Identification and origin of bitumen in Neolithic artefacts from Demirköy Höyük (8100 BC): Comparison with oil seeps and crude oils from southeastern Turkey

Organic Geochemistry Organic Geochemistry 37 (2006) 1752–1767 www.elsevier.com/locate/orggeochem

Identification and origin of bitumen in Neolithic artefacts from Demirko¨y Ho¨yu¨k (8100 BC): Comparison with oil seeps and crude oils from southeastern Turkey J. Connan a

a,*

, O. Kavak b, E. Akin c, M.N. Yalc¸in d, K. Imbus e, J. Zumberge

e

Laboratoire de Ge´ochimie Bioorganique, Universite´ Louis Pasteur, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France b Dicle Universitesi Muhendislik-Mimarlik Fakultesi, Maden Mu¨hendisligi Bolu¨mu¨, 21280 Diyarbakir, Turkey c Dicle Universitesi Fen-Edebiyat Fakultesi Arkeoloji Bolumu, 21280 Diyarbakir, Turkey d Istanbul Universitesi, Muhendislik Fakultesi, 34850 Avcilar, Istanbul, Turkey e GeoMark Research Ltd., 9748 Whitthorn Drive, Houston, TX 77095, USA Available online 20 October 2006

Abstract Two ring-like artefacts from the aceramic Neolithic site of Demirko¨y Ho¨yu¨k in southeastern Turkey were analysed using geochemical techniques in order to determine whether they were prepared using a bitumen amalgam or not. The artefacts, dated 8100 BC, are early evidence of the innovative use of a petroleum-based material to prepare pieces of ornaments (beads, rings, etc.) for the elite of a Neolithic settlement. In order to trace the source of the presumed bitumen, two oil seeps, Bog˘azko¨y and Yesßilli, were sampled. To complete the genetic references, geochemical data on crude oils from the main oil fields from the area were compiled. Basic geochemical data show that bitumen is present in the artefacts. Sterane and terpane patterns, as well as carbon isotopic data on C15+ saturated and C15+ aromatic hydrocarbons, allowed us to conclude that the Demirko¨y Ho¨yu¨k bitumen and the Bog˘azko¨y oil seep were generated from a Silurian source rock. The detailed geochemical characteristics show, however, that the Demirko¨y Ho¨yu¨k bitumen does not correlate perfectly with the Bog˘azko¨y oil. This discrepancy suggests several explanations: the real bitumen source may be elsewhere in the vicinity and has not been discovered or was at the Bog˘azko¨y oil seep location but with slightly different properties in Neolithic times, or has disappeared. Another possibility is that the slight molecular differences are due to weathering effects, which affected the pristine bitumen within the archaeological sample.  2006 Elsevier Ltd. All rights reserved.

1. Introduction Two ring-like objects with a diameter of a few cm have been discovered among the artefacts made by the inhabitants of Demirko¨y Ho¨yu¨k, an aceramic Neo*

Corresponding author. Tel.: +33 5 59149244. E-mail address: [email protected] (J. Connan).

lithic site located on the west bank of the Batman Cayi, a tributary of the Tigris river (Fig. 1). The site was excavated in 1997 by Rosenberg and co-workers (Rosenberg and Inal, 1998). The ring fragments and a cigar shaped bead were ascribed as having been made of a bituminous mixture and are interpreted as pieces of ornaments (necklaces, drop earrings, rings) specially manufactured for the elite of the settlement (Akin

0146-6380/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2006.07.023

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

Fig. 1. Location of samples.

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1754

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

et al., 2005). The objects, which are not the usual jewels but are exceptional, were not like those found at burial sites in the southern Arabian Gulf (Phillips, 2002), where a necklace of Ubaid bitumen beads (5th millennium BC) was discovered in situ. The ring-like objects were excavated from trenches within the habitats of Demirko¨y Ho¨yu¨k and close to each other. According to Rosenberg and Inal (1998), this presumed bitumenbased amalgam represents, with clay, the innovative use of plastic materials to prepare artefacts. Clay was used to make baked figurines and vessels and it was suggested that bitumen, if identified, might have a local source. The Batman area is presently a major petroleum province in Turkey. The goals of this study were primarily to establish that the ring-shaped objects were indeed prepared with a bituminous mixture and, subsequently, to try to determine the bitumen origin by analysing oil seeping in the vicinity of the excavations. During this phase of the study, new goals appeared and a significant effort was then devoted to establishing a correlation between the oil seeps analysed and the oil families in the area. In this respect, the study became a regional petroleum geochemistry investigation. 2. Samples Two archaeological samples (ring-shaped objects nos. 1818 and 1900) were collected from the Diyarbakir Museum (Fig. 2). A binocular examination reveals a likely bituminous mixture with sand grains and some plant imprint. The mixture is hard today and seems to have been shaped and ‘‘polished’’. Polishing, carried out on a dry mixture, is achieved by using obsidian or pebble objects. Along with clay used to make figurines and vessels, the bitumen represents the second innovative use of a plastic material to manufacture artefacts (Rosenberg and Inal, 1998). Two oil seeps (Figs. 1 and 2) were sampled, south of Demirko¨y Ho¨yu¨k, at two locations: Bog˘azko¨y in the Germav-Gercus formation (Palaeocene-Eocene) and Yesßilli in the Hoya formation (Eocene). Bog˘azko¨y occurs as pasty bitumen in non-impregnated clayey rocks, whereas Yesßilli is solid bitumen cementing shaly non-impregnated rocks. 3. Experimental The archaeological samples, as well as the oil seeps, were studied using the same analytical proce-

dures in order to allow a direct comparison of samples. This scheme, conducted at GeoMark Research Ltd., is very much like those applied in previous studies of archaeological bitumens (Connan and Deschesne, 1996; Connan, 1999). The experimental procedure may be summarized as follows: The CH2Cl2 extract, obtained using a soxhlet, was deasphalted using n-hexane. The desasphalted fraction was separated into saturated hydrocarbon, aromatic hydrocarbon and resin (NSO) fractions using gravity flow column chromatography with 100–200 mesh silica gel activated at 400 C prior to use. Hexane was used to elute the saturated hydrocarbons, CH2Cl2 the aromatic hydrocarbons and CH2Cl2/MeOH (50:50) the NSO fraction. Following solvent evaporation, the fractions were quantified gravimetrically (Table 1). The C15+ saturate hydrocarbon fraction was subjected to molecular sieve treatment (Union Carbide S-115 powder) after the technique described by West et al. (1990), in order to concentrate the branched/cyclic fraction. Stable carbon isotopic composition (13C/12C) of the C15+ saturate and C15+ aromatic hydrocarbon fractions was determined using the combustion technique of Sofer (1980) and a Finnigan Delta E isotope ratio mass spectrometer. Gas chromatography/mass spectrometry (GC/ MS) analysis of C15+ branched and cyclic hydrocarbon fractions was performed using a HP5890 GC (splitless injection) interfaced with a HP5971 mass spectrometer. An HP-2 column (50 m · 0.2 mm; 0.11 lm film thickness) was programmed from 150 to 325 C at 2 C/min and held for 10 min. The spectrometer was run in the selected ion mode (SIM), monitoring ions at m/z 177, 191, 205, 217, 218, 221, 231 and 259. For the aromatic fraction, m/z 133, 178, 184, 192, 198, 231, 245, 239 and 253 ions were monitored. In order to determine absolute concentrations of individual biomarkers, a deuterated internal standard (d4-C29aaa20R sterane, Chiron Lab, Norway) was added to the C15+ branched/cyclic hydrocarbon fraction. Response factors (RFs) were determined by comparing the mass spectral response at m/z 221 for the deuterated standard to hopane (m/z 191) and sterane (m/z 217) authentic standards. The RFs were ca. 1.4 for terpanes and 1.0 for steranes. Concentrations of individual biomarkers were determined using the following equation: Conc. (ppm) = (Peak height biomarker)(ng standard)/(Peak height standard)(RF)(mg B/C fraction).

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

1755

Fig. 2. Photograph of the archaeological samples excavated at Demirko¨y Ho¨yu¨k and of outcrops with oil seeps at Bog˘azko¨y and Yesßilli. Gross composition of extractable organic matter.

59.5 18.5

18.4

4.1. Gross properties (Table 1)

3.6 Refers to the formation in which the samples were discovered. a

Oil seep Yesßilli 1902

Geological

Germav-Gercus (Palaeocene-Eocene) Hoya of Midyat group (Eocene) Oil seep Bog˘azko¨y 1901

Geological

Selmoa (Pliocene) Ring-like artefacts Demirko¨y Ho¨yu¨k 1900

8100 BC

4. Results and discussion

15.15

32.6 21.2 26.8 19.4 12

41.6

68.1 27.7 2.1 2.1 4.7

resins

41.7 11.1

aro. sat.

5.6 0.7

Bituminous (?) mixture with quartz grains, lamellar minerals (gypsum?) and imprint of dissolved vegetal. The mixture is hard, black and ‘‘polished’’ at surface Bituminous (?) mixture with sand grains and rare plant imprint. The mixture is hard, grey–black and ‘‘polished’’ at the surface Pasty bitumen scraped from nonimpregnated clays Solid bitumen associated with shaly non-impregnated rocks Demirko¨y Ho¨yu¨k 1818

Ring-like artefacts

8100 BC

Selmoa (Pliocene)

Extractable organic matter (wt %) Macroscopic description Formation Approximate date Type Location Sample

Table 1 References and gross composition data for samples (% sat. = % C15+ saturates, % aro. = % C15+ aromatics, % asp. = % asphaltenes)

asp.

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

Gross composition (wt %)

1756

The extractable organic matter from the two archaeological samples represents, respectively, 0.7% and 4.7% weight of the raw sample. Such a concentration is extremely low for a very old bituminous amalgam since the most common concentration for bitumen encountered in archaeological bituminous mixtures from the Near East is around 30% (Connan, 1988, 1999). The content of extractable bitumen in the Ubaid beads (Phillips, 2002) from Umm alQaiwwain is around 15% of the whole mixture, i.e. much greater than in the Demirko¨y Ho¨yu¨k samples. We must underline that the tiny quantities of samples available for analysis did not allow preparation of thin sections to confirm microscopically that the samples were artificial mixtures; however, binocular examination of the raw material (Table 1) revealed the occurrence of sand grains and plant remains which are typical constituents of antique bituminous mixtures intentionally prepared. It should also be noted that the bitumen content measured herein refers only to the soluble part of the bitumen. It is very likely that a significant part of the original bitumen is present today in the artefact as insoluble organic matter formed by weathering (mainly oxidation). Therefore, the bitumen content evaluated via the soluble part alone is certainly underestimated. Nevertheless, the inhabitants of Demirko¨y Ho¨yu¨k did discover how to process bitumen with minerals and fibrous material to prepare a bitumen mastic suitable for moulding various decorative objects. To prepare modern mastics, which are currently manipulated at 180–200 C, 12–16% bitumen has to be incorporated (Forbes, 1964). According to our data on archaeological bituminous mixtures in the near East, it appears common practice to use an excess of bitumen, often more than 30% soluble bitumen, in the samples. This excess entails different mechanical properties: lower viscosity in the heat and a mixture easy to manipulate since it can be poured at lower temperature. Gross compositions of extracts (Table 1) from the archaeological samples, although not identical, are in good agreement with those of bitumen from archeological mixtures (Fig. 2). As usual, the C15+ saturated and C15+ aromatic hydrocarbons are minor components, whereas asphaltenes predominate (Connan et al., 1998; Connan and Nishiaki, 2003). Obviously, the two samples, collected on

Table 2 Basic information (Basin, depth range of reservoir, oil family) of Turkish crude oils used as references and d13C values of C15+ saturates and C15+ aromatics d13C[C15+sat.] = d13C of C15+ saturates (&/PDB), d13C[C15+aro.] = d13C of C15+ aromatics (&/PDB) Location

Oil field

Upper depth of reservoir (feet)

1901 1902 TK01 TK07 TK08 TK10 TK12 TK14 TK15

Bog˘azko¨y Yesßilli Kahta Cemberlitas Akpinar Adiyaman Firat West Cukurtas Karakus

Cemberlitas Cemberlitas East Turkey Cemberlitas Cemberlitas East Turkey East Turkey

TK19 TK21 TK22 TK23 TK24 TK25 TK26

Raman Garzan Magrip Camurlu Dincer Guney Kozluca Bati (South) Bati Raman (South)

Selmo-Raman Selmo-Raman Selmo-Raman Camurlu Camurlu Camurlu Selmo-Raman

656 6332 5873 3183 5332 1378

TK02 TK03 TK05 TK06 TK11 TK13 TK16 Tk17

Kurkan Sahaban Kayakoy Kayakoy-West Yenikoy Sincain Beykan Barbes

Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy Kurkan-Karakoy

2050 5374 5801 5076 3937 4692 2461 5824

TK20

Malatepe

Kurkan-Karakoy

4922

3642 9843 10175 5135 8125

Lower depth of reservoir (feet)

Age of reservoir

Upper Cretaceous Middle Cretaceous Campanian Upper Cretaceous Middle Cretaceous Midlle Cretaceous Campanian

820 6628 6103 5528

Upper Cretaceous Upper Cretaceous Upper Cretaceous Middle Cretaceous Middle Cretaceous

2034

Upper Cretaceous

2658 5883

Middle Middle Middle Middle Middle Middle Middle Middle

4958

Middle Cretaceous

5427 7113 5154 3980

Stable carbon isotope d13C[C15+sat]

3872 9908

8225

Type

Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous

d13C[C15+aro]

Oil seep Oil seep Oil Family 1 (Upper Cretaceous carbonate)

30.38 28.23 28.23 28.07 28.08 28.14 27.74 28.07 27.96

28.67 27.93 27.89 27.1 26.86 27.46 26.92 27.02 26.98

Oil Family 2 (Upper Jurassic/Lower Cretaceous carbonate)

28.18 28.25 27.8 28.39 27.58 27.92 28.66

27.37 27.57 27.06 27.83 27.52 27.81 27.75

Oil Family 4 (Silurian Shales)

29.69 29.83 29.63 29.74 29.64 29.79 29.57 29.76

28.22 28.37 28.12 28.33 28.11 28.44 28.2 28.22

29.91

28.61

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

Sample number

1757

1758

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

two different dates, did not come from the same archaeological artefacts, as their gross composition data are significantly different (Fig. 2). Comparison of archaeological samples to reference oil seeps shows a well known situation, namely the depletion of C15+ aromatic hydrocarbons in archaeological samples, due to their sensitivity to weathering and oxidation (Connan et al., 1992; Lemoine, 1996; Charrie´-Duhaut et al., 2000). The concentration of C15+ saturated hydrocarbons, of the same order of magnitude in Yesßilli bitumen and Demirko¨y Ho¨yu¨k bitumen, is much higher in Bog˘azko¨y oil seep. These results agree with the consistency of oil seeps: Yesßilli is a solid biodegraded oil seep whereas Bog˘azko¨y is still pasty bitumen.

area and from western southeast Anatolia (Fig. 3), used as references. A plot of d13C value of C15+ saturates vs. d13C value of C15+ aromatics in Fig. 4 shows that, if Yesßilli solid bitumen is closer to Family 1 + 2 defined as originating from Cretaceous carbonates, Bog˘azko¨y pasty oil seep is apparently related to Family 4 which was generated from Silurian shales (Zumberge et al., 1992). Family 3 oils, reservoired in Triassic carbonates and presumed to originate from organic-rich Triassic marls (or perhaps older sediments, possibly Infracambrian marls) are not represented in the samples in this study. The isotope values of the Demirko¨y Ho¨yu¨k samples were not acquired due to insufficient quantities of fractions. Archaeological bitumen-to-oil seeps correlation had therefore, to rely on molecular ratios obtained using biomarker chemistry.

4.2. Carbon isotopic composition of C15+ saturated and C15+ aromatic hydrocarbons

4.3. Biomarker chemistry: sterane and terpane ratios Stable carbon isotopic data for C15+ saturated and C15+ aromatic hydrocarbons are listed in Table 2, with those for Turkish crude oils from the same

C15+ branched and cyclic hydrocarbons were analysed using GC/MS in order to examine sterane

38.4 Latitude

Kurkan-Karakoy 11

38.2 13 16

2

Western Southeast Anatolia

20

17

5

3 6

Selmo-Raman

38 14 7

Demirköy Höyük

8 15

22 21

12

26

37.8

19 10 1

37.6

Cemberlitas

37.4

Camurlu 37.2

24 23

25

Longitude

37 38

38.5

39

39.5

40

40.5

41

41.5

Fig. 3. Geographical location of samples and of crude oils used as references.

42

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

1759

At a first glance, the Demirko¨y Ho¨yu¨k samples display sterane and terpane characteristics which are close to those found in the Bog˘azko¨y oil seep. Yesßilli oil seep is completely different and belongs to another genetic family. This preliminary conclusion is consistent with the locations of the samples: the Demirko¨y Ho¨yu¨k archaeological site is closer to the Bog˘azko¨y oil seep than to the Yesßilli one (Figs. 1 and 3). In order to cross check the preliminary conclusions about the origin of oil seeps based on d13C values of C15+ saturates and d13C values of C15+ aromatics, selected ratios, representative of the discriminating characteristics of steranes and terpanes, were compiled (Table 3). These ratios refer to the diagnostic molecular characteristics seen on the patterns: relative amount of diasteranes vs. regular steranes (C27Sdia/C27aaaR = 13b,17a-diacholestane 20S/5a,14a,17a-20S-cholestane), Ts/Tm (18a-22,29, 30-trisnorneohopane/17a-22,29,30-trisnorhopane) ratio widely used to define crude oils in this part of the world (Connan and Nishiaki, 2003), variation in gammacerane (GCRN/C31abHR = Gammacerane/ 17a,21b-22S-30-homohopane) and tricyclic terpane concentration (C24/4/C23/3 = de-E-hopane/C23tricyclopolyprenane). In addition we have considered the gross composition of regular steranes, expressed as % C27 = 5a,14b,17b-20S-cholestane, % C28 =

(m/z 217) and terpane (m/z 191) patterns which are currently used to elaborate genetic parameters allowing the differentiation of various bitumen sources. Steranes (Fig. 5) do not show obvious evidence of biodegradation, as seen in numerous archaeological samples (Connan, 1999). Short chain steranes (C21St and C22St) and C27–C29 steranes are well represented. As striking feature that one may notice is the abundance of diasteranes, C27Sdia and C27Rdia in particular, in Demirko¨y Ho¨yu¨k (nos. 1818 and 1900) and Bog˘azko¨y (no. 1901) samples but not in Yesßilli oil seep, where the regular steranes predominate. Terpanes (Fig. 6) confirm the grouping defined on the basis of steranes: Gammacerane, originating from various sources, namely eukaryotes including ciliates, protozoans, ferns and fungi but also bacteria (Volkman, 2005), is commonly found in marine sediments. Large quantities are often associated with saline and reducing conditions of deposition of the organic matter (Peters and Moldowan, 1993; Ten Haven et al., 1989). In the present study, gammacerane is rather low and comparable in the Demirko¨y Ho¨yu¨k and Bog˘azko¨y samples but is significantly enriched in Yesßilli oil seep. The Yesßilli sample is also differentiated by a lower concentration of tricyclic terpanes.

-26.6 δ13Caro. (‰ / PDB) Oils from Cretaceous carbonates

-26.8 -27

8 15 14

12

22

7

-27.2 19

-27.4

24 10

Oils from Silurian shales

-27.6 -27.8

21 26 23 1

25

-28 11 5

17 16

-28.2

2

-28.4

6

3

-28.6

13

20

δ13Csat. (‰ / PDB)

-28.8 -31

-30.5

-30

-29.5

-29

-28.5

-28

-27.5

-27

Fig. 4. Plot of d13C[C15+sat.], &/PDB vs. d13C[C15+aro.],in &/PDB : comparison of samples and crude oil references.

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J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

Fig. 5. Mass chromatograms (m/z 217) showing distribution of steranes from Bog˘azko¨y, Yesßilli and Demirko¨y Ho¨yu¨k. Significance of abbreviations: C21Ste = 5a,14b,17b-pregnane, C22ste = 5a,14b,17b-20-methylpregnane, 27Sdia = C27diacholestane 20S, 27aaaR = 5a,14a,17a-20R-cholestane, 29abbS = 5a,14b,17b-20S-24-ethylcholestane.

5a,14b,17b-20S-24-methylcholestane and % C29 = 5a,14b,17b-20S-24-ethylcholestane and measured on the m/z 218 mass chromaogram. The gross compositions of regular steranes (Table 3), used elsewhere as a discriminant characteristic for classifying archaeological bitumens, crude oils and oil seeps from the near East (Connan et al., 2005), are represented in a ternary diagram (Fig. 7). If data for Family 1 appear as a well differentiated population (Fig. 7a), all other data (crude oils from Family 2 and 4, Bog˘azko¨y and Yesßilli oil seeps, Demirko¨y Ho¨yu¨k archaeological samples, Fig. 7a and b) cluster in the same area of the diagrams. In particular, the regular sterane distribution, based on abb-20S-steranes, is unable to differentiate Family 2 and 4, but places Family 1 well apart. The differentiation of genetic families as well as the identification of the possible source rocks of the oil seeps and archaeological bitumen is achieved

by using the above ratios. They are represented in Fig. 8 (a: GCRN/C31abHR vs. C24/4/C23/3, b: C27Sdia/C27aaaR vs. Ts/Tm) and Fig. 9 (a: STER/ TERP vs. C27Sdia/C27aaaR, b: GCRN/C31abH vs. Ts/Tm). Figs. 8 and 9 strengthen what was seen with the regular sterane composition: none of the samples analysed shows genetic affinities with the crude oils of Family 1. Bog˘azko¨y and Yesßilli oil seeps, well differentiated, do not belong to the same genetic family. Bog˘azko¨y oil seep exhibits close molecular affinities with Family 4 (Figs. 8b and 9b) but also some discrepancies exist (Fig. 9a). Data from Demirko¨y Ho¨yu¨k archaeological samples are generally in the vicinity of the Bog˘azko¨y sample (Figs. 8 and 9). The Yesßilli oil seep matches the data for Family 2 (Figs. 8 and 9). The crude oils from producing wells in Turkey were separated into genetic families (1–4) using multivariate statistics (cluster and principal component

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

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Fig. 6. Mass chromatograms (m/z 191) showing distribution of terpanes from Bog˘azko¨y, Yesßilli and Demirko¨y Ho¨yu¨k. Significance of abbreviations: 23/3 = C23tricyclopolyprenane, 24/3 = C24tricyclopolyprenane, Ts = 18a-22,29,30-trisnorneohopane, Tm = 17a-22,29,30trisnorhopane, C29abH = 17a,21b-30-norhopane, C30abH = 17a,21b-hopane, C31abHR = 17a,21b-22R-30-homohopane, C35abHR = 17a,21b-22R-29-pentakishomohopane.

analyses) employing biomarker and carbon isotope ratios (Zumberge et al., 1992). Based on certain terpane ratios (e.g., C29/C30hopane, C24/C23 tricyclic terpane), Families 1 + 2 derive from marine carbonate source rocks and likely correspond to Cretaceous source rocks described by Iztan et al. (1991). Family 4 oils were clearly generated from distal marine shale sources, again based on distinctive biomarker ratios (Peters and Moldowan, 1993). Furthermore, Family 4 oils correlated with oils in Central Saudi Arabia known to be sourced from the basal Silurian ‘hot shale (Mahmoud et al., 1992). The locations of oil Family 1 (Cretaceous carbonate source), Family 2 (Cretaceous/Jurassic carbonate source) and Family 4 (Silurian shale source) is illustrated in Fig. 10. As clearly seen, the Bog˘azko¨y and Yesßilli oil seeps, as well as Demirko¨y Ho¨yu¨k archaeological samples, are from the same geographical area as Families 2 and 4. Family

1 oils, located westward, do not correlate with the seep samples. The Yesßilli oil seep is located in the vicinity of Camurlu oils, which belong to Family 2; the Bog˘azko¨y oil seep and Demirko¨y Ho¨yu¨k archaeological bitumens are located in the vicinity of Selmo-Raman oil fields where crude oils are also grouped with Family 2. Their oil field counterparts, namely Kurkan-Karakoy, in which crude oils from the Palaeozoic Family 4 cluster are, however, not too far from their locations. Family 4 oils, although reservoired in the Turonian Karababa dolomite/limestone formations, show a marine shale source signature. Their close compositional relationship with Palaeozoic Saudi Arabia oils (Zumberge et al., 1992), suggests that their origin is from Silurian shales which occur in the Dadas Formation (Soylu, 1987). Soylu (1987) divided the Dadas Formation into three members (Dadas I to III) and the more likely source rocks

Sample reference

Source rockd

Molecular ratios on steranes and terpanes Ts/Tm

GCRN/ C31abHR

Steranes/ Terpanes

C24/4/ C23/3

1901 1902 TK01 TK07 TK08 TK10 TK12 TK14 TK15

2.27 0.42 0.19 0.27 0.5 0.24 0.32 0.49 0.28

0.52 0.22 0.52 1.08 1.52 0.56 1.64 2.31 1.23

0.31 0.81 0.8 0.49 1.41 0.49 0.43 0.82 0.57

0.28 0.07 0.47 0.87 1.3 0.66 0.78 1.2 0.87

0.74 1.55 0.18 0.29 0.26 0.28 0.26 0.3 0.29

TK19 TK23 TK24 TK26

0.3 0.31 0.16 0.26

0.28 0.42 0.31 0.21

0.48 0.71 0.6 0.6

0.29 0.25 0.22 0.26

TK02 TK03 TK05 TK06 TK11 TK13 TK16 TK17 TK20

1.65 1.65 1.59 1.67 1.82 1.63 1.71 1.7 2.01

0.94 0.89 0.82 0.98 0.83 0.95 0.92 0.85 1.01

0.25 0.23 0.09 0.22 0.23 0.09 0.14 0.19 0.25

1818

1.26

0.89

1900

1.72

0.64

Depositional environmentd

Whole oil characteristics

Sterane composition based on abbS

Maturityd

Degree of biodegradationd

%C27

%C28

%C29

Biodegraded Biodegraded Biodegraded Non-degraded Non-degraded Mild biodegradation Non-degraded Non-degraded Non-degraded

33.9 29.2 38.7 38.3 38.9 39.1 36.3 35.1 38.5

25 23.7 36.3 36.1 34.5 35.6 34.3 36.8 35.2

41.1 47.1 25 25.6 26.6 25.3 29.4 28.1 26.3

Marine carbonate

Family 1a (Upper Cretaceous)

Moderate Moderate Moderate Low Moderate High Moderate

1.07 1.2 1.23 1.21

Marine carbonate

Family 2b (Upper Jurassic/lower Cretaceous)

low

Non-degraded Mild biodegradation Non-degraded Non-degraded

33.2 31.6 34 34.2

27.9 26.5 25.3 25.3

38.9 41.9 40.7 40.5

0.86 1.03 0.83 1.01 0.86 1.06 0.86 0.99 1.1

0.3 0.27 0.31 0.26 0.33 0.29 0.26 0.3 0.28

Distal marine shale

Family 4a (Silurian shales)

Moderate

Non-degraded

33.8 33.2 34.5 32 32.1 32.3 33.9 31.1 34.9

26 24.7 23.9 24.9 25.3 24.6 26.7 24 23.1

40.2 42.1 41.6 43.1 42.6 43.1 39.4 44.9 42

0.24

0.45

0.22

31.3

30.1

38.6

0.28

0.29

0.49

33.6

27.5

38.9

Family 4c (Silurian shales)

Abbreviations: C27Sdia/C27aaaR = C27diacholestane 20S/5a,14a,17a-20R-cholestane, Ts/Tm = 18a-22,29,30-trisnorneohopane/17a-22,29,30-trisnorhopane, GCRN/C31abHR = gammacerane/17a,21b-22R-homohopane, Steranes/Terpanes = Steranes/Terpanes measured on total steranes (from C27Sdia to C29aaaR) and total terpanes (from Ts to C35abHR), C24/4/C23/3 = de-E-hopane/C23tricyclopolyprenane, % C27 = % 5a,14b,17b-20S-cholestane, % C28 = % 5a,14b,17b-20S-24-methylcholestane, % C29 = % 5a,14b,17b-20S-24ethylcholestane. a Probable. b Suspected. c Present study. d After Zumberge et al., 1992.

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

C27Sdia/ C27aaaR

Oil familyd Age of source rockd

1762

Table 3 Basic geochemical information (depositional environment of source rock, maturity and biodegradation of whole oil after Zumberge et al., 1992) and biomarker ratios on reference crude oils and samples

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

a

% C28

1763

S

100 %

Family 1 (Upper Cretaceous)

50 % Family 2&4 40 Bo azköy-Demirköy Ye illi

% C29

10

% C27

S

100 % 0 -5

-25

50 %

S

100 % 15

50 55%

35

75

9

15

b % C28

S

100 %

Demirköy Höyük Family 2 Upper Jurassic50 Lower Cretaceous

% C29

10

50 %

50 %

Ye illi

S

Bo azköy

100 % 0

50 %

% C27

S

100 %

Fig. 7. Ternary diagram showing distribution of regular steranes as % C27abbS, % C28abbS, % C29abbS: comparaison of samples with data for reference oils from the same area for significance of abbreviations: see Table 3.

are associated with Dadas I and III members. The d13C values of their satutated and aromatic hydrocarbons are fully consistent with values inherent in crude oils of Family 4. Oils of Family 2 are reservoired in different limestones. They are suspected to have originated from Upper Jurassic/Lower Cretaceous carbonates, based on lower sterane C28/C29 ratios, likely related to source age. Oils of Family 1 are defined as probably generated from Upper Marine Cretaceous source rocks. Among potential source rocks within this interval the following formations are quoted: the Derdere Formation, the Ortabag For-

mation, the Kiradag Formation, the Karababa Formation, the Karabogaz Formation (Soylu, 1991; Wagner and Pehlivan, 1987) and the Kastel Formation, covering the whole Upper Cretaceous interval from Maastrichtian to Cenomanian. Iztan et al. (1991) suggested that the wackstone of the lower part of Derdere limestones is the likely source rock of the Raman oil field and that the muddy carbonates of the Karabogaz Formation are possible source rocks in the western part of our study, i.e. for Family 1. Limestones of the Karababa Formation have also contributed to oil fields in the western part (Soylu et al., 2005).

1764

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767 GCRN / C31αβHR

C27Sdia / C27αααR

1.6

2.5

a

b

8

1.4

2 1.2

1900 Demirköy Höyük

17 5

1

Family 1 (Upper Cretaceous)

14

23

1

24

15 26

19

10

Family 2 (Upper Jurassic/Lower Cretaceous)

7 12

0.4

Demirköy Höyük (1818)

11

6-3

0.2

Family 2 (Upper Jurassic/Lower Cretaceous)

20-2

16

17

0 0

0.2

8

0.4

19

0.6

C24/4 / C23/3

7

23

26

Family 4 (Silurian)

Family 1 (Upper Cretaceous)

0.5

Demirköy Höyük (1900)

5

13

13 2

1818 Demirköy Höyük

0.8

0.6

Family 4 (Silurian)

6 3

1.5

1

20

11 16

10

14 12

15

1

24

Ts / Tm

0 0.8

1

1.2

1.4

1.6

1.8

0

0.5

1

1.5

2

2.5

Fig. 8. Plot of GCRN/C31abHR vs. C24/4/C23/3 and C27Sdia/C27aaaR vs. Ts/Tm: comparison of samples with reference oils.

STER / TERP

GCRN / C31αβHS

1.4

1.2

1.6

a

Family 4 (Silurian)

8

b 1.4 8

14 13 3

1.2

6

1 7

17

Family 1 (Upper Cretaceous)

15

Family 2 (Upper Jurassic/Lower Cretaceous)

20

2 16

11

1

5

Family 1 (Upper Cretaceous)

0.8 12

0.8 23

10

14

1

0.6 26

24

0.6

Demirköy Höyük

1

19

10

15

0.4 19 26 24

0.2

0.4

Family 2 (Upper Jurassic/Lower Cretaceous)

3 2

23

12

7

11

0.2

1900-1818 Demirköy Höyük

C27Sdia / C27αααR

20 6

17 5

16 13

Family 4 (Silurian)

Ts / Tm

0

0 0

0.5

1

1.5

2

2.5

0

0.5

1

1.5

2

2.5

Fig. 9. Plot of STER/TERP vs. C27Sdia/C27aaaR and GCRN/C31abHS vs. Ts/Tm: comparison of samples with reference oils. Significance of abbreviations: see Table 3.

If it seems established that the bitumen from Demirko¨y Ho¨yu¨k artefacts and the Bog˘azko¨y oil seep belong to the same genetic family, most clo-

sely Family 4, one should notice that the molecular characteristics of the archaeological samples are not identical to those of the oil seep. For instance,

J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

38.4

Latitude

Family 4

Kurkan-Kayaköy 11

38.2 13 16

1765

2

20

17

Demirköy Höyük

5

3 6

Selmo-Raman

38 Western Southeast Anatolia 14

15

7

22

8 21

12

26

37.8

19 10

Family 1

1

37.6

Cemberlitas

Family 2

37.4

Camurlu

37.2

24 23

25

Longitude

37 38

38.5

39

39.5

40

40.5

41

41.5

42

Fig. 10. Genetic relationship between oils seep, archaeological bitumen of Demirko¨y Ho¨yu¨k and oils from main oil fields of the same geographical area.

the Demirko¨y Ho¨yu¨k terpanes (Fig. 5) are richer in tricyclic terpanes (C23/3 to C30/3) and neohopanes (cf. Ts/Tm) and the steranes mimic these variations, with more short chain steranes in the Demirko¨y Ho¨yu¨k samples. These differences may be interpreted as linked to variations in the degrees of maturity of bitumen or lithology effects (Peters and Moldowan, 1993). Considering the terpane patterns as reference, one may conclude that the Demirko¨y Ho¨yu¨k bitumen is slightly more mature than the Bog˘azko¨y oil. When considering the aromatic steroids, however, one may notice a higher triaromatic to monoaromatic steroid ratio in Bog˘azko¨y than in Demirko¨y Ho¨yu¨k, which suggests a greater maturity for the former. For the monoaromatics, more rearranged structures in the Bog˘azko¨y seep may reflect more clayey lithology for Bog˘azko¨y source rocks. Consequently, if the explanation of the molecular changes recorded between the archaeological and the geological samples is not clear, it remains a fact that the molecu-

lar fingerprints are not identical. If Bog˘azko¨y oil seeps provide a good geological analogue for the Demirko¨y Ho¨yu¨k bitumens, another bitumen source, yet to be found in the same area, may be the real one. One should consider that this antique source, used by Neolithic inhabitants may have disappeared as a result of erosion, collapse, human mining, etc. This possibility should always be kept in mind when aiming to reconstruct antic situations. A demonstrative example of the difficulties encountered was described recently by Jasim et al. (2005). They studied a large Neolithic graveyard in the Emirates and the main question raised was: why a Neolithic graveyard, containing up to 1000 inhumations, should occur in a present desert-type situation. The answer came from the excavations when it was discovered on the slope of the graveyard that patches of water had laid sinter. At Neolithic time the area was a spring mouth, a key point for populations which were nomadic herders.

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J. Connan et al. / Organic Geochemistry 37 (2006) 1752–1767

5. Conclusions

Acknowledgements

The two ring-shaped artefacts from the aceramic Neolithic site of Demirko¨y Ho¨yu¨k on the west bank of the Batman Cayi, a tributary of the Tigris River, have been shown to be bitumen-based amalgams. This bituminous mixture, moulded to create exceptional ornaments for the elite of Demirko¨y Ho¨yu¨k, represents, with clay, an innovative use of plastic material to prepare artefacts. These artefacts are dated at 8100 BC. Surprisingly, the content of bitumen is not high for extractable organic matter, representing 0.7 and 4.7 wt.% of the raw samples. This situation contrasts with that usually observed for archaeological mixtures where 30% is the average value recorded in many sites. These quantities were obviously adequate for obtaining mixtures suitable for moulding beads or rings, which would subsequently be polished prior to use as ornaments (necklaces, drop earrings, rings, etc.). The geological origin of the bitumen has been recognised for the Demirko¨y Ho¨yu¨k bitumen and belongs to the Silurian shales family, represented in the Kukan-Karakoy oil field. Two oil seeps, Bog˘azko¨y and Yesßilli, which were likely collected by the Neolithic populations, were sampled. Yesßilli, the farthest from Demirko¨y Ho¨yu¨k, shows geochemical properties consistent with crude oils from the Camurlu and Selmo-Raman oil fields. These oils originate from Cretaceous/Jurassic carbonate source rocks. The Yesßilli oil seep is not the source of the Demirko¨y Ho¨yu¨k bitumen. Bog˘azko¨y seep oil belongs to the same genetic family as Demirko¨y Ho¨yu¨k bitumen, likely generated from Silurian shales. Bog˘azko¨y oil seep appears as a likely candidate for the bitumen of Demirko¨y Ho¨yu¨k; however, a perfect geochemical match is not achieved when considering the molecular characteristics of the two sample sets. Consequently, the present day Bog˘azko¨y oil seep may be not the real source of the Demirko¨y Ho¨yu¨k bitumen. This conclusion suggests several hypotheses: the true bitumen source has to be discovered in another oil seep, or the source sampled in Neolithic time at Bog˘azko¨y was different from the present day one and has since disappeared, or the discrepancies between Bog˘azko¨y and Demirko¨y Ho¨yu¨k bitumen are due to different weathering histories. What is certainly apparent is that the Demirko¨y Ho¨yu¨k bitumen is closely related to the Bog˘azko¨y one but from a geochemical standpoint it is not strictly identical.

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