Tephrostratigraphy and chronology of the Quaternary Gölludağ and Acıgöl volcanic complexes (Central Anatolia, Turkey)
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The two Göllüdağ and Acıgöl volcanic complexes are located in Cappadocia and belong to the Central Anatolia Volcanic Province. Their activity covers a wide time range from Middle to Upper Pleistocene and the Holocene. The large amount of tephra emitted explains the regional importance of this activity; whereas, the study of obsidian associated with their activity relates to several archaeological topics and research questions. Intensive field work in and around both complexes allows to present here a detailed tephrostratigraphy. In addition, results of ~ 460 single grain geochemical analyses (about 5–10 analyses for each sample out of a total of 48 samples) as well as intensive mineral counting provide an accurate reference set of signatures of Pleistocene rhyolitic tephras in Cappadocia. Correlations are based on stratigraphic observation and characterization of the tephra layers, and are also supported by multivariate statistical analyses. Chronology, constrained by 18 radiometric data (mainly K/Ar), demonstrates the Middle Pleistocene age of the main Göllüdağ tuff (ca 1.3 Ma) and confirms the Middle to Upper Pleistocene age of the main Acıgöl tuff. Our studies, thus, produce a regional tephrostratigraphic reference, which may be used for long-distance correlation. Besides, the tephra studied and analysed also form key layers used here for geomorphologic reconstruction and dating of stratigraphic and archaeological sequences.
KeywordsTephrostratigraphy Rhyolitic complexes Central anatolian volcanic province (CAVP)
Establishing a confident stratigraphy of pyroclastic rocks on a regional scale requires that the formations erupted by volcanic complexes be characterised by a specific signature which can mainly be defined in terms of major element composition of glass shards and mineral content. Additional techniques, such as analyses of trace element composition and statistical treatments of all chemical elements, are also available for discriminating distinct eruptions emitted by a given volcanic complex. Additional indicators also contribute to discrimination: shapes of glass shards, morphology of pumice grains, mineral paragenesis and heavy mineral content.
Tephrochronology also requires sets of dates (whatever the dating method applied) associated with the mineral and geochemical characterization of the tephra layers. Tephras are then potential marker horizons for long-distance correlation. As an example, when applied to distal tephra layers, the results allow the chronological control of marine cores. In this domain and according to recent reviews of tephra layers in the Mediterranean region (Hamann et al. 2010; Zanchetta et al. 2011; Satow et al. 2015), the lack of knowledge about the pyroclastites of the CAVP is crucially obvious as it generates many unsupported hypotheses about the origin of several Late Pleistocene tephras from the Eastern Mediterranean region.
Indeed, Pleistocene and Holocene tephrochronological investigations are still scarce in Anatolia. Apart from the Minoan eruption (Thera-Santorini) which is now confidently identified in several lake sequences of western Anatolia (Bottema and Woldring 1984; Eastwood et al. 1999; Roberts et al. 1997; Sullivan 1990, 1988), only a few other Upper Pleistocene and Holocene tephras have been reported in sequences of the Western Anatolia (Platevoet et al. 2007; Kazancı et al. 2012), Tuz Gölü (Kashima 2002), Konya plain and Cappadocia (Inoue and Saito 1997; Kashima 2002; Kuzucuoğlu et al. 1998, 1997). Data on mineral and glass composition from these Anatolian tephras and pyroclastites are even rarer with some data available in (Kuzucuoğlu et al. 1997, 1998; Kürkçüoğlu et al. 1998; Pastre et al. 1998; Karabıyıoğlu et al. 1999).
The importance of Central Anatolian pyroclastic deposits related to the Göllüdağ and Acıgöl rhyolitic complexes also arises from increasingly challenging archaeological topics. In the Göllüdağ massif, recent surveys, excavations, and geoarchaeological investigations focused on prehistoric workshops associated with obsidian outcrops (Balkan-Atlı and Binder 2000; Balkan-Atlı et al. 2011; Kuhn et al. 2015). A significant amount of geochemical analyses for both artefacts and raw material in and around these ryholitic complex is now available (Binder et al. 2011; Poidevin 1998). So far, the pyroclastites associated with obsidian and those present in excavations have not been studied, with the exception of the Palaeolithic “Kaletepe Deresi 3” excavation (Mouralis et al. 2002; Mouralis 2003; Slimak et al. 2004, 2008; Tryon et al. 2009).
Thus, tephrostratigraphy contributes to the dating of human occupation of the region, and to the reconstruction of the morphological and palaeoenvironmental evolution of Cappadocia during the Middle and Late Pleistocene. Consequently, this paper aims at providing a detailed regional tephrostratigraphy based on the identification and characterization of the tephra layers related to the Quaternary rhyolithic complexes in Cappadocia, i.e., the Göllüdağ massif and the Acıgöl (Nevşehir) area. Apart from challenging the Eastern Mediterranean tephrochronology, the detailed analyses of the pyroclastites erupted by these rhyolitic volcanoes address three main palaeoenvironmental issues. (1) The large volumes of tephra emitted buried palaeotopography and palaeomorphology. (2) The obsidian erupted by these volcanoes was quarried and chopped by prehistoric people, while some tephra layers also bury human artefacts. (3) The volcanic activity covers a wide time range: from the Lower to the Middle Pleistocene in the Göllüdağ complex, and from Middle to Upper Pleistocene in the Acıgöl area where Holocene activity is also reported (Kuzucuoğlu et al. 1998). With regard to the necessity of completing our knowledge about these three related topics, our paper intends to produce a detailed tephrostratigraphy and chronology of both the Göllüdağ and the Acıgöl rhyolitic complexes. It is partially based on a project associating CNRS and Tübitak whose results have been reported in Türkecan et al. (2004), also including new stratigraphic observations as well as new chemical analyses and interpretations.
Regional geological setting
During the Quaternary, volcanic activity produced two composite volcanoes (Hasandağ and Erciyes), numerous monogenic vents (Doğan-Kulahcı et al. 2018), and two rhyolitic complexes (Fig. 2): Acıgöl to the north and Göllüdağ to the south (Mouralis et al. 2019, 2002) which are separated by the Erdaş Dağ andesitic massif respectively. Both complexes comprise voluminous pyroclastic deposits and domes extruded inside the main structures.
While the Göllüdağ complex has been poorly studied except for obsidian geochemistry, the Acıgöl complex was first described and identified as a caldera by (Yıldırım and Özgür 1981). Later, Druitt et al. (1995) studied its pyroclastic products, proposing a first stratigraphy. Kazancı et al. (1995) described the surges of the Eski Acıgöl maar located inside the complex. Kuzucuoğlu et al. (1998) identified seven tephra layers interstratified within the lake sediments of this maar; the 14C ages of these tephra layers range from 14 to 7 ka cal. BP (Kuzucuoğlu et al. 1998; Roberts et al. 2001).
Ages of both rhyolitic complexes have been obtained on obsidian by (mainly) Bigazzi et al. (1993, 1997) and Chataigner et al. (1998), dating the eruptive activity of Göllüdağ volcanoes Middle Pleistocene, and that of Acıgöl Middle to Upper Pleistocene. The stratigraphically subdivided Lower and Upper Acıgöl Tuffs (Druitt et al., 1995) were subsequently dated using U-Th and (U-Th)/He geochronology to ca. 190 and 160 ka, respectively (Schmitt et al. 2011, partially revised in Atici et al. 2019, this volume). Schmitt et al. (2011) also confirmed the 26–20 ka age of the rhyolitic domes which formed after the main eruption. Radiometric data compiled here not only confirm but also refine this chronology.
The tephrostratigraphy and tephrochronology proposed in this paper are based on: (1) the systematic study of the stratigraphy within and around the Göllüdağ and Acıgöl Quaternary complexes, combined with (2) establishing a regional tephra reference set based on the characterization of tephra layers (using petrography, glass chemistry and minerals association) and multivariate statistical analyses; (3) radiometric datingto constrain the chronology.
Stratigraphical correlations and characterization of tephra layers
The correlations between tephra layers are first based on field evidence: depositional facies and long-distance facies change; pumice morphologies, mineral paragenesis and texture, as well as petrographic compositions of lithics. Additional analyses performed in the laboratory completed the identification of tephra(s) through determination of the mineral associations, and glass geochemistry characterization (electron microprobe).
Single grain geochemical analyses (WDS). 48 samples were analysed through 460 single glass shards electron probe microanalyses (EPMA) using a Cameca SX100 microprobe at the “Magmas et Volcans” Laboratory (UMR 6524, Clermont-Ferrand), and in the “Camparis” Laboratory (Sorbonne University, Paris VI University, Paris). Nine major element contents were measured, according to a conventional protocol (Frogatt 1992; Lowe 2011): after mounting shards in epoxy and careful polishing, microprobe analyses were performed with a beam intensity of ~ 6–8 nA, with 15 kV accelerating potential. When analysing glass shards, the beam was defocused to 10 μm to limit the volatilization of alkaline elements. At least 5–10 different glass shards have been analysed for each sample. Results are expressed in mass percent of each oxide analysed.
We already published a small set of the data obtained in Tryon et al. 2009 (347 analyses). New sampling and analyses presented here improve this initial data set by including more tephra layers from Acıgöl and Göllüdağ as well as some geochemical data from Karadağ volcano (a composite volcano located in the Konya plain, near the well-known Çatalhöyük Neolithic site).
Regional tephra reference data set and multivariate analyses
To establish a reference data set, we sampled systematically the rhyolitic tephra layers from both the Göllüdağ and Acıgöl complexes. For comparisons, we also sampled tephra layers from the nearby composite Quaternary volcanoes of the CAVP (Hasandağ, Erciyes Dağ and Karadağ).
Summary data of major elements characterization using electron microprobe
Groups of tephra layers
To reduce and graphically interpret the variations observed within this dataset, we use multivariate analyses based on discriminant function analyses (DFA). It is one of the most powerful methods, allowing to test statistically the strength of our classification based on the stratigraphic evidences and to assign any distal tephra of unknown origin to one of the regional Quaternary volcanoes.
DFA are computed using Systat 12.02 for Windows. Data from all nine major elements analysed are treated through a classical discriminant analysis. Prior probabilities are weighted proportionally to group size differences within our samples. Data used in the model are not normalised because neither normalisation nor log ratio transformation showed improvement of the results discrimination.
Twenty-two K/Ar dates have been obtained at the LSCE (UMR 8212). All samples were dated using the unspiked K–Ar technique described by Charbit et al. (1998). Both K and Ar measurements were performed on the groundmass of lava samples, since the groundmass is considered to be representative of the phase that crystallised during the solidification of the lava. After crushing, sieving to the 250–125 mm fraction size, samples were washed in ultrasonically bath of acetic acid (1 N) during 45 min at a temperature of 60 °C, to remove any secondary mineral phases. Phenocrysts and xenocrysts, which may carry excess 40Ar, were then removed using heavy liquids of appropriate densities, and magnetic separations to produce a clean groundmass separate.
Potassium was analysed by atomic absorption and flame emission spectrophotometry. Argon was extracted from 1 to 2.6 g of groundmass sample by radio frequency heating induction in a high vacuum glass line, and purified with titanium sponge and Zr–Al getters. Argon was analysed using a 180°, 6-cm radius, 620-V accelerating potential mass spectrometer working in a semi-static mode. Beam sizes were measured simultaneously on a double Faraday collector in sets of 100 online acquisitions with a 1-s integration time. A manometrically calibrated dose of atmospheric Ar is used to convert beam intensities into atomic abundances. A separate measurement of atmospheric argon is used to monitor the atmospheric correction. The manometric calibration is based on periodic, replicate determinations of the international dating standard HD-B1 (24.21 ± 0.32 Ma), (Fuhrmann et al. 1987; Hautmann and Lippolt 2000; Hess and Lippolt 1994) using the same procedure as described in Charbit et al. (1998).
If the unspiked K–Ar method allows to measure accurately small amounts of radiogenic 40Ar (Guillou et al. 2011), it cannot check two important assumptions ruling the K–Ar clock, (1) that the initial 40Ar/36Ar ratio of the sample is of atmospheric composition and (2) that the isotopic system remained closed since the age of crystallisation. Therefore, K–Ar ages may be affected by unresolved excess argon or argon loss, fractionated 40Ar, implying real errors higher than the analytical ones.
Morgan et al. (2009), Flude et al. (2018) and Clay et al. (2015) demonstrate that mobility of 40Ar in obsidian glass may produce erroneous results. Flude et al. (2018) and Clay et al. (2015) observed this on hydrated and subglacial obsidians where interaction of water with the magma is an important disruptive vector of the K–Ar clock. Given the fact that the obsidians studied here emplaced subaerially, we consider that our obsidian samples did not suffer from this perturbation. Following Morgan et al. (2009) recommendations, to reduce at its maximum erroneous results due to atmospheric alteration effects on obsidian and lava flows all our samples were collected as far as possible from the rims of the flows and domes. This approach has produced accurate and reliable unspiked K–Ar ages (Le Bourdonnec et al. 2012) based on agreement with 40Ar/39Ar ages. Age bias due to Ar-isotope fractionation, however, remains a potential source of bias.
K/Ar dating of lava flows in and around Göllüdağ, Acıgöl volcanoes
Weight molten (g)
40Ar* (10−12 moles/g)
Age mean value
A—In and around Golludağ volcanic complex
Western part of the Bozköy-Kayırlı road
4.333 ± 0.043
6.25 ± 0.12
6.21 ± 0.09
6.17 ± 0.12
Top of Kayırlı village. Under the Main Golludağ Tuf.
0.963 ± 0.010
1.66 ± 0.04
1.71 ± 0.03
1.75 ± 0.04
Western part of Boztepe
3.711 ± 0.04
0.972 ± 0.02
0.966 ± 0.014
0.959 ± 0.02
Northeastern slope of the Göllüdağ
3.849 ± 0.038
0.868 ± 0.018
0.855 ± 0.013
0.842 ± 0.018
3.769 ± 0.038
1.09 ± 0.02
1.10 ± 0.02
1.12 ± 0.02
Western part of Boztepe
3.752 ± 0.038
1.07 ± 0.02
1.08 ± 0.02
1.10 ± 0.02
3.692 ± 0.037
0.430 ± 0.009
0.444 ± 0.007
0.459 ± 0.010
B—In and around Acıgol volcanic complex
0.960 ± 0.010
631 ± 15
618 ± 14
605 ± 13
Yukarı Kızıl Tepe (South of Inalli)
0.739 ± 0.007
536 ± 16
538 ± 12
540 ± 18
162 ± 4
160 ± 3
158 ± 4
Kızıl Tepe (Tuluce). South of Boğazköy
1.468 ± 0.015
154 ± 5
154 ± 4
153 ± 4
Kızıl Tepe (North). South of Boğazköy,
1.656 ± 0.017
130 ± 4
134 ± 3
138 ± 4
Özyayla Tepe. Top of the section
1.573 ± 0.016
105 ± 4
110 ± 5
116 ± 6
Ozyayla Tepe. Bottom of the section
1.517 ± 0.015
106 ± 4
109 ± 4
112 ± 4
East of Kocadağ
3.711 ± 0.037
95 ± 3
93 ± 2
90 ± 2
Kızıl Tepe (Kızılcın)
1.602 ± 0.016
82 ± 4
81 ± 4
79 ± 8
1.543 ± 0.015
32 ± 4
32 ± 3
31 ± 4
Moreover, a single 14C dating was performed by accelerated β counting at the UMR 1572 (M. Fontugne; LSCE, Gif-sur-Yvette) on a sample from a palaeosol interstratified within pyroclastites of the Acıgöl complex (complementary data 3).
Main characteristics of the tephra layers
Petrographic and mineralogical definition of pumice
Pumice erupted from the Acıgöl complex is aphyric, whereas pumice from the Göllüdağ and the Hasandağ eruptions is microphyric to porphyric with minerals < 0.5 mm and proportions of heavy minerals ranging between 0.01 and 4%. We did not perform exhaustive chemical analyses of minerals associated with each tephra, but focused on their relative content. The counting of heavy minerals within the samples collected in the Göllüdağ area reveals three main groups (Fig. 3): (1) Hasandağ pyroclastites contain a high amount of amphiboles; (2) pyroclastic deposits related to Göllüdağ associated with the paroxysmal eruption, noted TG-1 to TG-10, present a relative abundance of minerals in the following order: orthopyroxene, pyroxene, opaque minerals, clinopyroxene and amphibole; (3) pyroclastites related to extrusion of domes in and around the Göllüdağ complex differ from other groups by the dominance of amphibole and opaque minerals-rich products.
Analysis of the discriminant functions for the geochemical data set: correlations between element oxide abundance (in wt %) for the first two canonical axes of the reference set. Canonical discriminant functions standardised by within variances
Canonical variate 1
Canonical variate 2
Göllüdağ Tephra Layers (GDT), emitted by the Göllüdağ volcanic complex either during paroxysmal eruptions or during later dome extrusion (dated ca 1 Ma in Batum (1978) and Bigazzi et al. (1993, 1998).
Pyroclastic deposits associated with rhyolitic domes and maars extruded after the Acıgöl main tuff deposition during the Acıgöl terminal activity phase (ATT) and which are dated ca 30–20 ka according to Bigazzi et al. (1993) and Schmitt et al. (2011).
Discriminant function analyses (DFA)
Jackknifed classification matrix of volcanic sources and eruptive phases used in the linear discriminant analysis of the reference set (this paper), based on untransformed abundances (in wt. %) of all elements
% Correctly classified to known source
In both rhyolithic complexes, we distinguish two types of deposits related to two main eruption phases: (1) a “major tuff” mainly composed of ash and pumice flows emitted during the main activity phase; and (2) other pyroclastites linked to terminal activity (mainly maar formation and dome extrusions). These major tuffs are probably linked to collapse of part of each complexes, although the present morphology in both complexes lacks an expression of a caldera with the exception of a few fault-controlled cliffs.
In the case of the Göllüdağ complex, we group all Göllüdağ tephra layers into one geochemical group (GDT): the geochemical composition of major elements does not allow differentiating both eruptive phases. In the case of the Acıgöl complex, however, it is possible to distinguish the main tuff (AMT) from the terminal activity linked to later dome extrusions (ATT).
Tephrostratigraphy of the paroxysmal phase within Göllüdağ volcanic complex
The main Göllüdağ volcanic activity comprises post TG-1 pyroclastic flows and fall deposits (Fig. 7). The tephra layers TG-3, TG-6 and TG-7 are the thickest ones and are preserved in the western part of the complex (logs 14, 15, 16). TG-3 (15/2 and 16/7; Fig. 8c, d) is a 15-m thick, white and ashy flow, lithics poor and rich in accretionary lapilli. Its lower part is composed of surges identified by wavy features. The heavy mineral assemblage contains orthopyroxene and amphibole (25% each) associated with clinopyroxene, rare biotite and zircon.
TG-6 is a 10-m-thick, local, pyroclastic flow deposit only observed near sites 15 (unit 15/5) and 17 (unit 17/2). It is a pumice and lapilli flow containing pseudo-fibrous pumice. Its lithic fraction is composed of perlitic rhyolite and obsidian, with rare weathered basaltic and andesitic blocks. The heavy mineral assemblage is composed of clinopyroxene and orthopyroxene (30% each) associated with opaque minerals and amphibole (10%).
TG-7 is ubiquitous in most sections studied in the western part of the complex (14/11, 15/7, 16/10, 18A/4 and 18B/6). This flow is characterised by abundant lithics with obsidian reaching 15 cm in size, and with rhyolite and basalt clasts. The length of the fibrous and pseudo-fibrous pumice in this flow sometimes reaches 10 cm; pumice clasts are sub-aphyric, with a heavy mineral content < 0.1%.
The thickness of each of these pyroclastic flow deposits decreases from the centre to the periphery of the complex, suggesting radial centrifuge flow directions. These pyroclastic units bury an ancient river network underlined by alluvial deposits (15/1, 15/2) under TG-3 (the oldest) pyroclastic formation. All flows seem to have been channelized toward the present Çiftlik and Derinkuyu depressions, suggesting that a lowland palaeotopography with a river network existed at the start of volcanic events.
In addition to these pyroclastic flow deposits, four pumice fallout deposits have been identified in the field. Pumice fallout deposit TG-4 has only been observed in the eastern part of the complex (18B/2; 20/1; 22/3; 23/4 and 30/3). Its pumice present oriented vesicles and are aphyric. The thickness of the deposit is always < 1 m. TG-5 (14/8; 15/3; 16/9; 18A/2 and 18B/2) shows quartz and feldspar-rich pumice presenting unorganised vesicles. The heavy mineral composition associates opaque minerals, orthopyroxene, clinopyroxene and amphibole, with rare black mica and zircon. The lithic fraction contains weathered rhyolitic lava and obsidian lapilli. This deposit is composed of two units: a basal 2-m-thick pumice fall deposit is overlain by a ca. 3-m-thick surge deposit within which a thin ash fall is intercalated (site 21, units 3, 4 and 5).
On the southern slopes dominating the Çiftlik plain (sites 4–7), two additional pumice fall deposits, TG-8 and TG-9, cover both TG-3 and TG-5. TG-8 (5/3, 6/2 and 7/4) comprises two pumice fall deposits containing pumice with orthopyroxene, clinopyroxene and opaque minerals. TG-9 (5/5, 6/4, 7/5) shows a different paragenesis with black micas and opaque minerals.
Pyroclastic activity related to dome extrusion during the Göllüdağ terminal phase
After the eruption of the main tuff (TG-3 to TG-9), the extrusion of ten distinct domes ended in forming a cumulo-dome (Fig. 2) dominated by the highest one, the Büyük Göllüdağ (2172 m). The site 21 (Fig. 8e) shows fall and surge deposits associated with Büyük Göllüdağ dome. The fall deposits are bedded with inverse grading, while pumice forms ca. 80% of the clasts with size reaching 15 cm. The upper part of the section shows surge deposits with finer clasts (ash and lapilli), undulating layering and cross-bedding.
Morphostratigraphic evidence allows reconstructing the relative chronology of these extrusions, with younger domes overlying older ones (e.g., Kabak Tepe and Büyük Göllüdağ, Fig. 2). Most of the extrusions are associated with local pyroclastic deposits.
Tephra layers deposited after the end of the Göllüdağ volcanic activity
Mean and standard deviation of some distal tephra layers
Tephra layer top of Göllüdag tuff
Kaletepe Tephra fall deposits—TG13A Site 35a
Other tephra layer top of Göllüdag tuffb
Tephra layer top of Acigöl main tuff (2)
To test our data set and to classify these distal tephra layers of unknown origin, we have used our DFA model. The classification of the six single grain analyses from sample 24-4 and of seven analyses from sample 27-3, shows that these distal tephras pertain to the Hasandağ “Group of tephra layers” with a posterior probability of 0.9 and 1.0, respectively (complementary data 4).
Other tephra layers have been observed at site 35, which is a section opened during the “Kaletepe Dere 3” archaeological excavation. Here, five rhyolitic tephra layers (TG-13-A: see Fig. 7, log 35, unit 2a–2e) and a younger trachytic tephra layer are interstratified with the most recent occupation levels of this Palaeolithic site (Mouralis 2003; Mouralis et al. 2002; Slimak et al. 2004, 2008; Tryon et al. 2009). In previous publications, we demonstrated that the five rhyolitic tephra layers are associated with the emission of the Acıgöl Main Tuff. The classification associated with our new dataset confirms this initial identification (complementary data 4).
The main pyroclastites emitted by the Acıgöl volcanic complex (AMT)
As already pointed out by Druitt et al. (1995), the Acıgöl pyroclastic deposits are mainly observable in the eastern part of the Acıgöl complex (the Kumtepe hills: Fig. 2). In this area, thick pyroclastic deposits emitted during the main activity phase are overlain by deposition of alluvium and colluvium and then by younger pyroclastic deposits that were emitted during the extrusion of domes in and around the complex.
The initial activity is poorly documented. Site 51 (Figs. 9 and 10c) shows a 1.5-m-thick plinian unit (TA-1). Pumice clasts are dense with few small vesicles. A thin basaltic scoria layer (TA-2β) is intercalated between the lower and upper part of TA-1. At site 64, TA-1 overlays the Plio-Quaternary andesite substratum.
The basal group is composed of a fall deposit (TA-3) covered by a pyroclastic flow deposit (TA-4). At site 52, TA-3 fallout thickness exceeds 3 m. Pumice is aphyric with distinctive tubular and fibrous facies. Rhyolite dominates the lithic fraction; there are no obsidian clasts. The impressive size (20 cm) reached by the pumice points to the proximity of site 52 to the vent.
Overlying TA-3, TA-4 is composed of three pyroclastic flow units (52/2, 52/6 and 52/7), associated with a surge (52/3), an ash fallout (52/4) and lag-breccias (52/5). The flow units outcrop all around the northern and eastern parts of the complex, whereas the ash fall and surge deposits have a more local extension. At site 52, TA-4 total thickness reaches 17 m, of which 10 m are represented by flow deposits. Pumice is aphyric, with two main facies: (1) elongated and oriented vesicles, and (2) flexuous. The lithic fraction contains obsidian, rhyolite and diabase lapilli. This deposit is matrix-supported. The ashy unit (52/3) is interpreted as a co-ignimbritic ash fall. North-eastwards at site 69 (units 2–4), the lag breccia layer disappears because of a higher distance to the vent and the total thickness of TA-4 decreases to < 10 m. At site 80 (Fig. 2), TA-4 consists only of flow units and presents a total thickness < 6 m. Furthermore, TA-4 pyroclastites seem to have filled-in river channels directed northwards and eastwards.
The following pyroclastites (TA-5 to TA-7) are characterised by a plinian regime. TA-5 consists of surges (52/8) and a plinian fall (52/9). Surges are 3–5-m thick, with fibrous pumice. TA-6 includes an ash and pumice flow (52/10), a pumice fall (52/11) and a thinly bedded ash fall (52/12) interpreted as a co-ignimbritic fall probably linked to unit 10. TA-7 comprises fall deposits (52/13 and 52/14); their pumice clasts display elongated vesicles. Unit 13 is massive; whereas unit 14 presents a bedded framework with 10–20-cm-thick beds.
The uppermost and youngest group of pyroclastites (TA-β8 to TA-12) presents interbedding of scoria layers and rhyolitic pyroclastites. Two scoria fall deposits (TA-β8 and TA-β10) are interstratified within TA-9 rhyolitic pyroclastites. Also, at site 57, in the southern part of the Acıgöl complex, scoria layers are interstratified with rhyolitic pyroclastites. At the top of Sect. 52, a rhyolitic ash and pumice flow (TA-11) is overlain by lahars (TA-12).
Pyroclastic deposits associated with monogenic vents in and around Acıgöl complex
Most of the domes extruded in and around the Acıgöl complex are associated with pyroclastic products, especially with phreatomagmatic tephras. Four domes (Susamsivrisi, Kuzey, Asmadağı and Kocadağ) (Fig. 2) are partially overlain by TA-4 ash and pumice flow. This observation demonstrates that these domes are older than the AMT (i.e., “Acıgöl main tuff”).
On the other hand, many vents located inside the Acıgöl complex were active after the AMT. Three of them are domes extruded in maars (Güneydağ, Kaleci Tepe and Korudağ), one is a maar without a dome (Eski Acıgöl), and the other ones are scoria cones (e.g., Obruk Tepe). Sections in the three rhyolitic domes show an initial phreatomagmatic activity preceding the extrusion of the dome (Fig. 10d). Domes and scoria cones have emitted pyroclastic products of local extension (i.e., found near the vents and in a few sections only). These pyroclastic deposits, thus, do not play any significant role in the regional tephrostratigraphy, although in some cases they are good chronological markers of the local Late Pleistocene/Holocene landscape evolution.
For example, at the bottom of section site 53, the Acıgöl Main Tuff is overlain by three scoria falls and colluvium. Unit 53/11, a 20–40-cm-thick ash and lapilli-sized pumice fall is overlain by a palaeosol (53/12) the age of which is 29.9 ± 1 ka BP (Complementary data 3). The comparison between the geochemistry of this tephra layer and our regional referential database indicates that it has been emitted during the Acıgöl terminal activity. Complementary data 4 show the results of the classification using the DFA: 20 of the 22 single grain analyses are classified into ATT group of tephra layers, with a posterior probability of 0.9. However, the chemical analyses of major elements do not allow to specify the emitting vent.
Chronology of the volcanic activity of the Göllüdağ and Acıgöl complexes
To constrain the chronology of both complexes 17 K/Ar dates have been obtained from volcanic products (lava flows and extrusions) (Table 2). In addition, a single 14C date (complementary data 3) has been obtained from a palaeosol.
Radiometric ages in and around the Göllüdağ complex
In our dataset, two samples pre-date the volcanic activity of the Göllüdağ complex: DMO/TF51 (porphyric rhyodacite flow) and DMO/TF54 (basalt flow). Both flows were sampled in the western part of the complex, west of Bozköy-Kayırlı road (DMO/TF54) and above Kayırlı village (DMO/TF51). Both flows are covered by the Göllüdağ main tuff (TG-7). Their respective K/Ar age is 6.21 ± 0.09 (TF51) and 1.71 ± 0.03 Ma (TF54). In addition, five post-caldera domes have been K/Ar dated. Four of them yielded ages ranging from 1.1 ± 0.02 Ma to 0.855 ± 0.013 Ma, whereas the fifth one (Küçük Göllüdağ) has a younger K/Ar age of 0.444 ± 0.007 Ma.
Radiometric ages in and around Acıgöl complex
In the northern part of the Acıgöl complex, two scoria cones, the Asağı and the Yukarı Kızıl Tepe, have been K/Ar dated at 618 ± 14 ka (DM-05) and 538 ± 12 ka (DM-120), respectively. The flanks of these cones being covered by the AMT, the lava from both these cones predate the AMT.
The obsidian related to the setting of the Asmadağı Tepe dome, and covered by TA-4 pyroclastic deposit, yielded an age of 160 ± 3 ka (DAM-124). At site 56, obsidian intruded into the TA-4 deposit has been dated at 93 ± 2 ka (DAM-126).
Inside the Acıgöl complex, two scoria cones (Kızıl Tepe North and South), respectively, 154 ± 4 and 134 ± 3 ka old (DM-02 and DM-03), appear to be older than the AMT pyroclastites that overlie them. A third scoria cone (Obruk Tepe), dated to the late Pleistocene (32 ± 3 ka: DAM-126), produced basaltic ashes which, at site 55, are interstratified with rhyolitic tephra layers erupted from Korudağ (Acıgöl Terminal Activity).
In the southern part of the complex, two other scoria falls include > 1 m large bombs. These falls were emitted by the nearby Özyayla Tepe. They are interbedded with TA-9 tephra layer. The bottom scoria layer was K/Ar dated at 109 ± 4 ka (DM 07), whereas the top scoria layer has been K/Ar dated at 110 ± 5 ka (DM 06), thus dating TA-9 tephra emission. South of Özyayla Tepe, Küzlük Tepe was dated at 81 ± 4 ka (DMO/TF68).
At site 53 (Figs. 2 and 7), a palaeosol, overlain by a thin in situ pumice layer, has been 14C dated 29.950 ± 1.080 uncal. BP yrs (GIF-11,550: M. Fontugne, LSCE; complementary data 3). The age of these uppermost rhyolitic tephras (equal to that of the dome which produced them) is, thus, the youngest age in our tephrochronology dataset.
Stratigraphy of the tephra layers
Around the Göllüdağ complex, stratigraphic observation supports the assumption of three distinct eruptive stages. During the initial activity (1), a thin tephra layer (TG-1) was deposited in the valleys located in the western part of the complex. At the same time, another tephra layer was emitted from the Hasandağ (TG-2H). Both these pyroclastites were reworked by running water. During the paroxysmal stage (2), the main tuff was emitted: it is characterised by the deposition of tephra layers TG-3 to TG9, infilling and preserving paleo-valleys running southwards to the Çiftlik plain and eastwards to northwards to the Derinkuyu plain. During the final stage (3), domes were extruded within the complex. The tephra layers related to this late volcanic activity had only a local dispersion. A fourth group of pyroclastites identified in the Göllüdağ complex (4) corresponds to the tephra layers emitted by the neighbouring Acıgöl complex (TG13A, TG14A) and Hasandağ volcano (TG-11H, TG12H). All these late tephra layers are separated from the Göllüdağ pyroclastic units by alluvial or colluvial deposits that indicate a time-gap between the end of the Göllüdağ activity and the deposition of these younger tephra layers derived from external sources.
From TA-3 to TA-7, the absence of alluvium, colluvium or palaeosol points to the continuity of deposition. These TA-3 to TA-7 tephra layers form the Lower Acıgöl Tuff (LAT) defined by Druitt et al. (1995).
At the top of TA-7, interruption of the volcanic activity and related pyroclastic deposition are evidenced by: (1) interstratified basaltic scoria layers; (2) unconformity of the basaltic scoria layer TA-β10 and of young TA-11 and TA-12 rhyolitic units above the TA-3 to TA-9 units in Sect. 61. These TA-11 to TA-12 pyroclastic deposits form the Upper Acıgöl Tuff (UAT) defined by Druitt et al. (1995).
It is to be noticed that the sections we have observed in proximal situations do not show any palaeosol, in contrast to the description by Druitt et al. (1995) of a soil separating LAT and UAT. In sites 51, 57, 61 and 62, scoria layers are intercalated in-between the initial units TA-3 to TA-7 (corresponding to LAT) and TA-11 and TA-12 (corresponding to UAT) without any palaeosol. In a proximal situation, the volcanic activity of strombolian cones succeeded in inserting scoria layers in-between rhyolitic tephra layers (TA-3 to TA-7 and TA-11 to TA-12).
Chronology of both complexes
The chronology of both complexes is constrained here by 18 radiometric dates.
Chronology of Göllüdağ complex
In the north-western part of the complex, the substratum (Miocene, Pliocene and Early Pleistocene volcanics) has been locally dated at 1.71 Ma by DMO/TF-54. Other K/Ar dates obtained from volcanics in the Göllüdağ are from dome lavas extruded inside the volcanic complex after the eruption of the main Göllüdağ tuff. The oldest of these dated domes is the Kaletepe dome (ca 1.1 Ma). Accordingly, the main Göllüdağ tuff was emitted between 1.7 and 1.1 Ma. These data are in good agreement with the chronology published by Aydın et al. (2014): using U–Pb in zircon, these authors indicates a 1.083 Ma age on the southern slope of the Kaletepe dome, while we obtain a 1.1 Ma (K/Ar, DAM-129) on the south-eastern slope of the same dome.
In addition to the radiometric chronology, our field results refine the relative chronology of the extrusion of several domes. The palaeo-Kabak Tepe (dated 1.1 Ma), possibly one of the oldest domes, is cut and filled by volcanics from the younger Kabak Tepe and Kayışkıran Tepe domes. Kayışkıran Tepe is in turn cut-and-filled by volcanics from (1) the Bozdağ dome (0.966 Ma) and (2) the palaeo-Büyük Göllüdağ. Palaeo-Büyük Göllüdağ is in turn also partially destroyed by the younger Büyük Göllüdağ dome (0.855 Ma). This age (DMO/TF-75) is consistent with the one (0.899 Ma) published by Aydın et al. (2014) on pumice collected at site 21, associated with the extrusion of the Büyük Göllüdağ dome.
Finally, the youngest K/Ar age (0.4 Ma) was obtained from a rhyolite lava forming the basal cliff of the Küçük Göllüdağ. This cliff and other morphological characteristics point to this dome being the youngest of all domes inside the complex.
Chronology of the Acıgöl complex
Our tephrostratigraphy refines the chronology of the Acıgöl complex volcanic activity as defined by Schmitt et al. (2011). On the summit of the Asmadağı Tepe, TA-4 covers an obsidian K/Ar dated 160 ± 3 ka (DAM-124). The main Acıgöl pyroclastic units are thus younger than 160 ± 3 ka. The Acıgöl Main Tuff (AMT) is divided into two sub-groups as already noticed by Druitt et al. (1995) who distinguish the Lower Acıgöl Tuff (LAT) from the Upper Acıgöl Tuff (UAT). The earliest one corresponds to our TA-1 to TA-7 tephra layers ending with basaltic deposits (TA-β8 and TA-β10: see Sects. 52, 61, 90, 91, 92 and 93). At site 57, two basaltic bombs emitted by the Özyayla Tepe strombolian cone have been dated at 110 ka (DM-07 and DM-06). Our results also show that the AMT is contemporaneous of the activity of two small basaltic cones K/Ar dated 154 ± 4 (DM-02) and 134 ± 5 ka (DM-03). The TA-3 to TA-7 Acıgöl activity, thus, extends between 160 and 110 ka. Immediately after 110 ka, two younger rhyolitic tephra layers (TA-11 and TA-12) were emitted.
Subsequently, the volcanic activity persisted with the extrusion, within the volcanic complex, of the Kocadağ dome which is accompanied by an obsidian-filled dyke dated 93 ± 2 ka (DAM-126). This dyke intruded into the TA-4 pyroclastic deposit which, thus, predates de dyke.
After ~ 90 ka, an activity lag is indicated by a palaeosol and some colluvial deposits (site 53, 62 and 55). The volcanic activity started again with eruptions of (1) a basaltic scoria cone (Obruk Tepe dated 32 ± 3 ka K/Ar, DMO/TF-67), and (2) four rhyolitic maars and domes (Korudağ, Güneydağ, Eski-Acıgöl maar, Kaleci Tepe) all dated at 20 ka (Bigazzi et al. 1993; Schmitt et al. 2011). Our results provide also a more detailed, although relative, chronology of the activity of these three youngest vents of the complex. In the NW part of the complex, the Güneydağ dome extruded first into an initial maar. This dome was partly destructed during the eruption of the Eski-Acıgöl maar which cuts the older structures. Finally, Kaleci Tepe dome was extruded in an initial maar, the ring of which is today well preserved around the dome. During this final event, Kaleci Tepe tephra layers blanketed all previous volcanoes and their products. This relative chronology is in agreement with Schmitt et al. (2011) who dated these vents (using U/Th and U-Th/He geochronology) 23.8 ± 0.9 ka (Güneydağ), 23.2 ± 3 ka (Eski Acigöl) and 20.3 ± 0.6 ka (Kaleci Tepe). Noteworthy is a 28.3 ka uncal BP 14C date from a frost-deformed soil associated with a pure obsidian fall in the Göçü quarry NW of the Konya plain (Karabıyıoğlu et al. 1999; Kuzucuoğlu et al. 1998).
Quaternary volcano-tectonic structures
According to our field observation, the pyroclastic deposits assigned to GDT and AMT groups cover areas of ~ 720 and 1.100 km2 respectively (Fig. 2). In the case of Acıgöl, the value we report is close to that proposed by Druitt et al. (1995). Such a high amount of pyroclastic deposits produced by rhyolitic complexes deserves discussion about possible caldera structures.
The Göllüdağ complex is located in a depression positioned at the foot of cliffs cut-into a Mio-Pliocene substratum (the Şahinkalesi Tepe to the west; the Melendiz mountains, to the south-east). (Fig. 2).
Elevation values of the substratum in comparison to the pyroclastic layers also suggest a collapse of the central part of the complex. In the western part (Sect. 10), the substratum outcrops at 1760 m; whereas, in Sect. 16 it outcrops at 1660 m. In the southern part of the complex in Sects. 22 and 23, the substratum buried by the pyroclastites is situated at 1480 m elevation, while the top of the pyroclastites reaches only 1560 m. Thus, the elevation of the substratum–pyroclastite contact presents a 100–300-m altitude difference between the central part of the complex and in its periphery.
Moreover, in Sect. 15 (Fig. 8b), early alluvium contains well-rounded andesitic and basaltic pebbles reaching 15 cm in diameter, with no pumice. This alluvial deposit is tilted with a ~ 33° eastward dip, pointing to a collapse of the centre of the volcanic complex. Most units in the section also dip in the same direction but weaker (15°), suggesting a decrease of the subsidence rate with time.
However, field observation and careful mapping did not allow the precise identification of the limits of the collapsed centre and its surrounding structures.
In the case of the Acıgöl complex, the situation is more complex. Yıldırım and Özgür (1981) first identified and described a caldera. According to these authors, the size of the collapsed structure is 6 × 10 km, its southern limit being the Erdaş Dağ, and its eastern limit being the obsidian “wall” (cliff) east of the Kocadağ. Druitt et al. (1995) disagreed with this interpretation citing that topographic steps in these locations are not clearly identifiable.
We argue for the presence of a caldera based on four considerations (e.g. Ferrari et al., 1991): (1) the outcrops of the pre-caldera substratum are located outside the structure and never in its centre; (2) pyroclastic flows are associated with the structure without occurrence of any other alternative volcanic source; (3) domes extruded in the centre and around the collapse structure, leave untouched some morphological parts of the collapse fault scarps; (4) the volumes of both the emitted pyroclastic deposits and the collapsed part of the structure present a similar magnitude. Whereas, the volume of the collapse structures remains unconstrained due to their uncertain boundaries, the first three criteria of Ferrari et al. (1991) are fulfilled for both, the Göllüdağ and Acıgöl complexes.
Relationship with Tertiary calderas
It is noticeable that the studied complexes occur near the inferred location of Neogene collapse structures that must have accompanied the emission of the Cappadocian ignimbrites during the Mio-Pliocene. According to Froger et al. (1998), the Acıgöl-Nevşehir and Derinkuyu areas host significant negative Bouguer anomalies, usually attributed to calderas and acidic eruptions. Using Le Pennec et al. (1994)’s reconstructions of ignimbrite flow directions, Froger et al. (1998) showed that the “Kavak” and “Zelve” Neogene ignimbrites came from an area south of Nevşehir, where gravimetric data point to the presence of a caldera; whereas, the “Sarımaden”, “Cemilköy”, “Gördeles” and “Kızılkaya” Neogene ignimbrites were emitted by a caldera located in the Derinkuyu area.
The volcanic complexes analysed in the present paper have erupted voluminous pyroclastic deposits whose stratigraphy, petrographic and chemical characterization and dating are presented here for the first time altogether. Eruptive activity occurred around 1.3 Ma in the Göllüdağ complex, and around 150 ka in the Acıgöl complex. The large amount of tephras erupted during each of these major events buried and destroyed the previous morphology, largely modifying the regional landscape. As this volcanic activity probably re-activated Neogene structures, the morphology of the Neogene calderas became indistinguishable in the present landscape.
Intensive and systematic field observation allowed us to reconstruct the detailed regional tephro- and chronostratigraphy we present here. The robustness of the analysis of discriminant functions differentiating our geochemical data is well underlined by the obvious separation of the data within the multivariate space, as well as by the high proportion of correctly classified data.
It is noticeable that human populations were affected by the Middle to Upper Pleistocene Acıgöl eruption. For example, in the Palaeolithic “Kaletepe Dere 3” excavation, several tephra layers buried human artefacts (Mouralis et al. 2002, Mouralis 2003; Slimak et al. 2004, 2008; Tryon et al. 2009). In these archaeology-oriented publications, we demonstrated the capacity of our regional tephra reference to provide a chronological framework for archaeological studies.
This regional tephra reference is also useful for understanding landscape evolution. In Mouralis (2003), Mouralis et al. (2004) and Kuzucuoğlu (2004), we demonstrate that the studied tephra layers are key layers for the reconstruction of past landscapes and of their evolution under the influence of sediment erosion and/or accumulation.
Finally, the tephrostratigraphy and tephrochronology proposed here may not only be useful for understanding the volcanic complexes but also for establishing long-distance correlations that are important in different fields of research, from geomorphology to geoarchaeology, oceanography and climatology.
A part of the research presented here was conducted thanks mainly to the MTA-CNRS-TÜBITAK Project on “Upper Pleistocene Volcanism and Palaeogeography in Cappadocia, Turkey” (MTA-CNRS-TÜBITAK 2001–2003 RESEARCH PROGRAMME N° 101Y109) and to a Turkish-French TÜBITAK-CNRS agreement, both programmes co-directed by A. Türkecan and C. Kuzucuoğlu. The authors benefited from financial support from MTA, CNRS (LGP) and from French Ministry of Foreign Affairs (Bosphorus Programme). DM benefited from a PhD scholarship from the University of Paris 12/Créteil (under the direction of Prof. B. Dumas), from the technical and scientific support of Kaletepe excavation team (directed by Prof. N. Balkan-Atlı from Istanbul University & Prof. D. Binder from CEPAM Lab. In Sophia-Antipolis). DM thanks Dr. Lütfi Dokuzoğlu for his help and friendship in Aksaray and Cappadocia. The authors are grateful to A. Schmitt and an anonymous reviewer for numerous suggestions that have greatly contributed improving the initial manuscript.
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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