Introduction

Türkiye is located in a geographical transition corridor between Asia-Europe or ‘Eur(Asia)’, which has provided many endemic and global assets since the first human settlements, especially in terms of cultural, geological, geomorphological, vegetative and climatic diversity (Kazancı 2010, 2012; Kandemir and Köroğlu 2017; Köroğlu and Kandemir 2019; Özer and Mülayim 2022; Köroğlu and Mülayim 2023; Mülayim et al. 2024; Köroğlu 2024). The Eastern Black Sea region is a unique geographical location, containing sedimentary, igneous, and metamorphic rock groups belonging to different geological periods since the Pre-Paleozoic and differing morphologically in terms of topography.

The geological heritage and other components of the Earth have received and are given much more focus since the twenty-first century in multidisciplinary research groups to identify geosites, geoconservation, geodiversity, geoheritage, geotourism and geopark concepts. These are firmly linked and should be protected to ensure geoscience education and geotourism become elements of sustainable geoheritage (Theodossiou-Drandaki et al. 2004; Brilha et al. 2005; Dowling and Newsome 2005, 2010; Hose 2005; Ruban 2010; Henriques et al. 2011, 2019; Wimbledon and Smith-Meyers 2012; Dowling 2011, 2014; Brilha 2016, 2018; Köroğlu and Mülayim 2023).

The derivation of the term canyon, “a narrow valley between cliffs”, from Mexican Spanish is used to refer to geologic structures that are cut by a river. Canyons often develop as a deep valley or streambed with steep, cliff-like sides through which a dry or active river flows (Allaby 2008; https://www.etymonline.com/word/canyon). Although paleo-drainage networks cannot be fully observed today, the structures and remains formed by these networks provide insight into their existence. The Ziyarettepe Formation (Özsayar et al. 1982) consists of medium-bedded rocks, mainly composed of sparite-calcite limestone (CaCO3). These rock types can be eroded by climatic and hydrological conditions at the surface, by chemical reactions and by mechanical action. The effects of fluvial erosion and karstification are frequently observed in Cehennem Deresi Canyon(s) and in the area around the creek. Today, the canyon contains climatically and hydrologically controlled structures that developed over time in response to the chemical and physical properties of the carbonate rock. Studies show that there are canyon structures in the region that developed in two directions. These are divided into Cehennem Deresi Canyon NorthEast (CCNE) and Cehennem Deresi Canyon NorthWest (CCNW). Ultimately, the Cehennem Deresi Canyon(s), the creek and the morphological units that suddenly rise from streambed offer a unique view of the landscape with the clear river and then the Deriner Dam reservoir, which is easily exposed to human influence. Cehennem Deresi Canyon(s) have great potential for geotourism activities that can be sustainably developed in its immediate vicinity based on its geoheritage value. The city of Ardanuç (Artvin), where the canyon is located, has unique resources as it is an important destination for geotourism. Therefore, the 3G (geomorphology, geoheritage, and geotourism) value of Cehennem Deresi Canyon(s) has special characteristics compared to other canyons and valleys. It is important to examine the 3G characteristics of Cehennem Deresi Canyon(s) in Ardanuç (Artvin) as it has not been the subject of previous studies.

The unique and remarkable contribution of this study is that it will reveal the potential of hidden aspects of the Cehennem Deresi Canyon(s) in Ardanuç (Artvin) region and its surroundings in terms of 3G values.

Material and Methods

The study was conducted by using a field study, laboratory, remote sensing, and government archival research methods. Both topographic and geologic maps, rock samples and analyses, satellite imagery, and photographs of observations in the study area were used. Drawing software was used to convert the collected data into regional maps and descriptive photographs. The nomenclature followed in this study was prepared by Pena dos Reis and Henriques (2009), Kazancı (2010, 2012), Wimbledon and Smith-Meyers (2012), and Brilha (2016, 2018).

Regional Description and Geological Background

Cehennem Deresi Canyon(s) are located near Ardanuç (Artvin/Türkiye) at coordinates 41°07′59″ N—42°02′53″ E (Figs. 1a, b and 2). On the political map of Türkiye, Ardanuç in the Artvin province in the Eastern Black Sea region, is located in the eastern part of the region. The north of the region is also the political border between Türkiye and Georgia. Ardanuç, with an area of ~ 989 km2, is adjacent to Şavşat district in Artvin to the north, Yusufeli and Olur districts in Erzurum to the south, Ardahan to the east and Artvin to the west. Transportation access to the area is provided by a road connecting to Ardanuç county from the Artvin-Ardahan road, which starts from the Hopa junction on the coastal Black Sea motorway. The physical structure of the region comprises Karçal Mountain (4328 m) to the north and the Yalnızçam Mountain (3050 m) to the south, which also form steep topography. Berta Stream in the north and Bulanık Stream and Çoruh River in the west developed along valleys formed as a result of fluvial erosion and faulting of rocks that form these mountains.

Fig. 1
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a) Relief map of Türkiye and Caucasus (Mercator projection, modified from https://treehouse-maps.com/), b) Map of the study area in the Ardanuç region of Artvin, Türkiye (modified from Akıncı and Zeybek 2021)

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Fig. 2
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Geological map of Ardanuç (Artvin, Türkiye) (modified from Google Earth Pro and http://yerbilimleri.mta.gov.tr)

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The Eastern Sakarya Zone (previously Eastern Pontides) consists of a rectangular mountain chain with an approximate length of 600 km (E-W) and width 200 km (N-S) located in the east of the Black Sea Region (Özsayar et al. 1981; Okay and Şahintürk 1997; Okay and Tüysüz 1999) (Figs. 1a and 2). The study area corresponds to the northeast (Eastern Pontides) part of the tectonic unit located in the far east of the Sakarya Zone (Okay and Şahintürk 1997; Okay and Tüysüz 1999). Considering its paleotectonic history, the region is located within important tectonic belts (Şengör and Yılmaz 1981, 1983; Okay and Şahintürk 1997; Nikishin et al. 2015). During the Cretaceous-Paleogene, the Eastern Sakarya Zone was occupied by the Tethyan Ocean consisting of marine areas of the North and South branches (Şengör and Yılmaz 1981; Okay and Şahintürk 1997; Okay and Tüysüz 1999). Türkiye corresponds the first terrestrial area that emerged (Şengör and Yılmaz 1981; Okay and Şahintürk 1997; Özer et al. 2009; Barrier et al. 2018; Aydin et al. 2020). A subduction zone at the end of the Cretaceous, that formed the Alp-Himalayan orogeny, played a major role in shaping the region during the Mesozoic (Okay et al.1994; Okay and Şahintürk 1997; Karslı et al. 2012, 2018; Aydin 2014; Dokuz et al. 2019; Kandemir et al. 2019; Aydin et al. 2020). The separation into ‘North’ and ‘South’ zones in the region (Özsayar et al. 1982) provides information about the geodynamic processes. Unlike Kandemir et al. (2019), the zone boundaries were revised and both geochronological and biostratigraphical correlations were made between the arc zone and the fore-arc and back-arc areas. Linked to more detailed biostratigraphic and sedimentological inferences by Köroğlu et al. (2022a, b) and Köroğlu (2023), the environment was found to be neritic and hemi-pelagic evolving in a back-arc basin.

Ziyarettepe Formation

In the study entitled “Geology of Ardanuç Region (Artvin)”, Özsayar et al. (1982) named the Ziyarettepe Formation that unconformably overlies the basal conglomerate and Cretaceous (volcano-sedimentary) units. The limestones of the Ziyarettepe Formation in the Ardanuç (Artvin) district in the Eastern Sakarya Zone represent the neritic deposits in marginal areas of an extensive back-arc overlain by marl and siltstone associations of the Kızılcık Formation (Özsayar et al. 1982). Paleocene age was indicated by benthic foraminifera species within the unit (Özsayar et al. 1982). The unit, which includes facies transitions, was observed to include biosparite, sparite, biomicrite, biosparite, biomicrite and microsparite-sparite facies, according to Folk’s (1962) classification and was evaluated as representing the neritic/hemi-pelagic transition (Özsayar et al. 1982). Subsequent studies highlighted the Cretaceous-Paleogene transition in the region according to both benthic-planktic foraminifera and nannoplankton species in Maastrichtian-Thanetian levels within the Artvin-Bolnisi Zone (Kurt 1998; Aksay and Turhan 1998; Konak et al. 2001; Kurt et al. 2005). The recent extended study by Köroğlu et al. (2022a, b) and Köroğlu (2023) established the K-Pg transition in the Ziyarettepe Formation using several data approaches (Fig. 3).

Fig. 3
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K/Pg stratigraphy of the Ardanuç region and Ziyarettepe Formation

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Constitutional Evolution of Cehennem Deresi Canyon(s)

Cehennem Deresi Canyon(s) are located within the borders of Ardanuç county in Artvin province in the Eastern Black Sea region with geographical position 41°07′59″ N and 42°02′53″ E (Figs. 4, 5, 6, 7 and 8). The first judgement about this natural entity was made on 14.11.2003, while there was no previous study on a legal basis. Cehennem Deresi Canyon(s) were declared a 1st degree natural area by the registration decision “Trabzon K.T.V.K.B.K 14.11.2003/4870” from Trabzon Regional Board for Protection of Cultural and Natural Assets (Envanteri 2012) by describing it as follows.

“Cehennem Deresi Canyon Valley is located 7 km northwest of the centre of Ardanuç district and 25 km from the Artvin-Ardanuç motorway. It is one of the largest canyons in the world. It attracts the attention of visitors with landscapes which can be noticed on the way inland” (Envanteri 2012; page 132, translation from the original Turkish text)

Fig. 4
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a–b) The main entrance of Cehennem Deresi Canyon NorthEast (CCNE), c) The widest point of the canyon, d) A view towards the entrance (a and b)

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Fig. 5
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a) Cehennem Deresi Canyon NorthWest (CCNW) in Ardanuç, view of the canyon entrance (view direction Gevhernik Castle, Adakale District), b-c) View of the Artvin-Ardanuç-Ardahan motorway inside the canyon

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Fig. 6
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Ardanuç syncline, which formed as a result of tectonic phases and is seen within the Kızılçık Formation a) The synclinal axis and folds in the wide plan, b) Syncline and Ardanuç city centre, the observation point is at the red dot (in both a and b), in perspective concave shape

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Fig. 7
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a) Panoramic view of the city center of Ardanuç, geomorphology, and geological formations, b-f) canyon walls and floor within CCNE, g) Canyon walls and floor within CCNW

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Fig. 8
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Karstic cave structures and formations of (a-d) CCNE, and (e–f) CCNW

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Although there is no record of tourist activity, it is constantly flooded with visitors, except in winter, as it is a canyon on the Ardanuç-Ardahan motorway. There is no welcome centre in the area and no qualified visitor data and evaluations as there is no ticket office. Detailed studies about conservation and other tourism activities in the area have not been conducted. However, as of September 2020, there is just work to build a parking lot for tourists at the entrance of the canyon.

Geologically, there are descriptions in constitutional declarations related to the canyon (CCNE) (Envanteri 2012) and the NE direction as defined by İlhan et al (2017). However, the canyon in the NW direction (CCNW) starting from Ardanuç (Artvin) city centre to the Ferhatlı region has much larger and more magnificent structure than in the NE direction (Figs. 4 and 5).

Geomorphology

CCNE has dimensions of about X: 600 m, Y: 70 m, and Z: 6 to 60 m and developed in NE-SW direction (Fig. 4). There is a topographic elevation of 250 m between the canyon floor and the ground. CCNW dimensions are approximately X: 3 km, Y: 30–70 m, and Z: 200–250 m (Fig. 5).

The region is located in the southern part among the highest peaks of the Eastern Black Sea Mountain belt. The main geological structures are folds, thrusts, reverse faults, vertical faults, and strike-slip faults (Aksay and Turhan 1998; Konak et al. 2001). Thrust lines are observed on the Gümüşhane-Bayburt-İspir-Olur-Oltu-Ardanuç-Şavşat line in the southernmost part of the Eastern Black Sea region (Aksay and Turhan 1998; Konak et al. 2001; Kandemir et al. 2019). Folds and faults, which are common structures, are observed more intensely between Ardanuç and Şavşat, and there are anticlines and synclines in the study area (Fig. 6).

There is a disconformity surface between the Ovacık Formation (Kandemir et al. 2017) starting with the basal conglomerate (sandstone, gravel and blocks) on Upper Cretaceous volcano-sedimentary units. The presence of angular unconformities with the Ziyarettepe Formation (Özsayar et al. 1982), overlying the Ovacık Formation, indicates that the orogenic phases developing between these three units were geodynamic events in the Eastern Sakarya Zone. These geodynamic events are defined by various structural geological elements throughout the region. The existence of tectonic lines (fold axes, faults) developed in NE-SW and NW–SE directions throughout the region provides important insight into the paleotectonic history.

Due to NE-SW and NW–SE oriented tectonic lines that developed throughout the region, the main drainage networks and their tributaries formed. In the region, defined as a volcanic island arc (Kandemir et al. 2019; Dokuz et al. 2019; Aydin et al. 2020) which remained submerged until the end of the Upper Cretaceous, sedimentary rocks began with deep marine sediments in the Campanian (Kandemir et al. 2019; Aydin et al. 2020). These continued as Maastrichtian-Thanetian neritic sediments and as mudstone-sandstone-limestone intercalations until the lower Lutetian (Özsayar et al.1982; Aksay and Turhan 1998; Konak et al. 2001; Sarı et al. 2014; Hippolyte et al. 2015; Kandemir et al. 2019; Consorti and Köroğlu 2019; Consorti et al. 2020; Köroğlu et al. 2022a, b; Köroğlu 2023). As the units in the region up to the time of Upper Cretaceous are generally magmatic in origin, these erosion-resistant rocks form the basement of the drainage lines. The development of canyon morphology is seen in the Campanian-lower Eocene within sedimentary deposits. Cehennem Deresi Canyon(s) consist of mostly calcarenite-calcirudite and neritic limestones containing bioclasts with upper Campanian-Thanetian age (Aksay and Turhan 1998; Köroğlu et al. 2022a, b; Köroğlu 2023). Together with these geological features, fluvial erosional force increases with the high slope along the Cehennem Deresi basin. Due to the periodically changing flow velocity, chemical weathering is high during periods of low flow velocity, while both physical and chemical weathering and extension occur along the canyon walls during periods of high flow velocity (Fig. 7).

In addition, the canyon was created by regional uplift. The region passed into the terrestrial environment since the Paleocene and the entire Anatolian plate elevated up to 1 km with orogenic movements (Şengör and Yılmaz 1983; Okay and Tüysüz 1997; Keskin et al. 2011; Okay et al. 2020). In addition to global warming and cooling (Keller 2014) since the end of the Maastrichtian period and paleoclimatic changes from the Cenozoic to the present, transitions between glaciation and very hot periods have been recorded (Zachos et al. 2001). There are many studies showing that global average temperatures have increased between 0.15 °C and 0.20 °C since the industrial revolution (Hansen et al. 2010), as evidence that there is a climate crisis in modern times. The melting of glaciers and ice movements in the polar regions also confirm this conclusion.

Naki Akçar and his team drew conclusions about the paleoclimate in the region with the first cosmogenic 10Be isotope studies in the Kavron and Verçenik valleys in the Kaçkar Mountain belt (Akçar et al. 2007). The study of cosmogenic 10Be exposure age revealed that the timing of the Last Glacial Maximum (LGM) was during MIS-2 in the Eastern Black Sea Mountains (Akçar et al. 2007). However, the region contains records of the Last Glacial Maximum (LGM), Younger Dryas (YD), Little Ice Age (LIA), and Late Glacial Warming (LGW) within four different periods compatible with both the Earth and local paleoclimates. The region is the continuation of the Kaçkar Mountains (3937 m) surrounded by Karçal Mountain (4328 m) and the Yalnızçam Mountain (3050 m) in the NE Black Sea region. It is possible that the study area was very close to the Kaçkar Mountain belt during that time and the Ziyarettepe Formation and canyons around Ardanuç may have been affected by glaciation. At the present time, a sudden and rapidly developing drainage network is indicated by the streams descending to the valley floors not forming canyons in different directions, the collection of all drainage networks in a single valley and the terraces not having multiple steps. This also indicates that regional geology is suitable for the development of karstification. According to these data, the region was permanently altered by dramatic climatic events during the Holocene.

As a result of the combination of all extraterrestrial impacts, global and regional geological events, and the climate crisis, the most beautiful and almost impossible existence of the Earth’s heritage is revealed today. This heritage represents inestimable value for ecology, landscape, and sporting activities.

Geoheritage

In terms of landforms, the region has geoheritage elements whose geomorphology has been shaped by geology and tectonic processes, as well as streams controlled by climatic features. The basic geoheritage assets were evaluated in this study within canyons that developed near structures in the Ziyarettepe Formation (Figs. 3, 4, 5, 6 and 7). The formation of the main geoheritage assets in the region affected by the intensity and temporal changes in erosion of carbonized rocks with surface currents developing in drainage networks (previous and recent) on paleotectonic lines by Ardanuç Stream (Fig. 2). Moreover, thanks to the low-angle bed structure of the rocks and their carbonate composition, the canyon and its walls are observed in areas exposed to fluvial erosion. Hydrologically, the drainage networks developing in different directions caused the formation of caves and secondary canyons of different sizes (Fig. 8).

The wall surfaces of the canyons have a nearly vertical position (~90°), and reach a height of 250 m throughout the area (Figs. 4, 5, 7 and 8). The structures on the surfaces are not fully understood, because the former tectonic traces and effects are not preserved due to the instability of the sedimentary rocks to fluvial erosion. Fortunately, it is possible that the wall surfaces are ancient tectonic lines as evidenced by their parallel and linear extension. There is evidence that the walls reached their present state due to fluvial erosion and deposition along tectonic lines. There are meanders with small radii formed by the flow dynamics of Ardanuç Stream.

The canyons, which rank top on the scales of both the Earth and Türkiye scales and include Cehennem Deresi, are listed below. The seven largest canyons in the world are Colca Canyon, Peru (altitude: ~ 4.161 km, length: ~ 72.42 km), Copper Canyon, Mexico (altitude: ~ 2.4384 km, length: ~ 643.7 km), Verdon Gorge, France (altitude: ~ 0.701 km, length: ~ 20.921 km), Fish River Canyon, Namibia (altitude: ~ 0.5486 km, length: ~ 160 km), Antelope Canyon, Yellowstone Canyon, and Grand Canyon (altitude: ~ 1.8288 km, length: ~ 800 km) USA, Yarlung Tsangpo (altitude: ~ 4.877 km), Echidna Chasm, Australia, Wulingyuan Canyon, China and Tara River Canyon, Montenegro/Bosnia and Herzegovina (https://www.adventure-journal.com/2012/09/the-list-the-worlds-7-best-canyons/; https://whc.unesco.org/en/list/).

The world ranking does not include the top canyons in different regions of Türkiye in terms of height and length, which include 25 canyons of different dimensions: Valla Canyon (Kastamonu), Karacehennem Strait and Ersizlerdere Canyon, (Kastamonu), Köprülü Canyon (Antalya), Saklıkent Canyon (Muğla), Güver Canyon (Antalya), Lamas Canyon (Mersin), Göksü Canyon (Mersin), İnceğiz Canyon (Denizli), Çatak Canyon (Kastamonu), Göynük Canyon (Antalya), İncesu Canyon (Çorum), Kapuz Canyon (Muğla), Dark Canyon (Erzincan), Şahinderesi Canyon (Balıkesir), Ulubey Canyon (Uşak), Horma Canyon (Kastamonu), Yazılı Canyon (Isparta), Kirpe Canyon (Düzce), Kapıkaya Canyon (Adana), Şehriban Canyon (Kastamonu), Ihlara Canyon (Aksaray), Şahinkaya Canyon (Samsun), Sansarak Canyon (Bursa), Sapadere Canyon (Antalya) and Cehennem Deresi Canyon (Ardanuç) (Doğaner 2001; İlhan et al. 2017; https://listelist.com/turkiyedeki-kanyonlar/;https://www.goturkeytourism.com/).

K-Pg Transition

In a comprehensive assessment, fossil records from the Cambrian to the present day indicate 18 mass extinctions on Earth (Raup 1991; Bambach 2006; Racki 2020; Esmeray-Senlet 2020). The Cretaceous-Paleogene (K/Pg) extinction/transition, which is closest to the present day, had powerful effects and many theories developed about it. It has been extensively studied in multidisciplinary terms and occurred 66 Ma ago (Alvarez et al. 1980; MacLeod et al. 1997; Smit 1999; Gradstein et al. 2020; Esmeray-Senlet 2020).

Ziyarettepe Formation corresponds to the Upper Cretaceous Series (K) of planktic foraminifera (Premoli-Silva and Verga 2004; Sarı 2009; Coccioni and Premoli-Silva 2015; Petrizzo et al. 2020; Gradstein et al. 2020) and benthic foraminifera (Özcan and Özkan-Altıner 1997; Malarkodi et al. 2017; Robles-Salcedo et al. 2018; Simmons and Aretz 2020; Gradstein et al. 2020; Özcan et al. 2021) with upper Campanian–Maastrichtian age (Köroğlu 2023). Ziyarettepe Formation corresponds to Paleogene series (Pg) planktic foraminifers with Danian-Selandian age and Danian-Selandian-Thanetian benthic foraminifers from SBZ-1, SBZ-2, and SBZ-3 Zones (Serra-Kiel et al. 2020). In addition, Köroğlu (2023) stated that the Kızlcık Formation corresponds to Thanetian-Ypresian layers based on planktic foraminifers from Zone P3-P4 (Wade et al. 2011), nannoplankton from NP6-NP9 (Hippolyte et al. 2015), and ostracods (Lord et al. 2009) (Figs. 9, 10, 11 and 12).

Fig. 9
figure 9

Geotourism assets in Ardanuç (Artvin/Türkiye). a-b) Ardanuç Castle or Gevhernik Castle in Adakale District, c-d) Ferhatlı Castle or Ferhatkale, e–f) Traditional house in the Ardanuç (architectural and structural restorations undergone), g) Traditional agricultural tools, h) Turkish bath from the Ottoman period, i-l) Traditional billet or wooden house and shelters. Estimated years of construction are older than 50 years, m-p) Different views of İskenderpaşa Mosque in Adakale District, r-u) Different views of New Rabat Church in Bulanık Village, Ardanuç

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Fig. 10
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Minerals and industrial raw material resource map of Artvin (modified from General Directorate Mineral Research and Exploration)

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Fig. 11
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Criteria, indicators, and numeric parameters (modified from Brilha 2016) to quantify the scientific, educational, and touristic values, together with the degradation risk of the Cehennem Deresi Canyon geosites (compared studies Brilha 2016, 2018; Gürer et al. 2019; Mehdioui et al. 2020)

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Fig. 12
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Content types of ‘Relevance Grade’ and ‘Abstract Perceptiveness’ for geological objects with heritage value, and an open system of qualification of geological heritage contents, according to the types (modified from Fig. 1 and Fig. 13, Pena dos Reis and Henriques 2009). Criteria, indicators, and numeric parameters (modified from Brilha 2016), semicircles were evaluated as positive for Touristic Value (TV), Potential Educational Value (PEV), and Scientific Value (SV). As the numerical value for Degradation Risk Value (DRV) scoring increases, DRV creates a negative effect

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The K/Pg transition (Figs. 2 and 3) was identified with paleontologic and biostratigraphic data in the Tosunlu Tunnel (TT) section (Fig. 13) of the Ziyarettepe Formation (Köroğlu 2023).

Fig. 13
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Map showing the 3G (geomorphological, geoheritage and geotourism) values and their regional distribution in Ardanuç region (points between 1 and 6 show the basic values, modified from https://www.openstreetmap.org)

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Geotourism

Ardanuç (Artvin), located in the easternmost part of Black Sea Region, has served as a bridge between the Caucasus and northeastern Anatolia for centuries due to its geographical location, geomorphological and geological characteristics, vegetation, cultural, and historical assets (Özsayar et al. 1982; İlhan et al. 2017; Erdoğan 2019; Köroğlu et al. 2022a, b; Köroğlu 2023). Ardanuç is included in deep historical records spanning the A.D and B.C. periods. Although the earliest settlement records are not precisely known, there are few records from the Bronze Age in Ardanuç and its surroundings, it is possible to identify the Neolithic civilization known throughout the region as a result of new findings and detailed research (more information Envanteri 2012; Erdoğan 2019). Due to the demographic and political developments of civilizations living in the region, Ardanuç and the region were called Klarceti, Katarza, Kalarzen, Chorzene, etc., and Ildumuşa, Ardenoudj, Ardanautzion, and the Turkish names of “Ardan-uçtu” and “Arından-uçtu” specifically relating to Ardanuç (Envanteri 2012; Erdoğan 2019; http://www.ardanuc.gov.tr/ardanuc-tarihi; personal interview with locals). The civilizations included in the history of the region can be chronologically listed as follows; Urartians, Sakalar and Scythians Turks, Caspians, Barsels, Bagrats, Georgians, Anatolian Seljuks, Mongols, Timur, Karakoyunlu, Akkoyunlu, Iran Safavi, and Ottomans. The Erzurum beglerbeg İskender Pasha conquered Ardanuç in 1551 during the reign of the Suleyman the Magnificent. He established the first Ardanuç sanjak of the Ottomans (Erdoğan 2019; http://www.ardanuc.gov.tr/ardanuc-tarihi). The district, which was given to Russia with the agreement at the end of the Ottoman-Russian War (known as the 93 War, 1877–1878 Ottoman-Russian War), re-joined the Ottoman Empire during World War I as a result of a referendum (Erdoğan 2019; http://www.ardanuc.gov.tr/ardanuc-tarihi). After the Montreux Armistice, Ardanuç was conquered first by the British and then by the Georgians. It joined the Republic of Türkiye on March 7, 1921 with the Gümrü Treaty and took its place within the borders of today’s “Misak-ı Milli” or “National Pact” (http://www.ardanuc.gov.tr/ardanuc-tarihi).

For sustainability and development, geotourism is the best development strategy in regions lacking industrial development and commercial networks. However, information about the formation of canyons in Eastern Black Sea region and the use of these canyons for geotourism is still very limited. This is because there are many more igneous rocks than sedimentary rocks in the region and there are no erosion resistant rocks necessary for the development of valley floors and canyon structures. In this regard, there are two examples in the region, the relatively well-preserved Cehennem Deresi Canyon(s) located in the northeastern part of the region, and Şahinkaya Canyon (Samsun) which has invaluable potential for geotourism. In fact, the region of the canyons, which is located in the far east of the Eastern Black Sea in a region with a quiet lifestyle, can be considered a hidden paradise for implementation of the geotourism concept.

The hiking routes in the two canyons also place different demands on walkers. CCNE provides a more horizontal profile, while CCNW allows hiking at higher elevations. In addition, the canyon walls are a recording studio due to their differences in light and colour while providing spatial depth.

Until now these rock faces have not been evaluated with a professional approach for mountaineering or climbing routes. The rock faces with a length of about 200 m, both with negative and positive slope, and different levels of difficulty that could attract a lot of attention, have high value for geotourism, hiking, mountaineering, and climbing. The fact that the rock faces are carbonate and there is not much karstification and weathering on their surfaces, due to the terrestrial climatic zone, facilitates the formation of climbing routes on surfaces that do not contain block fault and fracture zones and have beds with low slopes.

In the Ardanuç (Artvin) region, there are many geotourism assets related to both cultural, historical, and geological features (Fig. 9a-u). These assets are presented below under different headings, including authenticity values. Along with these assets, many more assets are waiting to be discovered in the region.

Ardanuç Castle (Gevhernik Castle)

This is the most historical place in Ardanuç. Gevhernik Castle is located in the Ardanuç-Adakale district and was used as a centre of administration by the Bagratlı Kingdom, Çıldır Atabeks, and finally the Ottomans. The date of construction extends to the period before Christianity. The castle structure is one of the most important in the district. It is unique with its inner castle and city interior surrounded by walls and architecture. In addition to various ancient ruins, it contains an inscription of Süleyman (Suleiman) the Magnificent (Figs. 9a, b).

Ferhatkale (Ferhatlı Castle)

The castle is located before coming to the centre of Ardanuç. The stronghold was constructed on primary rock rising parallel to the valley near the left bank of Ardanuç Stream. Located 5 km from the centre of Ardanuç, the castle is rumoured to have been built by Vantang, the King of Iberian, in the fifth century (Figs. 9c, d).

Traditional houses in Ardanuç

These traditional architectural structures, which form a complex with both wood and stone workmanship, bear traces of various periods of regional history. The two-storey buildings, with classical period walls and Ottoman period woodwork, were built in mansion style for extended family life. In the houses, there are sections that serve to house farm animals and act as barns. Size and decorative ornaments are in direct proportion to social status and wealth (Figs. 9e, f).

Traditional Agricultural Tools

Traditional period hand tools used in agricultural activities are preserved in some parts of the region and conserved in memory. Despite limited agricultural production in the region due to climate and terrain conditions, it is considered to be a very important asset for understanding the human geography of the region in the past. These appear to be important cultural heritage assets for research about human and regional life based on agriculture (Fig. 9g).

Turkish Bath

The bath (Hamam, in Turkish), which is an important cultural and community health centre frequently found in the settlements from the Ottoman period, was established in the Adakale area of Ardanuç, as in all other settlements. The bath, which is not actively working today, is protected as a cultural heritage asset (Fig. 9h).

Traditional Billet or Wooden Houses and Shelters

Ardanuç is a particularly outstanding geotourism region with natural beauty as well as an authentic billet or wooden houses. They are the most beautiful examples of wooden buildings. The area has gained more interest for its original wooden architecture and local culture. Also, structural elements are an important geotourism asset (Figs. 9i-l).

İskenderpaşa Mosque

Construction was started in the period of Caliph St. Osman (644–656), and the mosque was repaired in 1553 and opened to worship again. It is important in terms of being the first mosque in the region and surviving to the present day. The mosque, which is an important representative of traditional building elements and rare handicrafts, has cultural heritage value both in terms of tourism and religion (Figs. 9m-p).

New Rabat Church

The New Rabat Church is located in Bulanık Village, 17 km from Çamlık (Rabat) in Ardanuç district. The exact construction time is not known, because there is no inscription tablet on the building. The church has some similarities to other churches in the surroundings. It is estimated to have been built by the Bagratian Kingdom, which ruled the area in the 10th or eleventh century. Triangular niches reflecting the inner plan in medieval architecture were used. Triangular niches are rarely used at the dome in the area. In this church, more niches can be seen than window spaces. There are cut stones embossed with nice plant patterns on both sides of the building (Figs. 9r-u).

Vulnerable Characteristics of Cehennem Deresi Canyon(s)

In view of the increasing demand for building materials around the world and in our country, continuous exploration for new raw material resources and mining activities are taking place intensively (Fig. 10).

Here, due to transportation infrastructure and regional developments, there is constant pressure to develop new mining sites and expand existing deposits. Since the most suitable rock group for the formation of canyon structures are rocks of sedimentary origin, this rock group is in constant demand for economic and industrial, as well as visual reasons. Calcium carbonate rocks (CaCO3) are the main raw materials in lime and cement production, and the majority of the rocks in the Ziyarettepe Formation and canyons comprise CaCO3. At the present time, these rocks, which are not used for industrial purposes (lime and cement) in the region, are used as construction materials (sand, gravel and fill material, etc.). In the stratigraphy of the region, the rocks with the above characteristics have a distribution along an east–west line as formations of Upper Jurassic-Lower Cretaceous and upper Campanian-Thanetian age (Figs. 2 and 3). Since this rock group usually forms steep valleys (Cehennem Deresi Canyon(s) in the Ardanuç region), they are rarely found near settlements. Thus, quarrying and raw material extraction permits can be easily granted for outcrops outside settlement areas.

The Black Sea region has a very dispersed population and built-up area, so infrastructure deficiencies are very common. The annual excess of rainfall in the region and the variable riverbed slopes cause flooding, which can spread pollutants very quickly. These floods trap both solid and hydraulic pollutants in alluvial bars that form based on the slope of the canyon floor.

A comparative study was conducted by Özşeker (2019a, b) along the stream bed passing through to Ardanuç (Table 1) following the criteria for freshwater sediment quality (SQG) developed by MacDonald et al. (2000), which are significantly considered in pollution studies. There are many metallic mineral deposits in Artvin and surroundings, and as a result of both hydrological and mechanical erosion, metallic elements (i.e., Cu and Pb) are transported along the Çoruh River and its associated drainage networks (Fig. 10). Heavy metals transported in the drainage system as suspension or sediment accumulate in areas with stagnant water, stream beds, and dam lakes where the gradient is reduced. The seasonal variations in Cu (349.22–484.99 ppm) and Pb (131.53–176.59 ppm) levels in Ardanuç Stream (see details in Fig. 3 of Özşeker 2019a) are toxic to freshwater ecosystems and it is classified in the medium-risk class in terms of metal pollution (Turgut et al. 2015; Özşeker 2019a, b).

Table 1 Areal and seasonal distribution of physicochemical properties in sediment and surface waters of Ardanuç Stream between June 2015 and September 2016, reported from three measuring stations (data modified from Fig. 1 and 5, and Table 5 see details Özşeker 2019a) *total dissolved solids (TDS)
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The canyons are located on the route of the Artvin-Ardanuç-Ardahan motorway. The existing motorway passes through the canyon valley; it is a protected area and it is impossible to widen the motorway. Such a motorway, within a tourist destination, is an obstacle both to rockfall on the canyon slopes and to the safety of tourist activities. It is likely that a safer motorway for the region will be constructed with parallel alignment. This project will create significant opportunities to increase the diversity of tourism activities (climbing, hiking, canoeing, and camping) in the canyons. The K/Pg transition, one of the most important events in Earth’s history, lies in these rocks. In this context, the common intersections in the region, such as transportation infrastructure, and all invaluable elements should be identified and arranged in line with the vision for the future of the region.

Evaluation System for Geological Heritage of Cehennem Deresi Canyons: Inventory, Quantitative Assessment, Integrated Qualification

Scott Davis, the economist, stated “The fact is that what is not measured is not managed” (Davis 2002). Indeed, the history of measurement begins with the humans requiring the attribution of value to sustain the concepts of quality/quantity. Thus, language, numbers, and units of measurement, etc., began as traditions in many different eras and are maintained with dedication in different regions today.

The Geological Heritage Rating System by Pena dos Reis and Henriques (2009) presents scientific and social qualification headings for ratings defined as (I) Relevance Grade and (II) Abstract Perceptiveness. It also provides a very important warning from Jose Brilha about these assessments. It is not a completely infallible method, and for these reasons, it is also wrong to mislead readers with a numerical final score, that is only apparent and objective and not indisputable (Brilha 2016, 2018).

“In spite of the numerical assessment method used for geoheritage and geodiversity sites, the numerical assessment method presented here is of course a proposal, and some of the criteria/indicators/parameters can be adapted to particular local circumstances, it should be emphasized that a final reflection about the obtained results is essential” (Brilha 2016, 2018).

The evaluation criteria, model, and graphs are based on the studies by Pena dos Reis and Henriques (2009) and Brilha (2016, 2018). However, the results from these two different approaches were reinterpreted, and applied interactively to the region for the first time. All the characteristics mentioned and explained in detail under the previous headings are evaluated both qualitatively and quantitatively in the following tables (Tables 2, 3 and 4).

Table 2 Criteria, indicators, and parameters used for the assessment of geosites chosen for qualitative and quantitative evaluation; Scientific Value (SV) of Cehennem Deresi Canyon(s) (based on Brilha 2016, 2018)
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Table 3 Criteria, indicators, and parameters used for the assessment of geosites chosen for qualitative and quantitative evaluation; Potential Educational Value (PEV) and Touristic Value (TV) of Cehennem Deresi Canyon(s) (according to Brilha 2016, 2018)
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Table 4 Criteria, indicators, and parameters used for the assessment of geosites chosen for qualitative and quantitative evaluation; Degradation Risk Value (DRV) of Cehennem Deresi Canyon(s) (according to Brilha 2016, 2018)
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The results are also shown in graphics (Figs. 11 and 12). The canyons have both scientific and social impact scores at the universal level. Thanks to these high scores from spatial assessments, it is clear that all these values should be obtained with a very sensitive approach for the assessment of the risk of deterioration. It is clear that as the DRV value increases, all values are also at risk (Fig. 12).

If the universal values included in this rating system are examined, it becomes very clear that the region has both scientific and social status. For instance, in the universal category, which provides universal content such as geological heritage in space, the canyon structure similar to others on Earth and formed within the same rock group (sedimentary) and also detected on the surface of Mars represent particular formations with universal content (Pena dos Reis and Henriques 2009). There are canyons at the top of the most common landforms (other structures, craters, faults, and folds) on planets. The largest canyon in the solar system is Valles Marineris, which is over 3000 km long, up to 600 km wide and 8 km deep. For a global comparison, the Grand Canyon (Arizona, USA) is 800 km long, 30 km wide, and 1.8 km deep (https://www.nasa.gov/multimedia/imagegallery/image_feature_83.html). It can be concluded that the data about structure formation obtained on Earth can be directly transferred to understand geological formations on other planets and has both social and scientific impact value.

Discussion

When the evaluation criteria for geosites (Brilha 2016, 2018; Gürer et al. 2019; Mehdioui et al. 2020) of tourist value (TV), potential educational value (PEV), scientific value (SV) and degradation risk value (DRV) are applied together with the degree of relevance and abstract insight (Pena dos Reis and Henriques 2009) to Ardanuç (Artvin, Türkiye), it is possible to make an assessment at the regional level.

Ardanuç (Artvin) and its surroundings are one of the leading areas in terms of geoheritage and geotourism potential in Türkiye with rich flora and fauna, geology, high mountain ranges, protected areas, glacial lakes, green highlands, historical mosques and churches, castles and arched bridges, traditional architecture, water sports, festivals, biosphere reserve, winter tourism destinations, topographical features suitable for various nature sports and unique landscapes (Özsayar et al. 1982; Aksay and Turhan 1998; İlhan et al. 2017; Erdoğan 2019; Akinci and Zeybek 2021; Köroğlu 2023; and others).

It is believed that the Ardanuç (Artvin) region can achieve great gains through a holistic assessment using more scientific and technical methods. The region is located in the northeast of Türkiye, bordering the Caucasus, with all assets emerging together with the geological history and cultural past of the region. This location offers both climatic, origin-related and cultural differences. Although it is only moderately large in terms of area, it is located at a unique point with a small-scale complex of 3G values (geomorphology, geoheritage and geotourism) and volumetric values.

In this context, promoting (advertising) the opening of Cehennem Deresi Canyon(s) for tourism activities and investments in order to meet the needs of incoming visitors will be a great contribution to tourism in Türkiye and the city of Artvin. Consequently, geotourism would allow the necessary plans for the expansion of tourism activities in Cehennem Deresi Canyon (s) and its immediate surroundings to be made and exploitation and protection arranged to ensure Türkiye and Artvin receive a share of the revenues from alternative tourism activities.

Conclusion

It is important to accept that the first step for the region is to extend the boundaries of the protected area in addition to the current protected status of Ardanuç district and Cehennem Deresi Canyon(s) and to declare Ardanuç and its surroundings a geotourism development zone. The development of tourism in the study area, all studies (scientific research, publications, local narratives, etc.) and the opinions and suggestions of local public organizations and non-governmental organizations will benefit from this to the greatest extent. It will contribute to the growth of the tourism market through economic development by developing tourist, cultural and natural resources that are little known and have very high potential in this rural area. It will also contribute to the protection of our natural and cultural heritage and increase recognition at national and global levels.

If the promotion of Ardanuç district attracts a wide tourist audience, it will require tourism planning and determination of the conservation-use balance around Cehennem Deresi Canyon(s). As a result of increasing awareness and promotional activities, geotourism activities and nature sports will provide opportunities for the development of the canyon and its surroundings. Route maps and activity groups should be prepared in cooperation with experts from potentially suitable areas for geotourism activities in the Cehennem Deresi Canyon(s) and immediate surroundings. Necessary precautions should be taken to protect wildlife, remains endemic plants and cultural heritage in and around the canyon. Expert opinions should also be sought while selecting the field (site) and precautions should be taken for sporting activities such as trekking, mountain biking, skiing, rafting, motocross, caving, climbing, off-roading, canyon crossing, nature and wildlife watching, etc. Though Cehennem Deresi Canyon(s) is close to active tourism activities, there are no trekking routes, trekking platforms, information and signs for the canyon. In order to use Cehennem Deresi Canyon(s) efficiently and according to plans, trekking routes need to be identified, trekking platforms need to be set up and signs need to be installed. Infrastructure works for basic needs should be completed and information and translation facilities should be provided. It will be necessary to isolate the canyons from intensive traffic through a new highway project to achieve a balance between protection and use. Stairs, trails and effective landscaping should be created in CCNE. Photo platforms should be built on different routes around the canyons (e.g., Gevhernik Castle, at the top of the canyons).

The Ardanuç district, where Cehennem Deresi Canyon(s) is located, should be strengthened in terms of tourism personnel and the locals should be equipped for tourism. In addition, the private sector should be encouraged to consider tourism development. These activities can promote development, improve economic opportunities and reduce unemployment and migration to big cities.

The quantitative assessment of the region shows that the values for TV, PEV and SV are high. The qualitative assessment also found that the region has universal values such as the degree of relevance and abstract perceptibility. However, it is necessary to increase scientific knowledge and use this information as a guide to determine the protection-use balance especially for all developments in the region with high DRV.

Taking into account all the proposals, the importance of the 3G region (geomorphology, geoheritage, and geotourism) is conveyed by showing all the locations on the map of the region in Fig. 13 and creating a route accordingly.