Extending layers

When planar layers or linear objects are extended along their lengths they can break or neck. This can create a characteristic segmented outcrop pattern, rather like strung-out links of sausage. And this gives these segments their name - boudins (after the French blood-sausage) and the process is called boudinage. Under this section you can see some examples. Pencil-like fossils called belemnites are commonly extended in the Alps - there's an example here. The white material between the dark segments of the once-continuous fossil is newly precipitated calcite. The other image shows a boudinaged amphibolite dyke embedded in gniesses. In all cases it is the strong material that breaks (or boudinages) with the less strong (lower viscosity) material flowing around.

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