PROCEEDING ERNATI N· LSYMPOSI N ENGJNEERINGGEOLOGY AND THE' RONME T,ORGANJZEDBYTHE REEK ATIONALGRO POF IAE ii ATHEN / REECE/23-27 JU E 1997

En inee · Geology and theE irorunent Editor.\

..MARINO Nellianal Technical Ulliversity of thells

G.C.KOUKTS {)1I/versirv (~f Parras

J.CT IAMBAOS Cel/tral Pllhlic Works Laboratory. Athl'IIS

G.C.STOLJRNARAS UI/il'ersit\ a/Athens

OFFPRINT ITIRE-A-PART

A.A. BALKEMAI ROTT RDAM / BR OKFIELD/1997

fcngineering Geology and fhe Environment, Marinos, Koukis, TSlambaos & Stournaras (eds) © 1997Balkema, Rotterdam, ISBN 90 5410 8770

Gerakas Gulf, Greece: A natural park and a geological monument

M. D. Derrn itzakis, H. Drirlia & M.VTriantaphyllou National University of Athens, Departmenl ofGeology. Section ofHistorical GeoloRy-PaleolJlOloK'j. Athens, Greece

ABSTRACT: Gerakas Gulf in Laganas Bay, SE of Zakynthos island, constitules the mo~t important remaining nesting area for the loggerhead se.a turtle Carella mrella in the whole Mediterranean, In addition, it compri~es an important geological monument as il is possible to recognise the Plio-Pleistocene boundary based on calcareous nannofossil hio.traligrapl1ic events. For these reasons, Gerakas Gulf is thought to represent a special site of Natura I heritDge.

1. INTRODUCTION

Gerakas Gulf i~ found in Ule SE side of Zakynthos island (Ionian ~ea) and constitutes pari of the Laganas bay (Fig. 1). One of the most reperesenlalive geological sections of Gerakas Gulf­Geraka~ section- has been studied in delail in order to estahlish the existence of a possible geological monument (definition of the Plio-Pleistocene boundary).

In addition special reference is made to lhe loggerhead sea-turtle Caret/a caretta - a threalened species - which its existellce depcnd~ entirely un the protection of the nesti ng area of Laganils bay.

The scope of this paper is to reini0re<:: the general consesus that Laganas bay and specially Gerakas Gulf represents a special site or Natural heritage. as it may combine a sea turtle Marine Park with a very impOTlant geological momunent.

2. GERAKAS GULF AS A SPECIAL ECOSYSTEM

Carella carella is the only of the seven speci,~~ of sea turtles of the world and the only of the three species of the Mediterranean which is nesting in our country. Several nesting beaches of the loggerhead sea-turtle Carella carella have been identified by the Sea Turtle Protection Society (STPS) in Greece. Laganas bay in Zakynthos - which includes the Gerakas area (Fig, 1)- is the most important remaining nesting area for the loggerheads in the whole Mediterranean, hosting 800 to 1800 nests, depending on the season, on a total of 4km of sandy bt:ach.

Sea turtles spend almost all their life in the sea, but their existence depends entirely 00 specilic beaches where female turtles lay their eggs. Every summer loggerheads trom different pans of the Mediterranean return to their nesting beaches in lhe bay of Laganas. The female turtle comes ashore at night to lay her eggs in the sand. Sea turtle eggs must remain Wldisturbed in the warm sand tor about 60 days before they hatch. From late July, hatchlings start making their appearance on the surface of the beach. They then make their way dO.....'ll [0 the sea.

Today, sea-turtles are con~idered a threatened species as the lUlcontrolled exploitation of the envirorunent by man has reduced their numbers. Sea­turtles, their nests, eggs and hatchlings as well as their breeding habitats are protected under greek and international legislation. The protection of the bay Ill' Laganas and Gerakas on Zakynlhos, the single most important loggerhead nesting area in the Mediterranean, has been a hoi envirorunental issue in Greece for over 10 years and has becn high on the agendas of illtemational conventions and medings. Progress has been made in smaJl but decisive sleps. The nesting beaches of (,agana~ bay, have bc.;n declart:d as "specially pmtccted areas tor nalure conservation" (1984. Presidential Decree). Fllr Greece, the establishment of the tirst sea-turtle Marine Park will be a major break through in conservation.

3. GERAKAS GULF: A GEOLOGICAL MONUMENT

Gerakas section is located in the SF sidc of Zakynthos along the coast of Geraka~ Gul f (Fig. 1).

------------------

Fig.I. Gerakas section in Laganas bay

It consists of three Depositional Sequences (Fig. 2), which are indicative of a coastal - shallow marine environment and are bounded by unconfonnities (Triantaphyllou et al., in press). Depositional Sequence I comprises "Seliniako Topio Unit" and covers the west edge of Gerakas coast. It is composed of 30m of laminated marls with occasional lenses or layers of fine to very fine grained siltstone and sandstone with dispersed macrofossils. Depositional Sequence II is composed of "Gerakas Unit". Most of the part of this Sequence is exposed along the rest of the coast up to the cape Gerakas. This part is mainly composed of 60m of clays, silty clays and calcarenites with dispersed thin conglomeratic channels i,n between. Depositional Sequence III consists, at its base, of parallel­laminated calcareous sandstones alternating with yelJow sandy marls which become more marly in a higher position.

Several papers have been published concerning planktonic and benthic foraminifera, ostracodes and calcareous nannofossils of Gearakas section (0ermitzakis, 1978, Dermitzakis et al. 1979,

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Dermitzakis & Georgiades-Dikeoulia, 1987, Tsapralis, 1981, TriantaphyIlou, 1996, Triantaphyllou et al,. in press).

Based on calcareous nannofossil biostratigraphic events (detection of medium Gephyrocapsa spp. FAD I bmG event), it is possible to determine the Pliocene-Pleistocene boundary in Depositional

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Fig.2. Depositional Sequences J (A) and H (B) in PlioceneIPleistocene boundary has been recognised

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Gerakas section. The frame shows where the

equence I of Geral< ection (Fig. J 4). It must be noted that the matter of the definition of

the Plio-Pleistocene boundary stralOtype remained in a controversial state for several years. Following a decade of study and discus ions the Working Group of International eological Correlation Program (IG P) Project 41 "Neogene-Quaternary B Wldary" and the International Union on study of the Quaternary (lNQUA). as well as the Committee on Mediterranean Neogene tratigraphy (CMNS) considered a section near Vrica S.1taly. as the potential Pliocene-P)eistocene boundary stratotype (Aguire & Pasini, t 985). ICS (International Commission on Stratigraphy) approved the definition of the Plio-Pleistocene bOWldary in Vrica section (Basset 1985).

The "golden spike" marking the boundary in Vrica section was placed at the base of a claystone lmit conformably overlying the sapropelic marker bed e. This Level has been shown to lie at r near the top of the Olduvai (C2n) Subchr nozone (Backman et al. 1983, Tauxe eJ al. 1983) indicating an age of 1.71 Ma (Berggren e/ al. 1995b,).

The establishment of a new global high-resolution biostratigraphy based on numerous calibrated nannofossil bioevents transformed to biochronologic datums (Rio et al. 1990, in press, Raffi et al. 1993, Berggren et ai. L995a) provided a detailed biostratigraphic and biochronologi framework for the Plio-Plei tocene time interval.

The biostratigraphic analysis based on calcareous narmofo sils of the marly deposits of Depositional Sequences I,n of Gerakas section lead to the following conclusions. The lower pmt of Depositional Sequence I can be assigned to MNN19a biozone (Rio el 01. 1990). The first appearance of medium Gephyrocapsa spp. (Gephyrocapsa oceanica s.l.) specimens -at about 36m from the base of the Sequence- allows at the specific poinl the definition of the PliocenelPleist cene boundary, based on biostratigraphic events and suggests an age of 1.67­1.70 Ma (Berggren et al. 1995a) for the specific stratigraphic interval. The uppermost part of Depositional Sequence r can be correlated with MNN19b biozone. The derived data point to uppermost Pliocene! lowermost Pleistocene time span. Concerning Depositional Sequence lJ the derived data point to lower Pleistocene in age (TriantaphyIJou el a1. in press).

4. DISCUSSION-CONCLUSIONS

A very important geological event has been

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'Fig.4. Biostratigraphic location of the studied Gerakas section (Depositional Sequences T and II) based on calcareou plankton biostratigraphy in the Mediterranean, correlated to chronostratigraphy and to the Geomagnetic Polarity Time Scale (Rio el aI., 1990. Magnetostratigraphy is based on Berggren el al., 1995a,b) .

re ognised in Gerakas Gulf. The determination of the Plio-Pleistocene boundary based on ca.lcareous Ilarmoplankton biostratigraphic events in the continuous sedimentary sequence of Gerakas section is unique in the greek area. This fact allows the attribution to the Gerakas section as a geological monument. The existence of the PLio-Pleistocene bOWldary in

the sequence of Gerakas ection in combination with the fact that Geraks Gulf constitutes the most important nesting area for Lhe sea turtl Caretta caretla in the whole Mediterranean, strongly supports the efforts of the Sea Turtle Protection Society (STPS) to declare Laganas ay Marine Park.

In the last couple of year , things have started to move in favour of tbe protection of Gerakas Gulf. This can be attributed to many factors: the persistence of the STPS to remain n the island and approach local auth rities and individuals, carnpaignjug both at local and international level for ' a National Marine Park; the close coo ration with local and other NGOs (Zakynthian Ecological Movement, WWF Greece, Greenp ase cc); the detennination of the greek government to go ahead with the National Marine Park speeding up Management Plan Stlldy that has en dragging on since 1991. Local communities, the Prefecture, tbe

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Ministry of nvironment, the con ervationists are online to develop viable proposals for the Marine Park. Recently the Prefectural Council oted for the immediate e tabLishment of a National Marine Park.. a real tum arowld from previous decisions.

We can all help the ea turtles by supporting the establi runCDt of a Marine Park. The uniqueness of the sea turtle habitat .in Zakynthos is at stake. Un ontrolled coastal velopment and increasing human interferense are exertIng enormous pre sures on the single most important loggerhead nesting area in the Mediterranean.

The be t hope for th ea turtle is the establishmcnt of a Marine Park in the bay of anas/Gerakas. This will regulate development create alternatives

for tile affected land owner, promote a sustainable tourism that respects the environment and at the arne time fully protects the nesting beaches. This

way we are giving the sea turtles a fair chance to survive.

5. REFERENCES

Aguire, J & G.Pasini, 1985. The Pli cene­Plei tocene boundary Episodes, 8(2): 116-120.

Backman,]., N.J.Shackleton & L.Talix , 1983. Quantitative nannofossil correlation to open o can deep- ea sections from Plio· Pleistocene boundary at Vrica, Italy. ature. 304: 156­158.

Bas et M.G., 1985. Towarsd .. ommon Ian age' in Stratigraphy. Episode.. 8(2):87­92.

Berggren W. " Hilgcn, F.J., Langereis, .G., Kent, n.v., Obrndovi h, J.D., Ratli, L, Raymo, M.. & N.J. Shackleton, 1995a. Late Neogene chronology: New perspectives in high-resolution stratigraphy. GSA Bulletin, 107(11):1272-1287.

Berggren, W.A., Kent, D.V., Swi her, C.., m & M.-P. Aubry, 1995b. A revised Cenoz ic geochronology and ch ronostratigraphy, in Berggren, W.A., Kent D.V., Aubry, M.-P. & Harden 01, J., Geochronology, time calcs and stratigraphic correlation: Framework for an historical ge logy: SEPM, Special Publicatioll, 54: 129-212.

Dermitzakis,M.,D.1978.Stratigraphy <U1d sedimentary history of the Miocene of Zakynthos (Ionian isllmds, Greece). Ann Geol. pays Hell., 29:47-186, cum.lit.

Dermitzaki ,M.D., Papanikolaou ,D. and Z.Karotsieri , 1979. The marine Quaternary formations SE Zakynthos island and their Paleogeographic implications. Proc.6lh Geol. Aegean Region, Athen 1977, 1:407-415.

Dermitzakis,M.D. & E.Georgiades-Dikeoulia, 1987. Bio tratigraphy and pale environmental reconstruction of the E part of Zakynthos island (W.Greece) during the Plio-Pleistocene. Interim-Colloquium, Evolution climalique dans Ie domaine mediterraneen au Neogen, R.C.M..8., Montpe/lier-Barcelona, September 21-25, 1987, coil. abstracts, p.28.

Ram,l., Backman,]., Rio,D. NJ.Shackl ton, L993. Plio-Pleistoccn nannofo sil bi stratigraphy and calibration to oxygen isotope stratigraphies from DSDP Site 607 and ODP Site 677.Paleoceanography, 8:387-408

Rio,D., Backman,J. and I.Ram, in press. Calcareous nannofossil biochronology and the Pliocene/Pleistocene boundary.ln Van Couvering,J .A. Ed.), The Neogel/e! Quaternary BOUllrklry, Final Report of the IGCP Project n.41.Cambridge, nited Kingdom, ambridge University PI' SSt

Rio,D., Raffi I. & G.Villa, 1990. Pliocene­Pleistocene calcareous nannofossil distribution attems in the Western Medi­terranean.In Kastens K.A., Ma c1e,J. et aI, Proc.ODP, Scient.Res., 107:513-533.

Tauxe,L., Opdyke N.D., Pasini, . and C. lmi, 1983. The paleomagnetism of the rica section (Calabria, Italy), the propo ed PliolPleistocene boundary stratotype section.Nalure, 304: 125-129.

Triantaphyllou, M.V., 1996. Biostatigraphical and ecoslratigraphical observations based on calcareous nannofossils, f the e.astem Mediterranean Plio-Pleisto- cene deposits. Gaia, ational and Kapodistrian University of Athen , Edition of the Department f Geology, I, pp.229.

Triantapbyllou, M.V., Drinia, H. & M.D.Dermitzakis, in press. The Plio­Pleistocene boundary in Gerakas sectJ n, Zakynthos (I nian islands). Biostratigra-phic and pal ecological observations. Nelles .1ahrbuchfur Geologie und Palaeontologie.

Tsapralis V., 1981. C ntribution to th' study of Plei tocenc of Zakynthos i land, W.Greece (ostracoda -paleoenvironment) PhD the is, pp.134, Patras.

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