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Microstylolites are fine dissolution surfaces, with a relief of only 20-40 microns, on which a thin film of silicic-clastic clay and platy silt is concentrated. They commonly form in slightly shaly limestone during secondary (overburden) compaction. Two causes appear to inhibit microstylolite growth: the film concentrate of clay and silt chokes the dissolution surface as a pathway for fluid migration, and acts as a glide plane to relieve stress along the surface.
Microstylolites can accentuate or distort primary sedimentary structures and appear to control the pattern of dolomitization. 1. They commonly accentuate stromatolitic or ripple laminations and outline limestone intraclasts. 2. Thinly-bedded, knobbly, nodular, lumpy, braided or boudinage limestones, characteristic of Paleozoic platform carbonates, appear to result from a microstylolitic induced distortion of originally thin, continuous beds of slightly shaly, pelleted lime muds interbedded with limy (now dolomitic) shale. "Swarms" of subhorizontal, interconnected microstylolites are present throughout both the dolomitic shale interbeds and the dolomitic areas between limestone knobbles. Thin swarms penetrate the sides of limestone knobbles, cutting off clots of limestone. The areas be ween adjacent knobbles have undergone 20-80% solution thinning, with tension fracturing of the brittle limestone knobbles and flowage along microstylolite surfaces into the area between knobbles. Overburden compaction with microstylolitic dissolution and flowage explains the knobbly bedding. 3. Zoned dolomite rhombs (less than 60 microns) are present in intimate association with microstylolites. In knobbly limestones these rhombs are much coarser than unzoned rhombs scattered throughout the limestone, and are so abundant that they cannot be explained as a simple stylolite solution concentration. Rather, some attribute of the microstylolites, i.e., permeability-controlled fluid migration, composition of concentrate, or differential pressure, provided preferential conditions for dolomitiza ion. Much of the fine-scale, primary or stratigraphic dolomite appears to be a product of preferential dolomitization along microstylolites.
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