Journal of the Graduate Research Center


Correlation is established on stratigraphic evidence in the Cretaceous lower Austin formation across Dallas County, Texas, using a particular bentonite bed approximately 8 inches thick. This bed is composed largely of the clay mineral, montmorillonite, along with subordinate amounts of illite and quartz. Montmorillonite occurs in adjacent calcareous beds, in place of illite, the more common clay mineral in the Austin formation. Therefore, an increase in montmorillonite content should indicate proximity to a bentonite bed. It is suggested that time-rock units may be established based on bentonite beds or upon intervals of high montmorillonite content in the limestone strata.

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