Late Cenozoic development of the Strouma and Mesta fluviolacustrine systems, SW Bulgaria and northern Greece

ARTICLE IN PRESS

Quaternary Science Reviews 26 (2007) 2783–2800

Late Cenozoic development of the Strouma and Mesta fluviolacustrine systems, SW Bulgaria and northern Greece Ivan Zagorchev Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria Received 2 August 2005; accepted 1 July 2007

Abstract The Strouma and Mesta are two of the largest rivers that drain across SW Bulgaria and northern Greece into the northern Aegean Sea. Their modern valleys, flanked by Quaternary river terraces, are incised into a diverse landscape, which records the region’s complex tectonic history. A network of lacustrine basins existed in the region in the Late Oligocene to earliest Miocene, but was disrupted by thrusting and folding related to Early Miocene transpression. This deformation was followed by a period of erosion, covering most of the Early and Middle Miocene, which probably marked the initiation of the Strouma and Mesta fluviolacustrine system, with geometries unrelated to the older systems. The first clear evidence of these river systems dates from the Middle Miocene (late Badenian to Sarmatian). The systems evolved in the Late Miocene (Maeotian to early Pontian), when lakes existed, characterized by diatomaceous algae and by occasional burial of abundant plant fragments and coal formation. Areas in the south, south of the Kerkini fault, were intermittently submerged beneath the Aegean Sea at this time. Intense localized uplift of horst blocks in late Pontian and Pliocene, associated with crustal extension, resulted in deposition of thick alluvial fans, with tilting of sedimentary successions in adjacent grabens evident by the end of the Pliocene. The highest horsts (Osogovo, Rila, Pirin, and Belasitsa) experienced additional uplift in the Pleistocene, in part as a result of regional uplift and in part through continued normal faulting. Pleistocene climate change also resulted in influxes of glacial and fluvioglacial systems. The present form of the Strouma and Mesta fluviolacustrine systems is thus the result of interplay between crustal extension, regional uplift, and global climate change. r 2007 Elsevier Ltd. All rights reserved.

1. Introduction Southwest Bulgaria, along with neighbouring parts of Macedonia, forms the northern margin of the Aegean extensional province (Figs. 1 and 2). Many people have discussed the timing, sense, and magnitude of the extension within this region. Serious differences exist between past interpretations of the Late Cenozoic evolution of SW Bulgaria (e.g., those by Zagorchev, 1992a, b; Burchfiel et al., 2000), as Westaway (2006) has recently highlighted. Work on this region to date, published in the international literature, has concentrated on documenting the active normal faulting associated with the Late Cenozoic extension. The main aim of the present study is, instead, to describe the Late Cenozoic palaeogeography, concentrating on the evolution of fluvial/lacustrine systems. This topic has been studied in detail over many years and E-mail address: [email protected] 0277-3791/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2007.07.017

published mainly in the Bulgarian and Greek local literature; the material is thus largely inaccessible to an international audience. Thus, Miocene and Pliocene environments in SW Bulgaria and adjoining parts of Greece (Fig. 2) have been described by Nedjalkov et al. (1986, 1988, 1990), Psilovicos and Syrides (1983, 1984), Psilovicos (1984, 1986), Syrides (2000), and Psilovicos et al. (1987). The Pleistocene fluvial terraces of the Strouma valley have been studied by Ivanov and Mihaylov (1965) and others; Vrablyanski (1970, 1974, 1977) made the first detailed instrumental measurements. Tchoumatchenco (1966) attempted reconstruction of the Pliocene palaeo-drainage in the northern part of the region. The evolution of the Mesta/Nestos fluviolacustrine system has been discussed by Choleev and Baltackov (1989), Baltackov and Choleev (2000), Riegel et al. (1995), and by Psilovicos and Vavliakis (1989). Dumurzanov (1997), Krstic´ et al. (1999), and Marovic et al. (1999) have discussed the evolution of the lake system in the western

ARTICLE IN PRESS 2784

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

Fig. 1. Map of the study region, showing the principal mountains, the present extent of the Strouma and Mesta rivers (the drainage catchment area is delimited with thick broken line) with the main tributaries and the major localities discussed in the text. The principal gorges are: ZG, Zemen Gorge; SG, Skrino Gorge; ZhG, Zheleznitsa Gorge; KG, Kresna Gorge; RG, Roupel Gorge; AG, Angitis Gorge; ChG, Chech Gorge. *Symbols indicate the former course of the Mesta/Nestos into the lower Strouma/Strymon.

Balkan Peninsula (Macedonia/Albania), giving rise to the concept of the ‘Aegean-Drim Neogene lacustrine sedimentation domain’, although this idea has been criticized (see Tzankov et al., 2000, and references therein) and contradicts other evidence (Zagorchev, 1992b). The present paper will thus summarize the evidence concerning the Late Cenozoic palaeogeography of the Strouma/Strymon area. The evidence will be discussed within the framework of knowledge regarding the palaeogeography and neotectonics of the wider North Aegean region (e.g., Jaranoff, 1963; Mercier, 1979; Dermitzakis and Papanikolaou, 1981; Schroeder, 1986; Kojumdgieva,

1987; Dermitzakis, 1990). Previously published evidence (Zagorchev, 1992a) will be used except where important new data require revised interpretations. Correlations between Mediterranean (standard) and Paratethys (regional) stages have recently been refined by Popov et al. (2004, 2006). Snel et al. (2006) have provided new data on the marine incursions in the northern periAegean, relating to the interplay between differential vertical tectonic movements and the isostatic uplift. Westaway (2006) reviewed the published data on the terraces of the Strouma and Mesta rivers and drew analogies with fluvial sequences in western Turkey.

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2785

Fig. 2. Map of the study region, showing Late Cenozoic sediments, faults, and localities discussed in the text.

The Late Cenozoic stratigraphy of the study region is summarized in Fig. 3. Some difficulties arise over interpretation, because different depocentres have been studied by different people, the taxonomy of fossils has not been standardized, and it has not always been clear precisely where in the stratigraphy reported fossils have been located. As a result, studies of particular deposits using different biostratigraphic techniques (e.g., mammals, gastropods, foraminifers, bivalves, megaflora, palynomorphs, or diatoms) have sometimes led to inconsistent age assignments. One may thus, for instance, contrast the data of Kojumdgieva et al. (1984a, b), Koufos et al. (1995), Nikolov (1985), Palamarev (1990), Palamarev and Ivanov (1998) Palamarev et al. (1999), Psilovicos et al. (1987), Temniskova-Topalova and Ognjanova-Rumenova (1997), Spassov (2000), Tzankov et al. (2000) and Vatsev and Petkova (1997). Nevertheless, the totality of the results obtained allows the Late Cenozoic palaeogeographic evolution to be reconstructed. The recent revision of the mammalian biostratigraphy by Spassov et al. (2006) is also most useful. It should be noted that the present Bulgarian territory has been a zone of continuous interaction between

the Aegean (marked by transitions from the Mediterranean to the Paratethys), the Central (Pannonian), and the Eastern (Dacian–Euxinian–Caspian) Paratethys. Following Kojumdgieva (1987) and others, the stratigraphic stages customarily used in Bulgaria follow the Central Paratethys nomenclature up to the beginning of the Sarmatian, and afterwards adopt the Eastern Paratethys nomenclature. This switching (from Central to Eastern Paratethys nomenclature) has often been (and still is) a source of misunderstanding. Fig. 3 indicates how these stage names relate to mammalian biozones and to the standard stage names that have been defined within the marine realm.

2. Present state of the Strouma and Mesta fluviolacustrine systems The term ‘fluviolacustrine system’ is used in this paper in a wide sense. It covers the whole drainage system of a large river from its source to the sea, and embraces all relevant terrestrial sedimentary environments, not only fluvial

ARTICLE IN PRESS 2786

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

Fig. 3. Time charts for the Late Cenozoic sedimentary formations within the Strouma fluviolacustrine system. Based on data from publications by E. Kojumdgieva and co-authors, Bakalov and Zhelev (1996), Dinter (1998), Gramann and Kockel (1969), Lalechos and Savoyat (1977), Zagorchev (1992a), Spassov et al. (2006) and others, using the Gradstein et al. (2004), Ro¨gl (1999), and Popov et al. (2004) chronology. The Brezhani Basin, illustrated, is one of the late Palaeogene sedimentary basins that precede the earliest Miocene phase of crustal shortening; its folded sediments and the boundary thrust itself are covered with depositional unconformity by the Pontian–Pliocene Kalimantsi Formation. The following Neogene formal lithostratigraphic units (details in Zagorchev, 1992a) are shown: Kyustendil graben: tv—Tavalichevo Fm., ko—Koilitsa Fm., sk—Skrinyano Fm., sp—Spasovitsa Fm.; Blagoevgrad graben: ba—Badino Fm., bk—Barakovo Fm., dz—Dzherman Fm., pk—Pokrovnik Fm., brc—basal red conglomerate; Simitli graben: ka— Kalimantsi Fm., si—Simitli Fm., ch—Cherniche Fm., cbf—coal-bearing (Oranovo) formation; Gotse Delchev graben: sr—Sreshnevo Fm., nv—Nevrokop Fm., bd—Baldevo Fm., vl—Valevitsa Fm.; Sandanski graben: ka1 and ka2—lower and upper member of Kalimantsi Fm., rb—red beds; kai—Ilindentsi Member of Kalimantsi Fm., sd—Sandanski Fm., dl—Delchevo Fm., kt—Katountsi Fm.; Serres graben: cg—carbonate (travertine), sp3–Micro Strongilo conglomerate, sp2—Spilia fine-grained sediments, sp1—Spilia sandstones, df—Dafni beds (mostly brackish), lf4—Lefkon breccia (of granite fragments), lf3—Lefkon conglomerate (marble and amphibolite pebbles), lf2—Lefkon fine-grained sediments, and lf1—Ano Metohi fanglomerate.

environments sensu stricto but also glacial, fluvioglacial, colluvial, deltaic, paludal, and lacustrine environments. The northern peri-Aegean province consists (from west to east) of the Aliakmonas, Vardar/Axios, Strouma/ Strymon, Mesta/Nestos, and Maritsa/Meric- /Evros fluviolacustrine systems, all flowing into the Aegean Sea. The province is separated from the Danube fluviolacustrine system to the north (flowing into the Black Sea) by the major drainage divide in the Stara-planina or Balkan Mountains (Fig. 1). The 415 km long River Strouma/Strymon has its source on the southern slope of the mountain Cherni Vruh in the Vitosha Mountain Range. It flows (Fig. 1) initially WSW, with loops due to control by Late Cenozoic faults. South of Zemen (in the Zemen Gorge) it changes its course towards the SE, again due to fault control. In the Kyustendil graben; after being joined by tributaries (the Dragovishtitsa, Bistritsa, and Eleshnitsa) it continues to the SE through the Skrino Gorge to Boboshevo, where it is joined by the

river Dzherman. From here the Strouma follows the trend of the Strouma fault to the SSE, being joined by several left-bank tributaries (coming from the Rila and Pirin massifs) and one major left-bank tributary, the 114 km long Stroumeshnitsa. South of the Belasitsa/Belles mountain range, the river changes direction to the ESE and enters the Aegean in the Strymon (Orphano) Gulf. The 273-km-long River Mesta/Nestos has its source in the high mountain area between the Rila and West Rhodope massifs. It flows initially SW, then changes direction to SSE in the Razlog graben. In the Gotse Delchev graben, its direction changes to the ESE and it passes through several narrow gorges before turning south near Xanthi (south of Lekanis Mountain) and entering the Aegean Sea via a large delta opposite Thassos island. Rivers in this region are thus characterized by loops and sudden direction changes. Their courses are typically controlled by lithology and by faulting. Close relationships therefore exist between the Late Cenozoic tectonic

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

evolution of the study region and its drainage, the elucidation of which is one of the main goals of this paper. Few natural lakes are now found within these fluviolacustrine systems (Fig. 1). Three types can be identified. First are small relict cirque lakes that resulted from glaciation in the highest mountains (Rila, Pirin). Second are relics of larger pre-Quaternary lakes that are either now peat bogs (e.g., the Obel Bog near the Bulgaria–Macedonia border; the Choklyovo Bog in the upper-middle Strouma; the Monospitovo Bog along the River Stroumeshnitsa in Macedonia) or are still lakes (the Langhada/Koronia and Volvi lakes in the Mygdonia graben in northern Greece). Third are lakes in the Aegean coastal plain, including lakes Vistonis and Ismaris and adjacent lagoons, as well as some small lakes (e.g., Aladjagiola) in the Nestos delta. All these lakes are typically o10 m deep, although their extent varies significantly by seasons and as a result of human activity. Lake Volvi is exceptional, being up to 24 m deep. 3. The setting of the late Cenozoic Strouma and Mesta systems The locations of the Late Eocene and Early Oligocene terrestrial basins of SW Bulgaria differed considerably from the present pattern of mountain ranges and river valleys. Thus, several lake basins connected by a river network existed in Late Eocene times throughout what is now SW Bulgaria. The SSE–NNW-trending lineation of the Strouma fault zone and sub-parallel Lisiya fault zone are thought to have already existed at this time (Zagorchev, 1998). The pattern of sedimentation did not change significantly with the development, during the latest Eocene and earliest Oligocene, of the shallow marine embayment in the Padesh–Piyanets area (coming from the Ovche-polye area in Macedonia and possibly related to the Mesohellenic basin) (Zagorchev, 1996; Fig. 4). The Eocene–Early Oligocene marine basin in the Eastern Rhodope region (peri-Aegean Thrace) extended westward to the vicinity of Xanthi, but there are no data on the drainage direction of the large lakes and rivers of the Mesta graben complex (Figs. 1, 2, and 4) at this time. The present Pirin horst (Fig. 4) was probably covered, at least in the south, by thick lower Palaeogene sediments. The situation changed with the marine regression in the early Late Oligocene. Transtension along the major Kraishtid (Strouma) lineament and the Maritsa and Sava lineaments led to the development of a number of lakes with coal-bearing sediments: at Aleksinac, in Serbia, and in Bulgaria at Krasava, Pernik, the Stanyovtsi graben complex, Bobovdol and Brezhani (Zagorchev, 1992a, 1996). This system of river-connected lakes was disrupted during a phase of compression in the earliest Miocene. The simultaneous right-lateral strike–slip along the Strouma lineament indicates a transpressional regime in the earliest Miocene (Zagorchev, 1992a, 1996). It can thus be ascertained that the Strouma fluviolacustrine system developed following the Mid-Oligocene Earth

2787

movements that led to Priabonian–Early Oligocene marine regression, but was modified as a result of the earliest Miocene compression. The northern Pirin horst has been subject of continuous uplift since the Mid-Oligocene, the total vertical component being 6 km. The subsequent (Early–Middle Miocene) tectonic quiescence led to the development of a peneplain (orthoplain after Lilienberg, 1966) that is recognized as the principal planation surface of the Balkan Peninsula (Table 1). It is striking that no post-Egerian Lower Miocene or lower Middle Miocene sediments have been identified in the central, eastern, and southern Balkan Peninsula in Bulgaria or Greece (although they are known in central and northern Serbia, in relation to the Pannonian Paratethys). It can thus be inferred that during this span of time, lasting 4–6 million years, as the relief became gradually levelled the region was drained by many small rivers that have left no recognizable sediments (or that all sediments have been subsequently eroded). The only exception are the lacustrine diatomaceous sediments NE of Hadzhidimovo and around Satovcha (Fig. 2) in the Western Rhodope Mountains, dated to the Lower to Middle Miocene (Karpatian–Ottnangian and Badenian) on the basis of fossil flora (Vatsev, 1999). 3.1. The palaeo-Strouma in the Middle Miocene ((?) Badenian to Sarmatian) Apart from the sites noted above, the oldest documented Late Cenozoic sediments within the study region have been assigned to the (? Late) Badenian or Sarmatian (Figs. 3–6). These deposits cover the aforementioned peneplain, beginning with basal conglomerate. Their composition (sandstone, clay, and limestone; also diatomite in the Kyustendil graben) and fossil contents suggests lacustrine environments (Nedjalkov et al., 1986, 1988). These deposits include the Skrinyano Formation in the Kyustendil basin; Vatsev and Bonev, 1994, Gaudant and Vatsev, 2006; the Delchevo Formation in the Sandanski graben; Kojumdgieva et al., 1982, Spassov et al., 2006; and the coal-bearing formations at Oranovo in the Simitli Basin (the Oranovo genetic lithocomplex of Spassov et al., 2006). Asteracian mammal ages (MN 6-8) have been reported for the coalbearing Skrinyano Formation (Kyustendil graben: Nikolov, 1985; Vatsev and Bonev, 1994; Gaudant and Vatsev, 2006) and the Delchevo Formation (Sandanski graben: Kojumdgieva et al., 1982). The scarce faunal remains within the Delchevo Formation have been now revised by Spassov et al. (2006) who attributed them to the Vallesian (MN 10) (i.e., indicating that their age is 9–10 Ma rather than 14 Ma as previously thought; Fig. 3). A similar age (Fig. 3) also seems probable for the red colluvial/alluvial conglomerates and sandstones of the Katountsi Formation in the Sandanski graben (Nedjalkov et al., 1986) and the red conglomerates at the base of the Late Cenozoic succession at the western periphery of the Blagoevgrad graben (Zagorchev, 1992a, b) and in the Kyustendil basin

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2788

Fig. 4. Deposits of the Strouma fluviolacustrine system of Sarmatian age. This map also locates sites discussed in the text: the Palaeogene Padesh basin is west of Blagoevgrad; the Palaeogene Mesta Graben Complex is in the northern part of the Late Cenozoic Mesta graben, in the vicinity of Razlog.

Table 1 Altitudes of erosion surfaces and pediments in SW Bulgaria Locality

Feature and inferred age Orthoplain (Early–Mid Miocene) Height a.s.l. (m)

Rila horst Pirin horst

Oroplain I (Maeotian) Height a.s.l. (m)

Oroplain II (Early Pliocene) Height a.s.l. (m)

Oroplain III ((?) Late Pliocene) Height a.s.l. (m)

Pediments (Pleistocene) Height a.s.l. (m)

2200–2600

1900–2400

1400–1800

1050–1350

550–1000

2400–2600 to 2000

2200–2300 to 1800

1450–1750 to 1250

1000–1150 to 850

460–800 350–550

Sandanski graben

1000

480–520 380–400

?

750–1070

500–600 320–380 (T6) 220–270 (T5)

Simitli graben

1200

?

?

?

440–560

1250–1400 to 1620

900–1200

650–800 to 1000

400–550 160–320

Ograzhden horst

250–1700 (deformed)

Data are after Zagorchev (1992a, 1995) with minor revision. Pediments labelled T6 and T5 in the Sandanski graben grade into the river terraces with the same names, indicated in Table 2.

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2789

Fig. 5. Sections through parts of the Sandanski graben. See online supplement Fig. S2 for section line locations.

Fig. 6. Delchevo Fm. covered by Sandanski Fm.

(Spasovitsa and Skrinyano formations; Vatsev and Bonev, 1994, Gaudant and Vatsev, 2006). However, the age of these deposits, and thus the onset of stacked fluviolacustrine deposition in the study region, remains subject to some uncertainty. The roughly synchronous start of sedimentation (Fig. 4) in each of the basins in SW Bulgaria, in the early Late Miocene (or Late Sarmatian), is thought to mark the start of the Late Cenozoic crustal extension in this region, the basins being located in the hanging walls of normal faults that became active at this time. The Pirin massif is inferred to have begun uplifting in the footwall of the normal faults bounding the Sandanski graben no later than the Late Sarmatian (it is already thought to have been a topographic high as a result of the Late Oligocene thrusting, evidenced by deformation of the sediments in the Brezhani basin), as documented by the pebble composition in the

adjacent graben. This time thus marks the apparent start of disintegration of the Early to Middle Miocene peneplain The sedimentary environments indicated at this time also provide the first evidence for a river that connected several lakes and coincided with parts of the present Strouma valley. The above discussion suggests that the Strouma fluviolacustrine system already existed in the Middle Miocene. Stacked lacustrine deposition, often with lignite seams, seems to have begun in the (? Late) Sarmatian (Fig. 3). The Skrinyano Formation in the Kyustendil graben is typical of the sedimentation at this time, consisting of clay, lignite, and diatomites. Alternations between marshy and lacustrine conditions produced the lignite and diatomite of the basal formation at the northern periphery of the Simitli graben. The lake in the Sandanski graben, near the present confluence of the rivers Stroumeshnitsa and Strouma (Nedjalkov et al., 1988; Spassov et al., 2006), was elongated along the latter and reached north of Sandanski town, represented mostly by clays and limestones (probably some oncolitic). The palaeo-Strouma river is thought to have flowed east of that lake (and of the present course of the Strouma), being fed from the uplifting Pirin horst to the east. Climatic conditions and fluvial regime probably changed several times during the Sarmatian. Thus, red colluvial/ alluvial conglomerates and sandstones are typical for the Katountsi Formation in the Sandanski graben (regarded as a lateral correlate of the Delchevo Formation: Nedjalkov et al., 1986) and similar red conglomerates occur at the base of the Late Cenozoic succession at the western periphery of the Blagoevgrad graben (Zagorchev, 1992a). The red colour of the matrix probably developed as a result of lateritic weathering (mostly over the marbles within the future Pirin horst) during the Early and Middle Miocene planation. The Delchevo Formation itself exhibits interbedding of red, brownish-red, greenish and grey conglom-

ARTICLE IN PRESS 2790

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

erates, sandstones and siltstones, with lenses of buried soils and calcrete (Kojumdgieva et al., 1982). According to current interpretations (Psilovicos and Syrides, 1983; Nedjalkov et al., 1988; Palamarev, 1990; Zagorchev, 1992a; Palamarev and Ivanov, 1998; Spassov et al., 2006), the climate varied from subtropical to warm temperate, with predominant humid or moderately humid conditions interspersed with aridification episodes. Further south in Greece, the continuation of the palaeoStrymon system in the Serres graben (Armour-Brown et al., 1977; Karistineos and Georgiades-Dikeoulia, 1986) may be recognized in the Ano Metohi fanglomerate, which includes red beds in its basal parts (Psilovicos and Syrides, 1983), and the Lefkoma lignite beds (Vallesian; MN 10), which represent a local lake or marsh. 3.2. The palaeo-Strouma and palaeo-Mesta in the Maeotian and early-middle Pontian The Strouma fluviolacustrine system developed in the Maeotian (8.4–6.1 Ma) and the Early (Novorossian)

Pontian (6.7–6.1 Ma) as a braided river system (Spassov et al., 2006; Fig. 7). Thick, well-sorted whitish or yellowish alluvial deposits, often with cross-bedding or graded bedding, indicate fluvial channels. At this time, a marine ingression flooded most of the Serres graben (ArmourBrown et al., 1977). At this time the Strouma fluviolacustrine system may have already developed north of the Kyustendil basin; its catchment at this time may indeed have included the Pernik area. The palaeo-Treklyanska and palaeo-Svetlya rivers (Tchoumatchenco, 1966) may have formed tributaries; the palaeo-Strouma continued SW from the present Zemen gorge, eroding the soft Palaeogene sediments of the Poletintsi graben. The Skrinyano Formation of the Kyustendil graben marks the interaction between colluvial and fluvial sedimentation of the palaeo-Strouma with the lacustrine sedimentation of the relict Kyustendil lake (or marsh). The link between this area and the Blagoevgrad graben is thought to have been north of the present course of the Struma (through the Skrino gorge). In the Blagoevgrad

Fig. 7. The Strouma fluviolacustrine system in the Maeotian to early Pontian. The most significant alluvial fans active at this time are indicated: I, Ilindentsi fan; K, Katountsi fan; S, Sidirokastron fan.

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

graben, the river channels within the plain are marked by the Dzherman Formation, with occasional influx of colluvium (Pokrovnik Formation) of the border fans (Nedjalkov et al., 1990). Further South, the alluvial and lacustrine sediments of the Simitli Formation, like the Sandanski Formation in the Sandanski graben (Figs. 4 and 5), mark the palaeo-Strouma course. However, the exact position of the river linking the two basins is not clear; it probably flowed east of the present Kresna gorge. The apparent expansion of the Strouma fluviolacustrine system in the Maeotian appears to relate to the development of normal faulting; gorges (e.g., Skrino, Kresna) have subsequently become gradually incised through horsts in footwalls of normal faults. The first evidence of the palaeo-Mesta fluviolacustrine system (the Proto-Mestian stage of Choleev and Baltackov, 1989 and Baltackov and Choleev, 2000) is also in the Maeotian. After initial alluvial and colluvial sedimentation in the Razlog and Gotse Delchev areas (Popov, 1963; Vatsev, 1980), lakes developed, with prolonged interlayering of diatomites (the Baldevo Formation in the Gotse Delchev graben; the Sivik Formation in the Satovcha graben; Vatsev and Pirumova, 1983; Temniskova-Topalova and Ognjanova-Rumenova, 1997) and lignites (including almost pure diatomites and diatom clays with perfectly preserved leaves of deciduous trees) periodically disturbed by massive import of tree trunks. Similar lignites (Marikostinovo and Hotovo coal seams) are also characteristic of the Early-Middle Pontian of the Strouma fluviolacustrine system, but the lack of diatomites (except in the Simitli graben during the (?)Sarmatian) indicates a lesser extent of open lake water. Only the large lake in the Serres and Drama grabens, further south in Greece, was favourable to development of diatom algae (Zagorchev and Ognyanova-Rumenova, 1995); this had intermittent influxes of seawater (Fig. 5) and a considerable influx of terrigenous matter. It is significant that the lakes (in the Serres and Drama grabens) were connected or may even have formed a single lake in which lignites and diatombearing marls were deposited, the latter being traced by the present author, thanks to cuttings along new roads, from Serres to Amphipolis, and from there through Rhodolivos to the southern edge of the Drama graben. It thus appears that in the Maeotian–Pontian parts of both the Menikion and Pangaion horsts (between the modern Serres and Drama grabens) were covered by the lake waters; the present relief is thus younger, and relates to Late Pliocene–Pleistocene normal faulting and the deposition of the thick Pliocene and Pleistocene deposits (Kaouras et al., 1991). As at present, the Pirin horst formed a barrier between the Strouma and Mesta systems in the Maeotian (and probably, also, in the (?) Badenian–Sarmatian). Evidence is provided by the well-rounded marble fragments (eroded from the Pirin horst) in the (?)Badenian–Sarmatian Katountsi Formation and the Maeotian Sandanski Formation (Sandanski graben; Fig. 7), and in the

2791

conglomerate ((?) Maeotian or Pontian) beneath the diatom-bearing marls near Amphipolis in the Serres graben. Savannah-type climate (with occasional aridification) and landscape is suggested by palaeobotanic (Palamarev, 1990) and faunal (Spassov et al., 2006) evidence. 3.3. The palaeo-Strouma and palaeo-Mesta in the Late Pontian The palaeo-Strouma and palaeo-Mesta fluviolacustrine systems experienced a dramatic change during the Late Pontian (the Bosphorian and Portaferian stages) (Fig. 8). This time (5.7–5.3 Ma; corresponding to the Late Pontian regression of the Black Sea) is marked by a massive influx of very coarse terrigenous material from the horsts, especially the Pirin horst, into the lakes and rivers of the adjacent grabens. Notably, the Ilindentsi Member of the Kalimantsi Formation in the Sandanski graben (Fig. 5) consists of huge angular fragments (with dimensions of metres to tens of metres) of marble derived from adjacent outcrops (of the Precambrian Dobrostan Formation) in the Pirin horst. The marble megabreccia passes laterally into breccia and conglomerate consisting of amphibolite and gneiss fragments, thus reflecting the composition of the source area (the immediately adjacent part of the Pirin horst). The subsequent sandstone member of the Kalimantsi Formation, of Pontian to Pliocene age, contains the first evidence of well-rounded pebbles derived from the Late Cretaceous and Palaeogene granites of the Pirin horst, indicating initial unroofing of these plutons in the Pontian (Zagorchev, 1968, 1970, 1992a). The Kalimantsi Formation, with its abundant granite pebbles, also overlies the Simitli Formation in the Simitli graben, and can be correlated with the Nevrokop Formation in the Gotse Delchev graben (of the Mesta fluviolacustrine system). The abundant well-rounded pebbles of Palaeogene granite are the most outstanding feature showing that the whole Pirin horst has experienced dramatic Late Cenozoic erosion, resulting in the partial destruction of the Maeotian oroplain (which formed previously over the marbles from the mantle of Late Cretaceous and Palaeogene granites) and the exhumation of this granite. Zagorchev (1992a) interpreted this erosion (and the contemporaneous sedimentation in the Sandanski and Gotse Delchev grabens) as a consequence of active normal faulting superimposed on regional uplift; he thus estimated the throw on the normal faults bounding the ENE margin of the Sandanski graben as 1200–1500 m since the beginning of the Late Pontian. Similar marble megabreccias (sometimes called olistostromes, although this term should be used for submarine gravity flows, not the colluvial, fluvial and lacustrine sediments considered here) occur also in the northern Serres graben at Sidirokastro and along the road from this town towards Ahladohori (see online supplement, Fig. S5). These megabreccias form irregular bodies within yellowish and reddish sandstones. They overlie and

ARTICLE IN PRESS 2792

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

Fig. 8. The Strouma and Mesta fluviolacustrine systems in the Late Pontian to Pliocene. Alluvial fans (with megabreccia) are labelled as in Fig. 7.

pass laterally into the thick (?)Maeotian sandstones of Lefcon 2 (Armour-Brown et al., 1977), and correspond to the marble/amphibolite breccia (Lefcon 3) followed by conglomerate that is rich in granite fragments (often with reddish matrix) of Lefcon 4. The Pontian evolution of the northern part of the Strouma fluviolacustrine system has been marked by the development of the palaeo-Treklyanska and palaeo-Svetlya rivers (Tchoumatchenco, 1966), which probably connected with the palaeo-Dzherman and palaeo-Strouma through the Bobovdol graben near Dyakovo (the incision of the Zemen Gorge began probably roughly at the same time). The interpretation of these palaeo-rivers is based on pockets of fluvial sediment preserved within the Pernik and Bobovdol basins, and futher south (around Dyakovo and Doupnitsa); such sediments are absent in the vicinity of the Zemen Gorge. In all places, the Pontian (and, subsequently, Pliocene) sediments of the Strouma fluviolacustrine system are represented by unlithified yellowish or whitish gravels and sands. The well-rounded clasts in the gravels consist of quartz, granite, and gneiss. Crossbedding and graded bedding are typical of the channel

sediments; more angular and less well-sorted sediments are found in alluvial fans, such as in the easternmost parts of the Simitli graben. As already mentioned, the Mesta fluviolacustrine system developed in the Pontian in a similar way to the Strouma. The diatomaceous sediment in the Gotse Delchev graben lake is dated to the Early-Middle Pontian (TemniskovaTopalova and Ognjanova-Rumenova, 1997), and was gradually superseded by the coarser sediment of the Nevrokop Formation, containing granite clasts derived from the uplifting Pirin horst. Thus, at the end of the Pontian time both fluviolacustrine systems possessed a well-developed drainage system, similar to the present-day configuration. A Mediterranean climate is thought to have existed at this time (Palamarev, 1990), with aridification episodes probably related to the Messinian salinity crisis (Spassov et al., 2006) 3.4. The palaeo-Strouma and palaeo-Mesta in the Pliocene No significant changes in the Pliocene are evident, for either the Strouma or the Mesta, relative to the conditions

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2793

Fig. 9. Fluvial sediments (Barakovo Formation, Pliocene), 500 m west of Pokrovnik on the road towards Padezh, at the western margin of the Blagoevgrad graben (see Fig. 1 for location).

established in the Pontian (Fig. 9). Layers of thin red silt and clay, interbedded between the two conglomeratesandstone members of the Kalimantsi Formation in the Sandanski graben (Fig. 5), are thought to have formed near the boundary between the Pontian (latest Miocene) and the Dacian (earliest Pliocene). This opinion is supported also by the scarce fossil evidence (Spassov et al., 2006). Similar layers and lenses are observed in the Kyustendil, Gotse Delchev, and Serres grabens (Psilovicos and Syrides, 1983). The principal change at this time, possibly as a result of continued extension, is that formerly isolated lacustrine basins became interconnected by rivers. Thus, a new course of the palaeo-Strouma, between the Simitli and Sandanski grabens, was incised through the Late Cretaceous granites of the Daoutov (North Pirin) pluton, then infilled by the second conglomerate-sandstone member of the Kalimantsi Formation that covered the weathered surface of the granite (e.g., Zagorchev, 1992a). Within the grabens, depocentres formed wide valleys of the braided river system with intermittent lacustrine or marshy conditions. Thus, the Barakovo Formation (Blagoevgrad graben; Fig. 9) and the upper parts of the Kalimantsi Formation (Simitli and Sandanski grabens) consist of gravels with relatively coarse but well-rounded clasts. There was also intermittent development of lacustrine conditions in the Drama and Serres grabens. In areas fed with limestone or marble pebbles from the adjacent horsts, the Pliocene sections are often capped by oncolitic limestones, several metres to tens of metres thick. Examples have been kindly shown to me by D. Kovachev near Kalimantsi in the Sandanski graben. They indicate small lakes with (at least) seasonally clear waters, where cyanobacteria developed under conditions of increased CO2 content. The palaeobo-

tanical data indicate changes in the Pliocene from tropical humid to arid through subtropical to semi-arid, and finally, to temperate climate (Psilovicos and Syrides, 1983; Palamarev, 1990; Syrides, 1995). The whole stacked succession of the Sandanski graben has been tilted ENE by 5–201, against the West Pirin fault zone (Zagorchev, 1970, 1992a). One important issue concerns the timing of the last significant slip on this and other SSE-striking normal faults in the region. The presence of 300–400 m of Early Pliocene (Dacian) sediments overlying the Late Pontian Ilindentsi Member suggests that significant slip on this fault system ceased during the Pliocene, possibly in the Mid-Pliocene. The exact time of cessation of significant slip is not established, but the suggestion that this timing was 4 Ma (Burchfiel et al., 2000; Westaway, 2006) seems plausible. The slip on this fault system created considerable relief, and thus influenced the region’s fluviolacustrine systems. It was followed by a relative quiescence during the Late Pliocene and Early Pleistocene (the ‘Eopleistocene’ of the Eastern European literature), associated with further development of the Strouma fluviolacustrine system and formation of erosion surfaces that truncate the older structures, including the West Pirin fault zone. The Pleistocene fan gravels that cover these surfaces (including the Badino Formation in the Blagoevgrad graben) slope away from the mountain horsts (Rila, Pirin), and unconformably overlie the Pliocene deposits (the Barakovo and Kalimantsi formations). However, some of the lateral variations in the heights of the Strouma terraces (indicated in Table 3; after Vrablyanski, 1977) have been attributed to minor components of Pleistocene normal slip on NNW–SSE-trending normal faults.

ARTICLE IN PRESS 2794

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

Some of the transverse (i.e., WSW–ENE-trending) grabens have also been affected by the Late Pliocene or younger normal faulting. Thus, the whole Neogene sequence of the Simitli graben has been tilted SE against the Kroupnik fault. Its disposition is thus similar to that of the ENE-tilted succession in the adjacent Sandanski graben. However, slip on the Kroupnik fault (and on other E–W- to NE–SW-striking normal faults) has continued to the present day (e.g., Zagorchev, 1992a), as evidenced by the region’s seismicity, whereas (as noted above) significant slip on the region’s NNE–SSW-striking normal faults ceased by the Mid-Pliocene. The palaeo-Vardar/palaeo-Axios fluviolacustrine system will not be discussed in the present paper. However, it is noted in passing that its lower reach has been characterized by lacustrine and marshy conditions since the Miocene. The drainage of the Mygdonia graben (the present Lakes Langada and Volvi, north of Thessaloniki) probably once formed part of the palaeo-Axios system, but is now isolated from it with a drainage divide at the western end of the graben. The graben interior now drains eastward towards the Strymon Gulf. Variations in the coastline are indicated by the presence of marine and brackish sediments in the Serres and Pieria grabens (Psilovicos and Syrides, 1983). The northern limit of marine influence seems to be the major normal fault forming the southern flank of the Belasitsa (Beles, Kerkini) mountain range (s. Jaranoff, 1963) and its westward and eastward continuations. This Middle Mesta fault has been a branch of the North-Anatolian Fault Zone (NAFZ), with substantial Late Cenozoic normal faulting and right-lateral strike–slip displacements. 4. Quaternary developments Pleistocene developments (Fig. 10) include continued increases in relief due to progressive slip on normal faults. The resulting footwall uplift (plus the effect of components of regional uplift; see below) has accentuated the effect of global cooling, leading to the development of glacial conditions at high altitudes. Thus, during Pleistocene cold stages, the highest mountains have been covered by glaciers (e.g., Velchev, 1995), including Vitosha, Osogovo, Rila, Pirin (and Slavyanka–Orvilos), as well as (further south, in Greece), Olympos. Three glacial periods are recognized, thought to correspond to the Mindel, Riss, and Wu¨rm of central Europe, when the snowline on Rila and Pirin reached as low as 2200–2300 m (e.g., Galabov, 1982; Velchev, 1995). Glacial and fluvioglacial deposits are widespread, as well as typical glacial landforms such as cirques, ‘roches moutonne´es’, and U-shaped valleys. Valley glaciers reached as low as 1300–1400 m, and even 1100 m at the northern margin of Vitosha (south of Sofia). Such valleys became dammed by terminal moraines, creating relict lakes that persisted during subsequent temperate stages, including the Holocene. Larger lakes developed south of the Middle Mesta fault zone, such as Doyran,

Boutkovo (Kerkini), Mygdonia (Lake Volvi), Drama, Volax, and Bistonis. The Middle–Late Pleistocene (i.e., the ‘Pleistocene’ of the Eastern European literature) evolution of the river systems is marked by cyclicity between incision and aggradation (Table 2). The heights of the fluvial terraces above the present river level have been extensively discussed in the Bulgarian literature since the classic studies of J. Cvijic, P. Jankovic, A. Penck, H. Louis, and D. Jaranoff, including some detailed morphometric studies (e.g., Ivanov and Mihaylov, 1965; Ivanov and Petrov, 1968; Vrablyanski, 1970, 1974, 1977; Konstantinov, 1984). This work has typically looked for explanations of the depositional cyclicity in terms of active faulting, attributing aggradation to times of relative quiescence and incision to times of fast uplift associated with normal-faulting earthquakes. Instrumental studies by Vrablianski (Table 3) confirmed the presence of Pleistocene displacements of the terraces by active faults that range between 15 and 50 m for T6 and between 5 and 15 m for T1. The amplitude for some of the bounding faults (West Rila fault zone) may reach 70–90 m (differences in T6). Westaway (2006) has shown that these river terrace deposits can also be plausibly correlated with cold-climate stages dating back to MIS 22, the observed sedimentary cyclicity thus reflecting climatic fluctuation and its effect on the hydrology of the river systems. The associated uplift was likewise reinterpreted as a consequence of regional-scale processes, forced by global climate change, in keeping with explanations of long-timescale fluvial sequences worldwide (Bridgland and Westaway, 2007). Nevertheless, the Strouma and Mesta flow across some active normal faults (e.g., the Kroupnik Fault), where local variations in terrace heights have been observed (Vrablyanski, 1974, 1977) due to superimposition of the vertical slip onto the regional uplift. River terraces are however absent in such localities, where the rivers flow through narrow gorges (e.g., the Kresna gorge, adjoining the Kroupnik Fault). In some cases significant drainage diversions have occurred. Thus, first, the Mesta left the old (palaeoMestian) course (marked by * symbol in Fig. 1) through the Kato Nevrokopion and Drama basins and along the palaeo-Angitis (finally entering the palaeo-Strymon near its mouth), and began to flow instead through the Chech Gorge of the palaeo-Dospat River to form its present course via Potami to the Nestos Delta (Baltackov and Choleev, 2000). Second, between the Simitli and Sandanski grabens, the Strouma abandoned a former course, 1 to 2 km east of its modern course, and began to incise what is now the Kresna Gorge. Active faulting along E–W-trending normal faults and strike–slip faults is most important near the Aegean coast. Thus, gypsum-bearing Upper Miocene (Messinian) beds (Snel et al., 2006) are uplifted and occur now in a graben structure (south of the Pangaion horst) near Akropotamos; locally the covering sediments have been folded (see online

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2795

Fig. 10. Map of Pleistocene deposits of the Strouma and Mesta fluviolacustrine systems

supplement, Fig, S6). These overlying folded sediments can thus be inferred to date from the Pliocene; their folding may indicate deformation related to slip on the NAFZ.

Deglaciation in the high mountains following Late Pleistocene stadials (Baltackov, 1988) has been associated with extreme discharge, mudflows, and gradual filling of

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2796 Table 2 Summary of river terrace heights Name

T7 T6 T5 T4 T3 T2 T1

Aged

Eopleistocene Early Pleistocene Early Pleistocene Middle Pleistocene Middle Pleistocene Late Pleistocene Late Pleistocene

River Stroumaa

Mestab

Maritsa

Westaway (2006)c

Height (m)

Height (m)

Height (m)

Nominal height (m)

MIS

? 120–130 85–100 (95–105) 60–65 (60–66) 40–45 (40–42) 20–22 (20–24) 8–12 (8–11) 5–7 (5–6)

100–110 80–90 60 40 (55–60) 20–22 (28–30) 18–24 (18–24) 8–12 (10–12)

95–110 72–80 60–65 45–57 30–37 18–27 8–12

110 90 63 40 21 10 6

22 16 12 8 6 4 2

Terrace heights are above present river level. Data are from Galabov (1982), Vrablyanski (1970, 1974, 1977), Choleev and Baltackov (1989), Zagorchev (1995), and Kopralev (2002). Supposed OIS correlation and altitudes based on modeling by Westaway (2006) in last column. a Terrace heights for the Strouma shown in brackets are from surveying; other data are interpolated from available maps. b Data for the Mesta shown in brackets are for the Razlog area, from Choleev and Baltackov (1989); other data are from the Gotse Delchev graben. c ‘‘Nominal heights’’ refer to the heights adopted by Westaway (2006) to create a composite dataset based primarily on the data from the Strouma, in order to model regional surface uplift; MIS stages denote the stages of the Marine Oxygen Isotope timescale inferred by Westaway (2006) as the timings when the fluvial deposits forming each individual terrace aggraded. d These ages were suggested in the local literature; and refer to the Eastern European usage of the term ‘‘Pleistocene’’; thus ‘‘Eopleistocene’’ means Early Pleistocene, ‘‘Early Pleistocene’’ means early Middle Pleistocene, and ‘‘Middle Pleistocene’’ means late Middle Pleistocene in terms of the standard international definition.

Table 3 Terraces of the Middle Strouma and its tributaries River reach

Terrace name T6 Height (m)

T5 Height (m)

T4 Height (m)

T3 Height (m)

T2 Height (m)

T1 Height (m)

Main Strouma channel Strouma, N Skrino Gorge Strouma, S Skrino Gorge Strouma, N Blagoevgrad graben Strouma, Simitli graben Strouma, Kresna Gorge Strouma, Sandanski graben

84.3 99.0 100.3 86 175 100.9

76.8 89.2 74.4 59 85 63.8

52.6 64.3 61.0 34 45 41.8

34.7 42.0 37.3 17 28 23.0

18.3 23.2 27.8 7 14 9.5

11.8 16.5 15.2 4 10 5.4

Tributaries River Dzhermana River Rilska Rekab R. Blagoevgradska Bistritsac River Gradevska Rekad River Kroupnishka Rekae River Stroumeshnitsaf

85.4 192.3 175.4 90 82.0 –

73.0 164.1 151.8 60 56.1 –

49.3 88.3 90.0 36 38.2 36.3

30.8 61.2 59.4 17 22.0 23.1

21.9 36.0 32.7 8 6.7 13.1

11.9 16.8 15.1 5 2.8 6.6

Mean heights of terraces (relative heights above present river level), measured by theodolite, after Vrablyanski (1970, 1974, 1977). Note the greater heights of the Strouma terraces in the Kresna Gorge, in the footwall of the Kroupnik Fault, where local footwall uplift is superimposed on the regional uplift. a The terrace heights are measured downstream (from N to S) at: SW of Doupnitsa; E of Gramade; N of Sopovo. b The terrace heights are measured at several points between the village of Pastra and the town of Rila, all in the Rila massif east of the West Rila fault zone. c The terrace heights are measured at several points between Bistritsa and Blagoevgrad. d The terrace heights are measured at several points downstream between the tributary Osenovska Reka and Oranovo. e The terrace heights are measured at several points downstream between Polena and Kroupnik. f The terrace heights are measured in the lower course of the river between Purvomay and the Strouma.

the relict lakes. Many small lakes of glacial origin have remained in the high mountains. Relict lakes and marshes (Choklyovo, Obel) are also evident in sections of river

channel that became abandoned as the discharge decreased (Konstantinov, 1984). Some large lakes persisted in the lower reaches of the main rivers (Axios, Strymon, and

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

2797

Fig. 11. Generalized cross-section through the Sandanski graben, Pirin horst and Gotse Delchev graben (after Zagorchev, 1995). Relics of planation surfaces: OP, principal peneplain (orthoplain) of Early–Middle Miocene age; O I, oroplain I of pre-Late Pontian age; O II and O III, oroplains II and III, of probable Late Pontian and Dacian age, respectively; P I, Early Pleistocene surface with unconformable gravel cover over the tilted Neogene beds and the boundary normal fault; P II and P III, younger Pleistocene surfaces over the tilted Neogene sediments. See also Table 1. Details about the correlations between surfaces and sediments may be found in Zagorchev (1992a).

Nestos). The present complex drainage system has thus developed as a result of fluvial activity, differential erosion of basement rocks and of soft Cenozoic rocks, slip on active faults and regional uplift. 5. Relationship between fluviolacustrine systems and crustal deformation The complex history of the study region indicates multiple phases of crustal deformation, each contributing to the overall pattern of vertical crustal motions. The evidence relating to the older phases (Palaeogene–earliest Miocene) has been summarized, and is discussed in more detail elsewhere (e.g., Zagorchev, 1970, 1971, 1992a). As Zagorchev (1992a, b) noted, during the region’s Late Cenozoic extension, local isostatic effects of active normal faulting have been superimposed onto a component of regional uplift. The extensional strain across the region has been moderate, estimated by Zagorchev (1992a) as probably 3–5% and certainly no more than 10%. Claims of vast amounts of extension, amounting to many tens of kilometres on individual normal fault systems (e.g., Burchfiel et al., 2000), are thus not supported by the local evidence. As Westaway (2006) has discussed, such misinterpretations have probably arisen because researchers from outside Bulgaria have made basic mistakes due to unfamiliarity with the field evidence and the local literature. Zagorchev’s, (1992a, b) interpretation of the interplay between regional uplift and normal faulting is summarized

in Fig. 11. Around the same time, Westaway (1993) suggested that a similar combination of processes has governed the Late Cenozoic development of western Turkey, another part of the Aegean extensional province with an erosion-dominated landscape and where the extensional strain is low. At the time this was considered a controversial idea, because the contrary view—that only the isostatic effects of normal faulting have been significant in this region—was deeply engrained. Subsequent investigations, involving detailed fieldwork, high-precision dating, and numerical modelling (e.g., Westaway et al., 2005, 2006) have confirmed that the Late Cenozoic uplift of western Turkey has been primarily the isostatic response to erosion. The same conclusion may well be true in SW Bulgaria, but is more difficult to demonstrate due to the more limited age control currently available. 6. Conclusions The evidence for the development of fluviolacustrine systems in SW Bulgaria and northern Greece since the Late Eocene has been summarized. In the Early and Middle Miocene, a time of no significant crustal deformation in this region, erosion created a low-relief landscape. The region’s subsequent Late Cenozoic extension has been associated with the deposition of thick (41500 m in the Simitli and Sandanski grabens; 3500 m in the Serres graben) colluvial, fluvial and lacustrine sediments. The region’s principal fluviolacustrine systems (the palaeoStrouma and palaeo-Mesta) have been separated through-

ARTICLE IN PRESS 2798

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

out this time by the uplifting Pirin horst and its prolongations in Northern Greece; the peri-Aegean coastal plain has been bounded to the north by the uplifting Belasitsa/Kerkini mountain range and its prolongations, in the footwall of the Middle Mesta normal fault. The evolution of these fluviolacustrine systems during this time has been influenced by climate change, active normal faulting, and regional uplift. Progressive erosion of mountain ranges between normal faults has resulted in changes in clast lithology, which permit fluvial sediments to be correlated, notably the (?)Late Pontian deformation of the Maeotian erosional surface (oroplain I) and the unroofing of the Palaeogene granite plutons in the Pirin mountains. The last intense normal faulting and graben tilting occurred in Late Pliocene (Romanian) time and was followed by partial remodelling of the fluvial systems with the development of new gorges. The highest parts of the region have experienced repeated Pleistocene glaciation, resulting in influxes of fluvioglacial sediment into the adjoining river systems. Staircases of fluvial terraces have developed since the late Early Pleistocene; the associated alternations of incision and aggradation reflect climate cyclicity and record fluvial incision in response to the regional uplift. Acknowledgements The author is grateful to colleagues from Bulgaria and Greece who have contributed directly or indirectly to the ideas presented here. I am particularly indebted to the late Dimitri Jaranoff and Ivan Vaptsarov, and would like this paper be a modest tribute to their memories. I also thank G. Baltackov, G. Clauzon, G. Fountoulis, I. Mariolakos, N. Ognyanova, N. Popov, A. Psilovicos, N. Spassov, S. Stiros, J.-P. Suc, G. Syrides, T. Tzankov, B. Vrablyanski, and R. Westaway with whom I have had the pleasure to exchange information and ideas on the Late Cenozoic evolution of the Balkan Peninsula. Editorial assistance by R. Westaway is also most gratefully acknowledged. This paper is a contribution to IGCP-449 ‘Global Correlation of Late Cenozoic fluvial deposits’, to IGCP 518 ‘Fluvial deposits as evidence for climate change and landscape evolution in the Late Cenozoic’ and to FLAG Focus 1. Appendix A. Supplementary materials Supplementary data associated with this article can be found in the online version at doi:10.1016/j.quascirev.2007.07.017

References Armour-Brown, A., de Bruijn, B., Maniati, C., Siatos, G., Niesen, P., 1977. The geology of the Neogene sediments north of Serrai and the use of rodent fauna for biostratigraphic control. In: Proceedings of the Sixth Colloquium on the Geology of the Aegean Region 2, 615–622.

Bakalov, P., Zhelev, V., 1996. Lithostratigraphy of the Neogene–Villafranchian sediments of the Kyustendil graben. Review of the Bulgarian Geological Society 57 (1), 75–82 (in Bulgarian). Baltackov, G., 1988. Quaternary geomorphology and palaeogeography. Sofia University, ‘‘Kliment Ohridski’’ Publishing House, (275pp., in Bulgarian). Baltackov, G., Choleev, I., 2000. Late Cenozoic evolution of the Mesta (Nestos) valley system. Annals of the University of Sofia ‘‘St. Kliment Ohridski,’’ l. 2-Geographie 90, 5–17. Bridgland, D.R., Westaway, R., 2007. Climatically controlled river terrace staircases: a worldwide Quaternary phenomenon. Geomorphology, in press. Burchfiel, C.B., Nakov, R., Tzankov, Tz., Royden, L., 2000. Cenozoic extension in Bulgaria and northern Greece: the northern part of the Aegean extensional regime. In: E. Bozkurt, J.A. Winchester, J.D.A. Piper (Eds.), Tectonics and magmatism in Turkey and Surrounding Area. Geological Society, London, Special Publication, vol. 173, pp. 325–352. Choleev, I., Baltackov, G., 1989. Basic features of Late Cenozoic evolution of the Mesta valley system in Bulgaria. Geographica Rhodopica 1, 14–17. Dermitzakis, M., 1990. The evolution of the Aegeis during the Late Cenozoic. Geologica Balcanica 20 (3), 3–16. Dermitzakis, M., Papanikolaou, D., 1981. Palaeogeography and geodynamics of the Aegean during the Neogene. Annales Geologiques des Pays Helleniques 4, 245–266. Dinter, D., 1998. Late Cenozoic extension of the Alpine collisional orogen, northeastern Greece: origin of the north Aegean basin. Geological Society of America Bulletin 110, 1208–1230. Dumurzanov, N., 1997. Lacustrine Neogene and Pleistocene in Macedonia. Special Publication of the Geoinstitute Belgrade 21, 31–36. Galabov, Zh. (Ed.), 1982. Geography of Bulgaria. Physical Geography, vol. 1. Academic Publishing House, Sofia, (513pp., in Bulgarian). Gaudant, J., Vatsev, M., 2006. Une ichtyofaune lacustre dans le Mioce`ne moyen du graben de Kjustendil (Bulgarie occidentale). Geodiversitas 28 (1), 55–70. Gradstein, F.M., Ogg, J.G., Smith, A.G., Bleeker, W., Lourens, L.J., 2004. A new geologic time scale with special reference to Precambrian and Neogene. Episodes 27, 83–100. Gramann, F., Kockel, F., 1969. Das Neogen im Strymon-Becken (Griechenland, Ostmazedonien). Geologisches Jahrbuch 87, 445–528. Ivanov, I., Mihaylov, Ts., 1965. Geomorphologic development of a part of the southwestern slope of Pirin mountain during the Quaternary. Bulletin of the Bulgarian Geographical Society 5, 3–18 (in Bulgarian). Ivanov, I., Petrov, P., 1968. Morphotectonic development of the valley of the river Strouma in the Skrino Gorge in Pliocene and Quaternary. Annuaire University of Sofia, Faculty of Geology and Geography, Livre 2-Geographie 61, 1–27 (in Bulgarian). Jaranoff, D., 1963. La neotectonique de la Bulgarie. Revue de Geographie Physique et de Geologie Dynamique 5 (2), 75–83. Kaouras, G., Antoniadis, P., Blickwede, H., Riegel, W., 1991. Petrographische und palynologische Untersuchungen an Braunkohlen im Becken von Drama, Ostmakedonien (Griechenland). Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, Monatsheften 3, 145–162. Karistineos, N.K., Georgiades-Dikeoulia, E., 1986. The marine transgression in the Serres basin. Annales Geologiques des Pays Helleniques 33, 321–332. Kojumdgieva, E., 1987. Evolution paleogeodynamique du bassin Ege´en pendant le Mioce`ne supe´rieur et ses relations a` la Paratethys Orientale. Geologica Balcanica 17 (1), 3–14. Kojumdgieva, E., Nedjalkov, P., Tsatsev, B., 1984a. Neogene stratigraphy and development of the Simitli graben. In: Zagorchev, I. (Ed.), Problems of the Geology of Southwest Bulgaria. Tehnika, Sofia, pp. 52–57 (in Bulgarian). Kojumdgieva, E., Nikolov, I., Mein, P., 1984b. Les associations de grands mammife`res du Mioce`ne supe´rieur en Bulgarie et leur correlations avec l’echelle regionale de la Paratethys. Comptes Rendues de l’Academie Bulgare des Sciences 37 (3), 341–343.

ARTICLE IN PRESS I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800 Kojumdgieva, E., Nikolov, I., Nedjalkov, P., Busev, A., 1982. Stratigraphy of the Neogene in the Sandanski graben. Geologica Balcanica 12 (3), 69–81. Konstantinov, H., 1984. Appliance of the dychotomic system as a geomorphological indicator for the development of the hydrographic network of the Upper Struma. Annuaire de l’Universite de Sofia ‘‘Kliment Ohridski,’’ Faculte´ de Ge´ologie et Ge´ographie, l. 2-Geographie 78, 14–25 (in Bulgarian). Kopralev, I. (Ed.), 2002. Geography of Bulgaria. ForKom, Sofia, 760pp. Koufos, G.D., Syrides, G.E., Kostopoulos, D.S., Koliadimou, K.K., 1995. Preliminary results about the stratigraphy and the palaeoenvironment of Mygdonia basin, Macedonia, Greece. Geobios 18, 243–249. Krstic´, N., Dumurdzanov, N., Bratuljevic, V., Milicevic, V., Simic, M., Radovanovic, S., Aleksic, I., 1999. Pliocene tectonics of Southern Serbia and adjoining regions. Bulletin de l’Academie serbe des Sciences et des Arts 69, 99–121. Lalechos, N., Savoyat, E., 1977. La sedimentation Neoge`ne dams le Fosse Nord Ege´en. In: Proceedings of the Sixth Colloquium on the Geology of the Aegean Region 2, 591–603. Lilienberg, D., 1966. Some problems of geomorphology, quaternary geology and neotectonics of Macedonia. Proc. (Referati) VI Congr. Sav. geol. dr. SFRJ., Ohrid I, 271–2299 (in Russian). Marovic, M., Krstic, N., Stanic, S., Cvetkovic, V., Petrovic, M., 1999. The evolution of Neogene sedimentation provinces of Central Balkan Peninsula. Bulletin of Geoinstitut, Belgrade 36, 25–94. Mercier, J., 1979. Signification neotectonique de l’Arc Ege´en. Une Revue de ide´es: Revue de Ge´ologie Dynamique et de Ge´ographie Physique 21, 5–15. Nedjalkov, P., Tcheremisin, N., Kojumdgieva, E., Tzatzev, B., Buzev, A., 1986. Facies and palaeogeographic features of the Neogene deposits in the Sandanski graben. Geologica Balcanica 16 (1), 69–80 (in Russian). Nedjalkov, P., Kojumdgieva, E., Bozhkov, I., 1988. Sedimentary cycles in the Neogene grabens along the Struma valley. Geologica Balcanica 18 (2), 61–66. Nedjalkov, P., Kojumdgieva, E., Tcheremisin, N., 1990. Facial and palaeogeographic features of the Neogene deposits in the Blagoevgrad graben. Review of the Bulgarian Geological Society 51 (1), 1–9 (in Bulgarian, with English summary). Nikolov, I., 1985. Catalogue of the localities of Tertiary mammals in Bulgaria. Palaeontology, Stratigraphy and Lithology [Sofia] 21, 43–62. Palamarev, E., 1990. Grundzeuge der palaeofloristischen Palaeosukzessionen im Spa¨tmioza¨n (Sarmatien–Pontien) Bulgariens. In: Global Biological Events in Earth’s History, Prague, pp. 1–18. Palamarev, E., Ivanov, D., 1998. U¨ber einige Besonderheiten der tertia¨ren Floren in Bulgarien und ihre Bedeutung fu¨r die Entwicklungsgeschichte der Pflanzenwelt in Europa. Acta Palaeobotanica 38 (1), 147–165. Palamarev, E., Ivanov, D., Bozukov, V., 1999. Pala¨oflorenkomplexe im Zentralbalkanischen Raum und ihre Entwicklungsgeschichte von der Wenfe Oligoza¨n/Mioza¨n bis ins Villafranchium. Flora Tertiaria Mediterranea 6 (5), 1–95. Popov, P., 1963. Notes on the geology of the Razlog valley. Review of the Bulgarian Geological Society 24 (2), 107–118 (in Bulgarian). Popov, S.V., Ro¨gl, F., Rozanov, A.Y., Steininger, F.F., Shcherba, I.G., Kovac, M. (Eds.), 2004. Lithological–Paleogeographic maps of Paratethys. 10 maps Late Eocene to Pliocene. Courier Forschungsinstitut Senckenberg 250, 1–46. Popov, S.V., Shcherba, I.G., Ilyina, L.B., Nevesskaya, L.A., Paramonova, N.P., Khondkarian, S.O., Magyar, I., 2006. Late Miocene to Pliocene palaeogeography of the Paratethys and its relation to the Mediterranean. Palaeogeography, Palaeoclimatology, Palaeoecology 238, 91–106. Psilovicos, A., 1984. Geomorphological and structural modification of the Serbomacedonian Massif during the neotectonic stage. Tectonophysics 110, 27–45. Psilovicos, A., 1986. Contribution to the geomorphology of the southwestern part of the Rhodope Massif (Greek East Macedonia). Geologica Balcanica 16 (5), 21–32.

2799

Psilovicos, A., Koufos, G., Syrides, G., 1987. The problem of red beds in northern Greece. Annales Institute Geological Publications Hungary 70, 509–516. Psilovicos, A., Syrides, G., 1983. Stratigraphy, sedimentation and paleogeography of the Strymon basin, Eastern Macedonia/Northern Aegean Sea, Greece. Clausthaler Geologische Abhandlungen 44, 55–87. Psilovicos, A., Syrides, G., 1984. Neogene and Quaternary palaeoenvironments in the Northern Aegean area. Annales Geologiques des Pays Helleniques 32, 105–114. Psilovicos, A., Vavliakis, E., 1989. Contribution to the evolution of the river Nestos valley in the Greek Rhodopes. Geographica Rhodopica 1, 26–33. Riegel, W., Kaouras, G., Velitzelos, E., 1995. Ecological aspects of coal formation in Neogene basins of Greece. Annales Geologiques des Pays Helleniques 36, 649–661. Ro¨gl, F., 1999. Mediterranean and Paratethys. Facts and hypotheses of an Oligocene to Miocene palaeogeography (short overview). Geologica Carpathica 50, 339–349. Schroeder, B., 1986. Das postorogene Kainozoikum in Griechenland/ Aegeis. In: Jacobshagen, V. (Ed.), Geologie von Griechenland. Gebru¨der Borntra¨ger, Berlin, pp. 209–240. Snel, E., Marunteanu, M., Meulenkamp, J.E., 2006. Calcareous nannofossil biostratigraphy and magnetostratigraphy of the upper Miocene and lower Pliocene of the Northern Aegean (Orphanic Gulf–Strymon Basin areas), Greece. Palaeogeography, Palaeoclimatology, Palaeoecology 238, 125–150. Spassov, N., 2000. The Turolian Hipparion-fauna and the character of the environment in the Late Miocene of West Bulgaria. Review of the Bulgarian Geological Society 61 (1–3), 47–59. Spassov, N., Tzankov, T., Geraads, D., 2006. Late Neogene stratigraphy, biochronology, faunal diversity and environments of South-west Bulgaria (Struma river valley). Geodiversitas 28 (3), 477–498. Syrides, G., 1995. Neogene mollusc faunas from Strymon Basin, Macedonia, Greece. First results for biochronology and palaeoenvironment. In: Gayet, M., Courtinat, B. (Eds), Proceedings of the First Congress of the European Palaeontological Association. Geobios, Special Issue, 18, pp. 381–388. Syrides, G., 2000. Neogene marine cycles in Strymon basin, Macedonia, Greece. Geological Society of Greece, Special Publication 9, 217–225. Tchoumatchenco, P., 1966. Sur les paleorivie`res dans une partie de la region de Kraichte. Bulletin of the Geological Institute 15, 279–287. Temniskova-Topalova, D., Ognjanova-Rumenova, N., 1997. Description, comparison and biostratigraphy of the non-marine Neogene diatom floras from southern Bulgaria. Geologica Balcanica 27 (1–2), 57–81. Tzankov, Tz., Spassov, N., Nikolov, G., 2000. On the character of the late Paleogene and Neogene relief and landscape building in South West Bulgaria. Reports in Geodesy, Warsaw University of Technology 4 (49), 137–143. Vatsev, M., 1980. Lithostratigraphy of the Neogene sedimentary rocks of the Gotse Delchev basin. Annales de l’Ecole superieure des Mines et de Geologie 25 (3), 169–179 (in Bulgarian). Vatsev, M., 1999. New data about the stratigraphy of the Neogene rocks from the Southwestern Rhodopes. Review of the Bulgarian Geological Society 60 (1-3), 127–137 (in Bulgarian). Vatsev, M., Bonev, P., 1994. Lithostratigraphy of the Neogene of the Kjustendil basin. Annals of the Mining and Geology University 40 (1), 43–50 (in Bulgarian). Vatsev, M., Petkova, A., 1997. New data on the stratigraphy of the Neogene of the Gotse Delchev basin (SW Bulgaria). Annals of the Mining and Geology University 41, 3–20 (in Bulgarian). Vatsev, M., Pirumova, I.G., 1983. Lithostratigraphy of the Tertiary sediments of the Satovcha graben. Annales de l’Ecole superieure des Mines et de Ge´ologie 27 (3), 103–115 (in Bulgarian). Velchev, A., 1995. Pleistocene glaciation of the Bulgarian mountains. Annuaire Universite´ de Sofia, Livre 2-Geographie 87, 53–65. Vrablyanski, B., 1970. Niveaux neotectoniques dans le bassin de la Struma moyenne. Bulletin of the Geological Institute 19, 153–166 (in Bulgarian, with French summary).

ARTICLE IN PRESS 2800

I. Zagorchev / Quaternary Science Reviews 26 (2007) 2783–2800

Vrablyanski, B., 1974. Neotectonic studies in the Simitli graben and its framework. Bulletin of the Geological Institute 23, 195–220 (in Bulgarian, with French summary). Vrablyanski, B., 1977. Neotectonic regime in the Strouma fault zone. Geotectonics, Tectonophysics and Geodynamics [Sofia] 7, 18–41 (in Bulgarian, with English summary). Westaway, R., 1993. Neogene evolution of the Denizli region of western Turkey. Journal of Structural Geology 15, 37–53. Westaway, R., 2006. Late Cenozoic extension in southwest Bulgaria: a synthesis. In: Robertson, A.H.F., Mountrakis, D. (Eds.), Tectonic Development of the Eastern Mediterranean Region. Geological Society, London, Special Publication, vol. 260, pp. 557–590. Westaway, R., Guillou, H., Yurtmen, S., Beck, A., Bridgland, D., Demir, T., Scaillet, S., Rowbotham, G., 2006. Late Cenozoic uplift of western Turkey: Improved dating of the Kula Quaternary volcanic field and numerical modelling of the Gediz river terrace staircase. Global and Planetary Change 51, 131–171. Westaway, R., Guillou, H., Yurtmen, S., Demir, T., Scaillet, S., Rowbotham, G., 2005. Investigation of the conditions at the start of the present phase of crustal extension in western Turkey, from

observations in and around the Denizli region. Geodinamica Acta 18, 209–238. Zagorchev, I., 1992a. Neotectonic development of the Struma (Kraistid) Lineament, southwest Bulgaria and northern Greece. Geological Magazine 129, 197–222. Zagorchev, I., 1992b. Neotectonics of the central parts of the Balkan Peninsula: basic features and concepts. Geologische Rundschau 81, 635–654. Zagorchev, I., 1995. Pirin. Geological Guidebook. ‘‘Prof. M. Drinov’’. Academic Publishing House, Sofia, 70pp. Zagorchev, I., 1996. Late Alpine (Palaeogene–Early Miocene) tectonics and neotectonics in the central parts of the Balkan Peninsula. Zeitschrift der Geologischen Wissenschaften 24 (1-2), 91–112. Zagorchev, I., 1998. Pre-Priabonian Palaeogene formations in southwest Bulgaria and northern Greece: stratigraphy and tectonic implications. Geological Magazine 135, 101–119. Zagorchev, I., Ognyanova-Rumenova, N., 1995. First finds of diatom clay and silt in the Neogene filling of the Serres graben, Struma rift, Northern Greece. In: Proceedings of the 15th Congress of the Carpathian–Balkan Geological Association. Geological Society of Greece, Special Publication 4, 304–309.