NUMERICAL ESTIMATES OF ANCIENT WAVES, WATER DEPTH AND FETCH

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Abstract
A series of carefully controlled marine experiments, in which sand of known grain diameter and essentially perfect sorting was exposed to waves of various sizes, was supplemented by study of lakes of various widths (and hence differing values for fetch), in an effort to obtain relationships between parameters measurable in sedimentary rocks (i.e., ripple‐mark spacing) and paleogeo‐graphic information (water depth, wave height, wave length, and fetch). The results were subjected to regression analysis.Two equations were obtained, relating ripple‐mark spacing to grain size, water wavelength and water depth, with predictive abilities higher than 80%. Two equations were obtained, relating ripple‐mark spacing to grain size, water wave‐height and water depth, with a predictive ability of 75%‐80%. Two useful equations involved water wave‐length, and two involved water wave‐height; in general those based on water wave‐length were superior to those based on water wave‐height.In shallow‐water work, the pairs of values which can be obtained from equations included in this paper are highly limited in range, and thus define the paleogeographic unknowns reasonably closely. These pairs (or single values, as may be appropriate) can be inserted into three additional equations, which relate fetch to various wave parameters.An application is made to Jurassic rocks (lower Morrison sandstones) in northern New Mexico, which are interpreted as deposits of a large, shallow lake. Shorelines, where they cannot be located by inspection of the rocks, can be inferred fairly closely from the fetch data.

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