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Salted Landscapes in the Tuz Gölü (Central Anatolia): The End Stage of a Tertiary Basin

  • Erman ÖzsayınEmail author
  • Alper Gürbüz
  • Catherine Kuzucuoğlu
  • Burçin Erdoğu
Chapter
Part of the World Geomorphological Landscapes book series (WGLC)

Abstract

Tuz Gölü (Salt Lake) is a large salt lake located in the heart of Anatolia. Long-term morphological development of the lake is controlled by the Tuz Gölü Fault Zone and the İnönü-Eskişehir Fault System. The Central Black Sea Mountains in the north and the Taurus Mountain Belt in the south are major climatic barriers generating a precipitation shadow effect on the Anatolian Plateau that worsens the continental climatic conditions characterized here by cold winter, hot summer and relative dryness. Climate, together with active tectonics, let Tuz Gölü to preserve a water depth of maximum 1.5 m. Besides the natural beauty of the outstanding landscapes provided by this shining white lake, numerous salt farms are spread over the lake and neighbouring small lakes. Archaeological data evidence that salt exploitation and trade centres around Tuz Gölü were established since prehistoric and during ancient historic times. This natural and cultural heritage is now threatened by anthropogenic and climatic factors that might lead to its disappearance in a foreseeable future.

Keywords

Central Anatolia Tuz Gölü Salt lake Evaporite Salt dome Ancient salt trade 

16.1 Introduction

Central Anatolian Plateau is located in the middle part of Turkey. This plateau is bounded by the Küre Mountains to the north and the Taurus Mountains to the south, which constitute the orographic barriers for the central part. These barriers establish a conservative, semi-arid climate with low precipitation and high evaporation values, partly explaining the sheep-herding specialized steppe landscapes widely seen in the area.

In the central part of this steppe landscape, the Tuz Gölü plain (the old name was “Tuz Çölü”—“The Salt Desert”) serves as one of the most important transportation routes. Between Şereflikoçhisar and Aksaray (Fig. 16.1), the road follows straight NW-SE-oriented cliffs dominating a wide and flat plain where salt shines wide into the horizon. This is the Tuz Gölü plain, much wider than the traveller can apprehend from the road, and with much more varied landscapes than he/she can see.
Fig. 16.1

Geological map of the Tuz Gölü area showing main structural elements controlling the Tuz Gölü depression.

Modified from Özsayın et al. 2013

In the plain, three fault-controlled lakes come into prominence—namely Tuz Gölü, Tersakan and Bolluk (Fig. 16.1). The Tuz Gölü is the second largest lake of Turkey (1665 km2). Standing at 905 m altitude, it is the lowest one of the numerous lake basins dispatched in the endorheic plateaus of Central Anatolia. This low altitude makes the Tuz Gölü plain the receptacle centre of groundwater flow of the central plateaus. Two saline water bodies neighbouring the Tuz Gölü, the Tersakan and Bolluk lakes, also contain significant concentrations of sodium sulphate.

Tectonic and climatic controls conceive magnificent structures around the Tuz Gölü. Several travertine cones related to faulting, and chimney formations developed within volcanic rocks due to erosion related mainly to climate and vegetation cover conditions are some outstanding natural landforms. Besides, glaring white crystals attract salt walk tourism in the northern part of the Tuz Gölü.

With a low superficial as well as groundwater input, the Tuz Gölü is now threatened with disappearance. Severe measures including control of groundwater usage, limitations in water withdrawal for agriculture and improving sewerage systems have been taken not only to allow continuity of production of evaporites but also to preserve the natural life around the lake.

16.2 Geological and Geographical Setting

16.2.1 Geological Framework and Long-Term Morphological Development

The Tuz Gölü basin is one of the largest closed depressions in the central part of Anatolia. Basin formation was initiated as a continental rifting depression due to NE-SW extension during the late Cretaceous (Çemen et al. 1999; Dirik and Erol 2003). The basement of the basin is composed of Palaeozoic metamorphic rocks and Upper Cretaceous ophiolitic units, which are unconformably overlain by Palaeocene red fluvial clastics at the margins, intercalated with an Upper Palaeocene-Middle Eocene shallow marine sequence in the central part. By the end of the Eocene, ca. N–S-oriented compressional regime occurred and marine conditions gave place to terrestrial environment. At the end of this marine phase, an important climatic and environmental change was recorded by extensive amounts of evaporites and thick clastic sequences sealing the marine sequence. During the Tortonian fluvial systems developed. NE-SW extension, which started during the Messinian, is the last but still ongoing tectonic regime in the Tuz Gölü area (Özsayın and Dirik 2011). Pleistocene deposition started with clastic units often intercalated with volcanic materials derived from the volcanoes located in the eastern and southeastern parts of the Tuz Gölü basin. These units are conformably overlain by thick freshwater lacustrine limestone–claystone alternations. During the Pleistocene, the continuing uplift (Schildgen et al. 2012; Yıldırım et al. 2013) of the Central Anatolian Plateau led to the increasing input of erosion material by the rivers (Doğan 2011; Özsayın et al. 2013; Çiner et al. 2015). During the Last Glacial Maximum (LGM), ca. 20,000 years ago, climatic conditions still favoured a ca. 35–40-m deep brackish lake to expand in the plain.

Today, two major fault systems control and shape the Tuz Gölü depression. The İnönü-Eskişehir Fault System delimits the western margin of the lake. It is a mega-shear zone located between the Tuz Gölü in the southeast and the Marmara Sea in the northwest (Özsayın and Dirik 2011). NW-SE trending Ilıca, Yeniceoba, Cihanbeyli and Sultanhanı Fault Zones (e.g., Melnick et al. 2017) of this system control the topography and linear drainage pattern of the western part of the lake basin (Fig. 16.1). Between Şereflikoçhisar and Aksaray, NW-trending Tuz Gölü Fault Zone limits the Tuz Gölü from the east. Both fault systems form as dextral strike-slip zone responding to collision between the African and Eurasian plates, which initiated the westward escape of the Anatolian plate. During the Quaternary, reactivated fault planes from these systems generated NE-SW extensional movements in the Tuz Gölü area (Özsayın and Dirik 2011). Morphological results of this extension are clearly visible in the local and regional landscapes where they are primarily characterized by normal faulting-related fault scarps, aligned alluvial fans, linear streams, triangular facets, stream captures and deep gorges incised through fault-line scarps (Fig. 16.1).

16.2.2 Climate and Hydrological Input

The Tuz Gölü is one of the largest hypersaline lakes in the world. Its geological, geomorphological and sedimentological features resemble those of Lake Urmia (Iran) and Great Salt Lake (USA). Hydrochemically it is also one of the saltiest lakes of the world, with 32.9% salinity (e.g., the Dead Sea—34.2%, Lake Vanda in Antarctica (35%) and Lake Assal in Djibouti—34.8%; Hammer 1986). Saline lakes are generally located in endorheic basins and are very sensitive to environmental changes. In addition, the absence of an outlet increases the impact of pollution (chemical or biologic) as non-evaporable products concentrate in the brine.

The total catchment area of the lake is about 15,000 km2, which is 1.56% of Turkey’s surface. Depending on seasonal and yearly variations in evaporation and water input, the total lake surface ranges between 1500 and 1665 km2. Several ephemeral streams feed the lake. Surface water input is mainly brought in by three main streams: the İnsuyu, Melendiz and Peçeneközü. The Peçeneközü stream, which arrives in the Tuz Gölü at Şereflikoçhisar town (Fig. 16.1), is the largest with a total annual discharge of ca. 1.760 m3/s (EİE 2000).

Climate in the Tuz Gölü basin is continental, as it is located in the rain shadow of the mountain ranges surrounding central Anatolia, mainly the Küre Mountains to the north and the Taurus Mountains to the south, but also the rising hills and massifs of western Anatolia. Considerable seasonal fluctuations in air temperature occur in this semi-arid climate where the annual average precipitation is about 320 mm/year. At Aksaray, the minimum average January temperature is 0.2 °C (with a mean minimum at −4.2 °C), and the minimum average July temperature is 22.8 °C (mean maximum: 30.4 °C) (source: climate-data.org).

Annual natural hydrological input to the Tuz Gölü is 1860 × 106 m3/year, of which 360 × 106 m3/year is from surface flow, 704 × 106 m3/year from precipitation and 741 × 106 m3/year through groundwater. As an output member, the evaporation rate is 1810 × 106 m3/year (ÖÇKKB 2001). Particularly in the last decades, the hydrological input to the lake has decreased markedly due to climatic change, water reservoir constructions on freshwater tributaries (e.g., Melendiz dam) and careless use of groundwater for agriculture (e.g., Örmeci and Ekercin 2007). The most important and controllable component of water input is the groundwater. According to official reports, the annual amount of groundwater input to the lake budget has decreased from 1000 × 106 m3 in 1974 to 741 × 106 m3 in 1995 (ÖÇKKB 2001; Örmeci and Ekercin 2007).

16.2.3 Morphological Interesting and Specific Features

16.2.3.1 Kuşça Chimneys

The chimneys are one of the world’s most amazing architecture shaped by atmospheric conditions on suitable rock types. Usually, such structures are formed by erosional processes in rocks easily erodible and frost-sensitive, and under rapidly changing conditions related to climate (e.g., drastic changes in rain intensity and runoff discharges, contraction of vegetation land cover), tectonics (e.g., uplift-subsidence movements opposing connected terranes), or land use (e.g., deforestation, practices disturbing soil coherence) (Sarıkaya et al. 2015).

In the Kuşça region located in the western part of the Tuz Gölü, Upper Miocene fluvial clastics cover older rock units with angular unconformity. The ignimbrite layer located in the uppermost part of this sequence is dated to 6.81 ± 0.24 Ma, and is in turn overlain by Pliocene lacustrine limestone (Fig. 16.2). These eroded units are bounded by the Yeniceoba Fault Zone, which forms the southern margin of the ancient Tuz Gölü plain (Özsayın et al. 2013). Kuşça chimneys are observed at the uppermost parts of the fluvial clastics composed of fine-grained conglomerate-mudstone-sandstone alternation. The height of the chimneys ranges between 3 and 25 m while their width differs from 2 to 10 m. In contrast with the ones located in the Cappadocia area, most of the chimneys are singular features representing the highest forms. Some of them situated near to the valley floor tend to cluster and have shorter height and wider base. The triggering factor generating this landscape in such alternatively hard/soft sediment layers is either climate because of lake level changes modifying longitudinal profiles of local rivers or, in addition with, local-to-regional uplift which would have caused runoff concentration and incision into the whole set of Miocene-to-Upper Pleistocene sediments. Once reached by the incision, the softest ones were rapidly eroded because of their mechanic sensitivity towards runoff processes.
Fig. 16.2

Chimneys located at the northeast of the Kuşça village. Note that the single chimney at the centre of the view is approximately 20 m high, the one in the inset picture is around 3 m

16.2.3.2 Bolluk Lake Travertine Cones

The Bolluk Lake is a saline and alkaline lake, like its neighbours the Tersakan and Tuz lakes (e.g., Gündoğan and Helvacı 1996). The lake depression is located to the south-west from the Tuz Gölü and created by the Altınekin Fault Zone (Fig. 16.1). Although no slip data is present from this fault zone, normal fault characteristics can be determined from E-W trending seismic profiles (Arıkan 1975).

In the Bolluk Lake area, aligned travertine cones form an unusual landscape in this depression. Here, Erol (1969) identified and mapped 44 such cones in the lake, and 9 other cones outside the lake. These 53 cones are rowed along fault-line trends consistent with the direction of long axis of the Bolluk Lake (Fig. 16.3). Their diameters are from 4 to 40 m while their heights range from 2 to 20 m. The thickness of the travertine varies between 1 and 20 m. There are also small-scaled travertine ridges between these cones, compatible with the alignment of the faults.
Fig. 16.3

Alignment of travertine cones (indicated by arrows) located around the Bolluk Lake (photographs are taken from the northern part of the lake), compatible with the extension of the Altınekin Fault Zone (Black circle indicates car for scale)

Geochemical properties of the travertines are specific to the geological context of the area. The basement is formed by an ophiolitic complex cut by andesitic volcanism and overlain by Mio-Pliocene gypsum-bearing lacustrine deposits. The subterranean presence of these rocks explains the sulphate (SO4) deposits (i.e., mirabilite, thenardite and bloedite) forming the Bolluk travertine cones. In addition, sulphate-bearing water discharged from these cones contributes to the high sulphate content of the lake water allowing commercial exploitation of sulphate crystallizing in production pools (e.g., Gündoğan and Helvacı 1996) (Fig. 16.4).
Fig. 16.4

General view of the Bolluk Lake and sulphate farms located in the northern part of the lake

16.2.3.3 Saltfarms of the Tuz Gölü

The Tuz Gölü is an essential natural salt supply with a huge reserve. The whole lake has a maximum length and width of 85 and 50 km, respectively. It is surrounded by salty marshes where salt-adapted steppe vegetation grows.

A natural sill barrier, possibly fault-controlled, separates the shallow and deeper parts of the Tuz Gölü. These two zones exhibit different chemical and mineralogical characteristics (Uygun and Şen 1978; Çamur and Mutlu 1996). For example, the Tuz Gölü water has salinity values of ~350 g/l in the main part and 80 g/l in the deeper part (Uygun and Şen 1978).

In spring, the lake reaches its highest level (March/April), with an average of 70 cm depth in its main part and 1.5 m in the eastern part. Starting in May, most of the lake water evaporates because of rainfall drop, decreasing runoff input and increasing temperatures. In summer or early autumn, the shallow part of the lake dries out and a 30-cm-thick salt crust covers its desiccated floor (ÖÇKKB 2005). On the other hand, in the “deep part”, water remains throughout the year. In spring, the lake depth is still >1 m. Since the early 1990s, the lake is divided into the northern and southern part by an artificial impoundment which aims at ensuring adequate water level for salt pools which are situated in the northern part (Fig. 16.5).
Fig. 16.5

Salt farms of Tuz Gölü located in the northern part of the lake

During the dry season (summer), salt precipitates over an approximate 1200 km2 area. It then forms a permanent halite bed, or halite crust, up to 30 cm thick. This thickness is reduced to almost one-half during the rainy period (April–May) because of dissolution (Tekin et al. 2007). Halite crystals show an upward pointing, zoned, primary structure (chevron halite; Gündoğan and Helvacı 1996). In this environment, salt farms produce halite using solar evaporation in numerous saltpans. The overall salt production by this method is about 2,500,000 t/year (Uyanık 2004). In the northern part, besides halite, mineralogy of the salt crust also includes gypsum, aragonite and calcite (Çamur and Mutlu 1996). Below the crust, mineralogy of the unconsolidated muddy sediments (ca. 25 cm thick) is mainly composed of gypsum, huntite and magnesite (e.g., Irion and Müller 1968; Ergun 1988). In the centre of the main part, polyhalite also occurs. In contrast, in the deeper zone sediments are composed of a thin layer of halite, gypsum and aragonite. Below, thin halite layer overlies carbonate sediments composed of Mg-calcite and dolomite (Çamur and Mutlu 1996).

16.3 Geomorphological Landscapes as a Record of Quaternary Environments

The geomorphological landscapes in the Tuz Gölü plain result from the interactions between:
  1. (i)

    the central hypersaline–alkaline shallow lake (<1 m deep);

     
  2. (ii)

    salt flats (brines) and marshes corresponding to seasonally or recently emerged lake floor;

     
  3. (iii)

    flat surfaces over lake deposits, gently declining from southeast to northwest. These terrace-like depositional surfaces develop mainly to the south and west of the lake. Their altitudes above the present lake level (a.l.l.) vary from 10 to 50 m;

     
  4. (iv)

    alluvial fans aligned at the foot of the eastern and southeastern highlands limiting the plain;

     
  5. (v)

    300-m-high fault-line scarps (cliffs) forming the eastern edge of the basin;

     
  6. (vi)
    uplands formed in Mio-Pliocene red bedrocks covering an ophiolite-rich basement (Fig. 16.6).
    Fig. 16.6

    Geomorphological map of the Tuz Gölü Plain

     

16.3.1 A Record of Lake Level Variations during the Late Pleistocene

The Quaternary evolution of the Tuz Gölü depression has been very similar to that of other lake depressions in Central Anatolia (Lahn 1948; Erol 1969, 1978). Often tectonically controlled, some of them are also influenced by karstic processes. They all sit within a much larger primary Neogene basin forming the surface of most plateaus of Central Anatolia.

The Plio-Quaternary units are mainly composed of fluvio-lacustrine and volcanoclastic deposits 190 m thick (Gürbüz and Kazancı 2015). The plain floor evidences a descending succession of coastal deposits recording former lake levels. This stepped morphology has been interpreted by Erol (1978) as “climatically triggered in a subsiding context”. Disentangling the respective roles of climate and tectonics in the geomorphological record evidenced by these past lake levels has been subject to increasingly detailed studies (Erol 1970; Kashima 2002; Dirik and Erol 2003; Gürbüz and Kazancı 2014).

16.3.1.1 Past Lake Level Changes

At 905 m a.s.l., today’s lake occupies the more or less geometric centre of the Quaternary basin. It is enclosed in stepped scarps associated with old coastal deposits and/or alluvial fans overlying the deeper lacustrine environments (Erol 1969, 1970; Kashima 2002; Gürbüz and Kazancı 2014).

In 1970, O. Erol published his famous geomorphological map of the Tuz Gölü plain where he identified remains of four erosion surfaces and six former lake levels. On the basis of their decreasing altitudes, he dated the erosion surfaces to the Middle and Upper Miocene, and to the Lower and Upper Pliocene, and the six lake levels to the Pleistocene. In order to characterize the depositional/erosional nature of the lake surfaces, Erol (1969) used depositional environments (facies analyses) and stratigraphy of the deposits which are mainly a succession of a deep lake clay, overlain successively by beach, fan deltas, fluvial and alluvial fan deposits (see also Gürbüz and Kazancı 2014). The height of the scarps separating the distinct lake levels decreases from 25 m for the two highest ones, through 15 m for the two ones below, descending to 10 and 5 m for the lowest ones. Fossil fauna in the sediment points to a freshwater or slightly brackish lake during the late Pleistocene, except during the period corresponding to the 7–3 m (a.s.l.) high coastline (late Holocene: Erol 1970).

The origin of the scarps underlined by coastal deposits remains problematic as, in the Tuz Gölü Pleistocene context, a scarp may respond to one or two causes or both: climate and/or tectonic (Gürbüz and Kazancı 2014).

16.3.1.2 Lake Levels as a Record of Climatic Change

Because absolute 14C dating was difficult to perform at these early times, Erol (1970) dated old erosion surfaces, as well as Quaternary lakeshore deposits and alluvial terraces, on the basis of their altitudes. As a result, the lake levels on the map are concentrically disposed around today’s lake and their ages become increasingly younger towards the centre of the plain. In his earliest papers, Erol attributed the old lake levels associated with lake landforms and deposits to “Pluvial” phases (or subpluvial phases in the case of the early/late Holocene) of the Pluvial/Interpluvial (Glacial/Interglacial) chronology of Quaternary climate used at the time.

16.3.2 LGM and the Late Glacial

The two highest terraces (1015 m and 980 m a.s.l.) are marked by well-preserved shore deposits, platforms, fan deltas, coastal landforms and wave-eroded cliffs (Erol 1970). Attributed to LGM lakes Erol (1970), they occupied an area corresponding to today’s whole plain. This attribution is confirmed by Kashima (2002) and Özsayın et al. (2013).

In the southeastern part of the Tuz Gölü plain, Kashima (2002) evidenced two lake phases separated by a coarse sand and gravel layer 1–2 m thick, becoming coarser and thicker landwards. The lowest layer is dated to LGM (20.7, 18.6, 18.9 ka cal BP); the youngest coincides with the LGM/Late Glacial transition (ca. 16 ka ago). Diatom assemblages from both clay layers point to low salinity water conditions, a result also confirming Erol’s (1969, 1970) observations. The top surface of the LGM lake clay unit is 920 m a.s.l. (i.e., 15 m a.l.l.). From the depositional environment (near shore) suggested by the brown colour of the lake clay and its slight sand content, Kashima (2002) inferred the lake level to have then been ca. 930 m a.s.l., i.e., 25 m above today’s lake floor. Such a lake highstand is common in the Turkish high plateau during the LGM, from Burdur to Konya and Van lakes.

The youngest clay layer studied by Kashima (2002) is dated ca. 18.6 and 16.8 cal ka BP. Because of the yellow-brown colour of the clay and its sand and small gravels content, the lake depth is estimated to have been relatively deeper than today (3–5 m), and the author positions the lake level at 15 m a.l.l. (i.e., 920 m a.s.l.).

16.3.3 Records of Environmental Variations during the Holocene

16.3.3.1 Lake Records

At the beginning of the Holocene, the lake level decreased and the lake bottom emerged, forming extensive flat surfaces. During the Holocene, small and shallow lakes persisted in subdepressions (Kulu, Yeniceoba, Altınekin, Bolluk, Tersakan; see Figs. 16.1, 16.6 and 16.7). All these subdepressions are directly limited by parallel fault scarps, which follow the main tectonic features of the basin (Fernandez-Blanco et al. 2013; Özsayın et al. 2013; Gürbüz and Kazancı 2014). These subdepressions were flooded during humid periods in the Holocene, when the underground water level rose above the surface of the depressions. As soon as the water level in the plain rises up to 915 m a.s.l., these subdepressions became connected.
Fig. 16.7

Quaternary evolution of Tuz Gölü, along an E-W section, divided into four stages. Sketch shows fragmentation of an earlier large lake while the basin has been gradually subsiding to gain its recent shape (Gürbüz and Kazancı 2014)

16.3.3.2 Alluvial Fans

Alluvial fans fringing the eastern cliffs of the Tuz Gölü are formed by successions of rounded gravel beds and beige-coloured silt flood layers. Gravel beds record processes triggered by high water discharged from the cliffs above. These beds are deposited by flash floods, most probably during winter and spring time. The interruptions signalled by silt deposition respond to lateral changes of water dynamics over the fan itself, and are never related to an incision. This type of pulsed deposition rhythm points to a more or less semi-arid climate, like today. In their specific location along the Tuz Gölü fault-line scarp, the alluvial fans are also impacted by fault activity, which contributes to colluvium load, later incorporated as slope-derived sediment transported by local streams.

A 14C chronology of construction of these fans is available from studies in quarries (Naruse et al. 1997), aligned sections documented in streams and cores (Kashima 2002), from terrestrial Mollusca species and organic matter in soil. Combination of these results shows that there is no evidence of any fan deposit from the early Holocene (i.e., 12–8 ka cal BP), and that after 8 ka cal BP, the record consists of two alluvial fan construction phases separated by a steep erosion unconformity dated ca. 5.2–5.0 ka cal BP. This incision was caused by a sharp humidity increase after dry conditions that lasted from ca. 5.75 to 5.2 ka cal BP. Ceramics found in top sediments prove the latest activity of the upper fan during Byzantine times (Kashima 2002).

16.3.3.3 Lake and Fan Context of Archaeological Settlements

Erol (1970) observed a strong connection between the coastlines of former lake levels at +7 and +3 m and the distribution of archaeological sites occupied from the Chalcolithic to the Middle Ages. Kashima (2002) also inferred a relationship between the geomorphological evolution of the upper alluvial fan since Bronze Age sites concentrate on the margins of the fans, while later sites (Roman, especially) settled on the lower parts of fans and former lake areas.

16.3.4 The Impact of Tectonic and Karstic Processes on the Landscapes

Based on O. Erol’s outstanding pioneer map published in 1970, Fig. 16.6 also stresses the geomorphological landscapes pointing to the possible impact of tectonics on the geomorphology of water divide, karstic network and dissolution landforms.

16.3.4.1 The Tuz Gölü Fault Zone

The major fault zones that have influenced the Plio-Quaternary evolution of the Tuz Gölü Basin are all oriented NW-SE (Özsayın et al. 2013). Figure 16.1 shows this tectonic control on relief organization of the plain. In addition to the activity of the Tuz Gölü Fault Zone (TFZ) in the eastern part of the plain, the best evidence of this control is to be found in the disposition of elongated depressions of the Altınekin, Bolluk and Tersakan lakes, as well as Yeniceoba elongated depressions.

The TFZ geological slip rate has been calculated for 0.08–0.13 mm/year near the central segment where the highest relief and steepest slopes are located (Özsayın et al. 2013). Aiming at defining today’s seismic risk in the TFZ area, morphometric analyses performed by Yıldırım (2014) on the stream profiles also evidence higher displacement in the central part of the eastern fault-line scarp (between Aksaray and Şereflikoçhisar). This activity concentration in the TFZ central zone postdates the Last Glacial Maximum (Özsayın et al. 2013). On the Şereflikoçhisar Peninsula, for example, the LGM palaeoshoreline (14C dated 21.9 ± 0.4 cal ka BP in carbonate: Özsayın et al. 2013) reaches 1015 m, i.e., 45 m higher than the other LGM shorelines identified at 970 m a.s.l. (Erol 1969, 1970). In the Şereflikoçhisar fault-related scarp vicinity, ca. 7.5 km SW of the mountain front and beyond the reach of Holocene alluvial fans, a ca. 1.5-m-high scarp deforms the present lake sediments (Kashima 2002).

16.3.4.2 The Water Divide

Several features observed on the water divide evidence drainage changes, which are potential important actors of the geomorphological evolution (Fig. 16.6).

Along the TFZ, geomorphological features suggest a trend towards the capture of the Tuz Gölü depression by an increasingly incising and “aggressive” the Kızılırmak River: (i) at the northern end of the Tuz Gölü, the regressive erosion of Kızılırmak River left bank tributaries are about to capture the depression; (ii) north of Aksaray, the headwaters of Kızılırmak tributaries are capturing source areas of two Tuz Gölü tributaries. The location of these captures converges towards the central part of the TFZ where uplift is more active.

This uplift also introduces a disjunction of the Peçeneközü stream valley drainage, which runs parallel to the Tuz Gölü shores. While this valley is today almost hanged above the lake plain at Şereflikoçhisar, its southern end is also connected in the opposite direction to the Aksaray area. This valley is thus on its way to become a dead cut at both ends by dynamics related to an active fault-scarp (north) and river incision (south). In addition, the head of one of its right-bank tributaries is possibly being captured by the Kızılırmak Basin. We may be thus witnessing an episode of the Tuz Gölü Basin captured by the Kızılırmak River Basin, which would end with an extreme narrowing of the eastern part of the Tuz Gölü closed basin.

16.3.4.3 The Karstic Touch

In the Tuz Gölü plain and surrounding Neogene plateaus, karstic features are mainly landscapes such as depressions (poljes, dolines) associated with swallow holes, lakes and wetlands (Fig. 16.6).

In the NW part of the Tuz Gölü Basin in the Kulu area, remains of palaeodrainage network record changes in the location of water divide and shape of drainage basins. These changes and associated fossil features are controlled by the addition of subsidence associated with karstic processes at work underground and on the surface. In the northern part, dissolution dolines are centred around swallow holes (e.g., Kulu) or lakes (e.g., Samsat) which are most probably connected underground. On the surface, the relationships of these dissolution features with the underground are mimicked by dry valleys linking them. These valleys are recognizable by their more or less recent (late Pleistocene?) alluvial floor.

At the northernmost end of the Tuz Gölü, the drainage of the “Düden” doline and swallow hole is directed towards the Kızılırmak River Basin (Fig. 16.6). Underground, these features may be connected to the Kulu area where another swallow hole is connected to the Tuz Gölü. Thus, this part possibly favours some hydraulic discharge of the Tuz Gölü Basin out of Central Anatolia.

In the SW part of the Tuz Gölü Basin, poljes are the main karstic landforms and these are also tectonically controlled since they have subsided between faults belonging to the Yeniceoba, Altınekin and Sultanhanı fault zones. These poljes are flooded in winter and spring. Their floor is blanketed by a reddish clay formation deposited by runoff eroding soils over limestone. These typical karstic landscapes provide well-watered grazing grounds for cattle and sheep herds.

16.4 Archaeology, the Salt Way and Ancient Salt Trade

Salt is an essential dietary item for both humans and animals. Although it has been used already in prehistoric times for flavouring, pickling, preserving and curing meat and fish and for tanning, it has also been used in culturally significant or emotionally intense situations such as religious, ritual, parturition or mortuary activity and in a variety of ceremonies involving food (e.g., Multhauf 1978; Adshead 1992; Kurlansky 2002). Anatolia has important sources of salt. Among them, the Tuz Gölü is the most important. The earliest archaeological evidence of using salt in the area comes from the Neolithic village of Çatalhöyük, ca. 7400–6000 cal. BC, where concentrated salt deposits were found in a number of food preparation and cooking areas. At least in one case (Building 17), salt deposits were found in oven rakeout with food preparation or cooking debris along with charred plant remains (Atalay and Hastorf 2005).

Salt production and trade is mentioned in Hittite cuneiform tablets, which also mention several different cities as related to salt production (Erkut 1990). For example, a bronze tablet of Hattuša (Boğazköy) gives important information related to Tuz Gölü (Erdoğu and Özbaşaran 2008). The tablet records a treaty of Tudhaliya IV King of Hattuša with Kurunta, King of Tarhuntašša who was given the “saltlick rights” (:lapanaliyanza). “Great saltlick rock” (:salli lapani waniya) mentioned in the tablet which was translated by Otten (1988) as “the great summer pasture and the saltlick”, which matches exactly characteristics of the Tuz Gölü region.

Writers in Antiquity have also mentioned Tuz Gölü. The ancient name of Tuz Gölü is Tatta. Pliny the Elder, the most important of these ancient writers who wrote on salt, gives the example of the Phrygian and Cappadocian salt lakes, of which the most important was Lake Tatta (Historia Naturalis XXXI, 84). According to Pliny, salt from Lake Tatta and Caunos was used in eye remedies (Historia Naturalis XXXI, 98–105). Tuz Gölü is also mentioned by Strabo as a natural salt pan (Geography XII, 5, 4). Dioscorides argues that salt extracted from the Lake Tatta was considered to have healing powers (De Materia Medica 5, 109, 1).

An alternative method for researchers working on ancient salt production, exchange and consumption involves the collection of ethnographical data. The main technique in the Tuz Gölü region was breaking up of the salt crust with iron tools and processing it into powder with the aid of grinding stones (Fig. 16.8). Another technique was to collect brine along the coast of the lake and to store it in clay pots where it was left to evaporate (Erdoğu and Özbaşaran 2008).
Fig. 16.8

Ancient grinding stone for salt powder

16.5 The Lake and Surrounding Wetlands: A High-Level Biodiversity Area in Turkey

16.5.1 An Important Breeding and Nesting Bird Area

In 2001, the lake (on the surface basis of its highest level), the surrounding waterbeds and some neighbouring steppe areas gained the official Turkish protection status of “Special Environmental Protection Area”. This was to protect an exceptional waterfowl and bird fauna, such as the main Turkish breeding colony of Greater flamingo (Phoenicopterus roseus), the breeding of Greater white-fronted goose (Anser albifrons) and of Lesser kestrel (Falco naumanni). In 2011, for example, while most of the 69,000 flamingos hatched in seven Mediterranean countries were in Turkey, 18,400 of those were at Tuz Gölü, giving the lake the largest flamingo chick population in West Africa and the Mediterranean. Also, the lake and its plain are a resting stop for migrating flocks of storks, pelicans and cranes. These colonies are attracted by halophytic plants, algae, animals and microorganisms living on and from salted grounds. All these living species concentrate along lakeshores and at the saltpan margins (e.g., Tekin et al. 2007).

In spite of this importance, Tuz Gölü is not on the Ramsar List of Wetlands to be primarily protected for their waterfowl fauna. It has however been submitted to the UNESCO’s Tentative List of World Heritage Natural Sites. In 2013, Nature Protection Associations signalled that the flamingo colony has collapsed to a handful due to a dramatic decrease in the saltwater shrimp they feed on. Cranes, white-fronted geese and other water birds that live in the area are also at risk, mainly because (but not only) Tuz Gölü water volume is decreasing at a high speed.

16.5.2 Vanishing Tuz Gölü

In the last 40 years, the surface area of the Tuz Gölü has decreased by more than 85%, an amount that occurred mostly in the last 10 years (Fig. 16.9). Today, the water level during spring is insufficient to flood the western part of the contracting lake. This area is now devoid of migrating birds as well as all other salt-dependent biologic systems.
Fig. 16.9

Satellite images representing water-level decrease in the Tuz Gölü (images are taken between 10th and 18th August of each year)

The drying trend of climate during the last 20 years is usually pointed out as the main cause of lake water depletion. But overdosed usage of groundwater via excess and unplanned wells as well as the increasing number of salt farms constitute major pressures on the lake budget and water quality. Moreover, the dams constructed on the rivers feeding Tuz Gölü are also prominent causes of water-level decrease in the lake.

In this context of increasing pressure on the water resource, the “Special Environmental Protection Area” status allocated by the Turkish Government to Tuz Gölü and its surroundings in 2001, implemented conservative measures for ensuring salt production quality and quantity needed by the country (three mines produce 63% of salt consumed in Turkey). Today, the General Directorate of State Hydraulic Works (DSİ) strictly controls well-digging permissions for fighting excessive groundwater usage and the implementation of illegal wells in agricultural areas. Sewerage systems are also under construction or improved by the municipalities in order to restore the lake water quality.

16.5.3 Other Threats

Until 2009, the primary source of water flow into Tuz Gölü was neither rivers nor rainfall, but sewage from the nearby city of Konya and local villages and towns. Polluted water from Tuz Gölü was not only used for processing human-used salt on the national scale, but also used by local villagers to irrigate their crops. These two facts made cleaning up the lake an urgent matter for human health as well as for the environment, an objective met by the operation of a wastewater-treatment plant at Konya in 2009, which allowed shutting down of the long-lasting Konya’s refusal waters diversion to Tuz Gölü.

Taking lately into account Turkey’s gas supply security and the lake natural structure which is quite suitable for gas storage, it is today planned to construct a gas storage plant consisting of 12 units (the capacity of 630.000 m3 each), estimated to provide 40 million m3 gas/day to Turkish natural gas network. This project will enable to store 1 billion m3 natural gas. It is planned to be completed in 2018. But dissolving the salt inside the underground caves requires huge amounts of water and will cause further pressure on existing limited fresh water resources in the region.

16.6 Conclusion

With its large-scale, Tuz Gölü is not only known to be a salt deposit but also a perfect laboratory for studying fault-controlled intracontinental depression. Semi-arid climate conditions help Tuz Gölü to preserve its magnificent white crystalline view, glancing at the Central Anatolian Plateau. The study of geomorphology and geology in the plain shows detailed records of climatic changes during the Upper Pleistocene and Holocene (lake levels, alluvial fans) and their relationships to human occupation. It also shows that basin capture is most probably active today on the northern and eastern water divides. Captures threaten the “heart of Central Anatolian Plateau” to be slowly discharged to the Black Sea-heading Kızılırmak River. This capturing threat is dominantly controlled by the activity of the Tuz Gölü Fault Zone. More immediate today’s concern is that evaporitic content of Tuz Gölü and neighbouring lakes are significant economical assets which have been positively influencing the cultural background of the area since historical times. However, in the last 40 years, the lake is facing the risk of vanishing. While two main measures have been taken to preserve both the natural and economical life of the basin (the designation as a Special Environmental Protection Area in 2001; the construction of a wastewater-treating plant at Konya), the implementation of conservation measures remains difficult in a context of increasing pressure on water resources, and lately on the underground gas storage capacities of the basement.

Notes

Acknowledgements

The authors are grateful to Mr. Yahya Cihan Darıcı and his company Vecihi Yüksek Çekim Teknolojisi for the visualization of aerial photographs.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Erman Özsayın
    • 1
    Email author
  • Alper Gürbüz
    • 2
  • Catherine Kuzucuoğlu
    • 3
  • Burçin Erdoğu
    • 4
  1. 1.Department of Geological EngineeringHacettepe UniversityCankaya Turkey
  2. 2.Department of Geological EngineeringNiğde UniversityNiğdeTurkey
  3. 3.Laboratory of Physical Geography (LGP, UMR 8591)CNRS, Universities of Paris 1 Panthéon-Sorbonne and Paris 12 U-PecMeudonFrance
  4. 4.Department of ArchaeologyTrakya UniversityEdirneTurkey

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