Chemical evolution of acid precipitation in the unsaturated zone of the Pennsylvanian siltstones and shale of central Ohio

The North Appalachian Experimental Watershed in Coshocton, Ohio, USA has recorded average pH of precipitation of 4.7 over a 30-year period. The area lies within the Pennsylvanian siltstones and shale, dominated by aluminosilicates and <5% calcite. A study was conducted to determine the evolution of acid deposition through an unsaturated to saturated zone composed of siltstone and shale in an isolated hill, precluding lateral flow and seepage. The results from water–rock chemical reactions modeled using PHREEQM demonstrate the percolating precipitation water is neutralized to pH 7.5 within the top 1.5 m. The model suggests that, along with calcite, dissolution of albite, illite, and kaolinite are the dominant mechanisms of neutralization. The cation exchange capacity of the siltstone and shale, in the range 54.6–386 meq/100 g, appears to be a function of high organic carbon content of 2.0–3.2%. While cation exchange is responsible for some of the Na⁺ in solution, it is not the primary source of Ca²⁺, Mg²⁺, or K⁺ ions. Exchange onto clays is occurring, but is secondary to exchange on organic matter. Chemical composition of groundwater perched within a coal seam is controlled by oxidation and dissolution of pyrite, returning pH to approximately 4.0.     

Matrix polynomial representation of the anisotropic magnetotelluric impedance tensor

A formalism based upon the equal penetration depth stratification assumption is extended to a layered anisotropic medium, yielding a recursive algorithm for the computation of the magnetotelluric impedance tensor elements. The development of this new procedure requires an appropriate layer-discretization as well as an extension of the reflection coefficient definition for the anisotropic layered model.This method transfers the differential problem into an algebraic one, and is independent of the electric and magnetic field vectors. The technique is a recursive process which gives a rational matrix polynomial representation for the magnetotelluric impedance tensor.The procedure involves the use of second-order matrices, rather than the fourth-order ones normally used for such a case. Using this representation, a separation of the contribution of the model parameters from that of the frequency is achieved. Consequently the elements of the magnetotelluric impedance tensor are computed, for each frequency, using coefficients which are evaluated just once for a given model.     

Clusters of black holes as point-like gamma-ray sources

The possibility of identifying some of Galactic gamma-ray sources as clusters of primordial black holes is discussed. The known scenarios of supermassive black hole formation indicate the multiple formation of lower-mass black holes. Our analysis demonstrates that due to Hawking evaporation the cluster of black holes with masses about 10¹⁵ g could be observed as a gamma-ray source. The total mass of typical cluster is ∼10 M_⊙. Detailed calculations have been performed on the basis of specific model of primordial black hole formation.     

Mechanisms accounting for variations in the proportions of carbonaceous and ordinary chondrites in different mass ranges

The number ratio of carbonaceous to ordinary chondrites (the CC/OC ratio) varies with mass. It is very high (≳90) in small mass ranges (10⁻⁸ to 10⁻¹² kg) among interplanetary dust particles and micrometeorites; it is moderately high (~5 to 30) for 1 to 10 m size fireball meteoroids (with estimated masses between ~10³ and ~10⁶ kg). In the range of most normal-sized meteorite falls (0.01–20 kg), the ratio is low (0.04–0.05); the ratio increases at greater mass ranges: at ≥200 kg, the ratio is 0.09; at ≥500 kg, the ratio is 0.20. The CC/OC ratio also increases from 0.05 to 0.16 for small meteorite finds (10⁻³ to 10⁻⁴ kg). High CC/OC ratios at low and high mass ranges are due to the predominance of CC material in the outer solar system. Small particles from this region spiral into the inner solar system typically in ≤10⁶ years due to Poynting–Robertson drag. Meter-sized meteoroids in this region are affected by Yarkovsky forces, pushing them into resonances where they are efficiently transferred to the inner solar system. Normal-sized meteorites are derived from centimeter-to-decimeter-sized meteoroids that have sluggish drift rates (i.e., they are less affected by the seasonal Yarkovsky effect) compared to larger bodies. Consequently, the centimeter-to-decimeter-sized meteoroids spend more time in interplanetary space (where they are subject to collisions) than larger objects. The greater friability of carbonaceous chondrites relative to ordinary chondrites tends to winnow the carbonaceous chondrites out in this size/mass range during their long interplanetary sojourn, thereby decreasing the CC/OC ratio.     

NWA 10214—An LL3 chondrite breccia with an assortment of metamorphosed,shocked, and unique chondrite clasts

NWA 10214 is an LL3‐6 breccia containing ~8 vol% clasts including LL5, LL6, and shocked‐darkened LL fragments as well as matrix‐rich Clast 6 (a new kind of chondrite). This clast is a dark‐colored, subrounded, 6.1 × 7.0 mm inclusion, consisting of 60 vol% fine‐grained matrix, 32 vol% coarse silicate grains, and 8 vol% coarse opaque grains. The large chondrules and chondrule fragments are mainly Type IB; one small chondrule is Type IIA. Also present are one 450 × 600 μm spinel‐pyroxene‐olivine CAI and one 85 × 110 μm AOI. Clast 6 possesses a unique set of properties. (1) It resembles carbonaceous chondrites in having relatively abundant matrix, CAIs, and AOIs; the clast's matrix composition is close to that in CV3 Vigarano. (2) It resembles type‐3 OC in its olivine and low‐Ca pyroxene compositional distributions, and in the Fe/Mn ratio of ferroan olivine grains. Its mean chondrule size is within 1σ of that of H chondrites. The O‐isotopic compositions of the chondrules are in the ordinary‐ and R‐chondrite ranges. (3) It resembles type‐3 enstatite chondrites in the minor element concentrations in low‐Ca pyroxene grains and in having a high low‐Ca pyroxene/olivine ratio in chondrules. Clast 6 is a new variety of type‐3 OC, somewhat more reduced than H chondrites or chondritic clasts in the Netschaevo IIE iron; the clast formed in a nebular region where aerodynamic radial drift processes deposited a high abundance of matrix material and CAIs. A chunk of this chondrite was ejected from its parent asteroid and later impacted the LL body at low relative velocity.     

Post-shock annealing of Miller Range 99301 (LL6): Implications for impact heating of ordinary chondrites

MIL 99301 is an LL chondrite that has experienced successive episodes of thermal metamorphism, shock metamorphism and annealing. The first recognizable petrogenetic episode resulted in thermal metamorphism of the rock to petrologic type 6 (as indicated by homogeneous olivine compositions, significant textural recrystallization, and the presence of coarse grains of plagioclase, metallic Fe-Ni and troilite). The source of heat for this thermal episode is not identified. The rock also experienced shock metamorphism to shock stage ∼S4 as indicated by extensive silicate darkening (caused by the dispersion within silicate grains of thin chromite melt veins and trails of metallic Fe-Ni and troilite blebs), polycrystalline troilite, myrmekitic plessite, a relatively high occurrence abundance (OA) of metallic Cu (3.6), the presence of numerous chromite-plagioclase assemblages, and coarse grains of low-Ca clinopyroxene with polysynthetic twinning. The shock event responsible for these effects must have occurred after the epoch of thermal metamorphism to type-6 levels; otherwise the polycrystallinity of the troilite would have disappeared and the low-Ca clinopyroxene would have transformed into orthopyroxene. Despite abundant evidence of strong shock, olivine and plagioclase in MIL 99301 exhibit sharp optical extinction, consistent with shock stage S1 and characteristic of an unshocked rock. This implies that an episode of post-shock annealing healed the damaged olivine and plagioclase crystal lattices and thereby changed undulose extinction into sharp extinction. The rock was probably annealed to metamorphic levels approximating petrologic type 4; more significant heating would have transformed the low-Ca clinopyroxene into orthopyroxene. It is not plausible that an episode of annealing occurring after the epoch of thermal metamorphism could have been caused by the decay of ²⁶Al because this isotope would have decayed away by that time. Impact heating is a more plausible source of post-metamorphic annealing of rocks in the vicinity of impact craters on low-density, high-porosity asteroids with rubble-pile structures.     

SIZE-DISTRIBUTIONS OF CHONDRULE TYPES IN THE INMAN AND ALLAN HILLS A77011 L3 CHONDRITES

A petrographc study of 9 thin sections of Inman (L3) and 18 thin sections of ALHA77011 (L3) served to determine the size-distributions of different chondrule textural types. Inman chondrules are significantly larger than those in ALHA77011, but in each chondrite, there is no statistically significant difference between the size-distributions of barred olivine and radial pyroxene plus cryptocrystalline chondrules. In ALHA77011, barred olivine chondrules outnumber radial pyroxene plus cryptocrystalline chondrules, whereas in Inman, the reverse is true. Because compound and cratered chondrules were formed by the collision of similarly-sized objects, the dustball precursors of chondrules must have been size-sorted prior to chondrule formation. The region of dustball size-sorting in the solar nebula must have been very large, similarly affecting the physically-separated precursors of different chondrule types. Size-sorting was probably accomplished by aerodynamic particle-gas interactions. Zones of dustball melting (i.e., chondrule formation) were relatively small, generally affecting only dustballs of one compositional type and relatively uniform size. Different chondrule types were then mixed together in somewhat variable ratios. Within the region where chondrites of a particular compositional group agglomerated, there were sub-reservoirs that contained (roughly) uniformly large or uniformly small chondrules with different mixtures of textural types.     

Croissance et reproduction de l'omble-chevalier,Salvelinus alpinus (L.), dans le lac de Neuchâtel (Suisse)

The arctic char (Salvelinus alpinus) which has disappeared from Lake Neuchatel near 1963, has been reintroduced into this lake since 1979. In this study, growth and reproduction of char have been analyzed 4 years after reintroduction. Age determination based on scales were more reliable then those based on otoliths. Growth rate decreased from the cohort born in 1979 to the cohort born in 1982. Nevertheless growth of char in Lake Neuchatel is fast compared to other char populations. About 33% of the males were sexually mature in the second year of life. At this age, no females, and in the third year of life, only 18% of the females were mature. Most fish of both sex were mature at an age of 4 years. A high correlation was found for data taken from other authors between fecundity and length of char. The data from Lake Neuchatel char (this study) fit very well with this general relation.      

Magnetic survey of Lake Kinneret-central Jordan Valley,Israel

A magnetic survey of Lake Kinneret (Sea of Galilee) was conducted on a 1 km grid of north-south and east-west lines. The results indicate that the margins of the lake are associated with large amplitude anomalies, while the centre is quite smooth. The largest anomaly, more than 500 nT, was detected in the vicinity of the entrance of the Jordan River into the lake. Its source is interpreted to be Late Cenozoic basaltic flows. The lake's margins are associated with faults, hot springs and magnetic anomalies. A broad magnetic anomaly trending east-northeast extends from Ginosar Valley into the lake through most of the lake's width. The distribution of basalt flows of different ages and the various structures of the magnetized layers are all contributing to the magnetic anomaly pattern.