Cristina Solla¹, Alexander L Densmore¹

(1) Trinity College Dublin, Dublin, Ireland

ABSTRACT: Flexural Modelling of the Rockall Trough and Northwestern Ireland

Thermochronologic and geologic data from northwestern Ireland reveal significant (~1-2 km) onshore Cenozoic denudation. Geomorphological observations, including fluvial knickpoints, are consistent with Cenozoic displacements on several northeast-striking faults. Up to three km of Cenozoic sediments have been deposited in the northeastern Rockall Trough, a major Mesozoic(?) and Cenozoic basin along the European continental margin. The Trough is underlain by stretched continental crust with variable thickness and flexural rigidity. Here we test the hypothesis that Cenozoic deposition in the Rockall Trough has driven flexural rock uplift and onshore denudation.

Using 2-D seismic reflection data, we mapped five regional Tertiary unconformities across the northern Rockall Trough. Age constraints are based on nannoplankton evidence from BGS boreholes. Evidence for prograding early Eocene fans suggests a relative shallowing event near the end of the Palaeocene. Eocene sediments decrease in thickness from north to south. The late Eocene unconformity represents a major deepening event in which much of the present deep water depths were achieved. Faults with normal and strike-slip displacements were active through the late Eocene.

We model the effects of sediment loading on the continental margin by assuming an elastic lithosphere overlying a viscous fluid. Sediment isopachs derived from our unconformity mapping are applied as loads to a model lithosphere. We evaluate both 1-D and 2-D deflection models, with particular emphasis on the predicted onshore flexural response. Model results will be compared with existing thermochronologic data to assess the role of flexure in the evolution of the margin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado