Chemostratigraphy of the Cenomanian-Turonian shallow-water carbonate: new correlation for the rudist levels from north Sinai,Egypt

The present study aims to provide carbon-isotope curves for the Cenomanian to Turonian rudist-dominated successions in north Sinai. The high-resolution carbon-isotope curves obtained from north Sinai sections provide new insight for calibrating the age of rudists as well as for evaluating the effects of the oceanic anoxic event 2 (OAE2) on rudist communities. The primary goals are (1) to provide a high-resolution sequence stratigraphic framework for the Cenomanian-Turonian succession, (2) to use rudist and ammonite biostratigraphic data to distinguish the stratigraphic levels of the rudist species, and (3) to integrate the chemostratigraphic (δ¹³C) profile and the rudist levels to improve the biostratigraphy based on the rudist distributions and the carbon-isotope data. The recognition of three ammonite zones through the Cenomanian-Turonian succession was utilized to identify four temporally significant rudist levels indicative of the Lower Cenomanian, Middle Cenomanian, Upper Cenomanian, and Middle Turonian, respectively. Most of the rudists occur in the highstand deposits of medium-scale sequences. Carbon- and oxygen-isotopic analyses were carried out on both rudists and surrounding carbonate units. Based on the variations in the carbon-isotope signals, 12 chronostratigraphic segments were identified in the studied sections. The Cenomanian carbon-isotope segments (C23–C30) were obtained from the Halal Formation at Gabal Yelleg and Gabal Maaza sections, while the Turonian segments (C30–C34) were measured from the Wata Formation at Gabal Yelleg section. The carbon-isotope record from the studied sections is consistent with the trends documented in previous studies of the Tethyan realm. The Cenomanian-Turonian boundary is placed at the onset of falling carbon-isotope values (δ¹³C) from 2.61 to ?0.25‰ in the upper part of OAE2 with the carbon-isotope segment C30 at Gabal Yelleg. The negative shift in δ¹³C values (C33) occurred in the Middle Turonian lowstand deposits characterizing the global sea level fall during this interval.     

Palaeoseismology of the Havran-Balıkesir Fault Zone: evidence for past earthquakes in the strike-slip-dominated contractional deformation along the southern branches of the North Anatolian fault in northwest Turkey

The Havran-Bal?kesir Fault Zone (HBFZ) is one of the major active structures of the Southern Marmara Region, which has been shaped by the southern branch of North Anatolian fault since the Pliocene. HBFZ is a 10–12 km wide, 120 km long, right-lateral strike-slip fault zone that consists of two ENE-striking main faults, namely, the Havran-Balya and Bal?kesir faults. The 90-km-long Havran-Balya fault exhibits right-stepping en echelon geometry and is made up of (1) Havran, (2) Osmanlar, (3) Turplu and (4) Ovac?k fault segments. On the eastern part, the 70-km-long Bal?kesir fault is divided into two fault segments; (1) Gökçeyaz? and (2) Kepsut. We estimated the long-term slip rate between 3.59 and 3.78 mm/yr using river offset. The Kepsut, Gökçeyaz? and Ovac?k fault segments are capable of generating an earthquake with a moment magnitude of up to 7.2. Detailed palaeoseismological studies show that the HBFZ is responsible for some surface faulting earthquakes with an average recurrence interval of 1000–2000 years during the late Holocene. Considering the fact that there was no evidence of a surface-ruptured earthquake for 2000 years, it can be stated that there is a seismic gap on the Gökçeyaz? fault segment.     

Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment

ABSTRACT

Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42?mg?m^?3 vs. 8.32?mg?m^?3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62?m vs. 6.48?m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment.     

A late Precambrian (∼ 710 Ma) high volcanicity rift in the southern Eastern Desert of Egypt

The late Precambrian Shadli Metavolcanics of SE Egypt constitute a slightly metamorphosed bimodal sequence that has been previously interpreted as manifesting volcanic activity at an island arc. We report the first Rb-Sr geochronologic, trace element (including REE), and Nd isotopic data for these rocks. Two types of basalt are recognized, the stratigraphically lower suite having compositions like N-MORB ferrobasalt while the overlying basalt is similar to slightly fractionated E-MORB. The two basalt types were derived from melting of a strongly depleted source, most likely within the upper 60–75 km of the upper mantle. The origin of the felsic melts is problematic, and these could either have fractionated from a mafic melt or resulted from melting of juvenile crust. The mafic and felsic lavas yield a Rb-Sr isochron age of 712±24 Ma that probably represents the time of volcanic eruption. The trace element characteristics of both mafic and felsic members of the Shadli Metavolcanics show few of the hallmarks of subduction-related melts, and we reject the hypothesis that these formed at an island arc. Instead, the field and geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift, where the eruption of large volumes of lava accompanied large-scale lithospheric extension. This inference suggests that the tectonic setting of the important 700–715 Ma crust-forming event in NE Africa and Arabia needs to be critically reexamined.

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Zusammenfassung Die spätpräkambrischen Shadli-Metavulkanite in der südöstlichen Eastern Desert von Ägypten sind eine schwach metamorphe bimodale Basalt-Rhyodazit-Abfolge, die bisher als Ausdruck eines Inselbogen-Vulkanismus gedeutet wurde. Zwei Basalt-Typen können aufgrund ihrer unterschiedlichen chemischen Zusammensetzung unterschieden werden: der stratigraphisch untere Typ ist ein N-MORB ähnlicher Ferrobasalt, während der überlagernde Typ Charakteristika eines leicht fraktionierten E-MORB aufweist. Die beiden Basaltvarietäten werden von stark an inkompatiblen Elementen verarmten Schmelzen aus den oberen 60–75 km des Mantels abgeleitet. Die Entstehung der sauren Metavulkanite ist nicht eindeutig geklärt; sowohl Fraktionierung aus einer mafischen Schmelze als auch Aufschmelzung juveniler Kruste vom Inselbogen-Typ sind denkbar. Die mafischen und felsischen Gesteine definieren zusammen ein Rb-Sr-Isochronenalter von 712 ± 24 Ma, das wir als den Zeitraum der Eruption deuten. Die Spurenelement-Verteilung der Shadli-Metavulkanite weist keine der charakteristischen Merkmale von Subduktionsmagmatismus auf, und wir sehen daher keinen direkten Zusammenhang mit einer Inselbogen-Entwicklung. Wir interpretieren den Shadli-Vulkanismus als Resultat eines Riftprozesses in junger kontinentaler Kruste, ähnlich dem Rio Grande-Rift oder dem Afar-Dreieck, wo starke Lithosphärendehnung die Förderung großer Lavamengen ermöglichte. Diese Interpretation stellt das einfache Schema einer panafrikanischen Krustenbildung durch Inselbogen-Addition im arabisch-nubischen Schild in Frage und erfordert eine Neubewertung bisheriger Modellvorstellungen.

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Résumé Les roches volcaniques faiblement métamorphisées du Précambrien tardif de Shadli dans le Sud-Est de l'Egypte se caractérisent par une séquence bimodale qui était jusqu'ici interprétée comme résultant d'un volcanisme d'arc insulaire. Nous présentons ici les premières données isotopiques (Rb-Sr, Nd) obtenues pour ces roches ainsi que des données d'éléments en trace (y compris les Terres Rares). Deux types principaux de basaltes peuvent être distingués: les basaltes qui se trouvent dans la partie inférieure de la colonne stratigraphique, ont une composition comparable aux ferrobasaltes de type N-MORB, tandis que les roches se trouvant dans la partie supérieure de la séquence s'apparentent plutôt aux E-MORB légèrement fractionnés. Les deux types de basalte proviennent de la fusion partielle d'un manteau fortement appauvri, et ce à une profondeur probable de 60 à 75 km dans le manteau supérieur. L'origine des laves acides pose, quant à elle, quelques problèmes: elles peuvent s'être formées par cristallisation fractionnée à partir d'un liquide basique, ou alors elles sont le produit de la fusion partielle d'une croûte juvénile. La combinaison des données Rb-Sr obtenues pour les roches acides et basiques permet l'obtention d'une isochrone définissant un âge de 712 ± 24 Ma. Cet âge est interprété comme datant les éruptions volcaniques. Les données d'éléments en traces obtenues pour les laves basiques et acides ne présentent aucune des caractéristiques associées au volcanisme d'arc insulaire. Par conséquent, nous rejetons l'hypothèse selon laquelle les roches volcaniques de Shadli se seraient formées dans un contexte d'arc insulaire. Les données géochimiques et de terrain seraient plutôt en accord avec une hypothèse selon laquelle les roches volcaniques métamorphiques de Shadli se seraient formées dans une zone de rift où de très volumineux épanchements de laves auraient succédé à une extension à grande échelle de la lithosphère. Cette interprétation des données nous conduit à suggérer un réexamen critique du contexte tectonique entourant la période de formation crustale se situant entre 700 a 715 Ma, dans le nord-est de l'Afrique ainsi qu'en Arabie.

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Shadli, - , — , . : , N — MORB MORB, . , , 60–75 . ; , . , Rb/Sr, 712 ± 24 . , . Shadli ; , Shadli, , , , . - ; .

     

Exosat observations of X-rays from classical novae during outburst stage

The initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime ofEXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984#1 (PW Vul), and two observations of Nova Vulpeculae 1984#2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is 2 to 3 years, which leads to the conclusion that the burned envelope massM _burn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9M , core luminosity of 2×10⁴ L , and envelope mass of 10^–6 M , can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have 1.1M core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind withM5×10^–7 M yr^–1 appears to be necessary. The few observations of Nova Vulpeculae 1984 #1 and Nova Vulpeculae 1984#2, during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F. R. G., 16–19 June, 1986.     

Solar rotation rate from stable sunspot tracings

Positions of sunspots between 1966 and 1976 as observed at Kandilli Observatory were used to determine the differential rotation of the Sun. A total of 202 sunspot groups which were E, F, G, H, and J-types were chosen, and a least-squares solution was calculated with their daily rotations. A gradient difference was found between the two hemispheres of the Sun.     

Seasonal and spatial variations in the scaling and correlation structure of streamflow data

Seasonal and spatial variability in scaling, correlation and wavelet variance parameter of daily streamflow data were investigated using 56 gauging stations from five basins located in two different climate zones. Multifractal temporal scaling properties were detected using a multiplicative cascade model. The wavelet variance parameter yielded persistence properties of the streamflow time series. Seasonal variations were found to be significant in that winter and spring seasons where large‐scale frontal events are dominant showed higher long‐term correlations and less multifractality than did summer and fall seasons. Coherent spatial variations were apparent. The Neches River basin located in a subtropic humid climate zone exhibited high persistence and long‐term correlation as well as less multifractality as compared with other basins. It is found that larger drainage areas tend to have smaller multifractality and higher persistence structure, and this tendency becomes apparent in regions that receive large amounts of precipitation and decreases towards arid regions. Copyright © 2012 John Wiley & Sons, Ltd.     

Molecular Absorption in Cen a on Vlbi Scales

Centaurus A, the nearest AGN shows molecular absorption in the millimeter and radio regime. By observing the absorption with VLBI, we try to constrain the distribution of the gas, in particular whether it resides in the circumnuclear region. Analysis of VLBA observations in four OH and two H₂CO transitions is presented here, as well as molecular excitation models parameterized with distance from the AGN. We conclude that the gas is most likely associated with the tilted molecular ring structure observed before in molecular emission and IR continuum. The formaldehyde absorption shows small-scale absorption which requires a different distribution than the hydroxyl.