Search results for "STRATIGRAPHY"
showing 10 items of 904 documents
Clastic injection dynamics during ice front oscillations: A case example from Sólheimajökull (Iceland).
2015
18 pages; International audience; Soft-sediment deformation structures are being increasingly used as a tool for reconstructing palaeoenvironments and porewater pressure conditions in glacial settings. However, the potential of hydrofractures and clastic injections in the reconstruction of ice dynamics remains poorly constrained. This paper presents the results of a detailed study of a clastic injection network outcropping in the Sólheimajökull forefield (South Iceland). Sedimentological descriptions are combined with microscopic to macroscopic analyses of clastic injection geometries, sediment-fills, and cross-cutting relationships. The 250 m long and 20 m high exposure observed along the …
Evidence from zircon dating for existence of approximately 2.1 Ga old crystalline basement in southern Bohemia, Czech Republic
1993
Zircon ages are reported for three Moldanubian amphibolite grade orthogneisses from the southern Bohemian Massif obtained by conventional U/Pb analyses. For two of these orthogneisses, conventional U/Pb data are supported by ion microprobe single zircon ages or single grain evaporation data. The amphibolite grade orthogneisses, occurring in three small tectonic lenses within the Varied Group close to the South Bohemian Main Thrust, are of tonalitic, granodioritic or quartz dioritic composition.
Fluid-pressure controlled soft-bed deformation sequence beneath the surging Breiðamerkurjökull (Iceland, Little Ice Age).
2009
16 pages; International audience; The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA…
Stratigraphy, geochemistry and geochronology of a Quaternary pyroclastic sequence of the Chichontepec volcano, El Salvador
2013
In this paper we present sedimentological, chemical and geochronological data on a pyroclasticsequence deposited at Chichontepeque Volcano (El Salvador) during a caldera-forming Plinian phase.Granulometric analyses and width distribution patterns of airfall pyroclastics showed that these are the result ofat least two eruptions, the oldest being the more complete. The Basal Fall, which marks the beginning of thePlinian eruption, shows the typical features of Plinian air-fall deposits.Chemical trends mirror roughly a downward tapping from a zoned magma chamber; inside each fall unit crys-tal fractionation trends can be recognized. 39Ar/40Ar dating of lavas underlying and overlying the pyrocla…
Tunable diode laser measurements of hydrothermal/volcanic CO<sub>2</sub> and implications for the global CO<sub&am…
2014
Abstract. Quantifying the CO2 flux sustained by low-temperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles' atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestati…
A geochemical traverse along the “Sperchios Basin – Evoikos Gulf” graben (Central Greece): Origin and evolution of the emitted fluids
2014
The studied area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). A high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 °C, that discharge along the normal faults bordering the graben. In the period 2004–2012, 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions. Two main groups of thermal water…
A fault-related coalification anomaly in the Blanzy-Montceau Coal Basin (Massif Central, France)
1997
Abstract The Stephanian intramontane Blanzy-Montceau Coal Basin is situated along a Variscan fault complex bordering the Upper Paleozoic Blanzy-Le Creusot-Bert graben. The deposition of coal-bearing strata was controlled by a complex of early faults known as the “Faille de Bordure” (FB, Border Fault). Another complex of Permian faults known as the “Faille de l'Est” (FE, Eastern Fault) is situated along the more central part of the coal basin. Coalification in the basin follows three main trends: (1) Increasing rank from upper to lower coal seams in accordance with a general vertical trend (Hilt, 1873). The gradient of volatile matter is higher than normal, ranging from 3% to I I% Vdaf per 1…
Mesozoic and Paleogene megabreccias in Southern Sicily: New data on the Triassic Paleomargin of the Siculo-Tunisian platform
1996
Mesozoic and Paleogene clastic carbonates in deep-water successions outcropping in the Sicani mountains (central southern Sicily) represent debris-flow and turbidite deposits accumulated in slope/base-of-slope sectors of the Sicanian Basin, a Permian to Miocene deep-water sedimentary domain of Sicily. Reef-derived carbonates of late Triassic age are frequently found among the clastic elements of these deposits, in association with other shallow and deep-water Mesozoic carbonates. The provide us with new data on the stratigraphic setting of a platform paleomargin now buried beneath the Sicilian thrust and fold belt. This paleomargin bounded the wide middle and upper Triassic carbonate platfo…
Coelobiontic communities in neptunian fissures of synsedimentary tectonic origin in Permian reef, southern Urals, Russia
2007
Sedimentary dykes in the Permian reef complexes of the Russian platform are well preserved and important in providing information about reef growth, the reef biota and, particularly, cavity-dwelling organisms and sediment sources. Two main fissure assemblages are recognized with N80° and N170° (late Asselian-early Sakmarian) and N130°–140° and N60° (Sakmarian-Artinskian) orientations. These contemporaneous orthogonal dyke sets present orientations corresponding to the regional tectonic fabric and a tectonic origin for fracturing associated with the foreland basin development. The largest dykes record eight lithofacies and several stages of fracture opening. Stromatoids and centimetre-thick …
Surface expression of eastern Mediterranean slab dynamics: Neogene topographic and structural evolution of the southwest margin of the Central Anatol…
2012
[1] The southwest margin of the Central Anatolian Plateau has experienced multiple phases of topographic growth, including the formation of localized highs prior to the Late Miocene that were later affected by wholesale uplift of the plateau margin. Our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1.5 km elevation to <7.17 Ma, and regional lithostratigraphic correlations imply that the age is <6.7 Ma. Single-grain CA-TIMS U-Pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10.6 Ma, indicating a maximum age that is consistent with the biostratigraphy. Our structural measurements within the upl…