User:NikelsenH/Cyclicity

In geology, cycles are hierarchically ordered time spans that can be either descriptive or contain an interpretive component regarding the source that generated the cycle. Commonly these sources are taken to be plate tectonics, Milankovitch cycles or a combination of both.

The longest cycles is commonly called the first order cycle, which is followed by the shorter second order cycle, followed by the third order cycle, fourth order cycle and fifth order cycle.

Definitions of these cycles vary between different authors, therefore it is important to make sure which concept is used in a given sitting. The concept of cyclicity has been criticized to be an arbitrary subdivision of a continuous spectrum that cannot be found in empirical evidence.WILKINSON 1996

Descriptive Approach
n a descriptive approach, the order of the cycles are used to describe the duration of the periodicity:
 * A first order cycle corresponds to sequences of 100 to 1000 ma duration
 * A second order cycle corresponds to sequences of 10 to 100 ma duration
 * A third order cycle corresponds to sequences of 1 to 10 ma duration
 * A fourth order cycle corresponds to sequences of 0.1 to 1 ma duration
 * A fourth order cycle corresponds to sequences of 0.01 to 1 ma duration

Genetic approach
In a genetic approach, the cycles are connected to external influences, which can for example be plate tectonics or Milankovitch cycles

one approach: : catuneanu 2006 74 mid-oceaan ridge
 * A first order cycle spans from 200 to 400 ma duration and is generated by the breakup of supercontinents
 * A second order cycle spans form 100 to 200 ma duration and is generated by Volume changes in
 * A third order cycle spans form 1 to 10 ma duration and is generated by regional plate tectonices

milankovich cyclicity: