Geo-environmental appraisal of the Meda creek, Saurashtra, Gujarat

JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.75, May 2010, pp.695-703

Geo-environmental Appraisal of the Meda Creek, Saurashtra, Gujarat JAYENDRA LAKHMAPURKAR1 and NILESH BHATT2 1

Gujarat Ecology Society, 3, Synergy House, Subhanpura, Vadodara - 390 023 2 Department of Geology, M.S. University of Baroda, Vadodara - 390 002 Email: [email protected]

Abstract: Water chemistry, sediment texture, clay mineralogy and foraminiferal contents from the bottom of Meda creek were studied to assess the geo-environmental status of the creek. Water quality data for three seasons suggests domination of marine environment as pH remained above 8 and salinity above 35‰ throughout. Clay dominate the bottom sediments, except near mouth. Montmorillonite, illite and kaolinite are the major clay minerals in the sediments. In absence of any source rock in the catchment of the Meda creek, the presence of illite and kaolinite indicates their transportation and depositions from near coastal waters during high tides. Ammonia sp. is the most dominating foraminifera. Reworked forms as well as angular asymmetric forms of foraminifera were dominant in clay rich areas of the creek. Keywords: Geo-environment, Clay minerals, Foraminifera, Creek, Saurashtra, Gujarat.

INTRODUCTION

STUDY AREA

Tidal creeks or creeks are widespread and abundant estuarine ecosystems, yet their ecological relevance is undervalued as reflected by the lack of research (Mallin and Lemitus, 2004). Due to human intervention the typical estuarine environment is lacking in many estuaries of the world. These human interventions include release of pollutants and constructing dams and barrage across the channel. Barrage construction is mainly done for the purpose of harvesting tidal power, fresh water storage and to control salinity ingress. In general, there is a dearth of study on tidal creek environment and only a very few studies are available giving detailed ecological status of a creek on post barrage conditions. However, these studies indicate that building barrage on the estuarine part, adversely affects the ecosystem (Sinha et al. 1996). Major impacts reported are reduction in freshwater inflow, increase in salinity regimes, reduced nutrient availability and movements of aquatic species (Mirza and Sarkar, 2004). Gujarat is endowed with the longest coastline of 1640 km. The coastline is marked by several small and large estuaries and creeks. In most of the estuaries tidal flow has stopped because of construction of barrage. Meda creek is one such estuary where a barrage was constructed in 1973 A.D. The present paper attempts to evaluate the geo-environmental status of this creek in post barrage condition.

Meda creek is located on western Saurashtra coast between Porbandar and Dwarka at Latitudes N 21°49.25' to 21°51.75' and Longitudes E 69°22.15' to 69°24.00' (Fig. 1). It remains as creek (sea inlet) during winter when fresh water does not come from the inland areas, and turns into a lagoon during summer when the spit extends northward and closes the mouth. Only during monsoon it turns into an estuary having interplay of saline and fresh water. The coastal stretch is marked by high wave energy with moderate tidal amplitude (Sengupta and Deshmukhe, 2000). Five seasonal rivers, Vartu, Sorti, Sindhi, Falku and Kaman meet the Arabian Sea through this creek; except three months of monsoon, all of these rivers remain dry. Geomorphologically, the Meda creek display a mosaic of landforms like beach/mouth bar complex, tidal channels, tidal flats, ancient tidal flats, coastal cliffs, spit and coastal plains (Fig.2). In 1973 A.D. as a part of mission against salinity ingress by the Kharland Development Board of Gujarat a barrage was constructed at about 3 km from the shore, which stopped the ingress of seawater further inside. The barrage also help store the freshwater runoff during the monsoon periods, which is later on used for the irrigation purpose. This has resulted into large-scale changes in the landforms of the area. As per SOI topographic sheet No.41G/5 (1970), 4.64 sq km area in the Meda creek was covered under mangroves. Barrage has lead to a large-scale loss of the mangroves and now a small patch of the scrubby

0016-7622/2010-75-5-695/$ 1.00 © GEOL. SOC. INDIA

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GUJARAT Vadodara Porbandar

Diu

Arabian Sea

4

Harshad

2 3

1

Barrage

Bridge

Miyani

21° 50’

5

Sampling points

N

AR A

BI AN

SE A

69° 20'

1 km

69° 24’

Fig.1. Map showing locations of the samples in the Meda creek, Gujarat.

and sparse mangroves dominated by a single species of Avicinia sp. (Singh, 2000) can be seen confined to a small patch on the right bank of the creek. Geologically, the catchment of Meda creek is dominated by the Deccan Trap Formation, mainly represented by the basalt and its derivatives. Porphyritic basalt with numerous 69° 24’

69° 20’ Shore platform Sand shoal Beach ridge/spit

joints is the most common rock type encountered in large part of the study area but, amygdaloidal basalt flows are also outcropped locally. The Deccan Trap is exposed in the form of NNW- SSE trending dykes around Movan, Ramgadh and Sidhpur in north and northeast of the Meda creek. The Harshad hill on western bank of the Meda creek also represents the Deccan Trap Formation. The Deccan Trap is covered by laterites that extend in a linear manner northwards from the Meda creek area. The rocks belonging to the Gaj Formation of Miocene age can be observed in some of the well sections and Meda-Kindari link canal trench in the form of fossiliferous marlstone bands within the Ashapura Clay Member of the Gaj Formation as well as the Kalyanpur Limestone Member of the Dwarka Formation (Bhatt, 2000). The deposits of Miliolite Formation occur in the form of costal cliffs, shore platforms, coastal dune ridges and obstacle dunes. They contain allochems and lithoclasts cemented in micrite and fine grained sparite cements. The coastal occurrences of Chaya Formation are mainly exposed as cliffs and benches, and are rich in large bioclasts like bivalves, gastropods, corals, algae and also fragments of older miliolite units. The study area is covered by the sediments of Holocene age in a variety of coastal geomorphic forms like beaches, spit, bars, coastal dunes, active mudflats, ancient mudflats and coastal alluvium. The set up of the Meda creek has facilitated the deposition of these sediments. Mouth of Meda creek is dominated by the wave formed landforms like sandy beaches, spits and mouth bar with sand shoals. The ancient mudflat areas above high waterline merge with the intertidal mudflats with similar sediments. They indicate higher level of the sea during the recent past.

Tidal channel

METHODOLOGY

Tidal flats Ancient tidal channel Ancient tidal flat Ancient beach ridges Harshad Hill Cliffs

Barrage

21° 50’

N

ARABIAN SEA

1 km

Fig.2. Geomorphology of the Meda creek and adjoining area.

Water sampling was carried out from the Meda creek during three seasons viz. pre-monsoon (April), monsoon (June) and post-monsoon (September), at 1 meter depth using Niskin water sampler from five selected stations (Fig.1). The water samples were analyzed for its pH, salinity, nutrients and DO properties, following the standard methods (Grasshoff et al. 1983). Sediment samples were collected by Van Veen Grab sampler from these five stations and analyzed for sedimentological and micropaleontological characteristics. The sand-silt-clay ratio was estimated by pipette method following Folk (1974), and clay mineralogy was done following Poppe et al. (2001) using Rigaku’s Ultima-II automatic XRD machine in the laboratory of ONGC at Vadodara. The samples were dispersed in distilled water and JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

GEO-ENVIRONMENTAL APPRAISAL OF THE MEDA CREEK, SAURASHTRA, GUJARAT

sodium hexametaphosphate solution was added to it. After a wet sieving sand size particles were taken for the separation and study of foraminifera. A genus level classification has been attempted using standard literature (Loeblich and Tappan, 1988; Murray, 2003; Buzas and Severin, 1982; Debenaya et al. 2001; Nigam and Khare, 1999; Rao et al. 1987; Talib and Faruqui, 2007; Kathal, 2005; Gandhi et al. 2002; Juvaux and Scott, 2003). Total number of foraminifera specimens per genus per sample was calculated. The relative abundance was studied by using the total foraminifera number (TFN) standardized to 1 gm of the sample. Morphogroups of the foraminifera were classified following the criterion of Severin (1983). The reworked foraminifera were identified based on their earthy look, abraded, polished and broken surfaces (Nigam and Shetty, 1980). Diversity of the foraminifera was analyzed following Shannon–Weiner formula (Simpson, 1949). RESULTS Physicochemical Environment

The water quality analyses of the Meda creek suggest a dominant influence of the seawater in comparison with the freshwater outflow from the rivers (Fig. 3). Total Suspended Solids (TSS) in the Meda creek water varies from nearly 300 mg/l to 490 mg/l with an exceptionally low value of 161 mg/l near the creek mouth. TSS is minimum at Station 4 where sand dominates the bottom sediments and the waves are not strong enough to bring it into the suspension. The minimum TSS at Station 5 is due to sandy nature of the sediments. In general, the average TSS value varies from 350 to 425 mg/l. pH varies in the range of 8.19 to 8.89 that indicates a profound control of the sea on the water quality of the creek (Fig. 3a). The lowest value of pH has been recorded near the Miyani jetty; this marginal reduction could be due to release of fresh water as sewage of the village. Average pH remains lower at Station 1 (8.44) and Station 3 (8.55) that could be due to acid generation by the decay of organic waste brought from the adjacent settlements and tourism activities. The pH value is maximum at Station 5 (8.76), close to the mouth, indicating high influence of the sea. Salinity of the water samples varies from 35 to 44‰ indicating a high salinity nature of the creek water (Fig. 3b). The average salinity being lowest at Station 1 (36.6‰), reflects the discharge of sewage water from the near by fisherman village, Miyani. Station 4 shows much higher salinity indicating its isolation and salt concentration due to evaporation. Lowest salinity is recorded during September, with average salinity going little below 40 ‰, which JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

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can be attributed to the fresh water input during monsoon. Concentration of nitrite nitrogen was found lower (0.024 mg/l) at stations 1 and 3 in comparison with other three stations (Fig. 3c). Nitrite nitrogen varied within a narrow range from 0.0013 to 0.0030 mg/l during premonsoon, which marginally increases to 0.0036 mg/l in postmonsoon samples. This indicates its positive correlation with the lower organic load and higher pH during summer. Nitrate nitrogen concentration varies from 0.074 to 0.215 mg/l (Fig. 3d). Average nitrate nitrogen value shows high concentration at station 1 (0.144 mg/l), which can be related to freshwater disposal and related algal growth on the bank of Miyani village. However, the concentration drastically reduces at Stations 2 (0.097 mg/l) and remains more or less constant at other Stations. This also supports the inference that the high nitrate at Station 1 is only a localized effect. Phosphate concentration in the creek water remains within the range of 0.013 to 0.037 mg/l (Fig. 3e). Station 5, on the mouth and station 4 down the bridge showed higher average values. Increased biological activities and fresh water inflow leading to dissolution of calcium phosphate from planktons can be seen during June as an increased phosphate value. Organic phosphate has been recorded in the range of 0.001 to 0.01 mg/l. Organic phosphate concentration is maximum (0.01 mg/l) at Station 5, near the mouth of the creek close to the calcareous sand, followed by Station 4 (max. 0.008 mg/l) under the bridge (Fig. 3f). These indicate a presence of organic source at these locations. The average concentration declines from pre-monsoon (0.04 mg/l) to monsoon (0.01 mg/l) time and again increases in postmonsoon period (0.06 mg/l). In general, Dissolved Oxygen (DO) availability varies in the range of 3.30 mg/l to 4.45 mg/l (Fig. 3g). Average DO reduces from March (4.21 mg/l) to June (3.72 mg/l) indicating increased biological activity as well as less frequent replenishment of DO by the sea, whereas, during September, sea water and fresh water influx contributes to the increased DO (4.35 mg/l). Throughout the year, Biochemical Oxygen Demand (BOD) varies within a narrow range of 0.41 to 2, indicating a healthy habitat nature of Meda creek. Average BOD remains high at station 1 and 3, due to the waste disposal on both the banks (Fig. 3h). Sediment Texture and Composition

In general, grain size analysis of the Meda creek shows that the bottom sediments are dominated by clays followed by silt (Table 1).

JAYENDRA LAKHMAPURKAR AND NILESH BHATT

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45

8.8

43

pH

Salinity %o

8.6

8.4

8.2

41 39 37 35

8 H1

H2

H3

H4

H1

H5

H2

H3

(a)

H5

(b)

0.005

0.25

Nitrate-N mg/l

Nitrite-N mg/l

H4

Stations

Stations

0.003

0.2

0.15

0.1

0.05

0.001 H1

H2

H3

H4

H1

H5

H2

Stations

H3

H4

H5

Stations

(c)

(d)

0.04

Organic-P mg/l

Phosphat-P mg/l

0.012

0.03

0.02

0.01 0.008 0.006 0.004 0.002

0.01

0

H1

H2

H3

H4

Stations

H5

H1

H2

Stations

H3

H4

H5

(f)

(e) 4.6

2.7

BOD mg/l

DO mg/l

4.2 3.8 3.4

2.1 1.5 0.9

3

0.3 H1

H2

H3

H4

H5

H1

Stations

H2

June

H4

H5

(h)

(g) March

H3

Stations

September

Average

Fig.3. Seasonal variation in the physicochemical parameters of the Meda creek water. For details see text.

Station 5 being close to the mouth bar is dominated by sand fraction. This indicates the bottom sediments at this Station have composition similar to that of the mouth bar and have sub aerial continuity of the mouth bar. Finer grain size at other stations is attributed to the mouth bar, which absorbs all the wave energy. Therefore, the creek almost

behaves as sheltered basin even from the landward side due to the barrage. Clay Mineralogy

Peak values of XRD plots of the raw data indicate presence of clay minerals like smectite, illite and kaolinite/ JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

GEO-ENVIRONMENTAL APPRAISAL OF THE MEDA CREEK, SAURASHTRA, GUJARAT Table 1. Sand, silt and clay percentage in the creek bottom sediments at various stations Sample No.

Sand

Silt

Clay

1 2 3 4 5

0.84 1.54 2.79 0.52 96.52

37.54 25.72 26.44 22.26 3.48

61.62 72.74 70.77 77.22 -

chlorite (Fig. 4). Smectite peak is the tallest in sample 4 followed by sample 1 and sample 2. In the study area major source of smectite must be the weathering of Deccan Trap basalt in the upstream, which gets transported by seasonal rivers as suspension load during monsoon. Smectite is also contributed by rivers of adjacent basins

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discharging the smectite into the Arabian Sea, which in turn enters into the creek during high tides. The presence of montmorillonite was confirmed by XRD analysis after its treatment with ethylene glycol; as after glycolation the peak intensity has increased and is shifted towards lesser 2θ angle i.e. around 5 (Fig. 4). Illite shows almost reverse trend compared to the montmorillonite, with maximum intensity at Station 2 and minimum at 4. Illite clay is a weathering product of alkaline rocks. However, upstream of Meda creek does not have major exposure of any alkaline rock, and therefore there are negligible chances of this mineral being derived from the upstream provenance. The illite is well represented in the sea sediments and in sea water as suspension load. Therefore, the presence of illite can be linked with the suspension load entering during high tide in

Smectite Illite1 Illite3

Kaolinite1 Kaolinite2 Illite2

Sample 4 Sample 2

Sample 1 2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Heated at 550° Glycolated Untreated Glycolated

Untreated Heated 2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Fig.4. XRD patterns of the clay samples from creek bottom sediments showing prominent peaks of illite, smectite and kaolinite confirmed using glycolation and heat treatment. JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

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JAYENDRA LAKHMAPURKAR AND NILESH BHATT

to the creek. Third major clay mineral present is kaolinite. There is not much variation in peak intensity of the kaolinite in the sample of the study area. Foraminifera

Total 22 benthic forminiferal species has been identified from the study area (Fig. 5), and this distribution within the Meda creek is shown in Table 2. The foraminifera recorded from the Meda creek bottom sediments are belonging to the suborders Milioliina (Quinqueloculina, Triloculina), Rotaliina (Ammonia, Cibicides, Rosalina, Astrorotalia, Rotalidium, Elphidium, Nonionella, Nonion) and Textularina (Loxostoma, Bolivina). The Ammonia emerges as the most dominating genus contributing to 45 % of the total population. This is followed by the Quinqueloculina sp, contributing about 15 % of the total population, which indicate low energy conditions of the Meda creek. These are followed by Elphidium (11%), Triloculina (9%) and Rotalidium (8%), indicating that the habitat conditions are favourable to both, Miliolidae and Rotaliina. The total foraminifera number (TFN) shows that the Stations 2 (TFN 216) and 3 (TFN 198) with silty clay bottom are most favoured by the foraminifera, followed by the Stations 1 (TFN 187) and 4 (TFN 173) having clayey silt. TFN is minimum (107) at Station 5 with the sandy bottom. Though rounded symmetrical forms dominate the creek, angular asymmetrical forms also show their significant presence at Stations 2, 3 and 4. The reworked foraminifera have highly polished and severely abraded nature, indicative of their transport by waves and currents. Interestingly, two types of reworked foraminifera have been found in the study area; (1) reworked fossilized foraminifera eroded from surrounding miliolite rocks, (2) recently dead forms with intra basinal transportation. The older foraminifera could be easily distinguished with smooth rounding of the test and are difficult to identify (Nigam and Shetty, 1980). Also, they have filling of secondary material and secondary mineralisation due to diagenetic processes. This type of foraminifera are maximum at Station 4, the inner most station of the creek. The reworked foraminifera belong to the genus Quinqueloculina, Cibicides and Ammonia. Recently reworked foraminifera show relatively less earthy colour, polished and partly broken tests indicative of short distance transport. Station 2 has maximum (29.94%) number of reworked forms followed by Station 3 (27.27%) whereas, Station 5 and 4 have recorded lower percent of reworked foraminifera.

DISCUSSION

The study has shown an increase in marine influence over the fresh water as indicated by water quality, sediment texture and foraminiferal species composition in the Meda creek area. There is dilution of salinity and enrichment of nutrients as observed in monsoon samples which may not be directly related to inflow from the catchments. Although the Meda creek has large catchment, factors like low rainfall, several dam schemes and the barrage constructed immediate upstream of the creek hinders entrance of freshwater into the downstream. However, no study is available for the similar parameters before the construction of barrage and so, direct comparison is not possible. The recovery of charophytes and brackish water pterapods from the subsurface samples (Lakhmapurkar, 2007) and presence of mangrove swamps much beyond the place of barrage (SOI topographic sheet No 41G/5, 1970) indicate a relatively less saline condition and regular freshwater discharge through the Meda creek during pre-barrage period. Domination of clay, except near the creek mouth, indicates sheltered nature of the basin. Mouth bar formed due to long shore currents forms a barrier, and absorbs and stops the wave energy from entering into the creek. Presence of montmorillonite clay is obvious as it is a weathering product of the basalts which are commonly found in the catchment area and being dominant rock types of the Saurashtra plateau. Kaolinite and illite, found are the weathered products of acidic igneous rock. However, there is no major acidic igneous rock or mica rich rock in the catchment of the creek. Although, a part of the Barda Hills consists of granophyres (Merh, 1995) but, it remains out of Meda catchment. Illite and kaolinite is dominantly present as suspension load in the coastal waters and continental shelf region of the Arabian Sea (Chauhan, 1994). Therefore, it can be inferred that these clay minerals are contributed by the sea. On comparing the Meda creek bottom sediments with those of the upstream of barrage, it is found that the sediments of this part are coarser and its clay mineralogy is also indicative of fluvial dominance (Lakhmapurkar, 2007). Profoundness of saline waters and low energy conditions in the Meda creek is reflected in the foraminiferal species composition. However, changes in microenvironments within the creek, indicated by water quality and sediment composition, seems to have some bearing on the species distribution. Ammonia sp. is the dominant species throughout the creek. This must be due to adaptation of the genus to the large variation of salinity. It also prefers fine sediments and a shallow depth (Goldstein and Moodley, 1993) and so, finds this creek as a favourable habitat. JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

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Fig.5. Photomicrographs of the identified foraminifera from the Meda creek bottom sediments. (1) Ammonia beccarii (Linne) (1a ventral, 1b dorsal), (2) Elphidium crispum (Linne), (3)Elphidium indicum Cushman, (4) Cibicides pseudoungeriana (Cushman), (5) Cibicides refulgens Montfort, (6) Quinqueloculina seminulum (Linne), (7) Quinqueloculina tenagos Parker, (8) Quinqueloculina vulgaris d’ Orbigny, (9) Quinqueloculina oblonga (Montagu), (10) Quinqueloculina curta Cushman, (11) Quinqueloculina undulose-costata Terquem, (12) Triloculina insignis (Brady), (13) Triloculina sp., (14) Pararotalia sp, (15) Rosalina globularis d’Orbign y (1a ventral, 1b dorsal), (16) Rotalidium annectens (Parker and Jones), (17) Nonion depressulus (Walker and Jecob), (18) Cancris oblonga Montfort, (19) Loxostomum sp. (20) Bolivina sp JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

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Table 2. Foraminifera species distribution in the Meda creek No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Species

Sampling stations

Triloculina insignis (Brady) Quinquiloculina curta Cushman Quinqueloculina tenagos Parker Triloculina sp. Quinqueloculina vulgaris d’ Orbigny Quinquiloculina undulose-costata Terquem Q. oblonga (Mintagu) Q. seminulum (Linne) Bolivina sp Loxostomum sp. Elphidium crispum (Linne) Elphidium indicum (Cushman) Ammonia beccarii (Linne) Ammonia sp. Cibicides pseudoungerianus (Cushman) Rosalina globularis d’ Orbigny Pararotalia sp. Nonion scaphum (Fichtel and Moll) Cibicides refulgens Montfort Nonion depresulus (Walker and jecobs) Cancris oblonga Rotalidium annectens (Parker and Jones) Species Symmetrical /Asymmetrical Total Foraminiferal Number (TFN) Reworked foraminifera % From Miliolite Recent Diversity

The significance of the variation in the foraminiferal morphogroups has been identified by various workers (Phleger 1956; Khare et al. 1995). The sediment turbulence caused by factors like currents, depths, morphology of shores and monsoon controls the distribution of morphogroups of foraminifera (Jayaraju and Reddi, 1997; Raj and Chamyal, 1998). The angular asymmetrical forms indicate less energy whereas, rounded symmetrical forms indicate turbulent environment. Rounded symmetrical forms are most abundant (ten times high) at Station 5 which is right on the mouth of the creek, indicating higher energy conditions and influence of the sea waves. The same forms show five times higher occurrence at Station 1 close to the fishermen jetty of Miyani which is frequently traversed by boats. This station lies on the lagoon terrace where breaking of waves might be leading to an increase in turbulence. These facts further substantiate the relationship between rounded symmetrical forms and the higher energy conditions. There is also a positive correlation between clay content and angular asymmetrical forms. The stations marked by higher percentage of angular asymmetrical forms also have a lower abundance of reworked foraminifera.

1

2

3

4

5

6.1 4.5 1.5 4.5 6.1 4.5

1.3 7.8 5.2 3.9 5.2 1.3 2.6 2.6 39.0 19.5 3.9 1.3 1.3 5.2 14 3.5 198

4.2

60.6 6.1 1.5 1.5 3.0 11 5.2 187

2.5 19.0 3.8 2.5 1.3 6.3 6.3 30.4 12.7 1.3 5.1 1.3 2.5 1.3 3.8 15 3.1 216

2.8 1.4 1.4 15.5 26.8 5.6 1.4 7.0 1.4 9.9 15 2.9 173

5.8 3.8 1.9 3.8 13.5 13.5 19.2 5.8 1.9 7.7 23.1 11 10.6 107

2.82 16.9 2.209

29.94 3.224

1.14 27.27 3.529

48.94 14.89 3.506

1.33 13.33 2.686

4.2 8.5 8.5 1.4

Species diversity indicates overall impact of the creek environment on the foraminifera. Species diversity is lowest at Station 1 and 2 and maximum at Station 3 followed by the Station 4. There could be several reasons for this but, the most prominent are lower salinity due to fresh water discharge and high TSS indicating turbid water. Sensitive species were either absent or in fewer numbers at Station 1. In contrast, sturdy Ammonia beccarii is dominant contributing 60% of the total population. From the above discussion it can be concluded that the geo-environment of the Meda creek is influenced by upstream barrage reducing fresh water income that has resulted in to an increased influence of the sea in terms of water quality, clay mineralogy and presence of foraminifera and mouth bar which absorbs all the wave energy, making it as sheltered lagoon. As far as foraminiferal diversity and morphogroups are concerned, none of the parameters singularly control the distribution of foraminifers, and so the foraminifera as a proxy of environment point towards more than one geo-ecological variable. Acknowledgements: This forms a part of doctoral JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010

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research of first author (JL). The chairman, Gujarat Ecology Society, Vadodara is thanked for kind permission. NB acknowledges the financial support from the DST, New Delhi (SR/S4/ES-21/KW/P6) for fieldwork. The Department

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of Geology, M.S. University of Baroda is gratefully acknowledged for all the infrastructural support. Dr. K.K. Das, ONGC Ltd. and Mr. Unmesh Wangikar, GES are acknowledged for XRD and chemical analyses, respectively.

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(Received: 6 April 2009; Revised form accepted: 13 January 2010) JOUR.GEOL.SOC.INDIA, VOL.75, MAY 2010