Indian Journal of Marine Sciences Vol. 29, December 2000, pp. 283-294

Beach lTIQr12hgtogy and the inferences from heav min~~al assemblage of \ -Mandapam to Kanyakumari, coast, southeast coast of India

~ -

- J:YAngusarny / G ictol" R-;j;n-;-nickam

(oepartment of Earth Sciences, Tamil University, Thanj avur-6 13 ooy XI*,-trrcL

E=Mai l: hemaanguehi @hotmail.com

vrajamanickam@yahoo.com

Received 21 .Iulle 1999. revised 16 Auglls/ 2000

On the basis of heavy mineral di stribution, the southern coast o' Tamil ~\has been divided into live blocks namely Mandapam, Yalinokkam, Tuticorin, Manappad, Kanyakumari blocks . The heavYrll ineral concentration by wt % vari es from 2 to 87%. Zircon , co lourless garnet , pink garnet , ch lorite and biotite are the predominant minerals . The abundance of these minerals vane;;- in each block.-Chlorit~~i llim;n-it~, mic;1 , few hornblendes and kyanite are characteristic of Mandapam block while biotite and glaucophane for Valinokkam block, euhedral zircon, hypersthene, tourmaline for Tuticorin block, broken zircon, andalusite and topaz for Manappad block and rounded zircon, rutile and monazite for KanyakunlJri block. Chlorite, mica and other !laky minerals are domin ant in Mandapam and Manappad blocks , whereas in Kanyakumari and Valinockam block, minerals like zircon, garnet and other denser heavy minerals are abundant. Granular minerals li ke zircon and garnet , 0 'J ) <J:; ~ L are presumed to have been derived from the recyc led sed imen~-Iowever, the immediate hinterland has not shown any _ presence of ancient sedimentary formations which are li kely to be the source for recycled sed iments. The minerals, not specilied under recycled sediments, are expected to have been originated from the rocks of igneous and metamorphics of the hinterland. On the other hand, the presence of prolilic Ilaky mineral s mainl y from the derivatives of green schi st facies po int out the presence of metamorphic rocks in the hinterland. However, the hinterl and is primarily occupied by Quaternary sediments. Such incompatibilit y of heavy mineral assemblage of Kanyakumari, Manappad and Mandapam blocks , enables to infer the deposition of sediments primarily by littoral transport , in addi ti on to the terrigenous contribution. This is well supported by the presence of well rounded garnets, zircons and strongly etched fl aky mineral s. The source for the heavy mineral assemblage is attributed to a mixture of low-grade metamorphic rocks, reworked sediments, charnockite, granite and grani te gneiss. This inference is also supported by the results of Q-mode factor analysis.

Heavy mineral s tudies are usefuy n infe rrin g th e

prove nance and maturity of the sedtJne nt s, and e ne rgy

conditions prevai le d during / the depos iti o n and

subsequent environment confined in the depositional

basi n . The re lati ve abundances of heavy mine ra ls

have been used to diffe rentiat e the different depo­

si tiona l e nvironme nts I , the stratigraphical boun-

d . 2-4 h k 5 6 h d . anes , t e source roc s" ,s orewar tran sporta tIon

of minerals and marine tra nsgress ion 7

, di spe rsal

patte rnS, a nd economic viability of the depos it s?

Moreover, heavy mineral distribution has also been

used to deduce the additional incre me nt of heavy

mine ra ls from offshore 10. AloIlg southeastern coast of

Indi a from Mandapa m to Kanyakumari, barring

de tailed geomorpho log ica l s tudies of Loveson II a nd

the occurrence of beach placersI2

. \." little work has

been done to understand the morpho logy of beaches

and the assembl age of heavy mine ra ls . This paper

a ims to highli g ht beach morphology, assemblage

of heavy minerals and their significance fo r

unde rstanding the provena nce of sedime nt s between

Mandapam and Kanyakumari.

Materials and Methods The s tudy a rea ex tends from Mandapam to

K a nyakumari 111 the southern coastal trac t of

Tamilnadu covering a bo ut 360 km (Fig. I ) . It is bound

in the northeas t by R a m eshwaram Is la nd, in the east

by B ay of Benga l, in the west by Eastern and W estern

Ghats and in the south by Kanyakumari being the

southe rn mos t tip of India , c haracte ri sed by the

confluence of Indi a n Ocean, Arabian Sea a nd Bay of

Bengal. The drainage pa tte rn of the a rea is m a inl y

controll ed by perennial rive rs like Vaigai,

Tamirabarani and minor rive rs like Vaippar, Gundar,

Vi rusuliar and Vembar.

The s tudy region is c hiefly under lain by the

c rysta lline rocks of Archean age consisting of

g neisses, charnockite, granites and Quate rnary

sedime ntsll

(Table I ) .

284 INDIAN J. MAR SCI. , VOL. 29, DECEMBER 2000

Muttup.tt-......u~_ s.t1Uc1loroi ~

l KiiaIcIroroi

1/embGf' Valinokkam P.S.pUrom K.R. PLrom

Sippikulam Voippor

tNot",

N o 8 - - .....

. / 45

Kollar

GULF OF MANNAR

~OKm

I 0001 Co/crete BAY OF

11:>1:> 1:>1 Coral/ine

10001 Sheet Rocks

1-- -I Sample Location

BENGAL

7830'

Fi g. I- Locati on Illap and class ifi cati on o r beaches by nature o r rocks

Since, no standard classification is made available for the beaches of thi s region , an attempt was made to group the beaches on the bas is of the nature of lithology, sediment composition and gradient. To understand the heavy mineral di stribution in thi s part of the beaches, au ger samples have been collected in the months of April-May/l 990 al ong the coast from low-, mid-, and hi gh- tides and berm regions from 32 stati ons (Fig. I). Each station is kept away from each other approximately of 10 km di stance. However, wherever marshy ground , parti cul arly near ri vel' mouths, and a bad land topography blocking the entry into the beach, causing unapproachability, such regions have been kept away from samples without maintaining the 10 km interval. In places where strong lithologica l differences by virtue of its grain size, black sand enrichment or mi xing up of other detrital materi als are observed, in such sectors the auger sampl ing was done in less than, 10 km in terval. The auger samples of I m depth have been taken fo r analys is to form sub-samples of 4 numbers having the depth intervals of 0-25 cm, 26-50 cm, 51-75 cm and 76- 100 crn . As the sub- samples have not shown an y vari ati on in the assemblage among them, an average of th osc four samples have been taken for the purpose of di scuss ion. After the remova l of organi c matter, carbonates and fe rrugenous coating on mineral grain ,

the samples were sieved at 1/4 n; interval in ASTM sieve sets by Ro-Tap sieve shaker for 15 minutes . From the sieved fract ions +80, + 140, +230 mesh sizes have been taken for heavy mineral separati on foll owing Milner '4. Th separated heavy mineral fracti ons have been further separa ted to remove magnetite using horse-shoe magnet. Over and above, the rest of the samples have been passed through Cook Isodynamic separator in vertical pos iti on in O. I amp current to remove the rest of the magneti cs. In inclined position of the isodynamic separator havin g the forward slope of 15° and side ti It 10", at 0.22 amper current , the rest of the opaques includi ng ilmenites have been removed. After the removal of the opaques the non opaque fractions were mounted on a micros lide usin g canada balsam'5 . By tak ing the average of heavy mineral assemblage of the samples anal ysed from low-, mid-, high-tides and berm regions, the results have been processed III

STATPAC package deve loped by Meisch'v. A cumulati ve analys is of heavy mineral assemblage by Q-mode fac tor anal ys is was attempted to un derstand the influence of diffe rent rock types in the respective blocks. Each eigen va lue in the tab le represents a fac tor (Table 2). Among 10 fac tors, 3 fac tors accoun t to 95 % of va ri ances, hence the same are considered for the purpose of interp retation.

ANGUSAMY & RAJAM AN ICKAM : BEACH MORPHOLOGY 285

Results and Discussion Class(fication of beaches

The beaches in the study region are composed of primarily of rocky/sandy material. Taking into account the dominance of a particular type of lithological presence , the beaches are grouped into

beach of coralline rock, crystalline rock, hard calcareous sand stone and calcrete (Fig. I). Coralline rocks are exposed in the coastal segment of Tuticorin­Alantalai region.

Age

Holocene to Recent

Pleistocene

Pliocene

Middle Eocene to

pper Palaeocene

Cretaceous to Upper Jurassic

Archean

At few places, the calcareous sandstone shows a clear stratification having a dip < I 0° towards the sea.

Table I-General stratigraphy of the st udy area (After Lo veson ll)

Formation

Ervadi , Devipattinam, Pullangudi , Yaigai ,

Lithostratigraphy

Allu vium, silt cl ay, lateritic and black cotton , soil s, shell lime stone and coralline sandstone

Locati ons

Ervadi, Devi­pattinam

------ --------------------- U ncon fonni t y -------------------------------------------------

Teri dune sand complex Red teri sand with lateritic

Tirunelve li

--------------------------- U nco n formi t y -- -----------------------------------------------

Pl!lIangudi , Yaigai, Guntar.

Hi ghl y fri able, poorly sorted, weathered, fine­coarse grai ned calcareous sandstone.

Southwest of Kamudi , K.R. Puram to Yembar

--------------------------- U ncon form i t y ----------------------------- -- ------------ ------

Silty calcareous sandstone, gritty siltstone.

subsurface (ONGC bore­well s at Mandapam).

--------------------------- Un con formi t y ---------------------------------- ---------------

(Upper Gondwana) Micaceous sand stone, graphite, basal bou lder bed

Si vagangai, Tirupattur, Kovilur and Kuttelar

and conglomeriti c areas. sandstone.

--------------------------- U nco n formi I y ------------------ ------------------------ ------

Charnockile and nepheline syenite, garnet i ferrous biotite gneiss.

Most part of the hinter land area of Ramnad , Chidambaranar Nellai Katta­bomman and Kanyakumari

Heavy minerals

sillimanite , garnet , kyanite quartz, amphiboles

Pyroxene, garnet, kyani te, ch lorite

garnet, kyanite amphibole, pyroxene

Rounded zircon, monazite. rutil e. Pink garnet, Colour -less garnet.magnetit e. biotite, hornblende. si II i manit e,k yan i te. tourmaline & pyroxene.

286 INDI AN J. MAR SCI. , VOL. 29 , DECEMBER 2000

Table 2-Eigen valu e and their percentage

Factor Eigen value Percentage

38.56 96.40

2 0.28 97.09

3 0.16 97.49

4 0.13 97.8 1

5 0.10 98 .07

6 0.84 98.28

7 0.78 98.47

8 0.73 98.66

9 0.7 1 98 .83

10 0.59 98.98

Moreover, nt many places beaches display 3 sets of joints which enable the waves to remove them in the form of rectangular blocks . The marine calcareous sandstones rich in quartz and feldspar with embedded shells of molluscs are exposed in many places like Mandapam, Timchendur and Manappad in the hi gh tide and berm zones. At Timchendur, the exposures of sandstone stands severa l metres above mean tide level, suggesting the relative Holocene sea level aiong this region probably after cementati on of the sand II.

Exposures of crystalline rocks of khondalite­charnockite abut the beach segment of Kanyakumar i­Periyathalai. The monsoonal wave climate may sometimes strip off the sandy beaches, expos ing the cliff to face the wave attack and eros ion. As a result, erosive features like kettle holes, sea caves and wave cut platforms are well developed in thi s part of the shore.

Depending upon the nature of beach sediments and their compos ition, sanely beaches can be grouped into calcareous beaches, si I iceous beaches , algal/seaweed rich beaches, heavy mineral- rich beaches and muddy beaches (Fig . 2). Medium-grai ned sands with intercalations of she ll fragments occur in the sandy beaches. Quartz, fe ldspar and other siliceous mineral s predominate in the beaches from Mandapam to Valinokka m. Lithifieel calcareous sand hill s for a length of 30 km occur within a few hundred metres from the coastal stretc h of Manappad. The entire foreshore and backshore regions with rich concentrati ons of black sands, with an ad mixture of quartz and feldspars ca rpet the beaches in Kall ar and Vaippar, Kud uthalai to Ka,nyakumari regions. Patches of dark grey to black muddy deposits dominantly cover the shores off Tamirabarani river.

The beaches, in general, show an inclination of 1_7°. However, on the basis of inclination, the entire shoreline can be classified into three broad groups­viz. inclination with (i) <30 (Mandapam-Sethukkarai) , (ii) 3°_5°, (Valinokkam-Tiruchendur) and (iii ) >5° (Manappad-Kuttankuli ) (Fig. 2). The configuration of coastline trends in four diffe rent directions such as E-W, NE-SW, N-S and NT'1E-SSW directions. Each direction is characteri sed by typical sedimentological parameters.

Consolidating the various factors invo lved in the configuration of coastline, beach morphology, etc., the study region is grouped into fi ve major blocks namely, (i) Mandapam block-B I (Mandapam-Valinokkam) (ii ) Valinokkam block -B2 (Valinokkam-Vaippar), (iii ) Tuticorin block-B3 (Vaippar -Tiruchendur) , (iv) Manappad block-B4 (Tiruchendur- Navaladi) , and (v) Kanyakulllari block­B5 (Navaladi-Kanyakumari) (Tab le 3).

Distribution of heavy minerals The principal heavy mi nerals, of beach placers In

the order of abundance are zircon ( 1.74-33.78%), co lourless garnet ( 10.61-37%), pink garnet (10.40-41.17 %), chlorite (0.47-39.96%), and biotite (0.19%-14.62%). The heavy mineral assemblage shows a characteristic variation from block to block. Similarl y, the shape, roundness, co lours , etc ., of heavy minerals like zircon, garnet, chlorite help to characteri se the respective block. Such differences in the nature of heavy mineral s in the five blocks are described below:

Tn Mandapam block, th e heavy mineral assemblage is predominantly represented by co lourless ga rnet (27.24%), chlorite (17.91 %), and pink garnet ( 14.26%) (Fig. 3). Chlorite, biotite, garnet and hyper­sthene show strong etcl ing. A criss-cross fracture pattern in zircons and well rounded garnets indicate their long transportation. At Pudumadam and Sethukkarai stations ch lorites show a two fo ld increase over Mandapam station .

The heavy mineral assemblage in Val inokkam block is similar to th at of Mandapam block wi th re latively hi gher zircon content especiall y in Vcmbal' (37 %) zone (Fig. 3). The absence of flaky mincral ~

like chl orite, biotite and muscovite is vcry much evident in this block.

In Tuticorin block, the Vaippar, Sippikulam and Kallar stations are marked by the abundance of garnet, zircon (rounded I I % to 2891"), rut ile,

Type of hard materi al

Composition

Gradient

Textural parameters

Contigurat ion

Wave ref-raction

Landforms

Heavy mi neral s

Mineral assemblage

SO

45'

£3 15'

. 77

ANGUSAMY & RAJAM AN ICKAM : BEACH MORPHOLOGY

TAMIL NADU

.,a d

10 0 0 1 Muddy Beach

~ Corolline Beach

o 10 20Km ----..

1+++1 Algae/Seaweed Enriched

1000 I Colcarews Beach

1===1 Heavy Minerals Enriched

1 ;: .... ':1 Siliceous

I;::: I Morine Calcareous Sand S tone

CIJ Gently Sloping

CD Steeply Sloping

[TI Moderately Sloping

7830' 790'£

Fig. 2-Classi lication of beaches by composition and gradient

287

Table 3-Classilicati on of the stud y area on the basis of beach morphology and heavy minerals

Mandapam Valinokkam Tuticorin Manappad Kanyakumari

Calcrete rocks Calcrete rocks Coralline rocks Marine calcareous Crystalline rocks (M andapam- Tuticorin- sandstone Kanyakumari-Sethukkarai Alantalai Manappad Periyath alai

Tiruchendur

Calcareous Siliceous heavy Calcareous muddy Siliceous Heavy mineral rich mineral Rich

Gently sloping Moderatley sloping Moderatley sloping Steeply sloping Gentl y sloping 1-3" 1-3"(Mandapm- 3-5" (Valinokkam 3-5"(Tuticorin- 5-7" Alantalai Ovari Vattakkott ai Sethukkari ) to Vaippar) Kayal Pattinam} Manappad Kanyakumari

Fine sand Medium-line sand Medium s::lI1d Fine sand moder- Medium to line sand moderately sorted moderately well moderatel y well ately sorted moderately well fine skewed sorted symmetri - sorted coarse- coarse skewed sorted coarse mesoku rti c call y skew.ed line skewed meso- Ieptokurtic skewed, mesokurti c

leptoku rtic very leptokurti c

E-W NE-SW NS NNE-SSW E-SW

Inept zone Divergence- Convergence- Inept- Convergence convergence divergence di vergcnce

Eight seri es of Marinc terraces Massive beach Coalescencc One series of beach ridges cuspate foreland ridges partia ll y of beach ri dges beach ridge longilUd inal stabilised dunes Massive Teri dunes mud Il ats spits dune complex

5- 10.59% 5.05-64.40% 7.7 1-63.78% 2.8 1-23 .51 % 8.46-86.92%

Chlorite, Biotite p. lallco- Euhedral zircon Broken zi rcon Rou nded zircon sillimanite phane h yperst hene topaz andalusile monazi te rutile

288

10 5 o

20

10

5

o

INDIAN J. MAR SCI , VOL. 29, DECEMBER 2000

MANDAPAM

PUDUMADAM

SETHUKKARAI

KILAKKARAI

ERVADI

30

30

40 30 20

o

VALINOKKAM

KILMUNDAL

TERKU MUKKAIYUR

Fi g. 3-Distribution of hcavy minerals in difrerent stati ons or Mand apam and Valinokbm blocks

ANGUSAMY & RAJAMANICKAM: BEACH MORPHOLOGY 289

tourmaline and topaz (Fig. 4). The zircon content varies from 2% (Vellar) to 7% (Kallar) of the total 40-55 % heavy mineral assmblage. But at Tuticorin and Kayalpattinam stations, the rounded zircons are reduced by 5% with a subsequent ups hoot in chlorites (20.22%-36.06%). Prismatic, elliptical and elongated forms of pink tourmaline are found in this block.

Colourless garnet with a characteristic dodeca­hedral cleavage, pink garnet and flaky minerals are preponderant with more topaz at Tiruchendur, Alantalai and Manappad stations in the Manappad block (Fig. 4). Rounded zircons are dominant over other minerals at Periyathalai and Ovari regions . Only at Ovari monazite makes an appearance by about 8%. From Kuduthalai to the end of this block, a complete reduction of flaky minerals is inferred from their distribution.

The heavy mineral assemblage in Kanyakumari block is represented by rounded zircons, (Fig. 4) overgrown and outgrown zircons to the tune of 40 to 50%. Euhedral zircons with minute apatite, zircon, opaque and gaseous inclusions or hour glass structure in zircon are common. The presence of minute inclusions provide a spotty appearance to some zircons . A few varieties of zircon show well developed crystal faces. However, the presence of outgrowths and overgrowths demonstrate the longer stay and post depositional diagenesis of the sediments in the depositional basin. A total reduction in flaky minerals together with the characteristic presence of monazite is characteristic of all the stations.

In general, Mandapam block registers the dominance of chlorite,biotite and glaucophane than zircon, tourmaline and rutile. A higher concentration of the flaky minerals can be attributable to the prevalence of low energy conditions caused due to strong divergence in all the three predominant wave directions (Table 4). Chlorites show a negative correlation with zircon (r=-0.39), garnet (r=-0.25), monazite (r=-0.44) , and tourmaline (r=-0.55) and positive correlation with biotite (r=0.67), muscovite (r=0.44) and tremolite (r=0.35) . Its antipathetic relationship with sorting of sediments (-0.56) indicates that strong winnowing action of waves acts as the controlling factor for chlorite's distribution . Highly rounded zircons and garnets indicate the role of recycled sediments rather than the contribution from nearby rivers. This region is serving as the place for the deposition of sediments brought by waves and littoral currents, advancing from downsouth d irection .

The movement of littoral currents in the study region prevails in the northerly direction I7

.18

• The influence of littoral sedimentation can be evidenced from the shallowness of the shelf region and strong progra­dation at Periyappattinam by way of hook like spit development, without the contribution of any riverine sediments 19.

In Valinokkam, glaucophane and ch lorite are admixed with garnet and tourmaline. This is ascribed to the prevalence of high energy environment or wave convergence in southeast wave direction and wave divergence in northwest and north north west directions (Table 4). Such condition leads to the sorting of heavies by strong winnowing action of the waves and the dumping of unsorted sediments in divergent condition. At Vembar, an increase in zircon distribution (35 %) is earmarked to the substantial input of sediments from the river and to strong convergence of wave orthogonals in southeast and northwest. As a result, selective segregation of heavies takes place. Slingerland20 has also suggested that the progressive sorting of heavy minerals plays an important role in the concentration of denser minerals.

In Tuticorin block, the abundance of garnet and zircon at Kallar and Vaippar stations is attributable to the strong convergence of wave orthogonals in most part of the year. An appreciable concentration of flaky minerals (12.5 %) at Sippikulam is assigned to the strong divergent conditions in northwest and south south west wave directions. The absence of topaz, glaucophane and rutile in Tuticorin beach is significant, because Tamirabarani river bed sediments consist of these minerals in appreciable quantity . This block has been situated adjacent to these rivers, the lack of topaz, glaucophane and rutile helps to infer that the Tamirabarani river sediments may not be reaching these beaches in a significant proportion 11 .

Similar studies on the sediments of the Vaippar river of Tamil Nadu21

, as well as the northern beach of Tamil Nadu22

.23 have shown the negligible contri­

bution of heavy minerals by these rivers to the respective beaches . Strongly etched chlorites, garnets and glaucophane in Tuticorin region suggests either a longer transportation of sediments or longer stay of sediments in the depositional basin .

In Manappad block, the predominance of zircons and garnets are earmarked to the accumulation of sediments in a trough like basin formed due to the tectonically controlled blocks24 .

Iv '-0 0

:!l (~~

-I>- ZIRCON I 0 GARNET (C.LESS)

~ GARNET PINK ...., HYPERSTHENt: :::r c HORNBLENDE

~ t/J 0 CHLORITE ~ - r <: ::l BIOTITE -< P

"tl P 0 >-l '"0 ...., MUSCOVITE P e r ... =tl r r ~ 0 TOPAZ "tl >-l P e "tl OJ ... P < GLAUCOPHANE P (j ::::: r :::::

'< -l P :l RUTILE -l 0

~ ::l - :;:l n 2 2 0 :.l >-:r. ~ fool <' ..... fUW~

» ~ ~. ..... Z

::l ZIRCON c.

~ GARNET (C.LESS)

3:: ~ GARNET PINK

» g Al

HYPERSTHENE Vl

~ 0 e "'C v , HORl\BLENDE

0 t"l (')

~ CHLORITE <: ::::: ~ 0 ~ 0 L

g BIOTITE ~ ~ p p <

MUSCOVITE c: 2 0

on .... -l P :2 0 SILLE\1ANITE r ~

-l P -l r

-l ANDALUSITE P ;:c "'C P N

"'C 'C

c TOPAZ - r p p r -n RUTILE

p r 0 >- 0

0 .... p - tTl

::::!. GLAUCOPHANE .... (') tTl

::l MONAZITE 3:: 3:: N " OJ

Fr CO

::l tTl

'-' ZIRCON Al

""Cl N ""Cl GARNET (C.LESS) 0.)

0

c. GARNET Pfi'iK :;::: 0

'-' 0

~ HYPERSTHt:NE P e e lIOR1'IBLEi'iDE :2 <: ~ CHLORITE -< P -l -l

~ BIOTITE ;...

~ ! " -l -l OJ 8 :< >- >-77" MVSCOVITE ~ :2 c TOPAZ ~

c: '"0 ~ :l ::::: >-0.) RUTlLt: p § .., r _.

STAUROLITE ::::: r ~ VlONAZITE

-< ..... ..... 0 r.

'" "or.

ANGUSAMY & RAJAMANICKAM: BEACH MORPHOLOGY 29 1

Table 4-Energy conditions prevailing in the study region in different wave directions

Area S45°E

6S SS

I. Mandapam I D

2. Pudumadam C C

3. Sethukkarai

4. Kil akkarai

5. Ervad i D

6. Valinokkam D C

7. Kilmundal D

S. Terkumukkaiyur I

9. K R Puram I

10. Vembar C I

II. Vaippar I C

12. Sippikulam C I

13. Kall ar I C

14. Tuticorin D C

15 . Kayalpattinam C

16. Tiruchendur C

17. Al anlalai D

IS. Manappad C

19. Periyathalai C

20. Kudlllhalai

2 1. Ovari

22. Kodivil ai I ?~ _J. KlIttankllli C

24. Vij ayapathi

25 . KlIttappalli

26. Variyur

27. Vattakkottai

2S. Kanyakllmari

I-Inept condition; D-Divergel~ ce; C-Convergence

The heavy mineral assemblage (zircon , monazite, rutile, hypersthene and garnet) in the Kanyakumari

b lock reflects the patterns of shoreline e rosion and accretion of denser hea vies. A reducti on in fl aky mincral s and amphiboles in these areas demonstrates se lecti ve remova l and transportation of the minerals by strong winnowing action of waves and northe rly littoral drift. The signifi cant contribution of zircons and ga rnet in Oregon areas has been attributed to

shoreline erosion by the continuous wave action 25.

The presence of mineral assemblage like c hlorite, mica, glaucophane, etc., in Mandapam block suggests the contribution o f low grade metamorphic rocks. But the catchme nt is manifested with onl y a ll uv ium sands . It is interesting to observe that the minera ls are

Wave Direction NW NN W

Wave Period IDS SS IDS SS

D C

C I

D

D D

D D D

C D D C

D D

I D

I I

C C I I

C D D D

D I C

C C C

C I I D

D D D D

C D D D

D D D D

C C D D

C

I

I

C

I

C

different to the ca tchment rocks. In Valinokkam block, the heavy mineral assemblage indicates the contribution from granitic gne iss and gran iti c rocks but the catchment area is represented by the presence of more of composite gneiss, c harnockite and al luvium. The Tuticorin block is suggestive of a predominant influence of recyc led sediments whil e the catchment in the hinte rland is c hiefly made of compos ite gneiss , granite, alluvium and cora lline rocks . Manappad sed iments di splay a close affinity to green sc hi st facies whereas the catchment beh ind is primaril y of c harnockite, minor amount of quart zi te and a llu viu m. The heavy mineral assembl age o f Kanyakumari block is represented by the predominance of minera ls li ke rounded and euhedral

292 INDIAN J. MAR SCI., VOL. 29, DECEMBER 2000

zircon, and garnets of recyc led nature. But, in Kanyakumari block, the entire region is barren of sedimentary formations and well developed drain age network. Such contrad ictory nature of assembl age enables us to po int out the ir deri vation mainly from offshore. Raj amanickam & Gujar26

.28 have shown

from the variation of tex ture and mineralogy of beach and offshore sediments that the landward mi grati on of sediments is a majo r phenomena tak ing place along the west coast of India. The sed iment distribution of Oregon's beaches29 and the beach place rs of east Australia30 a lso have shown the onshore migration of sediments.

Once the value of heavy mine ra l di stributions are normalised, the factor analysis with the necessary correlation has been initi ated . In that, after rotation, a ll the samples are observed to dep ict hi gh communality va lue which means that a good description of a ll the samples has been obta ined onl y by using three factors in the maxi mum theoreti ca l

va lue of 1.00. The communality va lue here, ranges fro m 0.776 to 0 .997 for all the sampl es.

Factor I consists of colourl ess garnet. hypersthene, topaz, chlorite, bi ot ite, mu scov ite, g laucophane, epidote, actino lite, tremolite and tourma line. It reflec ts the derivation of sed iments from granite gneiss, schi stose rocks and charnockite .

Factor II is represented by the dominance of euhedral, rounded, outgrown, overgrown, coloured, e lliptical zircon and hornblende. Th is indicates that the contributi on of sed iments is ma inly derived from recycled sedi ments of sandstone, limestone and alluvium.

Factor III is rich in zircon (broken), da rk and light pink garnet, chl orite, andal us ite, topaz and stauro lite. This assembl age points out the inf luence of low grade metamorphic rocks of green schi st fac ies in nature.

The Triangular diagram, prepared using these three factors after normali sing factor components, has shown a c lusteri ng of points in the c nte r sugges ti ng

1I GRANITES .AND GRANITE GNEISS, CHARNOCKITES

0.8

o o

c

o

o MANOAPAM

'* VAlINOKKN/;

eTUTlCORIN 1:, MANAPPAD

o KANYAKlJMARI

1IfL...---r----,~__r-__,--t---._-_,_-~-~---r RECYCLED SEDIMENTS) GR£ENSCHIST f ACIES SANDSTONE,. ALLUVIUM

Fig. 5-Q-Modc i'actor triangul ar diagram on the poly top oi' thrce end mcmbcr".

ANGUSAMY & RAJAMAN ICKAM: BEAC H MORP HOLOGY 293

the possible deri vation of sed iment from all the three different types of rocks (Fig. 5). However, Kanya­kumari block sediments are di stributed close to the terminal indicating recycled sediments. The Valinokkam and Mandapam block sed iments are, however, separated out from Kanyakumari suggesting their derivation fro m granite and green schi st facies, respective ly . The Manappad block is iso lated from the rest by being closer to the factor lIT, in other words, low grade metamorphic rocks.

The different nature of beach confi gurati on, composition and gradient influence the different littoral drift, particular to the wave refracti on pattern . The presence of promontories in Valinokkam and Manappad enable convergence In thi s region. Similarly , the Tamirabarani ri ver mouth also contributes strong convergence directin g the lack of terrestrial sedimentation in the adjacen t beaches. The dominant divergence existing in the Mandapam sp it enables a complete change in the compos ition of heavy mineral assemblage. Moreover, the coasta l configuration is also found to have a strong influence in the distribution of heavy mineral assemblage in the study region.

In view of the above factors, discussed so far on the di stributi on of heavy minerals in the study region, it is inferred that there is no relat ion between catchment mineral assemblage and the rea l di stributi on of heavy mineral assemblage in the coastal sector. It is therefore in ferred that the mineral assemblages in the investigated area are derived from mixed source of sed iments. Further, the incompatibl e heavy mineral assemb lage of the beach sediments with respect to the nature of catchment rocks in five different blocks of the study region has also indicated the possibility of heavy minerals suppl y from offshore.

Acknowledgement Authors are thankful to Department of Ocean

Development, New Delhi , for the financia l assis tance and the authorities of Tamil Uni vers ity for extending all the facilities to complete this work. We record our gratitude to Dr. V.J . Loveson, for hi s ass istance in sample co llect ion, Dr. P.M. Mohan and Mr. P. Udayaganesan for their assistance in factor ana lysis and invalu able suggestions and Mr. G. Ramachandran and Mrs. R. Sivagama Sundari for their cartographi c and typing ass istance.

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