A late Holocene record of environmental changes from Kotihi lagoon, Elis, Northwest Peloponnesus, Greece N. Kontopoulos * , A. Koutsios Department of Geology, University of Patras, 265 00 Patras, Greece article info Article history: Available online 18 October 2008 abstract The late Holocene instability of the coastline of Elis was investigated using two boreholes. Three evolutionary stages are distinguished. (A) From earlier than 7000 to 3810 cal BP there was a static coastline and predominantly lagoon floor sediments accumulated. (B) From 3810 to 1400 calBP, the rate of sedimentation was higher than the rate of relative sea level change, possibly because of the proximity of the mouth of the Peneus River, and predominantly fluvial sediments accumulated. (C) From 1400 cal BP to present time, landward migration of the coast and the re-establishment of lagoonal facies was probably the result of the avulsion of the Peneus River. From 150 calBP until present, the rate of sedimentation in lagoon area was high about 5.2 mm/a. Ó 2008 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Coastal stratigraphic studies allow the recognition of coastline changes, which are controlled by rates of sediment supply, rates of eustatic sea level changes and rates and types of tectonic move- ment. The lagoonal area under study is located within the Elis region in the northwestern part of the Peloponnesus, Greece, on the ancient delta of the Peneus River. Here, tectonic movements and variations in water and sediment yield from streams are associated with coastal change (Bird, 1985). The main purpose of this study is to attempt a chronologic reconstruction of the late Holocene environmental evolution of Kotihi lagoon. Furthermore, this study tries to shed some light on the avulsion of the Peneus River, the relationships between the relative sea level changes and the rate of sedimentation, and the human impact on the late Holocene evolution of the lagoon. 2. Geological and tectonic setting The Kotihi lagoon is located along a wave dominated and micro- tidal coast in the northwestern Peloponnesus, about 40 km southwest of the city of Patras (38  01 0 N 21  17 0 E) (Fig. 1). The lagoon is approximately orthogonal in shape and is situated on 6.32 ha of flat land at the northeastern tip of the Paleo-Peneus River. West- wards it is separated from the open sea by a low relief barrier island and has limited communication with the open sea, with a stable, short and narrow inlet. Eastwards, on the landward lagoonal margins, small-scale deltas have prograded into the lagoon. Inter- tidal and supratidal mud flats are developed among the deltas, covered with plants, e.g. Salicornia. The lagoon is polysaline and exhibits a salinity ranging between 8& and 17&, during the winter rainy season, and from 20& to 37& during the summer (Bouzos and Kontopoulos, 2004). The average depth of the lagoon is only 0.5 m. The surface sediment is dominantly sandy mud (75%) and the remainder is clay and mud (Bouzos and Kontopoulos, 1998). The C org content is 1.5–4% and CaCO 3 content ranges from 6% to 42% (Bouzos and Kontopoulos, 1998). The sediment is very poorly to extremely poorly sorted, with generally coarse to very coarse skewness (Bouzos, unpublished data). The water surface of the lagoon was permanently lowered between 1945 and 2000. This event is a result of human activities including deforestation and agriculture, rapidly changing the ecological and environmental situation of the lagoon (Avramidis et al., 2008). The old Peneus river delta was located south of the Kotihi lagoon. The present Peneus River delta has been established since the 17th century AD (National Bank of Greece Cultural Foundation, 2006) probably by artificial diversion (Raphael 1973, 1978)(Fig. 1). The broad area of the Kotihi lagoon is located at the north part of the Ellis graben. This structure lies very close to the convergent boundary between the African and European plate and the diapir- ism area of the evaporites that belong to the Alpine basement. The neotectonic fault zones that occur in this part display a complex pattern, comprising NNW-SSE, NNE-SSW and WNW-ESE trending faults. Tectonic activity has occurred through the Holocene (Lekkas et al., 1992) and the most recent strong earthquake event (Mw 6.3) was June 8, 2008. During this event significant vertical displacements, up to 25 cm identified along a major high angle * Corresponding author. Tel.: þ30 2610 997591; fax: þ30 2610 996272. E-mail addresses: kontopou@upatras.gr (N. Kontopoulos), koutsios@upatras.gr (A. Koutsios). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ – see front matter Ó 2008 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2008.10.001 Quaternary International 225 (2010) 191–198