[Comment on “Tidal rhythm record disputed”]

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Abstract

J. Goguel's suggestion (Eos, 63(17)) that the cyclic lamination of the late Precambrian Elatina Formation (see cover of Eos, 63(A)) records tidal rhythms on a tidal flat cannot be sustained for several reasons. 1. The cyclic portion of the Elatina Formation is composed mostly of vertically graded laminae ranging from very fine sand through clay grade. Sedimentological study of the sequence and adjacent formations indicates a periglacial lacustrine environment of deposition for the cyclic rocks. The graded laminae are best attributed to deposition by density underflows or turbidity currents, which is the dominant mechanism of deposition in many glacial lakes today. The lack of scouring, cross lamination, and shallow-water indicators in the Precambrian cyclic rocks indicates deposition below wave base in relatively deep water. A tidal flat origin for the cyclic lamination therefore can be rejected.

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