Page 328 - Carbonate Facies in Geologic History

The Stratigraphy of Dolomite 315

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Fig.X-21. Dolomite and limestone facies of the Red River (Ordovician) Formation, Williston
basin. Isopach lines in feet. Coarse dot pattern marks 100% dolomite; fine dots 50-100%
dolomite, and brick pattern mostly limestone. Center of basin indicated by closed 600 and
700 foot contours and by heavy line which encloses discrete anhydrite beds in upper part of
formation. The wide shelf peripheral to the basin is preferentially dolomitized; the formation
is termed the Big Horn or Whitewood Dolomite south and west of the basin. Heavy black
areas mark petroleum accumulations

(Alling and Briggs, 1961, Fig. 10), the Gatesburg-Conococheague facies from the
Adirondack axis into the Appalachian miogeosyncline (Wilson, 1952, p.319,
Fig. 4), the Shuaiba limestone at the top of the Thamama Group around the
fringes of its outcrop on the Arabian Shield, the Jurassic Arab Formation of the
Persian Gulf (Chapter IX) and the Edwards Formation of the Comanche platform
and San Marcos arch, central Texas (Fisher and Rodda, 1969, Fig. 7; Rose, 1972,
p. 57, 58). Berry and Boucot (1971) demonstrated that regionally North American
Silurian limestone surrounds the shelf area of the craton whose Silurian strata are
almost totally dolomitized. The Late Jurassic Gigas beds of the north German
subsurface were laid down along a narrow shelf south of the Pompeckj high and
were thoroughly dolomitized shortly after deposition. They pass southwards into
limestone of the Maim evaporite basin under the north German plain (Schmidt,
1965, p. 136, Fig. 12). Many other examples could be cited. In most of those noted
above, strata representing evaporite or carbonate tidal flat lagoons with restricted
circulation occur in the upper parts of the units.
l-Wzer-e cyclic sequences possess an anhydrite member, dolomite may be closely
associated in vertical or lateral sequence: Accepting the idea of downward reflux of
brines from evaporitic sabkha surfaces, one would expect that carbonates imme-
diately below the evaporite members of cycles would be the more thoroughly