Abstract - The geometry and evolution of vertically segmented
normal faults, with dip separations of ca 11.5m have been studied in a
coastal outcrop of finely bedded Cretaceous chalk at Flamborough Head,
U.K. Fault trace segments are offset across both compressional and extensional
offsets which have step, overlap or bend geometries. The location of fault
offsets is strongly controlled by lithology occurring at either thin (ca
1mm-8cm) and mechanically weak marl layers or partings between chalk units.
Fault segmentation occurs during either fault nucleation within, or propagation
through, the strongly anisotropic lithological sequence. An inverse relationship
between fault displacement and number of offsets per unit length of fault
reflects the progressive destruction of offsets during fault growth. The
preservation potential of fault offsets is therefore dependent on offset
width and fault displacement. Fault rock, comprising gouge and chalk breccia,
may vary in thickness by 1.5-2.0 orders of magnitude on individual fault
traces. Strongly heterogeneous fault rock distributions are most common
on small faults (<10cm displacement) and are produced mainly by destruction
of fault offsets. Shearing of fault rock with increasing displacement gives
rise to a more homogeneous distribution on large faults at the outcrop
scale.
Journal of Structural Geology 18, 1389-1397, 1996.