The hierarchy of cycles described herein is genetic in the sense that each rank in the hierarchy is related to a specific stratigraphic process (Fig. 6   The Genetic Hierarchy.ppt).  In particular, as described above, 4th, 5th and 6th order cycles (or sequences) are each related to a particular orbital forcing process involving the interplay of precession and eccentricity. Second and 3rd order sequences follow from the usage of Seismic and Sequence Stratigraphy in which the fundamental unit of Sequence Stratigraphy is the ‘3rd order sequence’ (a genetically related set of strata bounded by unconformities and their correlative conformities, Van Wagoner, et al., 1988). Although ‘sequences’ are not defined in terms of duration, in practice 3rd order sequences tend toward 2 ma in duration and 2nd order (b), supersequences, tend toward 10 ma in duration. The 4th, 5th and 6th order ranks used in this study are conceptually distinct from both parasequences and parasequence sets and thus from the hierarchy of stratal units employed in the Sequence Stratigraphy model (Van Wagoner et al., 1988; Kamola & Van Wagoner, 1995). The genetically specific ranks used in this paper are also distinct from the ‘orbitally related’ hierarchy of orders used by Goldhammer et al. (1990). Goldhammer et al. use time ranges in their definition of ranks in a hierarchy (i.e. 5th order is 10-100 ka and 4th order is 100-1000 ka). This kind of definition of ranks precludes a specific genetic connection to each rank in their hierarchy.

    In contrast Brett et al. (1990, Table 1) use a cyclic hierarchy that does attach specific periods to the ‘Milankovitch-level’ ranks. They also add a new rank (the sub sequence with a period of 1.0-1.5 ma) that changes the numbering of rank orders so that the 450 ka, 100 ka and 20 ka are now 5th, 6th and 7th order respectively. They then identify the larger two of these time specific ranks with parasequences sets and parasequences. This correlation is not consistent with the intent of the Sequence Stratigraphy definitions of these terms (Kamola and Van Wagoner, 1995). They also equate PACs of Goodwin and Anderson (1985; 1997) with the 100 ka rank. Note that this unit (the PAC) is now formerly defined as the product of the 20 ka precessional signal.

Stacking Patterns

    If complete preservation of the orbitally-forced hierarchy occurs, the predicted stacking pattern (where 6th order cycles are the product of precession) consists of five 6th order cycles in each 5th order sequence. At the next level, four 5th order sequences should occur in each 4th order sequence and at a larger scale, five 4th order sequences are predicted in a 3rd order sequence (Fig. 7   Milankovitch Stacking Patterns.ppt).  The largest facies changes occur at the bases of 6th order rock cycles and (by arbitrary definition) in the lower part of the second cycle or sequence in each of the larger scale bundles in the hierarchy (see Fig. 7 Milankovitch Stacking Patterns as a jpg below). Experience demonstrates that the basic cycle and the bundled sets of these cycles are asymmetric in facies distribution and it is then most parsimonious to have the bundled sets reach a shallowest point (or a minimal facies contrast across cycle boundaries) toward the top or termination of larger-scale sequences.