Level of Lake Iznik from late Neolithic to the last two millenia inferred from beachrock ages


Creative Commons License

Kiyak N. G., Erginal A. E., YİĞİTBAŞ E., BOZCU M., Öztürk M. Z., AVCIOĞLU M., ...More

2nd Symposium ARCH_RNT Archaeological Research and New Technologies, Rodos, Greece, 21 - 23 October 2010, pp.26

  • Publication Type: Conference Paper / Summary Text
  • City: Rodos
  • Country: Greece
  • Page Numbers: pp.26
  • Çanakkale Onsekiz Mart University Affiliated: Yes

Abstract

LEVEL OF LAKE İZNİK FROM LATE NEOLITHIC TO THE LAST TWO MILLENNIA INFERRED FROM BEACHROCK AGES

N.G. KIYAK1, A.E. ERGİNAL2, E. YİGİTBAS3, M. BOZCU3, M.Z. OZTURK1 , M. AVCIOGLU3 and E. OZTURA

1Department of Physics, Işık University, Turkey

kiyak@isikun.edu.tr

2Department of Geography, Canakkale Onsekiz Mart University, Turkey

aerginal@comu.edu.tr; muhammed.zeynel@gmail.com

3Department of Geology Engineering, Canakkale Onsekiz Mart University, Turkey

eyigitbas@comu.edu.tr; mbozcu@comu.edu.tr; m_avcioglu@comu.edu.tr

4Department of Geography Education, Canakkale Onsekiz Mart University, Turkey

erdaloztura@comu.edu.tr

Εισαγωγ? / Introduction: The carbonate-cemented beachrocks are of prime importance as they provide sound clues in interpretation of sea-level changes and paleoclimatical variations in coastal environments. Even though cementation of these coastal sandstones takes place through intertidal parts of tropical and subtropical coasts (Ginsburg 1953; Bricker 1971), an exceptional example of beachrock exists in many parts of the fresh-water Lake İznik coast in northwest Turkey. Thus, cementation appears to develop in such unusual environments in addition to the precipitation of connective carbonate cement from evaporation of marine waters (Stoddart and Cann 1965; Scoffin 1970), mixture of mateoric and marine waters (Schmalz 1971), shallow groundwaters (Hanor 1978) and biological processes (Krumbein, 1979). The formation of beachrock on Lake İznik coast can also correspond to better understanding of the archaeological history of environs of the lake when considering the existence of Ilipinar mound 2 km west of the lake coast.

Περιεχ?μενο/ Content: In this study, water level oscillations of the Lake İznik in the period from late Neolithic to the last two millennia was investigated on the basis of geomorphologic observations, microanalytical data and optically stimulated luminescence (OSL) dating estimations. The Ilipinar mound is considered here as a reference point as its settlement history dates back to 8000 years before present (Kayan 1995). The existing archaeological data show that water level of the lake during that time was a few metres higher than that in present when swamps were of greater area and the Ilipinar mound was at closer situation to the lake coast (Kayan 1987; 1996). Kayan (1987) suggested based on his detailed drill data that drier conditions, however, prevailed during climatic optimum at 6ka and 3ka BC, which gave rise to the formation of beachrocks under hotter temperatures at declined lake-level conditions.

Considering the above explanations, previous data suggested that the lake experienced two significant changes represented by higher water levels during late Neolithic to lower levels at last two millennia. To contribute to understanding of changed environmental conditions, we collected 11 samples of beachrocks from the southeast coast of the lake for microanalyses of beachrock cements and optical dating of quartz components. Samples were collected from different levels of seven different sites. The dating results show that age of beachrocks ranges between 7.406 ± 0.952 ka and 1.470 ± 0.201 ka. The older beachrocks typical of conglomerate in composition contain micrite envelops and, particularly, void fills consisting of 23.88% of CaCO3. The younger ones have, on the other hand, higher content of CaCO3 (29.55%) as well as lesser void ratios. The abundant carbonate content and cement fabrics of beachrocks is likely suggestive for rapid precipitation of connective material during effective evaporation. However, there is no data to suppose any significant decline in water level of the lake during the time interval of beachrock cementation. Furthermore, 1 m-thick beachrock beds show no change in microfabrics, chemical composition bedding and petrographical attributes, suggesting that water level of the lake as well as its water geochemistry that controlled the nature of precipitated carbonate was almost the same during cementation period.

Acknowledgements:

This study was supported financially by The Scientific and Technological Research Council of Turkey (TÜBİTAK, Project Number: 109Y143).

 

Αναφορ?ς/References:

Bricker, O.P. (1971) Introduction: beachrock and intertidal cement. In: Bricker OP., ed, Carbonate Cements. John Hopkins Press, Baltimore, MD, pp 1–3.

Ginsburg, R.N. (1953) Beachrock in South Florida. J Sed Petrol, 23,85-92.

Kayan, İ. (1987) Arkeolojik jeomorfoloji açısından Yenişehir ve İznik havzalarının çevre özellikleri. T.C. Kültür ve Turizm bakanlığı Eski Eserler ve Müzeler Genel müdürlüğü V. Araştırma Sonuçları Toplantısı II., 6-10 Nisan 1987, Ankara, p: 211-219 (in Turkish).

Kayan, İ. (1987) İznik Gölü batısındaki Ilıpınar Höyüğü çevresinde jeomorfolojik ve jeoarkeolojik araştırmalar. Ege Coğrafya Dergisi, 9, 43-70 (in Turkish with English abstract).

Krumbein, W.E. (1979). Photolithotropic and chemoorganotrophic activity of bacteria and algae as related to beachrock formation and degradation (Gulf of Aqaba, Sinai). Geomicrobiol J., 1,156-202.

Schmalz, R.F. (1971) Formation of beachrock at Eniwetok Atoll. In: Bricker OP (ed) Carbonate Cements. Johns Hopkins Press, Baltimore, MD, pp 17-24.

Scoffin, T.P. (1970) A conglomeratic beachrock in Bimini, Bahamas. J Sed Petrol., 40,756–758.

Stoddart, D.R. Cann, J.R. (1965) Nature and origin of beachrock. J Sed Petrol., 35, 243–247.