Way up structure

A way up structure, way up criterion, or geopetal indicator is a characteristic relationship observed in a sedimentary or volcanic rock, or sequence of rocks, that makes it possible to determine whether they are the right way up (i.e. in the attitude in which they were originally deposited, also known as "stratigraphic up") or have been overturned by subsequent deformation. This technique is particularly important in areas affected by thrusting and where there is a lack of other indications of the relative ages of beds within the sequence, such as in the Precambrian where fossils are rare.

The original definition comes from Bruno Sander in 1936, translated from German to English in 1951, which states:

Geopetal Fabrics - All the widely distributed spatial characters of a fabric that enable us to determine what was the relation of "top" to "bottom" at the time when the rock was formed are termed geopetal fabrics. Such fabrics are mechanical and chemical internal deposition; grains on a boundary surface; cross-bedding, etc.

In general, geopetal seems to be used in the U.S., while way up structure is used in the UK. "Geopetal structure", in some circles, is used exclusively for the void fill example, and nothing else. Some geologists use neither term, and might use something else, like topping indicator.

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