Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485747
Title: Architecture and sedimentology of submarine channel-levee systems: insights from the Upper Cretaceous Rosario Formation, Baja California, Mexico, and from laboratory experiments
Author: Kane, Ian Antony
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2007
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Abstract:
Submarine channel-levee systems are spectacular. geomorphological features extending down the continental slope and into the deep ocean basins. The evolution of channel-levee systems in relation to the flows which create them is particularly poorly understood, due to the inherent problems associated with direct monitoring. Additionally' previous lithofacies architecture models of submarine channel-levees, derived from seismic data, isolated core data and limited field studies currently have a limited resolution. Field observations of a submarine channel-levee complex within the Rosario Formation, Baja California, provide high resolution data of lithofacies and levee . depositional thickness decay along transects perpendicular to the channel axis. Within the levee, both sandstone thickness and the overall proportion of sandstone decrease away from the channel axis, in a channel-normal sense, according to a power-law.. Spatial variation in sedimentary structures away from the channel axis is also predictable and provides an important link to the depositional flow regime. The vertical succession within the levee indicates that the levee crest migrated outwards from the channel in response to increasing flow magnitudes and/or decreasing levee relief. Additionally, the spatial variation of ichnofacies within the levee is quantified and indicates a 'bioturbation front' which is indicative ofproximity to the channel. Intra-channel facies of the canyon confined portion of the· system include conglomerate scour fills and laterally amalgamated channel fills segregated vertically by overbank facies. Scours formed across previously 'quiet' areas, then coalesced into. what became the principal transport pathway. Scour fills can be traced laterally into thick sandstones which in tum pass laterally into a confined levee. Thin conglomerate bodies have a common facies association of matrix rich margins and a central wellsorted traction dominated deposit, these are interpreted as levees formed by frictionalfreezing at the margins of the flow. Axial parts of the channel fill are dominated by lateral accretion deposits indicating that these channels had a high degree of lateral mobility; this is also indicated by the rapid vertical alternation between thinly interbedded turbidites and thicker conglomerate packages. Laboratory modelling demonstrates that channel outer-bend sedimentation occurs from weakly confined flows, conversely more confined flows deposit at the inner bend; this may partly explain the spatio-temporal longevity of planform geometry commonly observed in submarine channels. The degree to which flows deposit overbank also relates to the degree of confinement, levee growth therefore reflects the degree of confinement. As levees increased in height their thickness along channel-normal profiles was increasingly well described by an exponential decay function. Additionally, sediment waves formed on the flanks of the levees, these commonly had intricate planform geometries which were found to relate to vortices which formed along channel margi~s due to the shear stress generated by faster moving and denser channelised flow. These vortices enlarge downstream and away from the channel as they decelerate across the overbank; in natural systems, vortex formation may explain the palaeocurrent swing which has been observed in both modem and ancient levee sandstones.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.485747  DOI: Not available
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