Sillimanite—disordering enthalpy by calorimetry

Heat of solution measurements in an oxide-melt were performed on samples of natural sillimanite heat-treated in the range 1200–1700°C at pressures of 16–23 kbar. A distinct enthalpy of solution decrement relative to the unheated sillimanite of about 1.3 kc/mole is shown by samples run at 1400–1550°C. Pressure variations in the range 16–23 kbar cause little change in the heat of solution in this temperature range. This pressure-independent ‘plateau’ in heat of solution is interpreted to be due to Al-Si disordering on tetrahedral sites in the sillimanite structure. A simple temperature-dependent disordering model developed by navrotsky and Kleppa (1967) for spinels leads to an Al-Si interchange enthalpy, Δ_Hnt, of16 ± 1 kcal/mole, in good agreement with the value derived by Holdaway(1971) on entirely different grounds.Above 1550°C, larger heat of solution decrements were observed. Microprobe analyses of quenched samples indicate that the sillimanite has not deviated significantly from the ideal formula. Some unknown profound disordering process may account for the heat effects in the very high temperature range.Unit cell volumes of quenched samples also describe a ‘plateau’ region in the temperature range 1400–1550°C. This plateau consists of an increase of the 6 crystallographic axis beginning at 1350°C without much change in the other axes in the range 1350–1550°C. A sudden expansion of the α-axis occurs between 1550 and 1630°C.We conclude that Al-Si disorder of the type postulated by Beger et al. (1970), and Holdaway (1971) has been confirmed calorimetrically for samples heated under pressure in the temperature range 1400–1550°C.     

Revision of the Carboniferous cystoporate bryozoan Fistulipora incrustans (Phillips, 1836), with remarks on the type species of Fistulipora M'Coy, 1849

The type species of the Palaeozoic cystoporate bryozoan genus Fistulipora M'Coy, 1849 is redescribed. Fistulipora minor M'Coy, 1849 is the type species, and was the first species described under the genus Fistulipora. Quantitative assessment of type and figured specimens of Calamopora incrustans Phillips, 1836 and F. minor has shown them to fall within the range of morphological variation exhibited by abundant comparative material collected at several horizons and they are referable to one morphologically variable taxon. F. minor is the junior subjective synonym of C. incrustans and the form can be quoted as F. minor M'Coy, 1849 = C. incrustans Phillips, 1836 with a valid name of F. incrustans (Phillips, 1836). However, this does not alter the name of the type species, which is F. minor M'Coy, 1849. The type specimen of Berenicea megastoma M'Coy, 1844 has also been examined, and this form is also conspecific with F. minor M'Coy, 1849 = C. incrustans Phillips, 1836. Examination of the type specimen of F. major M'Coy (1849) has shown it to be referable to the tabulate coral genus Chaetetes. A lectotype and paralectotypes are designated for F. minor and the status of the type specimens of F. incrustans is clarified.     

Feeding ecology of the northern pipefish,Syngnathus fuscus,in a seagrass community of the lower Chesapeake Bay

Examination of gut contents of the northern pipefish,Syngnathus fuscus, revealed that gammarid amphipods, caprellid amphipods, isopods, and calanoid copepods were the dominant food items during the sevenmonth study period.Gammarus mucronatus, calanoid copepods, andErichsonella attenuata were the seasonally dominant prey items in the spring, summer, and fall, respectively.G. mucronatus and calanoid copepods were consumed in approximate proportion to their numerical abundance in the environment, whileE. attenuata, present in rather uniform densities throughout the study period, was extensively consumed only in the late summer and fall. An ontogenetic pattern of prey consumption was evident, in addition to the seasonal pattern. Comparison ofG. mucronatus andE. attenuata size ranges from the field and in pipefish guts revealed thatS. fuscus preyed upon the smaller size classes of each species, and that mean size of prey consumed was positively related to fish size.     

A well‐established Early–Middle Pleistocene marine sequence on south‐east Zakynthos island,western Greece: Magneto‐biostratigraphic constraints and palaeoclimatic implications

The chronostratigraphy of a long, onshore Early–Middle Pleistocene marine sedimentary sequence on the south‐east part of Zakynthos island, Greece, is presented. Correlation of the succession with the isotope record of Ocean Drilling Program Site 963 reveals the combined influence of tectonics and eustacy in this area. The sequence is divided into three formations by two main unconformities that apparently relate to sea‐level lowstands associated with two major northern hemisphere glaciations, those of marine isotope stages (MIS) 22 and 12. The Zakynthos sequence in many ways is comparable with the Italian Valle di Manche section. Magnetostratigraphic and rock magnetic analyses, supported by biostratigraphy, document the position of the Matuyama/Brunhes Chron boundary (0.77 Ma), the top and base of the Jaramillo Subchron (0.99–1.07 Ma), the Cobb Mountain Subchron (1.173–1.185 Ma) and the top of the Olduvai Subchron (1.78 Ma). The underlying strata are constrained exclusively by detailed nannofossil biostratigraphy extending at least to the lowermost Pleistocene at around 2.54 Ma and therefore certainly incorporating the base of the Olduvai Subchron (1.95 Ma) and possibly the Gauss/Matuyama Chron boundary (2.58 Ma). In addition, a remarkable increase in sedimentation rate (from 3.2 and 28 cm ka^?1 to 167 cm ka^?1) and hence resolution above the Matuyama/Brunhes boundary (Middle Pleistocene) reveals one short‐lived magnetic excursion, possibly 17a (0.66 Ma), within the normal polarity Brunhes Chron. Copyright © 2011 John Wiley & Sons, Ltd.     

Flotation of germanium n and p with potassium ethyl xanthate

Steady-state potential of the germanium electrode, flotation tests and results of spectrophotometric ATR (Attenuated Total Reflection) measurements of germanium surface in the presence and absence of potassium ethyl xanthate are presented.On the basis of the steady-state potentials of the germanium electrode in ethyl xanthate solutions, the standard potential E⁰ of the reaction: Ge + 2EtX^? = Ge (EtX)₂ + 2e is estimated. The pH ranges of the dixanthogen (EtX)₂ and the germanium xanthate Ge(EtX)₂ species predominance in the bulk solution are calculated. It has been established that flotation of germanium is greater than the natural floatability (in the absence of collectors) in the pH ranges where (EtX)₂ or Ge (EtX)₂ are present in the bulk solution. Spectrophotometric results reveal the presence of (EtX)₂ and Ge (EtX)₂ on the surface in the same pH ranges as is calculated for the bulk reactions.No significant differences in the surface properties and the flotation behaviour between germanium n and p have been found.     

COSMOGENEIC RADIONUCLIDES IN THE HAVERÖ METEORITE

An 87-gram sample of the Haverö ureilite has been analyzed by non-destructive gamma-ray spectrometry. The results of the measurements, in dpm/kg at time of fall, are: ²²Na, 71 ± 3; ²⁶Al, 43 ± 3; ⁴⁶Sc, 3.4 ± 2.1; ⁵⁴Mn, 35 ± 6; ⁶⁰Co, 0.7, 2*** limit. Haverö has 77 ± 14% of the ²⁶Al activity calculated for its chemical composition. When averaged with previously-reported analyses of Goalpara and Novo Urei, ureilites as a class have 74 ± 7% of their expected ²⁶Al activity. The depletion in ²⁶Al could be the coincidental result of identical “shielding” effects in three meteorites of apparently very different preatmospheric sizes. Alternatively, ureilites may have been exposed to a lower cosmic-ray flux than that experienced by most chondrites, probably the result of characteristically different orbits     

Geology,petrography, shock petrography,and geochemistry of impactites and target rocks from the Kärdla crater,Estonia

Abstract— The Kärdla crater is a 4 km‐wide impact structure of Late Ordovician age located on Hiiumaa Island, Estonia. The 455 Ma‐old buried crater was formed in shallow seawater in Precambrian crystalline target rocks that were covered with sedimentary rocks. Basement and breccia samples from 13 drill cores were studied mineralogically, petrographically, and geochemically. Geochemical analyses of major and trace elements were performed on 90 samples from allochthonous breccias, sub‐crater and surrounding basement rocks. The breccia units do not include any melt rocks or suevites. The remarkably poorly mixed sedimentary and crystalline rocks were deposited separately within the allochthonous breccia suites of the crater. The most intensely shockmetamorphosed allochthonous granitoid crystalline‐derived breccia layers contain planar deformation features (PDFs) in quartz, indicating shock pressures of 20–35 GPa. An apparent K‐enrichment and Ca‐Na‐depletion of feldspar‐ and hornblende‐bearing rocks in the allochthonous breccia units and sub‐crater basement is interpreted to be the result of early stage alteration in an impact‐induced hydrothermal system. The chemical composition of the breccias shows no definite sign of an extraterrestrial contamination. By modeling of the different breccia units with HMX‐mixing, the indigenous component was determined. From the abundances of the siderophile elements (Cr, Co, Ni, Ir, and Au) in the breccia samples, no unambiguous evidence for the incorporation of a meteoritic component above about 0.1 wt% chondrite‐equivalent was found.     

Upper limit concentrations of trapped xenon in individual interplanetary dust particles from the stratosphere

Abstract— The Xe contents in 25 individual stratospheric interplanetary dust particles were measured in two different laboratories using focused laser micro‐gas extraction and (1) a conventional low‐blank magnetic sector mass spectrometer (Washington University), and (2) a resonance ionization time of flight mass spectrometer (RELAX‐University of Manchester). Data from both laboratories yielded a remarkably similar upper‐limit ¹³²Xe concentration in the IDPs (>2.7, 6.8 and 2.2 × 10^?8ccSTP/g for Washington University Run 1, Washington University Run 2 and University of Manchester analyses, respectively), which is up to a factor of five smaller than previous estimates. The upper‐limit ¹³²Xe/³⁶Ar ratio in the IDPs (¹³²Xe/³⁶Ar > ?8 × 10^?4for Run 1 and ¹³²Xe/³⁶Ar > ?19 × 10^?4for Run 2), computed using ³⁶Ar concentration data reported elsewhere is consistent with a mixture between implanted solar wind, primordial, and atmospheric noble gases. Most significantly, there is no evidence that IDPs are particularly enriched in primordial noble gases compared to chondritic meteorites, as implied by previous work.     

Principles of operation of solar magnetographs

The principles of operation of photoelectric solar magnetographs are described in terms of the Poincaré sphere. The performance of photographic methods for measuring solar magnetic fields is compared with that of photoelectric magnetographs.