Growth rates of Rhizocarpon geographicum lichens: a review with new data from Iceland

This paper reviews evidence from previous growth‐rate studies on lichens of the yellow‐green species of Subgenus Rhizocarpon—the family most commonly used in lichenometric dating. New data are presented from Rhizocarpon section Rhizocarpon thalli growing on a moraine in southern Iceland over a period of 4.33 yr. Measurements of 38 lichen thalli, between 2001 and 2005, show that diametral growth rate (DGR, mm yr^?1) is a function of thallus size. Growth rates increase rapidly in small thalli (<10 mm diameter), remain high (ca. 0.8 mm yr^?1) and then decrease gradually in larger thalli (>50 mm diameter). Mean DGR in southern Iceland, between 2001 and 2005, was 0.64 mm yr^?1 (SD = 0.24). The resultant growth‐rate curve is parabolic and is best described by a third‐order polynomial function. The striking similarity between these findings in Iceland and those of Armstrong ( 1983 ) in Wales implies that the shape of the growth‐rate curve may be characteristic of Rhizocarpon geographicum lichens. The difference between the absolute growth rate in southern Iceland and Wales (ca. 66% faster) is probably a function of climate and micro‐environment between the two sites. These findings have implications for previous lichenometric‐dating studies, namely, that those studies which assume constant lichen growth rates over many decades are probably unreliable. © British Geological Survey/Natural Environment Research Council copyright 2006. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

A Rhizocarpon geographicum growth curve for the Cascade Range of Washington and northern Oregon, usa

Lichen thallus measurements from 22 surfaces of known age on Mount Baker, Mount Hood, and Mount Rainier are used to construct a regional Rhizocarpon geographicum growth curve for the Cascade Range of Washington and northern Oregon. Growth rates determined by measuring the largest thallus diameters on the same surfaces at Mount Rainier in 1976 and 2002 are used for comparison with lichenometric data from Mount Baker and Mount Hood. Similar lichen thallus diameter vs age relationships identified in the data from the three mountains suggest the presence of uniform growth rates over the 400-km range. A regional growth curve developed during our study shows three growth phases of successively slower growth: a rapid phase from 8 to 20 yr, a linear phase from 20 to 145 yr, and a slow phase of unknown duration beyond ca. 145 yr. Uncertainty in lichen growth rates beyond 145 yr limits projection of the curve beyond that age; however, the age range of the constrained growth curve covers an important period of recent climate variability. When applied in appropriate settings, our growth curve can be used to determine numeric ages to ±10 yr for surfaces between 20 and 145 years old in areas where other techniques are not applicable or do not provide unique or well-constrained ages.     

Lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the Patagonian Andes, Argentina

This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.     

Quaternary glaciations of the Rongbuk Valley,Tibet

Randomisation tests on boulder weathering data distinguish moraines of four different ages in the Rongbuk Valley, all deposited by valley glaciers flowing northward into Tibet from the Himalaya. Lichenometry utilising subgenus Rhizocarpon distinguishes two groups of moraines, those <100 yr old and those older than several thousand years. The degree of soil development has a similar, limited utility in relative-age dating these moraines. The radiocarbon ages of calcium carbonate coatings in the lower horizons of moraine soils provide minimum-limiting ages of 1900 yr BP for the penultimate advance of the Rongbuk glacier (Samdopo moraine) and 9500 yr BP for the Rongbuk moraine, the moraine suggested by previous workers to represent the last glacial maximum. Equilibrium-line depression associated with the Rongbuk moraine probably was slight, <200 m. The small magnitude of this depression relative to glaciers in other mountain ranges could relate to a weakening of the monsoon in full glacial times, recent tectonic uplift, and/or to the insensitivity of these high-altitude glaciers to lowering temperatures in the rain shadow of Mount Everest.     

Colonization delay of Rhizocarpon geographicum: Study from the Gangotri glacier,northwestern Himalaya

Lichenometric application used mainly for the dating of moraines, involves the calibration of growth rate curve with the inclusion of colonization delay of a specific type of lichen. In the present study, the colonization delay of Rhizocarpon geographicum species of lichen found on the boulders of granite and gneisses in the Gangotri glacier environment has been interpreted. It has been concluded that the colonization delay for the said species is different for both the rock-types. It is about 78 years for granite and between 50 and 78 years for the gneisses. The study will help to establish the absolute ages of the various terminal moraines of the Gangotri glacier, which in turn will help to ascertain the recession history of the glacier.     

Lichenometry on calcareous substrates in the Canadian Rockies

Lichen distribution and growth were examined at several sites in the Canadian Rockies between Mt. Robson and Banff townsite to determine the feasibility of lichenometry on calcareous deposits. The only lichen common enough to be of use is Xanthoria elegans, a bright orange lichen with round or elliptical thalli. It is not an ideal species for lichenometry because (a) it grows fairly quickly and has a range of only a few centuries, (b) growth is influenced by the presence of animal dung, (c) parts of some thalli weather away before maximum size is attained, (d) thalli may thicken as well as grow laterally with age, (e) the species is succeeded by other species relatively quickly in heavily forested environments, and (f) the species is not abundant on some deposits due to sometimes-unexplained environmental influences. However, when used with caution the species is still useful for dating purposes.A growth curve for Xanthoria elegans was developed using moraines dated dendro-chronologically and man-made structures. After an ecesis interval of one or two decades the lichen grows at a rate of 0.68 mm/yr for several decades, then slows down to a rate of 0.22 mm/yr.     

碎石土三轴测试仿真建模及试样尺寸效应分析

借助离散单元理论与室内三轴试验, 分析碎石土物理实验中试样尺寸(直径和高度)变化对应力应变、体应变、粘聚力和内摩擦角等力学性能的尺寸效应影响。研究结果表明, 所提出的块体随机生成法则能较好地实现试样中不同形状碎石块的模拟。不同直径和高度的碎石土试样, 初始2%应变范围内的应力-应变曲线变化规律基本一致, 后部曲线变化较大。直径和高度越小, 围压越低, 应力软化现象越明显; 直径大于250 mm、高度大于350 mm后无应变软化, 残余应力恒定。峰值应力随试样直径增大以25%的增长率呈线性增长, 随高度的增大呈非线性增长, 高度小于200 mm时增长率为11.9%, 大于200 mm后为28.9%。体应变破坏峰值则表现为先增大后减小的趋势。同时粘聚力随直径的增大线性增长, 内摩擦角则减小, 而试件高度的变化对其影响规律则相反。      

西安地区部分古遗址考古地磁研究

通过对陕西耀州窑遗址内4个古窑,临潼兵马俑一号坑,西铜一级公路经过黄堡工地开挖的两个五代窑,以及耀州窑博物馆仓库工地内开挖的一个金代窑和一个春秋窑遗址的古地磁研究,初步得出了西安地区古地磁场变化的规律,为鉴定从春秋到金代西安地区的古遗址、古文物提供了考古地磁学上的一个粗略的标准。     

Recent macroids on the Kikai‐jima shelf,Central Ryukyu Islands,Japan

Sandy and gravelly carbonate sediments found off Kikai‐jima, southern Japan, a coral reef‐related island shelf, represent the northernmost sub‐tropical, carbonate deposits in the Central Ryukyu Islands (Ryukyus). On the Kikai‐jima shelf, at water depths of 61 to 105 m, these sediments are characterized by macroid pavements. Since the abundance of very small and of exceptionally large macroids may indicate specific hydrodynamic controls regarding constraints on growth and taphonomy, the detailed analysis of recent and fossil macroid pavements is meaningful ecologically and environmentally. Macroids, ranging in size from ca 25 to 130 mm in diameter, are spheroidal and sub‐spheroidal in shape and consist mainly of the encrusting foraminifer Acervulina inhaerens and subordinate thin encrusting and lumpy coralline algae. Accessory components include bryozoans, serpulids and, to a lesser extent, encrusting arborescent foraminifera (Homotrema and Miniacina). Low sedimentation rates and occasional movement due to current action are indicated by sizes, shapes and growth‐forms of the studied macroids, the Entobia–Gastrochaenolites–Trypanites–Maeandropolydora ichnocoenosis and the ‘Bioerosion Index’ for coated grains (introduced herein). The deep‐water tidally induced current energy was sufficient to maintain multi‐directional growth (spheroidal shapes) of the larger macroids and to initiate macroid growth using the diverse biogenic remnants as nuclei. The asymmetrical inner arrangement suggests possible periods of stability for the macroids. The residence time of the coated grain in its original environment determines the size and morphology of the macroid and the selection of coating organisms. The composition of the coating community is mainly a consequence of component growth rates in relation to turnover time and residence time. Long‐term studies are needed to assess the spatial and temporal resolution of present‐day encrusting communities across biogeographic provinces and shelf to slope regions.     

A new hypothesis for the origin of the supposed giant snail Dinocochlea from the Wealden of Sussex, England

When first described in 1922, Dinocochlea ingens, an Early Cretaceous (Valanginian) fossil from the Wadhurst Clay Formation (Wealden) of Hastings in Sussex, England, was regarded as the steinkern of a huge gastropod over 2 m in length and claimed to be the largest gastropod ever to have lived. Most subsequent researchers have doubted the identity of D. ingens as a gastropod, usually believing it to be a pseudofossil, but no convincing explanation has been proposed for its origin. Restudy of the type material leads to the new hypothesis that Dinocochlea originated as a horizontal, corkscrew-shaped burrow resembling Helicodromites that acted as a nucleus for concretion growth. Sectioned specimens of Dinocochlea are filled with concentrically banded sediment interpreted to be growth rings of a concretion. Modification of a computer simulation designed to illustrate gastropod shell growth shows how the development of a concretion around a corkscrew-shaped burrow could lead to the morphology seen in Dinocochlea. The most likely tracemaker for Dinocochlea was a capitellid polychaete (‘threadworm’) with a body just a few mm in diameter.     

在复杂地层钻进物探震源孔系列钻头的研制与应用

在密山一带休物探震源孔,外遇地层为胶泥、沙土、风化岩、青石板及河流石等。为此研制了一系列新式钻头,包括９８ｍｍ三牙轮钻头、９８ｍｍ刮刀式ＰＤＣ钻头及１１８ｍｍ砾石流沙炮眼防卡钻头,前２种钻头现场共应用９３０口井,创造了极好的经济效益和社会效益。     

Micro‐sampling Lu–Hf geochronology reveals episodic garnet growth and multiple high‐P metamorphic events

We present Lu–Hf dates from multiple growth zones within two large garnet porphyroblasts by a micro‐sampling method. A single eclogite sample, taken from the Huwan shear zone in the Hong'an orogen, was investigated with Lu–Hf geochronology by micro‐sampling and traditional bulk separation methods. The sample contains a few large garnet porphyroblasts up to several centimetres in diameter and a second major population of smaller (0.1–2.0 mm) garnet porphyroblasts, comprised of dark cores and pale rims. Elemental compositions and mineral inclusions in the garnet appear consistent with two garnet generations. Lu–Hf dates (c. 400–264 Ma) were determined from twelve micro‐sawed garnet sections from two large garnet porphyroblasts. These Lu–Hf dates overlap with age peaks defined by 115 SIMS zircon U–Pb analyses from the same eclogite sample. Bulk analyses of smaller garnet separates define a minimum date of c. 306 Ma and a maximum date of c. 252 Ma for the dark cores and pale rims respectively. These Lu–Hf dates were interpreted to bracket the period of garnet growth and the broad interval from c. 400 to 264 Ma is best explained by protracted and episodic garnet growth, which may require that these rocks experienced two subduction cycles that were initiated during the Devonian and terminated in the Triassic.     

Experimental study of stick-slip behaviour

Simple axi-symmetric uni-axial compression tests have been realized on dry loose samples of glass beads (diameters d: d=0.2 ± 0.05 mm, 0.75 ± 0.1 mm, or 3 mm) and on Hostun sand under small lateral confinement, σ₃<60 kPa, using different sample sizes. The experiments with the two smallest spheres (d=0.2 and 0.75 mm) exhibit stick-slips, which are characterized by (i) a rapid release Δq of the deviatoric stress q and by (ii) the strain Δε₁ separating two events. The samples which exhibit stick-slip also present a weakening of strength q(ε₁) as the rate of deformation dε₁/dt is increased. No stick-slip is generated during the first part of the q−ε₁ curve, i.e. when q grows fast with ε₁. Four different parameters helped us determine the statistics of Δq and Δε: the lateral pressure σ₃′, the rate of deformation dε₁/dt, the sample height H, and the diameter D. The statistics do not depend on rate history. They look like exponentials in small samples and/or in (large sample+fast dε₁/dt), and they look like Poissonian or Gaussian in (Large sample+small dε₁/dt). This change in statistics is attributed to a varying of triggering process starting from a single random event in small samples to multiple random events. We have interpreted this change of statistics as due to some finite size effect so that the representative elementary volume shall contain at least (200)³ grains. Localization of deformation is visible at the end of compression but cannot be detected from stick-slip statistics nor from q vs ε curve. Copyright © 2004 John Wiley & Sons, Ltd.     

U‐Th‐Pb systematics of some granitoids from the northeastern Yilgarn Block,Western Australia and implications for uranium source rock potential

The Mount Boreas‐type granite and spatially associated syenitic granitoid of Western Australia yield Pb‐Pb ages of 2370 ± 100 Ma and 2760 ± 210 Ma, respectively. Th‐Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U‐Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (< 3μg/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete‐hosted uranium deposits. The possibility remains that the Mount Boreas‐type granite that has been completely weathered during the Tertiary could have been a source for the calcrete‐type uranium deposits in W.A. Although the Mount Boreas‐type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (～ 20μg/g) and are associated with large roll‐type and other low temperature‐type uranium deposits.     

Towards a Higher Comparability of Geothermometric Data Obtained by Raman Spectroscopy of Carbonaceous Material. Part 2: A Revised Geothermometer

The estimation of the peak metamorphic temperature by Raman spectroscopy of carbonaceous material (RSCM) is influenced by several bias sources grouped in measuring conditions, spectral processing and sample heterogeneity. The measuring conditions (selected excitation wavelength) and the operator bias during spectral processing have a pronounced impact on the temperature estimate and thus on the comparability and portability of thermometric data obtained by RSCM. Several calibration lines of RSCM geothermometers are published already, but no standardised approach exists. Samples of carbonaceous material bearing metasediments with well‐established metamorphic conditions of the central and western Alps compile a reference series. By applying an automated, iterative and randomised curve‐fitting approach, a consistent and user input‐independent RSCM geothermometer is presented, which covers peak metamorphic temperatures from ca. 160 to 600 °C. The method is hardware independent because the measuring conditions bias is excluded by the use of the reference series and the automated curve‐fitting approach reduces the spectral processing bias effectively, increasing the method's comparability and portability. By distributing the reference series and the automated curve‐fitting software, a laboratory will be able to derive a laboratory specific calibration line for the RSCM geothermometer.     

采用多项式拟合修正法提高CCD垂线仪的测量精度

通过分析CZ型CCD垂线坐标仪的标定数据,提出了使用3段2次多项式拟合修正法减小仪器非线性误差,提高测量精度的方法。在实际应用中明显提高了该产品的测量精度。     

异烟酸-吡唑啉酮分光光度法测定地下水中氰化物的不确定度评定

采用不确定度连续传递模型,对异烟酸-吡唑啉酮分光光度法测定地下水中氰化物的不确定度进行评定。分析了不确定度的重要来源,包括样品制备、标准溶液配制、标准曲线拟合和仪器测量过程等引入的不确定度分量。采用x、y双误差回归方式对标准曲线进行拟合,通过分析得知,样品中氰化物浓度越低,其相对不确定度越大。     

Flow Characteristics of Cemented Paste Backfill

Cemented paste backfill (CPB) is primarily used for backfilling underground voids at George Fisher Mine (Mount Isa, Australia). The objective of this paper is to summarise the geotechnical characterisation of the tailings and the rheological properties of the CPB as determined from a laboratory testing program undertaken at James Cook University. Two binders were examined [a General Purpose cement and a slag blend cement] over a range of dosages from 0 to 6% and CPB mix solids content in the range of 72–78%. The slump tests were carried out using the standard cone (ASTM C 143) used for concrete and a cylinder with 110 mm (diameter) × 110 mm (height), whereas the yield stress was measured using a shear vane (Brookfield vane spindle V-73). The index characteristics of the tailings including the grain size distribution, liquid limit, plastic limit, specific gravity were determined as per ASTM standards. This paper will then discuss the interrelationships among the solid content, slump, saturated density and the yield stress of the CPB. It is shown that there is strong correlation between the two different slump test devices used in this study. The smaller cylindrical device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test. There is also strong inter-relationship among solid content, slump, yield stress, and bulk density. Increasing the solid content increases the bulk density and yield stress, but reduces the slump. While there is hardly any difference between the two binder types used in this study in terms of flow parameters, namely the yield stress and slump, the binder dosage has an effect. At any specific solid content, higher binder dosages lead to a drop in the slump and increase in the yield stress. The difference is more pronounced in dense slurries. It is also strongly believed that the trends and relationships developed in this study may be valuable for the other mining operations using CPB.     

Relative dating of Late Quaternary deposits using cluster and discriminant analysis, Audubon Cirque, Mt. Audubon, Colorado Front Range

Holocene and Late Quaternary talus, lobate rock glaciers, and moraines within Audubon Cirque, Colorado Front Range, were assigned reltive ages using the following age-dependent criteria: fresh-weathered ratio, pitting, weathering rind development, angularity, and surface, oxidation of boulders, together with lichen cover and largest lichen diameter. Principal Component scores, yielding four major groups of deposits (relative age units C, R, E and V, from youngest to oldest). Tentative correlation with other Colorado Late Quaternary sequences suggests that unit C is of Gannett Peak age (100–300 years B. P.), unit R of Audubon age (950–1850 years B. P.) unit E of Early Neoglacial age (3000–5000 years B. P.), and unit V of Late Pinedale age (about 10,000 Years B. P.). Correlation is problematic due to differences in operationsl definitions of relative dating parametrs between workers, and because climatic and lithologic variations between areas may confound the date.     

Carbonate alteration of the Upper Mount McRae Shale beneath the martite-microplaty hematite ore deposit at Mount Whaleback, Western Australia

The formation of large martite-microplaty hematite ore deposits in northwest Australia remains a contentious topic in part because important evidence supporting a unifying genetic model has not been observed at all deposits. Carbonate replacement of silica has been found along normal faults below ore at the Mount Tom Price and Giles Mini deposits, which suggests an early hypogene process during ore formation. However, such rocks have not been identified at the largest martite-microplaty hematite deposit, Mount Whaleback. In this study, samples of the Mount McRae Shale are examined for their chemistry, mineralogy and petrography. These samples were collected from several key locations, including an area that immediately underlies ore along the Mount Whaleback fault at Mount Whaleback. Compared to unaltered black Mount McRae Shale from Wittenoom Gorge in the north and altered black and red Mount McRae Shale at Mount Whaleback, reddish-green Mount McRae Shale along the Mount Whaleback fault is greatly enriched in MgO and CaO and depleted in SiO₂. This chemistry arises from significant amounts of fine- to medium-grained ferroan-dolomite and ankerite and cross-cutting chlorite and carbonate veins. The composition is distinct from that produced during regional metamorphism, and most likely represents hydrothermal alteration after metamorphism. The lack of carbonate-rich, silica-poor rocks in the overlying Dales Gorge Member at Mount Whaleback is consistent with pervasive oxidation of most rocks in the region during or after ore genesis, a process that removed carbonates. Although several questions remain unanswered, these results support models that invoke an early hypogene stage during the formation of the martite-microplaty hematite deposits in the Hamersley Province.Editorial Handling: B. Lehmann