The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin
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| Authors: | Ravnas, R; Cook, A; Engenes, K; Germs, H; Grecula, M; Haga, J; Harvey, C; Maceachern, JA |
| Year: | 2014 |
| Journal: | 46: 609-645 |
| Title: | The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin |
| Abstract: | The reservoirs of the giant Ormen Lange field, located off the More coast, consist of deep-marine turbidites within the Upper Maastrichtian Springar Formation and the Danian Egga sandstone unit. The two sandstone units are interpreted in terms of inner to middle and outer parts of two, stacked lower slope sandy fan systems, respectively. The two fan systems were sourced from an uplifted hinterland; the tectonic rejuvenation of this is related to rift-margin uplift in response to phased late Campanian to Danian rifting within the western More Basin. Rift-margin uplift was accompanied by basinward tilting and draped folding over deep-seated basement highs along the More Margin, which produced a stepped slope margin with local slope minibasins and terraces. Each phase of repeated hinterland uplift, basin-margin tilting and sandy fan development represents a time span of a few million years. The Springar and Egga turbidite systems evolved through fill-spill processes on the slope terraces or minibasin(s). Within an individual minibasin or slope terrace, an early phase of 'infilling' or smoothing of inherited topography appears to have been followed by a more organised backfilling or upslope onlapping combined with forestepping or outbuilding of the sandy fan across the individual terraces or minibasins. Compensationally stacked channel storeys and lobe storeys form the fundamental architectural elements and probably reflect major flooding events in the hinterland or drainage basin. Multistorey channel belts represent further outbuilding of the local terrace or minibasin-filling fan, with sediment bypass and delivery to further downslope minibasins and terraces. The uppermost parts of the fan systems appear less organised and contain disorganised, slumped and gravitationally re-sedimented units alternating with multistorey channel-fills. These less-organised facies associations formed in response to an early stage or initial tilting of the basin margin slope. Final backstepping and return to predominantly hemipelagic to pelagic slope deposition is attributed to renewed upslope or hinterland structuring, which resulted in capture of sand in proximal subbasins. |
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