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Plate XII. Laminites, Standard Microfacies 19

(A) Laminated dolomite-lime mudstone without bioclasts. Planar, rather even-
bedded mm laminite from the evaporitic top of a Duperow (Devonian) cycle.
Lighter layers are cryptocrystalline dolomite and larger scattered white specks are
dolomite rhombs, 25 microns in size. Note the small scale truncation of laminae.
Close interlamination of lime mudstone and dolomite indicates the very delicate
control of dolomitization in the tidal flat environment. Such lamination may be
induced by algal mats although no evidence of stromatolitic doming is seen.
Quartz silt grains are commonly scattered along certain laminae. Such a microfa-
cies occurs interbedded with sabkha anhydrite in the upper part of a regressive,
fill-in, carbonate-evaporite cycle (see Chapter X). Sample is from the Duperow
Formation in the subsurface of the Williston Basin, Shell Northern Pacific Richey
No. 1 well, 8 916 ft. Thin section, x 9
(B) Laminated pelleted mudstone-wackestone. Sample K-l is from unit B, of
the typical Lofer cycle of A.G.Fischer (1964). See ChapterX and facies MF-8,
Chapter VIII. Laminae are only a mm or two thick. The coarser layers show
peloids. The fabric was originally porous. Note the internal micritic sediment in
the thin desiccation sheet-cracks (fenestral fabric) at the top and even in the tiny
calcite cemented holes in the lower laminae (root or small burrows). The large
calcite blotch in the lower right is probably a horizontal burrow. Dachsteinkalk
on the Kehlstein highway below entrance to Kehlsteinhaus (Eagle's Nest) above
Berchtesgaden, West Germany. Thin section, x 18