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Title: The sequence stratigraphic and structural evolution of the early cretaceous, Outer Moray Firth, U.K. North Sea; comparison with outcrop analogues
Author: Lowe, Adrian Mark
ISNI:       0000 0001 3613 2548
Awarding Body: University of Manchester : University of Manchester
Current Institution: University of Manchester
Date of Award: 2001
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Aptian age sandstones within the early Cretaceous of the Britannia area, Outer Moray Firth, UK North Sea occurring within the early post-rift of an asymmetric half graben, are interpreted to be of deep-marine origin. A total of 22 2D regional seismic lines (11 000 km2) and 13 individual lines from a 3D seismic volume (1 104 km2) have been studied, along with 34 wells and eight cores (totalling >1000 metres) which penetrate the early Cretaceous of the Britannia area. Six early Cretaceous seismic horizons and five seismic sequences have been identified. Detailed seismic horizon mapping has enabled the identification of the spatial and temporal evolution of the basin-fill, as well as potential sediment input points into the Britannia area. Detailed sedimentological core logging was undertaken to identify sedimentary facies and depositional processes within the area. Six lithofacies have been identified which range in depositional process from; basin-floor hemi-pelagic fallout, high-concentration turbidity current, slurry flow and debris flow deposition to slump deposition. Integration of seismic reflection data, sedimentology and biostratigraphy has enabled the identification of four genetic stratigraphic sequences (early Barremian-late Aptian). Genetic Sequence I represents the background basin-floor deposition. Clean mud-poor sandstones deposited by channelised highconcentration turbidity currents dominate Genetic Sequence II. These sandstones are interpreted to have been deposited by flows that were transporting sediment axially, west to east through the Witch Ground Graben. Minor highconcentration turbidite deposition in the east Britannia area is interpreted to imply southerly transport through the South Viking Graben. Genetic Sequences III & IV are interpreted to be dominated by debris flow and slurry flow deposits which are thought to have been sourced from the Fladen Ground Spur. The results of heavy mineral analysis (supplied to the study by the sponsor) supports these interpretations by identifying the Halibut Horst, East Shetland Platform, Fladen Ground Spur, Utsira High and Renee Ridge as potential sediment source areas. Difficulties in the sub-surface identification and correlation of stratal surfaces have been aided by detailed fieldwork in a sequence stratigraphically well constrained field analogue (Guadalupian Brushy Canyon Formation, Guadalupe Mountains, West Texas). This fieldwork identified and characterised major stratal surfaces and their variability with proximity to sandstone. Three sedimentary logs, with an equivalent spacing to wells within the Britannia area (i.e. 3.3 km) have been used to create a pseudo sub-surface correlation. The mis-interpretations and mis-correlations using this pseudo subsurface correlation have highlighted the lack of resolution at which sub-surface correlattions are made. These mis-interpretations may have important Implications for production and drilling strategies developed upon sequence stratigraphic interpretations. In particular the detailed retrogradational facies architecture of the Upper Brushy Canyon Formation cannot be resolved on the pseudo sub-surface correlations having implications for reservoir compartmentalisation. The generally applied sequence stratigraphic models for deep-marine sedimentation and the development of submarine fan models will be shown to be inapplicable to the Outer Moray Firth. This study has shown that the major controls on sedimentation within the study area were regional tectonism, which caused a fall in relative sea-level and is associated with a change to a more arid climate during the Barremian and Aptian times. Other controls include the sediment provenance, controlling the spatial distribution of sandstone sedimentation, differential compaction and the stability regime of the submarine slopes controlling the temporal distribution of sandstone sedimentation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available