273 research outputs found
New findings of ancient Greek silver sources
Over the last 60 years, much analytical research has sought to determine the ore sources of ancient Greek silver artefacts. Lead isotopic analysis has played a key role in this endeavor. While most studies so far have limited their search to places mentioned in historical sources, the present study takes a different approach by first identifying Ag-bearing ore sources in the Aegean world based on their geological characteristics and then using Pb isotopes to determine whether they were exploited in antiquity. To this end, we have geolocated, sampled, and measured high-precision Pb isotopic compositions of 17 Ag-bearing mineralizations in Greece for which we have evidence of ancient mining activity, and a further 10 exhibiting minor Ag occurrences that may also have been exploited in ancient times. We found that Pb model ages provide better discrimination of ore sources than the more conventional plots of raw Pb isotope data
Rome’s urban history inferred from Pb-contaminated waters trapped in its ancient harbor basins
Heavy metals from urban runoff preserved in sedimentary deposits record long-term economic and industrial development via the expansion and contraction of a city’s infrastructure. Lead concentrations and isotopic compositions measured in the sediments of the harbor of Ostia—Rome’s first harbor—show that lead pipes used in the water supply networks of Rome and Ostia were the only source of radiogenic Pb, which, in geologically young central Italy, is the hallmark of urban pollution. High-resolution geochemical, isotopic, and 14C analyses of a sedimentary core from Ostia harbor have allowed us to date the commissioning of Rome’s lead pipe water distribution system to around the second century BC, considerably later than Rome’s first aqueduct built in the late fourth century BC. Even more significantly, the isotopic record of Pb pollution proves to be an unparalleled proxy for tracking the urban development of ancient Rome over more than a millennium, providing a semiquantitative record of the water system’s initial expansion, its later neglect, probably during the civil wars of the first century BC, and its peaking in extent during the relative stability of the early high Imperial period. This core record fills the gap in the system’s history before the appearance of more detailed literary and inscriptional evidence from the late first century BC onward. It also preserves evidence of the changes in the dynamics of the Tiber River that accompanied the construction of Rome’s artificial port, Portus, during the first and second centuries AD
A lead isotope perspective on urban development in ancient Naples
The influence of a sophisticated water distribution system on urban development in Roman times is tested against the impact of Vesuvius volcanic activity, in particular the great eruption of AD 79, on all of the ancient cities of the Bay of Naples (Neapolis). Written accounts on urbanization outside of Rome are scarce and the archaeological record sketchy, especially during the tumultuous fifth and sixth centuries AD when Neapolis became the dominant city in the region. Here we show that isotopic ratios of lead measured on a well-dated sedimentary sequence from Neapolis’ harbor covering the first six centuries CE have recorded how the AD 79 eruption was followed by a complete overhaul of Neapolis’ water supply network. The Pb isotopic signatures of the sediments further reveal that the previously steady growth of Neapolis’ water distribution system ceased during the collapse of the fifth century AD, although vital repairs to this critical infrastructure were still carried out in the aftermath of invasions and volcanic eruptions
The record of human impact in the sedimentary record at Portus, the harbor of ancient Rome
International audienceThe present study focuses on the analysis of palaeo-pollutions and the sedimentary environments in which they were trapped in the Roman Portus harbor. Portus received heavy-metals pollution both from local foundries, fulling, and tanning and from distal upstream development in Rome. Rome wastewaters, which accounted for up to 3 percent of the total Tiber discharge, were forwarded to Portus through a network of canals (Canale Romano and Canale Trasverso) connecting the river to the sea. In this manner, harbor basins accumulated both allochthonous and autochthonous heavy metals. We determined major and trace element concentrations as well as Pb isotope compositions in a high-resolution set of samples from sediment cores recovered in the Portus area. Principal component analysis of elements that are less prone to the influence of human activities, such as Ca, Mg, Mn, Zr, K, Al, Ti, Na, Sr, and Mn, was used in conjunction with metallic elements to break down the sedimentary load into local and regional components. The record of Pb concentrations and isotopic compositions reveals an overall general trend on which other signatures are superimposed. The geochemical background of the Tiber catchment (24.7-26.2 ppm Pb and 206 Pb/ 207 Pb ~ 1.198) represents geologically young (model age Tm <50 Ma) Pb derived from natural runoff over young sediments and volcanics in the Latium. From the 1 st century AD to the end of the roman period, the harbor regime evolved from a dominant fluvial (enriched in Al, Ti, Mg, K, and Zr) to a more marine influence (high Ca/Mg, Na/Al, Sr, and CaCO3) in the upper part of the harbor unit. "Imperial" Pb (90.5-35.4 ppm Pb and 20
Geodynamic implications for zonal and meridional isotopic patterns across the northern Lau and North Fiji Basins
We present new Sr-Nd-Pb-Hf-He isotopic data for sixty-five volcanic samples from the northern Lau and North Fiji Basin. This includes forty-seven lavas obtained from forty dredge sites spanning an east-west transect across the Lau and North Fiji basins, ten ocean island basalt (OIB)-type lavas collected from seven Fijian islands, and eight OIB lavas sampled on Rotuma. For the first time we are able to map clear north-south and east-west geochemical gradients in 87Sr/86Sr across the northern Lau and North Fiji Basins: lavas with the most geochemically enriched radiogenic isotopic signatures are located in the northeast Lau Basin, while signatures of geochemical enrichment are diminished to the south and west away from the Samoan hotspot. Based on these geochemical patterns and plate reconstructions of the region, these observations are best explained by the addition of Samoa, Rurutu, and Rarotonga hotspot material over the past 4 Ma. We suggest that underplated Samoan material has been advected into the Lau Basin over the past ∼4 Ma. As the slab migrated west (and toward the Samoan plume) via rollback over time, younger and hotter (and therefore less viscous) underplated Samoan plume material was entrained. Thus, entrainment efficiency of underplated plume material was enhanced, and Samoan plume signatures in the Lau Basin became stronger as the trench approached the Samoan hotspot. The addition of subducted volcanoes to the Cook-Austral Volcanic Lineament material, first from the Rarotonga hotspot, then followed by the Rurutu hotspot, contributes to the extreme geochemical signatures observed in the northeast Lau Basin
Upper Mantle Pollution during Afar Plume-Continental Rift Interaction
International audienceNew Pb, Sr, Nd, Hf, and He isotope data for Quaternary basalts, erupted from Debre Zeyit, Butajira, and the Wonji Fault Belt of the Main Ethiopian Rift, show systematic mixing relationships involving three distinct mantle sources. The Pb, Sr, Nd, and Hf isotopic arrays converge in a specific region of isotopic multi-space where they define the composition of the Afar mantle plume (centered about (206)Pb/(204)Pb = 19 center dot 5, (87)Sr/(86)Sr = 0 center dot 7035, epsilon(Nd) = +4 center dot 6, epsilon(Hf) = +9 center dot 3, (3)He/(4)He > 15 R(A)). This plume end-member has an identical composition to that observed previously in oceanic basalts. The distinct isotopic arrays for the various volcanic areas in the Main Ethiopian Rift vary spatially in a systematic manner, and may be viewed as pseudo-binary mixing arrays. This further suggests that the Afar mantle plume interacts with the local continental lithosphere and upper mantle asthenosphere (mid-ocean ridge basalt-like source) through an ordered sequence of mixing events. Simple mixing models require that the mass proportions of continental lithosphere and upper mantle involved in magma generation must be nearly constant within each volcanic area, but that the proportion of plume material decreases regularly with distance southwestward along the Main Ethiopian Rift, away from the central axis of the plume. This systematic behavior means that continental lithosphere can become detached and mixed into the shallow mantle prior to the flow of upwelling plume material beneath the developing rift system. Detachment and mixing into the asthenosphere during continental rift evolution is an important process for producing the range of ambient upper mantle compositions sampled by mid-ocean ridge volcanism away from island hotspots
Geochemical investigation of a sediment core from the Trajan basin at Portus, the harbor of ancient Rome
International audiencea journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t From the 1st century AD and for the duration of the Roman Empire, the Portus complex was the main harbor of Rome. Its location on the Tiber delta next to the Tyrrhenian Sea produced rapid environmental changes that, together with historical vicissitudes, largely determined the fate of the harbor. We have assembled data on the mineralogy, sedimentology, geochemistry, and ostracod populations of a sediment core drilled in the access channel of the hexagonal basin of Trajan, with the expectation that such a combined data set will shed new light on how the connections of the inland Trajan basin with the Tiber river, the earlier Claudius harbor on the nearby shoreline, and the sea evolved through the centuries. The data define four distinct periods which geochemistry characterizes by different conditions of salinity and oxygenation. These in turn can be related to historical periods and events by means of 1
Definition of a new approach in ancient harbor geoarchaeology: geochemistry and ostracod analyses at Portus (Tiber delta, central Italy)
International audiencePortus constituted the harbour complex of imperial Rome from the 1st century AD onward. Located in a deltaic environment, the harbour was subject to influences of the Tyrrhenian marine environment and of the fluvial waters of the Tiber River. Such complex sedimentary processes registered also rapid environ-mental changes. Our research is based on the study of a sediment core (TR14) drilled in the access channel of the hexagonal basin of Trajan (Fig. 1). The goal of our study is the reconstruction the palaeo-environmental dynamics of the water column of the harbour according to a geochemical and an ostra-codological approach. The analysis of the ostracod assemblage has evidenced several palaeo-environmental phases. These phases could be identified through the autoeco-logical analysis of the 25 recognised taxa and their classification in four eco-logical groups (MAZZINI et al., 2011). The results obtained present a succession of four environments, defined by variations in salinity and oxygenation. From the bottom to a depth of 643 cm, the environment was a marine to brackish lagoon influenced by strong marine inputs as evidenced by the vic-ariance of Cyprideis torosa and Pontocythere turbida. P. turbida is a typical phy-tal ostracod often found together with Posidonia oceanica remains. From 600 to 454 cm the coastal marine environment becomes more stable. This could be linked to the establishment of the harbour activities and maintenance. The sta-bility of the environment is still evident in the subsequent group, from 435 to 305 cm, characterised by the dominance of C. torosa and the lack of any fresh-water influence. The increase in salinity could be related to evaporative effects on a closed body of water. From 300 cm the freshwater input becomes clear and constant although the influence of the close sea/brackish body of water is still noticeable. In the last metres a typical freshwater assemblage is represent-ed, dominated by truly freshwater taxa (Candona sp. and Pseudocandona marchica), evidence for the occurrence of a freshwater marsh. The geochemical results were analysed by Principal Components Analy-sis (PCA). The samples were assembled in several groups based on a Hierar-chical Ascendant Classification (cluster analysis). Through PCA analysis, the geochemical and ostracological results of the "functional" harbour unit (800-300 cm) were combined. The different elements recorded in the geochemical analysis are distributed according to the main ostracod assemblages (from fresh water to brackish water and sea water). These elements have been grouped according to the model proposed by SAGEMAN & LYONS (2003). An evolution of these deposits in three stages is proposed. While the fluvial envi-ronments were quite well oxygenated, the harbour environment was more characterised by an increasing anoxia of the water column as it was observed by ELMALEH et al. (2012) in the harbor of Tyre. In a second phase, the varia-tions in salinity distinguished the nature of the fluvial environments and the degree of openness to the sea of the harbour environment. The final phase is specific to a body of water completely isolated from fluviatile and marin
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Helium isotopic textures in Earth’s upper mantle
We report ³He/⁴He for 150 mid-ocean ridge basalt (MORB) glasses from the Southeast Indian
Ridge (SEIR). Between 81°E and 101°E ³He/⁴He varies from 7.5 to 10.2 R[subscript A], encompassing more than half the
MORB range away from ocean island hot spots. Abrupt transitions are present and in one case the full range
occurs over ~10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite
or eclogite leads to lower ³He/⁴He, while ³He/⁴He above ~9 R[subscript A] likely indicates melting of pyroxenite-free
or eclogite-free mantle. Patterns in the length scales of variability represent a description of helium isotopic
texture. We utilize four complementary methods of spectral analysis to evaluate this texture, including
periodogram, redfit, multitaper method, and continuous wavelet transform. Long-wavelength lobes with
prominent power at 1000 and 500 km are present in all treatments, similar to hot spot-type spectra in Atlantic
periodograms. The densely sampled region of the SEIR considered separately shows significant power at
~100 and ~30–40 km, the latter scale resembling heterogeneity in the bimodal distribution of Hf and Pb
isotopes in the same sample suite. Wavelet transform coherence reveals that ³He/⁴He varies in-phase with
axial depth along the SEIR at ~1000 km length scale, suggesting a coupling between melt production,
³He/⁴He and regional variations in mantle temperature. Collectively, our results show that the length scales
of MORB ³He/⁴He variability are dominantly controlled by folding and stretching of heterogeneities during
regional (~1000 km) and mesoscale (~100 km) mantle flow, and by sampling during the partial melting
process (~30 km).Keywords: MORB, Mantle heterogeneity, Helium isotopes, Southeast Indian Ridge, Mid-ocean ridge
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