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1 September 2006 Bimodal Cross-Lamination in Wave-Ripple Form Sets: A Possible Origin
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Wave-ripple cross-lamination formed in a sandy lacustrine shoreface in the Canadian Great Lakes is characterized by (i) small, randomly superimposed sets of angle-of-repose cross lamination, with strongly bimodal dips; (ii) small, superimposed sets of angle-of-repose cross-lamination, where the thickest and most prevalent sets have onshore dips, and the thinner, subsidiary sets dip offshore. (iii) small, superimposed sets of angle-of-repose cross-lamination, with near unimodal landward dips; (iv) supercritical, sinusoidal lamination indicative of high rates of ripple climb. Preserved surface ripples frequently reveal form discordant internal structures with a set of landward-dipping cross-lamination superimposed on a lakeward-dipping unit, both within a near-symmetrical ripple form. The origin of this internal lamination is discussed in the context of the second-order theory proposed for mass transport in turbulent wave boundary layers. The characteristic increase and subsequent decrease in wave period generated during storms in this fetch-restricted environment leads to an offshore mass transport in the wave boundary layer at the height of the storm and an onshore flow as the storm decays. This would lead to a reversal in ripple migration and the possibility of generating the discordant formsets.

Brian Greenwood "Bimodal Cross-Lamination in Wave-Ripple Form Sets: A Possible Origin," Journal of Coastal Research 2006(225), 1220-1229, (1 September 2006).
Received: 12 January 2006; Accepted: 12 January 2006; Published: 1 September 2006

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