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Titre : | Revision of the Palaeozoic Carbonates in the Loppa High (Barents Sea). New insights on buildup stratigraphy and karst developments. |
Auteurs : | FLORIAN MIQUELIS |
Type de document : | Mémoire de fin d'études |
Année de publication : | 2009 |
Résumé : | Late Palaeozoic carbonates represented an important target for hydrocarbon exploration in the Norwegian Barents Sea over the last decades. Carbonate builups are considered to be some of the better reservoir targets. Because of the interplay between tectonism, climatic changes and biological evolution, the properties of those mounds, however, can vary significantly and are often overprinted by karst. So, one of the greatest exploration challenges is to better understand the spatial distribution of buildup growth and karstification regarding to their age, their lithology, climatic changes and structural settings.A recently reprocessed 3D seismic volume allowed revisiting the stratigraphy of the Loppa High (Barents Sea) in higher detail with focus on build-ups growth and karst development. A multi-techniques workflow, based on various seismic interpretation methods (surface based methods and volume based methods), has been set-up. In fact, volume based methods, especially the RGB blends from frequency decomposed data are very useful to reveal subtle 3D geometries and consequently to get highly detailed information that would have stayed hidden when using surface based methods. This concluded in revisiting the stratigraphy of the Palaeozoic carbonates platform of the Loppa High considering structural events, buildups growth and karst events. In order to better characterize and quantify the late Palaeozoic karst event, a new workflow for quantitative geomorphological analysis has been proposed, using an ArcGIS project combined with all the interpreted seismic data. This complete data integration allows spatial analysis and integrated multi-parameters analysis. Regarding the stratigraphy, this workflow permits to characterize different kind of buildups in seismic and to understand parameters controlling their development. Indeed, Palaeoaplysina/Tubiphytes buildups from the Ørn formation (Gipsdalen) develop in warm water carbonates. RGB blends reveal that such buildups, 40 meters thick, developed as linear ridges or as patch reefs on the top of the platform. Polarrev buildups of the Bjarmeland cold water carbonates are Bryozoan/Tubiphytes deep-water buildups, about 200 meters thick, forming polygonal ridges and enclosed polygonal mini-basin (2 km in diameter). RGB blends highlight their subsidence control. Indeed, the more there was subsidence, the larger buildups and the wider enclosed basins are. Those buildups develop as a continuous vertically stacking when accommodation allowed, as lateral migration toward the mini-basins when a regression in Upper Polarrev occurred (confirmed by a karst development in the highest part of the margin).Fault controlled buildup geometries permit to date the extensional event occurred at the start of the Bjarmeland. The new workflow was established to detect karst features from seismic using advanced attribute analyses, and subsequently quantifying these karst systems, classifying them in function of host-facies, structural trends and uplift. This has revealed that karst developed mainly in three geomorphologic zones: • A karsted plateau showing sinkholes developing parallel to the stratigraphy. Host carbonates facies (from Gipsdalen and Bjarmeland) revealed by the truncation seem to control the karst development • A proximal karsted slope where deep sinkholes and canyons developed in Bjarmeland carbonates. General top-Palaeozoic uplift and Palaeozoic structural trends seem to control the orientation of canyons. Sinkholes seem to be linked to the development of canyons. • A last zone at the feet of the slope showing some sinkholes re-using sometimes previous karsts and some re-emergent drainage systems. Key words: Barents Sea, Loppa High, Palaeozoic, buildup, karst, Gipsdalen, Bjarmeland, Tempelfjørden, Polarrev, platform, Palaeoaplysina, polygonal, sinkholes, canyons, seismic interpretation, RGB spectral decomposition, GIS. |
Spécialité : | Géologie |
Numéro de promo : | 69 |