Thermomagnetic characteristics in late orogenic granites and gneisses of the southern Appalachian Piedmont

Thermomagnetic curves have been obtained for samples from 25 granites and gneisses in Georgia, South Carolina, and North Carolina. This data set can be divided into two distinct curve types: Type I includes rocks which exhibit no distinct Curie points and a linear decrease in magnetization with increasing temperature; Type II curves exhibit a distinct Curie point over a range of temperatures expected for magnetite (500–580°C). Synthetic samples constructed from magnetite and hematite powder exhibit Type I behavior when the hematite to magnetite ratio is high (e.g. 15 : 1). Examination of polished sections shows relatively coarse-grained magnetite only in Type II rocks. We interpret our data to indicate that Type I thermomagnetic curves are dominated by relatively large hematite/magnetite ratios while Type II granites are characterized by relatively coarse-grained magnetite. Type I granite samples have low magnetic susceptibility values (less than 4 × 10^?4 cgs) while most Type II granite samples have higher values. The Type I granites are invariably¹⁸O-enriched whereas Type II granites typically exhibit low¹⁸O/¹⁶O ratios. These relationships are consistent with previously reported correlations of susceptibility (generally indicative of magnetite content) and oxygen isotopic trends in the southern Appalachian Piedmont.     

Relationship between pelagic tar,fluorescence and biological markers in the South Atlantic Ocean

Surface pelagic tar concentrations in the equatorial South Atlantic Ocean were low (< 0.001 to 14.6 mg m^?2). With one exception, concentrations were less than 0.5 mg m^?2. The tars were characterized by gravimetry, carbon isotopic composition, molecular compositions (gas chromatographically), sulphur content, total fluorescence spectra, and biological marker fingerprints. Most tars exhibited significant amounts of degradation. A total fluorescence technique was used to group the tars into two basic types. One type occurred at low concentrations and appeared to be due to chronic long-term oil pollution in the South Atlantic Ocean. The second group occurred at much higher concentrations and was associated with more coastal-influenced waters. Biological marker (triterpanes and steranes) fingerprints confirmed the fluorescence groupings. Carbon isotopic composition and pristane/phytane ratios exhibited few geographical trends.     

Strategies to improve the explanatory power of a dynamic slope stability model by enhancing land cover parameterisation and model complexity

Despite the importance of land cover on landscape hydrology and slope stability, the representation of land cover dynamics in physically based models and their associated ecohydrological effects on slope stability is rather scarce. In this study, we assess the impact of different levels of complexity in land cover parameterisation on the explanatory power of a dynamic and process-based spatial slope stability model. Firstly, we present available and collected data sets and account for the stepwise parameterisation of the model. Secondly, we present approaches to simulate land cover: 1) a grassland landscape without forest coverage; 2) spatially static forest conditions, in which we assume limited knowledge about forest composition; 3) more detailed information of forested areas based on the computation of leaf area development and the implementation of vegetation-related processes; 4) similar to the third approach but with the additional consideration of the spatial expansion and vertical growth of vegetation. Lastly, the model is calibrated based on meteorological data sets and groundwater measurements. The model results are quantitatively validated for two landslide-triggering events that occurred in Western Austria. Predictive performances are estimated using the Area Under the receiver operating characteristic Curve (AUC). Our findings indicate that the performance of the slope stability model was strongly determined by model complexity and land cover parameterisation. The implementation of leaf area development and land cover dynamics further yield an acceptable predictive performance (AUC ~0.71-0.75) and a better conservativeness of the predicted unstable areas (FoC ~0.71). The consideration of dynamic land cover expansion provided better performances than the solely consideration of leaf area development. The results of this study highlight that an increase of effort in the land cover parameterisation of a dynamic slope stability model can increase the explanatory power of the model. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

The Turbulence Structure of the Stable Atmospheric Boundary Layer Around a Coastal Headland: Aircraft Observations and Modelling Results

The turbulence structure of a stable marine atmospheric boundary layer in the vicinity of a coastal headland is examined using aircraft observations and numerical simulations. Measurements are drawn from a flight by the NCAR C-130 around Cape Mendocino on the coast of northern California on June 7 1996 during the Coastal Waves 96 field program. Local similarity scaling of the velocity variances is found to apply successfully within the continuously turbulent layer; the empirical scaling function is similar to that found by several previous studies. Excellent agreement is found between the modelled and observed scaling results. No significant change in scaling behaviour is observed for the region within the expansion fan that forms downstream of the Cape, suggesting that the scaling can be applied to horizontally heterogeneous conditions; however, the precise form of the function relating scaled velocities and stability is observed to change close to the surface. This result, differences between the scaling functions found here and in other studies, and the departure of these functions from the constant value predicted by the original theory, leads us to question the nature of the similarity functions observed. We hypothesize that the form of the functions is controlled by non-local contributions to the velocity variance budgets, and that differences in the non-local terms between studies explain the differences in the observed scaling functions.     

Reconnaissance seismic refraction surveys in the Malvern Hills Area

Seismic refraction profiles have been established in Eastnor Park (SO 745375) and in the Storridge area (SO 750486), respectively west and north of the Malvern Hills. The seismic results can be explained by a three-layered subsurface configuration. Layers 1 and 2 are roughly equivalent to Silurian and Cambrian strata and layer 3 is regarded as Precambrian basement. Under both profiles the Cambrian is much thinner than at the southern end of the Hill range where Groom (1902) estimated a minimum thickness of 2,500 ft (762 m). In Eastnor Park the basement dips westwards at about 10° and is overlain by approximately 1,000 ft (305 m) of Cambrian strata. At the western boundary of the Malvern Hills the Cambrian appears to be cut out locally by a pre-LIandovery fault. In the Storridge area the seismic results are consistent with a shallow basement overlain by a few hundred feet of Cambrian strata, as suggested in an earlier paper on the basis of gravity and magnetic interpretations (Brooks 1968).     

华南二叠系卡匹敦阶高分辨率浮点年代标尺

基于详细的生物地层学研究,以磁化率为古气候替代指标,对广西来宾铁桥剖面卡匹敦阶地层开展时间序列分析,建立高分辨率浮点年代标尺(FPTS).结果表明,磁化率记录了铁桥剖面中二叠世晚期沉积序列中的米兰科维奇旋回,卡匹敦阶上部磁化率突然增加与峨眉山玄武岩喷发和卡匹敦晚期全球性海退有关,这些事件导致同期沉积物中碎屑物质增加.铁桥剖面瓜德鲁普—乐平统界线附近磁化率和蓬莱滩剖面(乐平统底界GSSP)表现出一致的变化趋势,具可对比性.利用多窗谱法(MTM)和傅里叶变换(FT)从磁化率序列中识别出五个米兰科维奇周期:长偏心率周期(E2,405 ka)、短偏心率周期(E1,100 ka)、长地轴斜率周期(O2,44.1 ka)、长岁差周期(P2,20.95 ka)和短岁差周期(P1,17.7 ka).对比基于E2周期建立的磁性地层磁化率(MSS)带和标准参考带(SRZ),建立整个沉积序列的高分辨率(200 ka)FPTS,提出卡匹敦阶的时限为3.85 Ma(存在+0~0.28 Ma误差),整段沉积序列的平均沉积速率为2.91 cm·ka-1.同时计算出卡匹敦阶内部七个牙形石带的时限,从最短26.6 ka到最长2.3 Ma.另外,估算出峨眉山大火成岩省喷发启动时间为262.67 Ma,位于瓜德鲁普—乐平统界线之下1.42 Ma.     

The rubidium‐strontium ages of some Tasmanian igneous rocks

Rb‐Sr isotopic age measurements relate emplacement of the Pieman and Meredith Granites (356 ± 9 and 353 ± 7 m.y., respectively), and the Bischoff and Renison Bell Porphyries (349 ±4 and 355 ± 4 m.y., respectively) to the Tabberabberan Orogeny. The genetic relationship of the Bischoff Porphyry to mineralization and the agreement between the age of this porphyry and the age of the adjacent Meredith Granite, strongly suggests that the Bischoff mineralization resulted from granite intrusion.

The Pieman Granite is closely similar to the white Heemskirk Granite in displaying a high initial ⁸⁷Sr/⁸⁶Sr ratio (0.7354 ± 0.0018), feldspar discordance patterns and open system total‐rock behaviour. The high initial ⁸⁷Sr/⁸⁶Sr ratio is attributed to contamination during intrusion by Precambrian metasediments containing appreciable radiogenic strontium.

A basic intrusion (McIvors Hill Gabbro) gave a pre‐Tabberabberan age (518 ±133 m.y.) and a high initial ⁸⁷Sr/⁸⁶Sr ratio (0.7132 ± 0.0031).