Chemical compositions of Kilauea east-rift lava, 1968-1971

The major element chemical compositions of lava from four eruptionson the east rift zone of Kilauea between August 1968 and October1971 reflect three petrologic processes:

1. Production of chemically distinct batches of magma in the mantle.
2. Separation of olivine, augite, and plagioclase from liquidduringflow in the rift-zone conduits.
3. Mixing of differentmagmas during ascent to the surface.

Chemically none of the four Kilauea east-rift eruptions matchesthe preceding summit eruption in Halemaumau that ended in July1968. The Mauna Ulu eruption, May 1969 to October 1971 (thelast of flie east-rift eruptions), can be divided into fiveolivine-controlled and chemically distinct variants. Three ofthese characterize the first seven months of the eruption andare closest in composition to the 1967–8 Halemaumau eruption.Variants 4 and 5 were erupted later and have compositions thatare distinctly different from that of the 1967–8 eruption.Major differences are higher Al₂O₃ (0?15–0?23 per cent),and lower K₂O (0?07–0?10 per cent) and TiO₂ (0?12–0?23per cent) in variants 4 and 5 at the same MgO content. Somelavas from eruptions in August and October 1968 and February1969, have olivine-controlled magma compositions that are identicalto mixtures of Mauna Ulu variants 1–3 and the 1967–8composition. This observation fits an hypothesis advanced earlierby T. L. Wright and R. S. Fiske that magmas in the central magmachamber become mixed with magmas in the rift zone and can beidentified as mixing components of rift eruption magmas beforethey appear as distinctive magmas in summit eruptions. Lavas representing mixing of olivine-controlled magma with differentiatedmagma were erupted in October 1968, February 1969, and in Mayand December 1969. The changes in amount of K₂O and TiO₂ during the latter partof the 1969–71 Mauna Ulu eruption are the reverse of theoverall secular change in composition of Kilauea summit lavasfrom pre-1750 through 1967–8. The K₂O and TiO₂ contentsof the latest overflows during the 1969–71 Mauna Ulu eruption(April 1971) are comparable to that of lava erupted at Kilaueasummit prior to 1750. The changing chemistry of Kilauea magma is found to be of useas a ‘tracer’ in the complex Kilauea conduit system.Application of these data to older lava sequences is difficulbecause of the complexity of the processes controlling lavacomposition and the absence of detailed information about thetime-space chemical variation during individual eruptions.     

CELLULAR TOWER PROLIFERATION IN THE UNITED STATES

ABSTRACT. Since the early 1980s the growing popularity of cellular communication has wrought dramatic landscape changes on the American scene through an invasion of thousands of cellular telephone towers. Objections raised to new tower construction by local residents, interest groups, and regulatory boards range from visual impacts to perceived health risks. This essay traces the origins of wireless telephony, its proliferation across the United States, and the visual impacts associated with tower construction. Three stages in the geographical expansion of wireless networks are identified.     

Laboratory sustained turbidity currents form elongate ridges at channel mouths

The turbulent flow structure, suspended sediment dynamics and deposits of experimental sustained turbidity currents exiting a channel across a break in slope into a wide tank are documented. The data shed light on the flow evolution and deposit geometry of analogous natural channel‐fed submarine fans. Flows generated in a 0·3 m wide, sloping (0°, 6°, 9° or 20°) channel crossed an angular slope break and spread onto a horizontal tank floor. Flow development comprised: (i) channelized phase (unsteady channel flow developing into steady channel flow); (ii) initial lateral expansion phase (unsteady‐spreading wall jet phase); (iii) constant lateral expansion phase (steady‐spreading wall jet phase); and (iv) rapid waning phase. Phases (i) and (iv) are similar to laterally constrained turbidity currents, but phases (ii) and (iii) are considerably different from such two‐dimensional currents. Steeper channel slopes produced greater flow velocities and turbulence intensities, but these effects diminished markedly with distance from the channel mouth. Flow velocity vectors in the tank had similar patterns for all channel slopes, with a central core of faster velocity and narrow vector dispersion and slower flow with larger dispersion at the jet margins. Suspended sediment concentrations were higher within flow heads and dense basal layers in flow bodies. Time‐averaged acoustic backscatter data showed vertical concentration gradients, confirmed by siphon samples. The deposits comprised a thick central ridge, of similar order width to the channel mouth, with abrupt margins and a surrounding, very thin, fan‐like sheet. The ridge was coarser grained and better sorted than the original sediment, with grain‐size fining downstream, particularly over the fan‐like sheet. The formation of a central ridge suggests that, in the tank, vertical turbulent momentum exchange is more significant for sediment dynamics than spanwise momentum exchange due to lateral expansion. The streamwise elongate geometry of the ridge contrasts with conventional fan‐like geometry found with surge‐type turbidity flows, a result that has widespread stratigraphic and economic implications.     

Three-dimensional sequence analysis of a subsurface carbonate ramp, Mississippian Appalachian foreland basin, West Virginia, USA

Well‐cuttings, wireline logs and limited core and outcrop data were used to generate a regional, three‐dimensional sequence framework for Upper Mississippian (Chesterian), Greenbrier Group carbonates in the Appalachian foreland basin, West Virginia, USA. The resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio‐eustasy during the transition into ice‐house conditions. The ramp facies include inner ramp red beds and aeolianites, lagoonal muddy carbonates, mid‐ramp ooid and skeletal grainstone shoal complexes, and outer ramp wackestone–mudstone, that grades downslope into laminated silty lime mudstone. The facies make up fourth‐order sequences, a few metres to over 90 m (300 ft) thick. The sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones. On the ramp, sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites, and only a few are calichified. Maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units. On the shallow ramp, maximum flooding surfaces overlie siliciclastic‐prone transgressive systems tracts, that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones. The fourth‐order sequences are the major mappable subsurface units; they are bundled into weak composite sequences which are bounded by red beds. In spite of differential subsidence rates across the foreland basin (1 to 3 cm/k.y. up to 25 cm/k.y.), eustatic sea‐level changes controlled regional sequence development. Thrust‐load induced differential subsidence of fault‐blocks, coupled with in‐plane stress, controlled the rapid basinward thickening of the depositional wedge, whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin.     

High-density nitrogen inclusions in barite from a giant siderite vein: implications for Alpine evolution of the Variscan basement of Western Carpathians, Slovakia

Contrasting compositions and densities of fluid inclusions were revealed in siderite–barite intergrowths of the Dro?diak polymetallic vein hosted in Variscan basement of the Gemeric unit (Central European Carpathians). Primary two‐phase aqueous inclusions in siderite homogenized between 101 and 165 °C, total salinity ranged between 18 and 27 wt%, and CaCl₂/(NaCl + CaCl₂) weight ratios were fixed at 0.1–0.3. By contrast, mono‐ and two‐phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt%, and the CaCl₂/NaCl ratios ranged from NaCl‐ to CaCl₂‐dominated compositions. The aqueous inclusions in barite were closely associated with very high‐density (0.55–0.745 g cm^?3) nitrogen inclusions, in some cases containing up to 16 mol.% CO₂. Crystallization P–T conditions of siderite (175–210 °C, 1.2–1.7 kbar) constrained by the vertical oxygen isotope gradient along the studied vein, isochores of fluid inclusions and the K/Na exchange thermometer corresponded to minimal palaeodepths between 4.3 and 6.3 km, assuming lithostatic load and average crust density of 2.75 g cm^?3. Maximum fluid pressure during barite crystallization attained 3.6–4.4 kbar at 200–300 °C, and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2.2 kbar at 25 °C. Contrasting fluid compositions, increasing depths of burial (～4–14 km) and decreasing thermal gradients (～40–15 °C km^?1) during initial mineralization stages of the Dro?diak vein reflect Alpine orogenic processes, rather than an incipient Permian rifting suggested in previous metallogenetic models. Siderite crystallized at rising P–T in a closed, rock‐buffered hydrothermal system developed in the Variscan basement during the north‐vergent Cretaceous thrusting and thickening of the Gemeric crustal wedge. Variable salinities of the barite‐hosted inclusions reflect a fluid mixing in open hydrothermal system, and re‐equilibration textures (lengths of decrepitation cracks proportional to fluid inclusion sizes) correspond to retrograde crystallization trajectory coincidental with transpression or unroofing. Maximum recorded fluid pressures indicate ～12‐km‐thick pile of imbricated nappe units accumulated over the Gemeric basement during the Cretaceous collision.     

Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany

In this paper we briefly compare previously published data on four lateglacial sediment profiles from lakes Holzmaar and Meerfelder Maar in the Eifel region. Two of these profiles (one from each lake) are varvedated, whereas the other two pollen profiles are on depth scales. In general, the palynological signal in all profiles compares well, proving the regional validity of the individual data sets. There are some discrepancies between Holzmaar and Meerfelder Maar, however, mainly concerning varve dating of major lateglacial features, and these are explained after detailed correlation using a combination of varve dating and palynological signals. The result is a consistent varve-dated biostratigraphy for the Lateglacial in the Eifel region. Moreover, it is demonstrated that a combination of varve chronology and high resolution palynostratigraphy in several lake profiles enables even gaps of a few decades up to a few centuries to be detected, thus providing a valuable tool for precise regional palaeoenvironmental study. This multi-core study on two lakes from the same region demonstrates the likelihood of undetected errors in single-core studies on non-varved sediments.     

Physiological adaptations in Coleoptera on Spitsbergen

Metabolic rates and Q₁₀ values were determined for three species of Spitsbergen Coleoptera, Amara quenseli, Simplocaria metallica and Rhynchaenus flagellum . The beetles had metabolic rates which were elevated compared to values of Coleoptera from other regions. This is interpreted as an adaptation to the prevailing low temperatures and short activity period on Spitsbergen.
A. quenseli had rates of water loss comparable to values of beetles in temperate and tropical xeric habitats, indicating that the habitat of the beetles on Spitsbergen at least occasionally is xeric.
Determination of cold-hardiness parameters such as supercooling point and haemolymph melting point of A. quenseli beetles revealed that the beetles had values corresponding to those of active insects in the temperate and tropical region. They had no thermal hysteresis factors. Thus, during summer they show no physiological adaptations to cold.     

Optically Stimulated Luminescence (OSL) dating of glacial sediments from Arctic Russia - depositional bleaching and methodological aspects

Optical dating has been extensively used for stratigraphical correlation in the reconstruction of Eurasian ice-sheet dynamics and palaeoenvironmental changes during the last glaciation. In recent terrestrial studies in Arctic Russia, Optically Stimulated Luminescence (OSL) is the main chronological tool, and has been used across the whole of the Eurasian north. We report new OSL ages obtained on glaciofluvial and glaciolacustrine sediments from the Arkhangelsk and Taymyr regions of Arctic Russia and discuss the characteristics of the quartz OSL signal in terms of its saturation limit, variability among samples from the same location, and initial signal resetting in different depositional environments. It is shown that effect of partial bleaching in our mainly Weichselian samples is trivial because: modern analogues are well zeroed; there is good agreement between OSL and ¹⁴C ages in young samples; and skewness in the dose distribution of relatively older samples is mainly due to varying shapes of the growth curves. The overall reliability of the OSL ages from Arctic Russia, when compared with the limited independent age controls available, appears to be good.