THREE-DIMENSIONAL GEOMETRY OF GROWTH FAULTS DETERMINED FROM FLUME EXPERIMENTS

Growth faults are common in many sedimentary environments, particularly on passive margins. A series of growth faults were analyzed that formed in a large experimental flume (“Jurassic tank”) located in Saint Anthony Falls Hydraulic lab at the University of Minnesota. The growth faults are normal faults, with offset determined from the stratigraphy preserved in the flume. The growth faults step basinward in time and have a concave-up shape in cross-section. There are two sets of growth faults in the model, the earliest of which occurs during a rise in water level. The second sets occur during equilibrium conditions (no drop in the basin floor or rise in water level). We focused on the youngest (highest) of these growth faults systems, because of their simple geometry and clear view of depositional history.

Two-dimensional cross sections were taken approximately every 2.5 cm, which allow us to recreate the three-dimensional geometry of these growth fault systems. The three-dimensional visualization was done using Geoprobe volume interpretation software, which exhibits two geometric relations not observed in cross-section. First, the three-dimensional visualization indicates that the fault surfaces contain corrugations that are elongate in the movement direction of the fault (down-dip). The corrugations are not an artifact of the software, as non-growth faults in the flume do not show these features. Second, the growth faults are long and continuous, although locally smaller faults splay off the larger faults. The splay faults show an asymmetry with respect to the main channel of sediment input: Faults splay basinward away from the sediment channel. The results of these experiments are then compared to geological and geophysical observations of growth faults.