ty, a property that causes small megaripple undulations to grow with time. The origin of the instability is due to variations in megaripple height, which do not diminish over time, as well as to the inverse dependence of ripple drift velocity on height. Thus, the taller regions of ripples will move more slowly than the adjacent, shorter portions, an outcome that promotes further perturbation growth. Hezi Yizhaq of Ben-Gurion University of the Negev and colleagues provide an example, based on field work, of the transverse instability of megaripples. The instability growth rate depends on the difference between the heights of the different segments of the megaripple. Their results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples.
Vertical injectites of detachment carbonate ultracataclasite at White Mountain, Heart Mountain detachment, Wyoming
John P. Craddock et al., Geology Dept., Macalester College, St. Paul, Minnesota 55105, USA. Posted online 19 Mar. 2012; doi: 10.1130/G32734.1.
Carbonate ultracataclasite (CUC) is found as a veneer along the bedding plane portion of the Eocene Heart Mountain detachment (Wyoming, United States). At White Mountain, where the CUC is thickest, John P. Craddock of Macalester College (Minnesota) and colleagues report the discovery of six dikes, as much as 1 m wide, that were intruded vertically ~120 m from the detachment into the overlying Madison and Bighorn Formations.
World's largest extrusive body of sand?
Helge Lseth et al., Statoil Research Centre, Trondheim, Norway. Posted online 19 Mar. 2012; doi: 10.1130/G33117.1.
Using 3-D seismic and well data from the northern North Sea, Helge Lseth of the Statoil Research Center (Trondheim, Norway) and colleagues describe a large (10 cubic kilometers) body of sand and interpret it as extrusive. The authors note that to their kPage: 1 2 3 4 5 6 7 8 9 Related biology news :1
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