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# Geochemical analysis of bituminous samples from the Pre-Pottery Neolithic B site of Nahal Efe (Northern Negev, Israel): Earliest evidence in the region and an example of alteration of the Dead Sea bitumen

Jacques Connan<sup>a</sup>, Ferran Borrell<sup>b,*</sup>, Jacob Vardi<sup>c</sup>, Samuel Wolff<sup>d</sup>, Steven M. Ortiz<sup>e</sup>, Michael Engel<sup>f</sup>, Renaud Gley<sup>g</sup>, Alex Zumberge<sup>h</sup>

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## ARTICLE INFO

Associate Editor – Vincent Grossi

**Keywords:**

Dead Sea bitumen

Nahal Efe

Tel Gezer

Negev

Pre-Pottery Neolithic B

Geochemical analysis

Biomarkers

Steranes

Terpanes

Stable carbon and hydrogen isotopes

## ABSTRACT

Thirty-six bituminous samples from the Pre-Pottery Neolithic site of Nahal Efe (8000–7700 cal. BCE, Negev, Israel) were analysed to determine their origins. Most samples are mixtures of bitumen with minerals, predominantly quartz, calcite, dolomite and aragonite. The aragonite is from marine shells, which were crushed to be incorporated into the mixtures.

Dead Sea bitumen was identified in all samples. The Nahal Efe geochemical data were compared to samples from Tell Yarmuth (2800–1100 BCE), Tall Dhiban (700–800 cal. BCE), Tel Gezer (1250–700 cal. BCE) and to floating asphalt blocks from the Dead Sea. The stable carbon isotope values of resins and asphaltenes of the Nahal Efe bitumens differ from those of the Dead Sea floating blocks, Tell Yarmuth, Tel Gezer and Tall Dhiban, apparently a consequence of diagenesis. Thus, δ¹³C values of asphaltenes may not always be a reliable representative of the stable carbon isotope composition of the unaltered source bitumen. Surprisingly, the sterane and terpane patterns of the Nahal Efe samples are not severely biodegraded and clearly indicate a Dead Sea bitumen source. No difference was recorded between mixtures and pure bitumen. Some changes have, however, been observed when using quantitative data on biomarkers. The shifts in δ¹³C values of resins and asphaltenes is not related to biodegradation but rather to oxidation of the Nahal Efe samples.

This is the earliest and most complete evidence of Dead Sea bitumen exploitation and use, which included the preparation of different ‘recipes’, in the Negev and Sinai arid regions.

## 1. Introduction

Exploitation of Dead Sea bitumen has been assessed by geochemical analysis and/or visual characteristics at several prehistoric sites in the southern Levant dating from the early Neolithic (10th millennium cal. BCE) to the Iron Age (1st millennium cal. BCE) (Oron et al., 2015). The earliest evidence corresponds to the Pre-Pottery Neolithic (PPN, subdivided into PPNA 9700–8600 cal. BCE, Early PPNB 8600–8200 cal.

BCE, Middle PPNB 8200–7500 cal. BCE, Late PPNB 7500–7000/6900 cal. BCE and Final PPNB/PPNC 7000/6900–6500 cal. BCE), with bituminous remains having been identified at different sites in the region and documenting its use for different purposes. For example, bitumen has been identified as coatings of small and big baskets at Gilgal (PPNA, Schick, 2010; Connan et al., 1995), as traces of hafting on sickle blades and Beit Ta'amir knives at Nativ Hagdud (PPNA, Bar-Yosef et al., 1991; Connan, 2012), as coating of basketry at Beidha (PPNB, Kirkbride,

<footnote><sup>a</sup> Université de Strasbourg, 23 rue Antoine de Saint-Exupéry, 64000 Pau, France</footnote>

<footnote><sup>b</sup> IMF, CSIC, Egipllaques 15, 08001 Barcelona, Spain</footnote>

<footnote><sup>c</sup> Prehistoric Branch, Research Division, Israel Antiquities Authority, Nachman Avigad 1, Jerusalem 9370726, Israel</footnote>

<footnote><sup>d</sup> W.F. Albright Institute of Archaeological Research, 26 Salah ed-Din Street, Jerusalem, Israel</footnote>

<footnote><sup>e</sup> Lanier Center for Archaeology, Dpt of Archaeology, College of Liberal Arts and Sciences, Lipscomb University, One University Park Drive, Nashville, TH 37204, USA</footnote>

<footnote><sup>f</sup> School of Geosciences, The University of Oklahoma, 100 East Boyd Street, Norman, OK 73019-1009, USA</footnote>

<footnote><sup>g</sup> Laboratoire Interdisciplinaire des environnements continentaux, UMR7360, Site Chamois, 15 avenue de Chamois, 54500 Vandeuvre-les-Nancy, France</footnote>

<footnote><sup>h</sup> GeoMark Research Inc., 9748 Whithorn Drive, Houston, TX 77095, USA</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: connan.jacques@orange.fr (J. Connan), ferran.borrell@imf.csic.es (F. Borrell), jacobv@israntique.org.il (J. Vardi), steven.ortiz@lipscomb.edu (S.M. Ortiz), ab1635@ou.edu (M. Engel), renaud.gley@univ-lorraine.fr (R. Gley), azumberge@geomarkresearch.com (A. Zumberge).</footnote>
1967), as traces on flint implements at Jericho (PPNB, Crowfoot-Payne, 1983), as traces on flint implements at Yiftahel (PPNB, Marder et al., 2012), and as traces on sickle blades at Motza (Final PPNB, Vardi et al., 2022) and at Atlit Yam (PPNC, Galili et al., 2004). The nearby site of Nahal Hemar Cave has not been included in this list because the presence of asphalt/bitumen at the site, despite being repeatedly claimed and traditionally accepted (Bar-Yosef and Alon, 1988; Bar-Yosef and Bar-Yosef Mayer, 2002), has never been confirmed by analytical means. Additionally, initial, and more recent analyses of the black substance used for coating the skulls and the basketry or hafting the sickle blades, and other artefacts have been consistently identified as bovine collagen and *Styrax* resins (e.g., Connan et al., 1995; Solazzo et al., 2016).

Evidence from late prehistoric sites (Bronze Age and Iron Age) is even more abundant and varied (Connan et al., 1992). The study of these assemblages, including most analyses on the isotopic and chemical changes that have affected the Dead Sea bitumen, are available for: Tell Yarmuth (3000–1100 cal. BCE, Connan et al., 2022), Tall Dhiban (ca. 750 cal. BCE, Connan et al., 2022), Tel Miqne-Ekron (ca. 600 cal. BCE,

Connan et al., 2006).

This paper presents the results of the study of the bituminous remains from Nahal Efe, which is the largest Middle PPNB site in the Negev and Sinai deserts (Fig. 1). The mere presence of bituminous remains at Nahal Efe is doubly interesting. Firstly, because no bitumen remains had previously been reported in the Negev and Sinai region during the Pre-Pottery Neolithic. Secondly, the studied set comprises what a priori looked like both pure chunks and mixtures of bitumen with mineral matter, and thus might include samples that have a longer history and were more affected by alteration processes. The samples are, therefore, of particular interest to assess the possibility for isotopic and molecular changes of the chemical fractions of Dead Sea bitumen from this older occupation site. In addition to the samples from Nahal Efe, the present study includes five archaeological pure bitumen samples from the much later site of Tel Gezer (1250–700 cal. BCE) that, together with present day Dead Sea bitumen (1980 AD), have been used for comparative purposes as unaltered references.

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Location of Nahal Efe and other southern Levantine prehistoric sites mentioned in the text.</figcaption></figure>
## 2. Materials and methods

### 2.1. Bitumen at Nahal Efe

Nahal Efe is located in the northeastern Negev (Israel) on the steep slope of the Hatira ridge and overlooking the Nahal Efe stream, at approximately 320 masl. The site is 8 km west of the Dead Sea and 11 km south of the well-known PPNB cult site of Nahal Hemar Cave (Bar-Yosef and Alon, 1988; Borrell et al., 2020), which took its name from the eponymous dry river bed (Nahal Hemar, Asphalt River in Hebrew). Seven field seasons at Nahal Efe have revealed the largest and best preserved PPNB settlement in the Negev and Sinai, constituting a privileged data source for the study of hunter-gatherer communities that inhabited the Negev 10,000 years ago (e.g., Borrell et al., 2015; Borrell and Vardi, 2022; Vardi et al., 2018; Alcāntara et al., 2023). The main occupation of the site corresponds to the Middle PPNB and has been dated to ca. 8000–7700 cal. BCE, with an estimated size of 2000 m². The extensive excavation of approximately 315 m² of Sector 1 in the top and middle part of the hillside has revealed eight relatively large circular or sub-circular semi-subterranean buildings showing significant architectural complexity, which make up, together with the several circular unexcavated structures that are partly visible on the surface of the slope, what seems to be a large residential area structured on different levels of the slope (Fig. 2). The excavation of the dwelling units and the large outdoor areas around them has so far yielded a rich chipped lithic assemblage (Borrell and Vardi, 2022), as well as a repertoire of ground stone tools (e.g., grinding slabs, pounders, hammerstones, bowls, and shaft straighteners) and a few ornaments (beads). Botanical remains

(charcoals) are abundant and well preserved, while faunal remains are relatively limited in number and badly preserved (Alcāntara et al., 2023).

The presence of bitumen-like remains in Nahal Efe is abundant. During excavations from 2015 to 2022, a total of 139 samples were recovered from the Middle PPNB occupation of the site, most of them composed of several fragments (Fig. 2, Supplementary Table 1). Additionally, traces of a bituminous mixture were observed on the surface of a small pestle recovered in Unit 10. Their distribution in the excavated area is quite irregular, with a significant concentration of remains in and around the largest and better-preserved dwelling (Unit 8). Its presence in the rest of the excavated area is limited, except for another, albeit smaller, concentration around Unit 6. In this regard, it is important to remember that Units 8 and 6, together with Unit 9 (its excavation was ongoing), are the better-preserved buildings of the site with preserved walls up to 1.4 m high, a factor that has surely favoured the greater occurrence and better preservation of bituminous remains inside these buildings. The archaeological contexts in which the samples have been recovered are quite varied, including loci associated to both the use of the buildings and annexed installations as well as those related to its abandonment and collapse/fill. The nature of the samples recovered at the site is remarkably diverse, including several chunks/fragments of both pure bitumen and bituminous mixtures (n = 100), bituminous sediments (n = 21) and, finally, a few relatively small (4.5–12.5 cm long) limestones with their surface partially or fully covered by bitumen residues (n = 18). Most of the fragments of recovered pure and mixed bitumen are relatively small (0.5–2.5 cm) with a rather amorphous or rounded shape, although fragments measuring between 3 and 4 cm total

<figure><img src="image_4.png" /><figcaption>Fig. 2. Plan of Nahal Efe with the spatial distribution of the bitumen samples recovered at the site.</figcaption></figure>
length are not rare, and a few are up to 5–6 cm in length. The general appearance of the surfaces of the samples are mostly irregular and granular as a result of erosion and fracturing. However, it is worth noting that a significant number of fragments (n = 18) display (partially) flat surfaces negatives (in some cases with vegetal imprints) right angles or intentionally rounded surfaces (Fig. 3), thus indicating that these bitumen samples were attached to or in contact with worked or flat surfaces and subsequently shaped.

## 2.2. Bitumen at Tel Gezer

Tel Gezer is a large (c.33 acres) mound located at the western edge of the Judean foothills (Shephelah), just before it drops off to the coastal plain (Fig. 1). The most recent expedition, working from 2006 through 2017 on behalf of the Tandy Museum of Southwestern Baptist Theological Seminary, Fort Worth, Texas and currently by the Lanier Center of Archaeology, Lipscomb University, Nashville, Tennessee, further refined the previous achieved results (Ortiz and Wolff, 2017; Webster et al., 2023). The bitumen samples discussed below are from that excavation.

Five samples of pure bitumen were identified among the material revealed by the Tandy/Lanier expedition (Fig. 4). Contextual information on these samples is presented in Supplementary Table 2. A diagram indicating the location of each sample is presented in Supplementary Fig. 1; note the randomness of distribution of the bitumen samples. None of the samples and particular contexts add information regarding the use of bitumen (the only evidence of use being as adhesive for a stone cosmetic bowl with inlay dating to the 8th century BCE) for the chunks discovered are pristine pure bitumen that had never been processed. Most samples are derived from secure contexts (Supplementary Table 2). Bitumen was used at the site from c.1200 BCE to the Hellenistic period. The discovery of Dead Sea bitumen at the site is significant in that it represents a trade item that is often overlooked. If bitumen was traded directly (and not down-the-line or via a central place or another mode of trade), the most direct route would have been from the port of En-Gedi (Oron et al., 2015) to Tekoas/Bethlehem (Dorsey's route J33; Dorsey, 1991) and from there to Tel Gezer (J8) or neighbouring sites like Tel

Miqne-Ekron (J8-J8a-J5, Connan et al., 2006).

## 2.3. Archaeological samples analysed

A total of 30 of the samples recovered from Nahal Efe were selected for analysis and a total of 36 analyses (some samples were analysed two or three times) were undertaken (Supplementary Table 1). The sampling strategy was aimed at representing the observed variability regarding the nature of the samples recovered at the site (chunks of pure bitumen, bitumen mixtures and stones covered with bitumen) but also the distinctive features displayed such as vegetal imprints (Fig. 3). The majority of the samples analysed are obvious mixtures of bitumen with mineral matter, a good example of which is sample N°3516, which is a black shiny bitumen mixed with fairly big minerals. In contrast, sample N° 3504 is composed of typical chunks of pure bitumen, shiny with a conchoidal fracture. Sample N° 3537 is also composed of very black homogenous chunks (left top) thought to be pure bitumen. Sampling also included the analysis of stones covered with bitumen. For example, samples N° 3523 and 3523bis correspond to the bitumen that fully covered a small stone (approx. 9 × 6 × 6 cm) which was obviously used as pestle to grind minerals and bitumen (N° 3523 corresponds to the powder which was collected in the bag. N° 3523bis was the sample obtained by scraping the black matter from the stone and seems to be pure bitumen grains). Finally, the analysed samples included a chunk (N° 3533) displaying imprints of vegetal stems and flat fragments (N° 3538), one of which has an imprint of vegetal stem. Many of the samples analysed had an eroded, powdery and greyish exterior appearance, which made it necessary to fracture them to examine a fresh face to make an assessment of sample type.

The 5 samples from Tel Gezer (1250–700 cal. BCE) that were selected for analysis consist of chunks of pure Dead Sea bitumen (Supplementary Table 2, Fig. 4).

## 2.4. Analytical procedures

### 2.4.1. Total organic carbon (TOC)

Leco TOC analysis requires decarbonation of the rock sample by

<figure><img src="image_5.png" /><figcaption>Fig. 3. Photographs of some samples from Nahal Efe.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4. Photographs of the samples from Tel Gezer.</figcaption></figure>

treatment with hydrochloric acid (HCl). This is done by treating the samples with concentrated HCl (36%) for at least two hours. The samples are then rinsed with water and flushed through a filtration apparatus to remove the acid. The filter is then removed, placed into a LECO crucible, and dried in a low temperature oven (110 °C) for a minimum of 4 h. Samples may be weighed after this process to obtain a % carbonate value based on weight loss.

The LECO C230 instrument is calibrated with standards having known carbon contents. This is completed by combustion of these standards by heating to 1200 °C in the presence of oxygen. Both carbon monoxide and carbon dioxide are generated, and the carbon monoxide is converted to carbon dioxide by a catalyst. The carbon dioxide is measured by an IR cell. Combustion of unknowns is then completed and the response of unknowns per mass unit is compared to that of the calibration standard, thereby the TOC is determined. Standards are analysed as unknowns every 10 samples to check the variation and calibration of the analysis. Random and selected reruns are done to verify the data. The acceptable standard deviation for TOC is 3 % variation from established value.

### 2.4.2. Programmed pyrolysis: HAWK operating conditions

Approximately 100 mg of washed, ground (60 mesh) whole rock sample is analysed in the programmed pyrolysis instrument. The temperature is first held at 300 °C for 3 min (S1 = volatile organic compounds assumed to be hydrocarbons) and then ramped at 25 °C/min to at 650 °C and held for 1 min (S2 = pyrolyzate hydrocarbons). S1 and S2 are reported as mg HC/g TOC; Tmax is the temperature at maximum evolution of S2 hydrocarbons (°C). S3 is the CO₂ that evolves between 300 and 400 °C and reported as mg CO₂/g TOC. Organic rich samples are analysed at reduced weights whenever the S2 value exceeds 40.0 mg/g or TOC exceeds 7–8 %. Several useful parameters can be derived from these measurements: Hydrogen Index (HI) S2/TOC × 100, Oxygen Index (OI) (S3/TOC × 100); Normalized Oil Content (S1/TOC × 100), S2/S3, and the Production Index (PI): S1/ (S1 + S2).

Instrument calibration is achieved using a rock standard. Its values

were determined from a calibration curve to pure hydrocarbons of varying concentrations. This standard is analysed every 10 samples as an unknown to check the instrument calibration. If the analysis of the standard ran as an unknown does not meet specifications, those preceding data are rejected, the instrument recalibrated, and the samples analysed again. However, normal variations in the standard are used to adjust any variation in the calibration response. The standard deviation is considered acceptable under the following guidelines: S1, S2, and S3 within 10 % variation and Tmax ± 2 °C from the established value. Analytical data are checked selectively and randomly. Selected and random checks are completed on approximately 10 % of the samples.

### 2.4.3. Bitumen analysis

All archaeological and geological bitumen samples were subjected to the same analytical procedures conducted at GeoMark Research Ltd (Houston, TX USA) as previously reported (Connan et al., 2021, 2022, 2024). The dichloromethane extract was deasphalted using n-hexane. The deasphalted fraction was separated into C₁₅+saturated hydrocarbons, aromatic hydrocarbons, and resins using gravity flow column chromatography employing a 100–200 mesh silica gel support activated at 400 °C prior to use. Hexane was used to elute saturates, dichloromethane to elute the aromatic hydrocarbons and dichloromethane/methanol (50:50) to elute the resin (NSO) fraction. Following solvent evaporation, the recovered fractions were quantified gravimetrically. The C₁₅+saturated hydrocarbon fraction was subjected to molecular sieve filtration (Union Carbide S-115 powder) after the technique described by West et al. (1990). An aliquot of the total alkane fraction was not fractionated on silicalite to analyze the n-alkanes.

GC-MS analysis of the C₁₅+ branched and cyclic hydrocarbon fractions was performed using an Agilent 7890A (split injection) interfaced to an Agilent 5975C mass spectrometer. The HP-2 column (50 m × 0.2 mm, 0.11 µm film thickness) was temperature programmed from 150 °C to 325 °C at 2 °C/minute and held for 10 min. The mass spectrometer was run in the selected ion mode (SIM), monitoring ions *m/z* 177, 191, 205, 217, 218, 231 and 253 Da for branched and cyclic alkanes.
Quantitative data used peak area.

To determine the absolute concentration of individual biomarkers, a
deuterated internal standard (d4-C29ααα 20R sterane, Chiron lab, Nor-
way) was added to the C15+branched/cyclic hydrocarbon fraction.
Response factors (RF) at 221 Da for the deuterated standard relative to
authentic standards of hopane (m/z 191) and sterane (m/z 217) were
found to be 1.4 for terpanes and 1.0 for teranes. Concentration of in-
dividual biomarkers were determined using the following equation:
Conc. (in ppm) = (Ht biomarker) (ng standard)/ (Ht standard) (RF) (mg
B/C fraction).

The C15+saturates, C15+aromatics, asphaltenes and resins were analysed for their respective carbon isotope (δ13C, ‰/ VPDB) compositions. The asphaltenes and resins were also analysed for their stable hydrogen isotope compositions. Details for all the methods for stable isotope analyses are described in Connan et al. (2021).

2.4.4. Mineralogical analysis

All samples were ground prior to the XRD analysis. The mineralogy
was determined using a D8 Discover Bruker diffractometer equipped
with an X-ray tube emitting Cu-Kα1 radiation (λ = 1.5406 Å) at 40 kV
and 40 mA. X-ray diffraction patterns were recorded with a LynxEye
detector under ambient conditions and from 2.5° to 65° 2θ, with a step
size of 0.035° 2θ, and with a calculation time of 3 seconds per step.
Analyses were performed using DIFFRAC.EVA Bruker software and
diffraction peaks were identified using the powder diffraction file
database.

3. Results

3.1. *Gross composition of extractable organic matter*

Gross composition data of Nahal Efe (36 samples), Tel Gezer (5 samples) and Dead Sea floating blocks (1 sample) are listed in *Supplementary Table 3*.

A plot of % sat + aro vs. % resins vs. % asphaltenes in a ternary di-
agram shows that most samples of Nahal Efe are rich in asphaltenes
(Fig. 5A) and depleted in hydrocarbons as compared to Dead Sea

floating blocks (Nissenbaum et al., 1980). Some samples (N° 3527, 3516, 3526 and 3530), however, are apart from the main cluster and richer in resins. Most samples are comparable to samples already analysed at Tall Dhiban and Tell Yarmuth (Fig. 5C and 5B, Connan et al., 2022) and to samples of Tel Gezer (Fig. 5C). The compositions of archaeological samples characterized by an enrichment in asphaltenes compared to the Dead Sea floating blocks has been reported in many publications (Forbes, 1955; Marschner and Wright, 1978; Connan and Nishiaki, 2003; Connan and Carter, 2007; Connan, 2012; Connan et al., 1992, 2006, 2018, 2020, 2021, 2022; Nissenbaum and Connan, 1999; Schwartz and Hollander, 2016; Schwartz et al., 2000; Brown et al., 2014; Faraco et al., 2016; Daneels et al., 2018; Wendt and Lu, 2006).

A plot of % asphaltenes/EO vs. % EO/sample (EO = dichloromethane extractable organic matter) completes the gross compositional assessment of the Nahal Efe samples (Fig. 6). Most samples contain more asphaltenes than the Dead Sea reference. This is also the case for the Tell Yarmuth and Tel Gezer samples. As previously mentioned, 5 samples with amounts of bitumen lower than 20 %, also have reduced amounts of asphaltenes. Sample N° 3503 is not bitumen, as indicated by its sterane and terpane fingerprints (occurrence of diasteranes, low gamacerane), and the fingerprint is likely related to something else, probably soils. It is also important to note that there is no difference between samples of pure bitumen and samples which are obvious mixtures of bitumen and minerals. Such a property is, unexpectedly, not observed at Tell Yarmuth-Tel Gezer. In the case of Tell Yarmuth, the reduced % of asphaltenes observed in the bitumen coatings of the sherds analysed could be related to the addition of other substances or materials such as food residues, which has recently been identified as influencing isotopic data (Connan et al., 2024).

The average content of asphaltenes in Nahal Efe samples is 87.7 % (standard deviation = 13 %) for 26 % of extractable organic matter (standard deviation = 18 %). Data compiled with mixtures only gave 87.4 % for asphaltenes (standard deviation = 19 %) for 22 % of extractable organic matter (standard deviation = 14 %). The average content of extractable organic matter from 355 archaeological bituminous mixtures, dated between 6500 cal. BCE and 1100 CE with an average date of 2210 BCE is 23.4 % (Connan, 2012), i.e. close to the

<figure><img src="image_7.png" /><figcaption>Fig. 5. Gross composition of the dichloromethane extract in a ternary diagram: % sat + aro vs. % resins (NSO) vs. %asphaltenes.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Fig. 6. Plot of % asphaltenes vs. % extractable organic matter (EO/sample): comparison of Nahal Efe to Tell Yarmuth and Tel Gezer.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 7. Plot of δ¹³Csat vs. δ¹³Caro and δ¹³Cresins vs. δ¹³Casp: comparison of Nahal Efe, Tell Yarmuth, Tall Dhiban and Tel Gezer to the Dead Sea floating blocks.</figcaption></figure>
average value of Nahal Efe samples that are much older. As previously noted, the recipes of bituminous mixtures have not significantly changed from the Neolithic to the Medieval period (Connan, 2012).

## 3.2. Stable isotope data

Carbon and hydrogen isotope compositions data are listed in Supplementary Table 4. Plots of δ¹³Csat (‰/VPDB) vs. δ¹³Caro (‰/VPDB) and δ¹³Casp (‰/VPDB) vs. δ¹³Cresins (‰/VPDB) in Fig. 7 shows that δ¹³Caro (‰/VPDB) are of the same order of magnitude in bitumens of Tell Yarmuth, Tall Dhiban, Tel Gezer, and the Dead Sea floating blocks but are significantly enriched in ¹³C in Nahal Efe samples. Again, in Nahal Efe samples, no difference is observed between pure bitumens and asphalts from mixtures. Saturates are enriched in ¹³C in samples of Nahal Efe as in bitumen of potsherd from Tell Yarmuth (Fig. 7A).

The plot of δ¹³Casp (‰/VPDB) vs. δ¹³Cresins (‰/VPDB) confirms the significant difference between bitumens of Tell Yarmuth, Tall Dhiban, and Nahal Efe (Fig. 7B). Asphaltenes and resins of Nahal Efe are both enriched in ¹³C. These results indicate that the polar fractions of Nahal Efe cannot be used as genetic parameters, as both fractions are affected by oxidation (Charrié-Duhaut et al., 2000). Previous papers have claimed that carbon isotopes of asphaltenes are unaffected by alteration processes and therefore of use to trace the source of bitumen (Connan and Nishiaki, 2003). These new data show that δ¹³C of saturates, aromatics, resins and asphaltenes are all significantly shifted. The δ¹³Casp of -29.4 ‰/PDB as average value in Tell Yarmuth-Tall Dhiban and Dead Sea, is shifted of 0.6 ‰/PDB, i.e. to -28.8 ‰/PDB in Nahal Efe samples. Similar values (from -28.3 to -28.8 ‰/PDB, average -28.5 ‰/PDB) were recorded in Dead Sea bituminous mixture coating baskets of Gilgal (PPNA), dated around 9200 cal. BCE (Connan et al., 1995).

A plot of δDasp and δDNSO vs. δ¹³Casp and δ¹³Cresin in Supplementary Fig. 2 shows enrichments in ²H in Yarmuth and Nahal Efe

asphaltenes but no enrichment in resins. The enrichment in ²H in asphaltenes also may be due to oxidation (Charrié-Duhaut et al., 2000).

## 3.3. Steranes and terpanes

Mass fragmentograms of steranes (m/z 217) and terpanes (m/z 191) of two samples of Nahal Efe, a chunk of pure bitumen (N° 3502) and a mixture (N°3521), are shown in Fig. 8. They were compared to two pure bitumens (Fig. 9): the floating blocks of Dead Sea bitumen (N°1937, Connan et al., 1992) and one sample of Tel Gezer (N° 3384). Unlike the differences in carbon isotope values of chromatographic fractions, steranes and terpanes of Nahal Efe samples were all comparable to the pure Dead Sea bitumen and not severely biodegraded. Mass fragmentograms of terpanes (m/z 191, Fig. 8) and steranes (m/z 217, Fig. 8) display the typical patterns of Dead Sea bitumen (Fig. 9): abundant quantities of tricyclic terpanes (C19/3 to C29/3), high Tm/Ts (17α-22,29,30-trisnorhopane /18α-22,29,30-trisnorneohopane) ratio, high amount of gammacerane, C21Ste and C22Ste, low C27diasteranes, C27 > C28 > C29 steranes. At first glance, steranes and terpanes seem to be rather well preserved but some changes are observable. For instance, the amount of tricyclic terpanes and of C21-C22 steranes is reduced in Nahal Efe samples. By referring to quantitative data (Supplementary Table 5) and the plots of some parameters, for instance Ts/Tm vs. δ¹³Casp (‰/VPDB, Fig. 10) and Diasteranes/Regular Steranes vs. Steranes/Terpanes (Supplementary Fig. 3), biodegradation is detected to a limited extent. Ts/Tm and Diasteranes/Regular steranes increase in Nahal Efe either in pure bitumens or mixtures due to the selective biodegradation of Tm over Ts and to regular steranes over diasteranes (Bost et al., 2001; Connan et al., 2024). Samples of Tel Gezer are less affected and match the Dead Sea floating blocks and the pure bitumen of Tell Yarmuth. Biodegradation effects are also detected when considering the αββ-steranes composition in a ternary diagram %C27αββR&S steranes vs.

Nº 3502 Nahal Efe
Pure Bitumen

<figure><img src="image_10.png" /></figure>

**Fig. 8.** Mass fragmentograms of steranes (m/z 217) and terpanes (m/z 191) of two samples of Nahal Efe: pure bitumen (N°3502) and a mixture bitumen + minerals (N°3521). C29αβH = norhopane, C30αβH = 17α,21β-hopane, C31αβHR = 17α,21β,22R-30-homohopane, C27αββR + S = 5α,14β,17β-20R + 20S-cholestane, C28αββR + S = 5α,14β,17β-20R + 20S-24methylcholestane, C29αββR + S = 5α,14β,17β-20R + 20S-24ethylcholestane, C29ααα20S = 5α,14α,17α-20S-24ethylcholestane, Ts = 18α-22,29,30-trisnorneohopane, Tm = 17α-22,29,30-trisnorhopane, C34αβHS = C34-17α,21β-22S-extended hopane.

Nº 3521 Nahal Efe
Mature bitumen + minerals

<figure><img src="image_11.png" /></figure>
Nº 1937 Dead Sea
floating blocks

<figure><img src="image_12.png" /></figure>

Nº 3384 Tel Gezer
950 BCE

<figure><img src="image_13.png" /><figcaption>**Fig. 9.** Mass fragmentograms of steranes (m/z 217) and terpanes (m/z 191) of the Dead Sea floating blocks (Nº1937) and of one sample of Tel Gezer (Nº3384). Labels identical to those of Fig. 8.</figcaption></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /><figcaption>**Fig. 10.** Plot of Ts/Tm vs. δ¹³Casp (‰/VPDB): comparison of Nahal Efe to Tell Yarmuth, Tall Dhiban, Tel Gezer and the floating blocks. A: all samples. B: pure bitumens.</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Fig. 11. Composition of αββsteranesR + S in a ternary diagram C27αββR + S vs. C28αββR + S vs. C29αββR + S.</figcaption></figure>

%C28αββR&S steranes vs. %C29αββR&S steranes (Fig. 11). If steranes are unaltered in Tall Dhiban, Tel Gezer and pure bitumens of Tell Yarmuth, they are biodegraded in Nahal Efe and bitumens of potsherd from Tell Yarmuth. However, biodegradation is not affecting steranes in the same manner in Tell Yarmuth and Nahal Efe. In Tell Yarmuth, the C27 steranes are slightly removed whereas in Nahal Efe, it is the C28 steranes that are reduced. This is the reason for the selective stearate degradation are

unknown but may be related to the type of bacteria involved or to differences in preservation conditions.

### 3.4. Aromatics

Mass fragmentograms of phenanthrenes (m/z 178–192), dibenzothiophenes (m/z 184–198) and triaromatic steroids (m/z 231) of 4

<figure><img src="image_17.png" /><figcaption>Fig. 12. Mass fragmentograms of phenanthrenes (m/z 178–192) and dibenzothiophenes (m/z 184–198): Comparison of N°3110 (Tell Yarmouth), N°3384 (Tel Gezer) and Nahal Efe (N°3502 and 3521). P = Phenanthrene, 3, 2, 9, 1 = 3,2,9,1-methylphenanthrene, DBT = dibenzothiophene, 4,2 + 3, 1 = 4, 2 + 3, 1-methyldibenzothiophene.</figcaption></figure>
Triaromatic Steroids (m/z 231)

<figure><img src="image_18.png" /><figcaption>Fig. 13. Mass fragmentograms of triaromatic steroids (m/z 231): Comparison of Tell Yarmuth (Nº 3110), Tel Gezer (Nº 3384) and Nahal Efe (Nº 3502 and Nº 3521). C20 and C21 = C20 and C21 triaromatic sterane, C26S = C26S triaromatic sterane, C26R&C27S = C26R triaromatic sterane + C27S triaromatic sterane.</figcaption></figure>

samples: N° 3310 (Tell Yarmuth), N° 3384 (Tel Gezer), N° 3502 and N°3521 (Nahal Efe) are shown in Figs. 12 and 13 and Supplementary Table 6. They illustrate significant molecular changes that took place in the aromatics. Methylphenanthrenes are clearly detectable in all samples but methyldibenzothiophenes are only seen in Tell Yarmuth (Fig. 12) where they show the characteristic pattern of Dead Sea bitumen (Connan et al., 1992, 2022). Triaromatic steroids are generally slightly biodegraded but changes occur in molecular ratios (e.g., C26S/C28S). C20- C21 are completely removed from Nahal Efe samples (Fig. 13). Two samples (N°3537 and N°3538) are distinct (Supplementary Fig. 6), with triaromatic steroids that are severely altered.

The plot of some characteristic ratios (F1 vs. F2, MDR vs. MPI, TAS5 vs. TAS4,) in Supplementary Figs. 4 to 6 and Supplementary Table 6 shows the significant changes when archaeological samples of Tel Gezer, Tell Yarmuth, Tall Dhiban and Nahal Efe, are compared to present day Dead Sea bitumen. In that respect, bitumen samples from Nahal Efe and those from the Yarmuth potsherd appeared as the most altered ones. The observed changes may be ascribed to biodegradation that may be leading to the deep alteration of triaromatic steroids as in samples N°3537 and 3528 (Supplementary Fig. 6).

### 3.5. Mineralogical analysis

Results of the X-ray diffraction analysis on mixtures of Nahal Efe are presented in Table 1. The major minerals detected in Nahal Efe mixtures are quartz, calcite, dolomite and aragonite. The three first minerals have been detected in 89 archaeological bituminous mixtures of Mari,

Habuba Kabira in Syria, of Khorsabad, Harradum, Babylon, Larsa, Tello, Uruk, Oueili in Iraq, of Failaka and Karranah in the Gulf, of Ra's al-Jinz in Oman (Connan, 2012). An interesting feature of the coastal archaeological sites of Failaka Island is that they contain shell debris in the bitumen mixtures. The situation at Nahal Efe is identical with aragonite coming from shells present in significant amounts in samples N° 3514, 3516, 3536 in which the binocular observation, prior to X-ray diffraction analysis, found white pieces of broken shells. Interestingly, fragmented, and complete seashells from the Mediterranean and Red Sea, some of which are perforated and interpreted as ornaments, have been recovered at the site (Fig. 14), while freshwater shells are absent. Accordingly, it is assumed that debris of shells of marine molluscs was added to other minerals and crushed with bitumen to make mixtures. The occurrence of halite may be coming from the Dead Sea bitumen or from marine shells.

### 3.6. Rock-Eval analysis

The insoluble organic matter, which is a byproduct of the bitumen alteration (Connan and Carter, 2007), has been estimated by analysing the Total Organic Carbon (TOC) in the residues collected after the dichloromethane extraction (Supplementary Table 7). The TOC values of most samples vary from 2.6 to 11.2 % which means 3.25 to 14 % of insoluble organic matter in the residue. Insoluble organic matter is generally lower than the extractable organic matter in dichloromethane except for sample N° 3528 where the insoluble residue is 57 % for a soluble part of 12.6 %. Tmax of the insoluble bitumen varies between
<table><caption>Table 1
Results of the mineralogical analysis.</caption><thead><tr><th rowspan="2">Lab number</th><th rowspan="2">Quartz SiO2</th><th colspan="2">Carbonates</th><th colspan="2">Halite NaCl</th><th rowspan="2">Feldspars</th><th rowspan="2">Tremolite Ca2Mg5 [Si4O11(OH, F)]2</th><th rowspan="2">Phylosilicates</th><th rowspan="2">Bernalite Fe(OH)3</th><th rowspan="2">Koninckite Fe<sup>3</sup>-PO4</th><th rowspan="2">Brushite Ca (PO3OH)</th><th rowspan="2">Foshagite Ca4(Si3O9) (OH)2</th><th rowspan="2">Bulterite Fe3+(SO4) (OH)</th><th rowspan="2">Sphalerite ZnS</th></tr><tr><th>Calcite CaCO3</th><th>Dolomite CaMg(CO3) 2</th><th>Aragonite CaCO3</th></tr></thead><tbody><tr><td>3513</td><td>XXX</td><td>XXX</td><td>XXX</td><td>XX</td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3514</td><td>XXX</td><td>XXX</td><td>x</td><td>XXXX</td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3516</td><td>XXX</td><td>XXX</td><td>XXX</td><td>XXXX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3519</td><td>XXX</td><td>XXX</td><td>XX</td><td>XXX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3522</td><td>XXX</td><td>XXX</td><td>XXX</td><td>x</td><td></td><td>XX</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3525</td><td>XXX</td><td>XXX</td><td>XXX</td><td>XXX</td><td></td><td>x</td><td>XXX</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3528</td><td>XXX</td><td>XX</td><td>x</td><td>XX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td>x</td></tr><tr><td>3530</td><td>XXX</td><td>XXXX</td><td>XX</td><td>XX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>3531</td><td>XXX</td><td>XXXX</td><td>XX</td><td>XX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>3535</td><td>XXX</td><td>XXX</td><td>XX</td><td>XX</td><td></td><td>XX</td><td>XXX</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>3536</td><td>XX</td><td>XXX</td><td>XX</td><td>XX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>3537 bis</td><td>XXX</td><td>XXX</td><td>XXX</td><td>XXX</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td></tr></tbody></table>

420 and 429 °C, i.e. suggesting moderate maturities. Unexpectedly, when Hydrogen index (HI) decreases Oxygen Index (OI) also decreases. The opposite would have been expected in relation to oxidation phenomenon. No explanation was found to this unexpected feature.

## 4. General discussion

The analytical results, mainly from the fingerprints of steranes and terpanes, confirm that the bituminous samples recovered in Nahal Efe are Dead Sea bitumen. The possibility that bitumen and/or natural asphalts came from the closer Nahal Hemar dry riverbed has been discarded because bitumen found there is mixed with gravels and it is likely that the actual oil seep was covered with sediments during the Neolithic (Solazzo et al., 2016). Accordingly, the pure bitumen found at Nahal Efe could not have originated from the mixtures of oil with minerals found at Nahal Hemar.

This is the first time the exploitation and use of Dead Sea bitumen in the desert of the Negev and Sinai about 10,000 years ago (Middle PPNB) by communities of hunter-gatherers has been identified. This is extremely interesting because evidence of the widespread use of bitumen during the Pre-Pottery Neolithic B in the southern Levant came exclusively from farming sites from more humid regions and never from the Negev and Sinai deserts, despite numerous PPNB sites that have been excavated in that region, such as Nahal Karkom, Nahal Reuel, Nahal Issaron, Nahal Roded, Wadi Tbeik or Wadi Jibba I. Additionally, this fact stresses the previously noted importance of the site of Nahal Efe (Borrell and Vardi, 2022; Alcántara et al., 2023), displaying a combination of cultural traits traditionally assigned both to the large sedentary farming villages to the north (e.g., plastered floors, sickle blades, use of bitumen) and to the smaller and highly mobile groups of hunter-gatherers to the south (e.g., circular semisubterranean architecture).

Bituminous mixtures were prepared at the site by adding other minerals (e.g., crushed marine shells, quartz, calcite, etc), both to save the valued pure bitumen and, secondly, to modify (improve) the mechanical properties of the mixtures (in the same way as mineral or vegetal temper is added to clay to produce pottery). The use of the bituminous mixtures produced at the site, however, remains elusive though, as no direct evidence of it has been recovered to date (e.g., stone tools recovered at the site do not display bitumen on its surfaces). However, considering that the most common use of bitumen during the Neolithic period in the southern Levant was as an adhesive for hafting stone tools to the handles (e.g., Bar-Yosef, 1987), it is reasonable to assume that this was also its main use in Nahal Efe. In any case, evidence indicates that this might not have been its only use at the site. The amount of bitumen recovered at the site and the size of some fragments (many ranging between 2 and 4 cm) clearly exceeds the small quantities and volume required for such use. This, together with the identification of different mixtures ('recipes'), the presence of fragments of bitumen with vegetal imprints (some hardly relatable to its use as adhesive), the strong concentration identified in and around the best-preserved house at the site (fully collapsed in situ, Unit 8), point to alternative uses of bitumen in Nahal Efe, perhaps related to some aspects of the construction or maintenance of the buildings (waterproofing of the roof, coating wooden posts or other parts?) or coating basketry.

## 5. Conclusions

The geochemical study of 36 samples from the Pre-Pottery Neolithic site of Nahal Efe (Negev desert, Israel, 8000–7500 cal. BCE) has allowed us to identify Dead Sea bitumen in all samples, except for sample 3503 that is not bitumen. At Nahal Efe, most samples are mixtures of bitumen with minerals (calcite, quartz, dolomite), including aragonite that came from crushed seashells. The entire process of production and use of bituminous mixtures was carried out at the site, including the procurement of chunks of pure Dead Sea bitumen, the preparation of different mixtures (grinding pure bitumen and adding other materials) and finally
<figure><img src="image_19.png" /><figcaption>**Fig. 14.** Shells from Nahal Efe: A, B – *Acanthocardia tuberculata*, C- *Naria nebrites*, D- *Naria* cf. *turdus*, E- probably *Donax trunculus*, F, G – probably *Glycymeris nummaria*.</figcaption></figure>

their use.

Comparison of Nahal Efe with samples of Tel Gezer (1250–700 cal. BCE), Tell Yarmuth (2800–1100 cal. BCE), Tall Dhiban and the pure bitumen of the floating blocks of the Dead Sea, has shown that the bitumens of Nahal Efe are the most altered. This alteration affects ¹³C of both asphaltenes and resins. Consequently, the statement that δ¹³C of asphaltenes is always preserved and therefore is a source indicator must be revised. Surprisingly, steranes and terpanes are not severely degraded as expected and allowed to identify Dead Sea bitumen by its main geochemical characteristics. Dibenzothiophenes and triaromatic steroids are also degraded but phenanthrenes appear as more resistant and survive with some changes.

No obvious evidence of the specific use of the bituminous mixtures has been recognized at the site except some samples with vegetal imprints that may be coming, at least partially, from collapsed roofs. Flint implements do not show any macroscopic traces of bitumen, though the use of bitumen as adhesive for a range of stone instruments (sickle elements, projectile points, small grinding/pounding tools, etc) cannot be discarded.

### CRediT authorship contribution statement

**Jacques Connan:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Ferran Borrell:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. **Jacob Vardi:** Writing – review & editing, Validation, Resources, Project administration, Investigation, Funding acquisition, Data curation. **Samuel Wolff:** Writing – review & editing, Writing – original draft, Visualization, Validation, Resources, Investigation, Data curation. **Steven M. Ortiz:** Writing – review & editing, Visualization, Validation,

Resources. **Michael Engel:** Writing – review & editing, Visualization, Validation, Resources. **Renaud Gley:** Writing – review & editing, Visualization, Validation, Resources. **Alex Zumberge:** Writing – review & editing, Visualization, Validation, Resources.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data availability

Data will be made available on request.

### Acknowledgments

The excavation of Nahal Efe has been carried out with the permission and collaboration of the Israel Antiquities Authority (Licence numbers G-85\2015, G-93\2016, G-23\2018, G-40\2019, G-27\2020, G-61\2021 and G-83\2022). This research has been funded by the Israel Science foundation (grant No. 345/18), the project PID2022-139529NB-100 financed by the MCIN/AEI/10.13039/501100011033/FEDER, UE, the PALARQ Foundation, the Irene Levi Sala CARE Archaeological Foundation (2017); the Spanish National Research Council (PIAR), the Centre de Recherche Français à Jérusalem (CRFJ) and the Generalitat de Catalunya (SGR-2021-00501). The mineralogical study was done in the Pôle de compétence Physico-Chimie de l'Environnement, LIEC Laboratoire UMR 7360 CNRS-Université de Lorraine, France. Finally, we want to acknowledge the work of O. López Bultó, Emil Aladjem and A. Ruiz Cabanzón and D. Bar-Yosef Mayer, who helped us with the general inventory of the bitumen samples, the photogrammetry of the site and the identification of the marine shells, respectively. The comments and
suggestions made by three reviewers and the editors have allowed improving the final version of this paper.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.orggeochem.2024.104844.

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