In her recent paper on Gulf Coast shales, Capuano (1993, p. 1303) states that shales in the deep subsurface “… could support flow comparable to that in the sandstones.” A growing body of evidence—petrographic, mineralogic, and geochemical—supports the idea that, indeed, chemical modification in shales requires fluid-mediated material transport in amounts that challenge conventional notions about fluid flow in subsurface shales. Flow through microfractured shales potentially explains the large volumes of water involved in the quartz cementation of sandstones (Land, 1984), loss of potassium from sandstones as K-feldspars dissolve (Milliken et al., 1989), and...

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