J . Natn. Sci. Coun. Sri Lanka 1994 22(2): 157-187
GEOLOGICAL SIGNIFICANCE OF MARINE MOLLUSKAN BEDS :
EVIDENCE FROM SOUTHERN COASTAL ZONE OF SRI LANKA
J . KATUPOTHA
Department of Geography, University of Sri Jayewardenepura, Gangodawila,
Nugegoda.
(Received :24 December 1993, accepted :23 June 1994)
Abstract: Mollusks are invertebrate animals that live in brackishwater or
marine habitats. The diversity and complexity of these habitats are due to
winds, waves, tides, bottom features, daytime illumination, geologic origin of
shoreline and ecologicconditions of the oceans. Assembly ofbivalve and univalve
mollusks occur due to the eustatic changes and the prevalence of coastal hazards.
Stratigraphic sequencesof shell beds alongthesoutherncoastbetweenKalametiya
Kalapuwa (lagoon) and Bundala Lewaya (salt pan) clearly indicate that shells
have been piled up together with stone artifacts, pieces of pottery, human bones
and other animal bones. These were caused by severe storm wave action on
mounds in lagoon and lake bottoms, on sand dunes and headlands. The present
study shows that the shell valves of lagoon, lake and channel beds (floors of
marine and brackish pools) mostly accumulated in situ consequent to the
lowering of sea level between 5030 - 4390 and 3930 - 3290y B.P.
Key words: Marine molluscs, shell beds, south coast
INTRODUCTION
Assemblance of bivalve and univalve mollusks occur due to eustatic changes and
coastal hazards. They are used as a geoscientifictool to study former sea-level
stands.' Radiometric dating of the shells in different levels and quantitative
analysis of their deposition sequences are helpful for this purpose. The present
study attempts to reveal the geological significance of inland marine shell beds
on the southern coast of Sri Lanka at a site between Kalametiya Kalapuwa and
Bundala Lewaya in the dry zone (Fig. 1).The geological significance, extension
and evolution of these shell beds have not previously been investigated.
METHODS AND MATERIALS
Extension of the shell beds was mapped based on detailed field investigations.
From twenty locations, shell and soil samples were collectedfor geologic analysis
between March and December 1992. Each sample contained 1.5 22.0 kilogram
of shell and shell debris. All locations and sample heights were leveled to mean
sea-level (msl)using TC 1600 EDM (ElectronicDistance Measurement) theodolite (Set 3 B Sokkia) by a government licensed surveyor.
Separation of the grain sizes of the soil samples was undertaken using a BS
410, Laboratory Test Sieve (Endecotts, London). Before separation of grain
sizes, weighted amount of dried soil (125 - 150g) was treated with 20% HCl to
remove carbonates. The treated wet sample was dried in an oven at about 100°C
for at least eight hours. Approximately 500 - 600g shells were also cleaned by
J. Katupotha
80'
I
81 '
I
82'
I
RINCOHALEE
)
7-.
COLOMBO
= S E M I - A R I D ZONE
DZ = DRY ZONE
I Z = I N T E R M E D I A T E ZONE
H Z = WET ZONE
SAZ
KIRINDA
6O
-
-
Figure 1: Locationmap of the shell bed areas alongthe southern coastal
zone of Sri Lankn.
Marine Mobskan Beds in the South Coast
159
treating with 10% HC1 for identification of the shells, and about lOOg were
preserved for future radiometric dating. Colour of the soil samples and shell
embedded soils was determined using the revised standard soil colour charts.*
The profiles of the shell layers were drawn using Harvard graphics. The
laboratory work was conducted in the Department of Geography, University of
Sri Jayewardenepura. Shells were identified with the help of a published
~atalogue.'~
Physical setting of the s t u d y area
The study area, is situated between longitude 80'48'- 81°16'and latitude 6'03'6'09' Ambalangoda-and Hambantota topographic sheets (1:63,360) between
Kalametiya Kalapuwa and Bundala Lewaya (Fig. 2 from a to k). Geologically
the study area is underlain by the Highland complex rocks (undifferentiated
rocks) on the western bank of the Walawe ganga, while the eastern bank lies on
the Vijayan complex rocks (charnockite and charnockitic gneiss) of precambrian
rocks.' According to a Canada - Ceylon Colombo Plan Project (Resource of the
Walawe Ganga basin') the study sites consist of two types of rocks: (1)
hornblende and biotite gneiss with associated pegmatite and migmatite
(Vijayan complexrocks). (2) quartz0 feldspathic gneiss andgranulite (Khondalite
series rocks). The zone of the quaternary deposits here are also somewhat
narrow due to the extension of low hills and ridges close to the sea and lie on both
Highland and Vijayan complex rocks. Broadly, the study area can be divided into
three geomorphic units based on elevation and the composition of the deposits"
namely: (1) flat terrain (lowland I, <30 m, shpe is 1/2O or lo(60:l or 100:l in
gradient). (2) flat to slightly undulating terrain (lowland 11, c30 m). I t has l0to
3' slope or 60:l to 20:l gradient and can be designated as 'flood plain'. (3)
undulating terrain (lowland III,30-150 m). Slightly undulating, undulating and
rolling features appear particularly i n the area between Udawalawe and
Ridiyagama.
The shell beds are mainly concentrated in the flat terrain (lowland 1)beyond
the western a i d eastern sides of the Walawe ganga. The coastal beit which
included lowland 1has been altered by terrestrial, aeolien and marine processes,
and has formed narrow and long beaches, beach ridges with medium (3 - 5 m) and
somewhat high (8 - 12m) dunes. Sand spits are common features a t the estuaries
of the Walawe ganga and lagoons. Salterns, salt marshes and mangrove swamps
and mound topography (a hummock relief) lie behind them. Too small and low
bedrock outcrops appear a s erosional remnants. The stony gravel. beds and
alluviam are the terrestrial deposits transported from upland and mountainous
terrains.'
According to K oppen classification: the southern coastal zone, from Matara
to Bundala is included into 'Afwi', 'Amwi' and 'As?climates. Distribution of
rainfall of the Hambantota meteorological station shows.two maximum seasons
(Fig. 3) during the southwest monsoon (May to September) and convectionalcyclonic-depression (October to November).
.
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Marine Moluskan Beds in the South Coast
162
J. Katupotha
The soils of the study area have a close relationship with geologic characteristics, microrelief and the seasonal distribution of rainfall. Four main soil
groups1' of the study area have been identified as follows: (1) reddish brown
earths with high amount of gravel in subsoil & low humic glay soils (2) reddish
brown earths & solodized solonetz (both (a) and (b) types lie on the undulating
terrain) (3) alluvial soils of variable drainage and texture (flat valley bottoms,
water logged areas etc. covered by these soils) (4) regosols on recent beach and
dune sand. Barrier beaches, beach ridges, sand spits and dunes alongthe coast
are formed by such materials. Rocknob plains and erosional remnants in the
coastal plain are formed by granitic gneiss, quartzite, hornblende gneiss and
hornblende - biotite gneissic rocks.
The coastal lowlands are covered by barren lands mainly sand dunes. Most
of the dunes are covered by creeping vegetation (Spinifix littorerus; Smaharawana reula and Ipomoea pescaprae; S-mudubintamru) and scrublands.
The wetlands behind the 'sand dunes are occupied by mangroves along'the
estuary of the Walawe ganga and around lakes and lagoons. Salt-pans, salt and
brackishwater lakes of the area are subjected to daily tidal fluctuations.
Sonneratia alba (S-kililla)is the dominant mangrove species ofthe area. Among
other important mangroves are Nypa fiucticans (S-ginp.ol),which extends along
edges of lagoons and tidal creeks, Rhizophora (S-kadol), Bruguira (S-sirikanda)
and Ceriops (S-kaduru) spp. Lowlands which are slightly above the mean high
water springs level appear as freshwater marshes. Brackishwater and freshwater marshes are widely occupied by Typha angustifolia (S-hambupan) along the
lower part of the Walawe basin."
The undulating low ridge and valley topography (30- 150 m), behind the
coastal lowlands are covered by dry zone thorny forest and sparsely used
croplands, homesteads and chena cultivation. The paddy lands have been
concentrated in the fairly wide valley bottoms toward the inland form the coast.
~arine'mollusks
as a sea-levelindicator
Sea-level indicators such as raised marine deposits, coastal barrier sands,
beachrock, ooids, corals and reefs, coralline algae, marine notches, submerged
forests marine mollusks etc. differ widely in indicative value (accuracy). They
are important for the consideration of sea-level changes within the context of the
geological development of an area.12
Mollusks are a group invertebrates that are terrestrial, brackishwater or
marine in habitat. The diversity and complexity of their habitats are due to
winds, waves, tides, bottom features, daytime illumination, geologic origin of
shoreline and ecologic conditions of the oceans and create special zones (Fig. 4)
for different shell s p e ~ i e s . ~The
" ~ basic nature of the mollusks was determined
millions of years ago as the great land continents were drifting into their present
position. As the climate (atmospheric and oceanic), changed and vacillated, all
species came under new challenges to their ~urvival.'~
The least adaptable are
Marine Moluskan Beds in the South Coast
163
found today only as fossil remnants locked in tertiary beds; other populations
were divided; isolated and changed into new species, while more resistant oms
flourished and spread from terrestrial to pelagic areas. The phylum Molluska
contains six classes viz; Monoplacophora, Amphineura, Gastropoda, Scaphopoda,
Bivalvia and Cephalopoda.' Habe4states that seven classes of mollusks including Aplacophora with the above six are composed of 112,000 species.
-
p e l a g i cA
,
,
Figure 4: Extension of marine molluskan zones between supralittoral and,circumlittoral.
Aplacophora dates from the Lower Cambrian; the class has 10 species. The
worm-shaped creatures have no shells. The Monoplacophora (Neopilina Class)
well-known from the Pdaeozoic deposits of epicontinental seas, are today only
represented by those recently found from the deep sea, having a limpet-like (capshaped) shell. Scaphopoda (tusk shells), tube shaped shells which widen towards
the aperture, are known from the Devonian period. The Bivalvia (Pelecypoda)
are mainly found in areas close to the coast. The clams are covered with two
shells. They are known from the lower Devonian. The Gastropoda are the most
varied group within the molluska. They date from the Upper Cambrian.
Cephalopoda (Squid and Octopus Class) are all predatory, swimming carnivores
occurring in the major marine habitats. The Arnphineura (Polyplacophora Chiton Class) are found from temperate to tropical areas and they usually live
on rocky surfaces close to the shore. These date from the Ordovician to the
present. These mollusks inhabit all the different regions of the sea, from cold
polar regions to the warm equatorial belt, from surface water and intertidal
beaches down to abyssal depths, but the warm shallow seas where reefs and
rocks abound are thickly populated.
J. Katupotha
164
The continental shelf around Sri Lanka comprises of submergedrocks, sand
banks, sandstone and coral reefs. Most of these features are situated on the
mesolittoral zone, known also as the intertidal zone (it extends from the hightide mark to the normal low-tide mark). Intralittoral plane extends from the
lower limit of the mesolittoral to the lowest depths at which a certain family of
plants occur. The seas around Sri Lanka provide an ideal environment for a rich
variety of molluscan shells. Kirtisinghe13has pointed out that research on sea
shells of Sri Lanka occur sporadically in zoological journals and the records of
oceanographic surveys. He described about 530 species collected in the seas
around Sri Lanka." Many of these are also found throughout the Arabian sea
southward to the east of Australia, and along the coast of Australia.
Three types of marine mollusks are found in Sri Lanka1\ (1) Pelecypoda or
bivalve mollusks (bivalvia by Peterson1) (2) Gastropoda or snail-like mollusks
and (3) Cephalopoda.
RESULTS AND DISCUSSION
Microrelief ofashell Beds
The extension of the whole shell beds along the southern coastal zone is laid in
flat terrain, below 30 m. This is somewhat wider than the coastal belt which is
between south of the Kelani Ganga on the west coast and the Nilwala Ganga on
the south coast. Both monsoons blow parallel to the coast, rather than across it,
and the waves are largely constructive southerly swells." The coastal belt from
Tangalle to Bundala is formed of narrow and long barrier beaches and beach
ridges. Dune bearing barrier spits are common features at the outfalls of the
Walawe Ganga and the circular shaped lagoons. Garnet and ilmenite sands are
found in most shore deposits along the beach. Well drained and imperfectly
drained soils occupy these areas.
The wetlands are covered by lagoons and lakes, salt marshes and mangrove
swamps behind them. The lagoon and lakes are known locally as 'lewayas' and
these are not fed by large streams. Most of them are very saline due to the
persistent winds and dry climate. These conditions have been created by rapid
evaporation. Slight undulatings of the area extend as lobes sloping towards the
coast. Most of them appear as low outcrops along the coast.
Geological Significance of the Shell Beds
The shells were found to be concentrated in pockets around the Kalametiya
kalapuwa, Hungama, Lumnama kalapuwa, Mahasittrakala lewaya, the area
between Karagan lewaya, Pallemalala, Embilikala kalapuwa and Bundala
lewaya. The extension of the shell beds is shown in Figure 2. Meretrix spp. are
the doininant mollusks in the whole area. Beside this, Anadara spp. .and
Cerithidea spp: are also found mixed with.Meretrixspp. or separately (Plate 1).
Most of these are found in paddy fields, small mounds chummocks),.former
embayments and the bottoms of lagoons,'lakes and creeks. The shell beds at
Marine Moluskan Beds in the South Coast
165
Hatagala extend up to Miniethiliya about 4 kilometres i d a n d from the present
coast. The shell beds atkatagala - Ovitigoda yaya (paddy field) are composed of
Meretrix spp. They are somewhat large (below 55 mm in size). Highly weathered
pieces of elk bones and pottery fragments can be found from the mining pits
(Plate 2a).
The shells at Miniethiliya are mined from small mounds near the paddy fields
and small mounds slightly elevated from the paddy fields (Fig. 5, Location No.
1; Fig. 6, Location No. 2) about 0.5 ha. in size. Calcareous clay with sandy (little)
soil (Grayish Gray Soil - 10 YR 4 2 ) contain in the top layer. Tiny and small to
somewhat large size o'f shells can be found. Shells belong to Cerithidea spp.
(below 20 mm) and Meretrix spp. (below 40 mm in size). Elk bones (horn)together
with Meretrix spp. were found in Location No. 2. Shell debris, sub-rounded
quartzite pebbles, coarse to fine sand with clay and other animal remains are
embedded in the deposits. Although the shell beds of the area are about 4
kilometres inland from the present coast, the thickness of the layer is considerably high. The beds a t Hungama - Pallegama (Ihalagama Yaya) are also mixed
with univalve shells, Anadara spp., Meretrix spp. pottery fragments and animal
bones.
Similar features with very thick shell layers are found a t Hatagala Bogahagodella (Fig. 7, Location No. 3; Plate 3). Most of these shell mounds are
covered by thorn bushes and stunted trees. Shells, shell rubble mixed with
calcareous sand and clay (Light Gray - 10YR 711)in sample 1. The shell of sample
2 in the same location is mixed with Brownish Gray soil (10 YR 411). A pure
quartz pebble was found in this sample. Shells belong to Cerithidea spp. is below
20 mm and Meretrix spp. is also below 20 mm in size (Plate 3). The shell beds at
Debaragodella (Fig. 8, Location No. 4). are mixed with calcareous clay (Brownish
Gray soil (7.5YR 411)in sample 1. There are no pebbles or coarse sand, but pure
quartz fragments are found. Calcareous clay with fine sand and shells (grayish
brown soil - 7.5 YR 412) were in sample 2. The clay.was compact when dry. The
clams i.n live position were also found in this sample.
k coconut land' a t Hatagala (temple land, about 0.25 ha. in size) has a
considerable amount of shells (Fig. 9, location No. 5). Tiny and small size to large
size of shell gathered together with light gray sandy soil .(lOYR 7/1). Many
Cerithidea spp. are well preserved and they are below 20 mm in size. Meretrix
spp. of both samples are also below 55 mm in size. A thick shell layer of the
mound has been mixed with stone pebbles (appear as artifacts), human bones,
fragments of pottery etc. Highly weathered human skeletonswere found a t same
mound of location No. 6 (Fig 10). A part of a jaw with teeth, vertebral columns,
rib cages and radius are found in this location. The last teeth of the jaw indicate
that the skull belonged to a young human. Other conditions of the site are very
similar to location No. 5. Well polished oval-shaped stone artifacts, stone balls,
human bones, a head of a serpent and other animal bones a s well as pottery
fragments are mixed with these shell beds (Plates 2b, 4 and 5c).
'9 28 E S
' ON uo!?aq
(p 28 3) sauoq mmnq PUB (q)ptlaq s,$uadaas(8)sauoq qIa 30 s a q d (a)!ppg Apptrd aAeAepo%!?!ao amtl%un~
paatg (y) :Z a p l d
uroq (p) hawed 30 saoald putl (3) sauoq qIa '(q) uo!)pod %u!ng u! snaqs xp?aaaM (8)sa~qqada ~ r z w n b
'auoz p'lmoo araqlnos aqq 3uop spaq naqs aq?ut pauftl?uoo*dds(3)D J D ~ W V (8)p m !(q) m p ? y $ u a'(8)
~ xp$aJaty(v) :I a?eId
?tl
-
Marine Moluskan Beds in the South Coast
Gocatiou 2
- lluunp~lna(Miuiclhiliya 2)
Location 4
- HaLsgnln,(~cbsrngadcll6)
l
soil lapr
Figure 5,6,7 and 8:
RmP S I I ~ ULayer
CS1 T&
8011
Stratigraphic sequences of the shell beds at location nos.
1,2 (Hungama Miniethiliya),3 (Hungama -Bogahagodella)
and 4 (Hungama Debmagodella).
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J. Katupotha
Plate 3:
About 1 m thick shell layers at Hungama - Bogahagodella (location
wo. 3).
Plate 4:
(A) Debris of human bones, (B) Human and other animal bones and
stone artifacts from the shell beds at location no. 5 &'6.
Marine Moluskan Beds in the South Coast
Plate 5: (A) Stone artifacts collected from the shell beds at location no.5
(c),Nabadewa (5b same stone artefact of the Plate 9) and location no. 19 at Bungala (5a)..(B) backside of the same stone artifacts
(c', b' & a').
-
Two distinctive beds at Bataata - Gurupokuna and Kalametiya have been
deposited in morphologically different areas. The beds a t Gurupokuna 1(Fig. 11,
location No, 7 & Fig. 12, location No. 8) appear as about 3 m thick deposits
(horizontally deposited) on mounds and a former lagoonal beach (Plate 6).
Sample 1belongs to light gray shelly sand (10 YR 711). Clear quartz fragments
were in the sample. The size of the Meretrix spp. is below 35 mm and Cerithidea
spp. is below 25 mm. Sample 2 contains light gray shelly sand (10YR 711). The
Meretrix spp. is small (below 30 mm) and Cerithidea spp. appear as fragments.
Unidentified shell fragments are also found here. Sample 3 of this location is
classified as dull yellowish orange soil (10 YR 613). Meretrix spp. (below 50 mm
in size) and somewhat weathered Cerithidea spp. (below 20 mm in size) are
found. Sample 1of the location No. 8 is mainly composed of light gray sandy soil
(10 YR 711). Meretrix spp. of the sample is below 40 in size. Sample 2 is formed
by dull yellowish brown soil (10 YR 4/3), sand and shell rubble. Cerethidea spp.
(below 20 mm). Meretrix spp. (below 40 mm) and Anadara spp. (below 45 mm)
are the main shell types of this location.
J. Katupotha
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.
Locatinn 5 -- Hnhgala (Temple l a n d I )
IacmUon 6
- 8hb;hlh
m
n
D
n
I
.
,m
(Temple - h n d 2)
rnsh.lll~,.r
UT
9 =u
Figure 9,10,11 and 12: Stratigraphic sequences of the shell beds at Loc.
Nos. 5 , 6 (Hatagala Temple Land), 7 (Bataata
Gurupokuna) and 8 (Bataata Gurupokuna).
-
-
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Y
'(83 L -ON '301) uo~?ae
aalefi w o ? s Lq dn
pa@ aAeq SaAIaA ilays ay?a?a3FpuFe u n y o d m n ~e)ee?ag?a spaq naqs ay$$osrtraq~eduo~+~sodap
pguozyo~
(a3 y) :g a?aId
-
172
J. Katupotha
Kalarnetiya (Henagahapugala) beds (Fig: 13, Location No. 9) have been
deposited on arocky headland (with a thin soil cover)whichis 13.8 m above mean
sea level. The shells Meretrix spp. are below 40 in size. Brokenlarge shells mixed
together with brown soil (10 YR 43). Pottery fragments are also found. The
shells are gathered even in rocky splits. Based on the deposition pattern there
is a possible indication that shells were deposited in the area due to severe strong
wave action (Plate 7b). At location no. 10, brown fine sand with clay (10 YR 4 3 )
with shell and shell fragments appear in botlrshell samples (Fig. 14). The shells
belong to Meretrix spp. (below40 mm in size other comments are same as location
no. 9). Inorganic content and grain sizes of the soil sample (10.1) are shown in
Figure 17. Many pieces of pottery are mixed with the shell bed in this area (Plate
7a). The thickness and the height of the shell beds a t Kalametiya (location nos.
9 & 10) are different to the other locations (Table 1). Eleven shell bearing microlayers can be identified at Kalametiya, on a former lagoon, and contain Meretrix
and Cerithidea spp. This sample point is not levelled due to the physical
obstacles (Fig. 18, Plates 7b ancl 8).
Plate 7: (A) Pieces of different'typesof pottery are found from the shell beds
at Kalametiya (Loc. No. 9 & 10). (B) Peaty-clay with shells contained in the last series of the separate pit Kalametiya (Plate 8).
Marine Moluskan Beds in the South Coast
LocnUon 9
R.-t
-
Kalnmcliya I
lbck
S%.U hj.r
oTop U,
Locstion 12
- b r a ~ n n2 (Aunukolumulls)
I a o b m
an.ubmr
Eltovko
Figures 13,14,15 and 16: Stratigraphic sequences of the shell beds at location nos. 9,10 (Kalametiya l and 2),-11 and 12
(Karagan land 2).
J. Katupotha
1 74
1 = Bluish clay
2 = Shrll and shell fragments
mixed with few orqanic matter and calcareous clay
3 = Shell and shell fraqients
riled with mrc organic
matter and calcareous clay
4 = Shell c ~ p o s e dof different
kinds of shell fraqmrntr
5 = Shell mixed with sand
b = Yellowish weathered
shrll
fragments
7 = Shrll with plenty .of shell
fraqments
B = Grayish &and
9 = Shell layer
10 = Shell and shtll fraqrents
11 = Brown and gray soil
Plate 8: Stratigraphic sequences of the shell bed at Kalametiya. Eleven microlayers (series) are identified based on the type and size of shells and
constituents of other materials.
The shells from Godawaya to Mirijjawela are deposited a s small pockets in
depressions (lagoon and lake bottoms) between sandy beach and undulating
terrain which gradually increase in altitude inland. The beds a t Kiula Kalapuwa
consist of tiny and small to large Meretrix spp. They are below 50 mm i n size. The
top soil of the area is covered by dull yellowish brown medium to fine sand (10
YR 413). The soil layer which is below the shell layer contains medium to fine
brown soil (10 YR 4/4).
Somewhat large shell beds are found a t Hunukotumulla on former lagoon
beaches a s well as lagoon bottoms of the western bank of the Karagan Lewaya
(Fig. 15, location no. ll),these can presently be seen a s mounds. They are also
covered by thorny bushes, stunted trees and grass. Sample 1in this location is
formed of 7.5 YR 412 grayish brown medium to fine sand clay soil. The compact
layer has weathered pebbles of iron. Grain sizes and content of inorganic matter
of the sample 1(11.1)are shown in'Fig. 19. The shells have mixed with grayish
Marine Moluskan Beds in the South Coast
brown soil (7.5 YR 412). Meretrix spp. are below 40 mm in size. Three shells are
found in position of life (30 mm below in size). Somewhat compact, soilin sample
3 is grayish yellow brown (10 YR 412) in colour). Calcareous clay patches and
weathered ironstone pebbles are found. Grain sizes and content of inorganic
matter of the soil sample (11.3) are shown in Figure 19. Some beds at the
Location No. 12 (Fig. 16) have deposited by wave action. The shells mix with
Brown soil (7.5YR 413) and fine sand and calcareous materials. Pebbles arevery
few. Plant remains are evident. Meretrix spp. (below 45 mm) and Anadara spp.
(below 65 mm) are main shell types ofthe area. Grain sizes andinorganic content
of the soil sample (12.1) are shown in Fig. 17.
The shell pockets in the northwestern area of the Karagan Lewaya (Fig. 20,
location no. 13), Nelumpathvila compose of dull yellowish brown soil (10 YR 51
4) with fine sandy clay and shelly sand. Meretrix spp. ofthe sample is varied from
small to somewhat large (below 40 mm). The shell layer a t location no. 14 Karagan 4 (Nelumpathvila) composed of dull yellowish brown soil (10 YR 514)
with fine sandy clay and shelly sand (Fig. 21). Somewhat large Meretrix spp. are
below 40 mm. Sample 1a t the location no. 15 - Karagan 5 (Nelumpathvila) also
contains brownish gray soil (10 YR 611) with calcareous sand and clay (Fig. 22).
The shell layer is composed of dull yellowish brown soil (10 YR 514) with fine
sandy clay and shelly sand. Meretrix spp. ofthe sample is somewhat large (below
40 mm).
Extensive shell beds a t Sippikulana, around the Maha lewaya and
Koholankala (Koholankala lewaya) are found on slight undulatings (lobes). The
shell layers here are thin compared to the beds a t Gurupokuna, Hungama and
the Karagan lewaya (Table 1).Furthermore, many shell patches are found in the
area between Maha Lewaya and the Nabadewa, Pallemulla area, on the eastern.
bank of the Malala oya (Plates 5b and 9). These shell beds are composed of stone
artifacts and quartzite pebbles. Based on the colour of the quartzite pebbles, it
is possible to infer that these may have been fired. Some beds are more than 4
km inland from the present coast.
A considerable amount of shell beds are found.in the area between Malala
lewaya and Embilikala kalapuwa (around Pallemalala, location no.16). These
beds also appear on mounds and ditches of the area covered by scrublands and
stunted trees. The shells at this location contain grayish brown soil (7.5 YR 412)
with fine sand and clay, weathered pebbles, quartz fragments, plant remains.
Meretrix spp. is below 45 mm and weathered Cerithidea spp. appear as fragments
(Fig. 23).
J. Katupotha
Sample No. 10 (1)
Sample No. 12 (1)
Figure 17: Inorganic contents and grain size analysis of the.soil samples 10.1
and 12.1.
Marine Moluskan Beds in the South Coast
Plate 9:
.
Glossy and well preserved shells and stone artifacts (quartzite)
foundat Nagadewa, left bank of the Malala Area, about 4 km inland
from the present coastline. Thick fertile alluvial soils overlain on
the shell beds.
J. Katupotha
O
hd..
Iz3..¶,.s
m .d.6
m kd..
m hd..
hW
ad..
m hd..
m M"
m
Ed..
.
tt
to
8
7
s
6
4
#
rn Sd" r
I
"n.i.
F i g u r e 18:
I
Stratigraphic sequences of the shell bed at Kalametiya.
Extensive shell beds are found in many mounds along the northern beach of
Embilikala kalapuwa and on the side left of the Bundala road. The shell beds
around Bundala lewaya are somewhat high and thick (Table 1) compared to the
shell beds a t Maha lewaya and Embilikala kalapuwa (location nos. 17,18 & 19).
Dark Brown medium sand to fine sand with clay soil (7.5 YR 313) appear a t the
location no. 17 - Bundala road 1(near 4th krn). The soil is somewhat compact.
Plant roots and other organic matter are found. Damaged Meretrix spp. found
here are below 30 mm in size. Weathered Cerithidea spp. found here are below
20 mm in size (Fig 24). Dark Brown medium sand to fine sand with clay soil (7.5
YR 313) of samples 1& 2 in location no. 18 - Bundala road 2 (near 4th km) is
somewhat compact. Plant roots with other organic matter are found (Fig. 25).
The shells (sample 3) have deposited with grayish brown soil (7.5 YR 4/2),
medium to fine sand, calcareous, clay and feldspar pebbles (rare). Meretrix spp.
found here are below 30 mm and weathered Cerithidea spp. are below 20 mm
in size. Grain sizes and content of inorganic matter are shown i n Figures
28(18.1) and (18.2).
Marine Moluskan Beds in the South Coast
179
Table 1: Details of the Rziised Shell Beds on the Southern Coast
No
1
2
3
4
5
'
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Location
Miniethiliya 1
Miniethiliya 2
Hungama - Bogahagodella
Hungama - Debaragodella
Hunga.ma - Hatagala
Temple Land 1
Hungama - ~ a t a ~ a l a
Temple Land 2
Bataata - Gurupokuna
Bataata - Gurupokuna
Kalametiya 1
Kalametiya 2
Karagan Lewaya 1
Karagan Lewaya 2
Karagan Lewaya 3
Karagan Lewaya 4
Karagan Lewaya 5
Bundala - Embilikala
Bundala Road 1
Bundala Road 2
Bundala Road 3
Maha Lewaya
Lower level
of the
shell
layer
(metres)
Ground Thickness
level
of the
(metres)
shell
layers
(metres)
Relief
mound
mound
mound
mound
mound
mound
rocky mound
rocky mound
headland
headland
lag. coast
mound
lag. coast
lag. coast
lag. coast
mound
mound
mound
mound
lag. coast
Source: Field Survey
Stratigraphic conditions, types of shells and the soils of the location no. 19
are as same as locations 17 and 18 (Fig. 26 and Plate 5b). Shells mix with dull
yellowishbrown soil (10YR 413) at the locationno.20 - MahaLewaya (Koholankala)
with calcareous clay. Well preserved Meretrix spp. of the sample is below 35 mm
in size (Fig. 27). They are also deposited on former lagoon beaches. The top soil
(alluvial) cover of the Bundala area is about 1.5 m thick. In location No. 20 at
Maha Lewaya (Koholankala)the shells are mixed with dull yellowish brown soil
t10 YR 413)with calcareousclay. Well preserved Meretrix spp. of the sample here
are below 35 mm in size. Present extension of the shell beds indicated that they
have been deposited on mounds, along the lagoon and lake beaches as well as in
lagoon and lake bottoms. Most of the beds are presently covered by superficial
deposits (alluvium and wind blown sand).
J. Katupotha
U
Organic
30.63
Sample No. 1 1 (1)
Sample No. 1 1 (3)
Figure 19: Inorganic Contents and grain size analysis of the soil samples
11.1 and 11.2.
Marine Moluskan Beds in the South Coast
m
LccnLion 13
- bragan
I
&a
C
W
LJ-
L l l TW h o
- Karngnn 5 (Nelumpalhviln)
Location 15
I
Berlrr
3 (Aunukolumulls)
sb.11 ,hpr
I
f&m Berlrs Z
Figures 20,21,22 and 23:
I
b o 4r.r
~
mn
I d .h.U
a d .ban 1 y . r
1q.r
lacalion 18
7 - d
- Bundala (Embilikala)
Series J
Stratigraphic sequences of the shell beds at
location nos. 13,14,15 (Karagan 3,4 and 5) and 16
(Bundala I).,
J.Katupotha
Location 17
-11
-
layer
I d %.I1
hy.r
Lucation 18
l
ao b
Bnndsla Rnsd (Nvar 4th k m )
WZi &d =.u .~9.1
0Tw Sell
- Rundab
y r
Loestion 18
Uaa
- Bundnla
Rand 2 (Near 4Lh km)
lR2Jrn.11 b~
E3tg s o
Rand 3 (Near 4th km)
5 W shall Lmr
Figures 24,25,26 and 27:
EllT g
Pol
Stratigraphic sequences of the shell beds at location
nos. 17,18,19 (BundalaRoad 2) and 20 (Koholankala).
Marine Moluskan Beds in the South Coast
183
Inorganic
Organic
36.06
Sample No. 16 (1)
Sample No. 18 (2)
Figure 28: Inorganic contents and grain size analysis of the soil samples 18.1
and 18.2.
J.Katupotha
-
Shells
Buried corals
+ Emerged
corals
-
BOO0
1000
6000
5000
4000
3000
2000
MSL
\ODD
(Year B.P.)
Figure 29: Curve indicates three episodes of high sea-level in Sri Lanka..
The shells of the study area belong mainly to three families: Veneridae
(Venus clams), Arcidae (Ark shells) and Potamididae (Horn shells). The
Veneridae is a large and well-known family of hard- shelled clams (strong and
glossy). The shell valves in the beds from Kalametiya Kalapuwa to Bundala
Kalapuwa belong to a few species; of which the dominant species in Meretrix
meretrix (Plate 1).The family Arcidae a?e heavy, squarish, porcelainous clams
having a so-called taxodant hinge - a straight hinge with numerous small teeth,
about the same size. Most common ark shell specieslivein warm watersin sandy
or muddy areas, while a few are found near coral reefs. The shells of this family
of the study area belong to Anadaragranosa orAnadara uropygmelana (Plate 1).
The Potamididae included into Cerithideacingulata (Gmelin, 1791)or Cerithidea
ornata (Plate 1) is a large brackish water group with elongate, solid shells
usually dirty brown in colour and. many whorled. Most columella live in
mangrove and estuarine areas.
Marine Moluskan Beds in the South Coast
185
The levels of the shell layers, types of the constituents, colour of the soil etc.
are described in detail, and shown in Figures 5 to 28 and Plates 1to 9. The types
of shells, live position of the valves, rocky artifacts, animal bones, and human
bones which were found from these shell beds are shown in these plates. Many
layers of different thickness of constituents and depositionpatterns indicate that
the shell and shell fragments have been deposited by storm waves especially at
Bataata - Gruupokuna (Plate 6). The shell beds a t Kalametiya which appeared
in many micro-layers can be identified based on the deposition pattern (Plates
7b and 8). The top shell layers contained tiny and small to large shells (below 40
mm in size) ofMeretriz spp. and Cerethedea spp. with calcareous sand which had
been piled up by wave action, while the lower layers contained weathered shells
and shell fragments. They are mixed with weathered organic material (10YR
2/1) and calcareous clay. Bluish clay ofthe bottom layer indicates that the shells
have been deposited on a grass biomass.
Emerged Shell Beds and Their Relationship to Sea-level Change
Katupothal~ecentlyindicated that the mid-Holocene sea-level was at least
1.5 m above that of the present level with three episodes as follows;
a) 6240 - 5130 B.P. (first episode of high sea level)
b) 4390 - 3930 B.P. (second episode of high sea level)
C) 3280 - 2270 B.P. (third episode of high sea level)
Following these high sea-level episodes,.the former drainage basins were
submerged forming lagoon and lakes further inland, sometimes 3 to 4 km inland
from the present coast. The undulating lobes which were extended towards the
coast and outcrops became headland. As a result, headland-bay-beaches were
created in many areas along the southern coast. Furthermore, the corals
presently beingburied between Akurala andMatara thrived on such embayments
where factors were suitable for the growth of coral especially on the southwestern and southern coast, while mollusks lived in intermediate and dry zone
coastal embayments.
It is suggested that the beachrock,slightly above from the supratidal zone,
on the west coast had developed around 3,700 y B.P. during this .stage. As
evidenced from "C dating of shells embedded in emerged reef patches", " and
corals ( in a position of growth)from emergedreef p a t ~ h e s ~the
l " ~climaticchanges
have occurred after the .mid-Holocene high sea-level. The lowering of sea level
can be recognized between 5030-4390y B.P. and 3930-3290 y B.P. by "C dating
of shell beds (Fig. 29 and Table 2).
J. Katupotha
Table 2: Dated Shell Beds along t h e Southern Coastal Zone
No
Locality
Elevation
(in metres)
Age &r B.P.)
(half-life =
Laboratory
No
5568 f30
1
2
3
4
5
6
7
8
Hungama
Hungama
Kalametiya
Kalametiya
Kalametiya
Karagan
Udamalala
Udamalala
Source:Katupotha 1988b and 1988c.
The bulk of the shells of these beds have been piled up by severe storm wave
action on mounds, in lagoon, lake bottoms and on sand dunes and headlands.
Present investigations indicate further that the shell valves of lagoon, lake and
channel beds (floors of marine and brackish pools) mostly accumulated as in situ
consequently on the lowering of sea level. Hence, the sea level around 4700 and
3600y B.P. was at its present level or slightlybelow it. Further, "C datingof shell
beds along the southern coast in the Hambantota district prove such changes
have occurred during the late H~locene.".~'
Furthermore, the deposits had been intermittently covered by vast quantities of coral andlor shelly sand and various types of debris moved by severe
monsoon waves. Thisis shown, in Miniethiliya,Hatagala, Bataata- Gurupokuna,
Kalametiya, Hunukotumulla, Nelumpathvila, Nabadewa and around Malala
lewaya areas. The colour and constituents of the layers show that they are
subject to local weathering conditions. Thicknessofthe top soil covered by these
means varies locally and sometimes more than lm thick alluvial soil underline
the shell beds. The deposition sequences of some shell patches of the mounds at
Udamalala and on dune deposits help to infer that the valves have been
discarded by early inhabitants and animals.
Conclusion
Stratigraphic sequences of the emerged Holocene shell bedsalong the southern
coast between Kalametiyakalapuwa and Bundalalewaya clearly show that they
are marine in origin. The shells of many ofthese beds have been piled up together
with stone artifacts, pieces of pottery, human bones and other animal bones,by
severe storq wave action on mounds in lagoon and lake bottoms, on sand dunes
and headlands. Present investigations of theseshell beds,futther indicate that
the shell valves .of lagoon, lake and channel beds (floors of marine and brackish
'
Marine Moluskan Beds in the South Coast
187
pools) mostly accumulated in situ consequently to the lowering of sea level
between 5030-4390 and 3930 - 3290y B.P. The deposition sequences of some shell
patches of t b mounds a t Udarmalala and on dune deposits help to infer that the
valves have been discarded by early inhabitants and animals. The deposition
pattern and different types of artifacts are valuable indicators in the study of
geological, archaeological and palaeoenvironmental significance of these beds.
Acknowledgement
The author thanks P. Ekanayake for helping in the field survey. This study was
supported by the Natural Resources, Energy and Science Authority (RG/90/E/01).
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