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Geometry, architecture and the erosive nature of mass-transport deposits in deep-marine environments: Ainsa Basin (Pyrenees) and Buzzard Field (North Sea)

Dakin, NC; (2016) Geometry, architecture and the erosive nature of mass-transport deposits in deep-marine environments: Ainsa Basin (Pyrenees) and Buzzard Field (North Sea). Doctoral thesis , UCL (University College London). Green open access

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Abstract

Muddy mass-transport deposits (MTDs) and complexes (MTCs) form a significant component of the stratigraphic record in modern and ancient deep-water basins worldwide. This study evaluates the sedimentary characteristics and architecture of such deposits from ancient deep-marine submarine fans and related deposits in the Middle-Eocene Ainsa Basin, Spanish Pyrenees and the Late Jurassic Buzzard Field, North Sea. Outcrop measurements and descriptions have provided quantitative and semi-quantitative analyses to investigate the spatial and temporal distribution of these chaotic deposits across the Ainsa Basin, culminating in a new mass-transport classification scheme. Outcrops have provided important insights into mass-wasting processes, including the erosive nature at the base of cohesive flows, where associated erosive mechanisms are documented in the rock-record. Thin-section analyses of such erosive deposits show ‘grading’ of cohesive-flow deposits, interpreted as debris flows and concentrated density flows that entrained loosely consolidated sands on the seafloor. In some cases, deposits incorporate the compositional signature of the eroded sandy sediment gravity flow (SGF) deposit. Larger erosive features (megascours ~ 1 km width), formed from multiple mass-wasting events, are identified at outcrop to dramatically impact basin stratigraphy. MTDs appear to have been most erosive when they encountered changes in gradient, or when they accelerated and/or travelled at high velocity with high shear stresses, such as in a proximal submarine setting. The implications of erosive-flow processes are important for the degradation of sandstone reservoirs and the potential formation of mud-filled channels. Core images and wireline data from the Buzzard Field formed the basis of a sedimentological interpretation of the hydrocarbon field, leading to an improved understanding of thickness variability across the field. Comparisons of the Buzzard and Ainsa basins suggest that regional and local tectonics played an important part in causing sediment instability on the basin slopes, and contributed to the abrupt termination of sand deposition in the basin. Variable scales of mass-failure are considered as part of this study. Geometrical relationships of global deposits, and those documented in this research are compared. Results show outcrop measurements capture small-scale heterogeneities not observed in seismic datasets. Outcrop MTC dimensions (multiple stacked chaotic deposits) provide better parametres when scaling to seismicscale analogues, such as for the Buzzard Field.

Type: Thesis (Doctoral)
Title: Geometry, architecture and the erosive nature of mass-transport deposits in deep-marine environments: Ainsa Basin (Pyrenees) and Buzzard Field (North Sea)
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Third party copyright material has been removed from ethesis.
Keywords: MTDs, MTCs, basal erosion of debris-flow, geometry, architecture
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1485759
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