HR: 1330h
AN: T22A-0499    [PDF]
TI: Syn-Rift Stratigraphic Architecture Reveals the Growth History of a Sub-basinal Fault Population in the Outer Moray Firth, North Sea
AU: * Kane, K
EM: k.kane@imperial.ac.uk
AF: Dept. Earth Science and Engineering, Imperial College, Prince Consort Rd., London, SW7 2BP United Kingdom
AU: Gupta, S
EM: s.gupta@imperial.ac.uk
AF: Dept. Earth Science and Engineering, Imperial College, Prince Consort Rd., London, SW7 2BP United Kingdom
AU: Trudgill, B
EM: btrudgill@mines.edu
AF: Dept. Geology and Geological Engineering, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401 United States
AU: Johnson, H
EM: h.d.johnson@imperial.ac.uk
AF: Dept. Earth Science and Engineering, Imperial College, Prince Consort Rd., London, SW7 2BP United Kingdom
AB: Processes of normal fault propagation and linkage are recorded in the stratigraphic record by syn-rift sedimentary deposits that fill the generated accommodation volume. Using 3D seismic stratigraphic analysis, supported by well log and core interpretation, we investigate how the growth of an intrabasinal fault population led to the progressive development of an extensional sub-basin in the Moray Firth rift arm of the North Sea. The North Halibut Graben sub-basin has an E-W to WNW-ESE orientation and formed through the interaction of two main structural trends during late Jurassic rifting. E-W trending structural barriers bound the sub-basin to the north (Tartan and Petronella Ridges) and south (Halibut Horst Spur) whilst major NE-SW trending structures occur at the eastern margin. Spatial and temporal changes in syn-rift stratigraphic architecture reflect the history of faulting within the North Halibut Graben sub-basin. Fault parallel seismic profiles and intra-syn rift isochron maps demonstrate how faults initially developed as separate segments and subsequently linked to form longer strands through progressive growth and propagation. They also provide clear evidence that a major change in the structural framework occurred during rifting, supporting earlier studies advocating sequential rather than synchronous normal fault activity. The syn-rift sequence can be divided into at least two phases based on shifts in sedimentary packages and reorganistation of sequence thicknesses. Isochron maps illustrate that from late Oxfordian times (syn-rift phase I), early syn-rift sedimentation was controlled solely by NE-SW trending faults at the eastern margin of the basin. Strain was initially accommodated across several distributed, highly segmented faults but, with progressive linkage, stress became localised on one or two major through-going fault strands whilst shorter surrounding segments were switched off. From early-mid Volgian times we observe a progressive switch of extensional activity from NE-SW trending faults to newly generated E-W trending structures that suggests a rotation of the prevailing stress field. The syn-rift phase II isochron map (early-mid Volgian - Base Cretaceous) demonstrates how the linearly focused, NE-SW oriented thick deposited during syn-rift phase I is succeeded by a more distributed E-W trending depocentre. A detailed study of the depositional patterns of the Claymore Sandstone Member, a late Kimmeridgian to mid-Volgian syn-rift turbidite lobe system, reveals that migratory changes in dispersal patterns can be directly related to the structurally controlled modifications in basin-floor topography. Observations of turbidite distribution through time comply with and further enhance the model of structural reconfiguration developed through seismic analysis. Subtle changes in depocentre location and facies distribution document segmentation and linkage along individual fault strands. Our observations indicate that the growth history of a normal fault population can be reconstructed through the analysis of depositional systems of the syn-rift sequence. Lateral shifts in depocentre location, changes in thickness of sedimentary deposits, and facies transitions reflect propagation and linkage along individual fault arrays and, more significantly, the switch of activity from one fault set to another.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 8164 Stresses--crust and lithosphere
DE: 9335 Europe
SC: Tectonophysics [T]
MN: 2003 Fall Meeting