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 "younging upwards") 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. Unconformities - Clear angular unconformities provide unequivocal evidence of the relative age of two rock sequences. Cross-bedding (aka Cross-stratification) - These structures are common in rocks laid down by the action of wind or water currents and in some volcaniclastic rocks. Minor erosional events during the overall deposition give rise to small-scale angular unconformities. There are three ways a cross bed can be used: Troughs of trough cross beds, in which the concave part of the trough points up. The tangential (end) part of the cross bed is always on the bottom of the cross bed. Many cross beds are stacked, and truncation always happens up section. Graded bedding - In certain types of clastic sedimentary rock, the grain or clast size varies systematically from the base of the bed to its top. In a normally graded bed the grain or clast size is largest at the base and the bed is said to fine upwards. Beds deposited by density underflows such as turbidites typically show normal grading.