Ancient harbour areas represent a peculiar context where the cooperation between geosciences and archaeology may provide useful information about the mutual interactions involving natural settings and human society. Several multidisciplinary studies have recently focused on Mediterranean seaports evolution, furnishing a wide literature about past bio-sedimentary response to harbour activities (Marriner et al., 2010). On the contrast few geoarchaeological-palaeoecological data on strictly lacustrine harbours, where the importance of ostracods as bioindicators is enhanced by the lack of other organisms as foraminifers, are available. As a part of the “Magdala project” and in the framework of the late Hellenistic-Roman (167 BC-350 AD) sedimentary history reconstructed by Sarti et al. (in press) for Magdala harbour area (Kinneret Lake, north Israel), quantitative ostracod analyses were performed on 28 samples collected from two key stratigraphic sections excavated in front of the Roman harbour structures (docks and a flight of stairs). Along the sections, detailed described in terms of sedimentological features and anthropogenic artifacts (Lena, 2012; Sarti et al., in press), the abundant and well-preserved ostracod fauna show a very similar faunal composition and distribution. Despite the oligotypic character of the ostracod community, strongly dominated by the opportunistic, true euryhaline species Cyprideis torosa, two different associations were distinguished. Similarly to what observed within the present-day lake basin at ca. 5 m water depth (Mischke et al., 2010), comparable proportion of smooth and noded valves of C. torosa characterize the sandy interval barren in anthropogenic artifacts and interpreted as the natural lacustrine beach at the sections bottom (pre-harbour unit). At the passage to the overlying bay silty sands, containing several late Hellenistic archaeological artifacts, a sharp increase of noded C. torosa (up to 87% of total fauna) is recorded along with the occurrence of other species preferring fine-grained substrates and high-organic stagnant waters, as Pseudocandona albicans. This diagnostic change in ostracod content is paralleled by a sharp increase in concentration (up to double concentration values) of trace metals Zn, Pb and Cu within the silty sands interval, suggesting the establishment of an anthropogenically forced semi-protected basin with high levels of heavy-metal pollution during the late Hellenistic period (sin-harbour unit). In order to increase the quality of our palaeoenvironmental reconstructions and provide insights into the harbour water chemistry derived by human activities, ostracod geochemistry analyses (ICP-MS, …) are in progress on C. torosa valves recovered from the pre-harbour and sin-harbour units. The integration of palaeontological and geochemical analyses will potentially differentiate unpolluted from polluted conditions, avoiding complications related to grain-size partitioning. This methodological approach may also improve our knowledge about the “factor X” (van Harten, 2000) that contributes to the development of phenotypic nodes on C. torosa within freshwater-oligohaline settings. Comparing element concentrations with the frequency of noded forms and plotting shell chemistry of smooth versus noded valves can provide new information about ostracods, including C. torosa ecophenotypical features, as bioindicators of high pollution levels within ancient lacustrine harbours.

Environmental changes in the lacustrine ancient harbour of Magdala (Kinneret Lake, Israel) inferred from ostracod, geochemical and sedimentological analyses

SARTI, GIOVANNI
2013

Abstract

Ancient harbour areas represent a peculiar context where the cooperation between geosciences and archaeology may provide useful information about the mutual interactions involving natural settings and human society. Several multidisciplinary studies have recently focused on Mediterranean seaports evolution, furnishing a wide literature about past bio-sedimentary response to harbour activities (Marriner et al., 2010). On the contrast few geoarchaeological-palaeoecological data on strictly lacustrine harbours, where the importance of ostracods as bioindicators is enhanced by the lack of other organisms as foraminifers, are available. As a part of the “Magdala project” and in the framework of the late Hellenistic-Roman (167 BC-350 AD) sedimentary history reconstructed by Sarti et al. (in press) for Magdala harbour area (Kinneret Lake, north Israel), quantitative ostracod analyses were performed on 28 samples collected from two key stratigraphic sections excavated in front of the Roman harbour structures (docks and a flight of stairs). Along the sections, detailed described in terms of sedimentological features and anthropogenic artifacts (Lena, 2012; Sarti et al., in press), the abundant and well-preserved ostracod fauna show a very similar faunal composition and distribution. Despite the oligotypic character of the ostracod community, strongly dominated by the opportunistic, true euryhaline species Cyprideis torosa, two different associations were distinguished. Similarly to what observed within the present-day lake basin at ca. 5 m water depth (Mischke et al., 2010), comparable proportion of smooth and noded valves of C. torosa characterize the sandy interval barren in anthropogenic artifacts and interpreted as the natural lacustrine beach at the sections bottom (pre-harbour unit). At the passage to the overlying bay silty sands, containing several late Hellenistic archaeological artifacts, a sharp increase of noded C. torosa (up to 87% of total fauna) is recorded along with the occurrence of other species preferring fine-grained substrates and high-organic stagnant waters, as Pseudocandona albicans. This diagnostic change in ostracod content is paralleled by a sharp increase in concentration (up to double concentration values) of trace metals Zn, Pb and Cu within the silty sands interval, suggesting the establishment of an anthropogenically forced semi-protected basin with high levels of heavy-metal pollution during the late Hellenistic period (sin-harbour unit). In order to increase the quality of our palaeoenvironmental reconstructions and provide insights into the harbour water chemistry derived by human activities, ostracod geochemistry analyses (ICP-MS, …) are in progress on C. torosa valves recovered from the pre-harbour and sin-harbour units. The integration of palaeontological and geochemical analyses will potentially differentiate unpolluted from polluted conditions, avoiding complications related to grain-size partitioning. This methodological approach may also improve our knowledge about the “factor X” (van Harten, 2000) that contributes to the development of phenotypic nodes on C. torosa within freshwater-oligohaline settings. Comparing element concentrations with the frequency of noded forms and plotting shell chemistry of smooth versus noded valves can provide new information about ostracods, including C. torosa ecophenotypical features, as bioindicators of high pollution levels within ancient lacustrine harbours.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/224326
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