Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Biogeosciences Discuss., 7, 4641–4664, 2010 Biogeosciences www.biogeosciences-discuss.net/7/4641/2010/ Discussions BGD doi:10.5194/bgd-7-4641-2010 7, 4641–4664, 2010 © Author(s) 2010. CC Attribution 3.0 License. Evolution of ancient This discussion paper is/has been under review for the journal Biogeosciences (BG). Lake Ohrid: Please refer to the corresponding final paper in BG if available. a tectonic perspective N. Hoffmann et al. Evolution of ancient Lake Ohrid: Title Page a tectonic perspective Abstract Introduction N. Hoffmann1, K. Reicherter1, T. Fernandez-Steeger´ 2, and C. Grutzner¨ 1 Conclusions References 1Institute of Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, Germany Tables Figures 2Chair of Engineering Geology and Hydrogeology, RWTH Aachen University, Aachen, Germany J I Received: 14 May 2010 – Accepted: 31 May 2010 – Published: 16 June 2010 J I Correspondence to: N. Hoffmann (n.hoff[email protected]) Back Close Published by Copernicus Publications on behalf of the European Geosciences Union. Full Screen / Esc Printer-friendly Version Interactive Discussion 4641 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD Lake Ohrid Basin is a graben structure situated in the Dinarides at the border of the Former Yugoslavian Republic of Macedonia (FYROM) and Albania. It hosts one of 7, 4641–4664, 2010 the oldest lakes in Europe and is characterized by a basin and range-like geological 5 setting together with the half-graben basins of Korca, Erseka and Debar. The basin Evolution of ancient is surrounded by Palaeozoic metamorphics in the northeast and north and Mesozoic Lake Ohrid: ultramafic, carbonatic and magmatic rocks in the east, northwest, west and south. a tectonic Palaeocene to Pliocene units are present in the southwest. With the basin develop- perspective ment, Neogene sediments from Pliocene to recent deposited in the lows. Three major 10 deformation phases lead to the basin formation: A) NW–SE shortening from Late Cre- N. Hoffmann et al. taceous to Miocene; B) uplift and diminishing compression during Messinian - Pliocene; C) vertical uplift and (N)E–(S)W extension from Pliocene to recent. Neotectonic activity of the study area concentrates on N–S trending normal faults that flank the Ohrid Basin Title Page on the east and west. Seismic activity with moderate to strong events is documented Abstract Introduction 15 during the last 2000 y; the seismic hazard level is among the highest of the Balkan Peninsula. Activity of the youngest faults is evidenced by earthquake data and field ob- Conclusions References servations. Morphotectonic features like a wind-gap, fault scarps, a stepped series of Tables Figures active normal faults, deformed palaeosols, and fault-related hydrothermal activity are preserved around Lake Ohrid and allow delineating the tectonic history. It is shown that J I 20 the Lake Ohrid Basin can be characterized as a seismogenic landscape. This paper presents a tectonic history of the Lake Ohrid Basin and describes tectonic features J I that are preserved in the recent landscape. The analysis of morphotectonic features is used to derive the deformation history. The stratigraphy of the area is summarized and Back Close concentrates on the main units. Full Screen / Esc Printer-friendly Version Interactive Discussion 4642 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 Introduction BGD Lake Ohrid (693 m a.s.l.) in the southwest of the Former Yugoslavian Republic of Mace- donia (FYROM in the following referred to as Macedonia) and the east of Albania 7, 4641–4664, 2010 (Fig. 1) counts as one of the oldest lakes of Europe. Biological studies on endemic 5 fauna give hints on a Pliocene age (Stankovic, 1960). With a length of 30 km and Evolution of ancient 2 a width of 15 km it covers an area of 360 km and is larger than the neighbouring lakes Lake Ohrid: of Makro and Mikri Prespa. The lake is surrounded by the Mokra Mountains to the a tectonic west (1.514 m) and the Galicica Mountains to the east (2.265 m). The entire area can perspective be characterized as a seismic landscape (Michetti and Hancock, 1997; Michetti et al., 10 2005). Historical earthquake data and instrumental seismicity prove that the Ohrid area N. Hoffmann et al. is still tectonically active. The lake is of scientific interest for a number of disciplines. Biologists carry out re- search on endemic species that evolved in the almost 300 m deep lake. Hydrologists Title Page and hydrogeologists investigate the inflow rate variations, the chemical content and the Abstract Introduction 15 origin of the karst springs that mainly feed Lake Ohrid besides only small streamlets. Geoscientists focus their research on the evolution of the lake and the neighbouring in- Conclusions References tramontane basins. Palaeoclimatologists expect one of the furthest reaching sediment Tables Figures archives for the reconstruction of palaeoenvironmental conditions. This paper concentrates on the tectonic evolution of the Lake Ohrid area and de- J I 20 scribes tectonic features that are present in the basin surroundings. The geological and geodynamical settings are summarized and the main units are discussed. J I Back Close 2 Geodynamic setting Full Screen / Esc The geodynamics of Macedonia are mainly controlled by the Northern Hellenic Trench and the North Anatolian Fault Zone (Fig. 1). The Lake Ohrid Basin is the largest of Printer-friendly Version 25 a number of basins in the Dinaride-Alpine mountain belt that stretches along the west- ern shore of the Balkan Peninsula. This belt formed as a result of the ongoing Dinaric Interactive Discussion 4643 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | subduction, being characterised by a compressional stress regime nowadays. The Ohrid Basin, the Debar Basin to the north, the Korca and Erseka Basins to the south, BGD and the lakes of Mikri and Makro Prespa to the southwest are situated in a basin 7, 4641–4664, 2010 and range-like geodynamical setting (Figs. 2 and 3). The entire area is controlled by 5 present day E–W extension (Fig. 3). Lake Ohrid Basin marks the transition between the Palaeozoic orogen in the east (Pelagonian) and the Mesozoic rocks (Apulian) in Evolution of ancient the west (Robertson, 2004). Jozja and Neziraj (1998) and Tremblay et al. (2009) de- Lake Ohrid: scribe those units as Western Macedonian and Mirdita Ophiolite Zones. Today, the a tectonic main structural sections of the Eastern Adriatic coast can be subdivided into a com- perspective 10 pressional coastal domain, followed by a narrow zone of transition west of Lake Ohrid and the extensional domain in which the Neogene basins formed (see Fig. 3). The N. Hoffmann et al. roll back of the subducted slap (Fig. 3) leads over time to a westward migration of the entire system. This is also evidenced by the westward migration of the NS extensional domain of Eastern Macedonia, which is influenced by the North Anatolian Fault Zone Title Page 15 (Fig. 1) with its extension into the Aegean and the initiation of its right-lateral slip in the Abstract Introduction Early Pliocene (Dumurdzanov et al., 2005, Burchfiel et al., 2008). The older N-trending basins in Eastern Macedonia were disrupted by E–W trending basins, so the faults Conclusions References become younger to the west (Dumurdzanov et al., 2005). Tables Figures During Palaeozoic, a regional foliation developed in the Cambrian and Devonian 20 units. Thrusts and folds were the dominating deformations during the Mesozoic J I orogeny, later dominated by normal and strike-slip faulting, mainly in N–S direction. Fault patterns of the surroundings of Lake Ohrid indicate a diverse stress history. J I Ohrid Basin is a graben structure caused by the E–W directed extension, while the Back Close associated Korca and Erseka Basins are half-grabens, bordered by a NW–SE trending 25 normal fault on their eastern side. The sedimentation in the Ohrid Basin began in Late Full Screen / Esc Miocene with the formation of a pull-apart basin, controlled by right-lateral strike-slip movements. Subsidence and further extension account for the major dynamic compo- Printer-friendly Version nent since Pliocene-Pleistocene. Several 100 m of sediments accumulated since the Late Miocene (Dumurdzanov et al., 2004). According to Dumurdzanov et al. (2004) the Interactive Discussion 4644 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | oldest sediments in the lake are probably the Pliocene Piskupstina and Solnje Forma- tions. Today, sedimentation is likely to be compensated by subsidence. BGD Lake Ohrid Basin is flanked by active N–S trending normal faults that have a clear 7, 4641–4664, 2010 expression as fault scarps in the present-day landscape. These normal faulting can 5 also be derived from recent earthquake data (Fig. 2). Morphological features tend to trend mainly N–S in the west of the lake and N–S to NNE–SSW in the east. Further Evolution of ancient sets of NW–SE and E–W lineaments are also present. Latter are most likely related Lake Ohrid: to the E–W extension of the basin (Wagner et al., 2008). Active faulting along an E– a tectonic W trending fault has been described from Lake Prespa (Dumurdzanov et al., 2005). perspective 10 Between the lakes, the Galicica mountain range is separated from the Mali I Thate Mountains in the south by a normal fault that cuts the mountain ridge at ∼1500 m a.s.l. N. Hoffmann et al. (Aliaj, 2000). Fault surfaces and lineations are preserved in the entire area. Burchfiel (2006) reports recent slip-rates of not more than 2 mm/a with a very high uncertainty Title Page due to imprecise GPS data. Abstract Introduction 15 2.1 Seismicity and neotectonics Conclusions References In 518 AD, an earthquake destroyed the cities of Ohrid and Skopje (110 km NNE of Ohrid) (Petrovski, 2004).