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1.
Antnio M. Monge Soares Jos M. Matos Martins 《Journal of archaeological science》2009,36(12):2875-2881
Radiocarbon dates on marine shells have not been used as extensively as charcoal or bone dates for the setting up of absolute chronologies because interpreting these dates is complicated by the marine radiocarbon reservoir effect. Nevertheless marine shellfish were used widely at least during the Holocene and their shells are abundant and usually well preserved in archaeological deposits located near shorelines. Consequently prior research concerning the oceanographic conditions and the marine radiocarbon reservoir effect of a particular coastal area is needed in order to set up reliable chronologies for that region. Values of regional marine radiocarbon reservoir effect – ΔR – of coastal waters off Atlantic Iberia, some of its variability along the Holocene and its correlation with the upwelling phenomenon were determined during previous research. More data related to the ΔR values for western Portuguese coastal waters during the Late Neolithic and the Chalcolithic, a time interval badly sampled in previous research, were recently obtained. These values can be compared with ΔR values already determined for the Gulf of Cadiz. Besides the importance of these values for a better knowledge of the palaeoceanography and palaeoclimatology of Atlantic Iberia, from now on archaeologists can set up reliable chronologies for Late Neolithic and Chalcolithic contexts using marine shell samples of that origin for radiocarbon dating. 相似文献
2.
Freshwater resources in past diets can lead to inaccuracies when attempts are made to ascertain their radiocarbon ages or those of the consumers. Radiocarbon reservoir effects may lead to significant age offsets when the bones or other tissues of these consumers are radiocarbon dated. A number of recent studies have investigated freshwater reservoir offsets. However no study thus far has satisfactorily obtained a ubiquitous freshwater reservoir correction due to variability in the ecosystems analysed. This study tests the possibility of predicting freshwater reservoir effects from the carbonate alkalinity of the water with measurements on modern fish bone and water samples. A predictive capability would be especially valuable in the absence of well-preserved archaeological fish bone. We surveyed samples from lakes and rivers in varying geological settings in Britain and Ireland. Modern fish bone and water samples were analysed to investigate modern radiocarbon offsets from the atmosphere. Archaeological fish bone was also analysed to examine past reservoir offsets at selected sites. Stable carbon and nitrogen isotope values were measured to aid in interpretation of any variability in the offsets. Large freshwater reservoir offsets were measured in some modern and archaeological samples (maximum offset = 1638 14C years). The freshwater reservoir offsets in the fish bone were highly correlated with alkalinity of water in modern lake sites analysed. However, a high amount of variation within and between fish species was also evident in the results, precluding the possibility of providing regional corrections for freshwater reservoir offsets from alkalinity although this still may provide a general guideline. The variability is thought to be due to differences in the diet of individual fish. 相似文献
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This paper reviews the results of a long-term research project that used stable isotope analyses (δ13C, δ15N, δ34S) and Bayesian mixing models to better model the chronology for a presumed Viking Age cemetery at Hofstaðir, near Lake Mývatn in north-east Iceland. δ13C and radiocarbon dating indicated that many of the individuals consumed a large amount of marine protein, which results in a marine reservoir effect (MRE), making ages older than expected. In addition to the MRE, geological activity in the region has the potential to introduce massive quantities of radioactive ‘dead’ carbon into the freshwater system, resulting in a very large freshwater reservoir effect (FRE) that can offset radiocarbon ages on the order of a few thousand years. The radiocarbon dates of organisms that derive an unknown proportion of their carbon from both marine and freshwater reservoirs are extremely difficult to ‘correct’, or, more appropriately, model. The research not only highlights the complexities of dealing with multiple reservoirs, but also how important it is to develop models that are temporally and geographically relevant to the site under study. Finally, it shows how this data can be used to inform the development of chronological models for refining the dating for archaeological activity. 相似文献
4.
WAL AMBROSE FIONA PETCHEY PAMELA SWADLING HARRY BERAN ELIZABETH BONSHEK KATHERINE SZABO SIMON BICKLER GLENN SUMMERHAYES 《Archaeology in Oceania》2012,47(3):113-132
In the early 1900s thirteen engraved Conus shell valuables were dug from prehistoric midden mounds in Oro Province. Since the early 1970s nineteen undated surface finds have been found in the northern Massim of Milne Bay Province. When three artifacts became available for AMS radiocarbon dating, provided they were restored after sampling to their original visual appearance, a specialist team was assembled and this paper reports its findings regarding the thirty‐two shells. The paper covers sampling and conservation, dating (including new information on the local oceanic reservoir effect), distribution, art, depositional and cultural histories. These distinctive Conus shell valuables are part of the material culture found along the northern coast of the eastern tip of New Guinea and on the islands of the northern Massim during the Expansion Phase c.1000–500 BP. Their decoration is comparable to that produced by Milne Bay Province woodcarvers in historic times. This continuity makes them the oldest radiocarbon dated artifacts decorated in the Massim art style. 相似文献
5.
We present the first direct assessment of marine reservoir effects in the Moreton Bay region using radiocarbon dating of known‐age, pre‐AD 1950, shell samples from the east coast of Stradbroke Island and archaeological shell/charcoal pairs from Peel Island in Moreton Bay. The resulting ΔR value of 9±19 14C years for the open ocean conforms to regional values established for northeast Australia of 12±10 14C years. Negative ΔR values of −65±61 14C years and −216±94 14C years for southern Moreton Bay highlight the potential for larger offsets over the last ∼900 years. These may be linked to changing terrestrial inputs and local circulation patterns. 相似文献
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This paper presents preliminary results of new radiocarbon dating of human, faunal and fish skeletal remains from a number of the cemeteries from the Middle and Lower Dnieper Basin, Ukraine. The results appear to demonstrate the presence of a radiocarbon reservoir effect during the Neolithic–Eneolithic periods, the first time that this has been identified in this region. The data indicate that the radiocarbon reservoir effect is currently only evident during these periods, and not in the earlier Epipalaeolithic–Mesolithic periods, prompting the suggestion that the radiocarbon reservoir effect is associated with elevated fish consumption from the Neolithic period onwards. 相似文献
8.
In this paper, we attempt to differentiate hydrocarbon‐bearing reservoir horizons of the Junggar Basin of NW China based on the characteristics of diagenesis and associated elemental geochemistry. Reservoirs at this site have varying levels of oil saturation that correlate with the degree of dissolution in minerals (e.g., calcite and feldspar). Four different horizons with varying diagenetic mineral assemblages were observed, including (i) kaolinite‐rich, oil‐dominated horizons, (ii) kaolinite–pyrite–hematite‐rich, oil–water‐dominated horizons, (iii) siderite–chlorite‐rich, water‐dominated horizons, and (iv) chlorite‐rich horizons with negligible hydrocarbon production. The mean MnO content of the representative diagenetic mineral (e.g., calcite) in each of the above horizons is >2.5, 2.0–2.5, 1.5–2.0, and <1.0 wt%, respectively. We propose that the above methodology can be used for the identification of reservoir hydrocarbon‐bearing horizons. We argue that the indicators presented here can be applied in oil exploration across the Junggar Basin. 相似文献
9.
The interactions of nature and society are intimately reflected in the degradation of the vast, yet diverse, landscapes and ecosystems of arid western China. The development of agriculture, especially irrigation, has altered rivers, soils and ecosystems so much that major ecological rehabilitation and restoration efforts have been needed since 1950. The catchments of the Tarim River in southern Xinjiang (the Tarim Basin) and of the Black River (Hei He) in Gansu Province and western Inner Mongolia provide examples of the benefits, difficulties and conflicts involved in dryland water management. In the early stages of the human development of these catchments, agriculture depending on irrigation using water from these inland rivers was encouraged. The over‐exploitation of these water resources led to such ecological problems as desiccation of lakes, drying out of rivers, degradation of soils and vegetation and lowering of groundwater levels, with consequent environmental and economic impacts. Since 1990 several high‐cost, national projects to re‐establish ecosystems have been initiated. Water is now released from dams in the headwaters of the rivers in order to restore water flows to the dried out lake basins. Such schemes have inevitably led to social problems and difficulties for the people who depended on the water from the dams for local irrigation. The contrasts in adjustments and attitudes over the use of water for agriculture and other economic activities, as opposed to schemes of restoration of ecosystems and ecological engineering, stem largely from two issues; inconsistent provision of information from the scientific community, and differing ideologies, namely environmental protection versus economic development. 相似文献
10.
To quantify and rank gas wettability of coal as a key parameter affecting the extent of CO2 sequestration in coal and CH4 recovery from coal, we developed a contact angle measuring system based on a captive gas bubble technique. We used this system to study the gas wetting properties of an Australian coal from the Sydney Basin. Gas bubbles were generated and captivated beneath a coal sample within a distilled water‐filled (pH 5.7) pressurised cell. Because of the use of distilled water, and the continuous dissolution and shrinkage of the gas bubble in water during measurement, the contact angles measured correspond to a ‘transient receding’ contact angle. To take into account the mixed‐gas nature (CO2, CH4, and to a lesser extent N2) of coal seam gas in the basin, we evaluated the relative wettability of coal by CH4, CO2 and N2 gases in the presence of water. Measurements were taken at various pressures of up to 15 MPa for CH4 and N2, and up to 6 MPa for CO2 at a constant temperature of 22°C. Overall, our results show that CO2 wets coal more extensively than CH4, which in turn wets coal slightly more than N2. Moreover, the contact angle reduces as the pressure increases, and becomes < 90° at various pressures depending on the gas type. In other words, all three gases wet coal better than water under sufficiently high pressure. 相似文献