Contiguous multi‐proxy analyses (X‐radiography,diatom, pollen,and microcharcoal) of Holocene archaeological features at Kuk Swamp,Upper Wahgi Valley,Papua New Guinea

Contiguous multi‐proxy analyses (X‐radiography, diatom, pollen, and microcharcoal) have been conducted on the fills of early, mid‐, and mid‐late Holocene features at Kuk Swamp, Upper Wahgi Valley, Papua New Guinea. The features are associated with key periods of archaeological interest: plant exploitation (ca. 10,000 cal yr B.P.), earliest cultivation (6950–6440 cal yr B.P.), and earliest ditches (ca. 4000 cal yr B.P.). The analyses are designed to clarify uncertainties regarding the reliability and association of different samples within feature fills for the interpretation of human activities on the wetland in the past. Methodologically, these investigations have clarified site formation processes, including pedogenesis within feature fills, which enable a better determination of archaeological associations for different samples within those fills. Substantively, the results provide higher resolution interpretations of paleoenvironments and past human activities on the wetland margin. © 2009 Wiley Periodicals, Inc.     

Hydromagnetic vortices—I. The 11 December 1977 event

Through a synthesis of magnetometer, plasma, energetic particle and electric field data from the ISEE satellite pair, we describe the characteristics of the initial (11 December 1977) magnetotail plasma vortex event reported by Hones et al. (1978). The event is associated with a hot (β ～ 1) compressional hydromagnetic wave and apparent vortical motion is seen because at two points in the flow cycle the flow is field-aligned. The behaviour of the energetic ions receives special study : when combined with the thermal flow measurements energy dispersion is evident in the field-aligned flow, while the large pitch angle energetic ions reveal the presence of gradients. We argue that these gradients are wave-induced and use the data to determine the perpendicular wave wavelength together with the speed and direction of transverse wave propagation.     

The shallow plumbing system of Rabaul caldera: a partially intruded ring fault?

The floor of Rabaul caldera experiences complex deformation as revealed both in the geological and historical record, as well as through recent systematic monitoring. The observed deformation pattern has been modelled previously as being caused by tumescent strain above one or more point sources at shallow levels within the caldera block, or as a response of the caldera structure to deeper sources of deformation. Here, two-dimensional finite element modelling is used to re-interpret the pre-1994 eruption deformation data, demonstrating that the observed pattern may have been caused by dykes located in sectors of the ring fault system, as delimited by seismicity. Both a pressurised ring structure and a pair of arcuate sources are modelled. Maximum compressional stress results in a central position within the encompassed block, and a moat-like feature forms offset outwards from the intersection of the azimuth of the modelled deformation sources and the free surface. The modelled deformation generally fits well with the observed movements. That the shallow ring dyke appears not to be complete, existing as two discrete arcuate dykes, helps to explain observed changes in the indicated tilt directions through time. Changing areas of relative down-warping offset outwards from the seismically active ring structure, and north/south-oriented structural up-doming south of Matupit. The distribution of thermal anomalies, and the lack of evidence for shallow central caldera intrusions, can also be explained by this scenario. Associated normal faulting above these dykes, and/or the stress regime generated by simultaneous intrusions into opposite sides of the ring fault, are proposed to explain the apparent inward dip of the intrusions at very shallow levels, leading to the eruptive sites being offset outwards from the seismic zone. A conceptual model is proposed to try to explain the general behaviour of the caldera between 1971 and the eruption of 1994.     

Volatiles in submarine volcanic rocks from the spreading axis of the East Scotia Sea back-arc basin

The volatile content of glassy pillow rims from East Scotia Sea back-arc basin (BAB) lavas are unlike those of mid-ocean ridge (MOR) pillow-rim glasses, although non-volatile compositions of the two rock groups overlap. The East Scotia Sea samples have three to ten times greater water contents and nearly twice the average CO₂ and Cl contents of MOR samples; F contents are similar. S contents are only one-third those from MOR samples. H₂O and CO₂ contents of glassy pillow rims from Mariana island arc andesites are similar to those in the BAB lavas studied. Nevertheless, volatiles in the East Scotia Sea BAB magmas are probably not directly derived from the subducted slab, because there is no seismic evidence that the slab extends within 200 km of the spreading axis of the East Scotia Sea. Available data do not preclude the possibility that the magmas were contaminated by seawater prior to eruption or that the mantle under the East Scotia Sea spreading center is volatile-rich. The volatiles may have been added to the mantle during an earlier period of subduction, perhaps during the initial formation of the East Scotia Sea basin.     

Transverse geochemical variations across the Antarctic Peninsula: Implications for the genesis of calc-alkaline magmas

Magnetic activity throughout the Antarctic Peninsula and the South Shetland Islands has been dominantly of a calc-alkaline nature for the last 200 Ma. Chemically, the plutonic and volcanic products are typical of a continental margin magmatic arc, similar to those from western South America. Within any one area, volcanic and plutonic rocks are compositionally indistinguishable, and all magmatic products show increasing SiO₂, and increasing K/Si, Rb/Si, Th/Si and to a lesser extent Ce/Si and La/Si ratios away from the proposed trench axis. The calc-alkaline basaltic compositions also have high large ion lithophile (LIL; e.g. K, Rb, Th)/high field strength (HFS; e.g. Zr, Nb, Ti) ratios relative to non-orogenic counterparts, and increasing LIL/HFS element ratios with increasing fractionation. It is proposed that the high LIL/HFS element ratios in basaltic and andesitic melts are primary features due to dehydration processes with the subducted slab and to fractionation of minor mineral phases from the melt. The increasing LIL/HFS element ratios in more acid rocks are probably due to removal of minor mineral phases from the melt. Although zone refining may contribute to the spatial variations across the peninsula, we have proposed that an enriched subcontinental mantle provides a viable alternative source for the observed K-h variations and for the increased LIL-element contents found in continental margin calc-alkaline magmas.     

Sampling schemes for quality estimation of a flowing material

Four sampling schemes dealing with sampling of a continuous material flowing past the sampling point during a fixed time interval (0,T) are studied. Two of the schemes are the ones used in standard practice while the other two are the ones proposed as being possible sampling schemes to be coupled with a metal analyser developed by the CSIRO Division of Mineral Physics.Specific comparisons of the sampling schemes are made for a mathematical model of the functions describing a continuous stream based on simple and realistic assumptions. Discussion is provided on the advantages and disadvantages of the two new sampling schemes proposed for use with the analyser.     

Geochemistry of basalts drilled in the North Atlantic by IPOD Leg 49: Implications for mantle heterogeneity

IPOD Leg 49 recovered basalts from 9 holes at 7 sites along 3 transects across the Mid-Atlantic Ridge: 63°N (Reykjanes), 45°N and 36°N (FAMOUS area). This has provided further information on the nature of mantle heterogeneity in the North Atlantic by enabling studies to be made of the variation of basalt composition with depth and with time near critical areas (Iceland and the Azores) where deep mantle plumes are thought to exist. Over 150 samples have been analysed for up to 40 major and trace elements and the results used to place constraints on the petrogenesis of the erupted basalts and hence on the geochemical nature of their source regions.It is apparent that few of the recovered basalts have the geochemical characteristics of typical “depleted” midocean ridge basalts (MORB). An unusually wide range of basalt compositions may be erupted at a single site: the range of rare earth patterns within the short section cored at Site 413, for instance, encompasses the total variation of REE patterns previously reported from the FAMOUS area. Nevertheless it is possible to account for most of the compositional variation at a single site by partial melting processes (including dynamic melting) and fractional crystallization. Partial melting mechanisms seem to be the dominant processes relating basalt compositions, particularly at 36°N and 45°N, suggesting that long-lived sub-axial magma chambers may not be a consistent feature of the slow-spreading Mid-Atlantic Ridge.Comparisons of basalts erupted at the same ridge segment for periods of the order of 35 m.y. (now lying along the same mantle flow line) do show some significant inter-site differences in Rb/Sr, Ce/Yb,⁸⁷Sr/⁸⁶Sr, etc., which cannot be accounted for by fractionation mechanisms and which must reflect heterogeneities in the mantle source. However when hygromagmatophile (HYG) trace element levels and ratios are considered, it is the constancy or consistency of these HYG ratios which is the more remarkable, implying that the mantle source feeding a particular ridge segment was uniform with respect to these elements for periods of the order of 35 m.y. and probably since the opening of the Atlantic. Yet these HYG element ratios at 63°N are very different from those at 45°N and 36°N and significantly different from the values at 22°N and in “MORB”.The observed variations are difficult to reconcile with current concepts of mantle plumes and binary mixing models. The mantle is certainly heterogeneous, but there is not simply an “enriched” and a “depleted” source, but rather a range of sources heterogeneous on different scales for different elements — to an extent and volume depending on previous depletion/enrichment events. HYG element ratios offer the best method of defining compositionally different mantle segments since they are little modified by the fractionation processes associated with basalt generation.     

Mercury in plankton from a polluted Norwegian Fjord

Plankton of mixed composition has been collected from Sorfjørden and Hardangerfjørden, on the west coast of Norway and analysed for total mercury by flameless atomic absorption. Different methods of decomposing the samples prior to analysis were tested, showing no significant variations in the recovery of mercury. The high levels of mercury (0.52-25.21 ppm dry weight) are apparently associated with a source of industrial pollution. Indications of higher mercury concentrations in phytoplankton than in zooplankton were noticed and suggest a lack of food chain amplification within the lower trophic levels.     

Photogrammetric and laser altimetric reconstruction of water levels for extreme flood event analysis

This paper assesses the feasibility of estimating water levels using digital photogrammetry. A common problem during an extreme flood event is that automated water level recorders do not record the highest water levels, as a result of instrument malfunctioning. This paper explores two possible solutions to this problem based upon data acquired using synoptic remote sensing methods. The first method requires: (a) high-resolution elevation data (for example, in the form of a digital elevation model for the floodplain); and (b) information on the planimetric position of the maximum flood extent, such as from debris lines (known as wrack lines) visible on aerial imagery flown after the event. The planimetric data can then be used to segment the topographic data in order to identify water level elevations. The second method uses a digitial photogrammetric approach and is suitable where no topographic data are available, but aerial imagery is available, flown after the event. Provided this imagery is of the right scale, digital photogrammetric analysis may be used to identify the elevations of wrack lines visible on the imagery. In this paper, the second of these options is compared with the first. The research shows that desktop photogrammetric methods, using 1:4500 scale imagery, can yield water level estimates that are precise to ±0·147 m, on the basis of check data obtained from lidar data. This is a worst possible estimate of the acquired precision given uncertainties in the lidar data. When compared with the first option, based upon segmenting lidar data using flood outlines, the photogrammetric approach was found to be preferable given both the quality of the lidar and uncertainties over how to segment it.     

Crustal assimilation in basalt and jotunite: Constraints from layered intrusions

Massive continental volcanism and/or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years: the end-Permian, end-Cretaceous and end-Triassic extinctions. However, re-evaluation of the frequency of bolide impacts and plume-related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions, and so, in isolation, may not be responsible for the largest extinctions. Furthermore, the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions. Contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions. We present a statistical analysis of the probability of coincidence between volcanism and impact, and show that three random coincidences of these events in the last 300 m.y. are likely. No causal relationship between impact and volcanism is necessary. The lesser mass extinctions, on the other hand, may not require juxtaposition of two such catastrophic events; such coincidences occurring on more than three occasions during the last 300 m.y. become increasingly unlikely.