holocene and late pleistocene relative sea level fluctuations along the east coast of india

Holocene and Late Pleistocene relative sea level fluctuationsalong the east coast of India

P.K. Banerjee

Department of Geological Sciences, School of Oceanography, Jadavpur University, Calcutta 700 032, India

Received 15 October 1998; accepted 7 March 2000

Abstract

Hermatypic coral colonies and intertidal fossil bearing grainstone, packstone and sandstone beds of Holocene and of a LatePleistocene highstand are exposed above the present High Tide Level (HTL) at a number of locations along the east coast ofIndia from Cape Comorin to Rameswaram. Being a passive margin boundary, free from indications of Late Quaternaryseismogenic movements, this sector provides a benchmark for defining minor relative sea level perturbations during theLate Pleistocene and Holocene highstands along a tropical coast lying between latitudes 58N and 108N.

A series of marine terraces, carved on and locally blanketted by Late Pleistocene biotic and terrigenous accumulations, occurat different elevations (up to 4.4 m) above LTL at Manappad Point, possibly signifying discrete stillstand episodes followed byabrupt intervals of rising/falling sea level.

Sea level indicators of the Holocene highstand occur in this sector, as well as along the fringes of the Godavari delta furthernorth. The Holocene highstand reached nearly 3 m above LTL at 7.3 ka, remained stable for approximately 1.7 kyr and wasfollowed by a relative sea level fall. Between 5.2 and 4.2 ka, there was a second pulse of relative sea level rise of a few metresleading to a fresh spurt in coral growth along the northern coast of Mandapam and Rameswaram. This was nearly contem-poraneous with fresh melting of ice sheets of Antarctica. The Little Ice Age (LIA) witnessed a minor (.1 m) relative sea levelfall along this coast, resulting in rapid diagenetic hardening and infiltration of goethite into the emerged foreshore sand atKarikovil and its neighbourhood. This was followed by a rise of the sea level during the last few centuries.q 2000 ElsevierScience B.V. All rights reserved.

Keywords: Late Pleistocene; Sea level change; Holocene; Little Ice Age; Radiocarbon dates

1. Introduction

A major unresolved issue for most models of theLast Interglacial and Mid- to Late Holocene high-stands is the character of the eustatic sea levelcurve. For example, were these intervals characterisedby a long duration of relatively stable sea level or byepisodes of multiple, high frequency oscillations?(Fairbridge, 1976; Chappell et al., 1983; Kaufman,

1986; Ku et al., 1990; Blanchon and Shaw, 1995;Neuman and Hearty, 1996; Angulo and Lessa, 1997;Stirling et al., 1995, 1998). Sea level curves, based onaccurately dated emergent terraces along continentalor oceanic islands, close to subduction zones or hotspot tracks, e.g. Papua New Guinea (Aharon andChappell, 1986), Barbados (Ku et al., 1990) or Oahu(Szabo et al., 1994) suffer from inherent uncertaintydue to recurrent tectonic displacement at intervals oftens to thousands of years. These locations yield lessdependable proxies than aseismic passive margins.

Marine Geology 167 (2000) 243–260

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E-mail address:[email protected] (P.K. Banerjee).

Another complicating factor is the variable glacio-isostatic response at localities in close proximity toformerly glaciated regions as well as the hydro-isostatic response of the continental shelf to intermit-tent flooding during deglaciation (Clark et al., 1978;Pardi and Newman, 1987; Lambeck and Nakada,1992). These isostatic effects result in non-uniformchanges in the height and age of shorelines. Evenon aseismic coasts far from the Polar belt, localbathymetry and distance from the open sea playsignificant roles.

This paper presents (1) available uranium seriesdates (by alpha spectrometry) of emerged hermatypiccoral colonies and of intertidal shells embedded ingrainstone accumulations on Late Pleistocene marineterraces and (2) radiocarbon ages of emerged herma-typic coral reefs and of intertidal shell beds of Mid- toLate Holocene period, which are exposed at placesfrom Cape Comorin to Mandapam, flanking the Gulfof Mannar (Fig. 1) along the east coast of India.Around the Godavari delta, mid-Holocene intertidalbivalves in beach ridges and estuarine sandstonesprovide a less definitive but compatible sea levelproxy. It is also presented in this paper. Thegeomorphological, lithofacies and geochronologicaldata indicate relative sea level oscillation of a fewmetres during both the highstand periods. Becausemeasurement errors inherent in Th–U alpha count-ing technique are large with 1 s errors oftenexceeding ^10 kyr (Table 1), it has not beenpossible to precisely correlate the Late Pleistocenehighstand indicators along this coast. But there arediagnostic features like a series of marine terracesat Manappad Point (Fig. 1) that indicate a step-wise sea level rise and fall of a few metres duringthis period. Radiocarbon ages for the Holocenesea level indicators demonstrate millenial tocentury scale relative sea level change during thisinterval.

2. Study area and shoreline indicators

Critical exposures are present at the following loca-tions (Fig. 1).

• A: Late Pleistocene1.1. intertidal foraminiferal packstone at Cape

Comorin (Fig. 1, II);

1.2. intertidal shell bearing grainstone with peloidsand abundant bioturbated layers at Idindakarai(Fig. 1, III);

1.3. intertidal to supratidalLittorina, Scapharca,Cardita and Balanusbearing grainstone andpackstone on marine terraces at ManappadPoint (Fig. 1, V); and

1.4. hermatypic coral colonies (Fig. 2), one ofAcroporaand the other totally devoid of thisgenus and dominated byPorites; the formercolony is capped byAcropora-rich rubble andthe latter by a regressive parasequence of algalgrainstone with fragments ofPoritesand gran-ule sized forams as well as byAcropora-richrubble.

• B: Holocene2.5. shallowing upward sandstone parasequence

with a thin bed composed ofScapharcashellsnear Kovakulam, Cape Comorin (Fig. 1, I);

2.6. Poritescolony along the northern foreshore ofRameswaram, underlying shell-rich, friable,shoreface sandstone, exposed along the berm;

2.7. intertidal Anadara sp. bearing siltstone atKaikallur near Kolleru Lake, between theKrishna and Godavari deltas, 36 km inland;and

2.8. sandy beach ridge withArca, Ostrea, Venus,Cardium, Umbonium vestiarium, etc., 1.5 kminland from the Kakinada lighthouse.

Bruckner (1988, 1989) previously reporteduranium series (alpha counting) ages of 1121 8/25, 1201 7/210 and 1241 14/28 ka for coralsand shells sampled from the Pleistocene outcropsof the study area; new radiocarbon dates ofmolluscs from these localities reported in thisstudy also support a Late Pleistocene age (Table1). A few uncalibrated radiocarbon dates for Holo-cene corals exposed on the Rameswaram foreshorewere published by Stoddart and Gopinadha Pillai(1972) and Rajamanickam and Loveson (1990).The present paper provides additional uraniumseries (alpha count) ages from the Late PleistoceneAcropora and Porites colonies of Rameswaram(Table 2) and calibrated radiocarbon ages for Holo-cene coral colonies and shells from Cape Comorin,Rameswaram, Mandapam, Kakinada and Kaikallur(Table 3).

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Fig. 1. Outline map of the Indian Peninsula showing the locations of the study areas and illustrative stratigraphic sections.

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Table 1Radiocarbon and uranium series dates of Late Pleistocene sea level indicators along the Gulf of Mannar coast

Sl. No. Location Sample type Samplecode

Host rock Elevationabove LTL(m)

238U(ppm)

232Th(ppm)

234U/238U(AR)

230Th/234U(AR)

Th–U agein 103 yrB.P.

Measured14C date(^1s )

Remarks

1. 6 km west ofCape Comorin

Marine Shella Cape C Beachconglomerate

1.20 1.05^ 0.03

0.07^ 0.01

1.12^ 0.03

0.65^ 0.05

112(116/214)b

.46,600 The radiocarbon dates liebeyond the limit ofcalibration of14C dates(Stuiver and Reimer, 1993)

2. Cape Comorin Foramaggregate

BS 1207 Packstone oversample No.1

4.90 29,300^ 530

3. Idindakarai Marine shella Vija 52 0.153^ 0.006

0.014^ 0.003

1.08^ 0.04

0.688^ 0.040

124(114/28)b

4. Idindakarai Shellfragments

BS 1208 Grainstone 3.40 24,270^ 630

5. ManappadPoint

Balanussp.a Tuti 2b Beach rock 2.15 0.65^ 0.014

0.01^ 0.002

1.22^ 0.04

0.68^ 0.03

120(17/210)

High initial ratio of234U/238U suggestsgroundwater contamination(Hamelin et al., 1991)

6. ManappadPoint

Littorina aff.Littoria(aragonite)

BS 1222 Packstone overmarine terrace

4.50 25680^ 450

7. ManappadPoint

Scapharca aff.Inequivalvis(aragonite)

BS 1147 Packstone 2.70 23,330^ 640

8. ManappadPoint

Cardita sp.(calcite)

BS 1278 Grainstone 3.00 30950^ 1640

a Bruckner (1989)’s data.b All uranium series dates of mollusc samples have unknown departures from true age beyond the errors of counting statistics (Chappell et al., 1978).

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Fig. 2. Outline map of the Rameswaram Island showing the locations of emerged Late Pleistocene and Holocene coral colonies with illustrative stratigraphic sections.

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Table 2Th–U alpha count of hermatypic coral colonies at Rameswaram

Sl. No. Location Sampletypea

SampleCode

Elevationabove LTL(m)

238U(ppm)

232Th(ppm)

234U/238U(AR)b

230Th/234U(AR)b

Estimated agein 103 yr (^1s)

Remarks

1. RameswaramIsland north shore

Acropora PKB 8a 1.10 3.11^ 0.07

0.14^ 0.01

1.09^ 0.01

0.699^ 0.025

125.6(18.5/27.9)

In situ upright stem;aragonite,98%

2. RameswaramIsland terrace

Porites R5 2.90 2.21^ 0.08

0.030^ 0.006

1.11^ 0.01

0.70^ 0.04

104(110/210)

Extensive and bevelledcoral colony; aragonite,95%


Porites R6 2.90 2.57^ 0.09

0.09^ 0.01

1.13^ 0.02

0.65^ 0.03

92.0(16.5/26.5)

Coarse fibre aragonite,90%; diageneticcontamination indicatedby pools of welldeveloped calcite


Porites Vadakadu 4

2.40 2.86^ 0.04

0.06^ 0.01

1.09^ 0.02

0.65^ 0.02

112(18/25)

Bruckner, 1989


Porites R3 2.90 1.97^ 0.05

0.010^ 0.001

1.10^ 0.02

0.66^ 0.02

116(110/210)

Coarse fibre aragonite


Porites R7 2.90 1.95^ 0.04

0.075^ 0.007

1.13^ 0.02

0.63^ 0.02

104(110/210)

Fine aragonite

7. Near Narikulambeach

Porites 01/97 2.40 1.99^ 0.04

0.027^ 0.002

1.11^ 0.01

0.64^ 0.01

108(12/25)

Fine aragonite

a Identification at generic level only. All coral samples in growth position.b AR�Measured activity ratio.

3. Methods

Survey of India topographic sheets on scale1:63,360/1:50,000 were used to identify samplelocations and estimate distances between localitiesalthough contours for elevations below 20 m abovesea level (m.a.s.l.) are not drawn on these sheets.Elevations of terraces and outcrops given in thispaper measured with tape and abney level areconsidered accurate to within0.5 m.

Samples for geochronological measurements werecarefully extracted from in situ outcrops. Zones withpatchy discolouration, infiltrated extraneous matter,weathered/moss covered rinds and other visiblemarks of alteration were discarded. The selectedsamples were cleaned by immersion in H2O2 for48 h, washed with distilled water, dried and thencrushed in an agate mortar.

Samples were selected for dating on the basis ofthin section and X-ray diffraction (XRD) studies.Following Chappell et al. (1978), coral samplesmade up essentially of primary (.98%) aragonitewere selected for uranium series dating. Mineralogi-cal screening provided requisite alarm signals most ofthe time. Even for Holocene corals and shells, the bestradiocarbon dates were obtained from samples ofunaltered aragonite. Mollusc samples, even thosewhich are made up of primary aragonite, could haveunknown departures in their uranium series and radio-carbon ages from the true age of the host sedimentarybeds. In such cases the test for internal consistencyinvolved dating a number of mollusc samples from thesame site.

The need for caution in the high-resolution strati-graphic interpretation from radiocarbon dates ofpartly recrystallised fossils is illustrated in Tables 1and 4; deceptively young radiocarbon dates of 13–37 ka were obtained for recrystallised/altered coraland bivalve samples embedded in Late Pleistocenegrainstone, although the precision of the measure-ments was high ( 3%).

Radiocarbon dates were determined in the BirbalSahni Institute of Paleobotany, Lucknow (BSIP),following the procedure of Rajagopalan et al.(1978). The measured dates were recalculated usingthe radiocarbon calibration programme of Stuiver andReimer (1993) Rev. 3.0.3 of the Quarternary IsotopeLaboratory, University of Washington. The half-life

value was taken as 573040 yr; a reservoir correc-tion of 400 yr was incorporated and the13C value ofmarine organisms�215^ 2 mil� was used.

The uranium series (alpha count) ages, critical Th–U concentrations and isotope ratios of the East Coastcoral samples are presented in Tables 1 and 2. All238Uconcentrations fall within the range specified formodern and unaltered coral.

The anomalously high level of232Th e.g. in sampleR-18, Table 5 is possible due to non-carbonate detritalmaterial in the pore spaces of the coral skeleton(Stirling et al., 1995).

4. Differential crustal movements

Neither the coast along the Gulf of Mannar nor thedelta fringe of the Godavari shows evidence formarked differential crustal movement affecting theLate Quaternary sequence. Pre-quaternary faultscutting across the Paleogene and older basement [asindicated in reflection seismic profiles (e.g. Kumar,1983)], appear to stop below the Neogene cover. Atthe east Indian localities there is no hot spring, noreport of earthquake of historical antiquity and nowarping of Pleistocene marine terraces indicatingthat no tectonic activity has occurred there in therecent past. In contrast to fault controlled quaternarybasins (Dirik and Go¨ncuoglu, 1996), there are noalluvial fan deposits made up of subrounded,unsorted, weakly consolidated conglomerates asmarginal facies of the Holocene delta sequences inthe study area. The presence of one thousand yearold temples at Rameswaram and Kanyakumari andof the 450-yr old Portuguese church at Alantalai(near Tiruchendur) provide further direct evidenceof tectonic stability of the Tamilnadu coast alongthe Gulf of Mannar during the present millenium.

5. Results

5.1. Late Pleistocene highstand

Intertidal foraminifer, bivalve and gastropod bear-ing sedimentary rocks correlated with a Late Pleisto-cene sea level highstand occur on promontories atCape Comorin, Idindakarai and Manappad Point(Fig. 1). Some of the emerged coral colonies and

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Table 3Ages of the Mid- to Late Holocene sea level indicators around Rameswaram and Godavari delta

Sl. No. Sample type Sample

code

Location Host rock Nature of samplea Elevation above

LTL (m)

Measured14C date

(yr B.P.)

Calibration

curve

intercept

(yr B.P.)

Dendro-

calibrated 1s

range

(yr B.P.)

Aragonite

(%)

I. The first highstand

A. Rameswaram Island

1. Porites BS 1119 Villundi Theertham

shore

– In situ colony 1.40 6210

^ 120

6640 6740

–6470

95

2. Porites BS 1223 Villundi Theertham

shore; 400 m farther

west


^ 120

6330 6470

–6240

.97

3. Porites BS 1121 North of Pamban – In situ colony 1.40 5310

^ 120

5660 5830

–5570

.97

4. Porites BS 1310 Pisasu Munai – In situ colony 1.00 6450

^ 160

7300 7430

–7190

.97

5. Porites BS 997 1 km NE of CMFRI

farm at Munaikkadu


^ 110

5750 5920

–5660

.97

B. Godavari inter-deltaic plain

6. Anadarasp. BS 1274 Southern fringe of

Locamudi village near

Kaikallur close to

Kulleru lake

Brown and grey

siltstone

Disarticulated shells 3.90 5670

^ 120

6310 6430

–6220

.97

7. Arca sp. BS 1347 1 km inland from

Kakinada beach

lighthouse

Partly consolidated

beach ridge-sand


^ 520

II. First hydro-isostatic emergence (,5300–4300 B.P.)

A. Rameswaram Island

8. Arca1

Cardita

BS 1440 Narikulam sea shore Cross laminated friable

sandstone


^ 140

4450 4650

–4290

.97

9. Erronea BS 1410 600 m west of Villundi

Theertham

Calc tufa laterally

grading into 2–3 cm

thick colour banded

foreshore sandstone

5 cm long shells, later

occupied byLittorina

2.40 4860

^ 100

5199 5290

–4980

.97

B. Cape Comorin

10. Scapharca

sp.

BS 1209 600 m west of

Kovakulam

cross laminated

regressive facies

sandstone

Disarticulated shell 2.40 4400

^ 100

4560 4780

–4430

.97

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Table 3 (continued)

Sl. No. Sample type Sample

code

Location Host rock Nature of samplea Elevation above

LTL (m)

Measured14C date

(yr B.P.)

Calibration

curve

intercept

(yr B.P.)

Dendro-

calibrated 1s

range

(yr B.P.)

Aragonite

(%)

III. The second sea level rise (,4300–3600 B.P.)

Rameswaram Island and Mandapam

11. Porites BS 1224

BS 1249

1 km NE of CMFRI

farm at Munaikkadu

In situ colony above

0.5 m thick shelly

sandstone

1.70 4162

^ 115

4223 4390

–4050

.97

12. Terebrasp. BS 1276 Pamban coast at the base

of unconsolidated dune

and over shelly

sandstone

Calc tufa (20 cm thick) Centimetre sized shells 2.90 3800

^ 130

4120 4320

–3950

.97

13. Littorina sp. BS 1441 600m west of Villundi

Theertham

calc tufa (50 cm thick)

grading laterally into

colour banded

foreshore sandstone

Embedded shells with

disarticulated

fragments ofCardium

2.40 3840

^ 130

3799 3940

–3610

.97

IV. Little ice age sea level fall

14. Fragmented

Arca1

Astarte1

Venus

BS 1212

BS 1408

750 m SSE of Karikovil hard foreshore

grainstone with

goethite veinlets


^ 120

100

^ 1.6

510

V. Recent sea level rise

15. Arca,

Pteria,

Cardium

750 m SSE of Karikovil Loose sand on berm Loose and

disarticulated shells

2.90

a All corals in growth position.

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Table 4Anomalous radiocarbon dates of coral stems embedded in grainstone of Vadakadu–Narikulam Sector over Late Pleistocene coral colonies, Rameswaram Island

Sampletype

BSIP regd.number

Locality Elevationabove LTL(m)

Measured14Cdate(yr B.P.)

Calibrationcurve intercept(yr B.P.)

Dendrocalibrated1s age range (yrB.P.) after Stuiverand Reimer (1993)

Remarks

Goniopora BS 1116 Rameswarambeach

1.90 17700 280 20,050 20490–19650 Duplicate samples indicating goodmeasurement precision.

BS 1130 Rameswarambeach

1.90 17270 270 20,150 20600–19280 Material totally recrystallised,resulting in anomalous low ages.

Porites BS 1120 Olaikuda marineterrace

1.90 13170 200 14,730 15070–14420 Totally recrystallised into fine calcite.

Acropora BS 1117 Pisasu Munai 1.40 30790950 Coarse aragonite with discolourationand extraneous matter.

Acropora BS 1118 Pisasu Munai 1.15 371701230 Aragonite.90%Acropora BS 972 Vadakadu 1.90 31650980 Aragonite,80%

associated grainstone along the northern and easterncoasts of Rameswaram Island also formed during ahighstand of the Late Pleistocene. Some of the fossilswithin these units are diagenetically altered and yielduncertain ages. The following account places all of theavailable dates in their geological context.

(a) Cape Comorin: Nearly 4.9 m above the presentLTL and a few km east of the fossiliferousconglomerate bed near HTL, reported by Bru¨ckner(1988, 1989), there is a cavernous, nearly structure-less, packstone bed, exposed along the scarp face ofthe Gandhi Maidan terrace. This unit is 1.5 m thickwith abundant bioclasts ofAmmonia, Elphidium,Cibicides, Globigerinoides, Amphistegina andEpinoides, typical of intertidal environment. Nearly20% of the bioclasts are covered with a thin film ofiron oxide. Such iron oxide coated bioclasts ofsimilar species possibly reflect subaerial weather-ing of a part of the sequence during a minor episodeof relative sea level fall. An apparent Th–U alphacounting age of 1121 16/214 (1 s) was deter-mined for a marine shell sample from the beachconglomerate unit. The spatial proximity andstructural concordance between the conglomerateand the foraminiferal packstone and their Th–Uand radiocarbon dates (Table 1, Sl. Nos. 1 and 2)indicate that both are Late Pleistocene highstandaccumulations.(b) Idindakarai: Nearly 35 km northeast of CapeComorin on the Gulf of Mannar shore stands anemerged marine terrace 3.4 m above the presentLTL displaying a shallowing upward strandlinesequence. The lower bed is a 1.5-m thick, cross-lami-nated and rippled grainstone. Its upper contact is

bioturbated. This unit is overlain by a 0.6–1.0 mthick bed of cavernous grainstone with bioclasts ofsmall bivalves, peloids and abundant borings byorganisms diagnostic of intertidal environment(James, 1983). A fossil shell from this unit wasdated at 124 (114, 28) ka (Bruckner, 1988, 1989).Both the Idindakarai and Cape Comorin occurrencesand the marine terraces forming the upper surface ofthese sediments at Gandhi Maidan and Vinayaktemple standing approximately 4.9 m above thepresent LTL define Last Interglacial highstandpositions.(c) Seafront exposures at Manappad Point,approximately 40 km NE of Idindakarai, show fourstep-like marine terraces on consolidated, unfossili-ferous dune accumulations carrying diagnosticaeolian cross lamination (Fig. 1, V). The lowestterrace (T4) forming the seaward edgeof the coastlinestands only 1.0 m above LTL. The next terrace (T3) islocated 1.5 m above LTL and the third (T2) occurs atapproximately 2.7–3.4 m above LTL. The T2 terraceis laterally traceable over 100 m on the sea front. Itssurface is pockmarked with 4–30 cm diametercircular depressions (produced by churning actionof tides), some of which are occupied by 3–10 cmthick finely laminated stromatolites (algal mat);elsewhere there are accumulations of bioclasticpackstone with fragments of recrystallised marinebivalves and older grainstones. Shoreface faciesaccumulations of cross-laminated bivalve-richbeds also occur on the T2 surface between 3.7and 2.7 m above LTL. The top terrace (T1) at4.5 m above LTL is capped by thinly laminatedgastropod rich lagoonal facies (Tucker and Wright,1990) carbonate accumulations.


Table 5A comparative view of Th–U alpha count dates and calibrated radiocarbon ages of two samples ofPorites from the northwestern shore ofRameswaram Island, Tamilnadu

Samplecode

Nature ofsample

238U(ppm)

232Th(ppm)

230Th(dpm/g)

234U/238U(AR)

230Th/234U Th–U age(yr B.P.)(^1s)

Measured14C age(yr B.P.)

Calibration curveintercept (yr B.P.)after Stuiver andReimer, 1993

Dendro-calibrated1s age range afterStuiver andReimer, 1993

R-17 Aragonite.98%

2.60^ 0.11

0.16^ 0.01

0.15^ 0.08

1.14^ 0.02

0.059^ 0.004

6000^ 500

6450^ 160

7300 7430–7190

R-18 Aragonite,50%

2.36^ 0.10

0.81^ 0.04

0.22^ 0.01

1.16^ 0.02

0.093^ 0.006

9400^ 500a

5700^ 120

6330 6470–6240

a Anomalously old age due to contamination.

An in situ Balanusfrom the T2 terrace yielded aTh–U alpha count date of 120 (17, 210) ka(Bruckner, 1988, 1989). However Th–U ages formolluscs are not very reliable (Chappell et al.,1978) since their shells biologically excludeuranium while living, and cannot be used forprecise correlation. Therefore a Last Interglacialage is likely for the T2 terrace particularly givenits elevation at,3 m above LTL consistent withobservation from other tectonically stable LastInterglacial localities, but this is not definitivebased on the present data. The radiocarbon datesof the molluscs here and at Idindakarai (Table 1)yield anomalously young ages even where theshells are not recrystallised, possibly due to thepresence of post-depositional diagenetic coatingsof younger carbonate on the shells. At ManappadPoint, the step-like marine terraces on aeolinite atdifferent heights with the highest terrace standingup to 4.5 m above the present LTL reflect suddendrops in the Low Tide level between stillstands.Similar rapid changes in sea level have beeninferred from the Bahamaian corals of the LastInterglacial by Neuman and Hearty (1996).(d) On the northern coast of Rameswaram Islandnear Pisasu Munai, one km northwest of Narikulam(Fig. 2), a small (less than 1 sq. m in area) colony ofAcropora occurs in growth position along thepresent shore line only 1.0 m above LTL. In spiteof comprehensive screening of more than 30 speci-mens from this small outcrop, the best sample stillshowed traces of contamination (140 ppb of232Th)at 98% primary aragonite in contrast to the 0.5 ppbupper limit measured in modern corals fromoceanic islands that are far removed from detritalinputs (Edwards et al., 1987; Chen et al., 1991). Itsapparent Th–U (alpha count) age of 125.6 (18.5/27.9) ka, corresponding to oxygen isotope stage5 e cannot therefore be considered definitive.Only a 100 m south of theAcroporacolony thereis a large (approximately 10 sq. km) coral terrace(T2), located approximately 2.9 m above the LTL,whereAcroporais totally absent. This is a strikingcontrast. The dominant genus of this colony isPorites; other associates areDiploastrea, Cyclo-seris and Goniopora. More than 90% of coralshere are diagenetically altered, containing second-ary (coarse) aragonite, pools and veins of calcite,

high (1.48–3.53%) MgO and extensive patches ofdiscolouration. Prolonged annual flooding of thecoral terrace during the NE (October to December)and SW (June to September) monsoons is possiblya causative factor for such pervasive alteration ofthe corals. The least alteredPorites sample fromthis colony (sample 3, Table 1) yielded a Th–U(alpha count) age of 104 10 ka: Bruckner(1988, 1989) previously reported a Th–U (alphacount) age of 112 (18, 25) ka from a fractionallymore altered (as indicated by its232Th content)sample ofPorites from this colony.If the T2 terrace is correlated with the Last Inter-glacial highstand, its elevation at 2.9 m above thepresent sea level datum is comparable to that esti-mated for the Last Interglacial sea level highstandalong the west Australian coast (Stirling et al.,1998). However, given the large range of uncer-tainty in these Th–U ages, together with their ques-tionable accuracy due to diagenetic alteration, thepolygeneric coral assemblage of this terrace couldinstead have formed during the stage 5c interstadialevent at,105 ka.

At the end of the highstand, the sea level (LTLposition) fall here was neither rapid nor unidirec-tional. The parasequence lying over the coral terrace(T2) is made up two units (Fig. 2):

A. The lower unit is a 20–30 cm thick bed of peloi-dal limestone, exposed near Narikulam. Locally,4 cm long shells ofArca are embedded in thisunit. The peloids are up to 1 cm in diameter,ovoid, bulbous or irregular in shape, their corticesshowing many laminae composed of aragonite withsmall angular quartz grains. Their nuclei arefrequently made up of vermicular sparrite withmicrite in intervening spaces. This fabric is typicalof high-energy environments of deposition (Aaltoand Dill, 1996). Fenestrae are also common,suggesting that this unit was deposited in anupper intertidal environment (James, 1983; Tuckerand Wright, 1990). On the Narikulam berm, thelowest part of this unit is composed of light tochocolate brown micrite laminae, which drapeand locally infiltrate into thePorites colony,signifying the death of the corals before accumula-tion of this algal mat.B. The upper unit is a few metres thick and includes


the following: (1) 0.5–2.5 cm thick grainstone bedwith abundant fragments of bothAcropora andPorites. Locally, this bed is composed of packedaggregates ofAcroporalogs and stems with inversesize grading; (2) landward dipping, straight totrough shaped cross laminated sandstone beds onapproximately 10 cm thick cycles, possibly a shore-face megaripple deposit; (3) lenses of 50 cm thickstromatolytic packstone; and (4) local 5–6 m longcolonies of 4–6 cm sizedNaticasp.partly filled upwith strandline sand (bimodal quartz grains and afew grains of garnet and ilmenite). Set in micrite,the shells are diagenetically coated and veined bysparry calcite.

This parasequence suggests that the first phase ofsea level fall of approximately 1 m exposed the coralterrace that formed just below the LTL to an upperintertidal regime. This was followed by a short periodof relative sea level rise when bar to lower foreshorefacies sediments of unit B accumulated thereon.

A curious feature of unit A is the presence of gran-ules of foraminiferal (Rotaliina) grainstone within thealgal mat. Since the island lay submerged at that time,these granules could have been deposited by presentday type littoral transport from the foraminiferal rocksexposed 200 km south at Cape Comorin along theGulf of Mannar. This would have required strongmonsoon forcing during the Late Pleistocene high-stand (cf. Fontugne and Duplessy, 1986).

5.2. Holocene highstand

From the northern margin of the Indian Ocean atCape Comorin to the Godavari delta of the Bay ofBengal between N. latitudes 8 and 178, indicators ofthe Holocene highstand are intermittently exposedalong the east coast of India as emerged outcropsabove LTL. These indicators include: (1) hermatypiccoral colonies at Rameswaram similar to the presentday fringing reefs at water depths of approximately 3–4 m; (2) cross-laminated and shelly, shoreface sand-stone grading upwards into foreshore sandstone withgarnet/ilmenite interbands and shell fragments; and(3) estuarine facies molluscs in upper intertidal sedi-ments of microtidal regime. Among these, hermatypiccoral colonies (Fig. 3) and foreshore sandstone withparallel lamination of heavy and light mineralsprovide more precise estimates of sea level elevation

corresponding to the periods indicated by calibratedradiocarbon dates of the biota since this tectonicallystable coast is microtidal and the uncertainty on theestimated sea level elevation is at most^0.9 m.

5.3. The first stillstand

The oldest Holocene highstand date recorded by theemerged coral colony at Rameswaram (Fig. 2) is7300 yr B.P. (Table 3). Present day living coloniesof Acropora, Poritesetc. occur at the 3–4 m isobathas a submerged girdle on the same side of Palk Bay.Extrapolating from this habitat, it appears that theheight of sea level (LTL) during this mid-Holocenehighstand was around 3 m above the present datum.

At Rameswaram and at Mandapam on the adjoin-ing mainland, all these emerged colonies range in14C age between 7300 (1130/2110) yr B.P. and5660 (1170/290) yr B.P. and underlie a cross-lami-nated, poorly sorted, shell-rich sandstone of shorefaceaffinity. Along the Munaikkadu foreshore (Fig. 2), ayounger coral colony with a radiocarbon age of4223 yr B.P. overlies the sandstone unit. The oldercoral colony is also present at the same spot justbelow the sandstone, a conclusive proof that theseactually represent two distinct phases of coral growthwith a break in between, marked by the accumulationof regressive shoreface sand during an interval ofrelative sea level fall.

A similar dichotomy in coral dates was reported byKatupotha and Fujiwara (1988) from the southwestcoast of Sri Lanka on the Indian Ocean. Uncalibratedradiocarbon dates of 19 samples from emergedAcropora, Porites and other coral reef patches therecluster in two groups: 6170–5100 yr B.P. and 3210–2300 yr B.P. (Fig. 1). The measured dates of olderHolocene corals from Rameswaram (Table 3) showa close correspondence with the older set from SriLanka. Katupotha and Fujiwara (1988) had concludedthat (1) “the former MSL in both groups was at least1.0 m or more higher than the present MSL” and (2)there is a possibility of a “slight lowering in sea level”between the two age groups.

Farther north, approximately 900 km northeast ofRameswaram, in the delta fringe of the microtidalGodavari river, friable, grey intertidal siltstone with6310 (1 120/290) yr B.P. Anadara sp. and otherbivalves co-existing withTelescopium telescopium


P.K

.B

an

erje

e/

Ma

rine

Ge

olo

gy

16

7(2

00

0)

24

3–

26

0256

Fig. 3. Schematic illustration of relative sea level change of the east coast of India during Middle to Late Holocene.

(typical of backswamp facies) occurs 36 km inland(from the present coast) near Kaikallur, south ofKolleru lake at approximately 3.9 m above LTL.Therefore the tidal reach penetrated 36 km inland ofthe present shoreline during the first Holocene high-stand. This estimate is much closer to the presentcoastline than the earlier reconstruction by SambasivaRao and Vaidyanadhan (1979). At about 5 ka, thecoast was only 1 km inland from the present shorelineat Kakinada, as revealed by the age of molluscs inbeach ridges there (Table 3).

The estimated height of the first Holocene high-stand is comparable to the corresponding sea levelelevation along the east coast of Brazil fromRecife to Rio, south of equator (Fairbridge,1976). Near Recife on the northeastern part ofthe Brazilian coast, Late Holocene vermetid lime-stone accretions attached under overhanging wavecut rocky caves occur at 3.0–3.4 m and at 1.4–1.6 m above the present datum (Van Andel andLaborel, 1964). Further southeast between Parana-gua and Cananeia on the coast of Parana and SantaCatarina states, the sedimentary deposits of thecoastal plain as well as vermetid datings suggesta mid-Holocene sea level highstand between13.5and 14 m.

Similarly, on the microtidal coast of Mauritania inWest Africa, the mid-Holocene highstand reached amaximum of13 m above the mean sea level (MSL)(Einsele et al., 1974).

First phase of hydro-isostatic emergence: The tran-sition of a poorly sorted shoreface sandstone over theMid-Holocene coral colony at Rameswaram andMandapam upward into colour banded (colour bands2–3 cm thick) garnet-rich foreshore sandstone definesa period of relative sea level fall of approximately2 m. Apparently, the same event is reflected nearly300 km away along the Sri Lankan coast at Hikka-duwa [Table 1, nos. 14–16 of Katupotha and Fujiwara(1988)]. This regional fall in relative sea level iscompatible with the modelled far field hydro-isostaticresponse of tectonically stable continental marginslocated far from the major ice centres (Chappell,1974; Nakada and Lambeck, 1987).

The second sea level rise: Following the hydro-isostatic emergence, there was a second pulse of rela-tive sea level rise to ca 3 m above the present LTL, asindicated by the following:

(i) 4.1 kaPoritescolony on Munaikkadu foreshoreat 1.7 m above LTL;(ii) 4.1 kaTerebrain calc tufa at 2.9 m above LTLoverlying the shelly sandstone at Pamban;(iii) 3.8 ka Littorina sp. embedded in calc tufaabove the foreshore sand near Pamban at 2.4 mabove LTL.(iv) Veneridae of comparable age at Palalla–Weligama and at Kalmetiya 1.3–2.2 m above thepresent MSL along the south coast and of emergedcoral colonies (of uncalibrated radiocarbon ages3210–2250 yr B.P.) at elevations up to 1 m abovethe present MSL at Hikkaduwa, Aranwala andDenuwala on the south and southwest coast of SriLanka (Katupotha and Fujiwara, 1988, Table 1);and(v) Cardium of uncalibrated radiocarbon age of2740^ 40 yr B.P.in living positionca 2 m aboveLTL in an inland lagoonal sequence, 4 km west ofMandapam (Bru¨ckner, 1988, p. 60).

In summary, the first Holocene highstand atapproximately 3 m above the present LTL wasreached at 73001 130/2110 radiocarbon (calibrated)yr B.P. The ensuing stillstand prevailed over nearly1.7 kyr. Thereafter a relative fall in sea level ofapproximately 2 m affected the stable segments ofthe east coast of India probably as a result of continu-ing hydro-isostatic adjustment of increased load ofmelt water in the ocean basins. This was followedby a second pulse of minor sea level rise stabilisingnear the earlier highstand position and remainingstable from about 4.3 to 2.5 ka (calibrated radiocarbonage).

This stillstand at around13 m above present LTLprevailed for nearly 2 kyr on either side of the equatorand is manifest not only along the South Indian andSri Lankan coasts but also along the northwesterncoast of Africa and the eastern coast of Brazil.Along the microtidal coast of Mauritania, the mid-Holocene highstand at13 m (Nouakchottian stage)was followed approximately 1.5 kyr later by a relativesea level fall, when intertidal accumulations devel-oped more than 3 m below the present mean sealevel (Einsele et al., 1974).

Angulo and Lessa (1997) have questioned the relia-bility of previous sea level observations from south-east Brazil on the basis of shell middens and beach


ridges, but the vermetid indicators on wave cut over-hanging surfaces from the coast of Recife farthernorth are compatible with a secondary sea level oscil-lation of 2–3 m during the Mid- to Late Holocene.

It is unlikely that such secondary oscillations inrelative sea level of 2–3 m along a number of stablecontinental margins of the tropical belt in both thehemispheres was caused by contemporaneous tecton-ism. The simplest explanation would be that the LateHolocene interval was characterised by oscillatingrather than stable sea levels: a glacio-eustatic flucta-tion, caused by Late Holocene climate changes assuspected more than two decades ago by Fairbridge(1976). This is also reflected in the East Antarcticcontinental shelf where open marine conditions reap-peared at 4 ka (contemporaneous with the second sealevel rise along the east coast of India) after a gap of3.3 kyr (Domack et al., 1991).

5.4. Little Ice Age sea level fall

Banerjee (1993) had attributed the shoreline regres-sion from the vicinity of the 13th century Sun templeat Konark, Orissa eastwards by a few kilometres, nowmanifest as a series of beach ridges, to the onset of theLittle Ice Age (LIA). The magnitude of relative sealevel fall cannot be ascertained from such beachridges. Vaz and Banerjee (1997) had suggested thata drop in sea level during this period reduced the sizeand depth of the Pulicat lagoon. Farther south in theGulf of Mannar near Karikovil, sea level fall is mani-fest in a consolidated, foreshore facies grainstone onthe beach. Parallel interbands rich in ilmenite dip at avery low angle seaward. Shells ofArca, Astarte,Venusetc. embedded within the rock yielded near-LIA radiocarbon ages of 510 yr B.P. and younger.

During this episode of sea level fall, the foreshorefacies sand at Karikovil was stranded above theprevailing tidal reach of this microtidal region. Asa result, it was diagenetically hardened and locallyinfiltrated by goethite. This implies that the relativesea level had fallen below the present datum by aminimum of 0.9 m at that time.

5.5. Sea level rise after the Little Ice Age

At the end of the LIA, relative sea level rose to itsprevious position and brought the foreshore grain-stone of Karikovil and Kuttam within the tidal range

once again; it is now exposed as a moss covered, pot-holed sheet rock during low tide.

6. Discussion and conclusion

Secondary changes of relative sea level by a fewmetres after the mid-Holocene transgressive maxi-mum are not unique to the east coast of India. Einseleet al. (1974) had described a relative sea level drop to23:5^ 0:5 m at about 4100 yr B.P. following themaximum of 13 m at about 5500 yr B.P. from themicrotidal coast of Mauritania, W. Africa. This partof the West African coast is tectonically stable. Likethe Gulf of Mannar, it lies within the tropical belt andpreserves the sea level record in a shallowing upwardsequence of littoral to beach facies shell beds overlainby stromatolites, which form typically between MLW(Mean Low Water) and MHW (Mean High Water).Presently this shoreline marker occurs within thesabkha depression at 3.6 m below the mean sealevel (MSL). Fig. 3 of Einsele et al. (1974) portraystwo cycles of Holocene sea level oscillation, similar tothe record derived for the present study area. VanAndel and Laborel (1964) had reported from nearRecife, Brazil within the tropical belt, two phases ofrelative sea level rise, the first reaching up to 3.0–3.4 m above the present (as defined by the distributionof living vermetidae) sometime around 3.6–2.8 ka,and the second reaching 1.4–1.6 m above the presentat around 1.7–1.2 ka. Although the radiocarbon datesare uncalibrated, the double cycle of sea level rise is acommon feature in the Indian, Brazilian and W. Afri-can records. At some other tectonically stable loca-tions, however, there is no evidence for oscillating sealevels during the Holocene interval (e.g Chappell etal., 1983; Zwart et al., 1998). But these records aremodel dependent and may not have sufficient resolu-tion to detect short term (,1000 yr) oscillations in theeustatic sea level signal, particularly for the latter5000 yr of the Holocene.

It is therefore possible that the record of minor sealevel oscillation during the Mid- to Late Holocene,registered in the proxies from West Africa, NortheastBrazil and southeast coast of India might either beabsent or escape detection at these other localities.

This Mid- to Late Holocene pattern of secondaryoscillations may appear anomalous, especially if the


sea level during the highstand of oxygen isotope stage5e is taken as the standard for an interglacial period.Preserved and well studied sea level proxies for theLast Interglacial on stable margins as far apart as thewest coast of Australia and the Bahama islands indi-cate that over much of the period between 131 and116 ka, relative sea level was 2–6 m above the presentlevel (Zhu et al., 1993; Neuman and Hearty, 1996).This is broadly in accord with the reconstructionsfrom the 52.7 m long core from the Bermuda Rise(Adkins et al., 1997), not very far from the BahamaIslands. Planktonic and benthic oxygen isotope datarecord a full interglacial between 129 and 121 ka anda rapid shift in the oceanic conditions around 118 ka,nearly coinciding with the onset of sea level fall in theBahamas (Fig. 4 of Neuman and Hearty, 1996).

In their latest reconstruction on the basis of morethan seventy high precision TIMS U-series ages ofLast Interglacial reef growth along the coastal marginof Western Australia, Stirling et al. (1998) haveshown that the Last Interglacial sea level highstandpersisted from 128 1 to 116^ 1 ka; interruptedpossibly by a global cooling event at around 121 ka.

The major episode of reef building between 128and 121 ka possibly reflected a period of stillstand at13 m or more in Western Australia relative to thepresent day sea level. Stirling et al. (1998) reportthat after about 121 ka, sea level may have becomeunstable, perhaps oscillating about the present and asecond short lived stillstand event may have occurredat the closing stage of the Last Interglacial interval,when sea level was again close to present day levelsfor a prolonged period of time.

Although inconclusive, the most probable scanariowhich emerges from the available Th–U alpha countdates of the study area, the regressive–transgressiveparasequence overlying the coral terrace at Rames-waram and the flight of erosional terraces on the aeoli-nite ridge at Manappad Point is that during the LatePleistocene highstand here, relative sea level rosealong the east coast of India in pulses to14.5 mabove LTL and fell back in short pulses betweenlonger intervals of stillstand and occasional smalljumps. This pattern is compatible with the model ofLast Interglacial highstand position, as proposed byStirling et al. (1998) but is substantially differentfrom the picture of a relatively short (5–8 ka) butstable stillstand of the Last Interglacial (stage 5e;

event 5.51–5.53) covering the period from 129:7^

3:02 ka to 122:56^ 2:41 ka; as computed by Martin-son et al. (1987), for example, from astronomicalparameters.

The far field sea level record for the Mid- to LateHolocene interval, recorded at localities along thestable coasts of S. India, W. Africa and NE Brazilsuggests high-frequency oscillations of a few metresaround 4 ka and again during and after the LIA.

Acknowledgements

This work was funded by the Indian NationalScience Academy under Senior Scientist Scheme.

I am grateful to C.H. Stirling, Michael A. Arthurand an unknown reviewer for their extensive criticaland constructive suggestions for improvement of thispaper, to G.G. Vaz, S. Ramesh and Sam Armstrongwho assisted me in collection of samples from thefield, to S. Bardhan and J.K. Pal (JU) for identificationof some molluscs, to M.S. Srinivasan (BHU) for thedescription of foraminifera from the Cape Comorinpackstone, to B.L.K. Somayajulu and M.M. Sarin(PRL) for the Th–U (alpha count) dates of the coralsamples, and to G. Rajagopalan (BSIP) for radio-carbon dates. Ranjan Roy and L. Roy helped me indrafting the text and the diagrams.

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holocene and late pleistocene relative sea level fluctuations along the east coast of india

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