I'm not posting any real material to start this topic, rather I encourage the forums geologists (and other geologically inclined) to chip in there thoughts.
The question is, "How did the sea transgressions and regressions of the Earth's geologic history happen"? This is, as in the frame of mainstream old age thought. I don't want any "young Earth" flood geology in this topic.
I believe that most geologists would attribute inter-regional transgressions to plate tectonics in that a surge of mid-ocean ridge volcanism would swell the ridges to such an extent that they would displace seawater onto the continental masses.
ETA: This would be supported by the fact that the Cretaceous Period seems to be a time of increased ocean ridge volcanism (i.e., wide bands of Cretaceous sea floor on either side of the mid-ocean ridges) that would correspond to the Zuni transgression.
This would, of course result in global dimensions for the transgressions and yet we don't see evidence of such on all continents.
I recently read of the possibility that depending on climate, the degree of erosion going on at any one place might mask the effect of a transgression and/or regression. That would make some sense.
I'm also of the opinion that some continents might be undergoing a significant degree of orogeny due to the local effects of subduction or continental collision that would also affect the amount of both erosion and deposition.
What is the evidence that this increased ocean ridge volcanism occurred in the Cretaceous period? What is "Cretaceous sea floor?"
The width of the Cretaceous seafloor bands extending away from the mid-ocean ridges are wider for the number of years than other periods. This is known due to radiometric dating and correlation of magnetic signature of the oceanic crust. This suggests a temporary increase in the amount of seafloor spreading and the volcanism that would accompany it.
I don't understand why the focus on global and inter-regional transgressions. Aren't most transgressions/regressions more limited in extent and a result of local interactions between sea height and subsidence/elevation?
Most probably are more local or regional.
Cratonic Sequences are a unifying theory that blend a lot of data but don't provide a lot of details. In a way, it's kind of like evolution, but on a more modest level.
This is something I've tried to research in the past, and didn't come up with much information.
It may be difficult for you to have the information, but my question is, was this increased spreading rate confined to one ocean or was it multiple locations?
That's a good question. I don't know, but the Pacific Basin shows it more readily because the plates are moving so much faster. When there are continents associated with the plates they tend to move more slowly.
Also, was there increased subduction zone volcanism associated with this increased spreading rate?
Was there orogeny/mountain building associated with this increased spreading rate?
For western NA, most definitely. You see an increase in volcanism into the Tertiary and you see several orogenic episodes starting in the Jurassic. These are mostly related to increased subduction rates along the western edge of the NA Plate.
While these are regional effects, one might expect some global consequence since sea level is more or less a global feature. However, there are a lot more variables than just seafloor spreading activity.
So, to be clear, is all such dating to time periods done by radiometric methods? When it is said that mountains formed in such a such a time period, that's due to radiometric measurement? Of what, exactly? Is that how the Cratonic transgressions are dated?
Most absolute dates are radiometric. I think some are bioichronological. Relative ages are still how we describe them, such as Ordovician or Cretaceous.
quote:(And is anyone paying attention to all this in relation to the movement of the Supercontinents and the breakup of Pangaea and all that?
Yes, that's the whole idea. We are not like YECs in applying ad hoc solutions to questions.
Because the seafloor would not have spread as far in the Cretaceous as today for instance. Is all that being taken into account?
I'm not sure what you are asking.
ABE: So for instance if Pangaea broke up in the Jurassic there was really not a lot of seafloor formed by the Cretaceous? )
Well, yes that's pretty much what happened. For instance, there basically isn't much seafloor older than Jurassic unless it's been accreted to the continents. Part of that is due to more recent rifting as you suggest, but much is due to subduction which is kind of the ultimate fate of old, thick oceanic crust.
So, likewise, if rifting started in the Cretaceous, there would be less Cretacesous and no Jurassic seafloor.