Late Quaternary landscapes in Central Australia: sedimentary history and palaeoecology of Puritjarra rock shelter

Puritjarra rock shelter provides a long record of late Quaternary vegetation in the Australian arid zone. Analysis of the sedimentary history of this rock shelter is combined with reanalysis of charcoal and phytolith records to provide a first‐order picture of changing landscapes in western Central Australia. These show a landscape responding to increasing aridity from 45 ka with deflation of clay‐rich red palaeosols (<45 ka) and sharp declines in grassland and other vegetation at 40–36 ka, and at the beginning of the Last Glacial Maximum (LGM) (24 ka). Vegetation in the catchment of the rock shelter recovered after 15 ka with expansion of both acacia woodland and spinifex grasslands, registering stronger summer rainfall in the interior of the continent. By 8.3 ka re‐vegetation of local palaeosols and dunes had choked off sediment supply to the rock shelter and the character of the sediments changed abruptly. Poaceae values peaked at 5.8 ka, suggesting the early–mid Holocene climatic optimum in Central Australia is bracketed between 8.3 and 5.8 ka. Local vegetation was disrupted in the late Holocene with a sharp decline in Poaceae at 3.8 ka, coinciding with an abrupt intensification of ENSO. Local grasslands recovered over the next two millennia and by 1.5 ka the modern vegetation appears to have become established. Copyright © 2009 John Wiley & Sons, Ltd.     

Modelling the April 15 spectrum of Supernova 1993 J

We present the modeling of the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 with the HST and at Lick Observatory. A Monte Carlo code is employed in the modeling and a comparison is made between models reported by different groups. With an atmosphere similar to the Sun in chemical composition, the observed spectral lines are well reproduced by a power law density structure of index around 20 except the strong H and HeI λ5876 lines which have peculiar absorption profiles. The photospheric velocity is found to be 9500 km/s and the blackbody temperature of the spectrum is 7990 K. For H and HeI λ5876, we suggest a two-component density structure which has a smoother layer located immediately outside the steeply decreasing inner envelope. The power law indices are most probably 20 and 3, respectively, with the transition point at about 13 000 km/s. In addition, this outer smooth layer serves to flatten the far UV spectrum as observed.     

Strong magnetic field in W75N OH maser flare

A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the Very Long Baseline Array (VLBA) to be within 110 au from one of the ultracompact H  ii regions, Very Large Array 2 (VLA2). The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the magnetohydrodynamic shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes.     

长岭凹陷潜在地热初步探讨

根据长岭凹陷石油井地温测量和物探资料,从地热形成的4要素——储、盖、通、源以及地热具备的地质特征入手,分析了长岭凹陷潜在着地热资源。目前长岭盆地基本具备了储和盖,需要进一步寻找的是通和源。     

北部湾盆地涠西南凹陷断裂系统成因的砂箱实验研究及启示

北部湾盆地涠西南凹陷的断裂系统十分复杂,为了揭示其成因机制,在三维地震资料构造解析的基础上,应用砂箱物理模拟技术,对涠西南凹陷的形成机制进行了系统研究.结果表明,南北向的"不协调伸展作用实验模型"能够成功地模拟涠西南凹陷晚始新世以来复杂的断裂系统,断裂系统的主体特征在这一实验模型中均得到了很好的再现.涠两南凹陷复杂的断裂系统是在基底先1竽构造基础之上,在递进变形过程中逐渐形成的,其裂陷期(晚始新世一渐新世)断裂系统是在一个伸展期内形成(南北向伸展)、并非是多期构造叠加变形的结果.这一认识不但能够有效地指导涠西南凹陷三维地震资料的精细构造解释,同时也能够为南海周缘盆地的形成和演化研究提供借鉴.     

Formation of Fe-oxyhydroxides from the East Pacific Rise near latitude 13°N:Evidence from mineralogical and geochemical data

The mineralogical and geochemical characteristics of Fe-oxyhydroxide samples from one dredge station (long. 103°54.48'W, lat. 12°42.30'N, water depth 2655 m) on the East Pacific Rise near lat 13°N were analyzed by XRD, ICP-AES, and ICP-MS. Most Fe-oxyhydroxides are amorphous, with a few sphalerite microlites. In comparison with Fe-oxyhydroxides from other fields, the variable ranges in the chemical composition of Fe-oxyhydroxide samples are very narrow; their Fe, Si, and Mn contents were 39.90%, 8.92%, and 1.59%, respectively; they have high Cu (0.88%―1.85%) and Co (65×10?6―704×10?6) contents, and contain Co Cu Zn Ni> 1.01%. The trace-element (As, Co, Ni, Cu, Zn, Ba, Sr) and major-element (Fe, Ca, Al, Mg) contents of these samples are in the range of hydrothermal sulfide from the East Pacific Rise near 13°N, reflecting that this type of Fe-oxyhydroxide constitutes a secondary oxidation product of hydrothermal sulfide. The Fe-oxyhydroxide samples from one dredge station on the East Pacific Rise near 13°N are lower in ΣREE (5.44×10?6―17.01×10?6), with a distinct negative Ce anomaly (0.12 ― 0.28). The Fe-oxyhydroxide samples have similar chondrite-normalized rare-earth-element (REE) patterns to that of seawater, and they are very different from the REE composition characteristics of hydrothermal plume particles and hydrothermal fluids, showing that the REEs of Fe-oxyhydroxide are a major constituent of seawater and that the Fe-oxyhydroxides can become a sink of REE from seawater. The quick settling of hydrothermal plume particles resulted in the lower REE content and higher Mn content of these Fe-oxyhydroxides, which are captured in part of the V and P from seawater by adsorption. The Fe-oxyhydroxides from one dredge station on the East Pacific Rise near 13°N were formed by secondary oxidation in a low temperature, oxygenated environment. In comparison with the elemental (Zn, Cd, Pb, Fe, Co, Cu) average content of hydrothermal sulfide samples from the East Pacific Rise near 13°N, the Zn, Cd, and Pb contents of the Fe-oxyhydroxides are lower, and their Fe, Co, and Cu contents are higher.     

Impact angle influence in high velocity dust collisions during planetesimal formation

We have examined the influence of impact angle in collisions between small dust aggregates and larger dust targets through laboratory experiments. Targets consisted of μm-sized quartz dust and had a porosity of about 67%; the projectiles, between 1 and 5 mm in diameter, were slightly more compact (64% porosity). The collision velocity was centered at 20 m/s and impact angles range from 0° to 45°. At a given impact angle, the target gained mass for projectiles smaller than a threshold size, which decreases with increasing angle from about 3 mm to 1 mm. The fact that growth is possible up to the largest angles studied supports the idea of planetesimal formation by sweep-up of small dust aggregates.     

神木气田二叠系气藏有利区预测

神木气田二叠系储层以低孔、致密为特征,非均质性强,气田开发产能较低、开发难度大.在细分层系的基础上,研究沉积砂体和有效砂体空间展布特征,明确太原组、山西组沉积相类型,以及沉积作用是储层发育的主导因素;综合考虑沉积特征、储层发育程度和试气成果等,明确神木气田的主力层位,以太原组、山2段和山1段为3个单元,进行有利开发区块的优选,优选Ⅰ类有利区块8块,推荐叠合有利区.结果表明:在优选有利区内钻井开发效果好,以苏里格气田标准进行衡量Ⅰ+Ⅱ类井比例达到78%,神木气田分层系、优选有利区的开发思路正确,优选有利区准确,对气田产能建设起到促进作用.     

History of Star Formation and Chemical Enrichment in the Milky Way Disk

Based on a physical treatment of the star formation law similar to that given by Efstathiou, we have improved our two-component chemical evolution model for the Milky Way disk. Two gas infall rates are compared, one exponential, one Gaussian. It is shown that the star formation law adopted in this paper depends more strongly on the gas surface density than that in Chang et al. It has large effects on the history of star formation and gas evolution of the whole disk. In the solar neighborhood, the history of chemical evolution and star formation is not sensitive to whether the infall rate is Gaussian or exponential. For the same infall time scale, both forms predict the same behavior for the current properties of the Galactic disk. The model predictions do depend on whether or not the infall time scale varies with the radius, but current available observations cannot decide which case is the more realistic. Our results also show that it would be inadequate to describe the gradient evolution along the Gala