Acanthodian scales and worm tubes from the Kapp Kjeldsen Division of the Lower Devonian Wood Bay Formation, Spitsbergen

Results of a thin section study of bonebeds from the Kapp Kjeldsen Division are presented and discussed. The material for this study was collected in the talus on the south-eastern side of Bockfjorden, northern Spitsbergen. The stratigraphical position of the Kapp Kjeldsen Division within the Devonian strata of Spitsbergen is shown in Table 1.
The thin sections for this study were not made to standard thickness, but are slightly thicker for better resolution of the vertebrate material. Each thin section was individually polished. The photos are made with crossed nichols.     

Insect traces from nonmarine ephemeral puddles

Metz, Robert 1987 06 01: Insect traces from nonmarine ephemeral puddles. Boreas , Vol. 16, pp. 189–195. Oslo. ISSN 0300–9483.
Field observations of nonmarine clay-lined ephemeral puddles have revealed numerous exogenic traces formed by a variety of insects. Most of these traces are described here for the first time. A number of different insects produced similar appearing traces. Relatively rapid drying of the shallow puddles often traps the insect, so that the trace and its maker are initially well preserved. This dessication process, in contrast to many lakes, streams and ponds having deeper water conditions, offers high potential for the exogenic trace to be preserved as a trace fossil. Trace fossil forms similar to those documented for ephemeral puddles include Gordia, Cochlichnus, Lithographus, Helminthopis and Isopodichnus . Ephemeral puddles should be considered a prime candidate for the origin of many of the trace fossils found in ancient nonmarine sedimentary rocks.     

Isotopic and Chemical Evidence Concerning the Genesis and Contamination of Basaltic and Rhyolitic Magma Beneath the Yellowstone Plateau Volcanic Field

Since 2.2 Ma, the Yellowstone Plateau volcanic field has produced6000 km³ of rhyolite tuffs and lavas in >60 separate eruptions,as well as 100 km³ of tholeiitic basalt from >50 vents peripheralto the silicic focus. Intermediate eruptive products are absent.Large calderas collapsed at 2?0, 1?3, and 0?6 Ma on eruptionof ash-flow sheets representing at least 2500, 280, and 1000km³ of zoned magma. Early postcollapse rhyolites show largeshifts in Nd, Sr, Pb, and O isotopic compositions caused byassimilation of roof rocks and hydrothermal brines during collapseand resurgence. Younger intracaldera rhyolite lavas record partialisotopic recovery toward precaldera ration. Thirteen extracalderarhyolites show none of these effects and have sources independentof the subcaldera magma system. Contributions from the Archaeancrust have extreme values and wide ranges of Nd-, Sr-, and Pb-isotoperatios, but Yellowstone rhyolites have moderate values and limitedranges. This requires their deep-crustal sources to have beenpervasively hybridized (and the Archaean components diluted)by distributed intrusion of Cenozoic basalt, most of which wasprobably contemporaneous with the Pliocene and Qualernary volcanism.In hybrid sources yielding magmas parental to the subcalderarhyolites, half or more of the Nd and Sr may have been contributedby such young basalt. Parents for the extracaldera rhyolites,generated beyond the leading edge of the northeast-propagatingfocus of basaltic intrusion and deep-crustal mobilization, containedsmaller fractions of mantle-derived components. Most Yellowstone basalts had undergone cryptic clinopyroxenefractionation in the lower crust or crust-mantle transitionzone and, having also ascended through or adjacent to crustalzones of silicic-magma generation, most underwent some crustalcontamination. A high fraction of the Pb in most basalts isof crustal derivation. Anomalously low seismic velocities toa depth of 250 km and a high flux of ³He at Yellowstone suggestsublithospheric magma contributions. Elevated baseline Nd- andSr-isotopc ratios suggest additional contributions from oldlithospheric mantle, but this is hard to quantify because ofthe crustal overprint. Foundering of crustally contaminatedmain-stage cumulates into the low-viscosity upper mantle beneaththe principal focus of basaltic intrusion may influence theisotopic compositions of low-K tholeiites and Snake River olivinetholeiites subsequently generated along the Snake River Plainaxis in the wake of the main migrating melting anomaly.     

An Experimental Study of the Sulfur Content in Basaltic Melts Saturated with Immiscible Sulfide or Sulfate Liquids at 1300{degrees}C and 1{middle dot}0 GPa

The sulfur content in basaltic melts coexisting with eithersulfide or sulfate melts was determined experimentally. Theexperimental conditions were in the range of 1300–1355°Cand 1·0–1·6 GPa, conditions appropriatefor the melting of the upper mantle above subduction zones.Under these conditions, both sulfide and sulfate were presentas immiscible liquids, as inferred from the round geometriesof the quenched sulfide and sulfate phases. The measured S contentin basaltic melts saturated with sulfate liquids ([S] = 1·5± 0·2 wt %) was 10 times higher than the S contentin basaltic melts saturated with sulfide liquids ([S] = 0·14± 0·02 wt %). In our experiments, sulfate liquidswere stable at fO₂ as low as FMQ = +1·85 [FMQ = log (fO₂)_sample– log (fO₂)_FMQ, where FMQ is the fayalite–magnetite–quartzoxygen buffer], and evidence from other sources indicates thatsulfates will be stable at lower fO₂ in melts with lower activitiesof silica. Because chalcophile and highly siderophile elements,such as Cu, Ni, Au, and Pd, are partitioned preferentially intosulfide phases, melting of sufficiently oxidized sources, inwhich sulfides are not stable, would favor incorporation ofthese elements into the silicate melt produced. Such melts wouldhave a higher potential to generate ore deposits. This studyshows that the high sulfur contents of such oxidized basaltsalso means that relatively small amounts of such magmas canprovide significant amounts of sulfur to exsolving volatilephases and account for the bulk of the sulfur expelled in somevolcanic eruptions, such the 1991 eruption of Mount Pinatubo. KEY WORDS: basalt; mantle; oxidation state; sulfate; sulfur     

NOTES ON THE GEOLOGY OF LEICHOW PENINSULA,KWANGTUNG

Large areas of relatively level idle uplands which seem to be very suitablefor cultivation are found in the Leichow Peninsula (雷州半岛)~2.Many areunder the impression that these lands will permit an enormous expansion of cropproducing areas in Kwangtung prov     

RADAR-OBSERVED ’’FINE LINES‘‘ IN THE OPTICALLY CLEAR BOUNDARY LAYER: REFLECTIVITY CONTRIBUTIONS FROM AERIAL PLANKTON AND ITS PREDATORS

Sensitive Doppler radars regularly detect fine lines ofenhanced reflectivity in mesoscale boundary-layer convergence zones. Recent studies have concludedthat these fine lines are attributable primarily to backscatter fromconcentrations of small, weakly flying insects (aerial plankton)entrained in the convergence zones. Such concentrations are likely tobe attractive to aerial predators that feed on small insects, raising thequestion of whether the presence of the predators themselves maycontribute significantly to the radar-observed fine lines.In this paper, we examine the relative contributions of aerialplankton and its predators to fine-line reflectivity, using field datafrom visual and radar studies together with a compilation of literaturedata on radar cross sections of birds and insects. Visual counts ofbirds and dragonflies in convergence zones, together withsimultaneous remote radar observations during the CaPE project inFlorida, indicated that aerial predators usually contributed little tofine-line reflectivity (median contribution 2%). Assuming thatthe size distribution of insect targets was spatially invariant, thedensity of insects composing the aerial plankton was inferred to be,on average, about one order of magnitude higher inside convergencezones than in nearby areas.These results suggest that clear-air radar reflectivity may be auseful measure of the quantity of aerial plankton in boundary-layerconvergence zones. This finding is relevant to biology because itindicates that remote sensing techniques can be usefully employed todocument patterns and processes in the distribution of aerial plankton.The results presented here also have relevance for operationalmeteorology, because most of the organisms comprising the planktonprobably serve as passive tracers of horizontal air motions, and aretherefore ideal targets for remotely detecting wind patterns. Incontrast, the aerial predators move actively and rapidly, renderingthem less useful as tracers of wind fields in studies using Dopplerradars. The influence of atmospheric structure on the ecology ofaerial predators and their prey has received little attention, but webelieve that sensitive radars with clear-air observational capabilitiesoffer great potential as research platforms for future studies of aerialplankton and aerial planktivory.     

Dehydration Melting of Metabasalt at 8-32 kbar: Implications for Continental Growth and Crust-Mantle Recycling

We report the results of partial melting experiments between8 and 32 kbar, on four natural amphibolites representative ofmetamorphosed Archean tholeiite (greenstone), high-alumina basalt,low-potassium tholeiite and alkali-rich basalt. For each rock,we monitor changes in the relative proportions and compositionof partial melt and coexisting residual (crystalline) phasesfrom 1000 to 1150C, within and beyond the amphibole dehydrationreaction interval. Low percentage melts coexisting with an amphiboliteor garnet amphibolite residue at 1000–1025C and 8–16kbar are highly silicic (high-K₂O granitic at 5%; melting, low-Al₂O₃trondhjemitic at 5–10%). Greater than 20% melting is onlyachieved beyond the amphibole-out phase boundary. Silicic tointermediate composition liquids (high-Al₂O₃ trondhjemitic-tonalitic,granodioritic, quartz dioritic, dioritic) result from 20–40%melting between 1050 and 1100C, leaving a granulite (plagioclase+ clinopyroxene orthopyroxene olivine) residue at 8 kbarand garnet granulite to eclogite (garnet + clinopyroxene) residuesat 12–32 kbar. Still higher degrees of melting ( 40–60%)result in mafic liquids corresponding to low-MgO, high-Al₂O₃basaltic and basaltic andesite compositions, which coexist withgranulitic residues at 8 kbar and edogitic or garnet granulitic(garnet + clinopyroxene + plagioclase orthopyroxene) residuesat higher pressures (12–28 kbar). As much as 40% by volumehigh-Al₂O₃ trondhjemitic-tonalitic liquid coexists with an eclogiticresidue at 1100–1150C and 32 kbar. The experimental datasuggest that the Archean tonalite-trondhjemite-granodiorite(TTG) suite of rocks, and their Phanerozoic equivalents, thetonalite-trondhjemite-dacite suite (including ‘adakites’and other Na-rich granitoids), can be generated by 10–40%melting of partially hydrated metabasalt at pressures abovethe garnet-in phase boundary (12 kbar) and temperatures between1000 and 1100C. Anomalously hot and/or thick metabasaltic crustis implied. Although a rare occurrence along modern convergentplate margins, subductionrelated melting of young, hot oceaniccrust (e.g. ocean ridges) may have been an important (essential)element in the growth of the continental crust in the Archean,if plate tectonic processes were operative. Coupled silicicmelt generation-segregation and mafic restite disposal may alsooccur at the base of continental or primitive (sub-arc?) crust,where crustal overthickening is a consequence of underplatingand overaccretion of mafic magmas. In either setting, net growthof continental crust and crustmantle recycling may be facilitatedby relatively high degrees of melting and extreme density contrastsbetween trondhjemitictonalitic liquids and garnet-rich residues.Continuous chemical trends are apparent between the experimentalcrystalline residues, and mafic migmatites and garnet granulitexenoliths from the lower crust, although lower-crustal xenolithsin general record lower temperatures (600–900C) and pressures(5–13 kbar) than corresponding residual assemblages fromthe experiments. However, geo-thermobarometry on eclogite xenolithsin kimberlites from the subcontinental mantle indicates conditionsappropriate for melting through and beyond the amphibole reactioninterval and the granulite-eclogite transition. If these samplesrepresent ancient (eclogitized) remnants of subducted or otherwisefoundered basaltic crust, then the intervening history of theirprotoliths may in some cases include partial melting. KEY WORDS: dehydration melting; metabasalt; continental growth; crust–mantle recycling ^*Corresponding author. Present address: Mineral Physics Institute and Center for High Pressure Research, Department of Earth and Space Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA