Determination of slip sense along a fault in an unlithified sediment

It is usually difficult to measure slip sense along a fault in unlithified sediments due to the lack of mesoscopic indicators such as slickenlines. In this paper, scanning electron microscope (SEM) images of fault surfaces in mudstone at the sandstone-mudstone contacts are used for measuring the mic roscopic slickenlines formed by the scratching of sand grains. The lineatio ns are subparallel to the presumed slip direction deduced from a conjugate fault set. Therefore, even in the case of no mesoscopic slickenlines, a mic roscopic scratching by a sand grain on the fault surface where sandstone an d mudstone are juxtaposed by the fault is useful as an indicator of slip se nse along a fault in sediments lithified subsequent to faulting. (C) 2000 P ublished by Elsevier Science Ltd. All rights reserved.