Chapter II

GEOLOGICAL aETIING

Introduction :

In the coastal tract extending between Palghar and

Thai tne dominant lithological type is the Deccan basalt which, at places, is associated with other volcanic types including rhyolites, trachytes and pyroclastics. The basalt flows are often separated byfchin horizons of clayey rock of reddish brown colour, which are referred to as

’red beds’, and occasionally by shales. The volcanics are intruded by dykes or email bodies of diorites, gabbros, anorthositic gabbros, dolerites, lamprophyres and trachytic agglomerates. Laterites are commonly developed at higher altitudes, especially above 330 metres and they form cappings on many ofjthe higher hills. In the coastal zone, the igneous rocks are covered by consolidated and/or unconsolidated Quaternary sediments, which range in thickness from 1 metre to 20 metres. Alluvial deposits occur in the river valleys and along the foot of the hills there is extensive development of colluvium.

The distribution of these lithological units is shown in the geological maps (Fxgs.2.1, 2.2 and <:.3) INDEX TO FIG.2

Basalt 5 a ^ . x i

6

7

t ®a ' 8

9

10

A GAS HI

N

I

2 ® a s s e \ n __ I___ MILES

721SSE

Fig-2-1 Geological map of Palghar and Bassein sectors.

18

axis of the Panvel flexure also follows the courses of these rivers (Fig.2.6). Hot springs are located in fault zones, ^.g. the hot springs of /Conner and Varai. In the hills to the east of , two shear zon°s have been recognised which trend N 335°. Also along the w»3t^rn fringe of Tungar-Kamandurg hill range, a N 335° trending shear zone is recorded. A north-south trending fault to the west of , which corresponds to the Thana creek, can be traced from Thane to Parol along the ^astern fringe of the Tungar-Kamandurg hill range. Further to the north, it follows the course of Tansa river in a N 45°W to N 50°W direction and, can be traced to near the mouth of the iiur river in the Kelve area (Plate 2.5, Photos 1 and 2). In Bombay sector, a couple of faults have been reported. One of the faults trend N 10° p to M 15° ? and follows the eastern fringe of the ^astern ridge of the Bombay and jalesette islands. Further north, this fault merges into the Thane-Kelve fault, described above. On* more fault which trends N-S follows a line joining -Kanheri Caves and Gaimukh Bandar. This fault can be traced further to the north of Ulhas riv-T along the Nagli Dongar hill range upto

3ativli village in a N 335° to N 345° direction. A Borivli

Mahim Bay

BOMBAY

6 MILES

Fig • 2 • 2 Geological map of the Bombay sector 1MDEJL TO FIG.2.3 1 : Alluvium 2 : Mud

3 : Beach sand 4 : Beach rock 5 : Laterite 6 : Intertrappaan

7 : Andssite 6 : oolerite

9 : Basalt ' A ----- 1— t;— a— a ----- / ,A '----- (73'lodEr.--- >4-fQ _9 : A A A A| BOMBAY/ A ^ A A A >eU L._i A Panve\ cre ^ lA iv M .Panvel ELEPHANTA S-A::t'j \ 1 A / a 0 • - ~ i z r !7 ‘7 ’ ‘M / i i ? fw i l f / ' & ' V V BUTCHER / /A A, i A A|

*------<•---- -,s-i l\ I I » a t M

ARABIA N

SEA

J8 50 11

and their important field characters are outlined in the following pages.

Volcanic rocks j

The volcanic rocks present in the area under study include basalts, andesites, rhyolites, rhyoaacites and tiachytes.

a) Basalts j Basaltic flows related to Deccan volcanic activity occupy the greater part of the area covered by the present investigation. They vary in thickness from 5 metres to 135 metres and are seen to extend for considerable distance. Tha flow boundaries may be delineated on the basis of marked variation in the lithological characters, presence of red beds, volcanic breccia or zones of silicification or because of significant differences in the jointing and weathering patterns. The development of flat surfaces, corresponding with the presence of any of the above features has been taken as additional evidence of flow boundary, in many parts of the area studied flow boundaries may be demarcated on aerial photographs on the basis of tonal and structural variations. 12

In the area studied, the basalt flows comprise

of both 'pahoehoo' and ’aa* types. The •pahoehoe*

flows characteristically show a basal section with

pipe amygdales, a middle section of dense basalt and

a top highly vesicular section with spherical vesicles

filled with secondary minerals like silica, calcite, apophyllite and seolites. The ’aa* flows, on the other

hand, have a basal section of dense rock and a top

section of fragmentary rocks. The'pahoehoe’ type

being softer, is more easily eroded, it usually gives

rise to conical hills with smooth slopes or to *Vf

shaped valleys. In the dominantly ’pahoehoe* areas,

flat-topped hills are rare and the topography is that

of badlands. The uppermost, altered portions of ’aa*

flows weather easily and give rise to finer fragments.

The dense middle sections show spaeroxdal weathering and yield large boulders, in areas of *aa' flows, steep or vertical scraps are conspicuous. They form flat topped hills and broad »Uf shaped valleys. 3tep-like topograpnic terraces are also common.

Over much of the area covered by the present study

and especially in the SAhyadri, the flows are largely of the 'panoehoe' type. fAa» flows occur in the Bombay 13

group of islands and in the western part of the Bassein and Thai sectors. An idea about the relative proportions of these types and about their physical characteristics may be had from the description of flows in different areas given below.

in the Kaldurg hills of Palghar sector thirteen flows, varying in thickness from 10 metres to 110 metres, have been recognised. Most of these flows 3how characteristics of 'pahoehoe1 type. In the Tungar hills of the Bassein sector, seventeen flows varying in thickness from 7 metres to 110 metres are recorded. Out of these, eleven flows are of faaf type. In the -Belapur hill range of the Panvel sector, six 'pahoehoe* flows, varying in thickness from 30 metres to 132 metres, have been recognised. Out of these six fpahoehoef flows, two flows are porphyritic and the remaining four are non-porphyritic in nature. On Sheva island of the Panvel sector, two

*pahoehoe* flows have been reported, the lower flow exposed upto 20 metres above AaL is a compound 'pahoeboe' flow, comprising of two flow units. The upper flow having a thickness of about 25 metres is fine grained and dense, sparsely porphyritic in nature, and exhibits close 14

spaced jointing. ;even and five flows of ’pahoehoa1 type are present in the hills of and respectively. The thickness of these flows varies from 20 metres to 70 metres. In the Mira

Dongar hills of Pen sector, fifteen flows have baan recognised. Most of these are of *pahoehoe' type and five of them are porphyritic in nature. In tha

Kankeshwar hills of the Thai sector, nine flows exhibiting characteristics of ’aa ’ type are present.

In Bombay group of islands both fpahoehoe* and *aa' types of flows are present, but tha 'aa' types of flows dominate in most parts of the islands. As an illustration, the succession of flows observed in tha

Karlakhind hill is given in Table 2.1 and tfte spatial distribution of these flows is shown in Fig.2.4* A geological map of Thai sector showing different flows, prepared on the basis of aerial photograph study ia presented in Pig.2.5.

The colour of basalts ranges fro a greenish to dark gray. The^asalts are generally fine to medium grained

rocks. Some basaltic flows are porphyritic. Tha

phenocrysts of plagioclase feldspar range in length from

3 to 5 centimetres. At many places, there is development Table 2.1 t Succession of flows in tha Karlakhind hill, Thai sector.

Flow No, 11 t Gray, fine grained basalt ( 25 metres )

Flow Mo. 10 t Compact, medium grained. ( 30 metres) grey basalt.

Flow No, 9 t Compact, gray coloured* ( 20 metres) sparsely amygdaloidal basalt.

Flow No, 8 i Compact dark gray basalt ( 40 metres) with amygdalae.

Flow No, 7 t Compact dark basalt with ( 33 metres) fine white amygdalae.

Flow No. 6 i Hard compact, derk basalt. ( 25 metres ) Shows characteristic spheroidal weathering.

Flow No. 5 t Grey, medium grained ( 20 metres ) basalt.

Flow No, 4 i Dark, compact basalt with ( 33 metres ) less number of amygdales. small vesicles ar* also present.

Flow No, 3 t Compact, gray basalt. ( 13 metres )

Flow No, 2 t Compact, black to gray ( 6 metres ) basalt.

Flow No, 1 « Gray basalt, fine grained. ( 7 ) with large amygdalae. o o 4- + - Late rite Flow No-9 + + Flow No- 6 f- low No • 3 fo o Flow No-11 ■* • * J Flow No-8 m . Flow No- 5 Flow No 2

AI luvium Flow No %vl Flow No. Flow No -101-V__U-J 7 -1

Fig.7-L Geological map of the Karlakhind hill, Thai sector. - 8 N 50

0

Kms.

]8 > A 5' 70 >

> z

LO m >

18 lo ) M $ r v " 1. ; a , m s * '::m f '

M ud

■- v-_*. Beach sands

Beach rock/Alluvium

Basaltic flows

Fig-2-5 Lithological map of Thai sector, based on aerial photographs. 15

of spectacular columnar jointings; tha columns being upto 40m»tres in height. Such columnar joints are present in the hills of , and Borivli area of the Bombay sector (Plate 2.1, Photos 1 and 2).

Most of the basaltic flows show three major sets of dominantly vertical joints commonly along N-3, and E-W directions, sheeting joints or joints parallel to the upper ana lower surfaces of the flows, nave also been observed, some joints axe steeply aippin& (Plate

2.2, Photo 1). At places, i'or example, in the hills east of Mathane in Palghar sector, shattering (Plate

2.2, Photo 2) is observed in basalt because of shearing.

The basalts show typical weathering patterns. In dens* basalt, spheroidal weathering is a characteristic feature

(Plate 2.3, Photo 1). in the bed of Danisar river in the

Bombay sector, a typical pillow weathering pattern is observed (Plate 2.3, Photo 2).

In thin sections, the baoalts are fine to medium grained, non-porphyritic to porphyritic rocks with phenocrysts of labradorite, less commonly augite and rarely olivine. The basalts also exhibit subophitic or intergranular or intersertal textures. Plagioclases 17

this meridian display dips towards W to WSW. Tha amount of dip genarally decreases from north to south. In tha

Palghar sector, in the hills to the east of Palghar, the basaltic flows dip towards west at an angle of 29°. The maximum amount of dip is encountered in the hills to the east of Virar in Basaein sector, where tha basaltic flows dip at 25° to 58° towards west. Basaltic flows in tha

Bombay sector display dips of 12° to 20° towards W to

W5W. The flows in the Mumbra-Belapur hill range in the

Panvel sector dip at 3° to 5° towards W to WSW. In tha ssma sector, in Uran and Elephant a hills, the flows dip towards W or W3W with an angle of 8° to 12°. Tha flows in tha Kankeshwar hill of Thai sector, dip at 5° to 6° towards west. The hills to the east of Pen, in the Pen sector are constituted of almost horizontal lava flows.

Further In the south, the dip of the flows goes on decreasing and south of the Savitri river, they show no dips (Powar, et al, 197#).

.hear zones and faults are very common in the area under investigations (Fig.2.6). The courses of Surya and rivers partly correspond to the trace of an almost north-south trending fault and significantly the 19

similar fault is also present along the eastern fringe of the Western ridge of the Bombay islands. This fault also o trends in M 10 p to N 15° v direction. Two faults with F-V trena, cutting across the rastern ridge of Bombay

island have been reported by Sukheswaia (1953). Four faults, that are delineated along the Mumbra-Belapur ridge, have given rise to horst and troughs. Two of these faults can b» traced over a distance of about 20 kilometres. They trend N-3 and NfF-3SW» The throws of these faults vary from 45 metres to 100 metres. A fault zone is also reported along the Sasaune coast. This fault trends almost N-S and is evidenced by intense brecciation, with ’sweating effects’, of anorthositic gabbro (Plate 2.6, Photos 1 &. 2). A north-south trending sh°ar zone is recognised along the eastern fringe of the Kankeshwar hill range, which can be traced from Karlakhind to Sheva inland in the north. here are a number of loss intense shear zones, paralleling the above zone in this region. A prominent structural scrap is also developed. A number of shear zones have been reported in the Panvel and Pen sectors. They trend north- south, i.e. parallel to the axis of the Panvel flexure.

One such prominent shear can be traced along the line 20 joining Dighati-/r.antavli-Muigaon villages. There is also a shear zone trending M 40° W which can be traced in the region of Jite-Ambivli-Belevade Buiruk, and which has controlled the stream course in that region. It is also interesting to note that most of the trachytic agglomerate dykes described latter have been emplacea along the shear zones, and themselves show intense brecciation.

b) Andsites : Massive flows of andesitic composition are observed at Malabar, Comballa and Ivorli Hills within the Bombay group of islands and also to the east of Male Sopara railway station near Achola, in the Bassein area. They are about 20 to 25 metres thick, generally purplish to brownish in colour and exhibit a good stratification. Columnar jointing is usually observed, often on a specta­ cular scale. These flows dip at 10° to 20° towards west to w^3tsouthwest. Typically the andesite is a compact glassy rock of darK grey colour with a sub-conchoidal fracture and breaks into sharp angular fragments. In thin section tnese rocKs are fine grained and show inter)» pyroxene, opaques (generally iron oxides) and glass. 21

The groundmass plagioclase is andesine, while the ph*»nocrysts are more basic. In the andesites from the Eassein sector, plagioclase is the predominant mineral and is associated with subordinate amounts of augite, hornblende and biotite. The top portion of the andesites show predominantly andesine-labradorite f^ljspars and few grains of augxt" as phenocryst in a glassy groundmass, showing trachytic texture. The petrology ana petrochemistry of these rocks, has been detailed by . :athur and ,*aidu (1932), Sukheswaia (1953), Sukheswaia and ioldervaart (1958) and Sukheswaia dnd Sethna (1962).

c) rhyolites and rhyoaacites : Flows of rhyolites and rhyodacites representing acidic and sub-acidic volcanisra occur at Utan, Dongri, Manori, Mudh, , Khoroaivadi, , and some other localities in the Bombay group of iilanus. They also occur at Bassein and jasunavghar in the Bassein sector. The rhyolites in the Bo bay group of islands were first reported and described by fiathur and Naidu (1932). Subsequently,

Sukheswaia (1953), Sukheswaia and Polderv*art (1958) and sethna and Battiwala (1974, 1977) have detailed the petrography and petrochemistry of these rocks. 22

These rocks are grey to purplish in colour of ashy appparance and show characteristic flow structure. The fplsitic groundraass contain yellowish brown opaques, quartz and plagioclase feldspar, while orthoclase feldspar forms ph»nocrysts in a glassy groundmass. Th^se rocks also show microf«lsitic tpxture and contain vesicles, filled with well formed crystals of quartz and calcite in large proportion. Thesp vesicles have attainpd remarkable parallelis.r. giving the rock a flow structure.

RhyodacitP3 are associated with the rhyolites and a gradation between rhyoaacitps (lower part) and rhyolites

(upper part) may be observed in individual flows or sills (Sukheswala and Poldervaart, 195&). These rocks are slightly darker in colour and contain minute flakes of biotite. They show flow structure. in thin sections these rocks exhibit a porphyritic texture witn plagioclase and biotitp and phenocrysts set in felsitic to glassy groundraass. Sometimes, augite occurs as phenocrysts. The rhyolites and rhyodacitps of Utan, Dongri '!anori etc., contain many xenoliths of basaltic rock (jethna and

Battiwala, 1974, 1977).

The flows of rhyolites and rhyo acit°s dip 10° to 23

25° towards W to >SW in the region of 'ongri and Nianori. At Sasunavghar, they dip 10° to 15° towards west and at Bassein they have dips of 10° towaras WoW»

d) Trachytes : Flows of trachytic composition, ranging in thickness from 5 metres to 30 metres, occur at Khorodivadi, Manori, , Gaimukh Bandar, Andheri, -'alad, Kandivli, Borivli, Vehar Lake, Fowai Lake, Saki Naka, 3ion, i.urla, etc. localities of Bombay sector, a small exposure of trachyte is also recorded about 3-4 kilometres NF of Brahmanpaaa in the Bassein sector. It is possible that 30me of these trachytes may be ills. The trachytes show well developed columnar jointing and exhibit dips of ^bout 10° to 12° towards w®st.

The trachytes are medium grained, greyish-white coloured passive rocks. On alteration these become buff, while on extreme alteration they are converted to white clay. The trachytes from the bombay group of islands show basaltic xenoliths of various jises, which show hybridization effects along the margins. ±he petrography and petrochemistry of tnese rocks is 24 detailed by ’ athur and Naidu (1932), Sukheswala (1953), Sukbeswala and Poldervaart (1958), Sukheswala and Sethna (1962) and Sethna and Battiwala (1974, 1976, 1977, 1980). Sethna and Battiwala (1977) have grouped the trachytes into two categories viz quartz-rich trachytes and quartz- bearing trachytes, in thin sections, th°y show indistinct micrographic intergrowth of quartz and feldspar. In some thin sections they show a f^w mxcrophenocrysts of antip^rthitic feldspar which are turbid and are altered to clayey material and calcite. :>ome of the feldspars have au antiperthitxc core with a margin of more altered potasn faldspar. The groundmass is composed of laths of antiperthitic feldspar with a few isolated grains of orthoclase. The interstitial spaces between these laths are occupied by grains of quartz and granules of pyroxene and iron oxide and a few grains of apatite. Greenish brown chlorite occurs throughout the groundmass and is probably a product of alteration of pyroxene.

Pyroclastics :

The pyroclastics, including volcanic breccias and various types of tuffs and ashes are very common in the Bombay and Bessein sectors and are developed to a lesser 25

extent elsewhere. They are found between flows near Ghod Bandar, Borivli, Kandivli, Maiad, Ananeri, Tulsi Lake, Vehar Lake, Santacruz, Kurla, Sion, , , Hill etc. localities in the Bombay sector. They are also present at Sasunavghar, Kaman, Gokuivare, ^ale Sopara, jativli, Bikharipada, etc. localities in the Eassein sector. The volcanic agglomerates occurring at Kanheri Caves (Plate 2.7, Photos 1 and 2), Irombay and Sativli are made up of vesicular, elongated ana subangular bombs or blocks of brown cherts, trachytic material and small pxeces of yellow to reddish brown limonitic matter; all set in a matrix of dense, dull, light grey, amorphous material.

At places, the matrix resembles bauxite. Some agglomerates show fine banding with alternate layers of

sili.ca.ous ana tufxaceous ma&ter. The tock i3 reddish brown in colour and exhibits no joints.

Massive tuffs occurring at Ghod Bandar, ,]aki Naka, Andheri, Gaimukh Baniar in the Bombay sector and at sasunavghar Kaman, Bikharipada, Nale Sopara etc. localities in the Bassein sector, are variegated in colour. They commonly show varying grain size and often exhibit stratification. Generally, these tuffs are basic in composition.

The tuffs occurring at Jog^shwari, , Malad, Kandivli, Porivli, , Sewri, Antop Hill, Malabar Hill, Comballa Hill and Worli Hill and other localities of the Bombay group of islands ar° generally acidic in composition and exhibit a well developed stratification. These tuffs are variegated in colour, including white, grey, yellow and yellowish brown. Quartz and feldspar are the chief components present in these tuffs. The a grain size is variable, stratified tuffs of Malbar and Worli Hills are coars« grained and yellowish brown in colour. Th® stratified tuffs of the Cotton Green, as also the ash bed of Sawri, Cowpaty b^ach, Haji Ali Tomb, Worli show mud cracks, indicating submarine deposition. The thicknesses of these tuff beds vary from a few centimetres to 6 metres or more. These beds dip at 10° to 20° towards w*>st. The ash bed occurring at Pfath&nwadi to the east of Malad, shows recumbent folding

(Flate 2 . 6 , Fhoto 1). The axe3 of the fold generally trend E-W and plunge at 10° towards west. 27

Fed beds :

In the inland areas, the basaltic flows are often separated by thin horizons of clayey rocks. They have been referred to as ’red beds’ and may represent either fine grained pyroclastic material that was deposited over basaltic flows and subsequently redistributed, or they may have been produced due to thermal effects of newly erupted flows on palaeosoils anu weathered tops of basaltic flows (Pascoe, 1973)* These are predominantly red in colour but at places they may be brown, whitish- brown or greenieh-white or green. The thickness of these b»ds vari«s froT. a few centimetres to 3^ centimetres or more and can be traced discontinuously for a considerable distance. These horizons characteristically display a close spaced prismatic jointing pattern especially in the upper part. Sometimes they show a gradational relationship with the unaltered rock and contain relics of partly altered basalt. At places, they exhibit development of various zeolitic iainerals.

mtertrappeans :

Intertrappean bads of sedimentary origin are presert 28 at Malabar Hill, Coraballa Hill and Worli Hill of the Bombay islands. They are intercalated with the ash beds underlying the andesitic flows. The intertrappeans consist of carbonaceous shales of black colour. These shales have yielded fossils of frogs (hana pusilla; Owen, 1847 and Indobatrachus trivialis; Chiplonkar, 1940), turtles (Carterremys leltnll; Williams, 1953) and fish tooth. A shale bed, 2 to 3 metres in thickness is found in the hills to the east of P.asuna\ghar in Bassein sector, in a road cutting along the Western "xpress Highway. This intertrappean shale b*d exhibits a massive basal section, overlain by a section showing a well developed stratification (Plate 2 .9 , Photos 1 and 2). The bed shows dips of about 10° towards west. The shale is buff in colour and contains an abundance of oatracod shells (Padve, R.M., personal communication). This shale bed also shows warping and dislocations (Plate 2 . 8 , Photo 2 ) . The folis are asymmetrical with almost «ast-w^st trending fold axes. The fold axes plunge at 8° to 10° towards west.

Instrusiv°s :

In the area under study, the volcanic flows are 29

intruded by numerous dykes and plugs of trachytic agglomerate, dolerite, gaboro, anorthositic gabbro, lamprophyr^s and diorite.

a ) Trachytic ar.glomeratos : A number of dykes of trachytic composition axe present in Bassein, Bombay and Thai sectors. These dykes were first reported by N'atnur and Naidu (1932) in the Bassein ar®e. They are ag-'lom^ratic in nature and stand as narrow, linear ridges. The dyke roctc shows sharp contacts with the country rocks (Plat,* 2.10, Photo 1). ' ffects of shearing ani brecciat-ion ar® observed. The dyk^s show a typical weathering pattern (Plate 2.10, Photo 2) due to differential weathering of hard and soft layers and this pattern is, in some way, similar to spheroidal weathering. The a glomeratic dyke near Kolgaon (Fig.2.7) in Thai sector shows siickeri8id®s, intense brecciation and development of stalactitie limonite. The dykes forming prominent resistant ridges, occur at Sasunavghar, B&pane , Holhi; \,aiiv , Gokhivare , Nale bopara, wilemore ana other localities in Bassein sector. They are also common in Bombay sector and are present at Kajupada,

Ghod Bandar, Gaimukh 'Bandar, Binderpaaa, Vadvli, Bagvilapada and Manpada. Ihey vary in wiath fro-n a few Geological map of the Sasaune area , Thai sector. 30 metres to 100 metres and in length they may extend for more than 5 kilometres. In the Bombay sector they trend almost N-S, in Basaein sector they follow N 30° W to N 45° V,' direction, while the dyke near i\oigaon, in Thai sector, t re rids N 10° n1.

The trachytic agglomerate is typically a highly decomposed rock of pinkish colour. It is much kaolinised and stain°d by ferruginous matter, in thin sections, it shows a kaolinised reddish brown coloured material. Vithin clear patchps a fplsitic groundmass is observed.

b) Dolerites : Dolerites ot basaltic dolerites mainly occur in the form of small or large dykes (Plate 2.11, Photos 1 and 2). >mall detached intrusions of dolerite with more or less circular or oblong outlines are also noticed in Bassein sector. The general trend of tne longer axes of these intrusions is parallel to the general trend of the dykps. The dolerites occurring at Tulinj, Felhar, Brahmanpada, Payagaon, Shilottar and northern hilly portion of the Kamandurg Fort are circular to obiong in outline and the longer axes of these outcrops trend in a NMW-33Ti' direction, Holorite dy^es ranging in thickness 31 from a few centimetres to 50 metres ramify the basaltic flows. They exhibit a typical weathering pattern and either form depressions, as in areas subjected to shearing, or stand out as ridges. The dykes are dominantly vertical though some may show aips of upto 70°. A number of dolerit® dykes have been recorded (Fig.2.6) and their orientation measured. The data is presented in Table 2.2. and number (percentages) azimuth frequency is shown in Fig.2.6. it ia observed that most of the dykes occurring i.i the Pen, j anvel and Thai sectors exhibit N 10° 5, M 45° ^ and A 35° W trends. Dykes from the Bombay sector are typically oriented in a H-3 direction and those from Baasein and Palghar sectors trend either N 35° W or N 25° E. The dykes are more abundant in the ’pahoehoe’ flows. Dyke swarms occur in the Pen and Panvel sectors. Branching ana multiple injections are also noticed in some dykes. A ayke occuring in the hills to the east of Chirner shows multiple injection and branching. A few dykes which exhibit porphyritic texture, show unusual concentration of phenocrysts (about 2.5 centimetres in length) of plagioclase feldspar, an example is the dyke occurring in the hills,north of Javli Khuri in Pen sector, which Table 2.2 t Frequency distribution of dykes in the area between Palghar and Thai.

Azimuth Range Number of Frequency dykes %

270-279 1 0.51

280-289 9 4.57 290-299 0 0.00 300-309 2 1.02 310-319 16 8.12 320-329 1 0.51 330-339 15 7.61 340-349 6 3.05 350—359 23 11.67 0~ 9 47 23. 86 10- 19 16 8.12 20- 29 22 11.17 30- 39 3 1.52 40- 49 17 8.63 50- 59 0 0.00 60- 69 13 7.61 70- 79 4 2.03 80- 89 0 0.00

Total 197 32

is about 10 metres in width and can be traced from Chavne to Anbeghar. At some places, as at Jambhulpada in Thai sector, the dyk^s show an °n echelon pattern. The contacts between the dykes and the host basalts are sharp. The margins of the dykes are generally chilled and are glassy. Some of the broader dykes show coarsening of grain-size from margin to core. The dyk»s are characterised by three sets of the joints, viz. one set b»ing parallel to the walls of the dyke, second at right angles to the former and third being more or less horizontal, besides the cooling joints a conjugate set of 3haar joints, trending approximately and tP-Sfc is observed. Sucu shear joints are present in approximately trending dyk®s. The dykes of dolerite sometimes show intense shearing, it is also interesting to note that the most of. the dyk~s follow the trend of the Panvel flexure. Particularly, in Pen and Panvel sectors the dyk«*s and other shear zon*s trend N-S i.e. parallel to the axis of the flexure. Younger dyK^s of olivine aolarite are seen emplaced along shear zones and as at Sasaune, the dyne shows close spaced jointing and shearing (Plate 2.12, Photos 1 and 2), In some cas*s the. dykes, which are 33 shaared, exhibit ex-solution biebs of silica (Plate 2.6, Photos 1 and 2j. For example in a dyke at Kihim in Thai sector, which is about 2.5 metres wid« and extends over a length of about i+0 metres, the silica blebs vary in size, upto 6 centimetres along, the longest diameter. The oolerit® is typically a greyish black, medium to fine grained rock, in thin section, it is seen to be composed of pyroxene, plagioclase and opaques, usually snowing subophitic texture. The plagioclase ana pyroxene occur both as phenocrysts and the groundmass. The plagioclase is labrador-te which, commonly show3 zoning, and cruciform and interpenetration twins. Coppery red coloured iddingsite, pseudomorpnous after olivine are quite common. Glass occurs in irregular patches of yellowish to greenish colour. Opaques are generally skeletal crystals of iron ore ana Ilme^ite^ Apatite occurs in the form of needles.

Gabtaro : Three bodies of gabbro are observed in the hills to the east of Tulinj and Valaipada and to the w*st of Valiv. They ere in the form of elongate bodies with longer axes trending in a N 25° W direction. The gabbro is a coarse grained melaaocratic rock and shows 34 clearcut discordant relationship witja the Deccan basalts. In thin sections, plagioclase plates are seen to enclose pyroxene and olivine giving rise to a poiKilitic texture. The petrography and petrochemistry of the gabbro of Tulinj has been detailed by M&thur and Naidu (1932). A similar type of gabbroic intrusion has been reported by ‘■•ulay and Peshwa (1980) in the area of Raigarh district of .

d ) Anorthositic gabbro : A small body of anorthositic gabbro is exposed in the intertidal zone of "asaune arpa (Plate 2.13, Photos 1 and 2) in the Thai sector. Th“ plliptical outcrop is about 150 metres in l«ngth an1 75 metres in width, the longer axis trending N-S. Th^ pastern margin of the body is faulted and is marked by intpns* brecciation (Plate 2.6, Photos 1 2). ^xsolv^d silica occurs in blebs which decrease in size from 5 centimetres at the fault margin to almost microscopic siza in the inner part of the pluton. The anorthositic gabbro is cut by aa olivine dolerite dyke, about 50 nv»trps in width and trending N-S (B'ig.2.7). both tho anorthositic gabbro and the olivine dolerite exhibit identical set of shears suggestive of post- dolerite shearing. 35

The anorthositic gabbro is very coarse grained end consists mainly of plagioclase (An 50;-.) and few grains of augite and opaques. Apatite, in the fora of needles, occurs as inclusion in plagioclase. The augite i^ at places, altered to chlorite anti calcite. Thin sections from tne marginal parts show exsolvea silica occurring both interstitiaxly ana as inclusions in plagioclase, giving rise to granopnyric texture. Two other elliptical outcrops of anorthositic gabbro occur at Korlai and Lorlai about 20 Kilometres south of Inal.

e) Lamprophyrps : A lamprophyre dyke is present to the south of Parol in Fassein sector. it is exposed in the b«d of Tansa river and is of the carnptonite variety. The north-south trending dyke can b* traced for about 150 metres. It has a lenticul r shape and the contacts are conseal»d under the alluvium of Tansa river. The rock is porphyritic with large phenocrysts of pyroxene set in a black dense grounamass.

f) Diorites : Diontes are exposed in and around

Sativli village, about 6 Kilometres east of Bassein Road

railway station. Smaller exposures are found in the

north of pilkharipada and in the east of xelhar village 36

in the Bassein sector. The petrograph) and petro­ chemistry of these rocks has been detailed by oukheswa1a and Sethna (1962). In Bombay sector, the diorite occurs in the a m around Kajupade and Gaimukh Bandar, in the northernmost portion of the Salsette island. The diorites are intrusives into the basalts and tuffs. The diorite is generally leucocratic and coarse grained, though the grain-size sometimes shows variation from fine to coarse. The colour variation is from greyish black to almost white. Some parts of the diorit»s show small veinlpts of quartzof^ldspathic material. In Sativli ar°a the diorite is cut by a basaltic ayke. Under the microscope the diorites show wide variation in texture, from coarse grained granitic to f-ne grained porphyritic, with quartz and augite in varying amounts. Orthoclasp forms overgrowths on plagioclase and is distinguished by its turbid appearance. Zoning is common in plagioclase crystals. Pyroxenes occur as annedrai grains and show marginal alteration to nornblende. Hornolende is pseudomorphous after pyroxene, quartz occurs interstitia 11 y and forms large and small anhedral crystals. Apatite occurs as inclusions in the

plagioclases. 37

Laterltes :

Laterite in the form of a reddish brown, porous, ferruginous material occurs as cappings on 3om=> hills and is a sociat^d with bauxite. No laterites are observed in Palghar sector. xn Bassein sector, 6 to 7 metres thick laterite is dev<*loppd on Tungar hill. Within it, at places 0.3 to 1.2 metre thick bauxite is developed. In Bombay sector lat*»rif,p occurs at level s above 330 metres to the north of Vehar Lake, in fanvel sector there is no development, df latpritp. The only occurrence in Pen sector is that at Mira Dongar, where it occur3 above 600 metres fronn. MSL, It is mainly a vesicular and nodular material, about 2$ metres thick and is associated with bauxite. In Thai sector laterite occurs above 27^ metres on Kankethwar ana Karlakhind hills. At tne oase of the luterite « norizon of xxthoiuarge, a few centxmeties to a metre tLick, may be present. quaternary sediments :

quaternary deposits recorded in the area investigated include both consoixdatpd and unconsolidated sedxments.

The consoiidatpd sediments, which are generally called 38

"beach rock", are probably of Pleistocene age. Recent sediments include beach sands, dune sands and swamp deposits occurring along the present-day coast, alluvium is developed along stream channels in the inland area and colluvium is formed along the base of the hill slopes.

Bpach rock ; Mainland and island beaches all over tne worid ana especially in the warner regions, commonly show the development of compacted sediments which are referred to as "beach rock", such rocks, developed along the coast of , have previously been referred to as flittoral concrete' by Carter (1852) and Ahmed (1972), ’beach sandstone1 by Blanford (1872), ’raised beaches' or’raised marine conglomerates’ by Oldham (1885), ’calcareous grit' by h'athur and Maidu (1932) and ’beach rock' by 59tty ana v.agle (1972). Locally the rock is called "karal". This term has been retained by Guzdar (1980).

In view of its general acceptance all over the world the term "beach rock" is adopted in the present study. The beach rock, in the area investigated, is a friable to well cemented rock (Plate 2.14, Photos 1 and 2), which consists of mineral grains, rock fragments and calcareous debris cemented together by calcium carbonate. 39

It generally occurs in the regions just behind the line of the present-day sandy beaches and dunes. They are generally exposed in vertical sections along the tidal banks, in nala cuttings and are seen to rest upon the basalt. At places, as at Thai, they are covered by reddish brown soil. They are thickly vegetated with coconut, heetlenut and banana plants. The beach rock strata vary in thickness from a metre to 15 metres or more and exhibit a well developed stratification (Plate 2.15, Photo 1). The b®ach rock strata typically shows a basal layer of gravels and shell fragments, overlain by coarse sands and sand-sized shell fragments which in turn grade upward into medium to fine .ands and ultimately, into fine silts and clays cemented together with calcareous material. Occasional pebbly or gravelly layers may be present. The shell fragments are of gastropods and lamellibranchs in varying proportion.

Good exposures of beach rock are observed along the banks of the Panshet river-, about 4 kilometres of , in the Palgh^r sector (Plate 2.14, Photo 2). A section, about o metres in thickness, is exposed neer

Kelve along the banks of the Mur river in the Palghar 40

sector. At the same locality a 2vjiietre section of the beach rock is observed in a well cutting (Fig.2.8). The b®ach rock is also well developed along ftolipaJa-Kalamb- Bassein coast of the Bassein sector, in the Bombay group of islands these rocks are observed at Uian, ’anori, Marve, Vesava, , Mahim, arine Lines and other localities. J-n Panvel sector they occur along the coast of Uran. The section observed at Uran is illustrated in Fig.2.9a. Excellent exposures of this rock, are observed at Sasaune, Kiuirn and Thai in the Tnai sector. The section observed at Thai is shown in Fig.2.9b. The beach rock renerally constitute raised beaches, as at Mahim and Xalamb or raised dunes, as at Shirgaon, Kihim and Uran or raised sand bars es at , Bhuigaon Budruk, Marve, Vesava and Thai.

b) Unconsolidated sediments : The unconsolidated sands include dune sands and beach sands. The dune sands occur in disconnected patches throughout the coastal belt. They are in the form of mound3, 3 to 5 metres in height. They are medium to fine grained and contain fragments of gastrop«ds and lamellibrachs shells. The sand dunes occurring in the Bassein, Palghar and Bombay sectors are less in height (1-2 metres), compared with tuOoe occurring

T V G 1 0 3 Soil

Medium to fine grained consolidated sands and grave s

Coarse grained co^so! :a'*" sands and gravels

Compacted clay

Medium to fine grained compacted sands and gravels

Coarse grained compacted sands and gravels

A /\ A /v A. /v. A. /v. ^ A A A A A A A A Basalt

Fig. 2-8 Sedimentary section as observed in the well-cutting at Kelve , , ^hane District. 3-01

2-5------Fine sand & silt With little shells _• -.C-C y ^ .A / ^"'T A >/, v r » v) ' f " \ ' ' r^ ' & ~ <* 2-0 -

0 .* • o V.’o-^a '.-^ .^ V ------Beach rock with a predominance ot shells m. 1-5 - :b 1-0 - ^ 'S N"’\ — Beach rock with equal amount ot shells & gravels '-. • -... •■ > y-; p,. \ o - 0-5 - P • 'O ', - rs ' ■ '\'S< — Beach rock with a predominance ot qravels 0-0 ------SEA LEVEL

(a ) URAN

3-5-1

3.0- Medium sand with shells

2‘5 m.2-0 - Fine and medium sand with shells

1-5 Fine sand Fine sand and slit with shells 1-0 Fine sand with shells .o. '•'* Coarse and fine sand with shells 0-5 J . k i - SEA LEVEL

(b) THAL

Fig-2-9 Profiles of Qj-iaternary sediments 41

in the Thai and Panvel sectors (generally greater than 4 metres). The sand dunes in cross sections show well developed stratification. The stabilised aanti dunes are characterised by the growth of qpinifix squarossus, Vit“X negandu and Duranta plurr.erii plants because of high moisture and humus content of about 5% and 2.5% respectively (Untawale and Hair, 1974).

A good development of sand bars is observed at Rassein, Mahim, Juhu, f'arve, Uran, Fi.evas, ftihim and other localities. These are associated with sandy beaches. The beach sand is a medium to fine grained calcareous sand which contains admixtures of shell and rock fragments. It is exposed in the intertidal zone, the width of which is maximum at Bassein and Bombay coast3. Therearshore and forshore regions of sandy beaches are devoid of any vegetation. The bacKshore region of the sandy beach, which is nearly always exposed but occasionally gets submerged during exceptionally high tide waters, shows dominant growth of Ipomra p°s-cspree. Th° surface of the sandy beaches is charscteris°d by a variety of sedimentary structures such as 3and ripples, swash marks and number of other U2 ephemeral structures {Thigale and Barids, 1980; Thigale and Powar, 1980).

The sandy beaches are generally backed by dunes and beach rock (plate 2.15, Photo 2 ) . The general deposition of the Quaternary sediments is shown in F ig.2.10.

c) Swamp deposits ’• Swamps are the tidally submerged coastal woodlands. Mangrove swamps are very common along the coast of the area investigated. They are extensively developed at the mouth of the major as well as minor rivers. Large swamps occur at the mouth of Dudh river, Mur river, Sarvar creek, sopara creek, ..anori creek, Malad creek, Thana creek, Panvel creek, i.aranja creek and Dharamtar creek. The small creeks and tidal inlets have also developed swampy areas. The swamp deposits consists of mineral grains, shell debris, slit, clay and organic matter. The uplifted swamp deposits exhibit well developed stratification . Such raised swamps occur at Thai.

d ) Colluvlum • colluviurti is a part of the regolith i.e. the superficial mantle of unconsolidated rocK deons and soil on the earth’s surface. Specifically colluviun Coconut plantation 43 is that part which consists of heterogenous material of any particle ^-ize which accumulates at the lower parts of the hills or at th-^ base of slopes (Merrxll, 1897). Colluvial deposits (Plate 2.16, Photo 1) ranging in thickness from a few centimetres to 3 metres, are developed on slopes and at the base of the hill ranges in all sectors of the area investigated. As th<= valleys of the rivers in the area are mature, tne coiluvium interfingers with the alluvium. The coiluvium includes talus, cliff debris and related soils. Colluviu:n is particularly well developed in the area which is characterised by cliffs. For example, the coiluvium is well developed along the foot and on the slopes of Mumbra-belapur ridge in Panvel sector. In Thai sector it is well developed at the base of the Kanxeshwar hill.

e) Alluvium ; Alluvium is a more or less stratified deposit of gravel, sand, silt, clay or other debris, moved by streams from higher to lower ground (Thorp, 1968). The inner part of the area investigated is covered by a thin veneer of river alluvium (Plate 2.16, Photo 2), especially along the banks of the major streams like Dudh, Panshet, Mur, Vaitarns, Tansa, ivaman, Ulhas, Dahisar, Panvel, 44

Patalganga, Balganga, Bhogeshwar, Amba and Talavli rivers and their tributaries. The thickness of the alluvium ranges from 2 metr°s to 5 metres. The alluvium supports most of tlie paddy fields of the Konkan.

Soils :

The 5 0 il present in the area is mainly alluvial soil, though some residual soil is also present. The residual soil occurs mainly on the hill tops and on slopes, while the transported or alluvial soil occurs in river valleys. Tne basalts on weathering proauce large cuantitxes of fine &raineu material consisting of clays ana iron ores witn small amount of coarse basalt fragments. Such residual soil is clayey and ferruginous in nature, These soils show gradation into bedrock basalt with depth. The completely decomposed material at the surface is separated from the basalt below by material s n ^ m g intermediate stage of decomposition, the most familier of these being ’muru/c’ The alluvial soils are predominantly clayey with on iy irregular lens°s and pockets of coarser material, Sometimes these soils snow graaational bedding. -alt encrustation is v'jry common in both the types of soils of Konk.n, especially in the coastal belt. Plate 2.1

Photo 1 s Columnar jointing in basalt. Locality * Andheri, Bombay sector.

Photo 2 } Columnar Jointing in basalt. Locality s Malad, Bombay sector. P late 2-1

Photo 2 P la te 2 .2

Photo 1 i Steeply dipping joints in basalt* Locality J Sativli, Bassein sector

Photo 2 * Close-spaced jointing along shear zone in basalt. Locality * Mathane, Palghar sector , Plate 2-2

Photo 2 Plate 2.3

Photo 1 t Spheroidal weathering in basalt. Locality * Mandve, Thai sector.

Photo x Pillow weathering in basalt. Locality : Dahisar river bed, south of Kanheri caves, Bombajr sector. Plate 2-3

Photo 2 Plate 2.4

Photo 1 t Basaltic flows showing westerly dip of about 20 J. Locality s Kaldurg hill to the east of Palghar, viewed from north.

Photo 2 s Basaltic flows showing westsouth- westerly dip of about 10°. Locality * Uran hill, Panvel sector, viewed from northnorthwest. Plate 2-L

Photo 1

Photo 2 Plate 2.5

Photo 1 : A breed ated zone in basalt. Locality s Mahim-Kelve, Palghar sector.

Photo 2 * Close-up of the brecciated zone showing a typical fault breccia. Plate 2-5

Photo 2 Plate 2.6

Photo 1 s Exsolved silica blebs in anorthositic qabbro near fault. Locality I Sasaune, Thai sector.

Photo 2 i Close-up of the above showing the typical size and form of quartz blebs. Plate 2 • 6

Photo 2 Plate 2.7

Photo 1 i Caves carved in massive, pyroclastic rock. Locality t Kanheri Caves, Bombay sector.

Photo 2 i Close-up of the same pyroclastic rock showing angular bombs and rock fragments in the dense matrix. Plate 2-7

Photo 2 Plate 2.8

Photo 1 t Ash bed showing recumbent folding. Locality i Pathanwadi, east of Malad, Bombay sector.

Photo s Intertrappean shale bed showing warps and dislocation. Locality * Sasunavghar, Bassein sector. Plate 2-8

Photo 2 Plate 2.0

Photo 1 t Intertrappean shale bed showing stratified top and massive basal section. Locality t Sasunavghar, Bassein sector.

Photo 2 t Hand specimen from the top section of shale bed showing well developed stratification. Locality : Sasunavghar, Bassein sector. Plate 2-9 P la te 2.10

Photo 1 i Trachytic agglomerate dyke showing sharp contacts against basalt. Locality i Kolgaon, Thai sector.

Photo 2 i Typical weathering pattern observed in the trachytic agglomerate. Locality i Gaimukh Bandar, Bombay sector. Plate 2-10

Photo 2 Plate 2.11

Photo 1 t Doleritic dyke forming a low ridge. Locality i Ambeghar, Thai sector.

Photo 2 x Highly sheared olivine-dolerite dyke cutting anorthositic gabbro. Locality t Sasaune, Thai sector. Plate 2-11

Photo 1

Photo 2 Plate 2.12

Photo 1 } Closely spaced shear joints in olivine- dolerite dyke. Locality * Sasaune, Thai sector.

Photo i Silicification along closely spaced joints in olivine-dolerite dyke. Locality : Sasaune, Thai sector. Plate 2.12

Photo 2 Plate 2.13

Photo 1 } Outcrop of anorthositic gabhro, in intertidal zone, exposed during lowtide. Locality : Saiaune, Thai sector.

Photo 2 : Sharp contact between olivine dolerite dyke (left) and anorthositic gabbro (right). Locality t Sasaune, Thai sector. Plate 2-13

r

Photo 2 Plate 2.14

Photo : Loosely cemented beach rock. Locality * Shirg*on, Pilghar sector.

Photo 2 * Well cemented beach rock. Locality t Panshet river bed north­ east of Mahim-Kelve, Palghar sector. Plate 2-U Plate 2.15

Photo 1 j Beach rock showing well developed stratification. Locality > Navedar (Navaqaon), Thai Sector.

Photo 2 : Sandy beach backed by sand-dune and stabilised dune. Locality : Kihim, Thai sector. Plate 2-15

Photo 2 Plate 2.16

Photo 1 : Colluvlum occurring at the foot of hill slope. Locality : Mumbra, Panvel sector.

Photo 2 i River alluvium covering flat lov^ lands. Locality * Sangam, Thai sector. Plate 2-16

Photo 2