Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Forecasting of sea-state characteristics, with warning time of a few hours, appears a necessity in Operational Oceanography. linking sophisticated marine monitoring systems with forecasting modeling tools. In this paper, instead of using conventional numerical models, a Takagi-Sugeno-rule-based Fuzzy Inference System (FIS) was developed aiming at forecasting wave parameters based on the wind speed and direction, and the lagged-wave characteristics. Initial and final antecedent fuzzy membership functions were identified using the subtractive clustering method. The model was applied on the wind and wave dataset recorded in years 2000-2006 by an oceanographic buoy deployed in the Aegean Sea. The model showed perfect fit for the training period (2000-2005; 12,274 data points), and expanded its hindcasting ability during 2006 (1044 data points), as the verification part of the series. Model results, for a lead time of 3 h, showed good agreement between the predicted and the observed significant wave height (RMSE=0.216) and zero-up-crossing period (RMSE=0.315). According to other model performance criteria, the fuzzy model slightly underpredicted both wave characteristics (the linear regression slope was 0.911 for wave height and 0.788 for wave period), and reduced its forecasting ability at higher prediction intervals (+6 to + 12 h). Overall, model results illustrated that the developed FIS could serve as a valuable tool for the operational prediction of wave characteristics in Northern Aegean Sea, through the utilization of the POSEIDON network.
ISSN: 0029-8018

hal-00456020
https://hal.archives-ouvertes.fr/hal-00456020
DOI : 10.1016/j.oceaneng.2009.08.016

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
Andros is a key island for understanding both the timing of high-pressure–low-temperature(HP-LT) metamorphism and the dynamics of crustal-scale detachment systems exhuming high-gradeunits in the Cyclades (Greece). Using phengite 40Ar–39Ar geochronology coupled with thermobarometry,as well as data from literature, we constrain the pressure–temperature–time (P-T-t) paths of theMakrotantalon and Attic–Cycladic Blueschist units on Andros. Peak conditions of the HP-LT episodein the Makrotantalon unit are 550 °C and 18.5 kbar, dated at 116 Ma. We correlate this episode withEarly Cretaceous blueschist facies metamorphism recognized in the Pelagonian zone of continentalGreece. This is a new argument favouring a Pelagonian origin for the Makrotantalon unit. In the Attic–Cycladic Blueschist unit, the P-T-t path is characterized by: (1) exhumation after peak conditions inHP-LT conditions between 55 and 35 Ma; (2) isobaric heating at 7 kbar until 30 Ma; and (3) isothermaldecompression until 21 Ma. This thermal evolution and timing are similar to those of the neighbouringTinos Island, emphasizing major thermal re-equilibration at the transition between stable and retreatingsubduction. Modifications of the crustal thermal state played a major role in the evolution of the NorthCycladic Detachment System, below which Andros HP-LT units were exhumed.
ISSN: 0016-7568

insu-01114909
https://hal-insu.archives-ouvertes.fr/insu-01114909
DOI : 10.1017/S0016756814000661

Éditeur(s) : HAL CCSD
Résumé : International audience
The Kazdağ Massif exposes a metamorphic dome in the Biga Peninsula of northwest Turkey. An extensional origin has been proposed for the dome, limited on both flanks by detachments and/or shear zones. The northern flank is bounded by the extensional Alakeçi Shear Zone (ASZ), whose P-T-t path is still poorly known. We therefore focus on its metamorphic conditions and related temporal history to precise its tectono-metamorphic evolution. The local tectonostratigraphy in structurally ascending order comprises: (i) the high-grade metamorphic core rocks of the Kazdaǧ Massif (gneisses and micaschists intercalated with amphibolites and marbles); (ii) the two kilometer-thick ASZ; (iii) the overlaying unmetamorphosed pre-Cenomanian accretionary Çetmi mélange; and (iv) Neogene sedimentary and volcanic cover rocks. ASZ mylonites were derived from both the core rocks and the mélange lithologies. From the north to the south the mylonitic fabrics in the ASZ depict a top-to-the N-NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdaǧ Massif. The northward transition from ductile to brittle-ductile regime through the ASZ shows that the deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium within the mylonitic gneisses and schists contains Qtz + Fs + Ms + Bt + Grt ± St ± Sill, with late retrogressive chlorite after biotite and garnet. Four samples of ASZ rocks yielded pressures between 6.9-5.7 kbar and temperatures between 706-587°C. Three samples from the mylonitic rocks supplied in situ isochron 36Ar/40Ar mica ages between 31.2-24.2 Ma, which we interpret to date the cooling of the mylonites following the P-T decrease across the ASZ. The metamorphic and structural results support the extensional character of the ASZ, and sketch transition from sillimanite core gneisses in the deeper structural levels to chlorite schists towards the top of the shear zone. These new data allow to precise the peak P-T conditions and the temporal evolution in the northern flank of the Kazdaǧ Massif, where Late Oligocene extensional exhumation was assisted by NNE-directed ductile-brittle ASZ, which had operated from amphibolite to greenschist facies. At the regional scale, this tectono-metamorphic pattern is similar to those observed on other places of the north Aegean domain.
IOP Conference Series
Austin, TE, United States

hal-00642725
https://hal-brgm.archives-ouvertes.fr/hal-00642725
DOI : 10.1088/1755-1307/2/1/012012

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
We constrain the slip and cooling history of the Mykonos detachment footwall using thermochronometry. A U-Pb zircon age of 13.5 +/- 0.3 Ma dates intrusion of the Mykonos monzogranite. Ar-40/ Ar-39 homblende and biotite ages from the monzogranite are 12.7 +/- 0.6 Ma and 10.9 +/- 0.6 Ma, whereas zircon and apatite fission-track ages range from 13 +/- 0.8 Ma to 10.7 +/- 0.8 Ma and 12.5 +/- 2.2 Ma to 10.5 +/- 1.8 Ma. (U-Th)/He ages range from 13.6 +/- 0.6 Ma to 9.0 +/- 0.7 Ma for zircon and 11. +/- 10.5 Ma to 8.9 +/- 0.4 Ma for apatite. The ages in part overlap within 2 sigma errors and together with the long apatite fission-track lengths (>14 mu m) support rapid cooling at rates > 100 degrees C Ma(-1). The low-temperature thermochronometric ages decrease east-northeastwards in the direction of hanging-wall transport on the Mykonos detachment. Age-distance relationships show that the Mykonos detachment slipped at an average rate of 6.0 + 9.2/-2.4 km Ma(-1) c. 30 km of offset and c. 12 km of exhumation. This result indicates that Miocene low-angle normal faulting was not important for the exhumation of the Cycladic blueschist unit. The opening of the Aegean Sea basin in the Miocene was controlled by a few large-magnitude low-angle normal faults.
ISSN: 0016-7649

hal-00412177
https://hal.archives-ouvertes.fr/hal-00412177
DOI : 10.1144/0016-76492006-145

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
Diverse, abundant and usually well-preserved communities of skeletal organisms occur in the lower Pleistocene (Gelasian) siliciclastic deposits of the Greek island of Rhodes. Benthic foraminifers, molluscs and bryozoans have been studied in four measured and sampled sections located in the northern part of the island. Among these bottom-dwelling organisms, numerous extant taxa are good environmental indicators and, combined with field observations and sedimentological data, they provide information on the probable conditions in which they developed. The siliciclastic deposits of the Kritika Formation have been divided into 14 different bio- and lithofacies, which have been further grouped into four facies associations corresponding to four different environmental settings: (1) continental to fluviatile; (2) brackish-water (lagoonal/deltaic); (3) infralittoral (0–20 m); and (4) upper circalittoral (depths of 20–40 m, but also down to c. 50–60 m). Among the marine facies associations, several characteristic biocoenoses have been recognized: soft-bottoms (fine to coarse sands and gravels); seagrass meadows; biogenic calcareous crusts on drowned beachrock slabs; red algal rhodoliths; and bivalve shell beds. In the studied sections, 13 superimposed genetic sequences have been documented. The repetition of similar facies associations within each sequence suggests: (1) a possibly eustasy-controlled, cyclic sedimentation; (2) a general subsidence of Rhodes during the deposition of the studied facies associations; and (3) a mostly constant range of environmental conditions (i.e. sedimentation rates and temperature) throughout the Gelasian.
ISSN: 0016-7568

hal-01277829
https://hal.archives-ouvertes.fr/hal-01277829
DOI : 10.1017/S0016756815000230

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The distribution of the lagoon cockle Cerastoderma glaucum is strongly fragmented and usually restricted to isolated, shallow and nontidal lagoons. A high level of genetic structuring was found among the European populations of this species based on mtDNA (COI) sequences, as well as allozymic and microsatellite markers. However, the strengths and geographic locations of the major divisions differed among markers. In the present study we characterized the diversity of a new, potentially universal exon-primed intron-crossing marker, i34, for 17 C. glaucum populations. Allele frequency data at the i34 locus were informative and relevant with respect to geography. Multivariate analyses of new data together with previously published microsatellites confirmed the divergent character of the Ionian Sea and the Aegean-Ponto-Caspian populations, but also revealed the existence of a genetic cline from the Bay of Biscay to the Baltic Sea. Some noncongruent patterns among loci were detected, which may reflect either differential introgression along the genome at the hypothetical contact zone, or selective sweeps. This strong genetic differentiation, and the occurrence of private alleles, may hint at the presence of cryptic species within C. glaucum.
ISSN: 0260-1230

hal-01444646
https://hal.archives-ouvertes.fr/hal-01444646
DOI : 10.1093/mollus/eyw019

Éditeur(s) : HAL CCSD Elsevier
Résumé : While most rocks from active volcanoes display ((210)pb/Ra-226) activity ratios lower than or close to the equilibrium value of 1, several other have ratios much higher than 1. Transfer of Rn-222 by magmatic volatiles has often been advocated to explain both Pb-210 deficits and excesses. We develop here a model to account for Pb-210 excesses through Rn-222 accumulation. We show that large Pb-210 excesses can be readily obtained, even for moderate ratios of degassing magma over accumulating magma, in a closed-system model where the Rn-222 atoms produced by decay of Ra-226 in the degassing magma are continuously extracted by a gas phase. For a given duration of volatile transfer, relative Pb-210 excesses are expected to be much larger than Pb-210 deficits. This model is applied to samples from Santorini (Aegean arc) and Surtsey (Iceland) both of which show high ((210)pb/Ra-226) ratios of 6.7 and 2.3 respectively at the time of eruption. The agreement with field data suggests that Rn-222 accumulation leading to Pb-210 excesses might be a rather common process in zoned magma chambers as well as in individual lava flows, and that it can be described by a closed-system model.
ISSN: 0012-821X

hal-00496398
https://hal.archives-ouvertes.fr/hal-00496398
DOI : 10.1016/j.epsl.2010.02.048