The spring of Nadaouiyeh Aïn Askar — Paleoecology of a Paleolithic oasis in arid central Syria
Introduction
The area of El Kowm with the Nadaouiyeh Aïn Askar site is located in the arid interior of Syria, about 90 km NE of Palmyra. The region occupies a wide orographic gap between the Balas-Abu Ruimain Block and the Bishri Anticline in the central Palmyrides mountain range that runs from the Anti-Lebanon Mountains to the Euphrates, separating the northern plains from the Arabian Desert in the south (Fig. 1A). At present, and also during most of the Pleistocene, arid conditions prevailed in the wider area of El Kowm, whose small oasis profits from a contiguous cluster of active artesian springs (Fig. 1B). Within a zone less than 12 km across, about 30 natural springs created a number of local wetlands attracting game and humans from afar (Jagher and Le Tensorer, 2011, Jagher et al., 2015). Since the first documented arrival of hominins in the Middle East about 1.8 Ma ago, the wetland cluster of El Kowm oasis steadily has been frequented by people, leaving one of the richest Paleolithic legacies in the Levant in the length of history as well as in the intensity of human activities (Le Tensorer et al., 2001, Jagher et al., 2015).
The modern day springs in the El Kowm area present a particular hydrochemical setting with a high concentration of total dissolved solids (TDS), in average about 2300 mg/l, with a high percentage of sulfates and carbonates (Table 1) (Magueron, 1998). No freshwater springs from this basin are known nowadays. The wells discharge with temperatures between 24 and 32 °C, indicating aquifers about 350–500 m deep upwelling along faults of the Bishri fault system (Brew et al., 2001). Spring deposits occurred in two distinct settings, the first build substantial spring mounds, 200 m to 850 m across, rising up to 20 m over the original landscape (Le Tensorer et al., 2007, Jagher et al., 2015, Pümpin and Jagher, 2005). Other springs occur on karstic systems creating vast dolinas or depressions with extended water bodies or just discharge into the landscape (Jagher et al., 2015). With the diversity of spring types, the depending wetlands show different micro-ecological settings, with a limited extension according to the local topography and discharge intensity of each spring. The extent of these oases is difficult to estimate, but covered an area between a few to a few dozen hectares each, totalized to several square kilometers across the El Kowm Basin (Jagher et al., 2015).
Excavations at the well-site of Nadaouiyeh Aïn Askar have been carried out between 1989 and 2003 by a joint Syro-Swiss team (Directorate General of Antiquities and University of Basel) (Fig. 2), revealing an almost complete section of the Acheulean techno-complex (covering the period of about 550–350 ka ago; Jagher et al., 2015, Jagher, 2000, Jagher, 2011). In fact, Nadaouiyeh Aïn Askar is one of the key-sites for the Middle East to understand the environmental conditions permitting early human dispersal “out-of-Africa” and comprehend the evolution of hand-axe traditions (Jagher, 2000, Jagher, 2011).
The vent of the spring at Nadaouiyeh Aïn Askar created a vertical karst-system (Turberg, 1999, Le Tensorer et al., 2007) that regularly collapsed, giving origin to a succession of at least seven cave-ins opening dolinas up to 30–40 m across and several meters deep, opening lowered sedimentation-spaces protected from erosion. Within a composite stratigraphic column of about 33 m, 32 distinct archeological levels can be grouped, on the basis of their geological context, into seven units, permitting to retrace the evolution of Acheulean hand-axe tradition in a unique resolution of this cultural period in the Middle East (Jagher, 2000, Jagher, 2011).
The potential for a study of the ostracod fauna from this site was demonstrated by geoarcheological investigations with the detection of numerous ostracod shells visible in thin-sections (Fig. 3) and in sieved residues from granulometric analyses of unit VI (Pümpin, 2003).
According to the existing age models for Nadaouiyeh Aïn Askar (Jagher, 2011), unit VI can tentatively be dated to the second half of MIS 13. Within the excavated area of the archeological unit VI, no in situ preserved living floors were observed. The main settlement activity took place outside the excavated area, apparently in the dry area. Nevertheless rich archeological material of flint artifacts, including 168 hand axes, was discovered and copious paleontological material from hunted animals was excavated with occasionally bones still in anatomical connection. The remains of human presence were affected by post depositional effects, probably due to rising and falling water levels and the effect of oscillating waves, acting on the former banks of the pond aligning bones along to the original shorelines. The effects of rising and falling levels of water were clearly visible on different exposures of the layers adjacent to the studied profile, where these phenomena where only discernible in a more discrete manner. However, important human occupation occurred repeatedly during most of the deposition of unit VI.
The timing and regional significance of water availability and its influence on local wetland and spring systems in the central Syrian Desert environments during the Pleistocene are still poorly known, but important for the general understanding of these ecosystems (Pigati et al., 2014), especially in sites documenting early hominin dispersals. Studies on Middle Pleistocene non-marine ostracod faunas, which can be used to infer past environmental settings, are scanty for the eastern Mediterranean region in general (Mischke et al., 2014a, Rosenfeld et al., 2002, Rosenfeld et al., 2004) and missing for Central Syria. Only one additional lacustrine record from Saudi Arabia, dated tentatively to MIS 13, is known from the Arabian-eastern Mediterranean Desert area in this interglacial period, without mentioning microfaunal data (Rosenberg et al., 2013).
Problems based on postdepositional diagenetic processes within Pleistocene sediments from interior desert environments originating from this region did not provide ostracod records older than 93 ka (Kalbe et al., 2014, Mischke et al., 2015), emphasizing the importance and particular interest of the El Kowm spring cluster within the Middle East.
Section snippets
Material and methods
For the present pilot study, a section of the stratigraphy with a nearly continuous sedimentological record and changing conditions within the depositional environment was selected (Fig. 4). A total of 14 sediment samples from a 0.95 m section with a dry weight of 200 g each were used for micropaleontological analyses. The material, comprising limestones, siltstones and mudstones, originally was sampled in 2001 for geoarcheological studies. Samples were dried in a drying oven at 50 °C for 3 days.
Results
The studied sediment column of site Nadaouiyeh Aïn Askar consists mostly of homogenous, consolidated, carbonate rich silts (Fig. 4). Some of the layers contain particularly high numbers of ostracod valves (Figs. 3, 6, 7). At least nineteen different species were recorded; total numbers of ostracods are presented in Supplementary Table 1. Charophyte gyrogonites of Chara vulgaris L. are relatively abundant in the samples of the upper part of the section (Fig. 8 and Pümpin, 2003). Shells of
Discussion
The bulk of the deposits consists of very fine grained carbonate precipitations. TC content increases from the middle of Zone P7/A to the top of the section and displays the increasing carbonate content to the top of the section. The wide co-variation of S and TOC (Fig. 9) suggests that most of the sulfur seems to be related to organic compounds and displays rather the changing organic matter input than precipitated sulfates from the water column (Holmer and Storkholm, 2001, Gross et al., 2011
Conclusions
By their geographical location in the “middle of the road” of the dispersal route “out of Africa”, desert wetlands attracted animals and early humans to these water resources, even when they supply ecologically less optimal oligohaline or mesohaline waters. The adaption of aquatic organisms to fossil and recent desert wetland environments is poorly known for the northern Levant and the Arabian Peninsula. This study provides the first detailed ostracod data for the Middle Pleistocene of Central
Acknowledgements
The ostracod research on the sediments of Nadaouiyeh Aïn Askar was funded by the Deutsche Forschungsgemeinschaft (DFG, grant Mi 730/18-1). The Authors like to thank explicitly S. Mischke for supporting this study with the dataset from Mischke et al. (2014b) and application of the transfer function to the ostracod associations of Nadaouiyeh Aïn Askar. They are also grateful to him and I. Soulié-Märsche for discussions about the fauna and flora of aquatic desert environments. We thank A. Musiol
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