CGRG Bibliography of Canadian Geomorphology
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Author : Dumas, S.; and Arnott,R.W.C.
Date : 2006.
Title : Origin of hummocky and swaley cross-stratification— The controlling influence of unidirectional current strength and aggradation rate.
Publication : Geology
Issue : 34(12):
Page(s) : 1073-1076.
Abstract
A series of wave-tunnel experiments was conducted to investigate the conditions under which hummocky and swaley cross-stratification form. Isotropic 3-dimensional (3-D) hummocky bed forms were generated under long wave periods (8–10 s) and moderate oscillatory velocities (Uo 50–90 cm/s) with very weak (< 5 cm/s) to no unidirectional flow. Hummocks became anisotropic with the addition of only a small unidirectional current (5–10 cm/s), and began to resemble unidirectional dunes when the unidirectional current was increased above 10 cm/s. Synthetic aggradation of the hummocky bed forms at high (4.2 mm/min) and low (1 mm/min) rates generated stratification resembling hummocky and swaley cross-stratification, respectively. Based on these findings, we suggest that hummocky cross-stratification optimally forms above (but near) storm wave base where aggradation rates during storms are high enough to preserve hummocks but unidirectional current speeds are sufficiently low to generate low-angle, isotropic cross-stratification. Swaley cross-stratification is also hypothesized to be deposited by an aggrading hummocky bed between fair-weather and storm wave base, but in shallower water where aggradation rates are low enough to cause preferential preservation of swales.
Bibliography of Canadian Geomorphology