期刊
GEOLOGY
卷 34, 期 12, 页码 1073-1076出版社
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G22930A.1
关键词
shallow marine; combined flow; bed forms; hummocky cross-stratification; swaley cross-stratification
类别
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 (similar to 8-10 s) and moderate oscillatory velocities (U-o similar to 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.
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