Genesis of yellow manganese-rich elbaite from the Canary mining area,Lundazi, Zambia     

Brendan M. Laurs  William B. Simmons  Alexander U. Falster  Björn Anckar 《Applied Geochemistry》2009

The most important source of yellow gem elbaite is the Canary mining area in the Lundazi District of eastern Zambia. The tourmaline has been mined since 1983 from both pegmatite and eluvial/alluvial deposits, in colors typically ranging from yellow-green to yellow to orange and brown; much of the orange-to-brown material is heated to attain a ‘golden’ or ‘canary’ yellow color. The elbaite is Mn-rich (up to 9.18 wt% MnO documented in the literature) and contains small amounts of Ti and little or no Fe. The distinctive composition of this tourmaline is probably the result of the early crystallization of abundant schorl from an unusual B-rich, Li-poor pegmatite melt, which depleted Fe while conserving Mn until the late-stage crystallization of gem pockets. The simple mineralogy of the pegmatite consists of feldspars, quartz, and tourmaline; the lack of micas, phosphates, or Li minerals, and the presence of very little garnet, allowed Mn to fractionate to high levels during pegmatite crystallization. The presence of abundant gem tourmaline in a Li-poor pegmatite is highly unusual.  相似文献   

Detecting genotoxicity using the Comet assay following chronic exposure of Manila clam Tapes semidecussatus to polluted estuarine sediments   总被引：1，自引：0，他引：1  

Coughlan BM  Hartl MG  O'Reilly SJ  Sheehan D  Morthersill C  van Pelt FN  O'Halloran J  O'Brien NM 《Marine pollution bulletin》2002,44(12):1359-1365

Sediments frequently cause damage to biota due to the accumulation of toxic compounds and the bioavailability of sediment-bound contaminants. Damage can be assessed using biomarkers, such as the degree of genotoxic impact following in vivo exposure to pollutants. Genotoxic damage, expressed as single-strand DNA breaks, was measured in cells isolated from haemolymph, gill and digestive gland from the clam Tapes semidecussatus, using the single cell gel electrophoresis (Comet assay). Clams were exposed for three weeks to sediment samples collected from a polluted site and a ‘clean’ reference site.

The level of DNA damage was assessed using an image analysis package and expressed as Tail Moment. Throughout the study, significant differences in DNA damage were recorded for each tissue type between clams exposed to the two sediment samples. We conclude that the Comet assay is a useful tool for the detection of DNA damage in clams chronically exposed to polluted sediments.  相似文献   

Cadomian Orogens, peri-Gondwanan correlatives and Laurentia–Baltica connections     

J. Brendan Murphy  Luis Eguiluz  Gernold Zulauf 《Tectonophysics》2002,352(1-2)

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A critical assessment of the analysis and distributions of scytonemin and related UV screening pigments in sediments   总被引：1，自引：0，他引：1  

Angela H. Squier  Dominic A. Hodgson  Brendan J. Keely   《Organic Geochemistry》2004,35(11-12):1221

High performance liquid chromatography-mass spectrometry has been used to identify the cyanophyta-derived ultraviolet screening pigment scytonemin and its reduced counterpart in an Antarctic lake sediment. The formation of an artefact during the analysis has been demonstrated, enabling the recovery of improved estimates of the scytonemin and reduced scytonemin signals. The overall pigment composition records a primary producer community comprising both oxygenic and anoxygenic photoautotrophs, with variations in the abundance of scytonemin relative to the chlorophylls and carotenoids that are consistent with changes in response to variations in the light regime over time.  相似文献   

Kinematics of the Rockland Brook Fault, Nova Scotia: Implications for the interaction of the Meguma and Avalon terranes     

Brent V. Miller  R. Damian Nance  J. Brendan Murphy 《Journal of Geodynamics》1995,19(3-4)

The Cobequid-Chedabucto fault system of northern mainland Nova Scotia represents the surface expression of the Avalon-Meguma terrane boundary, but because it is exposed at high crustal levels in the Cobequid Highlands, the fault system provides little information as to the kinematic relationships of the two terranes in this area. In the eastern Cobequid Highlands, the Rockland Brook Fault (RBF) is exposed within the more deeply eroded highlands massif and juxtaposes units of widely varying ages and lithologies. Therefore, this fault is better suited to define the nature and timing of fault movement associated with Avalon-Meguma terrane interaction.In several large Carboniferous plutons along the length of the RBF, and in previously deformed Precambrian rocks, mylonitic foliation orientations are predominantly east-west trending and mineral lineations plunge southeast. Kinematic indicators such as minor fold vergence, porphyroclast systems, asymmetric boudins, shear-band fabrics, and preferred recrystallization orientations indicate dextral shear. These data are taken to infer that the central section of the RBF is dominated by dextral strike-slip motion. Transpression occurs locally where the RBF curves into restraining bends. Kinematic data in these bends indicate top to the northwest thrusting. At the easternmost extent of the RBF, high-level brittle normal faults predominate in the locally extensional environment. The timing of RBF movement is constrained only by the ca 360 Ma granite bodies which it deforms and by the Westphalian sedimentary rocks which are affected by only the latest stages of movement.These kinematic data are consistent with previously published kinematic models for the interaction of the southern margin of the Avalon Composite Terrane with the Meguma Terrane in mainland Nova Scotia. These models suggest that regional dextral shear was accompanied by localized components of transpressional thrusting, wrench tectonism, and small-scale sedimentary basin development during Devonian to Carboniferous terrane interaction.  相似文献   

Use of active source geophones for passive source imaging: Examples from the Bighorn Arch Seismic Experiment, Wyoming, USA     

Anne Sheehan  Steven Plesci  Seth Haines  Lindsay Worthington 《《地质学报》英文版》2018,92(Z1):276-276

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Discussion of “Strength and Consolidation Characteristics for Cement Stabilized Cohesive Soil Considering Consistency Index” by Ahmed F. Zidan,published in Geotechnical and Geological Engineering,https://doi.org/10.1007/s10706-020-01367-6     

O’Kelly  Brendan C. 《Geotechnical and Geological Engineering》2021,39(6):4659-4662

Geotechnical and Geological Engineering -  相似文献   

Assessing potential environmental influences on killer whale (Orcinus orca) distribution patterns in the Bremer Canyon,south-west Australia     

Alexandra Jones  Eleanor Bruce  Kevin P. Davies  Michelle Blewitt  Scott Sheehan 《The Australian geographer》2019,50(3):381-405

ABSTRACT

Submarine canyons play an important role in the regional distribution, abundance and dispersal of marine biota and are increasingly being recognised as geomorphic features of high conservation significance along Australia’s continental margin. Certain canyons have been described as foraging ‘hotspots’ attributable to the high abundance of apex cetacean species aggregating in these areas. Anecdotal evidence of large seasonal aggregations of killer whales in the Bremer Canyon, south-west Australia, has attracted significant research attention in the last decade. To identify important environmental drivers influencing aggregation patterns, a predictive spatial habitat model using the Maxent model was developed based on presence-only whale sighting data. In addition, remotely sensed sea surface temperature and chlorophyll-a concentrations were assessed to investigate the spatio-temporal variation in sea surface conditions. Habitat preference was predicted in areas between canyon heads, with the most influential predictor variables being depth and distance from the continental shelf break. Analysis of remote-sensing data highlighted low localised variability in surface waters and illustrated the seasonal trends of the Leeuwin Current. This study demonstrates the influence of bathymetry and submarine geomorphology on enhanced cetacean abundance and highlights the need for recognition of this potential foraging area in marine reserve planning.  相似文献   

Mapping areas of asynchronous‐temporal interaction in animal‐telemetry data     

Brendan A. Hoover  Jennifer A. Miller  Jed Long 《Transactions in GIS》2020,24(3):573-586

Animal interactions are a crucial aspect of behavioral ecology that affect mating, territorial behavior, resource use, and disease spread. Commonly, animals will interact because of shared resources. Recent methods have used time geography to map landscape areas where interactions were possible. However, such methods do not identify areas of less direct interaction, like through smell or sight. These indirect or asynchronous interactions are also a crucial aspect of animal behavioral ecology and affect group behaviors such as leading/following hierarchies and joint resource use. Asynchronous interactions are difficult to map because they can occur in a synchronous space at asynchronous times, as well as in asynchronous spaces at a synchronous time. Here, we present a method termed the temporally asynchronous‐joint potential path area (ta‐jPPA) that maps areas of potential temporally asynchronous–spatially synchronous interactions. We used simulated data to statistically test ta‐jPPA and empirical data to demonstrate how ta‐jPPA can find patterns in habitat use.  相似文献   

Cultural responses to the altithermal: The role of aquifer-related water resources     

Michael S. Sheehan 《Geoarchaeology》1994,9(2):113-137

The focus of this research is Early Archaic adaptation to the hot and dry Altithermal in the North American Great Plains. The view presented here suggests a direct link between Altithermal climatic conditions and cultural responses to those conditions. Water was a key factor in cultural adaptation to arid Altithermal conditions. Statistical analysis reveals a significant relationship between Early Archaic site location and certain sources of groundwater that is not apparent during the periods preceding and succeeding the Altithermal. The distribution of Early Archaic sites may reflect increased emphasis on predictable water supplies offered by aquifers. © 1994 John Wiley & Sons, Inc.  相似文献