Search results for "Sedimentary"
showing 10 items of 455 documents
Fabric transitions from shell accumulations to reefs: an introduction with Palaeozoic examples
2007
One unresolved conceptual problem in some Palaeozoic sedimentary strata is the boundary between the concepts of ‘shell concentration’ and ‘reef’. In fact, numerous bioclastic strata are transitional coquina–reef deposits, because either distinct frame-building skeletons are not commonly preserved in growth position, or skeletal remains are episodically encrusted by ‘stabilizer’ (reef-like) organisms, such as calcareous and problematic algae, encrusting microbes, bryozoans, foraminifers and sponges. The term ‘parabiostrome’, coined by Kershaw, can be used to describe some stratiform bioclastic deposits formed through the growth and destruction, by fair-weather wave and storm wave action, of …
Geochemical characteristics of Archaean and Late Proterozoic to Palaeozoic fine-grained sediments from Southern Africa and significance for the evolu…
1985
Chemical data for pelitic rocks (shallow-marine platform sediments) of the ∼ 2.9 Ga old Pongola Supergroup, South Africa, and the 550–700 Ma old Nama Group, Namibia, revealed clearly different compositions in both groups. A comparison of the Pongola and Nama data with literature values for sedimentary rocks shows a trend for Cr/TiO2 and Cr/Zn ratios as well as the absolute Cr and Ni concentrations to lower values with decreasing age, whereas the Cr/Ni ratios seem to remain broadly constant through time. REE patterns of Pongola and Nama sediments show no significant difference, thus giving the impression of a post-Archaean origin for the demonstrably Archaean Pongola sediments. However, a pl…
Formation processes at a high resolution Middle Paleolithic site: Cueva Antón (Murcia, Spain)
2013
Cueva Anton is a Middle Paleolithic rockshelter located in the valley of the River Mula (Murcia, Spain). The archeological investigation of the site, which began with salvage work in 1991, resumed in 2006 and is still ongoing, uncovered a succession spanning most of MIS 3 and MIS 4 (ca. 75–36 ka) and featuring a well preserved human occupation record. This paper presents the first information about site stratigraphy and site formation processes. Geoarcheological data collected in the field and through micromorphological observation show that the archeological succession at Cueva Anton is mainly composed of alluvial sediments, with thin intercalations of gravitational and slope material. The…
Permian-Cenozoic deep-water carbonate rocks of the Southern Tethyan Domain. The case of Central Sicily
2016
We present an integrated stratigraphy of the outcropping and buried Permian-Cenozoic deep-water carbonate successions, forming some of the tectonic units mostly buried beneath the Late Neogene sedimentary cover in the fold and thrust belt of Central Sicily. Three main successions, pertaining to the well known Lercara, Imerese and Sicanian domains, have been reconstructed on the basis of a detailed facies analysis, seismostratigraphic interpretation, bio -stratigraphy (mostly based on palynological data) and comparison between outcropping and subsurface deep-water sediments. The main results reveal a continuous sedimentation of the deep-water Southern Tethyan Sicilian succession since the Pe…
Tetrapod footprint ichno-associations from French Permian basins. Comparisons with other Euramerican ichnofaunas.
2006
21 pages; In order to take into account the studies of the European and American (USA) collections carried out by one of the authors, and of the recent nomenclatural revisions from new footprint discoveries, which have occurred during the last decade, the authors present a critical review of the French Permian palichnofauna. The distribution of the ichnospecies in the stratigraphy of the Lodève Basin, taken as a reference, is outlined. The ichno-associations are then compared with those of other French (Provence), European (Italy, Germany) and USA basins. Based on the ages of different ichnofossiliferous formations, three successive ichnofaunal units can be distinguished in the Permian of E…
Sedimentary features reveal transport paths for Holocene sediments on the Kristianstad coastal plain, SE Sweden.
2017
AbstractWe have investigated coastal and aeolian deposits on the Kristianstad plain in southernmost Sweden by a combination of methods that has yielded data on sedimentary features such as grain-size variations, shape and character of quartz grain surfaces (determined in light microscope and scanning electron microscope), and mineralogical composition. Such sedimentary techniques have been not applied to coastal deposits in this part of the Baltic Sea region before. The littoral, foredune and parabolic dune sands are sedimentologically similar, only a slight grain-size transformation by aeolian processes in the foredune was observed. Sand in straight-crested dunes, on the other hand, origin…
Foreland Basin System Evolution along the Sicilian Fold and Thrust Belt
2016
Foreland Basin System tettono-sedimentary evolution along the Sicilian Fold and Thrust Belt
Testing a portable laser-induced breakdown spectroscopy system on geological samples.
2012
9 pages; International audience; This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sediments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives …
Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition …
2018
Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900–3700 m/s, 2.06–2.37 g/cm3, and 20–35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements…
Rare earth elements and hydrothermal ore formation processes
1992
Abstract The geochemical behaviour of REE is influenced by nearly all important hydrothermal ore formation processes including fluid-rock interactions, fluid precipitations, adsorption and scavenging onto particles, and changes in fluid temperature, pressure, pH, Eh, alkalinity and ligand concentration. Destabilization of REE complexes in response to these physicochemical changes and possible chemical-crystallographic controls determine the concentration and distribution of REE within hydrothermal minerals, mineraloids and amorphous phases. Alteration assemblages of intrusive related mineralisations may exhibit a wide range of REE distributions and REE fractionation trends. The REE distribu…