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Extensive roadcuts on U.S. Highway 90 in the vicinity of Langtry in west Texas display superb exposures of well-bedded chalky limestones comprising the lowest 27 m (89 ft) of the Austin Chalk equivalent. The limestone occurs as highly persistent beds averaging about 40 cm (15 in.) thick and separated by shale partings averaging 2-3 cm (about 1 in.). Limestone-shale contacts are very sharp. Nannoplankton indicate a Turonian to Santonian age and an outer shelf source; sedimentary features suggest redeposition by moderately low-density turbidity currents in a midfan setting characterized by distinctive distributary channels with channel-mouth bars and levees.
The informal term "Langtry formation" is applied to these strata, which flank shallower water platform facies to the east, north, and west (Austin Chalk and San Vicente Member of the Boquillas Formation), and pass into basinal limestones of the San Felipe Formation in the La Mula basin to the south.
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