Holocene chronologies from mollusk shells at archeological sites on the southern Arabian Peninsula
Prehistory and World Archaeology
Final Report Abstract
The southern part of the Arabian Peninsula is rich in archaeological sites and might have been a passage of humans from Africa to Asia and Europe along the coast. However, dating of these sites faces several difficulties, in particular because organic matter for radiocarbon dating, such as bone collagen, is rarely preserved. Instead, aragonitic marine shells are frequently found in excavations and form waste deposits, the so called shell middens. Basically, they can also be used for radiocarbon dating, however, their radiocarbon age are up to hundreds to thousands of years older than the real age. The reason is the incorporation of old marine carbon in the shells which needs to be corrected. This so called reservoir effect is generated by storage of deep ocean waters over thousands of years. During this time the ocean water becomes depleted due to partial decay of initially incorporated atmospheric radiocarbon which is not replenished in the deep sea. Correcting for this effect for a given period and location is required to establish reliable chronologies. This is of particular importance along the coast of the Gulf of Oman where deep ocean waters are upwelling and oceanic circulation changed over time. Our study aimed at understanding and quantifying the marine reservoir effect with respect to site-related factors and temporal variation in southern Arabia and to improve archaeological chronologies in this region. The suitability of shells for environmental monitoring is investigated using sclerochronology and stable isotopes and interpreted on the basis of background information on diet and habitat of respective mollusc species. The archaeological site of Kalba was chosen as main study area. Kalba is located between the Gulf of Oman and the Hajar Mountains and provides shells of different species from a mangrove forest that has existed since at least the mid-Holocene (ca. 7000 cal BP). Archaeological sites in Kalba dating to Neolithic and to the Bronze Age offer sediment layers rich in shells. Additionally, Kalba offers the unique possibility to monitor seasonal ocean circulation patterns where upwelling from the Arabian Sea to the South alternates with saline, dense outflow of Arabian Gulf waters. The study concentrated on two shell species from Kalba, the bivalve Anadara uropigimelana and the gastropod Terebralia palustris, because they are often found in archaeological contexts. In order to determine the reservoir effect, radiocarbon ages of shells must be correlated to ages of organic carbon. This combination can be found in ash layers of human-made fire. Such shell and charcoal pairs were recovered from four layers representing two periods, Neolithic and Bronze Age, to evaluate temporal changes in the species-specific reservoir effect. For A. uropigimelana a drop in reservoir effect ΔR from 576 ± 90 to 112 ± 44 years over this period was calculated, whereas for T. palustris the values decreases from 389 ± 66 to -19 ± 36 years. This species-specific reservoir effect likely reflects differences in habitat and/or dietary habits. T. palustris with a mainly terrestrial diet yielded a significantly lower ΔR compared to the mainly marine influenced A. uropigimelana. The temporal changes are probably explained by reduced upwelling in the Arabian Sea as observed in marine sediment cores, due to a decrease in summer monsoon strength and reflect environmental changes as well as changes in ocean currents and sea level. Therefore, shells can be used as palaeoenvironmental archive, too. This also applies to heated shells. For the first time we could show, that heating does not affect radiocarbon ages and stable isotope signatures, hence both can be reliably used for dating. Moreover, we tested if terrestrial gastropod shells may be also used for radiocarbon dating when their hardwater effect is known. Here, the geological substrate is crucial. We could show that silicate rocks show a lower hardwater effect compared to carbonate rocks, but also other environmental factors have to be taken into account to come up with reliable ages. The lack of living specimen prevented further progress in this approach.
Publications
- (2016): Investigating the Local Reservoir Age and Stable Isotopes of Shells from South-East Arabia. Radiocarbon 2016, 1-18
Lindauer, S., Marali, S., Schöne, B.R., Uerpmann, H.-P., Kromer, B. & Hinderer, M.
(See online at https://doi.org/10.1017/RDC.2016.80) - (2017): The Local Marine Reservoir Effect at Kalba (UAE) between Neolithic and Bronze Age: An indicator of Sea Level and Climate Changes. Quaternary Geochronology 42: 105-116
Lindauer, S., Guaciara, S., Steinhof, A., Yousif, E., Phillips, C.S., Jasmin, S.A., H.-P. Uerpmann, Hinderer, M.
(See online at https://doi.org/10.1016/j.quageo.2017.09.003) - (2018): Heating mollusc shells - a radiocarbon and microstructure perspective from archaeological shells recovered from Kalba, Sharjah Emirate, UAE. Journal of Archaeological Science - Reports 21: 528-537
Lindauer, S., Milano, S., Steinhof, A., Hinderer, M.
(See online at https://doi.org/10.1016/j.jasrep.2018.08.041) - (2018): HLO1-South: An Early Neolithic Site in the Wadi al-Hilo (Sharjah, UAE). Arabian Archaeology and Epigraphy, 29: 1- 9
Uerpmann, H.-P., Uerpmann, M. with contributions from Ghukasyan, R., Hinderer, M., Keyesan, S., Lindauer, S., Neureiter, C., Petrosyan, A.
(See online at https://doi.org/10.1111/aae.12107) - (2019): Highly-Resolved Radiocarbon Measurements on Shells using Carbonate Handling System and Gas Ion Source with MICADAS. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 455: 146-153
Lindauer, S., Friedrich, R., van Gyseghem, R., Schöne, B. R., Hinderer, M.
(See online at https://doi.org/10.1016/j.nimb.2018.12.020)
