Search results for "Silicic"

Volatiles and trace elements content in melt inclusions from the zoned Green Tuff ignimbrite (Pantelleria, Sicily): petrological inferences

2018

International audience; The island of Pantelleria is one of the best known localities of bimodal mafic-felsic magmatism (alkali basalt and trachyte-pantellerite). Among the felsic rocks, the coexistence in a single eruption of products of both trachyte and pantellerite compositions is limited to few occurrences, the Green Tuff (GT) ignimbrite being one of these. The GT is compositionally zoned from pantellerite (70.1 wt% SiO2, mol Na+K/Al = 1.86, 1871 ppm Zr) at the base to crystal-rich (>30 vol%) comenditic trachyte (63.4 wt% SiO2, mol Na+K/Al = 1.10, 265 ppm Zr) at the top, although the pantellertic compositions dominate the erupted volume. We present here new data on melt inclusions (MIs…

Predicting breakthrough of vanadium in fixed-bed absorbent columns with complex groundwater chemistries: A multi-component granular ferric hydroxide−…

2020

Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater che…

Erratum to “The oxidation state of iron in silicic melt at 500 MPa water pressure” [Chem. Geol. 189 (2002) 55–67]

2003

Stranded jellyfish in the lowermost Cambrian (Corduban) of Spain

2021

Ninety discoid structures of big size occurring on a bedding plane of Nemakit-Daldynian to Tommotian sandstones (i.e. Corduban in the Spanish scale of Cambrian stages) from south-western Spain are described. Cross-cutting relationships between discoid structures and associated trace fossils, as well as evidence for penecontemporaneous deformation of sediment laminae below the discoids, permit to interprete these structures as impressions of ancient, soft-bodied marine organisms. Taphonomic, biometric, and morphological studies suggest that they are outer moulds of both sides, subumbrellar and exumbrellar, of ancient jellyfish of hydrozoan coelenterates, whose canals resemble the modern genu…

New trepostomate bryozoans from the Upper Ordovician of Morocco and the temperature influence on zooid size

2015

AbstractNew Upper Ordovician trepostomate bryozoans from the eastern Anti-Atlas of Morocco have been identified. They have been collected from the lower and intermediate units of the Khabt-el-Hajar Formation, late Katian in age, representing, respectively, bryozoan-pelmatozoan meadows with siliciclastic input, degraded by wave activity in a mid-ramp setting, and outer-ramp environments with marly substrates. Ten species of the generaCyphotrypa,Calloporella,Diplotrypa,Parvohallopora,Dekayia, andAostiporaare described. Of them, three species are new:Cyphotrypa regularisJiménez-Sánchez,Parvohallopora cystataJiménez-Sánchez, andAostipora elongataJiménez-Sánchez. Univariate statistical analyses …

Bioinspired Fabrication of Bio-Silica-Based Bone-Substitution Materials

2010

The gold standard for bone reconstruction is the use of autogeneic grafts from various donor regions, since they possess osteoinductive as well as osteoconductive potential. Only a few synthetic materials possess/display properties that allow optimal bone reconstitution. Previously, we showed that the natural product, bio-silica, comprises osteoinductive, and probably also osteoconductive activity. Bio-silica is formed enzymatically via silicatein; this enzyme has been isolated from siliceous sponges and has also been cloned and prepared recombinantly. In the present study, silicatein was encapsulated together with its substrate, sodium metasilicate, in poly(D,L-lactide)/poly(vinyl pyrrolid…

Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple

2006

The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop-scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine-grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg-sulfates and also include Ca-sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedfor…

In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars.

2004

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The …

Two Years at Meridiani Planum: Results from the Opportunity Rover

2006

The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling ∼8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict “hopper crystals” that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergon…

The Opportunity Rover's Athena Science Investigation at Meridiani Planum, Mars

2004

The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by e…