Search results for "PROCESSES"
showing 10 items of 3831 documents
Retrieval of daily gross primary production over Europe and Africa from an ensemble of SEVIRI/MSG products
2018
The main goal of this paper is to derive a method for a daily gross primary production (GPP) product over Europe and Africa taking the full advantage of the SEVIRI/MSG satellite products from the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) sensors delivered from the Satellite Application Facility for Land Surface Analysis (LSA SAF) system. Special attention is paid to model the daily GPP response from an optimized Montheith's light use efficiency model under dry conditions by controlling water shortage limitations from the actual evapotranspiration and the potential evapotranspiration (PET). The PET was parameterized using the mean daily air temperatur…
Hydrochemical mercury distribution and air-sea exchange over the submarine hydrothermal vents off-shore Panarea Island (Aeolian arc, Tyrrhenian Sea)
2017
Abstract There is a growing concern about the mercury (Hg) vented from submarine hydrothermal fluids to the marine surrounding and exchange of dissolved gaseous mercury (DGM) between the sea surface and the atmosphere. A geochemical survey of thermal waters collected from submarine vents at Panarea Island (Aeolian Islands, southern Italy) was carried out in 2015 (15–17th June and 17–18th November), in order to investigate the concentration of Hg species in hydrothermal fluids and the vertical distribution in the overlying water column close to the submarine exhalative area. Specific sampling methods were employed by Scuba divers at five submarine vents located along the main regional tecton…
Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica islandica) and their function as paleotemperature proxies
2011
International audience; The Sr/Ca and Mg/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374 year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a LA-ICP-MS. The shells were collected alive in 1868, 1986 and 2003 from three different localities around Iceland. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5.17 mmol/mol) and Mg/Ca values (max. …
Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey - Evidence for southward subduction of Paleotethys
2016
Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recry…
Late Palaeozoic to Mesozoic kinematic history of the Talas-Ferghana strike-slip Fault (Kyrgyz West Tianshan) as revealed by 40Ar/39Ar dating of syn-k…
2013
International audience; The NW-trending Talas-Ferghana Fault (TFF) in Kyrgyzstan, Central Asia, is one of the largest intracontinental strike-slip faults in the world. It extends over a distance of more than 2000 km from southern Tourghai to western Tarim and exhibits a maximum dextral offset of ∼200 km during the late Palaeozoic to present. The history of the fault provides important insights for the understanding of the evolution of southern Central Asia but remains poorly constrained due to lack of reliable geochronological data. We present new Ar-Ar ages and structural data from the Kyrgyz West Tianshan, that elucidate the kinematic history of the TFF in the Palaeozoic and Mesozoic. 40A…
Phanerozoic geological evolution of Northern and Central Africa: An overview.
2005
61 pages; International audience; The principal paleogeographic characteristics of North and Central Africa during the Paleozoic were the permanency of large exposed lands over central Africa, surrounded by northerly and northwesterly dipping pediplanes episodically flooded by epicontinental seas related to the Paleotethys Ocean. The intra-continental Congo–Zaire Basin was also a long-lived feature, as well as the Somali Basin from Late Carboniferous times, in conjunction with the development of the Karoo basins of southern Africa. This configuration, in combination with eustatic sea-level fluctuations, had a strong influence on facies distributions. Significant transgressions occurred duri…
Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi bas…
2018
The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposi…
A new ichnofauna from the Permian of the Zat Valley in the Marrakech High Atlas of Morocco
2020
Abstract A new ichnofauna from the Permian of Morocco is described in details: it is the first Palaeozoic ichnofauna from the Zat Valley in Marrakech High Atlas. The new tracksite was found in the Tighdouine region, in the middle-upper Permian of the Cham-el-Houa Siltstone Formation. An abundant and diverse ichnoassemblage composed of both protostomian (probably arthropods and annelids) traces and vertebrate tracks is recorded. The presence of protostomian burrows and traceways, associated with tetrapod tracks corresponds to the Scoyenia ichnofacies. Protostomian traces are ascribed to Diplichnites gouldi, Diplopodichnus biformis, Scoyenia cf. gracilis and Spongeliomorpha carlsbergi. Tetrap…
Plio-Pleistocene Dust Traps on Paleokarst Surfaces: A Case Study From the Carpathian Basin
2020
Plio-Pleistocene silt/clay-rich deposits and paleo-karst fissure sediments from sites of the northern and southern parts of the Carpathian Basin were investigated. These materials were supposed to be mixed during transport before being captured in karstified fissures. Evidence that the eolian fissure sediments of Plio-Pleistocene age in the older Triassic–Cretaceous limestones are derived from eolian silt and clay includes compositional and textural matches, especially decreasing grain-size trends observed downwards from the paleo-surface of the former landscape. Various environmental factors could be recognized by the statistical evaluation of grain-size distribution curves of fissure fill…
Secondary minerals from salt caves in the Atacama Desert (Chile): a hyperarid and hypersaline environment with potential analogies to the Martian sub…
2017
Over the past 15 years several expeditions by French, American and especially Italian cavers have unveiled over 50 caves in the Cordillera de la Sal (Atacama Desert, Northern Chile). Many of these caves contain a variety of speleothems and minerals, some of which have rarely been observed within karst systems. Most of the secondary deposits in these caves are composed of halite, but also other halide, carbonate, sulphate, nitrate, phosphate, and silicate minerals have been found. Among the sixteen cave mineral species recognized, atacamite, darapskite, blödite, leonite, anhydrite, and especially antarcticite are worth mentioning. In one of the samples an unknown Ca-Sr-bearing chloride miner…