Heavy mineral distribution and sediment movement at ...

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Department of Studies in Geology, Karnatak University, Dharwad - 580003, Karnataka, India. Received ... nance and sediment movement along the study area.
Indian Journal of Marine Sciences Vol. 28, September 1999, pp. 257-262

Heavy mineral distribution and sediment movement at K wada and Belekeri Bay Beaches, west coast of India P T Hanamgond Department of Geology, G.S. Science College, Belgaum - 590006, Karnataka, India

PB Gawali Indi an Institute of Geomagnetism, Colaba, Mumbai - 400 005, India and

V C Chavadi Department of Studies in Geology, Karnatak University, Dharwad - 580003, Karnataka, Indi a.

Received 7 January /998, revised 3/ March /999 The present study on the heavy mineral assemblage from the sediments of beaches was made in order to understand the spatial, seasonal and longshore distributions, source of the sediment (Provenance) and the sediment movement. The study has indicated the presence of Magnetite, Ilmenite, Hornblende, Tourmaline, Sillimanite, Rutile, Garnet, Zircon, Kyanite etc.; they are enriched in tiner sand fractions . The heavy mineral assemblage of this stretch indicates the mixed provenance or Igneous and Metamorphic rocks with reworked sediments especially at Belekeri bay beaches.

The mineralogy of the clastic sediments is important to understand their provenance and transportation history. Each type of source rock tends to yield a distinctive suite of minerals, hence are exceptionally useful clues to the nature and type of source rocks l . 2. Source of sediments and strength/energy of the current carrying the sediments are claimed to be the influencing factors of grain size characters and mineralogical composition 3 , and the light minerals such as feldspars are impoverished along the direction of transport 4 •5 . The present work, aims at the understanding of the heavy mineral distribution, provenance and sediment movement along the study area.

beaches are separated by rocky headlands and intermittent sandy stretches, especially between Kodar and Aligadde Beach; and between Mudga and Kodar Beach. The entire coast is bordered by Western Ghats on the eastern side and Arabian Sea on the west. Fifteen locations (Fig. I) were se lected from the Kwada and Belekeri Bay Beaches. The heavy minerals were separated from varying sizes (-60 +80 to -170 +230) of mid foreshore sediment sampl es collected at all the locations along the beach during monsoon (August, 1989). As the concentration of heavy minerals was fairly large6 at Harwada beach, mid foreshore samples collected during postmonsoon

Materials and Methods The investigated area is confined to the coastal tract between Aligadde and Harwada beaches (Fig. 1), situated on central west coast of India. The study area includes four beaches of two bays, Kwada Bay (Aligadde Beach and Kodar Beach) and Belekeri Bay (Mudga Beach and Harwada Beach), which lie between latitudes 14° 42'to 14° 47' N and longitudes 74° 9' to 74° 17' E, and are oriented NW-SE (140° w. r. t N) except Aligadde beach which orients E-W (90° w. r. t N). Belekeri Bay is a sheltered and deeply incised type compared to Kwada Bay exhibiting different physiographic and geomorphic setup. The

14· 47'

'~:::=::=::::I N 14·

L-------------.:.......l-:;;7';;;.1::;;-'7. 42' "og,

Fig. l--Location map of the study area.

258

INDIAN J MAR.

sel., VOL. 28, SEPTEMBER 1999

(November, 1988 and 1989); and samples collected across the foreshore (high, mid and low water levels, at st 13, were also subjected for heavy mineral study. The minerals were identified based on their optical properties. The mineral abundance has been studied by counting individual grains (> 300 grains) and number percentages were calculated.

Results and Discussion The heavy mineral species were identified and quantified in -80 + 120 mesh from the sediments. The percentages of heavy minerals in the beach sediment of the study area (Table 1) range between 0.2% to 89% by weight in -60 +80, between 0.2% to 97% in -80 +120, between 2% to 98% in -120 +170 and between 18% to 94% in -170 +230 mesh. In general, the heavies increase in their percent by weight in the finer mesh sizes. The percentage of heavy minerals by weight increase invariably from st 9 onwards and the concentration is found high at sts 14 and 15. Translucent minerals dominate Opaques in the entire study area except at sts 14 and 15, where the Opaques dominate non Opaques. Among Opaques Ilmenite dominate Magnetite except at st 14. Longshore variability of the heavy mineral assemblages is considerable. Distribution of Opaques, Rutile, Tourmaline and Zircon (Table 2) reveals that the concentrations are found in the southern end of the study area and progressively decrease towards north (Aligadde). Conversely, the concentration of Hypersthene, Sillimanite and Kyanite increase in abundance towards north . . The longshore variations at Harwada beach (Fig. 2) show that- (i) during postmonsoon (Novemberl988) the concentration of heavies are more at sts 12 and 14 compared to their adjacent stations (13 and 15), (ii) during monsoon (August 1989), the concentration of heavies are more at the southern portion, particularly at st 14 the concentration is appreciably high, (iii) during postmonsoon (November 1989) the central locations show high concentration of heavies. The cross-shore variations (across the foreshore , Fig. 3), at st 13 shows that, the percentages of heavies decrease seaward; and are fairly large at the high and mid water levels during postmonsoon seasons (November, 1988 and 1989). This is probably due to the erosion of seaward berm and upper foreshore parts during these seasons. Due to this erosion, the heavies present in the sediment are concentrated owing to the churning effect of waves (swash-backwash). During this process the heavy minerals were dispersed on the

sloping foreshore (from upper foreshore towards lower foreshore), seaward depending upon the density, shape and size of the minerals. The high concentration of Opaques, Rutile, Tourmaline, Gamet and Zircon at sts 14 and 15 indicate that these stations have experienced erosion 7 and high energy conditions during that season. The erosion leading to the concentration of these placers involves the selective removal and transportati on of the light minerals either offshore and or in the longshore direction. This is well supported by the textural study along this stretch 8 . Figure 4 shows the compositional variations of heavies/lights (index I), the ratio of thei r respective weights 7 • The value of 'I' is higher at sIs I , 10, 14 and 15 (maximum being at st 14). Station I is located near the Manzel Creek; sts 14 and 15 are located near Belekeri river; and st \0 is near to the seasonal backwater creek at Mudga; where erosion of the beach and berm persists involving selective transportation and concentration of heavies. However, re st of the locations show I = < I . Therefore the hi gh concentration of heavies occur at the Belekeri Bay, wh ic h is further supported by the longshore di stribution of Opaques (in glkg, Fig. 5). From this observation it is clear that, there is a relation between energy and concentration Postmonsoon 1989 Monsoon 1989 Poslmonsoon 1988

o

20

40

60

80

100

Heavy wt % in 120 mesh OSln 12 • SIn 13 IIStn 14 Cl Stn 15

Fig. 2-Seasonal and annu al vari ati on in wei gh t percentages of heavy minerals along Harwada beach.

postmonsoon~;;;=;==~~~~~ 1989 II

1989!~~~~~~=~=~;

Monsoon Postmonsoon

1988

o

4

8 12 Heavy wI % in 120 mesh

16

20

a Low water II Mid water 0 High wa le, Fig. 3--Seasonal and annu al vari atio n in wci ght pcrcentages of heavy mineral s across Harwada beach at station 13.

,,'

HANAMGOND el al.: HEAVY MINERAL DISTRIBUTION AND SEDIMENTS MOVEMENT

259

Table I-Weight percentages, heavyllight (HIL) ratio and glkg of minerals in the mid tide sediments St. no.

Sample no.

Fraction no.

Heavy mineral wt%

Light mineral wt%

Magnetic at O.IA

Magnetic at 0.4 A

Non magnetic at 0.4 A

H/L ratio

Opaques g1kg

IM9

80 120 80 120 80 120 80 120 170 80 120 170 230 80 120 80 120 80 120 170 230 80 120 170 80 120 170 230 80 120 170 80 120 170 230 80 120 170 80 120 170 230 80 120 170 230

01.07 06.40 00.53 04.97 00.51 03.85 00.27 01.41 11 .93 00.15 01.54 17.85 35.32 00.42 00.48 00.30 03.06 00.25 00.22 01.73 18.37 00.77 04.84 26.95 08.92 18.50 69.00 93 .90 06.48 09.25 29.30 06.84 06.26 17.38 43 .59 06.33 05.00 06.94 89.35 96.57 97.73 92.10 08.21 18.70 45 .10 67 .90

98.93 93.60 99.47 95.03 99.49 96.15 99.73 98.59 88.07 99.85 98.46 82.15 64.68 97.88 99.52 99.70 96.94 99.75 99.78 98.27 81.63 99.23 95 .16 73.05 91.08 81.50 31 .00 06.10 93 .52 90.74 70.70 93 .16 93.74 82.62 56.41 93.67 95 .00 93.06 10.65 03 .43 02.26 07.90 91.79 81.30 54.90 32.10

04.14 02.00 00.53 00.48 00.65 01.00 06.45 05.10 05.00 01.35 01.15 00.33 05.80 01.05 00.39 01.54 01.05 00.99 01.14 01.74 04.63 02.00 00.22 00.31 01.99 02.91 08.68 31.45 01.35 37.93 05.05 01.67 01.25 01.31 22.13 03 .50 03.67 04.88 32.13 46.26 53.97 65.28 12.44 14.01 14.05 90.27

11.92 16.00 11.17 08.70 06.53 08.00 05.64 10.54 10.67 24.32 14.94 08.91 42.03 09.47 15.63 15.38 13.68 05.94 12.50 04.65 06.48 11 .00 09.67 04.10 16.25 18.06 28.58 53.17 13.88 05 .17 10.10 10.74 08.27 06.02 09.84 06.95 07.82 07.41 32.78 34.75 38.80 29.86 18.88 27 .35 29 .72 00.54

83.94 82.00 88.30 90.82 92.81 91.00 87.90 84.35 83.42 74.32 83.90 90.76 52.17 89.47 83.98 83.10 85.20 93.07 86.36 93.60 88.80 87.00 90.10 95.61 81.75 79.03 62.74 15.38 84.76 56.89 84.85 87.58 90.49 92.67 68 .03 89.55 88.50 87.71 35.09 18.98 07.23 04.86 68.68 58.64 56.22 09 .19

0.011 0.068 0.005 0.052 0.005 0.040 0.002 0.014 0. 135 0.001 0.020 0.220 0.550 0.004 0.004 0.003 0.032 0.002 0.002 0.018 0.230 0.007 0.050 0.370 0. 100 0.230 2.230 15.390 0.070 0.102 0.420 0.073 0.070 0.210 0.780 0.070 0.053 0.080 8.400 28.150 43 .240 11.700 0.009 0.230 0.821 2. 150

160.62 180.00 117.00 091.78 071.90 090.00 120.97 156.51 166.00 256.76 160.92 092.40 478 .30 105.26 160.16 169.23 147.37 069.31 136.36 064.00 116.50 130.00 098 .99 044.00 182.50 209 .73 372.60 846.00 140.15 431 .03 151.50 124.19 095.13 073 .00 320.00 104.51 114.99 123 .00 649 .08 810.16 927 .70 951.40 3 13. 13 41 3.61 437.75 908.00

2

2M9

3

3M9

4

4M9

5

5M9

6

6M9

7

7M9

8

8M9

9

9M9

10

IOM9

II

I1M9

12

12M9

13

13M9

14

14M9

15

15M9

.....

...,

Note: 0eagues (at 0.1, 0.4 A) and non Oeague minerals (at 0.4 A) were seearated b:t Iso d:tnamic masnetic seearator.

of heavies. It is observed from the earlier studies6. 8. 9 that, the Harwada beach in Belekeri Bay and Aligadde beach in Kwada Bay experience higher energy conditions, which is mainly due to the presence of Belekeri River and Manzel Creek in the respective

bays; and also due to presence of Arge headland and Arge cape at Aligadde beach . The variations in heavy mineral distribution are also studied using simple statistical correlation coefficient analysis. The correlation coefficient (r) bet-

INDIAN J MAR. SCI. , VOL. 28 , SEPTEMBER 1999

Table 2-Distribution of different species of heavy minerals in the Kwada and Bclckeri Bay b cachc~ ill 120 Il1c,il S:unplc no.

Opaques (wt %)

IM9 21'.19 31'.19 4M9 5M9 61\19 71'.19 8M9 9M9 IOM9 IIM9 12M9 13M9 14M9 15M9

13H9 13M9 13L9

:::x

100

§.

10

Rut

Gar

18.00 09.18 09.00 15.64 16.09 16.02 14.73 13.64 09.89 20.97 43.10 09.52 11 .49 81.01 41.36

11.14 05 .53 05 .90 07 . 14 04.60 06.09 06.8 3 21.90 32. 13 51.74 36.3 1 40.88 27 .56 67 .41 40.76

05 .87 07.69 05 .31 06.83 04.91 04. 17 03 .73 07.49 02 .1 0 02.41 04.47 05 .00 09 .59 06.41 02. 17

Number ~ercenta~es of translucent heav~ minerals Sil Hbl Hyp Kyn Tou Longshore vari ation 35. 19 04 .99 00.59 40. 18 02.05 60.65 15.68 05.03 05.62 60.47 03. 53 16.52 00.88 06.49 58.39 23.91 00.93 02. 17 58.59 12.58 13. 19 03.99 58.97 14.74 12.50 03.53 64.29 18.94 03 . 11 03 . 11 47.55 16.43 01.44 00.58 04.61 42 .04 07.5 1 12.01 04.20 32.17 04.56 03.49 04.56 37.71 05 .87 01.68 06.15 04.47 32.35 07 .94 04.41 00.59 08.82 20.35 04.94 04.65 02.91 11.70 00.28 12.53 12.50 01.90 33.17 05.98

16.31 11.49 11.70

59.0 1 57.56 53.74

05.23 • 09.59 04.1 6

18.60 20.35 28 .25

Shore normal variation 04.94 04.94 04.65 04.94 04.99 03.60

-+-80 mesh

Gl "0

-+-120 mesh

0

i

II:

.E

0.1

Ol

:J

.....

~

0.01