The repetitive patterns in sedimentary rock successions have long been described and studied by geologists. Geologists were and are still fascinated by these patterns when they observe them in outcrops.
They generally interpret them as cycles. However, cycles are related to time and are characterized by a recurrence interval or periodicity.
Unfortunately the periodicity cannot easily be seen or obtained from the outcrop and to find out whether a repetitive pattern has a cyclic periodicity, a statistical analysis should be carried out. During this lecture Dr. Djin NIO discussed only cycles.
Cycles can be generated by a whole range of entirely different processes and the (geological) time for producing a single couplet or bundle within a cycle may vary greatly. Cycles in sediments occur worldwide and are formed in every depositional and stratigraphic systems.
Two types of cycles can be distinguished in sediments - autocyclic and allocyclic patterns. Autocyclic patterns are generated by the depositional system, while allocyclic patterns are related to mechanisms outside the depositional system. The differences between these two types of cyclic patterns were discussed.
Cycles with different time scales of their recurrence interval with examples from outcrops of different stratigraphic periods were presented. First, short-term cycles produced by tidal action, and how they have developed in geological time.
Subsequently, long-term cycles, which are related to periodic changes of climate were introduced. Demonstration was made how to determine these cycles and how they appear in outcrop. These long-term or "stratigraphic" cycles have an important component due to orbitally-forced climatic change.
The discussion is in how far these low and high frequency climatic changes can be considered as the primary driving force on the variability as we see in the stratigraphic record.
Finally, Dr. Djin NIO discussed the use of these cycles in predicting faces variability and the possibility of constructing an orbitally-tuned geological timescale.