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SM Dippenaar 《African Journal of Marine Science》2016,38(1):1-5
Current knowledge of the biodiversity of the symbiotic marine siphonostomatoids from South African waters (136 species) is sparse compared to that globally (1 388 species). The difference is especially apparent when taking into account the diversity of fish (more than 2 000 species) and invertebrates (approximately 12 914 species) found in South African waters, all of which are all potential hosts of symbiotic siphonostomatoids. Most reports of symbiotic siphonostomatoids from South African waters are from Chondrichthyes and represent 80% of the currently known families and about 66% of the known genera. Taxonomic studies on the siphonostomatoids also provide information about their morphology, biology, habitat preference and host association, as well as the distribution of species and their associated host taxa. Molecular analysis, especially sequencing, provides additional information on the existence of cryptic species and population structure, but has high financial costs and a very low success rate in DNA isolation and PCR amplification. Reported declines in abundance of piscivorous fish species, for example, as a result of fishing pressure, with possible synergistic effects of environmental changes, and also the reported potential effects of anthropogenic and climate change on the broader coastal biota, may result in the loss of siphonostomatoid species before they can be described. Furthermore, in South Africa, there is a lack of professional taxonomists to study poorly known groups and this situation will not improve while research emphasis remains on commercially important groups and while taxonomic studies are not recognised for their value in research programmes. 相似文献
3.
Axel K. Schmitt Kevin R. Chamberlain Susan M. Swapp T. Mark Harrison 《Chemical Geology》2010,269(3-4):386-395
We introduce a technique for U–Pb dating of baddeleyite using secondary ion mass spectrometry (SIMS) in situ analysis of ng-mass crystals that cannot be efficiently extracted by conventional mineral separation techniques. Average 207Pb/206Pb ages for Precambrian baddeleyite crystals are within < 0.3% of the respective isotope dilution thermal ionization mass spectrometry (ID-TIMS) ages. 206Pb/238U ratios are corrected for instrumental fractionation calibrated through linear regression in a Pb/U relative sensitivity vs. UO2+/U+ calibration plot. Calibration is performed on separated baddeleyite crystals (～ 100–200 μm in maximum dimension) mounted in random crystallographic orientation. 206Pb/238U ages for baddeleyite from Duluth gabbro (FC4b) and Kovdor are accurate within 1–2% when averaging 15–30 individual spot analyses and relative sensitivities calibrated on Phalaborwa baddeleyite. The relative difference of 206Pb/238U between large crystals and micro-baddeleyite from FC4b is within ～ 1%. Comparison between silicate glass and baddeleyite, as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in Pb/U sensitivity in baddeleyite due to variable crystal orientations. We successfully utilized oxygen flooding and a UO2+/U+-based calibration to significantly reduce orientation dependent bias. 相似文献
4.
Kevin R. Chamberlain Axel K. Schmitt Susan M. Swapp T. Mark Harrison Norbert Swoboda-Colberg Wouter Bleeker Tony D. Peterson Charles W. Jefferson Andrei K. Khudoley 《Precambrian Research》2010
An in situ U–Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 μm is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3–7% for Phanerozoic rocks. Results establish a 2689 ± 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 ± 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 ± 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples. 相似文献
5.
SM Salem 《Arabian Journal of Geosciences》2017,10(7):166
The ironstone succession at El Gedida-Ghorabi-Naser area of El Bahariya depression is subdivided into lagoonal manganiferous mud and fossiliferous ironstone consisting mainly of hematite and goethite-hydrogoethite. The application of the ASD field spectroradiometer measurements (spectral range) in the ASTER data led to the interpretation of the presence of ferruginous units as quartzitic sandstone, gluconitic sandy clay, and pink marly limestone. The existing iron ore minerals in the iron ore localities were also classified into high Mn hematite, low Mn hematite, goethite, hydrogoethite as well as low- and high-grade Hematite and Barite. Quartz, feldspars, rutile, and clay minerals (e.g., kaolinite and illite) are mainly associated with the iron ore. Accessory minerals of manganese, e.g., psilomelane and pyrolusite, were also present. The Barite mineral is recorded as a common mineral association with the iron ore deposits at El Gedida and Ghorabi localities. The stratigraphical units investigated in the study area include the oldest gravely clayey sandstones of the Bahariya Formation overlain by the fossiliferous and oolitic limestones of the El-Hamra, Qazzun, and Naqb Formations. Quartztic sandstones and clayey sandstones of the Radwan Formation and youngest Quaternary sediments of sandy-clayey materials were often found as intermittent cover and overburden in unconformity surfaces over the iron ore bands. 相似文献
6.
Kay L. Achenbach Michael J. Cheadle Ulrich Faul Peter Kelemen Susan Swapp 《Earth and Planetary Science Letters》2011,301(1-2):199-212
Eleven harzburgites and one dunite from Ocean Drilling Program Leg 209 Hole 1274A preserve high-temperature mantle textures. Electron backscatter diffraction (EBSD) analysis shows moderately developed crystal lattice preferred orientations (LPOs) in olivine and orthopyroxene (M-indices ≈ 0.1) indicative of crystal-plastic deformation at ~ 1250 °C. These rocks preserve a protogranular texture with a weak olivine foliation, a very weak or absent orthopyroxene foliation that may be decoupled from the orthopyroxene LPO, and minor interstitial clinopyroxene and spinel. Olivine grain size distributions, along with melt-related microstructures in orthopyroxene, clinopyroxene and spinel suggest that high-temperature deformation textures have been overprinted by pervasive post-deformation melt-rock interaction. Paleomagnetic data constrain the olivine [100] axes to be subhorizontal and oriented at low angle (≤ 28.6° ± 10.6°) to the ridge axis at the onset of serpentinization. This orientation is consistent with either complex 3-D mantle upwelling or 2-D mantle upwelling coupled with complex 3-D tectonic emplacement to the seafloor. 相似文献
7.
On the occurrence,trace element geochemistry,and crystallization history of zircon from in situ ocean lithosphere 总被引：10，自引：2，他引：8
Craig B. Grimes Barbara E. John Michael J. Cheadle Frank K. Mazdab Joseph L. Wooden Susan Swapp Joshua J. Schwartz 《Contributions to Mineralogy and Petrology》2009,158(6):757-783
We characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite, evolved gabbro,
and metamorphosed ultramafic host-rocks collected along present-day slow and ultraslow spreading mid-ocean ridges (MORs).
The geochemistry of 267 zircon grains was measured by sensitive high-resolution ion microprobe-reverse geometry at the USGS-Stanford
Ion Microprobe facility. Three types of zircon are recognized based on texture and geochemistry. Most ocean crustal zircons
resemble young magmatic zircon from other crustal settings, occurring as pristine, colorless euhedral (Type 1) or subhedral
to anhedral (Type 2) grains. In these grains, Hf and most trace elements vary systematically with Ti, typically becoming enriched
with falling Ti-in-zircon temperature. Ti-in-zircon temperatures range from 1,040 to 660°C (corrected for a
TiO2 ≈ 0.7, a
SiO2 ≈ 1.0, pressure ≈ 2 kbar); intra-sample variation is typically ~60–150°C. Decreasing Ti correlates with enrichment in Hf
to ~2 wt%, while additional Hf-enrichment occurs at relatively constant temperature. Trends between Ti and U, Y, REE, and
Eu/Eu* exhibit a similar inflection, which may denote the onset of eutectic crystallization; the inflection is well-defined
by zircons from plagiogranite and implies solidus temperatures of ~680–740°C. A third type of zircon is defined as being porous
and colored with chaotic CL zoning, and occurs in ~25% of rock samples studied. These features, along with high measured La,
Cl, S, Ca, and Fe, and low (Sm/La)N ratios are suggestive of interaction with aqueous fluids. Non-porous, luminescent CL overgrowth rims on porous grains record
uniform temperatures averaging 615 ± 26°C (2SD, n = 7), implying zircon formation below the wet-granite solidus and under water-saturated conditions. Zircon geochemistry reflects,
in part, source region; elevated HREE coupled with low U concentrations allow effective discrimination of ~80% of zircon formed
at modern MORs from zircon in continental crust. The geochemistry and textural observations reported here serve as an important
database for comparison with detrital, xenocrystic, and metamorphosed mafic rock-hosted zircon populations to evaluate provenance. 相似文献
8.
Squalus acutipinnis (previously included in S. megalops) individuals caught off the east, south and west coasts of South Africa were examined for siphonostomatoid copepod infection. Collected siphonostomatoids were fixed and preserved in 70% ethanol and studied under microscopes using both transmitted and incidental light. The copepods were identified and the host-parasite associations estimated by calculating their prevalence, mean intensity and mean abundance. The siphonostomatoids represented four families and six species, and included new host records for Nemesis sp., Lernaeopoda sp. and Eudactylina acanthii, and a new geographical record for E. acanthii. Squalus acutipinnis individuals were infected by relatively low loads of siphonostomatoids. The most commonly found species was Achtheinus pinguis, the only species found off all three coasts. There was no difference in the prevalence of A. pinguis in sharks sampled off the three coasts but the highest mean intensity was found on the East Coast followed by the West Coast. The overall prevalence of A. pinguis was 33.6%, and was an order of magnitude higher than that of the other siphonostomatoids recorded. At such low levels of infection it will thus be necessary to examine a large number of hosts to determine the biodiversity of siphonostomatoids and geographical differences in prevalence in South African waters. 相似文献
9.
Geomatics Based Analysis of Predicted Sea Level Rise and its Impacts in Parts of Tamil Nadu Coast,India 总被引：1，自引：0，他引：1
SM. Ramasamy C. J. Kumanan J. Saravanavel A. S. Rajawat V. Tamilarasan Ajay 《Journal of the Indian Society of Remote Sensing》2010,38(4):640-653
The coastal zones around the world are very densely populated and hence heavily packed with related infrastructures. So, the
territorial nations have obvious apprehensions against the IPCC SRES (Intergovernmental Panel on Climate Change, Special Report
on Emission Scenario) predicted sea level rise, as it would cause flooding of the low lying coasts and also other related
chains of environmental endangers. This has driven these nations to initiate research studies in multiple directions for scientifically
evaluating the phenomenon and impacts of sea level rise using all possible technologies including the Geomatics which possesses
unique credentials in geosystem mapping. But certain advanced virtues available with Geomatics technology are yet to be capitalized
deservingly in this. In addition, almost all the earlier studies have focused only on the impacts of sea level rise (SLR)
and not on the predicted shift of high tide line (HTL) and the related inter tidal activities, which would cause a series
of environmental disaster. Hence, the present research study was undertaken in a test site of 750 km2 in central Tamil Nadu coast to visualize the areas prone to submergence due to predicted SLR and areas prone to environmental
disasters/degradation viz. erosion, deposition, salination of agricultural lands, pollution of aquifers, etc. due to predicted
shift of HTL, using digital elevation models derived from SRTM data (Shuttle Radar Topographic Mission), geomorphology and
land use/cover maps interpreted using IRS P6 LISS IV satellite data. The paper narrates the certain newer concepts and methodologies
adopted in the study and the results. 相似文献
10.
Declines in the abundance of bottlenose dolphins in the Bay of Islands and in Doubtful Sound have contributed to the species being classified as Nationally Endangered in New Zealand waters. Updated information on distribution and abundance nationwide is therefore a high priority. This study presents data from the first photo-identification surveys of Paterson Inlet, Stewart Island, conducted to document bottlenose dolphin presence, abundance and residency. Open-population mark-recapture models indicate that 18 (95%CI = 15–20) dolphins regularly use Paterson Inlet. Photo-identification of dolphins from unknown populations during two chance encounters in Otago Harbour and Dusky Sound included 11 individuals previously identified at Stewart Island. These results indicate that dolphins found regularly at Stewart Island are part of a larger, wide ranging southern population with a minimum population abundance of 92 (95%CI = 80–111) individuals. 相似文献