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 Manedalen Fault Zon e on Traill O, East Greenland, reveals how diagenetic carbonate cement affe cts the deformational behaviour of sandstones. A siliciclastic sequence of beds (similar or equal to 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) Po rous sandstones with little carbonate cement, (2) low-porosity sandstones r ich 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. Viewed in a microscope, porous sandstones show disaggregated zones with por osity reduced by 40-60%, and cataclastic bands. The development of groups o f cataclastic bands was governed by strain-hardening. The low-porous sandst ones show cataclastic bands with minor textural change towards the bands. T he 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 o r equal to D, appear to follow linear trends. The least-square regression m ethod gives the following values for the power-law exponent; C = 1.01 for 9 93 faults in the porous sandstones, C = 0.70 for 457 faults in carbonate-ce mented sandstones, and C = 0.38 for 166 faults in the carbonate-cemented sa ndstones 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 enco untered along the traverses. Thus, the lithological heterogeneity arising f rom local calcite precipitation is thought to be the cause for the differen ces in deformational style and scaling behaviour. (C) 1999 Elsevier Science Ltd. All rights reserved.