The formation and growth of pressure solution seams in clastic rocks: A field and analytical study

Pressure solution seams (PSSs) are closing mode structures of localised dissolution resulting in a volume reduction. We present new observations constraining the processes by which PSSs initiate and grow in low porosity clastic rocks from southern Ireland. PSSs initiate as inter-granular PSSs at quartz grain to grain contacts. As quartz dissolves, clay remains as a residue along the contacts as well as filling the adjacent pores to form incipient PSSs involving multiple grain boundaries. Further lengthening and thickening occurs by lateral linkage and transverse coalescence of neighbouring segments of incipient PSSs. Multiple PSS segments are observed to concentrate in thin tabular zones that appear as single macroscopic PSSs visible in hand samples. Published numerical modelling results show the ability of both lateral and transverse growth of PSSs due to the presence of asperities on their flanks, which confirm our interpretations based on our laboratory and field observations.

► We use field and microanalytical techniques to describe PSSs in clastic rocks.
► Many microscopic incipient PSSs localise in zones to form macroscopic PSSs.
► PSS growth occurs by lateral and transverse linkage of neighbouring segments.
► Asperities on PSS flanks concentrate stresses to make transverse growth possible.