Journal of Coastal Research 22 2 424-438 West Palm Beach, Florida March 2006 Paleoenvironmental Evolution of the Coastal Plain of Marathon, Greece, during the Late Holocene: Depositional Environment, Climate, and Sea Level Changes Kosmas Pavlopoulos t , Panagiotis Karkanas*, Maria Triantaphyllou 1 , Efthimios Karymbalist, Theodora Tsourout, and Nikolaos Palyvos"t tHarokopio University Faculty of Geography 70 El. Venizelou Str. 17671 Athens, Greece kpavlop@hua.gr *Ephoreia of Paleoanthropology- Speleology Ardittou 34b 11636 Athens, Greece §University of Athens Department of Geology Section of Hist. Geology- Paleontology Panepistimioupolis 15784 Athens, Greece tUniversity of Athens Department of Geology Section of Geography- Climatology Panepistimioupolis 15784 Athens, Greece ABSTRACT PAVLOPOULOS, K.; KARKANAS, P.; TRIANTAPHYLLOU, M.; KARYMBALIS, E.; TSOUROU, T., and PALYVOS, N., 2006. Paleoenvironmental Evolution of the Coastal Plain of Marathon, Greece, during the Late Holocene: Depo- sition Environment, Climate, and Sea Level Changes. Journal of Coastal Research, 22(2), 424-438. West Palm Beach (Florida), ISSN 0749-0208. The Middle-Late Holocene infill of the coastal plain of Marathon, Greece, consists of lagoonal deposits related to the decrease of the sea level rise rate. Between a little earlier than 5800 and 3500 Cal BP, mesohaline-oligohaline lagoonal carbonate muds were uninterruptedly accumulating in the central and more seaward areas of the embayment. At the same time in the nearshore environment, oligohaline pelloidal charophytic muds were deposited during periods of a relatively increased rate of sea level rise, whereas during periods with lower rates of sea level rise, extensive marshes were forming in supratidal settings. The formation of framboidal pyrite and evaporitic minerals point to a periodic anoxic, sulfidic, and schizohaline environment. In addition, a warm, strongly seasonal climate under the influence of resurgent continental groundwater is suggested. After 3500 Cal BP, the lagoon witnessed a relatively abrupt change to palustrine mud deposition. The embayment was frequently exposed, and communication with the sea was not perennial. This period, terminated at about 2400 Cal BP, is most likely associated with a wetter and probably more temperate climate. The uppermost depositional unit is dominated mostly by fluvial sediments deposited in a wetland with no recorded communication with the sea. The sea level rise, indicated by several peat formations, is estimated to be lower than that predicted by the glacio-hydroisostatic model and the data from other Greek areas that are considered relatively stable. Hence, a tectonic uplift of the area is suggested at a rate of about 0.4-0.5 mm/y, which almost counterbalances the predicted rate of relative sea level rise of about 0.6-0.7 mm/y for the last 2000 years. This is a plausible explanation for the relative geomorphological stability, since at least Classical times, suggested by the historical documents. ADDITIONAL INDEX WORDS: Lagoonal sedimentation, paleoecology, paleoclimate, sea level changes. INTRODUCTION Holocene sea level and climate changes and anthropogenic effects are recorded in the sediments of coastal marshes and wetlands (CLAVA et al., 2001; COLE and Liu, 1994; VELLA and PROVENSAL, 2000). In particular, coastal marshes are sensitive to local paleoenvironmental changes and can pro- vide a powerful tool for studying coastal changes over the last thousands of years. The Marathon coastal plain, located in NE Attika, Greece, has been inhabited since the Neolithic, demonstrating great historical and archaeological significance. The area is famous for the ancient battle of 490 BC, fought between the Athen- ians and the Persians. After Athens won the competition for DOI:10.2112/03-0145.1 received 4 February 2004; accepted in revi- sion 17 February 2004. Part of this work was financially supported by the Ministry of Public Works and the Environment and especially by the Athens 2004 Service. the 2004 Olympic Games, the Marathon area was proclaimed as a national park by the Greek government, and a rowing center was constructed. Given the great environmental and archaeological importance of the area, its paleoenvironmental condition in antiquity gave rise to much controversy. Accord- ing to archaeologists, its geomorphic features have remained relatively stable since at least the Classical times. If the above statement is true, the mere fact of its stability makes it a valuable study area (KRAFT, 1972). BAETEMAN (1985) presented a detailed study of several sediment cores drilled in the area, giving information on the stratigraphic sequence of the plain, lacking, however, a com- plete description of sediment facies and microfossils. There- fore, several questions regarding the paleogeographic and pa- leoenvironmental changes of the area have remained unan- swered. This study attempts to determine the depositional environ- ments since about 6000 BP, as well as climate and sea level changes recorded during that period, with the use of micro- if#1 1114.