Walther's law of correlation of facies can be illustrated by the facies associations of the Castile Formation (Upper Permian) in the Delaware basin of Texas and New Mexico. Two major stratigraphic successions are represented by two lithofacies composed of calcite-anhydrite laminations in the western part of the basin intercalated with carbonate-laminated, anhydrite-halite bands in the eastern two-thirds of the basin. Organically rich layers are common to all the laminae types. The laminations were formed simultaneously over a large area of the basin at a relatively constant rate. The alternating laminae of the two components forming side by side in the two lithotopes (areas of uniform deposition) are interpreted as representing an annual layer of sedimentation, a varve. T e lateral and vertical persistence of the varves provides the best model of rock correlation where time lines are well established by applying statistical-correlation techniques to stratigraphically correlated laminations. All the primary characteristics of the two lithofacies--their gross appearance, sonic and electric-log properties, trace-element contents, petrologic variations, and component associations--are significant in determining the depositional environment of the Delaware basin.

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