Search results for "Authigenic"

Sulfuric acid speleogenesis (SAS) close to the water table: Examples from southern France, Austria, and Sicily

2016

Caves formed by rising sulfuric waters have been described from all over the world in a wide variety of climate settings, from arid regions to mid-latitude and alpine areas. H2S is generally formed at depth by reduction of sulfates in the presence of hydrocarbons and is transported in solution through the deep aquifers. In tectonically disturbed areas major fractures eventually allow these H2S-bearing fluids to rise to the surface where oxidation processes can become active producing sulfuric acid. This extremely strong acid reacts with the carbonate bedrock creating caves, some of which are among the largest and most spectacular in the world. Production of sulfuric acid mostly occurs at or…

Methane-derived carbonate conduits from the late Aptian of Salinac (Marne Bleues, Vocontian Basin, France): Petrology and biosignatures

2015

Abstract Peculiar carbonate bodies occur in distinct marl layers of the Marnes Bleues Formation (Aptian–Albian, Vocontian Basin, Southern France). The carbonate conduits exhibit pipe- or sausage-like forms and a central channel. Their sizes range between 30 and 60 cm in length and 5–10 cm in diameter. The conduit carbonates consist of automicrite authigenically formed within the sediment. Millimeter-sized aggregates of framboidal pyrite are abundant within the conduit automicrites, probably representing former colonies of sulfate reducing bacteria. The central channel reflects former pathways of reduced fluids in the carbonate conduit. Ni-enrichments at the margins of the central cavity are…

Suspended particulate matter fluxes along with their associated metals, organic matter and carbonates in a coastal Mediterranean area affected by min…

2016

International audience; A study of suspended particulate matter (SPM) fluxes along with their associated metals, organic matter and carbonates, was conducted off the Mejerda River outlet in May 2011 and in March and July 2012 at depths of 10, 20 and 40 m using sediment traps. SPM fluxes are more significant near the Mejerda outlet, especially in winter, but dissipate further offshore. Normalization reveals that the Mejerda is a major source of Pb, Zn, Cd, Cu, Ni, and Co, all of which are the result of human activities. In contrast, Fe, Mn and N are of authigenic origin. The enrichment factor shows that Pb, Zn and especially Cd are the most highly polluting metals off the Mejerda outlet. Thi…

The Billiemi breccia: the record of Rhaetian/lowermost Jurassic brittle deformations along the Panormide shelf edge

2010

Meromixis origin and recent trophic evolution in the Spanish mountain lake La Cruz

1998

A sediment core from a Mediterranean karstic lake was studied through its pollen, diatom, chydorid, ostracod, charcoal and authigenic mineral composition. Information about environmental history recorded in the sediment sequence since the Middle Ages is presented. The main fluctuations of water volume and trophic status of the lake occurred during periods of great change in land management and during climatic cold phases. The synergetic effect of these two factors led to a high water level phase and triggered a rising of the trophic level which produced meromixis. The onset of meromictic conditions at about 1700 AD coincides with the Maunder minimum in the Little Ice Age as well as with a p…