Search results for "DIAGENESI"
showing 10 items of 130 documents
Petrography and high-resolution geochemical records of Lower Jurassic manganese-rich deposits from Monte Mangart, Julian Alps
2016
Deposits with unusually high Mn contents sampled at Monte Mangart in the Julian Alps include organic-rich marlstone and black shale with interbedded manganoan and siliceous limestone, which were deposited during the early Toarcian Oceanic Anoxic Event. Mn enrichment during that period has been related to global sea-level change coincident with increasing subsidence rate. The formation of Fe-Mn nodules, marking a hardground at the base of the Monte Mangart section, seems to be triggered by release of Mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed. However, very high Mn contents in carbonate phases above the har…
The Potential Geosite of the “Libeccio Antico” Quarries: a Sedimentological and Stratigraphic Characterisation of Ornamental Stone from Mt Cocuccio, …
2018
The Custonaci marble district of western Sicily is known for the production of a valuable ornamental stone that has been, and nowadays is exploited due to its suitable properties and aesthetic qualities. The “Libeccio Antico” was, among the “marbles”, the most appreciated ornamental stone during the Baroque Age (the XVII–XVIII centuries), due to its strong polychrome contrasts from ivory to yellow, green or dark red. This polychrome pattern is the result of dissolution processes that involved an Upper Triassic peritidal limestone. The varicoloured sediments in paleocavities, collapse breccias, paleosols and neptunian dykes that occur in the “Libeccio Antico” represent the peculiar character…
A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, U…
2016
17 pages; International audience; n the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present p…
�ber den ?Hygrophyllit? im Rotliegenden des Saar-Nahe-Gebietes, ein Beitrag zur Diagenese pyroklastischer Gesteine
1971
In certain areas rhyolitic tuffs of the Upper Rotliegend include a greenish, talc-like substance, called “Hygrophyllit”. It has been found too at the base of the Rotliegend in the Saarland. It is shown, that Hygrophyllit corresponds to decomposed pumice, related to the acid permian volcanism. X-ray, DTA and chemical investigations yielded, that Hygrophyllit consists essentially of a mixed layer mica-Ca-montmorillonite with random interstratification and previously about 33 % expandable layers. In consequence there are in the Rotliegend of the Saar-Nahe-Basin three different diagenetic developments of acid pyroclastic rocks: The formation of Kaolinite in the Lower Rotliegend, of devitrificat…
Chemostratigraphy of the early Pliocene diatomite interval from MIS AND-1B core (Antarctica): Palaeoenvironment implications
2013
The AND-1B drill core (1285m-long) was recovered, inside the ANDRILL (ANtarctic geological DRILLing) Program, during the austral summer of 2006/07 from beneath the floating McMurdo Ice Shelf. Drilling recovered a stratigraphic succession of alternating diamictites, diatomites and volcaniclastic sediments spanning about the last 14Ma. A core portion between 350 and 480mbsf, including a 80m-thick diatomite interval recording the early Pliocene warming event, was investigated in term of opal biogenic content and element geochemistry. Across the diatomite interval, in spite of the lithological uniformity, a fluctuating biogenic opal profile mirrors the δ18O record, testifying a decrease in prod…
Formation of secondary carbonates and native sulphur in sulphate-rich Messinian strata, Sicily
2010
Abstract Microbially formed authigenic carbonates accompanied by native sulphur are present in the ‘Calcare Solfifero’ below a thick succession of gypsum deposited during the Messinian salinity crisis in Sicily. We sampled these carbonates and associated sulphur in five former sulphur mines to subject them to a detailed petrographic and geochemical study in order to explore their different modes of formation. Native sulphur formed in conjunction with microbial sulphate reduction, which is reflected in its depletion in 34S (δ34S values as low as − 2‰ vs. V-CDT) and an enrichment of 34S in the residual sulphate (δ34S values as high as + 61‰). The oxidation of organic matter by sulphate reduct…
Microstratigraphy of the Magdalenian sequence at Cendres Cave (Teulada-Moraira, Alicante, Spain): Formation and diagenesis
2013
Abstract This microstratigraphic study of the Magdalenian sequence in the Cendres Cave (Teulada-Moraira, Alicante, Spain) shows the detailed evolutionary history of the deposit, revealing a wide variety of pedosedimentary (formation and diagenesis), biogenic and anthropic processes. The sequence begins with Cendres XII, culturally attributed to the Early and Middle Magdalenian, with high probability (95%) dating placing it between 19,270 and 16,530 cal BP with some chronological hiatus. It was formed from biogenic sedimentation associated with bat guano mainly of an insectivorous type, and from anthropic sedimentation related to occupation floors made up of highly complex plant beds with tr…
Long-Term Consequences of Water Pumping on the Ecosystem Functioning of Lake Sekšu, Latvia
2020
Cultural eutrophication, the process by which pollution due to human activity speeds up natural eutrophication, is a widespread and consequential issue. Here, we present the 85-year history of a small, initially Lobelia&ndash
Preservation of successive diagenetic stages in Middle Triassic bonebeds: Evidence from in situ trace element and strontium isotope analysis of verte…
2015
Abstract Bonebeds comprise reworked and time averaged constituents of different phosphatic vertebrate remains and, hence, provide an ideal substrate for the study of long and short term diagenetic processes. To test whether trace elements (U, Sr, REE) and 87 Sr/ 86 Sr ratios can be used for distinguishing between successive diagenetic signals, we performed geochemical analyses on vertebrate remains (bones, teeth, scales and coprolites) from two Triassic bonebeds located near Palzem (Germany). Trace element analysis was done on 170 vertebrate remains by LA-ICP-MS while 87 Sr/ 86 Sr ratios were determined for 39 bioclasts using LA-MC-ICP-MS. Although a low inter- and intra-bioclast REE variab…
Morphometry of microstromatolites in calcrete laminar crusts and a fractal model of their growth
1996
The laminar crust, constituting the upper part of calcretes (terrestrial CaCO3 accumulations inside surficial sediments), is a succession of thin layers of various colors and shapes resembling micro-stromatolites. The crust structure and its diagenetic evolution are similar to stromatolites. A quantitative study of its structure was made using image analysis. Euclidian parameters were calculated to describe lamina shape. Eight hundred and eighty-six laminae were divided into six classes from the flatest forms to columnar shapes. The geometrical relationships between the shapes are interpreted as steps in the growth process of the microstromatolite. A fractal model of laminar crust growth wa…