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Geoarchaeological study of Katarraktes cave system (Macedonia, Greece): isotopic evidence for environmental alterations

Étude géoarchéologique de la grotte de Katarraktes (Macédoine, Grèce) : mise en évidence isotopique des modifications environnementales
David Psomiadis, Elissavet Dotsika, Nikoleta Zisi, Christos Pennos, Sophia Pechlivanidou, Konstantinos Albanakis, Anastasios Syros et Markos Vaxevanopoulos
p. 229-240

Résumés

Des fouilles archéologiques ont débutées en 2004 dans la grotte de Katarraktes située à proximité de Sidiokastro en Macédoine (Grèce). Elles ont mis à jour un nombre important de trouvailles datant des périodes préhistorique et historique. Un abri sous roche et de nombreux artefacts datant du début de l’Age du Bronze ont été trouvés. Les principales activités liées à l’occupation du site semblent avoir été la préparation et le stockage de nourriture. Dans le but d’étudier les relations entre l’utilisation de cette grotte et l’évolution des conditions environnementales pendant les périodes préhistorique et historique, une étude isotopique a été menée sur des dépôts calciques et organiques provenant d’une stalagmite trouvée dans la grotte étudiée. L’analyse des rapports isotopiques δ13C et δ18O effectuée à partir des sédiments carbonatés a permis préciser les conditions environnementales qui prévalaient à l’époque de la précipitation des matériaux carbonatés à l’intérieur de la grotte. Une alternance de phases sèches et humides a été mise en évidence. Une reconstitution globale des données environnementales sur la période d’occupation humaine dans les grottes de Katarraktes a été réalisée en exploitant les données archéologiques, géomorphologiques et isotopiques. Les signatures isotopiques du spéléothème indiquent de rapides modifications des conditions atmosphériques et doivent être associés au changement climatique global survenu au cours Subboréal dans la région méditerranéenne entre 3500 et 4500 BP.

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Notes de la rédaction

Article soumis le 8 juin 2009, accepté le 30 septembre 2009

Texte intégral

The authors would like to express their gratitude to Dr. Philippe Audra and two other anonymous reviewers as well as to Pr. Gilles Arnaud-Fassetta, Editor-in-Chief, for their significant contribution to this paper by their crucial remarks and recommendations. They would also like to thank Dr. Matthieu Ghilardi, convener of session GM11.1 of EGU 2009 General Assembly, Vienna, who contributed to the completion of this work.

Introduction

1Caves and rockshelters offer a suitable and reliable environment for geoarchaeological and palaeoenvironmental studies. Much of what we know about the Paleolithic, Mesolithic, and Neolithic cultures of the Mediterranean region and adjacent areas is derived from cultural remains preserved in rockshelter and cave sediment records (e.g., Gamble, 1986; Straus et al., 1996; Bailey et al., 1999; Karkanas, 2001). Cave sediment records offer many advantages over open sites because they provide both stratigraphic control and environmental context for the archaeological and geological record (Collcutt, 1979; Farrand, 1988; Goldberg, 1992; Macphail and Goldberg, 2000; Courty and Vallverdu, 2001). The cultural history of the Late Pleistocene and Holocene in the region of Mediterranean records the demise of the Neanderthals, the emergence of anatomically modern humans in Europe, the beginnings of domestication and agriculture at the end of the last cold stage and the advance to the Neolithic and modern cultures (Bronze age and Iron age civilizations; e.g., Bar-Yosef and Belferohen, 1992; Gamble, 1994; Mellars, 1994). Our knowledge of these pivotal stages in human history has largely been pieced together from materials excavated from sedimentary sequences in rockshelter and cave sites. It is, therefore, important to develop advanced methods and robust conceptual models for the interpretation of cave sediment records so that these cultural sequences can be considered in their proper environmental context. Recent advanced studies in Mediterranean region (e.g., southern Italy, Ghinassi et al., 2009; Spain, Angelucci, 2003; southern France, Jaillet et al., 2007) have combined geomorphological investigation and sedimentary records in order to restructure the palaeoclimatic and palaeoenvironmental conditions during anthropic use of caves and rock-shelters. Karst features have been studied for environmental and climatic variations, which are contemporary with human activities (Delannoy et al., 2009). By combining data from analyses of sediment series and from speleothems, it has been possible to decipher the contemporaneous morphogenic dynamics of cold and wet periods or climate deterioration (Audra, 1994). The use of modern advanced techniques like stable isotopes may provide the necessary tools in order to enhance geoarchaeological research by means of climatic information and to correlate anthropogenic and natural influence and alterations. Stable isotopes of speleothems (δ13C and δ18O) have been widely used, aiming to interpret climatic changes in centennial, annual or even sub-annual level (e.g., Fairchild et al., 2001; McDermott, 2004; Bar-Matthews and Ayalon, 2005; Losson et al., 2006; Lachniet, 2009). In this study, an effort to extract detailed sedimentary and geomorphological archives in correlation with isotopic fingerprints of carbonate sediments has taken place, with the aim of reconstructing the palaeoenvironmental and palaeoclimatic conditions during human occupation. Moreover, this study attempts to correlate geoarchaeological and palaeoclimatic data by putting the environmental alterations imprinted in speleothems on the defined archaeological time window, based on the natural and anthropogenic sedimentological characteristics of the site.

Setting of the area

2Katarraktes cave system is located approximately 2 km northwest from Sidirokastro, in northern Greece, in the basin of Krousovitis River (fig. 1), 65 km inland and at 94 m altitude. The region is characterised by high geomorphological relief and belongs to the tectonic graben of Serres. The main bedrock formations include gneiss, marbles, conglomerates and Neogene sediments (fig. 2). The Krousovitis River forms a canyon, where the caves have been formed, indicating older levels of river flow (Lazaridis, 2004). Krousovitis basin had experienced multiple phases of uplift and sedimentation processes. The canyon that formed during the pre-Neogene uplifts has filled with Neogene sediments, mainly conglomerates of granitic composition as well as silty sands, which covered partly the surficial marble. The Late Pliocene uplift caused the erosion of these Neogene sediments and eventually formed Krousovitis basin, which cut through the marble bedrock and the Neogene deposits. Quaternary tectonic movements in the region produced new less intense uplifts, which seem to have shaped the structure of the canyon during Middle-Late Pleistocene (Psilovikos et al., 1981). The study cave is part of an extensive karst system, hosted in the marble conglomerate formations. The surficial coverage in the area is characterised by large slide-blocks of marble breccias derived from higher altitudes of the basin. These blocks are the result of differential erosion between the marble breccia and the Neogene sediments which are weathered more rapidly. The quantitative geomorphological analysis of the area showed that the tectonic activity is still intense, flood events are common and the slopes of the canyon are steep. The total surface of Krousovitis basin is noticeably wide, reaching almost 300 km2 (Papafilippou-Pennou, 2004). The climatic data for the area come from the meteorological station of Sidirokastro (90 m altitude) and report a mean annual temperature of 14.6 oC and mean annual precipitation equal to 600 mm. Given the listed characteristics of the basin, it is expected that flood events are frequent and quite intense. According to C. Balafoutis (1977), frequent and intense storm events are reported in northern Greece during spring, due to the action of heavily humid Saharan winds. The steep slopes are related to highly erosional phenomena during these floods affecting even the levels of cave entrances.

Fig. 1 – Location of the study site.
Fig. 1 – Localisation du site étudié.

Fig. 1 – Location of the study site.Fig. 1 – Localisation du site étudié.

1 : Katarraktes cave and rockshelter (see fig. 2) ; 2 : Lake Kerkini. Krousovitis River flows north of Mt. Vrontou (1850 m), forming a wide hydrological basin.
1 : grotte et abri sous roche de Katarraktes (voir fig. 2) ; 2 : Lac Kerkini. La rivière Krousovitis s’écoule au nord du Mt. Vrontou (1850 m) et draine un large bassin-versant.

Fig. 2 – Stratigraphic section of the Krousovitis valley where Katarraktes cave is located.
Fig. 2 – Coupe stratigraphique transversale de la vallée de la Krousovitis où est localisée la grotte de Katarraktes.

Fig. 2 – Stratigraphic section of the Krousovitis valley where Katarraktes cave is located.Fig. 2 – Coupe stratigraphique transversale de la vallée de la Krousovitis où est localisée la grotte de Katarraktes.

1 : marble conglomerate ; 2 : fluvial and colluvial deposits ; 3 : fluvial deposits ; 4 : collapsed blocks ; 5 : cave entrance. The conglomerate represents mainly the Neogene sequence while Quaternary sediments consist of fluvial deposits. See fig. 1 for location.
1 : conglomérats de marbre ; 2 : dépôts fluviatiles et colluviaux ; 3 : dépôts fluviatiles ; 4 : blocs effondrés ; 5 : entrée de la grotte. Les conglomérats datent du Néogène tandis que les dépôts fluviatiles sont d'âge quaternaire. Voir fig. 1 pour la localisation.

Archaeological data

3Between 2004 and 2008, from when the first archaeological findings were excavated in Katarraktes cave system, a great number of archaeological and geological missions revealed an intense presence of people in these caves (Poulaki-Pantermali et al., 2006; Syros et al., 2008). The archaeological site is located in a cave at the south river bed, 10 m higher than the river level, and is composed of a wide rockshelter with two chambers. The rockshelter is 620 m2 and its height reaches 34 m. On the surface layers, Bronze Age to modern findings are numerous. It is noticeable though, that although the mobile findings such as pottery and tools from a variety of chronological phases are truly abundant, respective stratigraphical levels cannot be discerned. Specific historical phases are represented mainly by pits and potholes. Three main prehistoric phases of occupation are clearly present (fig. 3), basically characterised by earthen floors, as well as by the use of spars and clay as structural materials. The first phase is located more than half a meter below the surface. Part of a building that was bedded on wedged spars (spar-based) was discovered there, as well as seeds, ceramics and burned objects. The destruction of this phase has been radiocarbon dated at 5020-5340 BP. The second phase shows a smaller area of occupation, located 20-30 cm from the surface. Pottery and tools as well as burned building residues, seeds and cereal are among the findings. The packed clay floors are sealed by the stratum of destruction (unconsolidated grey-colored clay sediments containing small percentage of micas and including dense breccia layers and burned residues). It is dated back to 5000 BP. The third phase includes disturbed superficial layers. Charcoal deposits seal the earthen surface and structural clays are overlaid (Efstratiou, 1989). Ceramics date this phase to Early Bronze Age (approximately 4500-5000 BP), showing similarities to Kostolats, Vuĉedol and Baden cultures (Papadopoulos, 2002). Charcoal uncalibrated radiocarbon age has been calculated 4550-4880 BP. A large spar-based building represents the architecture of this phase. The specific period is characterised by the phases Sitagroi V (Sherratt, 1986) and Dikili Tash IIIB (Seferiades, 1983) for eastern Macedonia and Ezero B for Bulgaria. The first and second phases are related to storage and food preparation use of the cave. They indict similar cultural origin, proximate age and they totally differ from the third phase. Ceramics of these two phases seem to confirm their absolute age at the end of the 4th millennium BC, bridging with the phases Sitagroi IV (Sherratt, 1986) and Dikili Tash IIIA (Seferiades, 1983) of Eastern Macedonia and showing obvious influence by the early stages of Baden cultural complex (Papadopoulos, 2002). The rockshelter included representations from all the three phases of occupation.

Fig. 3 – Stratigraphic section of the cave sediments according to excavation of the three archaeological phases.
Fig. 3 – Coupe stratigraphique réalisée dans les sédiments provenant de la grotte et réalisée à partir des résultats de la fouille des trois niveaux archéologiques.

Fig. 3 – Stratigraphic section of the cave sediments according to excavation of the three archaeological phases. Fig. 3 – Coupe stratigraphique réalisée dans les sédiments provenant de la grotte et réalisée à partir des résultats de la fouille des trois niveaux archéologiques.

Stratigraphical infillings consist of fine sediments (clay to fine sand) including granitic pebbles and breccias. The altitude is report is relative to cave floor. 1 : discontinuity surfaces ; 2 : floors of archaeological layers ; 3 : destruction layers, including charcoal deposits ; 4 : residues of spar-based buildings ; 5 : seeds and cereal ; 6 : ceramics ; 7 : tools ; 8 : limestone breccia. The position of the excavated pits is shown in fig. 4. 
Les remplissages sédimentaires sont constitués d’une matrice constituée de sédiments fins (argiles à sables fins) comprenant des galets de granite et des brèches. L'altitude est exprimée par rapport au plancher de la caverne. 1 : surfaces de discontinuité ; 2 : niveaux archéologiques ; 3 : niveaux de destruction comprenant des dépôts de charbon ; 4 : résidus de bâtiment ; 5 : graines et céréales ; 6 : céramiques ; 7 : outils ; 8 : brèche calcaire. La position des fosses creusées est indiquée sur fig. 4.

Morphological features

4At the entrance of the cave, colluvial deposits are present due to regressive erosion and landslides of the steep slopes of the canyon. At the central space of the rockshelter, the ground slopes are very low (0-7%) and they are increasingly steeper close to the north edges (maximum 77%; fig. 4; from Pennos et al., 2008). This morphology favours the deposition of fine sediments at the central area and the drainage of the cave during flood events following the general slope of the floor to the north. The slopes of the modern floor indicate the outflow path of the sediments during flooding periods of Krousovitis River (Pennos et al., 2008). The cave environment is characterised as closed and low-energy. However, during flooding of the entrance, it is believed that most of the cave surface was covered by water. Extended floods are indicated by the deposition of fine sediments (clay to fine sand) including granitic pebbles, shingles and breccias, characteristic of high-energy events such as river floods and not slow runoff along the slopes or seepage. Sediments are characterised by the presence of anthropogenic materials and by layers of charcoal deposits. Discontinuities in stratigraphical sections (fig. 3) are related to external high-energy processes. In particular, Krousovitis River flood events probably were catastrophic for several archaeological layers, as indicated by sedimentological and stratigraphical characteristics described above. Moreover, the floor of the second archaeological phase is drooped, succumbing to the weight of limestone breccia blocks coming from breakdown morphology characteristics. The absence of cracks and breaks indicates plastic deformation and thus supports the above assumption rather than a violent event (e.g., earthquake). Inside the cave near the entrance, travertine depositions are observed, including pieces of ceramics and pottery (fig. 4) and reaching up to a level of 1m above cave floor. Their position as well as the stratigraphical deposition of sediments at their base (cave floor) indicate sediment outflow due to flood events and erosional phenomena of the palaeo-floor surface. These flood events formed different floor surfaces inside the cave (fig. 3) and show a general repeatability indicated by the successive stratigraphical discontinuities.

Fig. 4 – Ground plan of the cave (contour lines express altitude relatively to m asl).
Fig. 4 – Plan du sol de la grotte (les isohypses sont exprimées par rapport au niveau moyen de la mer).

Fig. 4 – Ground plan of the cave (contour lines express altitude relatively to m asl). Fig. 4 – Plan du sol de la grotte (les isohypses sont exprimées par rapport au niveau moyen de la mer).

1: fragments of pottery included in the travertine; 2: sampling position of the KTR_01 stalagmite; 3: travertine formation. Limestone breccia also visible in the inset picture; 4: cave entrance; 5: position of the excavation pits (corresponding also to fig. 3); 6: area under the rockshelter, also visible from external view in the inset picture.
1 : fragments de poterie incorporés dans des dépôts de travertin ; 2 : point d'échantillonnage de la stalagmite KTR_01 ; 3 : formation travertineuse (brèche calcaire visible également sur l'image d'insert) ; 4 : entrée de la cave ; 5 : position des fosses de fouille (voir aussi fig. 3) ; 6 : secteur sous l'abri (également visible depuis l'extérieur dans l'image d'insert).

Stable isotopes

5The cave conditions and processes render the specific environment as an active (humid) karst setting (Woodward and Goldberg, 2001) with on-going drip-flow. A noticeable number of carbonate deposits (speleothems) in the cave system presented a very “fresh” and rapid precipitation of carbonate material, indicated mainly by their porous texture. The carbonate precipitation in stalagmites was probably simultaneous to the use of the caves by people during prehistoric time and later, indicated by their position, texture and form of deposition (see below for details). Carbon stable isotope (δ13C) in speleothems may provide information as to the origin of CO3- precipitated while δ18O indicates the environmental conditions (e.g., temperature, humidity) during calcite precipitation. Isotopic fractionation should be investigated in order to render the results as reliable for interpretation (Hendy, 1971).

6A stalagmite (KTR_01) with archaeological interest was selected for isotopic analysis from deep within the cave. KTR_01 was located approximately 1 m above the mean surface level of the cave entrance. Its main connection to the archaeological findings is that it was developed on a charcoal layer probably of anthropogenic origin, which was deposited at the interior of the cave. The position of the charcoal layer deep inside the cave in combination to the fact that there were no similar layers out of the entrance’s sedimentary sequences designates that the charcoal comes from the archaeological layers during the human occupation of the cave and it was not transported by the river from other sites of the valley. KTR_01 generally kept to all necessary conditions for isotopic analysis (Hendy, 1971) which mainly are a deep spot in the cave, not very close to air-circulation exits (i.e., cave entrance) and not in very high chambers (the distance of the drip water during its falling from the cave ceiling may induce isotopic fractionation). KTR_01, which was 161 mm high and its base diameter was 105 mm, was cut-sectioned and subsampled. Three samples of organic matter were extracted from different laminae. The organic matter samples were either pure charcoal layer or a mixture of charcoal with geogenic calcite. δ13C and δ18O isotopic ratios of calcitic stalagmite layers were measured (vs. PDB standard) on a Thermo Delta V Plus isotope ratio mass spectrometer equipped with a GasBench II device at Stable Isotope Unit, NCSR Demokritos, Athens, after addition of H3PO4 for CO2 production. Subsampling was conducted with a bench microdrill, using a 0.7 mm diameter drill bit, providing approximately 300-500 micrograms of carbonate powder. Organic samples were analysed for the determination of δ13C isotopic ratio on a Thermo Delta V Plus isotope ratio mass spectrometer equipped with an Elementar Analyzer Flash1112 device, Stable Isotope Unit, NCSR Demokritos, Athens. Analytical reproducibility is better than 0.1‰ for δ13C and δ18O. In total, 28 subsamples of calcitic material (fig. 5; section S1, 103 mm) were taken from the area above the older stalagmite (fig. 5, OS). The identification of the older stalagmite is based on the different texture (compacted deposition), the different growth axis and the depositional discontinuity evident below layer 1 (fig. 5). Furthermore, 50 subsamples were extracted from 5 different laminae (3, 10, 16, 21 and 27) for the execution of Hendy tests (fig. 6). Three positions of organic material in fresh-state were spotted, and the organic matter was sampled for isotopic analysis (samples OG_#). The organic matter was located in-between calcite layers (OG_01 and OG_02) in form of mixed calcitic and organic material, as well as at the bottom sedimentary series (fig. 5, BS) of the stalagmite as thin lamina (OG_03). Sample OG_03 was identified as charcoal deposition by microscopic observation.

7Isotopic fractionation was excluded after conducting the proposed tests by C.H. Hendy (1971) along the flanks of the stalagmite, which showed negligible kinetic effects (fig. 6). The tests were performed on five laminae along the growth axis of KTR_01, including 10 subsamples in each lamina. The δ18O values along individual laminae are generally constant (variation <0.5‰), whereas δ13C values vary up to 1.66‰ and are not correlated with δ18O. δ13C values (Tab. 1) range from -8.7‰ (samples KTR_01_S1_05 and 08) to -5.32‰ (sample KTR_01_S1_01). Carbon stable isotopes of calcite show in general two lighter and two heavier phases of isotopic composition (fig. 7). This indicates a repeated alteration of the initial carbon isotopic value. The δ18Ο values (Tab. 1) follow a smoother alteration along the same segments of the stalagmite section (fig. 7). These variations show the same phases of alteration as in δ13C results. δ18O values range from -5.27‰ (sample KTR_01_S1_08) to -3.09‰ (sample KTR_01_S1_01). δ13C measurements of organic samples (OG_##) presented two mixed materials (samples OG_01 and OG_02) with intermediate values (-13.28 and -13.46‰ respectively) and a pure charcoal deposition (sample OG_03), as indicated by microscopic observation, with representative C3-origin carbon isotopic composition (-26.85‰).

Tab. 1 – Isotopic composition of calcite and organic samples of KTR_01 stalagmite (‰, VPDB).
Tab. 1 – Composition isotopique des échantillons calciques et organiques prélevés sur la stalagmite KTR_01 (‰, VPDB).

Samples

δ13C ‰, vs. V-PDB

δ18O ‰, vs. V-PDB

KTR_01_S1_01

-5.32

-3.09

KTR_01_S1_02

-8.23

-4.31

KTR_01_S1_03

-7.53

-3.99

KTR_01_S1_04

-7.97

-4.02

KTR_01_S1_05

-8.70

-4.75

KTR_01_S1_06

-8.53

-4.88

KTR_01_S1_07

-7.36

-4.90

KTR_01_S1_08

-8.70

-5.27

KTR_01_S1_09

-5.80

-4.70

KTR_01_S1_10

-6.44

-4.89

KTR_01_S1_11

-6.00

-4.81

KTR_01_S1_12

-7.14

-4.93

KTR_01_S1_13

-5.54

-4.23

KTR_01_S1_14

-6.75

-4.61

KTR_01_S1_15

-6.79

-5.14

KTR_01_S1_16

-6.72

-4.37

KTR_01_S1_17

-6.95

-4.61

KTR_01_S1_18

-6.52

-4.13

KTR_01_S1_19

-6.79

-3.88

KTR_01_S1_20

-8.30

-4.58

KTR_01_S1_21

-7.28

-5.02

KTR_01_S1_22

-7.82

-4.82

KTR_01_S1_23

-7.70

-5.01

KTR_01_S1_24

-7.83

-5.09

KTR_01_S1_25

-5.77

-3.59

KTR_01_S1_26

-8.10

-4.66

KTR_01_S1_27

-6.66

-3.75

KTR_01_S1_28

-6.41

-4.01

KTR_01_OG_01

-13.28

  

KTR_01_OG_02

-13.46

  

KTR_01_OG_03

-26.85

  

Fig. 5 – Longitudinal cut section of KTR_01 stalagmite (Katarraktes cave).
Fig. 5 – Profil longitudinal de la stalagmite KTR_01 (grotte de Kattaraktes).

Fig. 5 – Longitudinal cut section of KTR_01 stalagmite (Katarraktes cave).Fig. 5 – Profil longitudinal de la stalagmite KTR_01 (grotte de Kattaraktes).

Black-dots : sub-sampling positions for isotopic analysis (small black-dots indicate the sub-samples for the Hendy-tests) ; S1 : sampling section ; OG_## : sampling positions of organic matter ; OS : old stalagmite formation ; BS : sedimentary series under the stalagmite.
Les cercles noirs indiquent les lieux de prélèvement pour l’analyse isotopique (les plus petits cercles noirs indiquent les sous-échantillons pour les Hendy-Tests) ; S1 : section prélevée ; OG_## : position des échantillons de matière organique prélevés ; OS : ancienne formation de stalagmite ; BS : couches sédimentaires sous la stalagmite.

Fig. 6 – Plots showing the δ18O and δ13C variations (VPDB) for representative different laminae (A :3, B :10, C :16, D :21, E :27) of KTR_01 stalagmite as measured along the length of the laminae
Fig. 6 – Variations du rapport isotopique (δ18O-δ13C) (VPDB) des différentes laminae (A :3, B :10, C :16, D :21, E :27) de la stalagmite KTR_01

Fig. 6 – Plots showing the δ18O and δ13C variations (VPDB) for representative different laminae (A :3, B :10, C :16, D :21, E :27) of KTR_01 stalagmite as measured along the length of the laminae Fig. 6 – Variations du rapport isotopique (δ18O-δ13C) (VPDB) des différentes laminae (A :3, B :10, C :16, D :21, E :27) de la stalagmite KTR_01

(see also fig. 5). The isotopic trends indicate minor variations in δ18O and wider variations in δ13C. These trends are in accordance with suggested criteria for equilibrium (Hendy, 1971).
(voir aussi fig. 5). Les variations isotopiques correspondent à des variations mineures pour δ18O mais plus importantes pour δ13C. Ces variations sont en accord avec les critères suggérés pour l'équilibre isotopique (Hendy, 1971).

Discussion

8The stalagmite texture was porous, indicating very fast deposition of carbonates from not highly saturated water, resulting in wide pores not filled with carbonate precipitation and also the entrapment of organic material in thin layers. This fact influenced our subsampling resolution along the growth axis of KTR_01. The top of the stalagmite was eroded by undersaturated drip water, until a depth of 1 cm. The drip water seemed to dilute the carbonate from the top of the stalagmite and re-deposited materials at lower layers. Drip water dissolution indicates undersatured water flow during the last phases of the cave evolution. The abundance of organic material between the stalagmite layers, not leached out by water may indicate the relatively young age of the speleothem. Furthermore, the erosional phenomena observed in cave sediments may be more prominent during changes from cold to milder conditions. This conclusion is also favoured by A. Demitrack (1986) in her study of the sedimentary history of Thessaly during the late Pleistocene. The main reason is that the climatic destabilization of a previous cold and arid environment may be more pronounced than the deterioration of the environment during a change to a colder event (Demitrack, 1986). The travertine (fig. 4) represents residue of a larger weathered formation, baring evident signs of fragmentation. Flowing water was on the other hand the main factor of sediment erosion at the base of the formation, leaving the travertine at its present position (max. 1 m above cave floor). Hence, possible frost fragmentation which splintered the travertine during cold and arid conditions was succeeded by milder wet conditions, which incurred intense water flow that in turn caused the sediment erosion at the base of the travertine (Courty and Vallverdu, 2001).

9Stable isotopes are used in this study in order to determine climatic trends in the cave environment, associated to its geomorphological features as well as the archaeological findings. Variations in δ13C of cave deposits could be attributed to: i) length of flow path and rates of CO2 degassing which favour speleothem δ13C enrichment when the surface recharge is low under drier environment; ii) greater respiratory activity of soils under wetter conditions resulting in lower δ13C calcite values; iii) biogenic CO2 (lighter values-warmer climate) vs. atmospheric CO2 (heavier values-cooler climate; McDermott, 2004). Respectively, oxygen isotopic composition of stalagmites may vary due to: i) evaporation effect during arid climatic conditions accompanied by enrichment in δ18O; ii) amount effect, i.e., augmented rainfalls, resulting in δ18O decrease in meteoric water (Rozanski et al., 1993; Bard et al., 2002; Straight et al., 2004); iii) lower deposition temperatures resulting in higher δ18O values in carbonate precipitations (Gascoyne, 1992; Bar-Matthews et al., 1996; McDermott, 2004). The temperature variability for Mediterranean region has a negligible effect on speleothem δ18O during the Holocene and as a major controller of speleothem δ18O the quantity of rainfall effect is likely to be more important (Bar-Matthews et al., 2000; Zanchetta et al., 2007). Consequently, the stalagmite δ18O which has a range of ~2.2‰ (fig. 7) substantially can reflect changes in the quantity of rainfall taking place in the period of its growth. The positive covariation in both δ13C and δ18O in KTR_01 across layers 9-13 (fig. 7A) and layer 25 (fig. 7B) suggests the similar governing regime that most probably is a quantity of rainfall effect. This enrichment indicates drier climatic conditions during carbonate precipitation, in contrast to a wetter environment during the deposition of the other layers. Published work for Mediterranean region record a pronounced arid phase located around 4 ka BP (from ca. 3.5 to 4.5 ka BP), which coincides with low water level of African lakes, confirmed by other natural archives (Gasse, 2000; Drysdale et al., 2006; Zhornyak et al., 2008). This phase has been suggested as responsible for the collapse of Old World civilizations in the region (Drysdale et al., 2006). The isotopic signature of KTR_01 stalagmite resembles that of the climatic variation during Late Holocene, imprinting the change of that warm and dry period in the area. The development of KTR_01 stalagmite over charcoal deposition (sample OG_03; fig. 5), most probably of anthropogenic origin according to microscopic and sedimentary features, confirms the hypothesis that this stalagmite is contemporary and younger in relation to the Early Bronze Age human occupation of the cave.

10In relation to the archaeological data, it seems that alterations of humid and arid environment were common in the area of Krousovitis River and due to its geomorphological characteristics; they had a severe impact on the cave entrance and interior environment. Human occupation of the cave was favoured during mild periods, when Krousovitis flowed in relatively low levels and the entrance was free of floods. However, flooding events were not scarce and the settlements suffered several catastrophic phases. The radiocarbon ages of the three phases of human occupation date the catastrophic events from ca. 4500 to 5340 BP. These ages (fig. 8C) are before the dry period identified around 3500-4500 BP in the Mediterranean area (Gasse, 2000; Drysdale et al., 2006; Zhornyak et al., 2008; fig. 8A). According also to the fact that the stalagmite developed contemporaneously and after the presence of people in the cave, as indicated by the stalagmite development over an anthropogenic charcoal layer, it is observed that the respective layers of KTR_01 stalagmite for period C present the lightest values of δ13C, probably related to the presence of organic traces in the laminae. Lighter isotopic fingerprints of these layers could be attributed to deposition of charcoal particles [δ13Ccharcoal=-22 to -27‰ for C3-type plants (Ferrio et al., 2006; Ascough et al., 2008)] during the human-induced fire events traced in archaeological excavations, which strongly supports the hypothesised presence of people in the cave during the deposition of these laminae. Such inclusions in stalagmite layers have been given this interpretation elsewhere (e.g., White, 1981; Ramseyer et al., 1997; Van Beynen et al., 2001), also reflecting human activity (Aven de la Portalerie; Delannoy et al., 2009). The influence of organic matter in stalagmite layers is confirmed by samples OG_01 and OG_02 isotopic composition (-13.28 and -13.46‰ respectively) which seem to have a depleting effect on δ13C of their respective layers (8 and 20). The final values of -13.28 and -13.46‰ reflect the mixed composition of the two end-members (geogenic calcite and pure charcoal-sample OG_03 with δ13C=-26.85‰).

Fig. 7 – Results of isotopic measurements (VPDB) : variation of carbon and oxygen isotopes across sampling section.
Fig. 7 – Résultats des mesures isotopiques (VPDB) : variation des isotopes du carbone et de l’oxygène le long de la section échantillonnée.

Fig. 7 – Results of isotopic measurements (VPDB) : variation of carbon and oxygen isotopes across sampling section.Fig. 7 – Résultats des mesures isotopiques (VPDB) : variation des isotopes du carbone et de l’oxygène le long de la section échantillonnée.

A and B represent segments of contemporaneous isotopic enrichment. This enrichment indicates drier climatic conditions during precipitation, in contrast to wetter environment during the deposition of the other layers.
A et B représentent des segments d’enrichissement isotopique contemporain. L’enrichissement isotopique montre des conditions climatiques plus sèches pendant les phases de précipitations. Les conditions climatiques humides caractérisent quant à elles les autres surfaces.

Fig. 8 – Schematic representation of climatic alteration during the development of KTR_01 stalagmite.
Fig. 8 – Représentation schématique des modifications climatiques pendant le développement de la stalagmite KTR_01.

Fig. 8 – Schematic representation of climatic alteration during the development of KTR_01 stalagmite.Fig. 8 – Représentation schématique des modifications climatiques pendant le développement de la stalagmite KTR_01.

A and B represent segments of contemporaneous isotopic enrichment. C covers the assumed period of human occupation of the cave. The date and palaeoclimatic interpretation is developed in text (discussion).
A et B représentent des segments d’enrichissement isotopique contemporain. C couvre la période d’occupation humaine de la grotte. L’âge et l’interprétation paléoclimatique sont développés dans le texte (discussion).

Conclusions

11Katarraktes cave system provides a suitable environment for geoarchaeological investigation of prehistoric to historical human occupation in relation to environmental conditions inside the cave. Three phases of human presence are evident, with abundant material and building remains from Early Bronze Age. Layers of destruction and fire events are also found. Human occupation has strongly influenced the sediment deposition inside the cave (archaeological layers) forming anthropogenic microfacies and features, as well as the air composition with charcoal particles. The isotopic signatures of the KTR_01 stalagmite reflect the abrupt changes of the atmospheric conditions inside the cave (drier and wetter periods), which are correlated to changes in precipitation during 3500-4500 BP in Mediterranean region. Humid atmospheric conditions during human occupation of the cave, which favoured higher precipitation, are imprinted in both the stalagmite layers (isotopic data) and the sedimentological characteristics (flood events). On the other hand, the isotope data appears to show that a drier period follows the human occupation of the cave. This drier period can be associated with the recorded warm and dry phase in the region, taking into account the chronological significance of the overlying stalagmite formation on the anthropogenic charcoal deposits.

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Annexe

  

Version française abrégée

L’étude géoarchéologique et paléoenvironnementale de grottes ou d’abris sous roche offre la possibilité d’obtenir d’importantes informations sur l’histoire de leur occupation et de leur utilisation. La plupart des informations concernant les cultures paléolithique, mésolithique et néolithique dans l’aire méditerranéenne nous sont fournies à partir de l’interprétation de restes préservés et prélevés dans des abris sous roche et dans les sédiments qui s’y sont accumulés (i.e., Gamble, 1986 ; Straus et al., 1996 ; Bailey et al., 1999 ; Karkanas, 2001). L’avantage de ces enregistrements sédimentaires est de proposer une double étude stratigraphique et paléoenvironnementale (Collcutt, 1979 ; Farrand, 1988 ; Goldberg, 1992 ; Macphail et Goldberg, 2000 ; Courty et Vallverdu, 2001). L’étude des rapports isotopiques δ13C et δ18O a été privilégiée pour tenter d’apprécier les modifications climatiques à l’échelle centennale, décennale ou pluriannuelle (i.e., Fairchild et al., 2001 ; McDermott, 2004 ; Bar-Matthews et Ayalon, 2005 ; Losson et al., 2006 ; Lachniet, 2009).

Le site archéologique de Katarraktes est situé dans le nord de la Grèce, dans la province de Macédoine, à 2 km au nord-ouest de Sidirokastro dans le bassin-versant du Krousovitis (fig. 1). La géologie de la région est caractérisée par la forte présence de roches carbonatées de type marbre. On y trouve également des conglomérats et des dépôts d’âge néogène. Le fleuve Krousovitis a creusé de profondes gorges et de nombreuses entrées de grottes affleurent le long des parois de ces dernières. À la faveur d’alternances de phases d’accalmie ou de crise hydrologique, l’installation des populations s’est effectuée à différents niveaux d’altitude dans la vallée. De 2004 à 2008, de nombreuses missions ont mis en évidence l’intense occupation humaine de la grotte de Katarraktes (Poulaki-Pantermali et al., 2006 ; Syros et al., 2008). Situé à 10 m au-dessus du niveau actuel du fleuve, le site archéologique est composé d’un large abri sous roche et de deux pièces annexes. Cet ensemble a essentiellement été utilisé pour le stockage de denrées alimentaires et la préparation culinaire, comme l’atteste les nombreuses graines retrouvées. L’abri principal occupe une superficie de 620 m² pour une hauteur maximale de 34 m. Dans les couches superficielles, de nombreux objets datant de l’Age du Bronze jusqu’à nos jours ont pu être identifiés. Trois phases principales d’occupation ont pu être précisément datées grâce à des datations sur céramique et au radiocarbone. La première phase d’occupation est située à +50 cm par rapport au plancher de la caverne. La deuxième phase est située entre -20 et -30 cm par rapport au plancher est datée de la fin du 4e millénaire avant notre ère. La troisième phase, la plus superficielle, date du début de l’Age du Bronze (charbons datés entre 4550 et 4800 BP). À l’entrée de la grotte, des dépôts colluviaux indiquent des dynamiques de versant dans les gorges du fleuve Krousovitis. La morphologie de la grotte, qui présente un sol plan en pente douce (0-7 %) et des parois plus abruptes (pente maximale : 77 %), a favorisé une sédimentation fine au centre due à une stagnation des eaux en période de fortes crues. Il est d’ailleurs fort probable que durant des phases de forte activité hydrologique, le fond de la grotte ait subi de fréquentes inondations. Les analyses sédimentologiques révèlent la présence de niveaux de charbons et de tessons. Les niveaux argilo-sableux contenant des galets de granite ne peuvent, de toute évidence, avoir été transportés par le fleuve : ils doivent avoir été apportés par l’Homme. A proximité de l’entrée de la grotte, des formations de travertins contenant des tessons de céramique ont été identifiées (fig. 4) à +1 m par rapport au sol de la grotte. Cela indique clairement l’existence de phénomènes d’écoulement des eaux et des sédiments vers l’extérieur, en lien avec des phénomènes d’érosion de paléosols lors de violentes inondations.

Une stalagmite (KTR_01) provenant d’un endroit préservé de la grotte a été prélevée (fig. 4) au regard de son intérêt archéologique. Le spéléothème a été échantillonné pour analyses isotopiques (Hendy, 1971 ; fig. 6). KTR_01 mesure 161 mm de long et 105 mm de diamètre à sa base. Trois échantillons de matière organique ont servi de support à l’analyse isotopique (δ13C). Le rapport isotopique des différents cernes de croissance de la stalagmite a été déterminé pour δ13C et δ18O. De même, 28 échantillons de matériel calcique (fig. 5 ; section S1, 103 mm) situés au-dessus de l’ancienne stalagmite ont été prélevés. La texture de la stalagmite révèle une forte porosité, indiquant un dépôt rapide des carbonates et englobe des niveaux organiques. Les analyses isotopiques ont été utilisées pour mettre en évidence des fluctuations climatiques en lien avec l’occupation de la grotte. Des phases humides et arides se sont succédées de manière très fréquente dans le bassin du fleuve Krousovitis, modifiant ainsi régulièrement les conditions paléoenvironnementales et la morphologie de l’entrée de la grotte. Les phases d’occupation correspondent à des phases de calme hydrologique alors que les phases d’abandon sont synchrones de crues fluviales, les datations par le radiocarbone indiquent que les événements plus catastrophiques ont eu lieu entre 4500 et 5340 BP.

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Table des illustrations

Titre Fig. 1 – Location of the study site.Fig. 1 – Localisation du site étudié.
Légende 1 : Katarraktes cave and rockshelter (see fig. 2) ; 2 : Lake Kerkini. Krousovitis River flows north of Mt. Vrontou (1850 m), forming a wide hydrological basin.1 : grotte et abri sous roche de Katarraktes (voir fig. 2) ; 2 : Lac Kerkini. La rivière Krousovitis s’écoule au nord du Mt. Vrontou (1850 m) et draine un large bassin-versant.
URL http://geomorphologie.revues.org/docannexe/image/7694/img-1.jpg
Fichier image/jpeg, 124k
Titre Fig. 2 – Stratigraphic section of the Krousovitis valley where Katarraktes cave is located.Fig. 2 – Coupe stratigraphique transversale de la vallée de la Krousovitis où est localisée la grotte de Katarraktes.
Légende 1 : marble conglomerate ; 2 : fluvial and colluvial deposits ; 3 : fluvial deposits ; 4 : collapsed blocks ; 5 : cave entrance. The conglomerate represents mainly the Neogene sequence while Quaternary sediments consist of fluvial deposits. See fig. 1 for location.1 : conglomérats de marbre ; 2 : dépôts fluviatiles et colluviaux ; 3 : dépôts fluviatiles ; 4 : blocs effondrés ; 5 : entrée de la grotte. Les conglomérats datent du Néogène tandis que les dépôts fluviatiles sont d'âge quaternaire. Voir fig. 1 pour la localisation.
URL http://geomorphologie.revues.org/docannexe/image/7694/img-2.jpg
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Titre Fig. 3 – Stratigraphic section of the cave sediments according to excavation of the three archaeological phases. Fig. 3 – Coupe stratigraphique réalisée dans les sédiments provenant de la grotte et réalisée à partir des résultats de la fouille des trois niveaux archéologiques.
Légende Stratigraphical infillings consist of fine sediments (clay to fine sand) including granitic pebbles and breccias. The altitude is report is relative to cave floor. 1 : discontinuity surfaces ; 2 : floors of archaeological layers ; 3 : destruction layers, including charcoal deposits ; 4 : residues of spar-based buildings ; 5 : seeds and cereal ; 6 : ceramics ; 7 : tools ; 8 : limestone breccia. The position of the excavated pits is shown in fig. 4. Les remplissages sédimentaires sont constitués d’une matrice constituée de sédiments fins (argiles à sables fins) comprenant des galets de granite et des brèches. L'altitude est exprimée par rapport au plancher de la caverne. 1 : surfaces de discontinuité ; 2 : niveaux archéologiques ; 3 : niveaux de destruction comprenant des dépôts de charbon ; 4 : résidus de bâtiment ; 5 : graines et céréales ; 6 : céramiques ; 7 : outils ; 8 : brèche calcaire. La position des fosses creusées est indiquée sur fig. 4.
URL http://geomorphologie.revues.org/docannexe/image/7694/img-3.jpg
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Titre Fig. 4 – Ground plan of the cave (contour lines express altitude relatively to m asl). Fig. 4 – Plan du sol de la grotte (les isohypses sont exprimées par rapport au niveau moyen de la mer).
Légende 1: fragments of pottery included in the travertine; 2: sampling position of the KTR_01 stalagmite; 3: travertine formation. Limestone breccia also visible in the inset picture; 4: cave entrance; 5: position of the excavation pits (corresponding also to fig. 3); 6: area under the rockshelter, also visible from external view in the inset picture.1 : fragments de poterie incorporés dans des dépôts de travertin ; 2 : point d'échantillonnage de la stalagmite KTR_01 ; 3 : formation travertineuse (brèche calcaire visible également sur l'image d'insert) ; 4 : entrée de la cave ; 5 : position des fosses de fouille (voir aussi fig. 3) ; 6 : secteur sous l'abri (également visible depuis l'extérieur dans l'image d'insert).
URL http://geomorphologie.revues.org/docannexe/image/7694/img-4.jpg
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Titre Fig. 5 – Longitudinal cut section of KTR_01 stalagmite (Katarraktes cave).Fig. 5 – Profil longitudinal de la stalagmite KTR_01 (grotte de Kattaraktes).
Légende Black-dots : sub-sampling positions for isotopic analysis (small black-dots indicate the sub-samples for the Hendy-tests) ; S1 : sampling section ; OG_## : sampling positions of organic matter ; OS : old stalagmite formation ; BS : sedimentary series under the stalagmite.Les cercles noirs indiquent les lieux de prélèvement pour l’analyse isotopique (les plus petits cercles noirs indiquent les sous-échantillons pour les Hendy-Tests) ; S1 : section prélevée ; OG_## : position des échantillons de matière organique prélevés ; OS : ancienne formation de stalagmite ; BS : couches sédimentaires sous la stalagmite.
URL http://geomorphologie.revues.org/docannexe/image/7694/img-5.jpg
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Titre Fig. 6 – Plots showing the δ18O and δ13C variations (VPDB) for representative different laminae (A :3, B :10, C :16, D :21, E :27) of KTR_01 stalagmite as measured along the length of the laminae Fig. 6 – Variations du rapport isotopique (δ18O-δ13C) (VPDB) des différentes laminae (A :3, B :10, C :16, D :21, E :27) de la stalagmite KTR_01
Légende (see also fig. 5). The isotopic trends indicate minor variations in δ18O and wider variations in δ13C. These trends are in accordance with suggested criteria for equilibrium (Hendy, 1971).(voir aussi fig. 5). Les variations isotopiques correspondent à des variations mineures pour δ18O mais plus importantes pour δ13C. Ces variations sont en accord avec les critères suggérés pour l'équilibre isotopique (Hendy, 1971).
URL http://geomorphologie.revues.org/docannexe/image/7694/img-6.jpg
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Titre Fig. 7 – Results of isotopic measurements (VPDB) : variation of carbon and oxygen isotopes across sampling section.Fig. 7 – Résultats des mesures isotopiques (VPDB) : variation des isotopes du carbone et de l’oxygène le long de la section échantillonnée.
Légende A and B represent segments of contemporaneous isotopic enrichment. This enrichment indicates drier climatic conditions during precipitation, in contrast to wetter environment during the deposition of the other layers.A et B représentent des segments d’enrichissement isotopique contemporain. L’enrichissement isotopique montre des conditions climatiques plus sèches pendant les phases de précipitations. Les conditions climatiques humides caractérisent quant à elles les autres surfaces.
URL http://geomorphologie.revues.org/docannexe/image/7694/img-7.jpg
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Titre Fig. 8 – Schematic representation of climatic alteration during the development of KTR_01 stalagmite.Fig. 8 – Représentation schématique des modifications climatiques pendant le développement de la stalagmite KTR_01.
Légende A and B represent segments of contemporaneous isotopic enrichment. C covers the assumed period of human occupation of the cave. The date and palaeoclimatic interpretation is developed in text (discussion). A et B représentent des segments d’enrichissement isotopique contemporain. C couvre la période d’occupation humaine de la grotte. L’âge et l’interprétation paléoclimatique sont développés dans le texte (discussion).
URL http://geomorphologie.revues.org/docannexe/image/7694/img-8.jpg
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David Psomiadis, Elissavet Dotsika, Nikoleta Zisi, Christos Pennos, Sophia Pechlivanidou, Konstantinos Albanakis, Anastasios Syros et Markos Vaxevanopoulos, « Geoarchaeological study of Katarraktes cave system (Macedonia, Greece): isotopic evidence for environmental alterations », Géomorphologie : relief, processus, environnement, vol. 15 - n° 4 | 2009, 229-240.

Référence électronique

David Psomiadis, Elissavet Dotsika, Nikoleta Zisi, Christos Pennos, Sophia Pechlivanidou, Konstantinos Albanakis, Anastasios Syros et Markos Vaxevanopoulos, « Geoarchaeological study of Katarraktes cave system (Macedonia, Greece): isotopic evidence for environmental alterations », Géomorphologie : relief, processus, environnement [En ligne], vol. 15 - n° 4 | 2009, mis en ligne le 01 janvier 2012, consulté le 26 mars 2017. URL : http://geomorphologie.revues.org/7694 ; DOI : 10.4000/geomorphologie.7694

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Auteurs

David Psomiadis

NCSR Demokritos, Institute of Materials Science, Aghia Paraskevi, 15310 Attiki, Greece (dapsom@ims.demokritos.gr); Aristotle University of Thessaloniki, Department of Physical and Environmental Geography, School of Geology, 55131 Thessaloniki, Greece

Elissavet Dotsika

NCSR Demokritos, Institute of Materials Science, Aghia Paraskevi, 15310 Attiki, Greece (dapsom@ims.demokritos.gr

Nikoleta Zisi

Aristotle University of Thessaloniki, Department of Geology, School of Geology, 55131 Thessaloniki, Greece); Aristotle University of Thessaloniki, Department of Geology, School of Geology, 55131 Thessaloniki, Greece

Christos Pennos

Aristotle University of Thessaloniki, Department of Physical and Environmental Geography, School of Geology, 55131 Thessaloniki, Greece

Sophia Pechlivanidou

Aristotle University of Thessaloniki, Department of Physical and Environmental Geography, School of Geology, 55131 Thessaloniki, Greece

Konstantinos Albanakis

Aristotle University of Thessaloniki, Department of Physical and Environmental Geography, School of Geology, 55131 Thessaloniki, Greece

Anastasios Syros

Ephorate of Palaeoanthropology and Speleology of Northern Greece, 55131 Thessaloniki, Greece.

Markos Vaxevanopoulos

Ephorate of Palaeoanthropology and Speleology of Northern Greece, 55131 Thessaloniki, Greece

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