Molecular archaeology: Export of Dead Sea asphalt to Canaan and Egypt in the Chalcolithic-Early Bronze Age (4th-3rd millennium BC

Geochimica el Cosmochimica Acra Vol. 56, pp. 2743-2759 Cop&h1 0 1992 Pergamon Prcs Ltd. Printed in U.S.A.

0016-7037/92/s5.00 + 00

Molecular archaeology: Export of Dead Sea asphalt to Canaan and Egypt in the Chalcolithic-Early Bronze Age (4th-3rd millennium BC)

JACQUES CONNAN, ’ ARIE NISSENBAUM, * and DANIEL DESSORT ’ ‘Elf Aquitaine, CSTJF, 640 I8 Pau-Cedex, France. ‘Weizmann Institute of Science, Rehovot, 76100 Israel.

(Received March 14, 1991; accepled in revisedform April 6, 1992)

Abstract-Nine archaeological bitumens from excavations in Canaan, Sinai, and Egypt (Tel Irani, Ein Zik, Palmahim, Tel Arad, Jerusalem, Ein Besor-Site H, Sheik Awad, and Maadi), dated 3900-2200 BC, and two natural asphalts of the Dead Sea area (Ein Gedi floating blocks and Nahal Heimar) have been compared using the following geochemical techniques: chloroform extraction and GC and GC-MS analyses of C,,, alkanes and Cls+ aromatics, isotopic analysis ( 613C and 6D) on chloroform extracts and asphahenes, and Rock-Eva1 pyrolysis of the insoluble organic residue.

All samples are genetically related and are different from other archaeological bitumens from Syria and Iraq. Tel Irani archaeological bitumen was found to be identical to the floating block asphalts of the Dead Sea. Other archaeological bitumens were recognized as having been weathered and biodegraded to various degrees at archaeological sites in the course of the millennia. They are regarded as counterparts of floating block asphalts altered by aging.

This study is the first evidence of the trade and export of raw bitumens from the Dead Sea area within Canaan and to Egyptian trading centers on the mainland route to Egypt between 3900 and 2200 BC, prior to the extensive utilization of bitumen for mummification in ancient Egypt.

INTRODLJCTION

TRADE BETWEEN THE LAND of Canaan and Egypt is anchored in ancient times. Although written documentation about this trade is abundant in Canaan (the Bible states, “And the horses which Solomon brought out of Egypt,” 1 Rings 10:28) and appears in inscriptions and Egyptian wall paintings and pa- pyri, many aspects are still unclear.

The earliest material evidence for this trade is from the Chalcolithic period (4th millennium BC). A few pieces of Egyptian pottery were found in northern Sinai; a fragment of an Egyptian alabaster vessel is known from Ein Gedi, near the Dead Sea; and mollusc shells from the Nile River were found in excavations in southern Israel ( GONEN, 1989 ).

RIZKANA and SEEHER ( 1989) have reviewed the economic implications of the Maadi excavations in Egypt and shown that Chalcolithic strata contain imported items from Canaan. According to these authors, the items of Canaanite origin in Maadi include pottery, basalt bowls and spindle whorls, flint scrapers and blades, and perhaps copper and copper ore. The collapse of the Chalcolithic culture towards the end of the 4th millennium did not sever this trade connection. The booming trade between Egypt and Canaan in the Early Bronze period probably came to an end with the destruction of the Early Bronze cultural stage, and, although some trade may have continued, a major revival occurred only hundreds of years later.

There is an abundance of Egyptian trade items in archaeological excavations in Canaan, but it is not always clear what was exported from Canaan to Egypt. Since the land of Canaan was poor in natural resources other than agricultural products, it seems reasonable to consider that products such as wheat, barley, honey, and olive oil were transported by land to Egypt ( BEN-T• R, 1986). It has been suggested that perhaps other low-volume, high-priced items such as cos-

metics and tree resins were also exported. However, until now, no unequivocal evidence for perishable Canaanite items in Egypt was available.

This study demonstrates that detailed organic geochemical analysis permits the identification in Maadi excavations (3900-3500 BC) in Egypt of asphalt imported from the Dead Sea and enables the reconstruction ofthe bitumen trade routes within Canaan and to Egypt.

USES OF DEAD SEA BITUMEN IN ANTIQUITY

Natural asphalts were widely used in the ancient world. Perhaps their earliest use was in making reed baskets im- permeable to liquids. Evidence for this was found in the pre- ceramic Neolithic excavation of Gilgal, Israel, dating back to about 9000 BC (Connan and Nissenbaum, unpubl. data), and in the Neolithic excavation of Beidha (9000-6500 BC; KIRKBRIDE, 199 1 ), north of Petra in Jordan. A common use in ancient Mesopotamia was its utilization as building material and particularly as mortar and cement. For example, in the story of the Tower of Babel, “and slime they had for mortar” (Genesis 11:3), where “slime” is a translation of the Hebrew word “hemar,” which means asphalt. Natural asphalt was used to pave roads, to waterproof pipes, to caulk boats, to make fire, and to make jewelry, as well as for agricultural uses as a protection against insects, for decorative purposes, for use in medicine and magic, and for use as an adhesive (FORBES, 1964; NISSENBAUM, 1978; CONNAN and DESCHESNE, 199 1). The major uses of Dead Sea asphalt in the periods up to the Chalcolithic were probably for the gluing of flint inserts to wooden handles (e.g., in the Canaanite city of Tel Arad; NISSENBAUM et al., 1984), for waterproofing vessels, and for medical uses.

The most extraordinary use of Dead Sea bitumen has been its later utilization as one ingredient of balms in Egyptian

2743

2144 J. Connan, A. Nissenbaum, and D. Dessert

mummies. Indeed, a long-standing controversy between ancient historians, who claimed the export of Dead Sea asphalt to Egypt, and modem Egyptologists, who disputed this claim, was solved only recently when geochemical analysis showed the presence of Dead Sea asphalt in mummies dated from 1200 BC to 300 AD ( RULLK~TTER and NISSENBAUM, 1988;

CONNAN and DESSORT, 1989, 199 1). Since asphalt is found in only a few localities in Egypt (in oil springs at Jebel Zeit, termed Mons Petrolius by the Romans, or in sandstones at Helwan, south of Cairo; ABRAHAM, 1960), the widespread demand for it in that country led to its becoming a significant trade item. Recent analyses of balms contained in mummies (CONNAN and DESSORT, 1991) confirm this statement by showing that bitumens identified in balms originate from at least two sources: the Dead Sea area, and the Hit-Abu Jir area in Iraq. The trade in Dead Sea bitumens probably became extremely important after 1500 BC, when mummification was widespread, but may have started much earlier, perhaps because their purity facilitated their use in ancient civilizations with relatively primitive technologies.

MATERIALS AND METHODS

Materials

Samples of Dead Sea asphalts for this study were taken from the remnants of a floating block ( NISSENBAUM et al., 1980) found onshore north of Kibbutz Ein Gedi (Fig. I ). Nahal Heimar asphalts (Fig. I), collected from a recent seep (probably three or four years old) in an Upper Cretaceous dolomite, were chosen as being typical for biodegraded asphalts in which the biological marker composition may have been a&ted (RULLK~ITER et al., 1985).

Archaeological asphalt was found in Chalcolithic and Early Bronze Age excavations from various sites in mainland Egypt, the Sinai Pen- insula, and southern and central Israel (Fig. I ). The asphalt occurs as black lumps, occasionally reaching weights of up to I kg (e.g., at Maadi; RIZKANA and SEEHER, 1989), and showing no evidence of any treatment. In hand specimens, they are an exact match for the natural asphalt blocks from the Dead Sea.

In this study, we analyzed samples from Ein Besor (Site H, Early Bronze Ia. 3200-2900 BC: GOPHNA. 1989). Maadi (Naaada I-Earlv II, 3900-3500 BC; RIZKANA and SEEHE,’ 1984, 1985,’ I989), Ein Zik (Early-Middle Bronze I, 3200-2900 BC), Palmahim (Early Bronze I, 3200-2900 L%C) , and Tel Irani (Early Bronze I, 3200-2900 BC). Site locations are given in Fig. 1. Additional samples from Je- rusalem (Early Bronze IV, 2350-2200 BC), Tel Arad (Early Bronze II, 2900-2650 BC; NISSENBAUM et al., 1984), and Sheik Awad (Early Bronze II, 2350-2200 BC) in southern Sinai (BEIT-ARIEH, 1980) were subsequently analyzed to complete the results of the present study. Maadi black material, found in 1932 by MENGHIN and AMER ( 1936) has been a subject of controversy. Subsequent to his chemical work on this material (based mainly on solubilities in various sol- vents), GANGL ( 1936) concluded that the material is similar to Syrian- Palestinian asphalts, but LUCAS and HARRIS ( 1962), at the same time, ended with a different conclusion, which was that “the black material is an oleo-resin from which the oil of turpentine had been lost.” Later on, Lucas reevaluated the sample and modified the previous diagnosis by regarding the black material as “mainly fatty matter which had become oxidized and partly decomposed” (LUCAS and HARRIS, 1962). On the basis of its solubility in petroleum spirit, LUCAS and HARRIS ( 1962) pointed out that the material “could not be mineral bitumen (asphalt).”

Methods

The analytical procedures used are identical to those already described in previous papers on archaeological bitumens (CONNAN,

FIG. I. Location map for the samples investigated.

1988; CONNAN et al., 1990). Natural asphalts and archaeological samples were extracted using chloroform in a Soxhlet apparatus. The chloroform extract composition was determined by using a Iatroscan MK IV analyzer ( BERRUT and JONATHAN, f984), which provides the percentage of alkanes, aromatics, and polars (i.e., resins plus asphaltenes)

The percentage of asphaltenes is obtained separately when asphaltenes are isolated by precipitation with n-hexane. Isotopic analyses (6D and d “C) were carried out on both the chloroform extract and the asphaltenes fractions.

Deasphalted bitumens were subsequently fractionated into alkanes, aromatics, and resins using an automated medium-pressure liquid chromatography. Alkanes were separated by GC applying the following conditions: column, 50 m X 0.2 I mm i.d., coated with OV I ; film thickness, 0.1 I Hrn; temperature program from 80-300°C at 1.6”C min-I; and Hz as the carrier gas. Aromatics were examined by GC with an apparatus equipped with two detectors, an FID and an FPD. Chromatographic conditions were as follows: column, 50 m X 0.25 mm i.d., coated with SE 54, film thickness, 0. I7 pm; temperature program from 80-300°C at 1.6”C min-‘; and H2 as the carrier gas.

Biological marker distributions were obtained by GC/MS of the saturated and aromatic fractions using a Finn&an 4500 mass spec- trometer coupled with an INCOS data system. The experimental conditions were as follows: column, 60 m X 0.25 mm id., DB5; film thickness, 0.10 Mm; temperature program from 80-300°C at 2.5”C min-‘; and EI = 70 eV.

RESULTS

Previous Geochemical Results on Natural Asphalts from the Dead Sea Area

The area around the Dead Sea has been associated with asphalts for thousands of years. The asphalts are found in certain areas around the Dead Sea, at the surface and in the subsurface. They are encountered in drillings throughout the

Molecular structure of archaeological asphalts 2145

EIN ZIK A 215

1 PISLMAHIM A

40- ARCHAEOLOGICAL BITUMENSL FROM IRAQ AND SYRIA

(CONNAN,1988,1990)

30-

00 0 10 20 30 40 50 60 70 60 90 1

ASPHALTENES (‘A)

1

FIG. 2. Graph of Sasphaltenes vs. Wchloroform extracts. Comparison of data from this study with data for archaeological bitumens from Iraq (CONNAN, 1988).

rock section down to a depth of 3600 m ( NISSENBAUM and as a cement of dry river gravels and conglomerates. The most GOLDBERG, 1980; TANNENBAUM and AIZENSHTAT, 1985 ). striking occurrence of asphalt is in the form of large pure At the surface, the asphalt occurs as veins, as vug fillings, and asphalt blocks (weighing several tons) occasionally found

TABLE 1. Gross composition data for archaeological bitumens and natural asphalts.

2146 J. Connan, A. Nissenbaum, and D. Dessort

floating on the lake, which are then swept by winds and cur- rents to the shore ( NISSENBAUM et al., 1980). The source of this asphalt is unknown but it presumably originates from thermally immature bituminous chalks of the Upper Cre- taceous age in the middle of the Rift Valley and has migrated upward to the bottom of the Dead Sea ( RULLK~TTER et al., 1985; TANNENBAUM and AIZENSHTAT, 1985).

Dead Sea asphalt is characterized by a high sulfur content (ca. 11% ), richness in asphaltenes and resins, and a moderate amount of n-alkanes. The near-surface samples are heavily biodegraded, but deep samples and the floating blocks are apparently fresh. Biomarker analyses of the asphalts showed a strong predominance of DPEP-type vanadylporphyrins (AIZENSHTAT and SUNDARARAMAN, 1989), a low pristane/ phytane ratio of around 0.5 (NISSENBAUM et al., 1980), a lack of diasteranes, a low ratio of tri- to monoaromatic steroid hydrocarbons, and a high content of gammacerane (RULLK~TTER et al., 1985).

Geochemical Data from this Study

Gross composition

The two natural asphalts are almost completely soluble in chloroform (SPIRO et al., 1983), whereas archaeological samples exhibit diverse behavior with residues ranging from zero to 85% (Fig. 2; Table 1). The residues are organic-carbon-rich, as shown by high TOC values recorded in Maadi

and Ein Besor bitumens (Table 1) . All archaeological samples should, however, be referred to as archaeological bitumens.

The gross composition of the chloroform extracts, separated into asphaltenes, resins, aromatics, and saturates, is given in Table 1 and Fig. 3. The hydrocarbon content of archaeological bitumens is generally low, as previously seen in other archaeological bitumens from Iraq ( CONNAN, 1988) and Syria (CONNAN et al., 1990). As observed elsewhere, archaeological bitumens tend to be severely depleted in hydrocarbons, especially aromatics, compared to natural asphalt counterparts from present-day active oil seepages. In fact, archaeological bitumens are predominantly composed of asphaltenes (Fig. 3) sometimes associated with significant organic residues as in Maadi. Exceptions to this behavior are the Tel Irani archaeological bitumens, which possess a gross composition pattern almost identical to those of the floating block asphalts. Such close chemical similarity suggests that Tel Irani bitumens are probably raw Dead Sea asphalts from the floating blocks. Sulfur data on chloroform extracts and asphaltenes (Table 1) confirm previous results ( AMIT and BEIN, 1979; TANNENBAUM and AIZENSHTAT, 1985; NISSEN- BAUM et al., 1980, 1984), i.e., 6-10% sulfur in surface asphalts and their associated asphaltenes.

Isotopic data

All bitumens of this study show 6 13C values for both chloroform extracts and asphaltenes within the -27.5 to -29.5%0

SATUFATES

AROMATICS

RESINS ARC”AEdoGlCAL BITUMENS

FRDM IRAQ AND SYRIA

ASPHALTENES

(CONNAN,lS89;CONNAN at aL1990)

FIG. 3. Ternary diagram showing the gross composition of chloroform extracts and comparable data for archaeological bitumens from Iraq.


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S”C ASPHALTENES ( %./POB)

FIG. 4. Isotopic composition of asphaltenes (6 “C vs. 6D) comparing bitumens investigated in other archaeological bitumens from the Middle East (CONNAN, 1988; CONNAN et al., 1990).

range (Table 1) . Comparable values have been reported previously in Senonian bituminous source rocks ( TANNENBAUM and AIZENSHTAT, 1985) and in asphalts and asphaltenes ( TANNENBAUM and AIZENSHTAT, 1985; NISSENBAUM et al., 1980) from the Dead Sea area.

Comparison of asphaltene values in a 6 13C vs. 6D diagram (Fig. 4)) including data on other archaeological bitumens from Iraq ( Abu Jir-Hit-Babylon, Tell es-Sawwan, Larsa, and Tell el Oueili ) , Iran ( Susa ) , and Syria ( Ras Shamra and Lat- taquie), clearly indicates that the asphalts in this study are well differentiated from other asphalts of the Middle East.

It should be noted that though 613C values are fairly con- stant in most samples of this study, 6D values in asphaltenes vary from - 106 to -7O%/SMOW. 6D values in asphaltenes tend to increase with the percentage of asphaltenes in the bitumens.

Isotopic data for the chloroform extract (6 “C = -22.8!%/ PDB; 6D = - 130L/SMOW), the asphaltenes (6 13C = -22.8XolPDB; 6D = - 116%0/SMOW), and the insoluble residue (613C = -23.0%/PDB; 6D = -127L/PDB) ofthe Sheik Awad bitumen suggest that this asphalt does not belong to the Dead Sea asphalt family.

this study to numerous

Detailed Analysis of Total Alkane Fraction

Gas chromatograms of total alkanes

Examples of gas chromatograms of total alkanes are reproduced in Fig. 5. All samples contain n-alkanes. However, in Nahal Heimar asphalts, which are clearly biodegraded (AMIT and BEIN, 1979; SPIRO et al., 1983; RULLKO’ITER et al., 1985), the n-alkanes have been almost completely removed by bacterial action.

The characteristics of archaeological bitumens vary between Dead Sea and Nahal Heimar asphalts, as shown in Figs. 5 and 6. Selective removal of n-alkanes by bacteria causes a progressive increase in the ratio of pristane to n-C,, and phytane to n-C,*, allowing us to propose the following biodegradation sequence for the bitumens (Fig. 6): Tel Irani and Maadi asphalts, similar to Dead Sea bitumens, appear to be unaltered; Ein Zik and Ein Besor bitumens are slightly biodegraded; Palmahim and Nahal Heimar asphalts are more drastically biodegraded.

Pristane to phytane ratios (Table 1) show a narrow range of values (e.g., 0.28 to 0.4 I), which is in agreement with published data (SPIRO et al., 1983; RULLK~T~ER et al., 1985)

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FIG. 6. Plot of Log,, (pristane/n-&) vs. Log,, (phytane/n&) reflecting the effect of biodegradation on n-alkanes.

and confirms that all bitumens originate from carbonate source rocks (Senonian bituminous rocks?) deposited in hypersaline environments. Even-over-odd preferences, noticed in n-alkanes (Fig. 5 ) , are in accordance with highly reducing conditions in the depositional environments of the source rocks ( TISSOT, 198 1) .

CC-MS analyses of steranes and terpanes

Analysis of total alkanes by computerized GC-MS gave access to the sterane and terpane distribution patterns presented in Figs. 7 and 8. Molecular ratios related to biomarkers are compiled in Tables 2 and 3.

Sterane distribution patterns (m/z 217; Fig. 7) bear the following similar characteristics: lack of C+& diasteranes, predominance of C2,-CZ9 regular steranes and of CZ1-& short-chain steranes, and an occurrence of subordinate methylsteranes. These distributions match those found in Senonian source rocks (TANNENBAUM and AIZENSHTAT, 1985) and in oils and asphalts (RULLK~TTER et al., 1985; Fig. 9) from the Dead Sea area, as well as those recorded in balms of Egyptian mummies (RULLK~TTER and NISSEN- BAUM, 1988; CONNAN and DESSORT, 1991).

Furthermore, whereas sterane distribution patterns of Dead Sea and Iraqi bitumens are both devoid of diasteranes, their detailed G-G9 regular sterane compositions are clearly different, as shown in Fig. 9. In this figure, sterane patterns of natural and archaeological bitumens from Iraq have been selected from among representative ones, i.e., those unat&cted by severe biodegradation. Intense biodegradation preferen- tially affects C2, steranes ( SEIFERT and MOLDOWAN, 1979;

CHOSSON et al., 199 1 ), as is seen also in Nahal Heimar surface asphalts when old seeps are compared to recent active ones (Fig. 9; based on data from RULLK~~ER et al., 1985 ) .

The sterane distribution pattern of the Sheik Awad bitumen (Fig. 10) exhibits a different fingerprint, in which diasteranes can be easily identified. Bitumens from Jerusalem and Tel Arad display characteristic sterane patterns of the Dead Sea asphalt family.

Terpane distribution patterns are similar as exemplified by the four m/z 191 mass fmgmentograms in Fig. 8. One striking characteristic is the fairly high concentration of gammacerane, which has been observed before by other authors ( TANNENBAUM~~~AIZENSHTAT, 1985; RULLK&TER~~& 1985) and attributed to the hypersaline depositional envi- ronment of the source rocks for the bitumens. A more in- depth examination of terpanes reveals the following properties: dominant families are tricyclopolyprenanes ( CZS,~ to C&,3), 17a(H),21@(H)-hopanes (a@ hopanes), and Tm and Ts; subordinate molecular classes and methyl-hopanes (2~ methyl-aghopanes; SUMMONS and JAHNKE, 1990), and

17@(H), 2 1 (u( H)-hopanes and hexahydrobenzohopanes ( CONNAN and DE&SORT, 1987 ) . A comparison with terpane distribution patterns of archaeological bitumens from Iraq ( CONNAN, 1988) clearly shows well-differentiated molecular properties, as documented in Table 4. Bitumens from Iraq are richer in secohopanes, 2cY-methyl-aphopanes, and hexahydrobenzohopanes but leaner in their proportions of tricyclopolyprenanes ( CZs,~ to C28,3) and gammacerane. In addition, their triterpane-to-sterane ratios are much higher, in- dicating a more abundant bacterial contribution in their source rock kerogen. Consequently, terpane distribution of

Connan, A. Nissenbaum, and D. Desert


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FTG. 8. Terpane distribution patterns (m/z 19 1) for Dead Sea asphalt and three archaeological bitumens.

the bitumens in this study clearly differentiate them from Sea family; however, the fingerprint of the Sheik Awad bi- archaeological asphalts of Iraq. tumen (Fig. 10) is obviously different because tricyclopoly-

Terpane distribution patterns of the bitumens from Je- prenanes are completely lacking and gammacerane is ab- rusalem and Tel Arad are very similar to those of the Dead normally concentrated. Such a distribution has not been


TABLE 2. Characteristic biomarker ratios of terpanes calculated from m/z 19 1 (unless otherwise specified) .*

ARAMETER NUMBER 1 2 3 4 5 6 7 0 9 10 11 12 13 14

I I I I I I I I I I I

I ‘92 I MMM 1 0.70 1 21 1 23.30 1 4.93 1 0.03 1 0.41 1 0.21 1 1.44 1 5.07 1 0.30 1 0.10 1 0.94 1 0.W 1 0 1

I lsb I EIN BfSOR 1 0.00 1 24 1 21.29 1 5.03 1 0.03 1 0.52 1 0.13 1 1.39 1 5.16 1 0.26 1 0.09 1 0.50 1 0.01 1 0 1

I 214 I m IRAN, 1 0.74 1 25 1 23.30 1 3.22 1 0.01 1 0.30 1 0.11 1 1.45 1 5.11 1 0.24 1 0.10 1 0.49 1 0.01 1 0 1

I 215 I EIN ZIU 1 0.90 1 25 1 37.60 1 4.02 1 0.01 1 0.41 1 0.15 ) 1.30 1 5.90 1 0.19 1 0.06 1 0.50 1 0.01 1 0 1

I ! I I I I I I I I I I I I I I I 1

* List of abbreviations: I. CZ9H = 17a( H),2 l/3( H)-norhopane (C&3H), and C30H = 17a( H),2 I@( H)-hopane (Cw&H); 2. Tm = 1701( H)-22,29,30-trinozhopane, and Ts = 18a( H)-22,29,30-trinozhopane; 3. 23 / 3 = CZj tricyclopolyprenane, and 24/4 = Cz4 17,21 secohopane (CZ4 tetracyclic terpane); 4. 21st = 5a(H),l4B(H),17@(H)-pregnane (from m/z217); 5. 29/ 5 = 17-methyl-28,30-dinorhopane; 6. Cm = gammacerane; 7. 35/6 = hexahydrobenzohopane (C,,), and 35H = C,,q3- hopane (Cp&H); 8. 33H = C3&-hopane (C,&H); 9.29 + 30 = CZ9H + C,0H; 10.28/5 = C&3hopane (r&&H); 11. See terms defined in 2 and 10; 12. MC,.&H = 2a-methyl-olfi-norhopane ( C30); 13. MHopanes = sum of methylhopanes (m/z 205 integral), and Hopanes = sum of hopanes (m/z 19 1 integral); and 14. SEC0.H = sum of secohopanes (m/z 123 integral), and 29(+) 30H = CZ9H + C&H.

served in natural asphalts or archaeological bitumens from

Iraq.

Gas chromatograms of total aromatics

Four gas chromatograms are presented in Fig. 1 I. All depict total aromatic fractions in which organic sulfur compounds

are predominant. A striking feature is that C,,, aromatics of Tel Irani archaeological bitumens and floating block asphalt show distribution patterns that correlate peak by peak. These aromatics are particularly enriched in benzothiophenes (Fig.

11). In other samples, except in Nahal Heimar natural asphalts, benzothiophenes are missing; whereas dibenzothio-

TABLE 3. Characteristic biomarker ratios of steranes calculated from m/z 2 17 (unless otherwise specified).*

* List of abbreviations: 15. 2766s = Soi( 14@( H),17B(H),20Scholestane, and 27aaR = 501(H), 14ol(H), 17a(H),20R_cholestane; 16. 27araS = 5~(H),14Lu(H),l7a(H),ZOS-cholestane; 17. 21St = 5oI(H),14P(H),17@(H),pregnane, and 22St = Sa(H),l4@(H), 17P(H),methyl-2O-pregnane; 18. 29flm = 51~(H),14~(H),17/3(H),20S-24-ethylcholestane, and 29wR = 5a(H),l4a(H),l?ar(H),2OS- 24-ethylcholestane; 19. 29~s = 5a(H), 14ru( H), 1701( H) ,20S-24-ethylcholestane; 20. 22 4Me = C 22 4-methylsterane; 2 1. See terms defined in 17 and 20. 22. %C2,St = %C2, steranes (~uolol-&, R + S)/total steranes; 23. %C2$t = %CZs steranes (olcucu-cu&3, R + S)/ total steranes; 24. %C&t = %CZ9 steranes (a~-&I& R + S)/total steranes; 25. 27St = C2, steranes, and 29St = C29 steranes; 26. TT/ ST = triterpane to sterane ratio: ratio of m/z 19 I integral for C2,-Cj5 terpanes to m/z 2 17 integral for C&Zz9 steranes; 27. 27-30H = Cz,-C&Shopanes (m/z 191); 28. TT+St = Cz,-&terpanes (m/z I9 I ) + Cr,-C#teranes; and 29. 27-30H = C&&w@-hopanes (m/z 191), and 27-30H + 29St = Cz,-C30&-hopanes (m/z 191) + C29 steranes (m/z 217).

Molecular structure of archaeobgical a~phaks 2753

C2SSTERANES

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(r 011s FROM THE DEAD SEA AREA + ASPHALTS FROM THE DEAD SEA AREA

10[1

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0 ARCHAEOLOGICAL Bll’llMENS FROM IRiG (CONNAN,lW e AVERAGE VALUE ON 19 ARCHAEOLOGICAL BITWENS FROM IRAQ A THIS STUDY -ARCHAEOLOGICAL BITUMENS

Ffc .9. Ttxmry com~~o~~ diagram for C&-C, regular stez-anesz comparison with data an 03s and asphalts fmm the Dead Sea area (~ULLKCfTTZR et aL, 1985 ) and with data on natural asphalts and archaeological bitumens fmm Iraq (CONNAN, 1988). Note that all measurements were not carried out using the same procedure. The data of Ruts KOTTER et al. ( 1985) are for 14fl( H) and 17,9( H )-steranes (m/z 2 18). Our measurements report both (Y(YIY and a&3 R + S steranes (m/z 217).

phene isomers are easily recognizable. Crs+ aromatics of Na- ha1 Neimar asphalt (not shown) are different from others and are characterized by a hump-type pattern in which monoaromatic steroids and benzohopanes are detectable. This pattern has also been found in archaeological bitumens From Jerusalem.

GC44S analyses of CIS+ aromatics

An investigation of C,sc aromatics using W-MS enabled us to determine the major molecular families present in all fractions. Clr+ aromatics of Dead Sea asphalts and Tel Irani bitumens were found to be almost identical. Their molecular composition consists predominantly of benzothiophenes (trimethyl- and tetramethyl-BT); dibenzothiophenes (mono-, di-, tri-, and tetramethyl-DBT); and monoaromatic steroids associated with su~rdinate amounts of rne~yl~~l~nz~n~ f 2-m~yl-~~~l~~o~iophenes and 2-alkyl4methyL ~~~thiop~n~ ) , naphthalenes, phenanthrenes, benzohopanes, and triaromatic steroids.

Notable features include the occurrence of long-chain al- kylbenzothiophenes (m/z 162) and alkyldibenzothiophenes (m/z 198 ) and the lack of alkylbenzenes (M/Z 9 l-92). This last characteristic may be indicative of a &it biodegradation of Dead Sea and Tel Irani asphalts, referred to as unaltered.

However, the absence of alkylbenzenes as well as of mono- and dimethylbenzothiophenes in both samples may also be related to source.

A comparison of other Crs+ aromatics with those of the Dead Sea-Tel Irani bitumens clearly shows that these fractions have all been affected by bi~~tion phenomena to varying extents. In fact, Cu+ aromatics of Dead Sea asphalts may be transformed into other aromatic fractions by a step- by-step biodegradation of various molecular families. The removal sequence in aromatics through biodegradation is as folIows: alkylbenzen~ naph~~en~ ~~op~n~ (Cl-> Cz-, Cj-, alkyl-BT ), phen~n~~n~, and di~nzo~ophen~ (Ci-, CZ-, C3-, alkyl-DB’I’) .

The removal by biodegradation of these compound classes, especially the prominent benzo- and dibenzothiophenes, results in the survival of only bacterially resistant families, i.e., mono- and triaromatic steroids and benzohopanes as seen in the Nahal Heimar and JerusaIem asphalts, The sequence of removal of C,,, aromatics enables classification of bitumens in terms of their increasing degree of biodegradation (see Table 5).

In addition to the studies of biodegradation effects, evident in the aromatics fraction, attempts were also made to evaluate the maturities of bitumen samples on the basis of aromatic parameters.


GAS CHROMATOGRAM OF TOTAL ALKANES

-STEMNES(lW/Z 217) AND TERPANES(M/Z 1911

FIG. 10. Sterane (m/z 2 17 ) and terpane (m/z 19 I ) distribution patterns of the Sheik Awad archaeological bitumen, showing that this sample does not belong to the Dead Sea asphalt family (cf. Figs. 7 and 8).

Hence, we have assumed that the most reliable parameters are to be found by reference to abundant bacterially resistant families such as aromatic steroids and dibenzothiophenes and their parameters. Methyldibenzothiophene indices (MDBTI 1 and 3, MDBT 4/l; CONNAN et al., 1986; RADKE et al., 1982) and steroid aromatization ratios (triaromatic steroids/ triaromatic + monoaromatic steroids; MACKENZIE, 1984)

are given in Table 5. Steroid aromatization ratios ( 12-34%, Table 5 ) measured

for this set of samples are consistent with those values (5- 35%) already reported for natural asphalts of the Dead Sea

area ( RUUKOTTER et al., 1985 ). The values are much lower than those of oils reservoired at depth in the Dead Sea area and suggest that all the bitumens analyzed herein are of fairly low maturity. Such low maturity is also confirmed by the distribution patterns of methyldibenzothiophenes, which show a predominance of the l-MDBT, i.e., the less stable isomer (Fig. 11). However, methyldibenzothiophene indices are not only maturity-dependent but are also affected by biodegradation. ZMDBT/DBT, for instance, increases by biodegradation because DBT is removed prior to MDBT (Table 5).

Molecular structure of archaeological asphalts

TABLE 4. Comparison using some characteristic terpane ratios of asphalts from this study with those from Iraq.

PARAMETERS

lol Cm TRICYCLICTERPANE I c, TETRACYCLIC TERPANE

GA~ACERANE/l7a(H),Zl~(tl)~ IKIPANE

2 x C~H~HYD#B~~P~~ C, a@ HOPANES

2 a-~HYL-a~~~ES/a~ HOPANES

SECOHOPANESl Up HOPANES

~ TRlTERPANES/BTERANES

THIS STUDY

8 SAMPLES

i [ 1

2.8 19.3 27

7.0 23.1 42.4

I.27 0.41 0.52

b03 0.16 0.37

IO1 0.02 0.04

0 0 0

2.0 2.9 4.3

lELL EL OUEIL

IRA@

22 SAMPLES’

0.35 0.24 0%

0.04 0.10 0.3!

7.2 15.9 25.1

BITUMEHS

IRAQ- 19 SAMPLES**

2755

* AU SAJ4PLES FRO&f TELL EL OUEIU I~LU~ SEVERELY R~DEGRADED ONES IN WHICH STERANES AND TERPANES MAY HAVE BEEN ALTERED (after ~~~1~)

‘* NATURAL ABPHALTB AND ARCRAEOLOGICAL BITUMWS FROM IRAO (TELi EL ~ElLl,K~SA8AD,~,BABYL~,LA~~TELLO) WfTH UNALTEREO STERANEB (after CONNAN,1988)

DISCUSSION

Ori@ of Archaeological Bitumens

Geochemical characteristics (6 13C!, steranes, and terpanes) clearly differentiate the archaeological bitumens of this study from those already studied in Syria, Iran, Iraq, Kuwait, and Bahrain. By reference to oils and asphalts from the Dead Sea area, we have established that these ~haeol~~ bitumens, except the Sheik Awad asphalt, are genetically related to natural asphalts of that area. One archaeological bitumen, found at Tel Irani, has been shown to be identical to floating block asphalts of the Dead Sea.

Weathering and Bi~~~dation of Bitumens: A Likely Long-term Alteration Process at Archaeological Sites

Both alkanes and aromatics have been exposed to biodegradation to various extents. Biodegradation may affect alkanes and aromatics differently, as documented in laboratory ex- periments ( FED~RAK et al., 1983). On the basis of increasing degrees of bi~~dation in both alkanes and aromatics, we propose the following classification of samples.

The floating block asphalt and the Tel Irani bitumens were found to be almost identical and represent the reference samples defined as unaltered or perhaps sli8btly altered if the lack of alkylbcnzenes and of mono- and dime~yl~~o~ophen~ is regarded as a bi~~tion effect. Maadi bitumens offered a puzzling situation, with alkanes comparable to Dead Sea asphalts, but with aromatics obviously biodegraded. Such a situation has been reproduced partly in laboratory experi- ments by FEDORAK et al. ( 1983 ). Ein Zik, Ein Besor, and Palmahim bitumens are obviously biodegraded by more conventional aerobic pathways since both aromatics and al-

kanes are significantly modified. Nahal Heimar asphalt is the most severely biodegraded counterpart, since both hydrocarbon fractions are extensively altered.

Biodegradation may have occurred in a geological setting and would therefore have been present when the bitumens were exported. Alternatively, it may have occurred later on when the asphalts were exposed to weathering and aging at the archaeological site. The occurrence of weathering effects during the long period of exposure to atmospheric and un- derground agents is suggested by several features. Most archaeological bitumens display well-differentiated properties when compared to natural asphalts or oil seepages from the same geographical area. They contain much lower amounts of hydrocarbons, especially aromatics, and resins coupled with a comparable enrichment in the asphaltenes. This phenom- enon has been recorded in this study (our data are supported by those of RULLK~~TER et al., 1985); in southwestern Iran ( MARSCHNER et al., 1978); and in Iraq, Syria, and Pakistan (Connan, unpubl. data),

The step-by-step increase of asphaltenes has been registered during the aging of asphalts used for paving roads ( DOAN et

al., 1977). The same tendency can be observed at Nahal Heimar by comparing recent seeps with old ones (RULL- K~TTER et al., 1985 ). Asphalts from recent seepages contain 2% saturates, 23% aromatics, and 29% asphaltenes, whereas asphalts of old seeps show a modified composition of 2.8% saturates, 2.3% aromatics, and 39% asphaltenes.

Most frequently, the gross composition of chloroform extracts from archaeological bitumens matches the composition of highly weathered bitumens. Weathering is also detected by the occurrence of high amounts of insoluble organic residues, as seen in Maadi and Ein Besor bitumens, as well as by a significant shiff in the 61) values of ~phaltenes.


I+ 0. 25. 50. 75. 100. 125. 1 so. Mlnutm

DEAQ SEA FLoplTlwo t!UXKS

i

I

J 0. 25. 50. 75. 100. 125. 150. wnut*s

FPD

, / _

I

ENZOHOPANES

0. 25. 50. 75. 100. 125. 150. Minuta

FIG. 1 I. Gas chromatograms of aromatics for selected samples, showing the step-by-step removal of molecular families by biodegradation.

Molecular structure of archaeological asphalts

TABLE 5. Geochemical characteristics of aromatics showing the effect of increasing biodegradation. * J

2757

I REMOVAL SEQUENCE IN AROMATICS - BY INCREASING BIODEGRADATION +

P P

P P

P A

i

P P

P P

A P

GC - MS ANALYSIS GC ANALYSIS

FPD DETECTOR

- 1.00 -

0.92 -

0.n - D.82 - 0.87 -

0.79 -

* List of abbreviations: MBT-DMBT-TRIMBT = Methyl-, dimethyl-, trimethyl-benzothiophenes; ALKYL-BT = Long-chain . . . . . . . _ . . . . . . - alkyl-5enzottuophenes (Z-methyl4alkyl-benzotluophenes and 2-alkyl4methyl-benzothiophenes); MP-DMP-TMP = Methyl-, dimethyl-, trimethyl-phenanthrenes; MDBT-DMDBT-TMDBT = Methyl-, dimethyl-, trimethyl-dibenzothiophenes; ALKYL-DBT = Long- chain alkyl-dibenzothiophenes; MDBT 1 = 1.5(4-MDBT + 2-MDBT + 3-MDBT)/DBT + 2-MDBT + 3-MDBT + I-MDBT, MDBT 3 = 4-MDBT + 2-MDBT + 3-MDBT/2-MDBT + 3-MDBT + I-MDBT; MDBT 4/ 1 = 4-MDBT/ I-MDBT; ZMDBT/ DBT = 4-MDBT + 2-MDBT + 3-MDBT + I-MDBT/DBT: and DBT/P = Dibenzothiophene/Phenanthrene.

’ A = absent, P = present, and TR = traces.

Consequently, the properties of archaeological bitumens are the result of interrelated chemical and biodegradation processes, including evaporation, water washing, oxidation, photodegradation, and bioxidation. These combined phenomena produce changes in gross composition and molecular properties. Alkanes, aromatics, and resins are reduced in rel- ative abundance, but asphaltenes and insoluble organic residues are formed. Aromatics appear to be more drastically affected than alkanes, but both fractions generally show evidence of biodegradation. Under exceptional environmental conditions, pristine asphalts from the Dead Sea floating blocks have been preserved at the Tel Irani archaeological site. All other archaeological bitumens may be regarded as floating blocks of the Dead Sea asphalts, which have been changed by several millennia of weathering. Aging is responsible for the peculiar properties of the Maadi asphalt. Its alkane composition, more or less unaffected, with obvious n-alkanes show Dead Sea type sterane and terpane composition, but its aromatics are biodegraded, and the benzothiophene families are lacking. In this asphalt, an abundant insoluble organic residue occurs.

As a consequence of this bitumen study for archaeologists, we wish to point out that the examination of total alkane patterns is an inadequate means of evaluating the extent of alteration processes on asphalts from surface seepages. This study clearly demonstrates that information from hydrocarbon fractions and also more polar ones, including insoluble organic residues, requires integration to diagnose conclusively the origin of a surface sample of natural asphalt.

Canaanite Trade with Egypt

The trade between Canaan and Egypt became intensive during a comparatively short period in the Early Bronze Age

( BEN-T• R, 1986). In the 150 years from approximately 3250-3100 BC, corresponding to the Early Bronze I period in Canaan and the Naqada III (predynastic or Dynasty 0 period in Egypt), numerous Egyptian wares or Egyptian-related materials are found in Canaan. For example, Brandel (in BEN-T• R, 1989) reports more than 1000 Egyptian vessels from the Early Bronze I levels in Tel Irani (Fig. 1) where unaltered Dead Sea asphalt has been found. Another example is the sixty clay seals with Egyptian inscriptions discovered at Ein Besor (Fig. 1) by PORAT ( 1989 ) in Early Bronze I levels where Dead Sea asphalt was also present. Both locations were used as Egyptian trading stations. It has been suggested that southern Canaan was under Egyptian military rule, but recent investigators favour largely the idea of peaceful relations, with the Egyptian population coexisting with the native Canaanite population (WRIGHT, 1985; BEN-T• R, 1989). The reason for the settlement of Egyptians in Canaan was mainly economical, raising the following critical question: What were the exports from Canaan to Egypt?

The only evidence for undisputably Canaanite products in Egypt is the presence of Canaanite vessels that were probably used for the transfer of perishable agricultural products, such as oil and wine ( PORAT, 1989; BEN-T• R, 1989). No geochemical analysis of other items of possible Canaanite origin has been reported. Thus, the data given in this report provide the first evidence for the presence of raw material from Canaan, not only in Egypt itself but also in Egyptian trade posts on the route to mainland Egypt.

Between 3900 and 3100 BC, the raw asphalts from the floating blocks of the Dead Sea exported to Egypt were not used there for mummification purposes. Embalming with conifer resins mixed with bitumens did not appear before the Fourth Dynasty, i.e., around 2600 BC (PECK, 1980;

2158 J. Connan, A. Nissenbaum, and D. Dessort

BUCAILLE, 1987). Consequently, the most likely utilization of bitumens during the earlier epoch would be for using glue to attach flint implements in sickles, as in Arad ( NISSENBAUM

et al., 1984), or as a waterproofing agent to caulk baskets, as seen in Gilgal (9000 BC, Israel) and elsewhere (Beidha, Jor- dan; Mehrgahr, Pakistan; Susa, Iran; Tell el Oueili, Iraq, etc.). At Maadi, the occurrences of asphalt in predynastic settlements (3900-3500 BC) still remain problematic. A black substance has been found attached to one flint sickle stone ( RIZKANA and SEEHER, 1989); it may also have been used in incense burners ( RIZKANA and SEEHER, 1988). However, no analyses have been carried out to investigate these hypotheses.

Trade Routes of Bitumen from the Dead Sea

The city of Arad in the northern Negev highlands (Fig. 1) served as one of the major depots for the Canaanite trade with Egypt and the Sinai ( AMIRAN et al., 1973). Jars and fme wares were carried from Arad as far as southern Sinai, although the exact route of transportation is not known. Since Arad is the largest city of this period in the area close to the Dead Sea, it probably served as a major distribution point of Dead Sea asphalt. Indeed, many lumps of asphalt from the Dead Sea were found in Arad, widely distributed through private and public buildings, even including holy temples.

From Arad, the asphalt was transported to the north (Je- rusalem) and northwest (Tel Irani and Palmahim). Asphalt was thought to be exported to southern Sinai probably through Ein Zik (Fig. 1); however, the analysis of a bitumen lump from Sheik Awad, dated between 2900 and 2650 BC, has not confirmed this hypothesis. This bitumen of unknown origin (Sinai?) does not correlate with Dead Sea asphalts (occurrence of diasteranes; different terpane pattern) nor with natural asphalts from Iraq ( CONNAN, 1988).

The route along which the asphalt was exported probably included trading posts in the Mediterranean coastal plain. The site of Ein Besor (Fig. 1) might have been an important trading point. Its strong commercial connections with Egypt are attested to by the presence of large amounts of Egyptian- derived objects (GOPHNA, 1989; RIZKANA and SEEHER, 1989) in Ein Besor-Site H. From there, the asphalt was probably moved by land through northern Sinai to the Nile delta and to Maadi. This overland route between Egypt and Canaan was described by OREN ( 1973 ) on the basis of archaeological evidence. Following the Early Bronze period, it was rehabili- tated as a major land bridge from 16th century BC, and it is depicted in Egyptian paintings and writings as the “Way of Horus” ( OREN, 1987 ) . It is possible that the asphalt was also exported by sea from the Mediterranean coast of Canaan to the Nile delta. Indeed, the finding of asphalt in Palmahim, which is situated on the Mediterranean coast, may be related to this trade route (see discussion of the trade routes between Egypt and Canaan in RIZKANA and SEEHER, 1989).

The intensive trade relations between Egypt and Canaan probably declined by the second dynasty. However, the export of asphalt from the Dead Sea continued to locations closer to the Dead Sea, such as Jerusalem and Ein Zik, in Canaan for another couple of hundred years.

CONCLUSIONS

Lumps of archaeological bitumens, found in excavations of Canaan and Egypt, dated 3900-2200 BC, have been ge-

netically linked to natural asphalts of the Dead Sea area. One of them, the Tel Irani bitumen, Early Bronze I in age, has been shown to be identical to floating block Dead Sea asphalts. All other archaeological bitumens, biodegraded to various degrees, have been recognized as floating block asphalts that have been subsequently weathered at archaeological sites.

Weathering of floating-block Dead Sea asphalts entails a reduction in C ,s+ aromatics and NSO compounds but an enrichment in asphaltenes and, sometimes, formation of an organic residue insoluble in chloroform. Fortunately, sterane and terpane patterns that have not been biodegraded allow correlation of archaeological bitumens with their parent natural asphalts, i.e., the floating asphalt blocks from the Dead Sea.

The data presented herein provide the first evidence of export and trade of raw bitumen from Canaan not only to Egypt (Maadi ) but also to Egyptian trading posts (Ein Besor, Tel Irani, etc.) on the route to mainland Egypt as early as 3900 BC.

Unfortunately, the utilization of the raw bitumen discovered in excavations cannot be discerned; but, most likely, uses for the raw bitumen are as a glue to fix flint implements to wooden handles and as a proofing agent for caulking baskets.

Acknowledgments-The authors wish to thank Dr. J. Seeher, German Archaeological Mission, Istanbul; Prof. R. Gophna, Tel Aviv Uni- versity; Dr. B. Brandel, Dr. E. Brown, Dr. R. Cohen, and Dr. E. Eisenberg, Antiquities Authority, Jerusalem; and Prof. I. Beit-Arieh, Tel Aviv University, for the archaeological asphalt samples, helpful advice, fruitful discussions, and useful documentation.

This paper has benefited greatly from reviews by Paul Comet, Si- mon Brassell, and an anonymous reviewer, who provided language corrections and critical suggestions which have been incorporated in the final version.

We are indebted to the Exploration Directorate and the Research and Innovation Directorate of Elf Aquitaine for their authorization and financial support, which have enabled us to accomplish this study and publish its results.

Thanks are also due to all technicians of the organic chemistry section of the Laboratory Department of the Exploration Directorate of Elf Aquitaine, who have contributed actively to the production of key data.

Editorial handling: S. C. Brassell

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Documents

Molecular archaeology: Export of Dead Sea asphalt to Canaan and Egypt in the Chalcolithic-Early Bronze Age (4th-3rd millennium BC