Heavy Mineral Contents and Provenance of Late Quaternary Sediments of Southern Kerala, Southwest India
Indian Journal of Geo-Marine Sciences Vol. 42(6), October 2013, pp. 749-757
Heavy mineral contents and provenance of Late Quaternary sediments of southern Kerala, Southwest India
S Anooja, D Padmalal*, K Maya, S Vishnu Mohan & B Baburaj Centre for Earth Science Studies, Thiruvananthapuram 695 031, India *[E-mail: [email protected]] Received 21 March 2012; revised 22 August 2012
Present paper deals with provenance and depositional history of the Late Quaternary sediments including heavy mineral placers in the coastal lands of Kollam district, SW India. Kollam coast is endowed with estuaries, old coastal plains with ridge-runnel systems and barrier beaches. Mineralogical analysis reveals that sediments in the estuarine basins that are seen entrenched over the Neogene sedimentary deposits were derived from dual sources. Heavy mineral residues of the upper estuarine zones are generally garnet bearing and are of alluvial origin. At the same time, sediments in the lower estuary are garnet-free and are derived from the nearby littoral zones during the tidal processes. Heavy mineralogical data together with statistical analysis discloses that the garnet and pyribole-free heavy mineral suite in the beaches and nearby coastal plains of the Kollam coast are primarily derived from denudation of the Neogene sedimentary deposits in the coastal lands. They are evolved during the rising phases of the sea level in the Late Quaternary period.
[Keywords: Late Quaternary, Heavy mineral, Holocene, Provenance, Neogene]
Introduction Materials and Methods
Southern Kerala coast, south of the Achankovil Shear Area selected for the present study falls mainly within Zone (ASZ) is endowed with coast parallel and coast the coastal lands of Kollam district and partly within perpendicular water bodies. The former falls under the Thiruvananthapuram district. Major landform features ‘Partly Closed’ and ‘Closed’ category of lagoons of the coastal lands of the study area include barrier whereas the latter under the ‘Estuarine Lagoon’ beaches, ridges and swales, tidal flats, lagoons, flood- category. Estuarine Lagoons are seen entrenched over tide islands, bay-head delta, etc. (Fig. 1). The study area the Warkalli and Quilon Formations of Neogene age. is located between North latitudes 8°45'-9°50' and East Holocene sediments in the coastal lowlands, inclusive of longitudes 76°25'-76°45'. The region is generally the Estuarine Lagoons have a maximum thickness of undulating with low altitude hillocks ranging in height between 10 m and 40 m. Study area forms a part of the ~40 m. These sediments are deposited under a complex 8,9 depositional regime of the Holocene epoch marked by South Kerala Sedimentary Basin (SKSB) with fluctuating sea level positions and climatic conditions1. maximum sediment fill of ca. 700 m around Interestingly, the coastal stretch of Kollam and parts of Ambalappuzha. Morphotectonic and sea level oscillation Thiruvananthapuram districts, considered for the present studies of the coastal tracts of the southwestern coast of study, is known for many economically viable and India reveal that a major part of the SKSB is in a strategically significant deposits of heavy mineral submerged block, and areas in the south and north of it placers. A micro-level review of literature reveals that, are characterised by cliffs and bays indicating emergence and subsequent erosion under the rising sea although many studies have been carried out on the 10,11 heavy mineral deposits/contents in the coastal sands of levels in the Late Quaternary period . Though the southern Kerala2-7 adequate attention has not been given region covers only a small portion of Kerala, geologically it is the most important formation in the to unfold the provenance and sedimentation history of 12 these deposits. Therefore, a detailed study has been entire west coast, south of Narmada rift . Estuaries performed here to characterise the quantity and quality along the southwestern part of peninsula such as the of heavy minerals in the finer sand fraction of sediments Kayamkulam estuary, Ashtamudi estuary, Paravur in the coastal lands of Kollam and parts of estuary and Nadayara estuary are seen successively Thiruvananthapuram districts, using a set of borehole towards the southern part of the Achankovil Shear Zone. cores and surface sediment samples. Out of these, the latter three estuaries show antecedent ______characteristics and are entrenched over the Neogene *Corresponding author: sedimentary deposits. In addition to this, Sasthamkotta 750 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013
Table 1 Salient features of various sub-environments of the study area Sl No. Sub-Environment Length Area Width Depth Remarks (km) (km2) (km) (m) River 1 Pallikkal river 42 220 Coastal plain river18 2 Kallada river 121 1699 Mountainous river18 3 Ithikkara river 56 660 Lowland river18 4 Ayroor river 17 66 Coastal plain river18 Lagoon/Estuaries 5 Kayamkulam Lagoon 30 23 3 6 Coast parallel 6 Ashtamudi estuary 16 54 3 10 Coast perpendicular 7 Paravur estuary 5.70 4.16 1.40 7 Coast perpendicular 8 Nadayara estuary 5.20 4.87 1.10 5 Coast perpendicular
Lake, the largest freshwater lake in Kerala, and several dominant sediments. Organic rich sediments lying other wetland bodies like Chelupola, Chittumalachira, below the sand yeilded an age of 6117 ± 101 yrs BP in Polachira, and Kotta lakes, are also located in the Puthenthuruthu borehole and 5350 ± 100 yrs BP in the uplifted block12. Table 1 summarises the salient features Pozhikkara borehole. This clearly indicates that the of the lagoons and their feeder channels. sands in the coastal area have been deposited during A total of 26 borehole cores with a depth range of 6- Middle to Late Holocene. But the initiation of the 32 m were collected using rotary drilling. Upper sand deposition was in the end phase of Holocene Climatic dominant litho units ranging in thickness from 1.5 to 12 Optimum (HCO) when the sea level had risen 3 to 4 m m were chosen for analysis. A total of 115 subsamples above the present sea level11,15. Oldest date recorded in of 10 cm thickness were taken at 1 m interval and were the study area is 12504 ± 148 yrs BP at 31 m in the subjected to the present study. In addition to the Puthenthuruthu borehole. borehole samples, 51 surface sediment samples were also collected from various sub-environments such as Heavy minerals contents beach, older coastal plain and rivers debouching into the The total heavy mineral content in the fine sand estuary and subjected to heavy mineral examinations. fraction of the Kayamkulam lagoon varies from 6.92% Fig. 1 shows the location of the borehole cores and to 13.79% (av. 10.84). Heavy mineral residue surface samples. Sand samples were subjected to dry comprises opaques (av. 72.88%, range: 54.15-87.5%) sieving on a Ro-Tap sieve shaker using a standard set of and sillimanite (av. 23.51%, range: 7.5-42.96%) as the ASTM sieves13. Fine sand fractions were separated major minerals (i.e. mineral with number percentage from the sieve sets and subjected to heavy mineral >5%), zircon as minor mineral (with number percentage separation, using bromoform with specific gravity 2.89 1-5%) and rutile and monazite as the trace minerals at 20°C. Stain/iron oxide coating over the grains was (Table 2). Pallikkal river is the major drainage system removed boiling the sample with SnCl2-HCl mixture bringing sediments from the landward side. River and the mineral grains were spread over glass slides and merges with the lagoon in its southern arm near Vatta mounted using Canada balsm. Heavy fractions in the kayal. THM content in the fine sand fraction of the river fine sands, thus obtained, were studied for mineral varies from 4.85% to 19.57% (av.11.01%). Heavy species following Mange and Maurer14. Radiocarbon mineral residue comprises opaque and sillimanite as the (C14) dates of a few organic rich sediments at specific major minerals and garnet as the minor mineral (Table depths were determined at Birbal Sahni Institute of 2). These three minerals together constitute 95.36% of Palaeobotany, Lucknow for establishing chronological the total heavy mineral species. Rutile, monazite and control of various lithounits including the sand layer in pyribole are seen only in traces. the borehole cores. Based on the energy regime prevailing in the Ashtamudi Estuary16, the entire system can be divided Results into three zones: 1) lower estuary 2) central basin and 3) upper estuary. Lower estuary is subjected to constant Lithologic characteristics ebbing and flooding and has a high energy regime in Figure 2 depicts the lithological characteristics of the most part of the year. Many flood-tide islands are borehole cores selected for the present study. Borehole developed in the landward side of the tidal inlet. cores are generally composed of an upper sand dominant Eastern arm of the upper estuary, influenced by the influenced by the Kallada river, also enjoys high layer which is followed downward by silt and clay ANOOJA et al.: HEAVY MINERAL CONTENTS & PROVENANCE OF LATE QUATERNARY SEDIMENTS 751
Fig. 1 Study area showing locations of surface and boreholecore sediments energy regime due to river influx. Central basin is not mineral suite in the upper estuarine zone is quite considered for the present study as the region is different from that of the lower estuary. THM content floored essentially by silt and clay. Borehole core varies from 4.23% to 46.67% (av. 14.52%). Major retrieved from the Puthenthuruthu island a flood tide minerals noticed in the upper estuary include opaque, island begins with 12 m thick sand which is sillimanite and garnet (almandine variety). Pyriboles subjected to detailed heavy mineral study. THM (pyroxene amphibole); zircon and biotite occur as content in the borehole core varies from 8.27% to minor minerals and, monazite and rutile occur as trace 20.50% (av.14.29%). Heavy mineral species include minerals. THM content in the Kallada river is almost opaque (av. 85.67%) and sillimanite (av. 8.71%) as similar to that of the upper estuary. the major member and zircon (av. 3.96%) as the Like the case of the Ashtamudi Estuary, the energy minor member. Rutile and monazite are recorded in regime prevailing in the lower estuary, central basin trace quantities (Table 2). Interestingly, the heavy and upper estuary are almost similar in the case of 752 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013
14 Fig. 2 Lithologs of the borehole cores chosen for the present study. Note the C dates at specific levels of the borehole cores. Depth is given in metres
Paravur estuary as well. THM content of the lowe Nadayara Estuary is fed by the Ayroor river which estuary varies from 2.61% to 43.78% (14.87%). Heavy is a small coastal plain river (Table 1). In the mineral residue comprises opaque and sillimanite as the Nadayara Estuary, the heavy mineralogical study is major minerals and zircon the minor mineral. Rutile and confined only to the upper estuary. THM content of monazite occur in trace amounts. Upper estuarine region the Nadayara Estuary varies from 3.44 to 14.74% (av. comprises opaque and sillimanite as major mineral, 7.32%). Heavy mineral residue comprises opaques zircon as the minor and, monazite and garnet as trace and sillimanite as the major minerals, zircon and minerals. Ithikkara river sediments exhibit almost garnet as minor mineral, and monazite and pyribole similar content of heavy minerals as that of the upper as trace minerals. Ayroor river exhibits an almost estuary. THM content in the river sediment varies from similar variation in the heavy mineral content as that 8.27% to 13.95% (av. 10.88%). Opaques and sillimanite of the upper estuary. occur as major minerals and, garnet and zircon as the Coastal sand comprises two categories - beach sand minor minerals. Minerals like rutile and pyribole are and strand plain/old coastal sand. THM content in the seen in trace quantities. beach sand between Parvur and Alappad varies from ANOOJA et al.: HEAVY MINERAL CONTENTS & PROVENANCE OF LATE QUATERNARY SEDIMENTS 753
Table 2 Mean and standard deviation of total heavy minerals (Wt %) and various heavy mineral species (number %) in the sediment samples of the study area Location/sample THM Opaques Sillimanite Zircon Rutile Monazite Garnet Pyriboles Biotite Sphene Borehole cores
Puthenthuruthu 14.29 85.67 8.71 3.96 0.46 0.55 0.39 0.32 (8.27-20.5) (79.4-90.69) (4.9-14.16) (2.94-4.72) (0.29-0.64) (0.43-0.64) (0.29-0.49) Pangod 11.11 16.12 45.36 4.21 1.45 11.82 5.74 20.87 1.04 ( 4.23-23.19) (4.37-26.42) (32.2-60.28) (1.25-7.58) (0.63-2.27) (1.04-22.73) (3.0-8.77) (1.54-53.13) Sasthamkotta 26.53 64.61 16.25 1.96 1.29 19.51 3.55 (main) (13.19-46.67) (43.01-86.96) (9.49-29.89) (1.15-2.9) (0.57-2.01) (4.03-28.29) (2.19-5.38) West Kallada 11.51 13.67 26.27 2.22 1.11 45.09 8.49 3.99
(7.45-17.29) (6.98-18.89) (16.67-39.13) (0-4.44) (0-2.22) (33.04-65.12) (2.22-15.59) (1.74-6.67) Munrothuruthu 8.31 35.42 30.20 35.67 7.6 5.25 1.09 0.55 (5.23 -11.77) (24.79-43.17) (14.11-53.55) (25.88-45.45) (5.79-9.41) (4.71-5.79) Ashtamudi 8.15 68.29 16.79 1.59 0.94 6.62 3.78 2.44 0.48 (7.14-9.13) (54.85-79.86) (11.03-23.31) (0.69-2.91) (0.48 -1.39) (1.39-11.03) (2.21-5.34) (1.47-3.4) Kotapuram 11.16 33.96 18.02 2.13 - 12.53 32.21 (10.58-11.63) (29.55-38.89) (14.12-22.22) (1.85-2.35) (10.59-15.43) (20.37-40.15) Kidappuram 15.22 50.03 13.58 2.68 0.71 21.32 5.78 3.47 (13.65-17.14) (41.72-56.9) (10.77-17.81) (1.15-4.10) (0.38-1.03) (12.64-28.83) (1.23-9.04) (1.15-6.75) Pozhikkara 16.47 64.69 29.13 4.08 0.91 0.97 5.89 (2.61-43.78) (27.62 -90.85) (3.88-69.77) (2.62 -6.38) (0.68-1.14) (0.57-1.41) (0.68-11.11) Nedungolam 10.32 38.99 38.53 1.11 1.10 3.86 (4.31-17.38) (15.0-62.74) (17.22-54.74) (0.73-1.63) (0.4-1.63) (0.4-8.76) Adichanalloor 10.83 34.81 62.94 0.88 0.48 - (9.93-12.10) (30.28-41.35) (56.39-67.31) (0.75-0.96) Nadayara 7.32 42.03 52.49 2.49 0.48 1.88 1.28 1.71 (3.44-14.74) (22.72-67.65) (27.94-71.15) (1.62-4.08) (0.40-0.58) (0.58-3.95) (0.86-1.71) Tevalakkara 9.78 64.31 28.51 1.85 1.20 1.36 6.04 (4.51-23.73) (49.6-87.5) (7.50-43.20) (1.60-2.17) (0.86-1.60) (1.09-1.60) (0.8-10.0) Chavara 20.94 87.09 5.67 5.19 0.68 1.35 - (18.35-24.40) (82.09-91.43) (3.09-9.95) (2.86-6.47) (0.50-0.90) (0.62-2.26) Maruthadi 11.22 67.87 30.10 0.98 0.33 0.33 0.33 (8.79-13.65) (55.37-80.36) (17.86-42.34) Kollam 14.12 43.98 52.50 1.62 1.39 1.02 - (13.14-15.10) (40-47.96) (47.96-57.04) (1.02-2.22) (0.74-2.04) Eravipuram 10.98 50.53 46.16 2.80 1.01 0.72 0.3 (3.39-21.44) (23.03-73.43) (19.58-76.36) (0.51-5.59) (0.30-1.86) (0.51-0.93) Ayiramthengu 15.54 45.89 43.18 3.59 0.69 2.39 1.33 0.94 1.17 1.41 (3.93-37.39) (26.67-60.12) (30.35-58.75) (2.42-6.67) (0.62-0.75) (0.62-6.67) (0.68-1.78) (0.62-1.38) (0.68-1.67) (0.68-2.42) Surface sediments
Beach 74.57 83.10 4.42 9.45 1.92 1.62 1.15 (PVR - ALPD) (27.3-99.37) (70.35-93.88) (0.8-14.19) (3.11-20.35) (0.74-3.38) ( 0.45-4.07) (0.68-1.49) Kollam (ASRM- 17.09 55.31 41.72 1.64 1.29 0.45 PLMK) (5.03-32.78) (45.81-64.88) (30.45-51.61) (0.54-3.18) (0.42-1.95) Kayamkulam 10.84 72.88 23.51 2.78 0.44 0.63 0.79 0.5 (6.92-13.79) (54.15-87.5) (7.5-42.96) (1.39-5.08) (0.36-0.55) (0.36-1.17) (0.58-1.0) Pallikkal thodu 11.01 65.28 2.73 0.52 0.70 3.29 1.15 1.15 (4.85-19.57) (36.11-84.82) (1.05-7.89) (0.27-0.85) (0.43-1.19) (0.33-11.97) (0.56 -2.14) (0.43-2.21) Red sand 27.68 60.08 32.38 3.77 3.42 0.69 (22.12-33.23) (59.05-61.11) (31.43-33.33) (2.77-4.76) (2.08-4.76) Warkalli 14.50 62.88 33.77 1.58 (7.82-24.40) (37.27-91.43) (4.29-59.01) (0.62-2.86)
PVR-Paravur, ALPD-Alappad, ASRM-Asramam, PLMK-Pallimukku, THM-Total heavy minerals
754 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013
Table 3 Heavy mineral contents in the Pozhikkara and Pangod borehole cores Sample location and Depth (m) THM Opaques Sillimanite Zircon Rutile Monazite Garnet Pyriboles Biotite Sphene Pozhikkara 1.0 43.78 90.85 3.88 4.23 1.41 3.5 6.29 58.29 37.14 2.86 1.14 0.57 6.5 2.61 27.62 69.77 2.62 10.5 6.79 73.47 20.41 4.76 0.68 0.68 19.5 12.39 82.98 9.57 6.38 1.06 29.0 13.53 65.87 18.65 2.78 0.79 11.11 Pangod 0.5 4.23 23.49 60.28 4.70 1.34 1.68 3.36 1.5 6.02 26.42 59.58 3.63 1.54 1.04 1.54 1.04 3.6 9.51 10.00 42.42 - 14.00 25.00 4.5 5.16 4.37 32.20 1.25 0.63 9.39 7.51 53.13 5.7 23.19 18.94 37.36 7.58 2.27 22.73 3.00 3.00 7.5 13.42 14.91 38.59 3.51 21.93 8.77 8.77 27.30 to 99.37% with an average 74.57%. Among the borehole core which is located in the littoral zone of the two categories of coastal sands, the beach sand exhibits Paravur basin, the THM content exhibited an increasing the highest content of THM. Heavy mineral assemblage trend towards the top of the borehole core (Table 3). consists of opaque, sillimanite and zircon as the major This has been resulted from the constant winnowing of minerals, rutile and monazite as the minor and garnet as finer and lighter detrital grains seaward attributing a the trace minerals. Contrary to beach sand, the strand preferential enrichment of heavies rich in high dense plain sand exhibits marked difference in the content of minerals like opaque and monazite. Contrary to the heavy minerals. Opaques and sillimanite are present as Pozhikkara borehole core, the core collected near the the major minerals, zircon as the minor and, monazite estuarine head at Pangod in the Ashtamudi estuary and garnet as the trace minerals. Content of total heavy revealed marked variation in the distribution of heavy minerals (THM) in the fine sand fraction of the Tertiary mineral species (Table 3). In general, sediments in the sediments exposed in the boundary of the lagoons vary river influenced upper estuarine regions show garnet as from 7.82% to 24.40% with an average of 14.50%. On the major heavy mineral and are derived from the an average, the heavy mineral residue is composed of khondalitic suite of rocks in the hinterlands. However, 62.88% of opaque and 37.12% of non-opaque the upper yellowish layer in the Pangod borehole core is minerals.Non-opaque comprised of sillimanite (av. devoid of garnet compared to the lower unaltered sand 33.77%, range: 4.29 - 59.01%) as the major mineral. layer. This observed variation may be attributed to post Traces of garnet, monazite and some other unidentified depositional oxidation of garnets and other iron heavies are also noticed in the sample. containing less stable minerals like pyriboles (pyroxene represented by hypersthene and amphibole represented Discussion by hornblende) under exposed conditions. Study of detrital minerals received considerable Spatial distribution of heavy minerals in the surface importance as it is one of the reliable tools to unfold sediments of the Ashtamudi estuary reveals that the depositional regimes and source rock characteristics of content of minerals in the estuarine mouth is sedimentary environments17. In the present paper, the substantially high due to the input of heavy mineral rich results of the detailed analysis of heavy minerals in the sands from the adjacent beach/near shore areas 16. fine sand fractions of the coastal lands of southern Spatial distribution of garnet indicated in Fig. 3 reveals Kerala comprising the Kayamkulam, Ashtamudi, the extent of riverine processes taking place in the upper Paravur and Nadayara estuaries as well as the adjoining estuary and adjoining regions. In short, the estuarine landforms are discussed to decode the provenance and head is dominated by river input whereas the estuarine depositional history of sediments. mouth by tidal processes, leaving the central part of the Downcore variations of heavy minerals revealed estuary a calm environment favourable for the marked changes in the quantity and quality of minerals deposition of mud dominated sediments. Such a process in certain borehole cores retrieved from the nearshore could be seen in the Paravur and Nadayara estuaries as regions as well as estuarine heads. In the Pozhikkara well. ANOOJA et al.: HEAVY MINERAL CONTENTS & PROVENANCE OF LATE QUATERNARY SEDIMENTS 755
Table 4 gives the summary of the heavy mineral among the various sources worked out from the heavy investigations in various sub-environments of the coastal mineralogical data is depicted in Fig. 4. It is revealed lands of Kollam district. The interrelationship existing from Fig. 4 that the beach environment is a lone component in the cluster-tree, indicating its unique depositional behaviour under the high energy, wave- dominated regime. This peculiar energy regime is favourable for the deposition of high dense heavy minerals and transportation of low dense (lighter) components by the long shore current. Comparative low content of heavy mineral residue in the older coastal plain may be attributed to the role of aeolian activity in enriching the lighter minerals compared to heavier, denser minerals. Most of the garnet rich upper estuarine samples are closely knitted and deviation if any noticed is attributed to the contribution of garnet poor heavies Fig. 3 Variation of Garnet and Sillimanite along a transect from West Kallada (WK) to Estuarine Mouth (EM); RC River from the Tertiary/ Neogene formations. One of the confluence with the Ashtamudi estuary striking observations noticed in the examination of
Table 4 Summary table of the heavy mineralogical studies carried out in the study area Sl. Environment/ Reach Major heavies Minor heavies Traces (<1%) Remarks/ observations No. sub-envi- (>5%) (1-5%) ronment
1 Kayamkulam Opaques, Zircon Rutile, Monazite Kayamkulam Lagoon is a coast parallel, Lagoon sillimanite partly closed lagoon separated from the Arabian Sea by a barrier beach. 2 Ashtamudi Lower Opaques, Zircon Rutile, monazite Estuary estuary sillimanite Ashtamudi Lagoon is a coast perpendicular 'Estuarine Lagoon' seen Upper estuary Opaques, Pyribole, zircon, Monazite, rutile. entrenched over the Neogene sedimentary sillimanite, biotite formations. garnet
3 Paravur Lower Opaques, Zircon Rutile, monazite. Lagoon character and setting are similar Estuary estuary sillimanite to the above; the lower part of the borehole core (28.5-29m) collected from Upper estuary Opaques, Zircon Monazite, garnet. the estuarine mouth is composed of high sillimanite. content (11.11%) of garnet. 4 Nadayara Upper estuary Opaques, Zircon, garnet Monazite, Lagoon character and setting are similar Estuary sillimanite pyribole. to that of the earlier cases. Garnet is not a major member in the upper estuary; instead the mineral occurs as minor or even in trace amounts. 5 Rivers Opaques, Zircon, pyribole Garnet in some sillimanite, samples, rutile. garnet 6 Coastal sand Beach Opaque, Rutile, monazite Garnet in some The opaque minerals contain substantial (littoral zone) sillimanite, samples. percentage of magnetite. zircon Ridges and Opaque, sillimanite Zircon, Rutile Monazite, garnet The thickness of this sand is <10m in runnels/strand in some samples certain borehole cores, the bottom sand is plains riverine and with high contents of garnet. 7 Red sand Opaque, sillimanite Zircon, Rutile Monazite, garnet. Occurrence of red sand is noticed as pockets, especially in Karunagappalli and Edava. 8 Warkalli Opaque, sillimanite Zircon Monazite, rutile. Warkalli sand stones of Kundara, sand stone Shsthamkotta and Varkala are examined (Neogene under this category. sediments) 756 INDIAN J. MAR. SCI., VOL. 42, NO. 6, OCTOBER 2013
features of high energy hydrodynamic regime. The present study highlights the fact that although the Kerala Khondalite Belt is the primary source of the heavy minerals in the study area, the garnet-free sediments might have evolved from chemical weathering and leaching of the minerals under exposed conditions. Therefore, the probable source of the garnet- free suite of minerals in the study area is the Neogene formations which was subjected to erosion during the rising spells of sea in the Late Quaternary period. On the other hand, the garnet and pyribole suite of minerals in the river mouth areas might have derived from the Kerala Khondalite Belt in the more recent erosive phases of Holocene.
Acknowledgements Authors are thankful to the Director, Centre for Earth
Science Studies (CESS), Thiruvananthapuram and Dr K. Fig. 4 Dendrogram showing linkages existing among various P. N. Kumaran, AGI, Pune for encouragements and sample/sample groups. Note the deviation of beach-borne heavy minerals from the rest of the samples support. Dr. C. M. Nautiyal, Senior Scientist, BSIP, Luknow for C14 dates. One of the authors (SVM) heavy mineral species is that the monazite grains in the acknowledges CSIR, New Delhi for SRF beach and coastal plains resemble to that the Tertiary [09/909(0005)/2012-EMR-I]. sediments. The study highlights that although the Kerala Khondalite Belt is the prime source of heavy minerals in References the study area, the garnet-free suite in the beach and 1 D, Silting up of a Holocene mega lagoon along Kerala coastal plains might have evolved due to chemical Padmalal D, Kumaran K P N, Nair K M, Baijulal B, Limaye weathering and dissolution of Fe- rich minerals under R B & Vishnu Mohan S, Evolution of the coastal wetland exposed conditions prior to deposition in the beach and systems of SW India during the Holocene: Evidence from coastal plains. Further, from the geomorphic view point, marine and terrestrial archives of Kollam coast, Kerala, Quat. Int., 237 (2011) 123-139. the coastal areas of southern Kerala host well developed 2 Rao G P, Sediments of the nearshore region of Neendakara cliffs. A large part of the Tertiary cliff would have been coast and Ashtamudi and Vembanad estuaries, Kerala, India, eroded by wave activity (i.e., cliff retreat) during the Bull. Natl. Inst. Sci., 30 (1968) 513-551. rising spells of sea in the Quaternary period. Therefore, 3 Sajan K, Studies on Mineralogy, geochemistry and Origin of the heavy minerals derived from the Tertiary sediments modern sediments of the Ashtamudi lake, Kerala, PhD Thesis submitted to Cochin University of Science and especially that of the Warkalli Formation, may be the Technology, Kochi, (1998) 199pp. probable source of heavy minerals in the beach, coastal 4 Babu D S S & Thrivikramji K P, Palaeogeographic plain and the nearshore environments. interpretation of Kerala beach placers, southwest coast of India, Ind. J. Mar. Sci., 22 (1993) 203-208. Conclusions 5 Prakash T N, Sediment distribution and placer mineral enrichment in the inner shelf of Quilon, SW coast of India, The content of heavy mineral residue of the sand Ind. J. Mar. Sci., 29 (2000) 120-127. 6 Vinodkumar N, Sedimentology of the placer sands of Kerala dominant sediments ranges from 4.23% to 46.67% in the coast, PhD Thesis submitted to the university of Kerala, Ashtamudi estuary, 2.61% to 43.78% in the Paravur Thiruvananthapuram, (2003) 117pp. estuary and 3.44% to 14.74% in the Nadayara estuary. 7 Ravindrakumar G R & Sreejith C, Relationship between heavy Respective heavy mineral contents in the beach and mineral placer deposits and hinterland rocks of southern Kerala: inland coastal sands are 27.3%-99.37% and 5.03%- A new approach for source to sink link from the chemistry of garnets, Ind. J. Geo-Mar. Sci., 39 (2010), 562-571. 32.78%, respectively. Minerals include opaques, 8 Nair K M, Sajikumar S & Padmalal coast, In National sillimanite and garnet as the major minerals and zircon, seminar on coastal evolution, process and products, KUSAT, rutile, monazite and pyriboles as the minor/trace Kochi, (1998) 12pp. minerals in the river influenced areas. Marine 9 Nair K M, Padmalal D & Kumaran K P N, Quaternary Geology of South Kerala Sedimentary Basin – an outline, J. influenced areas, on the other hand, are generally devoid Geol. Soc. Ind., 67 (2006) 165-179. of garnets and pyriboles. Further, the minerals in the sea- 10 Bruckner H., Late Quaternary shorelines. In: Scott DB et al., ward side are polycyclic and contain surface textural (eds.), Late quaternary sea level correlations and applications, ANOOJA et al.: HEAVY MINERAL CONTENTS & PROVENANCE OF LATE QUATERNARY SEDIMENTS 757
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