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Title: The subsidence of sedimentary basins
Author: Turner, Jonathan David
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Theoretical models for the evolution of extensional sedimentary basins make a number of simple, testable predictions for subsidence behaviour. These are that active extension (the syn-rift) will generally be accompanied by rapid subsidence on the downthrown side of normal faults. Once faulting has ceased (the post-rift) the entire basin is predicted to subside at an exponentially decreasing rate, driven by the cooling and thickening of the lithosphere. The aim of this thesis is to determine the significance of second-order departures from this predicted subsidence. Three periods of North Sea subsidence appear to violate these simple predictions: anomalously slow Late Jurassic/Early Cretaceous subsidence, which marks the syn-rift/post-rift transition, and two periods of accelerated post-rift subsidence during the Early Paleogene and Plio-Quaternary. Subsidence data from over 300 boreholes from several basins with different rifting histories on the Northwest European continental plate have been analysed to determine the spatial and temporal distribution of these and other second-order subsidence anomalies. Uncertainties and errors in the observed subsidence calculations cannot explain the anomalous behaviour recognised. The periods of apparently anomalous subsidence are, instead, shown to be the result of geological or tectonic processes that modified either the subsidence history or record of subsidence of the basins studied. Apparent slow Late Jurassic/Early Cretaceous subsidence in the North Sea was the result of well siting and sediment starvation. Analysis of wells from the downthrown side of normal faults in several basins reveals an excellent correlation between rapid subsidence (often >1000m in 10My) and active extension (as documented from other sources of geological information). This was obscured by intense sediment starvation (sedimentation rates <20m/My) in the Central North Sea during Late Jurassic times which generated the apparent subsidence anomaly. Sedimentation rate maps reveal an expansion of the area of sediment starvation during late Jurassic times and into the Early Cretaceous. Cretaceous to Recent sedimentation patterns were then dominated by the interplay between the location and erosion history of extra-basinal sediment source areas and the remnant underfilled Jurassic rift topography.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available