Talk:Stratigraphic cycles

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Are Milankovitch cycles 4th or 5th order? And what of sequences that are not specifically or completely related to eustatic sea level change?

Certainly, when there is glaciation (ice house), Milankovitch cycles do affect short-time scale eustasy sea level cycles; but, in the 1st order hot houses, rhythmic facies changes and rhythmic faunal discontinuities never-the-less occur and those in the Cretaceous at least have recently been shown to have correlation with Milankovitch cycles in the absence of changes in glaciation (perhaps only influencing wide changes in precipitation and aquifer storage). The prior interpretation of Western Interior Seaway cyclicity has naturally assumed sea-level change or tectonic shoreline displacement, but climatic zone shifts can also account for facies and species changes without significant sea-level change. In other words, is the Stratigraphic cycle concept exclusive to sea-level changes? If Sequence Stratigraphy is exclusive to marine-terrestrial cycles, then I can understand the restriction to sea-level change, in which case Milankovitch cycles only conditionally influence cyclic eustatic sea level change, but otherwise generally influence cyclic sedimentation change.

• Cyclostratigraphy of the Upper Cretaceous Niobrara Formation, Western Interior, U.S.A.: A Coniacian–Santonian orbital timescale
• Milankovitch Cycles in Upper Jurassic and Lower Cretaceous Radiolarites of The Equatorial Pacific: Spectral Analysis and Sedimentation Rate Curves
• Evidence for Milankovitch periodicities in Cenomanian-Turonian lithologic and geochemical cycles, Western Interior U.S.A.

IveGoneAway (talk) 14:28, 6 May 2021 (UTC) IveGoneAway (talk) 15:11, 6 May 2021 (UTC)[reply]

I have found limited references that describe the Milankovitch cycles as sixth or seventh order, but with some of the Milankovitch cycles on the order of 100,000-400,000 years there is overlap with the forth order sequence definition. Honestly, as a set, the Milankovitch cycles, really can not be assigned to a single order.

IveGoneAway (talk) 18:50, 12 September 2021 (UTC)[reply]

In the context of discussing the higher-order sequences, the following paper also lists additional lower-order.

Kauffman, E. G. and Caldwell, W G. E., 1993, The Western Interior Basin in space and time, in Caldwell, WG.E. and Kauffman, E.G., eds., Evolution of the Western Interior Basin: Geological Association of Canada, Special Paper 39, p. 1-30.

• The entirely of the Western Interior Seaway is a first-order sequence.
• Within that first-order sequence are several second-order sequences seen and are named for the representative formations (e.g., Skull Creek, Greenhorn, and Claggett Marine Cycles).
• Within some of these second-order sequences, some third and even fourth-order sequences are detected.
• However, fifth, sixth, and seventh order sequences are discussed, but there are no real subaerial unconformities. Nevertheless, these cycles as seen in the sediments here are described in sequence terms. The paper does mention that the question of climate-driven "sequences" is debated.

Hmmm.

400 k. y. is at the extreme for Milankovitch cycles. The paper seems to make distinction between the N-order and "Milankovitch- scale".

Ah, the effects Milankovitch cycles in this global-ice-free context are not really sequences in the strictest subaerial unconformity sense. Rather they are rhythmic facies change events that can be traced from shoreline to shoreline though deep marine sediments, with ongoing efforts to trace on into correlated terrestrial sediments.

IveGoneAway (talk) 02:41, 17 September 2021 (UTC)[reply]

I get it that geologists may speak of "transgression events" and "regression events" and may even speak of an individual stratigraphic cycle as an "event", but such stratigraphic cycle events often have durations on the order of millions of years, and that very fact prevents rock dating to high precision, resulting in inconsistencies and errors in identifying rocks and fossils. So, discussions of such long events do not seem to address the primary scientific values of the sorts of events as "... large storm, landslide, volcanic eruption, or flood ... ash falls [especially], lava flows, lahars, and glacial ice-dam breaks; ...", which may have durations ranging from months to minutes.

I could see this section further developed to address these finer scales and even split.

IveGoneAway (talk) 19:26, 12 September 2021 (UTC)[reply]