Mussel reefs on soft sediments: a severely reduced but important habitat for macroinvertebrates and fishes in New Zealand     

IM McLeod  DM Parsons  MA Morrison  SG Van Dijken  RB Taylor 《新西兰海洋与淡水研究杂志》2013,47(1):48-59

Green-lipped mussels (Perna canaliculus) formed extensive reefs on soft sediments in sheltered embayments around northern New Zealand until overfishing and/or increased sediment input caused their virtual disappearance by 1980. To determine the role of mussel reefs as habitat for other animals, we located remnant soft-sediment reefs in five locations and compared the density, biomass, productivity and composition of mobile macroinvertebrate communities, and the density of small fishes associated with mussels, with fauna in the surrounding soft sediments. The mussel reefs had a distinct assemblage of macroinvertebrates, which had 3.5 times the density, 3.4 times the biomass and 3.5 times the productivity of surrounding areas. The density of small fishes was 13.7 times higher than in surrounding areas. These results show that soft-sediment mussel reefs support an abundant and productive fauna, highlighting the probable large loss of productivity associated with the historical decline in mussel habitat and the consequent desirability of restoration efforts.  相似文献   

Constraining Holocene sea levels using U‐Th ages of phreatic overgrowths on speleothems from coastal caves in Mallorca (Western Mediterranean)     

Paola Tuccimei  Michele Soligo  Joaquin Ginés  Angel Ginés  Joan Fornós  Jan Kramers  Igor Maria Villa 《地球表面变化过程与地形》2010,35(7):782-790

Phreatic overgrowths on speleothems (POS) are carbonate formations deposited at the water table of caves in unique karstic coastal settings having morphologies that can be directly related to sea level at the time of formation. The U‐Th ages of calcite and aragonite overgrowths collected from the modern water table in coastal caves on Mallorca (Cova de Cala Varques A and Cova des Pas de Vallgornera) were determined using high‐precision MC‐ICPMS techniques. U‐Th ages indicate that phreatic carbonate deposition occurred between ca 2·8 and at least 0·6 ka BP and are in accord with an archeologically estimated age of 3·7–3·0 ka BP for a drowned prehistoric construction at a depth of 1 m below current sea level in a cave from the same area. Speleothem δ¹³C and δ¹⁸O and chemical composition of cave pools provide supportive evidence that POS reflect mixing between seawater and brackish water table. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Uranium pollution in an estuary affected by pyrite acid mine drainage and releases of naturally occurring radioactive materials     

Villa M  Manjón G  Hurtado S  García-Tenorio R 《Marine pollution bulletin》2011,62(7):1521-1529

After the termination of phosphogypsum discharges to the Huelva estuary (SW Spain), a unique opportunity was presented to study the response of a contaminated environmental compartment after the cessation of its main source of pollution. The evolution over time of uranium concentrations in the estuary is presented to supply new insights into the decontamination of a scenario affected by Naturally Occurring Radioactive Material (NORM) discharges. The cleaning of uranium isotopes from the area has not taken place as rapidly as expected due to leaching from phosphogypsum stacks.An in-depth study using various techniques of analysis, including ²³⁴U/²³⁸U and ²³⁰Th/²³²Th ratios and the decreasing rates of the uranium concentration, enabled a second source of uranium contamination to be discovered. Increased uranium levels due to acid mine drainage from pyrite mines located in the Iberian Pyrite Belt (SW Spain) prevent complete uranium decontamination and, therefore, result in levels nearly twice those of natural background levels.  相似文献   

Mo isotope composition in Mo-rich high- and low-T hydrothermal systems from the Swiss Alps     

Nicolas D. Greber  Beda A. Hofmann  Igor M. Villa  Thomas F. Nägler 《Geochimica et cosmochimica acta》2011,75(21):6600-6609

We analyzed the molybdenum (Mo) isotope compositions (IC) of 59 samples from two molybdenite mineralizations (Alpjahorn and Grimsel) and from a Mo-rich hydrothermal breccia (Grimsel) from the Aar Massif, Switzerland. The formation temperature of the Late Paleozoic Mo mineralizations (300-600 °C) is much higher than that of the Pliocene breccia (100-160 °C). The Mo IC of the molybdenites varies over 1.35‰. Even in a single hand specimen it spans 0.45‰, indicating that fractionation processes during molybdenite precipitation can vary on a cm scale. The Mo IC of most molybdenites analyzed here are significantly heavier than that of the host rock (δ^98/95Mo = (0.05 ± 0.1)‰) and show a bimodal distribution centered around δ^98/95Mo ≈ 1.1‰ and 0.2‰. This result rules out single stage Rayleigh fractionation as the relevant formation mechanism and instead, redox variations are suggested to be a main factor controlling the Mo IC of the studied high-temperature Mo deposits. The range of the Mo IC in one single deposit, the Alpjahorn, overlaps with the variation range of almost all other published values for Mo IC in Mo deposits. Compared to the molybdenites, the breccia shows an even wider variation of 3.0‰ (δ^98/95Mo between −1.6‰ and +1.4‰). In contrast to the high-T molybdenite deposits, here the Mo was transported via oxidized surface waters into the breccia system, where it was reduced and precipitated. This indicates that oxidation and reduction of Mo complexes may lead to highly variable Mo IC in hydrothermal systems.  相似文献   

Data reporting norms for 40Ar/39Ar geochronology     

Paul R. Renne  Alan L. Deino  Willis E. Hames  Matthew T. Heizler  Sidney R. Hemming  Kip V. Hodges  Anthony A.P. Koppers  Darren F. Mark  Leah E. Morgan  David Phillips  Brad S. Singer  Brent D. Turrin  Igor M. Villa  Mike Villeneuve  Jan R. Wijbrans 《Quaternary Geochronology》2009,4(5):346-352

Data reported in ⁴⁰Ar/³⁹Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all ⁴⁰Ar/³⁹Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses).  相似文献   

Choice of conodont Idiognathodus simulator （sensu stricto） as the event marker for the base of the global Gzhelian Stage （Upper Pennsylvanian Series,Carboniferous System）   总被引：3，自引：0，他引：3  

Philip H. Heckel  ;Aleksandr S. Alekseev  ;James E. Barrick  ;Darwin R. Boardman  ;Natalya V. Goreva  ;Tatiana N. Isakova  ;Tamara I. Nemyrovska  ;Katsumi Ueno  ;Elisa Villa  ;David M. Work 《《幕》》2008,31(3):319-325

We propose that the level at which the conodont species Idiognathodus simulator （Ellison 1941） （sensu stricto） first appears be selected to mark the base of the Gzhelian Stage, because we believe that this is the optimal level by which this boundary can be correlated. This taxon has a short range and a wide distribution, as shown by correlation of glacial-eustatic cyclothems across the Kasimovian-Gzhelian boundary interval among Midcontinent North America and the Moscow and Donets basins of eastern Europe, based on scale of the cyclothems along with several aspects of biostrati- graphy. Outside of these areas, I. simulator （sensu stricto） is known also from other parts of the U.S., and is reported from the southern Urals and south-central China in its expected position between other widespread taxa. Its first appearance is consistent with the current ammonoid placement of the boundary （first appearance of Shumardites cuyleri）, and it is also compatible with certain aspects of the distribution of Eurasian fusulinid faunas （e.g., lectotype ofRauserites rossicus）.  相似文献   

K-Ar datability of altered rocks: variability of excess Ar in hydrothermal minerals     

Igor M Villa  Giorgio Taddeucci 《Bulletin of Volcanology》1991,54(1):84-86

⁴⁰Ar/³⁹ Ar stepwise heating on one hydrothermal anhydrite and two partly hydrothermalized feldspars from a borehole in Vulcano volcano show that the initial trapped Ar does not have a constant isotopic composition. The constant ⁴⁰Ar/³⁶Ar ratio of the anhydrite, 306±3, is not a well-defined endmember for the two feldspars, which record a variety of fluid compositions. As the system is young (<100 ka), radiogenic Ar is much less than excess Ar.  相似文献   

Enriched asthenosphere melting beneath the nascent North African margin: trace element and Nd isotope evidence in middle–late Triassic alkali basalts from central Sicily (Italy)     

Rosolino Cirrincione  Patrizia Fiannacca  Michele Lustrino  Vanessa Romano  Annunziata Tranchina  Igor M. Villa 《International Journal of Earth Sciences》2016,105(2):595-609

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Occurrence and40Ar/39Ar dating of a granite in Thera (Santorini,Greece)     

Nikos Skarpelis  Konstantinos Kyriakopoulos  Igor Villa 《International Journal of Earth Sciences》1992,81(3):729-735

A granite was drilled in the prevolcanic basement of Thera, an island of the Attico-Cycladic belt. It intruded the blueschist facies country rocks. K-Ar biotite ages and Ar-Ar plateau ages on two feldspars indicate rapid cooling, as all ages cluster around 9.5 Ma. Its occurrence indicates that the thermometamorphic evolution that characterizes the Attiko-Cycladic belt extends as far as Thera.

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Zusammenfassung Auf der Insel Thera, im Attiko-Kykladishen Gürtel, ist ein Granitkörper in einer Tiefe von ca. 250 m durch eine Bohrung aufgedeckt. Dieser Granitkörper ist in metamorphen Gesteinen von Blauschiefer-Facies intrudiert. K-Ar-Biotit- und Ar-Ar-Feldspat-Altersbestimmungen streuen um 9.5 Ma. Diese Alter weisen auf rasche Abkühlung des Granitkörpers hin. Es zeigt sich somit, daß die thermometamorphe Entwicklung des Attiko-Kykladischen Gürtels bis zur Insel Thera reicht.

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Résumé Un forage a été pratiqué dans un granite du socle pré-volcanique de l'île de Thera, qui appartient à la ceinture attico-cycladique. Ce granite a intrudé les roches encaissantes de facies schistes bleus. Les datations effectuées sur les biotites par la méthode K-Ar et les âges-plateau des feldspaths obtenus par la méthode Ar-Ar indiquent un refroidissement rapide, puisque tous les âges sont de l'ordre de 9,5 Ma. Ce granite montre que l'évolution thermométamorphique qui caractérise la ceinture Attico-Cycladique s'étend jusqu'à l'île de Thera.

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Thera 250 . . / / 9,5 . , . .. , Thera.

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Coastal uplift rate at Matanzas (Cuba) inferred from MIS5e phreatic overgrowths on speleothems          下载免费PDF全文

Jo De Waele  Ilenia M. D'Angeli  Nicola Tisato  Paola Tuccimei  Michele Soligo  Joaquín Ginés  Angel Ginés  Joan J. Fornós  Igor M. Villa  Esteban R. Grau González  Stefano M. Bernasconi  Tomaso R. R. Bontognali 《地学学报》2017,29(2):98-105

Many morphological elements in Cuba's landscape (e.g. marine terraces, tidal notches) demonstrate that coastal uplift has taken place, but the rate at which this occurs is not known. Carbonate phreatic overgrowths on speleothems have been found in a cave in Central North Cuba, ~1 km from the present coastline at 16 m asl. They form exceptional and unique mushroom‐shaped speleothems and balconies decorating the walls of the rooms. These phreatic overgrowths on speleothems (POS) formed at the oscillating air–water interface in sea‐level controlled anchialine lakes. U/Th dating of these overgrowths suggests ages that are compatible with the Marine Isotope Stage 5e (i.e. 130–115 ka). These POS have fixed this sea‐level highstand and demonstrate that this part of Cuba has been subjected to a much lower uplift rate than previously reported, that is, less than 0.1 mm/year since the last interglacial.  相似文献