Page 105 - Carbonate Facies in Geologic History

92 Outline of Carbonate Petrography

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C, • TOP OF CYCLE I
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B
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SAND AND SILT PRESENT IN THESE DOLOMITES t., .
0- 8 --Pia, +·C.
Fig. III -4. Areas of strongest gamma ray deflections and sand-silt distribution in several evapo-
rative dolomites in tops of cycles of lower Duperow Formation of Williston basin, Montana,
North Dakota, and Saskatchewan. The markers C 2 , P l , P 2 , and B are very thin, silty zones in
gray-green dolomite micrite associated with anhydrites. Patterns plus occurrence of sands
indicates source of fine terrigenous (wind-blown?) material to south. From Wilson (1967b,
Fig. 13). See also Chapter X for discussion and maps of Duperow beds

land areas east of the Ordovician Appalachian geosyncline and winds from the
northeast low-latitude trades of Ordovician time distributed ash as far west as
Ohio. Bentonites have been used in subsurface correlations within Middle
Permian (Word) strata in the San Andres Formation in west Texas, east of the
Central Basin platform. Bentonites are also recognized in Upper Cretaceous
(Senonian) strata in the Boquillas and San Felipe formations of West Texas and
northern Mexico. The even thin-bedding, sharp segregation of carbonate and