ABSTRACT

Extensive roadcuts on US Highway 90 in the vicinity of Langtry, West Texas, display superb exposures of well bedded chalky limestones comprising the lowest 27 m (89 ft) of the Austin Chalk equivalent. The limestones occur as highly persistent beds averaging about 40 cm (15 in.) thickness and separated by shale partings averaging 2 or 3 cm (about one 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 mid-fan setting characterized by distinctive distributary channels with channel-mouth bars and levees.

The informal name "Langtry formation" (informal terminology requires this) is applied to these strata, which flank shallower-water platform facies to the east, north and west (Austin Chalk and San Vicente Member of Boquillas Formation) and pass into basinal limestones of the San Felipe Formation in the La Mula Basin to the south.