Wave modelling and hydrodynamics : COLLINS J. I., 1976. Spec. Publs Soc. econ. Palaeont. Miner., Tulsa, 24: 54–68

Abstract

This paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern Canadian continental shelf. In order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found, and thereafter to relate the subsequent terminology to any diagnostic, generic characteristic identifiable from the records.Sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples. These latter features are identifiable adopting the classification of Dalrymple et al. (1978) which proves adequate for the acoustic differentiation of 2-D and 3-D types; though we observed a greater coherence in bedform spacing of the 2-D types than reported hitherto.Sand ridges were adequately defined and recognised using the description of Swift et al. (1978) with respect to storm-generated ridges and that of Off (1963) and others with respect to tidal-current ridges. Such ridges appear not to be uniquely described by ratios of their metrics.The bedforms on the southeastern Canadian continental shelf are abundant and wide-spread. Virtually all types of bedforms, recognisable on the U.S. shelf are present to the north. The majority of these bedforms appear to be storm generated and are considered intermittently active. Many of the sand waves (s.s.) have no measureable relief though retaining their distinctive spatial geometry.Both active and moribund sand ridges were found. Of these ridges both tidal- and storm-generated types were identified. The storm-generated ridges were further broken down into shoreface-connected ridges and offshore ridges.A metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height—length ratios provided the bedforms are active and fully developed. There is some overlap between megaripples and small sand waves and indeed between 2-D and 3-D megaripples, yet the distinction is good between sand waves and sand ridges (even moribund types). Sand ribbons in general can be confused with moribund sand waves and megaripples. A detailed morphological examination is required to distinguish each feature.Data from sand ridges of the eastern Canadian shelf, combined with data from similar features found globally, shows that ridge heights tend to cluster into three distinctive modes. These modes are at heights of 7, 13 and 27 m. The first mode is correlated with storm-generated ridges, the second with tidal-current ridges and the third possibly with submerged barrier islands.