Search results for "Siliciclastic"
showing 10 items of 51 documents
Seismic and sedimentologic features of Oxfordian-Kimmeridgian syn-rift sediments on the eastern margin of the Lusitanian Basin
1989
Following deposition of widespread middle Oxfordian lacustrine carbonates and evaporites, the Lusitanian Basin was differentiated into a number of sub-basins. The Arruda sub-basin is a half graben basin situated some 30 km north of Lisbon. It accumulated over 2.5 km of Kimmeridgian siliciclastic sediments, and is bounded to the east by the Vila Franca de Xira fault zone. Carbonate deposition persisted over horsts along the fault zone from the Oxfordian to the early Kimmeridgian, and in places to the late Kimmeridgian, and shows a pronounced west-east facies zonation, with higher energy framestones and grainstones accumulating along the exposed western margins. Seismic data indicate a major …
Facies and facies association of the siliciclastic Brak River and carbonate Gemsbok formations in the Lower Ugab River valley, Namibia, W. Africa
2007
Abstract The Neoproterozoic Zerrissene Turbidite Complex of central-western Namibia comprises five turbiditic units. From the base to the top they are the Zebraputs Formation (greywacke and pelite), Brandberg West Formation (marble and pelite), Brak River Formation (greywacke and pelite with dropstones), Gemsbok River Formation (marble and pelite) and Amis River Formation (greywacke and pelites with rare carbonates and quartz-wacke). In the Lower Ugab River valley, five siliciclastic facies were recognised in the Brak River Formation. These are massive and laminated sandstones, classical turbidites (thick- and thin-bedded), mudrock, rare conglomerate and breccia. For the carbonate Gemsbok R…
Impact of storms on mixed carbonate and siliciclastic shelves: insights from combined diffusive and fluid-flow transport stratigraphic forward model
2004
Abstract A quantitative stratigraphic model of mixed carbonate/siliciclastic continental shelves is presented to investigate the relationships between depositional processes and stratigraphic responses at long‐term, large spatial scales. A diffusion model is combined with a fluid‐flow approach to simulate both long‐term factors, i.e. the processes controlling large‐scale architecture, and short‐term processes, i.e. sediment redistribution by storms. Any net sediment accumulation is the result of the succession of a storm and a fair‐weather period. Sediments are mobilized by waves and advected by low‐frequency currents during storm events. Sediments are then reworked and redistributed downsl…
Deep-seated gravitational slope deformations in western Sicily: Controlling factors, triggering mechanisms, and morphoevolutionary models
2014
Abstract A study of deep-seated gravitational slope deformation (DSGSD) phenomena affecting areas of various geological and geomorphological settings in western Sicily is described. Western Sicily is underlain by a thin-skinned imbricate wedge of Meso–Cenozoic carbonate and siliciclastic rocks that formed by the stacking of several thrust nappes over the Iblean foreland. Locally, the original thrust sheets are folded and cut by high-angle faults. Large areas of western Sicily now display high relief energy due to Plio-Pleistocene block-faulting and uplifting, and the Quaternary morphogenetic phases are characterised by incision, thereby triggering widespread DSGSDs. To identify controlling …
Sequence stratigraphy and paleo-oceanography of an open-marine mixed carbonate/siliciclastic succession (Late Jurassic, Southern Germany)
1992
The Late Jurassic epicontinental sea of South Germany protruded far to the North forming a wide bay which was rimmed by shallow-water platforms (Swiss and French Jura). This wide shelf is characterized by extensive downslope mud accumulations including siliceous sponge buildups. The bioherms are aligned along the more pericontinental parts of this shelf, which graded to the South into the Helvetic Basin of the Tethys Ocean.
Tectonic evolution of the southern Kaoko belt, Namibia
2002
Abstract The tectonic evolution at the junction of the Panafrican Kaoko and Damara belts is well recorded in the siliciclastic and carbonate successions of the Neoproterozoic Zerrissene turbidite system, metamorphosed to the biotite zone of the greenschist facies. The structures in the turbidites are attributed to two main deformational events. The older one generated two continuous folding phases, D1 and D2, and the younger one resulted in D3 deformation. D1, of dominant E–W shortening, caused upright kilometre-scale folds with well-developed axial planar cleavage, N–S trending axial planes and subhorizontal axes. This phase graded into D2 that refolded the first folds coaxialy and develop…
Systems tracts and depositional sequences in a carbonate setting: a study of continuous outcrops from platform to basin at the scale of seismic lines
1991
Abstract The application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application. The continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the Southern Vercors Plateau (western Alps, France) confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems. From the stratal patterns displayed in outcrop, we determined that carbonate lowstand systems tracts are major components in the basin, even in the deep pelagic realm. Transgressive and highstand systems tracts are very thin, a response to starvation. In co…
Taphonomy of the vertebrate bone beds from the Klūnas fossil site, Upper Devonian Tērvete Formation of Latvia
2012
Combined sedimentological and taphonomical study of the siliciclastic sequence of the Tērvete Formation in the stratotypical area was aimed at revealing the formation of the three oryctocoenoses discovered and related structural and textural features of the deposits, as well as at detailed observation of the taphonomical peculiarities of the obtained palaeontological material. The fossil vertebrate assemblage is represented by 14 taxa comprising placoderms, acanthodians, sarcopterygians and actinopterygians. The three oryctocoenoses, first recognized in 2010, differ in the proportions of repeatedly buried material, in the number and degree of preservation of small and fragile skeletal eleme…
Nitrogen isotope evidence for stepwise oxygenation of the ocean during the Great Oxidation Event
2019
24 pages; International audience; The Earth’s oxygenation represents one of the most important environmental drivers of life’s evolution, with the first rise, known as ‘the Great Oxidation Event’ (GOE), corresponding to unpreceded accumulation of atmospheric O2, changes in the flux of marine nutrients and possibly global glaciations. However, the detailed evolution of the GOE is still debated, as for instance the accumulation trends of oceanic versus atmospheric oxygen and the nature of biogeochemical responses to oxygenation. Here, we combine organic carbon and bulk nitrogen isotope compositions with major element concentrations and iron speciation data of sedimentary rocks recovered from …
Archaean Granitoid–Greenstone Geology of the Southeastern Part of the Kaapvaal Craton
2019
The southeastern Kaapvaal Craton is a Palaeoarchaean granitoid–greenstone terrain. Supracrustal rocks are dominated by metamorphosed mafic–ultramafic volcanic rocks intercalated with minor felsic volcanic and chemical sedimentary rocks, including carbonaceous chert and minor iron formation. Siliciclastic sedimentary rocks are rare. The greenstones occur in the Schapenburg and Dwalile fragments close to the Barberton greenstone belt, the Assegaai, De Kraalen, Witrivier and Commondale fragments in the vicinity of Piet Retief, and the Nondweni and Ilangwe greenstone belts together with several smaller fragments in the southern part of the craton. The greenstones are locally in tectonic contact…