Search results for " diagenesis"
showing 9 items of 9 documents
Spongy-like porosity in peritidal carbonates: An interaction of cyclic sea-level oscillations, fresh water supply and sediment texture
2016
Abstract This paper focuses upon the analysis of a complex paleokarstic system recorded within uppermost Triassic peritidal cycles in northwestern Sicily. Besides documenting spectacular karstification at the Triassic/Jurassic boundary, it provides an example of stratabound ‘spongy’ or ‘swiss-cheese’ dissolution. On the base of field observations, microfacies analysis, transmitted-light and cathodoluminescence petrography and stable-isotope analyses we put forward an original model for the formation of this peculiar stratabound dissolution. It implies a complex interaction of several controlling factors at the interface between the marine and meteoric diagenetic realms during the relative c…
Carbon, iron and sulphur cycling in the sediments of a Mediterranean lagoon (Ghar El Melh, Tunisia)
2019
Coastal lagoon sediments are important for the biogeochemical carbon cycle at the land-ocean transition, as they form hotspots for organic carbon burial, as well as potential sites for authigenic carbonate formation. Here, we employ an early diagenetic model to quantify the coupled redox cycling of carbon, iron and sulphur in the sediments of the shallow Ghar El Melh (GEM) lagoon (Tunisia). The model simulated depth profiles show a good correspondence with available pore water data (dissolved inorganic carbon, NH 4 + , total alkalinity, Ca 2+ , Fe 2+ and SO 4 2− ) and solid phase data (organic matter, pyrite, calcium carbonate and iron (oxyhydr)oxides). This indicates that the model is abl…
Influence of a major exposure surface on the development of microporous micritic limestones - Example of the Upper Mishrif Formation (Cenomanian) of …
2017
18 pages; International audience; Microporous platform top limestones of the Cenomanian Mishrif Formation (offshore Qatar) were studied in order to investigate the diagenetic processes associated with the top-Mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates. Petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the Mishrif Formation, including pervasive dissolution and meteoric cementation, as well as neomorphism of the micritic matrix. Micrites at the top of the Mishrif Formation are coarse (i.e. > 2 μm), sub-rounded and very dull luminescent under cathodoluminesc…
Bulk carbonate isotope stratigraphy from CRP-3 core (Victoria Land Basin, Antarctica): evidence for Eocene–Oligocene palaeoclimatic evolution
2005
Bulk carbonate isotope compositions and carbonate petrography from upper Eocene and lower Oligocene siliciclastic sediments of the CRP-3 sediment core (Victoria Land Basin, Antarctica) have been investigated with the aim of contributing to reconstruction of the Antarctic Cenozoic palaeoclimate. Most of the carbonate is calcite cement occurring as patches, nodules and horizons and consisting of equant and/or drusy sparry calcite, pervasive blocky calcite and rare poikilotopic calcite spar. 18O-depleted values (from −17 to −8 δ‰) of the CRP-3 carbonates suggest that the precipitating fluids were a mixing between marine and meteoric waters from melting glaciers. The δ18O record exhibits a numb…
Microbially-induced Fe and Mn oxides in condensed pelagic sediments (Middle -Upper Jurassic, Western Sicily)
2011
Abstract This article presents a petrographic comparison of the Rosso Ammonitico facies of Western Sicily and the original Rosso Ammonitico Veronese of Northern Italy based on a total of 27 sections. The Rosso Ammonitico has been the subject of numerous controversies that range from bathyal to shallow-water platform sedimentation. Therefore it seemed interesting to verify if the term Rosso Ammonitico has the same geologic connotation from region to region. The Middle-Upper Jurassic Rosso Ammonitico of Western Sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the Ionian Ocean. Slope-to-basin or pelagic carbonate deposi…
A genetic link between synsedimentary tectonics-expelled fluids, microbial sulfate reduction and cone-in-cone structures
2018
14 pages; International audience; The late Jurassic (Tithonian) marlstones of the Boulonnais area (English Channel, France) contains diagenetic carbonate beds and nodules. Some nodules exhibit cone-in-cone structures on their lower face. We studied such nodules using various techniques of imaging and chemical (major and trace-elements) and isotopic analyses (Ccarb, Corg, O and S stable isotopes). We interpret the cone-in-cone to be the end product of carbonate-nodule formation during early diagenesis. The diagenetic carbonate precipitation was induced by microbial activity (bacteria and(?) archeae) fueled by upward-migrating fluids. Fluid expulsion was itself triggered by synsedimentary fau…
Mollusk carbonate thermal behaviour and its implications in understanding prehistoric fire events in shell middens
2018
Abstract Archaeological shell middens are particularly important for reconstructing prehistoric human subsistence strategies. However, very little is known about shellfish processing, especially when related to the use of fire for dietary and disposal purposes. To shed light on prehistoric food processing techniques, an experimental study was undertaken on modern gastropod shells (Phorcus lineatus). The shells were exposed to high temperatures (200–700 °C) to investigate subsequent mineralogy and macro- and microstructural changes. Afterwards, the three-pronged approach was applied to archaeological shells from Haua Fteah cave, Libya (Phorcus turbinatus) and from shell midden sites in the U…
Multi-scale dissolution events in Western-Tethyan peritidal carbonates close to the Triassic/Jurassic boundary
2015
The stratigraphical and sedimentological study of uppermost Triassic-lowermost Jurassic sections of peritidal carbonates, in north-western Sicily, allows to differentiate multi-scale dissolution events that affected the carbonate platform interior during the uppermost Rhaetian. The Triassic cycles show extensive phenomena of stratabound dissolution that can be differentiated in three main types: vug, moldic and “spongy-like”. The dissolution horizons are particularly concentrated in the subtidal members of cycles. The creation of different type of porosity seems to be mainly controlled by the textural characters of the host-rock. In particular the cm-scale bioturbation in muddy sediments, p…
Kalcīts un tā veidošanās apstākļi Franas stāva smilšakmeņos un dolomītos Latvijā
2019
Maģistra darbā “Kalcīts un tā veidošanās apstākļi Franas stāva smilšakmeņos un dolomītos Latvijā” raksturotas kalcīta fizikālās īpašības, ķīmiskais sastāvs un veidošanās apstākļi. Pētījumi veikti 16 Amatas, Pļaviņu, Daugavas un Stipinu svītas atradnēs un atsegumos. Dokumentēti ģeoloģiskie griezumi, pētītas kalcīta fluorescences izpausmes un citas fizikālās īpašības, attiecības ar smilšakmens un dolomīta komponentiem plānslīpējumos, noteikts kalcīta ķīmiskais sastāvs un oglekļa stabilo izotopu attiecības. Secināts, ka kalcīts Amatas svītas smilšakmeņos un Pļaviņu, Daugavas un Stipinu svītas dolomītos kristalizējies līdzīgos apstākļos – no atmosfēras izcelsmes pazemes ūdeņiem sauszemes apstāk…