-quartzite are found interbedded with hornblende schists near Kankavli. Minor bands are also noticed near Kasal, Katta, and along coast south of Malvan. 13

Pelitic schists and gneisses This unit of rock is represented by phyllites, a variety of schists with variable proportions of garnet, staurolite and kyanite and composed largely of hornblende, actinolite, chlorite, mica, at times talc and various g ranulites. These rock types appear to cover the greater portion of the area away from the coast. The schistose rocks show NW-SE to NNW-SSE trend. The gneisses show varying thicknesses of alternate dark coloured bands consist­ ing of mafic minerals such as amphiboles and mica and light coloured bands of quartz-felspathic material. The occurrence of the gneissic rocks in Sindhudurg district show a marked disparity in the strike and dip. In South, No rth and South-East of , strike is E-W with obscure and uncertain dip, while gneisses South-West of Sawantwadi show NW-SE strike. A little further north in the river, the rocks strike N-S.

Amphibolites : The amphibolites of this region characteristically occur as a number of elongated, Gisconnected outcrops. They are invariably dark, greenish black in colour, and show various degrees of foliation from almost non-foliated to we ll foliated ones. They range from fine to coarse grained a nd usually show a concordant relationship with the associated metasediments and show the same strike and dip. These amphibolites are characterised by different textures and 14 structures; some of them occur as small elongated lenticles parallel to the foliation of the rocks. These lenticles are generally sporadically distributed throughout the rock. Som e amphibolites are non-foliated and compact and lack the lenticles. They appear to be subjected to crushing as they are much fractured and contain many thin quartz veins along these fractures. A few xenoliths of amphibolites are coarse grained, well foliated narrow elongated patches; and are made up of greenish black hornblende and dirty white lime feldspar.

Gr a nitic rocks :

The granitic rocks of the area show two different mod e s of occurrence and are separated into two types, namely granites and granitic gneisses and the presence of quartz, aplite, pegmatite veins.

Good outcrops of granites showing their intrusive r e l a tionship with the Dharwars are noticed near Kankavli,

Kat ta and Kochra (Fig. l. 1 and 2. l) . This granite is fine to medium grained, h3.s a uniformed grev colour and is de vo id of any foliation. It shows cross-cutting r e lationship with the adjoining metamorphics\ Thi£ granite is well· jointed. Weathering has given rise to nearly spherical tors.

The granitic gneisses can be subdivided into two t ypes according to textural and structural variations, the 15 porphyroblastic gneiss and augen gneiss. In the gneissic varieties, the foliation trend varies between N l0°W to N 50 °W in conformation to the strike of the adjascent schistose rocks. These occur as more or less tabular s he ets a nd show concordant relationships with the enveloping me tasediments. The more important occurrences of these roc k s are located at Adeli, Tulus, and Bambarde (Fi g .l.l, 2.1).

The intrusion of granitic magma along the planes of s chistos ity appears to have g iven rise to the mi gmatites.

The mi g ma tites a re typically banded rocks of pinkish white a nd g r eyish black colour. The leucocratic bands within it a re c om posed almost entirely of qua~tz and mostly white and pink fe ldspar. These bands are from a few millimeters to a few centimete rs in width. The melanocratic bands with varying width are dominantly constituted of hornblende. At times, pa t c hes of melanocratic material are observed within the l e ucccratic bands.

Numerous minor injections of quartz, pegmatite and a pli t e i n the form of veins sometimes of considerable length a r e fo und traversing the schistose roc ks. The mica bearing peg ma tite at Kadwal is about 550 m long and 200 m wide.

The e xposed g ranites mostly with the proximity of either gr oundwa t e r, or pond, nala or/and stream water are found to be sho\ving considerable amount of decomposition giv ing rise to c l ays which are of kaolinitic type, and are found to be c ove r i ng the gr a nitic rocks. 16

The thicknesses of the clay formation vary from a few ems to few meters. The prominent exposures have been found at various places such as Kumbharmatt (Malvan), Pat (Kudal), Tak (Vengurla).

Basic and ultrabasic intrusives Numerous small dykes of basic and ultrabasic rocks, intrude the Archaeans. Their thickness does not exceed five metres. They are fine to coarse grained and compact and do not show foliation in hand specimens. They typically exhibit spheroidal weathering. They comprise dolerites, olivine­ dolerite, picrite and chromite bearing serpentinites. These form minor intrusions in the form of dykes and at some places as an irregular mond like intrusive mass. The dykes are conspicuous at the southwest of the village Kochra, northwest of Arvali, Banda, Vapholi, Vadga and along Mangaon, Akeri, Vengurla-, Kankauli-Harkul and Sawantwadi-Aronda roads. Picrite is noticed on Danoti-Banda road, chromite bearing serpentine rocks near Kankauli and Vadga and Olivine norite near Vengurla. In their directional pattern, these rocks fall generally into three groups such as NW-SE, N-S and ENE-WSW trendings.

Sometimes, the basic rocks are altered to epidiorites. They occur in the form of small veins, dykes or sill-like exposures in the country rocks. Epidiorites are exposed on Kankauli-Harkul road, near Kasal bridge, at Varad and Vengurla­ Belgaum, Sawantwadi-Aronda road and near village Otavane.

Kaladgis : Rocks of the Kaladgi group are represented by conglomerates, quartzites, sandstones and shales. They are found in the form of numerous detached inliers, separated form one another by the overlying Deccan Trap. 17

Infra-trappean beds : Beds of loose water-worn pebbles intervening between the trap flows and the Archaean rocks are supposed to be infra-trappean beds. Two isolated patches of these beds are e xposed north of Kankauli and south-east of Kasal.

Deccan Trap Deccan Trap overlying the Archaeans and Kaladgi rock formations are exposed only in some parts of Sindhudurg district such as along Devgad and Kasal road, near Malvan and Sawantwadi. The greater part of the exposed trap is generally covered by thick beds of laterite. Laterite : Extensive spreads of laterite are noticed through­ out the district. They generally form a flat plateaux with an elevation between about 30 and 100 mts. The laterite formation at and Devgad is ferruginous and contains few seggregations of bauxitic nodules. Near Malvan, laterite is found capping the Kaladgi quartzites and at places, a regular gradation from quartzites to laterite is noticed. Near Vengurla and Gad river, near Highway Bridge. Laterite is found capping all the rock formations.

Recent and sub-recent deposits Quaternary deposits :

Quaternary deposits both consolidated and unconsolidated are found near coast at Malvan and Vengurla. These are mostly calcareous, medium to fine grained with varying proportions of shell fragments. These deposits are locally known as 'Karal'. The pebbly and gravel beds are rather inland from the coast. Alluvium : In the area under investigation, alluvium forms very sm all patches in scattered way, especially on the banks o f Gad and Karli rivers, on either banks of the river Kas a l near Adeli, are the occurrences of few alluvi patches. South of Vengurla and Mal van along the coast occurs the alluvium. These alluvium patches are found to be fertile lands where usually the paddy crop is grown .

• Plate 3

Photo 1 Exposure of granite rocks

near Kankauli.

Photo 2 Exposure of granite rocks

near Katta.

Photo 3 Exposure of granite rocks

near Kochra. PLATE 3

Photo

Phot0 2

Photo 3 Plate 4

Photo 1 Exposure of g ranite rocks

along Kudal-Akeri road.

Photo 2 Exposure of granitic rocks in

the river bed of Janauli.

Photo 3 Exposure o f pink g ranite in

the river bed of Gad. PLATE 4

Phot 0 1

Ph0to 2

Photo 3