Architecture, deformation style and petrophysical properties of growth fault systems: the Late Triassic deltaic succession of southern Edgeøya (East Svalbard)
K. Ogata, M.J. Mulrooney, A. Braathen, H. Maher, P.T. Osmundsen, I. Anell, A.A. Smyrak-Sikora and F. Balsamo
Journal name: Basin Research
Issue: Vol 30, No 5, October 2018 pp. 1042 - 1073
Info: Article, PDF ( 29.4Mb )
The Late Triassic outcrops on southern Edgeøya, East Svalbard, allow a multiscale study of syn-sedimentary listric growth faults located in the prodelta region of a regional prograding system. At least three hierarchical orders of growth faults have been recognized, each showing different deformation mechanisms, styles and stratigraphic locations of the associated detachment interval. The faults, characterized by mutually influencing deformation envelopes over space-time, generally show SW- to SE-dipping directions, indicating a counter-regional trend with respect to the inferred W-NW directed progradation of the associated delta system. The down-dip movement is accommodated by polyphase deformation, with the different fault architectural elements recording a time-dependent transition from fluidal-hydroplastic to ductile-brittle deformation, which is also conceptually scale-dependent, from the smaller- (3rd order) to the larger-scale (1st order) end-member faults respectively. A shift from distributed strain to strain localization towards the fault cores is observed at the meso to microscale (<1 mm), and in the variation in petrophysical parameters of the litho-structural facies across and along the fault envelope, with bulk porosity, density, pore size and microcrack intensity varying accordingly to deformation and reworking intensity of inherited structural fabrics. The second- and third-order listric fault nucleation points appear to be located above blind fault tip-related monoclines involving cemented organic shales. Close to planar, through-going, first-order faults cut across this boundary, eventually connecting with other favourable lower-hierarchy fault to create seismic- scale fault zones similar to those imaged in the nearby offshore areas. The inferred large-scale driving mechanisms for the first-order faults are related to the combined effect of tectonic reactivation of deeper Palaeozoic structures in a far field stress regime due to the Uralide orogeny, and differential compaction associated with increased sand sedimentary input in a fine-grained, water-saturated, low-accommodation, prodeltaic depositional environment. In synergy to this large-scale picture, small-scale causative factors favouring second- and third-order faulting seem to be related to mechanicalrheological instabilities related to localized shallow diagenesis and liquidization fronts.