Homo floresiensis and the late Pleistocene environments of eastern Indonesia: defining the nature of the relationship

Evidence from Liang Bua, a limestone cave on the island of Flores in East Indonesia, provides a unique opportunity to explore the long term relationship between hominins and their environment. Occupation deposits at the site span ～95 ka and contain abundant stone artefacts, well preserved faunal remains and evidence for an endemic species of hominin: Homo floresiensis. Work at the site included detailed geomorphological and environmental analysis, which has enabled comparisons to be drawn between changes in the occupational intensity in the cave, using stone tool and faunal counts, and changes in the environmental conditions, using the characteristics of the sedimentary layers in the cave and speleothem records. These comparisons demonstrate that H. floresiensis endured rapidly fluctuating environmental conditions over the last ～100 ka, which influenced the geomorphological processes in the cave and their occupational conditions. The intensity of occupation in the cave changed significantly between 95 and 17 ka, with peaks in occupation occurring at 100–95, 74–61 and 18–17 ka. These correlate with episodes of channel formation and erosion in the cave, which in turn correspond with high rainfall, thick soils and high bio-productivity outside. In contrast, periods of low occupational intensity correlate with reduced channel activity and pooling associated with drier periods from 94 to 75 and 36 to 19 ka. This apparent link between intensity of hominin use of the cave and the general conditions outside relates to the expansion and contraction of the rainforest and the ability of H. floresiensis to adapt to habitat changes. This interpretation implies that these diminutive hominins were able to survive abrupt and prolonged environmental changes by changing their favoured occupation sites. These data provide the basis for a model of human–environment interactions on the island of Flores. With the addition of extra data from other sites on Flores, this model will provide a greater understanding of H. floresiensis as a unique human species.     

A sustained +21 m sea-level highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda

A small, protected karstic feature exposed in a limestone quarry in Bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase, still-stand, and regressive phase of a sea-level in excess of 21.3 m above present during Marine Isotope Stage (MIS) 11 (400 ka) as determined by U/Th dating and amino acid racemization. Cobbles and marine sediments deposited during the high-energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment. This was succeeded stratigraphically by a still-stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates, probably upogebiid shrimp, that could not be produced under any condition other than sustained marine submergence. Overlying this were pure carbonate beach sands of a low-energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates. The considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run-up waves over a minimum duration of months, if not years. The maximum duration has yet to be determined but probably did not exceed one or two thousand years. The most abundant snails in this fauna are two species indicative of brackish water and high-tide line showing that a Ghyben-Herzberg lens must have existed at > + 20 m. The nature of these sediments and fossil accumulation is incompatible with tsunami deposition and, given the absence of evidence for tectonic uplift of the Bermuda pedestal or platform, provide proof that sea-level during MIS 11 exceeded +20 m, a fact that has widespread ramifications for geologists, biogeographers, and human demographics along the world's coastlines.     

A demonstration of the high variability of chars produced from wood in bushfires

Vegetation fires play a major role in global C cycling through the addition of inert carbon (char) to the environment. The objective of this study was to compare and contrast the chemical composition of 53 natural chars collected from the soil surface 6–32 years after a natural fire. In order to achieve this, we applied a recently developed nuclear magnetic resonance (NMR) technique that gauges the degree of condensation of aromatic structures within chars. Our results show that the degree of condensation varied considerably among char samples (n = 4–5), collected from burnt-out tree stumps at each of the 11 fire sites. This demonstrates that there is a great degree of variability in the composition of the char produced in natural fires, which is likely to be reflected in widely varying rates of char decomposition. This highlights a major difficulty in quantifying the effects of vegetation fires on global C cycling. Importantly, no differences could be discerned between chars of different ages, indicating that ageing of this type of char in this environment is slow on the decadal timescale. Finally, this study demonstrates that although char samples appear to preserve a record of fire conditions, great care must be taken when interpreting this record to account for the high degree of heterogeneity in char composition. Bulking of char samples would alleviate this problem to some extent; however, bulking would mask the inter-particle heterogeneity clearly evident in this study.     

Chironomids as a tool for inferring Holocene climate: an assessment based on six sites in southern Scandinavia

Chironomid subfossil assemblages from six low-alpine and sub-alpine Holocene stratigraphies are presented and compared. They are from five lakes in mid-southern and western Norway and one in central Sweden. When comparing the chironomid-inferred July air temperatures, there are many time segments with a poor among-lake fit in inferred temperatures. Possible environmental variables influencing the fossil chironomid assemblages are discussed using a modern Norwegian calibration data set to indicate taxon–environment relationships. These analyses indicate that local changes in pH, water chemistry, and productivity at times may have overridden the regional temperature signal. In addition, other causes of poor among-site temperature fit are discussed, in particular those related to chronological uncertainties. Holocene temperature inferences from single cores based on chironomids may not always be able to provide a reliable regional temperature signal, but can act as a guide from which hypotheses about past environmental conditions can be tested with the aid of chironomid-inferred temperatures from several sites and from other environmental proxies. We have obtained a regional picture of Holocene summer temperature change by developing a consensus reconstruction based on the overall temperature signal from all six sites. This consensus is developed by fitting a smoother through all 330 site-specific temperature-deviations from the Holocene mean. The consensus temperature deviations vary from −0.8 °C at 8800 cal years BP to +0.8 °C at 6500 cal years BP.     

Vegetation change,goats, and religion: a 2000-year history of land use in southern Morocco

Understanding past human–climate–environment interactions is essential for assessing the vulnerability of landscapes and ecosystems to future climate change. This is particularly important in southern Morocco where the current vegetation is impacted by pastoralism, and the region is highly sensitive to climate variability. Here, we present a 2000-year record of vegetation, sedimentation rate, XRF chemical element intensities, and particle size from two decadal-resolved, marine sediment cores, raised from offshore Cape Ghir, southern Morocco. The results show that between 650 and 850 AD the sedimentation rate increased dramatically from 100 cm/1000 years to 300 cm/1000 years, and the Fe/Ca and pollen flux doubled, together indicating higher inputs of terrestrial sediment. Particle size measurements and end-member modelling suggest increased fluvial transport of the sediment. Beginning at 650 AD pollen levels from Cichorioideae species show a sharp rise from 10% to 20%. Pollen from Atemisia and Plantago, also increase from this time. Deciduous oak pollen percentages show a decline, whereas those of evergreen oak barely change. The abrupt increase in terrestrial/fluvial input from 650 to 850 AD occurs, within the age uncertainty, of the arrival of Islam (Islamisation) in Morocco at around 700 AD. Historical evidence suggests Islamisation led to population increase and development of southern Morocco, including expanded pastoralism, deforestation and agriculture. Livestock pressure may have changed the vegetation structure, accounting for the increase in pollen from Cichorioideae, Plantago, and Artemisia, which include many weedy species. Goats in particular may have played a dominant role as agents of erosion, and intense browsing may have led to the decline in deciduous oak; evergreen oak is more likely to survive as it re-sprouts more vigorously after browsing. From 850 AD to present sedimentation rates, Fe/Ca ratios and fluvial discharge remain stable, whereas pollen results suggest continued degradation. Pollen results from the past 150 years suggest expanded cultivation of olives and the native argan tree, and the introduction of Australian eucalyptus trees. The rapidly increasing population in southern Morocco is causing continued pressure to expand pastoralism and agriculture. The history of land degradation presented here suggests that the vegetation in southern Morocco may have been degraded for a longer period than previously thought and may be particularly sensitive to further land use changes. These results should be included in land management strategies for southern Morocco.     

Optical and thermoluminescence dating of Middle Stone Age and Kintampo bearing sediments at Birimi,a multi-component archaeological site in Ghana

We report the first luminescence ages for the archeological and geological sediments forming the substrate of the Birimi archaeological site in the Northern Region of Ghana. The site's significance rests on the fact that it contains a rich collection of artifact assemblages representative of three distinct cultures, and that, on the basis of artifact typology, the earliest assemblage is diagnostic of the Middle Stone Age (MSA). In situ occurrences of MSA artifacts are found at over 1 m below today's surface. They are overlain by a ceramic-rich complex of a sedentary or semi-sendentary Later Stone Age culture known as the Kintampo. The western half of the site is dominated by the industrial remains of Iron Age smelting activity.Elemental, mineralogical, and sedimentological analysis of the cultural and sub-cultural sedimentary horizons at the site revealed at least three distinct lithostratigraphic units. The quartz sediments are derived from the sandstone of the Gambaga escarpment, mass wasted and accreted fluvially at a rate of 3.2 cm/ka, forming a wide terrace at Birimi. Silts and finer fractions derive from windblown dust, likely from White Volta River and granitic sources to the north. Soil forming processes and wide fluctuations in moisture have progressively reduced the sediments at depth to the resistant quartz and kaolinite, with rich iron oxide coatings, and created two ironstone horizons composed of goethite-cemented quartz nodules.Multiple aliquot green-light stimulated optical ages for 125–150 μm quartz grains yielded ages of 23.6±2.9 and 40.8±11.8 ka for the MSA-bearing sediments, and 58.4±15.3 ka for the base of the terrace. Radiocarbon ages on charcoal from Kintampo-bearing units are 3.36–3.83 ka cal BP, and are supported by thermoluminescence (TL) ages on pottery sherds and burnt house daub fragments of this cultural complex. A 0.4 ka age on sediment from the site's surface confirms that the quartz zeroes well when exposed to natural light. Sediments bearing the Kintampo artifacts, however, yielded ages of 7.8–16.9 ka. These ages were obtained on sediments from large pits, some over 50 cm deep, and they deviate only slightly from the ages expected for naturally aggraded sediments at these depths. We conclude, therefore, that extensive digging of pits by the Kintampo dwellers was followed by rapid refilling, and that the bulk mobilization of the matrix did not permit the sedimentary quartz grains to experience any appreciable zeroing at that time.     

Earth's oldest preserved unconformity — Prospect of a beginning in the tectono-sedimentary continental cycle?

Earth's oldest preserved conglomerates and basaltic pillow lavas at Isua, Greenland, provide robust field evidence for deep- and shallow-water environments on our planet within the first billion years of its formation. The conglomerates represent the first Paleoarchaean archive of sub-aerial erosion and shallow water sedimentation. These ca. 3700 million year old sedimentary rocks, now metamorphosed at amphibolite grade, comprise units of rounded quartz pebbles set in a sandy to muddy matrix that unconformably overlie an ophiolite sequence. The pillow lavas of the ophiolite are variolitic and essentially vesicle-free, indicative of formation in a deep water environment. Locally, an unconformity separates the conglomerates from the deformed ophiolite-related rocks; elsewhere the contact between these units is tectonic. Such field relationship between deep and shallow water environments resemble those preserved in younger orogenic belts, where obducted oceanic crust has been tectonically emplaced across terrestrial platforms or subaerial parts of forearc and backarc basins.     

Understanding caldera structure and development: An overview of analogue models compared to natural calderas

Understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation. Geological data, including that from analysis of deeply eroded examples, allow the overall surface setting of calderas to be defined, whereas deep drillings and geophysical investigations provide insights on their subsurface structure. Collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types (downsag, piston, funnel, piecemeal, trapdoor), being viewed as end-members. Despite its importance, such a classification does not adequately examine: (a) the structure of calderas (particularly the nature of the caldera's bounding faults); and (b) how this is achieved (including the genetic relationships among the five caldera types). Various sets of analogue models, specifically devoted to study caldera architecture and development, have been recently performed, under different conditions (apparatus, materials, scaling parameters, stress conditions).The first part of this study reviews these experiments, which induce collapse as a result of underpressure or overpressure within the chamber analogue. The experiments simulating overpressure display consistent results, but the experimental depressions require an exceptional amount of doming, seldom observed in nature, to form; therefore, these experiments are not appropriate to understand the structure and formation of most natural calderas. The experiments simulating underpressure reveal a consistent scenario for caldera structure and development, regardless of their different boundary conditions. These show that complete collapse proceeds through four main stages, proportional to the amount of subsidence, progressively characterized by: (1) downsag; (2) reverse ring fault; (3) peripheral downsag; (4) peripheral normal ring fault.The second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas. This shows that all the experimental structures, as well as their progressive development, are commonly observed at natural calderas, highlighting a consistency between models and nature. As the shallow structure of experimental calderas corresponds to a precise architecture at depth, it provides a unique key to infer the deeper structure of natural calderas: recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context. The general relationship between the evolutionary stage of a caldera and its d/s (diameter/subsidence) ratio allows such a quantification, with stage 1 calderas characterized by d/s > 40, stage 2 by 18 < d/s < 40, stage 3 by 14 < d/s < 18 and stage 4 by d/s < 14. The consistency between experiments and nature suggests that, in principle, the d/s ratio may permit to evaluate the overall structure and evolutionary stage of a caldera even when its surface structure is poorly known. The volume of erupted magma associated with caldera collapse is poorly dependent on the d/s ratio or evolutionary stage; however, the location of sin- and post-collapse volcanism may depend not only upon the amount of collapse, but also on the roof aspect ratio. As the regional tectonic control is concerned, the experiments explain the ellipticity of a part of natural calderas elongated parallel to the regional extension; the control of pre-existing structures may explain the elongation of elliptic calderas oblique or parallel to the regional structures.The four stages adequately explain the architecture and development of the established caldera end-members along a continuum, where one or more end-members (downsag, piston, funnel, piecemeal, trapdoor) may correspond to a specific stage. While such a continuum is controlled by progressive subsidence, specific collapse geometries will result from secondary contributory factors (roof aspect ratio, collapse symmetry, pre-existing faults). These considerations allow proposing an original classification of calderas, incorporating their structural and genetic features.     

Environmental history,palaeoecology and human activity at the early Neolithic forager/cultivator site at Kuahuqiao,Hangzhou, eastern China

The date and location of the adoption of rice cultivation by foraging cultures in China are of considerable current interest but its understanding is hampered by lack of information regarding its palaeoenvironmental context. We present detailed multi-proxy palaeoecological research at the earliest-dated site of rice cultivation in the coastal littoral of east China which has revealed the precise environmental setting of this early Neolithic settlement and its incipient cultivation at ca 7750 cal BP. Regional and local environmental changes governed the character of the site and the duration of human activity. After an episode of marine conditions, natural hydrological succession and terrestrialisation of the site preceded fire clearance of marsh fen-carr alder scrub that prepared the ground for cultivation and then maintained a reedswamp-type wet grassland in which rice was grown. Cropping of Typha stands may have formed part of the subsistence base before the site was overwhelmed by marine inundation ca 7200 cal BP, after which rice cultivation spread to Neolithic sites of Hemudu type elsewhere in the coastal lowlands. We suggest that integrated multi-proxy palaeoecological studies are vitally important for the full understanding of such key wetland archaeological sites.     

Re-evaluating the origins of late Pleistocene fire areas on Santa Rosa Island,California, USA

At the close of the Pleistocene, fire regimes in North America changed significantly in response to climate change, megafaunal extinctions, anthropogenic burning and, possibly, even an extraterrestrial impact. On California's Channel Islands, researchers have long debated the nature of late Pleistocene “fire areas,” discrete red zones in sedimentary deposits, interpreted by some as prehistoric mammoth-roasting pits created by humans. Further research found no evidence that these red zones were cultural in origin, and two hypotheses were advanced to explain their origin: natural fires and groundwater processes. Radiocarbon dating, X-ray diffraction analysis, and identification of charcoal from six red zones on Santa Rosa Island suggest that the studied features date between ~ 27,500 and 11,400 cal yr BP and resulted from burning or heating, not from groundwater processes. Our results show that fire was a component of late Pleistocene Channel Island ecology prior to and after human colonization of the islands, with no clear evidence for increased fire frequency coincident with Paleoindian settlement, extinction of pygmy mammoths, or a proposed Younger Dryas impact event.     

A late Pleistocene human presence at Huaca Prieta,Peru, and early Pacific Coastal adaptations

Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded new evidence of late Pleistocene cultural deposits that shed insights into the early human occupation of the Pacific coast of South America. Radiocarbon dates place this occupation between ~ 14,200 and 13,300 cal yr BP. The cultural evidence shares certain basic technological and subsistence traits, including maritime resources and simple flake tools, with previously discovered late Pleistocene sites along the Pacific coast of Peru and Chile. The results help to expand our knowledge of early maritime societies and human adaption to changing coastal environments.     

Roles of xenomelts,xenoliths, xenocrysts,xenovolatiles, residues,and skarns in the genesis,transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations.     

Veracity of Neoproterozoic negative C-isotope values: The termination of the Shuram negative excursion

There is widespread interest in the Neoproterozoic period of the Earth's history (1000 to 542 Ma) because of unprecedented δ¹³C fluctuations to < − 10‰ PDB through thick (> 1000 m) succession of stratigraphically complex sedimentary rocks deposited during tens of millions of years. In contrast, Phanerozoic large negative C-isotope excursions have been interpreted as the result of diagenetic fluid mixing during carbonate stabilization and burial and are less enigmatic due to the excellent biostratigraphic control on their timing and duration.The Ediacaran Nafun Group of Oman (part of the Huqf Supergroup spanning the Cryogenian–Early Cambrian) contains a large δ¹³C negative excursion (the Shuram excursion) reaching values as negative as − 12‰ at the base of the Shuram Formation. A steady recovery to positive values occurs over the entire Shuram and half through the overlying Buah Formation, suggesting a duration on the order of tens of My. Based on trace metal, chemostratigraphic and sedimentological analyses, the carbon isotope record obtained from the Buah Formation of northern Oman indicates a systematic and reproducible shift of δ¹³C values from − 6‰ to + 1‰ in 1 — a demonstrably diagenetic altered carbonate-cemented siliciclastic facies, and 2 — a least diagenetically altered stromatolitic facies. The identical reproducible isotopic pattern in these time-equivalent sections combined to the presence of exceptionally preserved δ¹⁸O values around − 2 to + 1‰ associated with the most negative δ¹³C values rules out isotopic resetting by diagenetic fluids as a mechanism to explain these values.It is concluded that it is possible to retain depositional δ¹³C values in demonstrably diagenetically altered carbonates. This raises the issue of the ability to recognize diagenetic alteration of C-isotopic values in Neoproterozoic rocks where a robust time frame to support reproducibility is not available. The results of this study provide strong support to a non diagenetic origin of the negative Shuram C-isotope excursion, believed to be the most profound (in terms of amplitude and duration) in the Earth's history.     

One million years of cultural evolution in a stable environment at Atapuerca (Burgos,Spain)

The present paper analyses the evidence provided by three sites (Sima del Elefante, Gran Dolina, and Galería) located in the Trinchera del Ferrocarril of the Sierra de Atapuerca. These three sites are cave infillings that contain sediments deposited from approximately 1.2 Ma to 200 kyr. Pollen, herpetofauna, and small and large mammal remains are used as proxies to obtain a general picture of the environmental changes that occurred at the Sierra de Atapuerca throughout the one million-year period represented at these sites. Similarly, cultural changes are tracked analyzing the evidence of human behavior obtained from the study of several bone and lithic assemblages from these three sites. At least three periods with different cultural features, involving technology, subsistence and behavior, are determined from the available evidence. The first two periods correspond to the Mode 1 technology and Homo antecessor: the first is dated around 1.2 to 1.0 Ma and reflects opportunistic behavior both in technology and subsistence. The second period is around 800 kyr BP. Mode 1 technology is still maintained, but subsistence strategies include systematic hunting and the use of base camps. The third period is dated between 500 ka and 200 ka and corresponds to the Mode 2 technology and the acquisition of directional hunting and other organizational strategies by Homo heidelbergensis. A transition from Mode 2 to Mode 3 seems to appear at the end of this time-range, and may reflect the early phases of a fourth cultural change. With regard to the environment, our main conclusion is that there was an absence of extremely harsh conditions at Atapuerca throughout this time period. The presence of Mediterranean taxa was constant and the dominant landscape was a savannah-like open environment, probably with small forest patches. An alternation of Mediterranean and mesic species as the dominant component of the tree storey was induced by the climatic cycles, and steppes spread across the landscape during the drier periods. In any case, it is not possible to establish clear cut-off points separating entirely different environmental episodes. Our results show no evidence of any relationship between environmental change and cultural change at the Sierra de Atapuerca.     

Crustal structure in the Tengchong volcanic area and position of the magma chambers

In this paper, we extract 1500 P receiver functions in the Tengchong volcanic area from 211 teleseismic events recorded at nine digital seismic stations. A common conversion point stacking technique is used to improve the signal-to-noise ratio and to get the time delays of the Ps, PpPs, PsPs + PpSs phases within grids of 10 km × 10 km. Finally, the crustal thickness and Poisson’s ratio are calculated. The results show that the crustal thickness ranges from 28 to 40 km and the Poisson’s ratio ranges from 0.28 to 0.36. There exist two mantle-uplifting sites each with a horizontal scale of about 30 km × 30 km, one in Mazhan–Tengchong–Maanshan and the other in Wuhe–Longjiang–Tuantian. The high Poisson’s ratio is consistently located within these two sites. Recorded shocks with Ms > 2.0 reveal that most of the shocks are distributed around the two sites and few are located at the centers. The shocks, the geothermal distribution, and the crustal structure suggest that the magma is still active, and the two mantle-uplifting sites detected may be the positions of two magma chambers in the crust.     

Explosive volcanism during the Holocene in the Upper Limay River Basin: The effects of ashfalls on human societies,Northern Patagonia,Argentina

In order to understand human response to Holocene ashfall events, tephra layers found in archaeological sites along the upper Limay River basin, Northern Patagonia, Argentina were bracketed with radiocarbon dates and correlated with tephra from a lacustrine sediment core and from outcrops and the archaeological evidence was analyzed.A dark tephra associated with seismic activity was identified in the El Trébol rockshelter filling interstices between fallen blocks together with remains of human activity and bones of extinct fauna, marking a seismo-volcanic event occurring between 11 758 and 12 866 cal yr BP. This same seismic event affected the Cuyín Manzano site, where the roof collapse made the site uninhabitable for a time. A white tephra, present in Epullán Grande, Epullán Chica and Traful I caves is correlated with Nahuel Huapi tephra (NHT), equivalent to Laya's Río Blanco and Río Pereyra members, (Río Pireco Formation). NHT is considered to have been derived from the same eruptive event, with dates ranging between ca. 1950–2500 cal yr BP. A dark tephra from Ortega's cave and several tephra from Puerto Tranquilo I rockshelter ranging between 521 and 2069 cal yr BP show how the mobile hunters–gatherers of Northern Patagonia were able to cope with the changing circumstances.     

An unusual occurrence of an exploitable K-feldspar deposit hosted in the Ordovician Porphyroids (Southern Sardinia): Geology,mineralogy, geochemical features and economic potential

An atypical potassium feldspar deposit of real economic potential has been found at Arcu de su Bentu, Southern Sardinia, Italy. The massive mineralization occurs in the Middle Ordovician Porphyroids' metavolcanic complex, which consists of dominant metarhyolite and minor metarhyodacite lavas and/or ignimbritic flows, erupted in a sub-aerial environment. During Variscan orogenesis, the mineralized area was affected by low-grade (anchizone to greenschist facies) metamorphism.The deposit generally shows uniform macroscopic textural features over the entire outcrop, the significant presence of K-feldspar (sanidine) and quartz megacrystals, the latter being generally smaller than the former. Mafic minerals do not occur in significant proportions although minor amounts of biotite and muscovite occur locally. Besides the uncommon lithological type, the typical feature of this deposit is the unusual coarseness (10 to 20 cm in diameter) of the potassium feldspar crystals.The favourable geomorphological conditions of the area, high K₂O contents (6 to 8 wt.%), high proportion of K-feldspar in the mineralized rock (35 to 51 vol.%), and large reserves (estimated at 4,368,000 t in just one restricted part of the deposit), are all favourable conditions for future economic exploitation. In spite of this, mineralogical and chemical impurities may adversely affect the possible use of K-feldspar from Arcu de su Bentu in some conventional applications (e.g., manufacture of high-quality products such as ceramics). To assess the real future economic development of the deposit, market-specific beneficiation is required, although it is important to note that the bulk raw materials, even if they have a lower market value, could be still be targeted to specific industrial sectors (e.g., red grès).     

Selenium speciation,distribution, and transport in a river catchment affected by mercury mining and smelting in Wanshan,China

Selenium (Se) is an important co-existing elemental component of the mineral matrix of mercury (Hg) ore deposits. The hazards associated with Se contamination of the aquatic ecosystems in Hg mining areas; however, are often overlooked by environmental researchers due to a preoccupation with Hg. Selenium may also pose a long-term risk to the local ecosystem, and further complicate the situation as Se may also play an important antagonistic role against Hg. Furthermore, most studies on Se pollution have focused only on total Se, whereas the toxicity, bioavailability, and bioaccumulation of Se in aquatic ecosystems is primarily determined by its site-specific individual species. In this study, the concentrations of total Se, inorganic Se (tetravalent and hexavalent), and organic Se were determined in water samples collected from 41 typical sites selected in rivers, tributaries, and springs in Wanshan, China, where Hg and Se co-occur due to historic Hg mining and retorting activities. Se concentrations were observed to decrease with distance from mine-waste calcines, which indicated that mine-waste calcines may be significant sources of the elevated Se in the rivers, especially in downstream areas within 8 km from the mine-waste calcines. The concentration of total aqueous Se throughout the study area was highly variable (3.8 ± 6.0 μg L⁻¹) and on average was one order of magnitude greater than that in natural river systems worldwide (0.1–0.3 μg L⁻¹). The majority of the Se was hexavalent (3.1 ± 4.9 μg L⁻¹; 65%), followed by tetravalent (0.53 ± 0.86 μg L⁻¹; 15%) and organic forms (0.85 ± 1.5 μg L⁻¹; 20%), possibly due to the generally alkaline conditions. Se concentrations in some sampling sites exceeded certain recommended limit of values. However, the existing criteria for Se in aquatic system are mainly based on total Se and the recommended limit of values in different countries or organizations are inconsistent with one another. Therefore, the need to consider Se speciation rather than only total Se is highlighted for future studies.     

Nickel sulfide deposits in Australia: Characteristics,resources, and potential

Australia's nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at Kambalda in the Eastern Goldfields of Western Australia. Periods of buoyant nickel prices and high demand, speculative exploration, and frenetic investment (the ‘nickel boom’ years) have been interspersed by protracted periods of relatively depressed metal prices, exploration inactivity, and low discovery rates. Despite this unpredictable evolution, the industry has had a significant impact on the world nickel scene with Australia having a global resource of nickel metal from sulfide ores of ∼ 12.9 Mt, five world-class deposits (> 1 Mt contained Ni), and a production status of number three after Russia and Canada. More than 90% of the nation's known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973. Australia's nickel sulfide deposits are associated with ultramafic and/or mafic igneous rocks in three major geotectonic settings: (1) Archean komatiites emplaced in rift zones of granite–greenstone belts; (2) Precambrian tholeiitic mafic–ultramafic intrusions emplaced in rift zones of Archean cratons and Proterozoic orogens; and (3) hydrothermal-remobilized deposits of various ages and settings. The komatiitic association is economically by far the most important, accounting for more than 95% of the nation's identified nickel sulfide resources. The ages of Australian komatiitic- and tholeiitic-hosted deposits generally correlate with three major global-scale nickel-metallogenic events at ∼ 3000 Ma, ∼ 2700 Ma, and ∼ 1900 Ma. These events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large-scale mantle overturn and mantle plume activities. There is considerable potential for the further discovery of komatiite-hosted deposits in Archean granite–greenstone terranes including both large, and smaller high-grade (5 to 9% Ni) deposits, that may be enriched in PGEs (2 to 5 g/t), especially where the host ultramafic sequences are poorly exposed.Analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late Archean (∼ 2700 Ma) or Paleoproterozoic (∼ 1900 Ma) age, have dominantly Al-undepleted (Al₂O₃/TiO₂ = 15 to 25) chemical affinities, and often occur with sulfur-bearing country rocks in dynamic high-magma-flux environments, such as compound sheet flows with internal pathways facies (Kambalda-type) or dunitic compound sheet flow facies (Mt Keith-type). Most Precambrian provinces in Australia, particularly the Proterozoic orogenic belts, contain an abundance of sulfur-saturated tholeiitic mafic ± ultramafic intrusions that have not been fully investigated for their potential to host basal Ni–Cu sulfides (Voisey's Bay-type mineralization). The major exploration challenges for finding these deposits are to determine the pre-deformational geometries and younging directions of the intrusions, and to locate structural depressions in the basal contacts and feeder conduits under cover. Stratabound PGE–Ni–Cu ± Cr deposits hosted by large Archean–Proterozoic layered mafic–ultramafic intrusions (Munni Munni, Panton) of tholeiitic affinity have comparable global nickel resources to many komatiite deposits, but low-grades (< 0.2% Ni). There are also hydrothermal nickel sulfide deposits, including the unusual Avebury deposit in western Tasmania, and some potential for ‘Noril'sk-type’ Ni–Cu–PGE deposits associated with major flood basaltic provinces in western and northern Australia.     

Evidence for millennial-scale climatic events in the sedimentary infilling of a macrotidal estuarine system,the Seine estuary (NW France)

High-resolution sedimentological and rock magnetic analyses from sediment cores collected in the Seine estuary record changes in coastal sedimentary dynamics linked to climatic variations during the late Holocene. Using AMS ¹⁴C and paleomagnetic data we present a first attempt in developing a reliable age model on macrotidal estuarine archives, with a decadal resolution. Correlations between sedimentary successions from the outer Seine estuary document the main sedimentary infilling phases of the system during the last 3000 years. Between 3000 and 1150 cal. BP sedimentary patterns reveal that sequence deposition and preservation are predominantly controlled by marine and tidal hydrodynamics while severe storm events are recorded at ca. 2700 and 1250 cal. BP in the outermost estuary. Conversely, the Medieval Warm Period (MWP; 900–1200 AD) is characterized by a drastic waning of the influence of marine hydrodynamics on sediment preservation. Pronounced episodes of Seine river floods indicate a much stronger impact of continental inputs on sedimentary patterns during this period. The onset of the Little Ice Age marks a diminishing influence of continental inputs while tidal and open marine hydrodynamics again exerted a primary control on the sedimentary evolution of the system during 1200–2003 AD. Coastal sedimentary dynamics as preserved within sedimentary successions appear to have been largely influenced by changes in storminess during the last 3000 years. We have matched the preservation of MWP Seine river floods, as revealed by sedimentological and rock magnetic proxy data, to a prolonged interval of weakened storminess in Normandy permitting the preservation of estuarine flood deposits within a context of reduced coastal erosion in northern Europe. The preservation of sedimentary successions in the Seine estuary is therefore maximal when climate conditions resembled those of the preferred low phase of the NAO on multidecadal timescales such as during 800–1200 AD (MWP). In contrast, increased removal and transport of estuarine sediments occur when winter storm activity greatly intensified over northwestern France. We report four prominent centennial-scale periods of stronger storminess, occurring with a pacing of ～1500 years, which are likely to be related to the last four Bond's Holocene cold events. Our results documenting a close link between coastal sedimentary dynamics, millennial-scale variations in Holocene climate and North Atlantic atmospheric circulation are fairly consistent with other records from Scandinavia, central Greenland and southern Europe.