The Clayton sands, thin discontinuous sand bodies found at or near the Cretaceous-Tertiary (K-T) boundary at various sites in Alabama, previously have been attributed to (1) catastrophic tsunami deposition associated with a K-T boundary impact or, alternatively, (2) noncatastrophic transgressive infilling of incised valleys cut during a preceding sea-level low-stand. New observations on the geometry and ichnosedimentologic character of a Clayton sand body, enveloping strata, and associated bounding surfaces exposed along Mussel Creek (central Alabama) refute the tsunami origin and support the latter mechanism. Studies of other boundary deposits in the gulf region, which may similarly benefit from ichnofossil investigations, should consider more rigorously the evidence for sea-level change near the K-T transition.

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