Effects of lithology on geometry and scaling of small faults in Triassic sandstones, East Greenland

A study of the Lower Triassic sandstones exposed in the Månedalen Fault Zone on Traill Ö, East Greenland, reveals how diagenetic carbonate cement affects the deformational behaviour of sandstones. A siliciclastic sequence of beds (≂300 m thick) is variably cemented because of the precipitation of carbonate close to stromatolitic interbeds. Displacements or throws of minor faults (<1.8 m) were sampled along lines through damage zones of major faults (throws >9 m) in three different lithologies: (1) Porous sandstones with little carbonate cement, (2) low-porosity sandstones rich in carbonate cement, and (3) thin beds of carbonate-cemented sandstone in mudstone. The latter shows a strong anisotropy causing fault refraction with syn-kinematic calcite growth in the sandstone beds. in a microscope, porous sandstones show disaggregated zones with porosity reduced by 40–60%, and cataclastic bands. The development of groups of cataclastic bands was governed by strain-hardening. The low-porous sandstones show cataclastic bands with minor textural change towards the bands. The apparent strength of these sandstones suggests that strain-hardening was much less significant for the development of the faults. Logarithmic plots of N vs D, where N is the cumulative number of faults with throw greater or equal to D, appear to follow linear trends. The least-square regression method gives the following values for the power-law exponent; C=1.01 for 993 faults in the porous sandstones, C=0.70 for 457 faults in carbonate-cemented sandstones, and C=0.38 for 166 faults in the carbonate-cemented sandstones interbedded with mudstones. The estimated confidence intervals for C indicate a true difference in scaling relationships of the samples. The different scaling relationships cannot be linked to strain differences encountered along the traverses. Thus, the lithological heterogeneity arising from local calcite precipitation is thought to be the cause for the differences in deformational style and scaling behaviour.