中国西南天山西域砾岩的磁性地层年代与地质意义*

西域组是我国西部一重要并广泛引用的晚新生代地层,关于其年代和成因至今尚存争议。在西南天山喀什远源盆地喀什-阿图什褶皱带不同构造部位选择有代表性的5~6个晚新生代地层剖面开展了详细的沉积学、磁性地层年代学对比研究,据此限定了不同构造的起始变形时间以及西域砾岩的沉积年代。西域砾岩并非一年代地层单位,作为一岩石地层单位,其底界具有穿时特征,从山体(北)向喀什前陆盆地(南)逐渐变新。其底界年龄在盆地北部近源区约为15.5Ma^[1],在盆地中部中源区约为8.6Ma^[1],在盆地南部远源区的阿图什背斜为1.9Ma,喀什背斜为1.6~0.7Ma。这一穿时的砾岩沉积楔体的起始堆积起因于盆地北部边界逆冲断层(KBT)的活动。构造变形是由北南脉冲式迁移扩展的,其速率是非均匀的,在约15.5Ma至4.0Ma期间为1.4~3.4mm/a,在约4.0Ma以来剧增至>10mm/a。西域砾岩沉积前缘向南进积速率与构造变形前缘迁移速率有很好的一致性,但在时间上较构造变形可能滞后2.0Ma。这表明构造变形前缘向南的脉冲式扩展是西域砾岩进积并发生侧向和垂向上岩相突变的主因。     

Laboratory kinetics of C2H radical reactions with ethane, propane, and n-butane at T = 96-296 K: implications for Titan

The kinetics of the reactions of C₂H radical with ethane (k₁), propane (k₂), and n-butane (k₃) are studied over the temperature range of T = 96-296 K with a pulsed Laval nozzle apparatus that utilizes a pulsed laser photolysis-chemiluminescence technique. The C₂H decay profiles in the presence of both the alkane reactant and O₂ are monitored by the CH(A²Δ) chemiluminescence tracer method. The results, together with available literature data, yield the following Arrhenius expressions: k₁(T) = (0.51 ± 0.06) × 10⁻¹⁰ exp[(−76 ± 30)K/T] cm³ molecule⁻¹ s⁻¹ (T = 96-800 K), k₂(T) = (0.98 ± 0.32) × 10⁻¹⁰exp[(−71 ± 60)K/T] cm³ molecule⁻¹ s⁻¹ (T = 96-361 K), and k₃(T) = (1.23 ± 0.26) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ (T = 96-297 K). At T = 296 K, k₁ is measured as a function of total pressure and has little or no pressure dependence. The results from this work support a direct hydrogen abstraction mechanism for the title reactions. Implications to the atmospheric chemistry of Titan are discussed.     

Trends in the solubility of iron,aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean

The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO₄²⁻, NO₃⁻) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean.     

Models for the motions of flare loops and ribbons

We have found a conformal mapping which is valid for any magnetic boundary condition at the photosphere and which can be used to determine the evolution of an open, two-dimensional magnetic field configuration as it relaxes to a closed one. Solutions obtained with this mapping are in quasi-static equilibrium, and they contain a vertical current sheet and have line-tied boundary conditions. As a specific example, we determine the solution for a boundary condition corresponding to a submerged, two-dimensional dipole below the photosphere. We assume that the outer edges of the hottest X-ray loops correspond to field lines mapping from the outer edges of the H ribbon to the lower tip of the current sheet where field lines reconnect at aY-type neutral line which rises with time. The cooler H loops are assumed to lie along the field lines mapping to the inner edges of the flare ribbons. With this correspondence between the plasma structures and the magnetic field we determine the shrinkage that field lines are observed to undergo as they are disconnected from the neutral line. During the early phase of the flare, we predict that shrinkage inferred from the height of the H and X-ray loops is close to 100% of the loop height. However, the shrinkage should rapidly decrease with time to values on the order of 20% by the late phase. We also predict that the shrinkage in very large loops obeys a universal scaling law which is independent of the boundary condition, provided that the field becomes self-similar (i.e., all field lines have the same shape) at large distances. Specifically, for any self-similar field containing aY-type neutral line, the observed shrinkage at large distances should decrease as (X/X _R)^–2/3, where X is the ribbon width andX _Ris the ribbon separation. Finally, we discuss the relation between the electric field at the neutral line and the motions of the flare loops and ribbons.     

Below- and Aboveground Spartina alterniflora Production in a Louisiana Salt Marsh

The monthly variations of below- and aboveground biomass of Spartina alterniflora were documented for a south Louisiana salt marsh from March 2004 to March 2005, and in March 2006 and 2007. The annual production rate above- and belowground was 1821 and 11,676 g m^?2, respectively (Smalley method), and the annual production rate per biomass belowground was 10.7 g dry weight^?1, which are highs along the latitudinal distributions of the plant’s range. The average root + rhizome/shoot ratio (R&R/S) was 2.6:1, which is lower than the R&R/S ratios of 4 to 5.1 reported for Spartina sp. marshes in the northeastern US. The belowground biomass increased from July to September and fluctuated between October and November, after which it declined until February when the growing season began. The belowground biomass was dominated by rhizomes, which declined precipitously in spring and then rose to a seasonal high in the month before declining again as the late summer rise in inflorescence began. Over half of the root biomass in a 30-cm soil profile was in the upper 10 cm, and in the 10- to 20-cm profile for rhizomes. The maximum March biomass above- and belowground was four to five times that of the minimum biomass over the four sampling years. The net standing stock (NSS) of N and P in live biomass aboveground compared to that in the belowground biomass was about 1.7 times higher and equal, respectively, but the NSS of N and P for the live + dead biomass was about six times higher belowground. The average nitrogen/phosphorous molar ratios of 16:1 aboveground is in agreement with the often tested N limitation of biomass accumulation aboveground, whereas the 37:1 belowground ratio suggests that there is an influence of P on R&R foraging for P belowground. Some implications for management and restoration are, in part, that salt marshes should be evaluated and examined using information on the plant’s physiology and production both below- and aboveground.     

The total number of spicules on the solar surface and their role in heating and mass balanace in the solar corona

A critical review of determinations of the number of spicules is presented, and the role of both classical and Type 2 spicules in heating and mass balance in the corona is considered. The total number of Type 2 spicules is determined, together with the upward fluxes of energy and mass to which they give rise. The total number of Type 2 spicules on the solar surface is found to be ~10⁵, close to values obtained in other studies. The associated particle flux toward the corona is 2.5 × 10¹⁴ cm^?2 s^?1, an order of magnitude lower than the corresponding flux for classical spicules. The associated energy flux is 10⁴ erg cm^?2 s^?1, an order of magnaitude lower than estimates obtained in other studies. The results indicate that Type 2 spicules can supply the mass lost from the corona, but are not able to fully explain coronal energy losses.     

Tectonic environments of ancient civilizations in the eastern hemisphere

The map distribution of ancient civilizations shows a remarkable correspondence with tectonic boundaries related to the southern margin of the Eurasian plate. Quantification of this observation shows that the association is indeed significant, and both historical records and archaeoseismological work show that these civilizations commonly suffered earthquake damage. Close association of ancient civilizations with tectonic activity seems to be a pattern of some kind. In the hope that dividing the civilizations into subsets might clarify the meaning of this relation, primary and derivative civilizations were compared. Derivative civilizations prove to be far more closely related to the tectonic boundaries. Similarly, the civilizations that endured the longest (and that have been described as most static) are systematically the farthest from plate boundaries. It is still unclear how the relation actually worked in ancient cultures, i.e., what aspects of tectonism promoted complexity. Linkages to water and other resources, trade (broadly construed), and societal response seem likely. Volcanism appears not to be involved. © 2008 Wiley Periodicals, Inc.     

Complex history of a zircon aggregate from lunar breccia 73235

Results are reported of an investigation of the age and origin of the exceptional zircon aggregate in an anorthositic clast from lunar breccia 73235. Cathodoluminescence and birefringence images show that the aggregate consists of numerous angular fragments of sector zoned primary zircon in a matrix of secondary zircon with an overall texture that resembles a pseudotachylite. SIMS U-Pb analyses of the primary fragments and the matrix yielded two clearly defined ages, an age of 4.315 ± 0.015 Ga and initial Th/U ratio of 0.21-0.35 for the primary zircon and an age of 4.187 ± 0.011 Ga and Th/U of 0.04-0.17, for the secondary zircon matrix. A Raman spectroscopic study the secondary matrix zircon was undertaken to investigate its structure. Results showed that the matrix has a zircon structure but there is also evidence for the presence of an amorphous component. Implications of the structural and U-Pb age data are discussed in terms of the origin and evolution of the aggregate and the history of lunar events. It is proposed that an original single, millimetre-sized, sector zoned zircon, formed at 4.31 Ga, was subjected to a severe shock event at 4.18 Ga. This event resulted in the fracturing of the zircon, the displacement and rotation of fragments, the compression of the aggregate to a lensoid shape, and the shock reduction of zircon to sub-micron-sized and amorphous granules in crush zones in the mosaic of fractures. Volatilisation loss of Pb and the addition of U to the secondary zircon is attributed to processes activated by the extreme thermal pulse which accompanied the 4.18 Ga shock event. Shock effects are seen in some of the primary fragments but Raman spectra of the primary and secondary zircon show no evidence for pressure-induced transformation of zircon to a scheelite structure. The zircon U-Pb system has not been affected by the ca. 3.95 Ga thermal pulse that accompanied formation of the host breccia although this event has largely reset the K-Ar systems.     

Marine biotic signals across a late Eocene impact layer at Massignano,Italy: evidence for long‐term environmental perturbations?

The Eocene–Oligocene transition marks the passage from 'greenhouse' conditions to an 'icehouse' state, with progressive global cooling starting in the early middle Eocene. The late Eocene presents substantial evidence for extraterrestrial impacts whose effects on living organisms and climatic changes are still not completely clear. A high-resolution, microfloral and faunal investigation has been carried out in a 4-m-thick segment of the Massignano Global Stratotype Section and Point for the Eocene–Oligocene boundary. The studied interval includes a late Eocene (35.7 ± 0.4 Myr old) impactoclastic layer containing several cosmic signatures. The impact event recorded at Massignano had no abrupt, dramatic effects on marine biota in terms of extinction. However, significant quantitative changes in the calcareous plankton and dinoflagellate cyst assemblages occurred 60 kyr after the impact event. The observed pattern is intepreted as reflecting a long-term re-organization of water structure.