Did the Flood really happen?

Message 64 of 1255 (857251) 07-07-2019 4:46 AM

Reply to: Message 62 by Faith 07-07-2019 3:22 AM

The deposition age of the Siberian Traps, one of the largest volcanic events in Earth's history, started in the late Paleozoic and ended in the early Mesozoic. The bulk of Paleozoic sediments (Great Flood deposits to you) are stratigraphically below (older than) those volcanics and the bulk of Mesozoic (Great Flood deposits to you) are stratigraphically above (younger than) those volcanics.

Thus, the volcanic event must have happened during your Great Flood. I offhand find no reference to that the volcanics were a submarine event.

Moose

Message 754 of 1255 (859079) 07-28-2019 1:22 AM

Reply to: Message 698 by Percy 07-26-2019 8:11 AM

Just because the Silurian strata is vertical or near vertical at that location does not mean that it is near vertical everywhere. Indeed, if that strata is found over a large area, it must be much more horizontal in general. And the cross section diagram is covering that large area.

Perhaps it is some more intense local folding??? A small detail that isn't going to show up in "the big picture"???

What would be nice, would be to have a good geologic map and/or cross section that only covers a few miles of lateral distance from that location. I can't find such online.

Moose

Message 1094 of 1255 (860189) 08-06-2019 2:11 AM

Reply to: Message 1027 by JonF 08-05-2019 10:31 AM

A (not THE) geological column refers to the vertical sequence of rocks at a single location/point of the Earth. In concept, a true A geological column is a 1 dimensional object (AKA a vertical line). In practical reality, a A geological column would be a compilation/generalization of a collection of adjacent true A geological columns.

An example of a practical reality A geological column would be the rocks of a drill coring, of which there are many examples upthread (of course that would actually be just the top part of that A geological column, as the core does not go to the center of the Earth). But even in that object of 3 dimensions, there would be some variations from 1 vertical (1 dimensional) line to the other vertical lines of the core. Going down the left side of the core would not be a precise mirroring of going down the right edge.

The Earth's geology is the compilation of an infinite number of these A geological columns, those of every point of the Earth, be it continental or oceanic.

When a geologist refers to THE geological column, he/she is actually referring to a A geological column of a quite specific location. Or more likely is referring to what is better termed as the geological time scale.

So, getting back to the coin stack concept.

On stack of coins is one column. Of course, the left edge of the stack is not precisely the same as the right edge of the stack. You are deviating from a 1 dimensional object and are starting to generalize.

A second adjacent stack is a second column. If the second stack is right side by side to the first stack, then one might generalize that into being a single column. But then you are getting into even more deviations in the 2nd and 3rd dimensions.

Returning to the above quoted:

Wrong. A (not THE) geological column is the rocks underlying a single point on the Earth. There are an infinite number of A geological columns, that underlie every point on the Earth.

Now there is a muddled mess of a message. Maybe a mooseage. I don't know if all this hair splitting is of any value to the discussion.

Moose

Message 1133 of 1255 (860331) 08-06-2019 8:17 PM

Reply to: Message 1097 by JonF 08-06-2019 9:21 AM

If a geologist refers to "the" geologic column, he is either referring to "a" specific individual geologic column at a specific location OR he is referring to the geologic time scale, which is independent of any specific location of the Earth. Which one would be apparent from the discussion context.

I strongly encourage the going to the Geologic Column topic started by NosyNed back in 2003 (16+ years ago!). Edge did a nice message 3 there.

Moose

Message 1172 of 1255 (860488) 08-07-2019 9:21 PM

Reply to: Message 1162 by JonF 08-07-2019 4:09 PM

https://geology.com/plate-tectonics.shtml
https://www.thoughtco.com/...es-and-their-boundaries-1441098

There is 3 types of plate boundaries:

1) Divergent - Essentially synonymous with mid-ocean spreading centers, the notable exception being the east Africa rift valley, which is rather a proto-mid-ocean spreading center. These are areas of tension (aka negative pressure). Not directly relevant to continental deformations.

2) Convergent - Essentially synonymous with subduction zones, mostly at ocean crust/continental crust boundaries, although there are also ocean crust/ocean crust subduction zones. The big example is the Pacific ring of fire.

An exception to being subduction zones, is the case of continental plate/continental plate collision, the great example being the north end of the India plate. Another exception would be what I'll call obduction zones - Oceanic crust being thrust up upon continental crust, resulting in continental ophiolite complexes.

3) Transform faults - Such as the San Andreas fault in California and the Alpine fault in New Zealand.

What percentage of plate boundaries are in the ocean?

The bulk of those plate boundaries are mid-ocean spreading centers. The ocean/continent boundaries are mostly subduction zones or transform faults.

An "off the cuff" summary. I'm sure there could be some quibbles about the details.

The origins of the Appalachians is complex, but a big part of it was that the was a continental/continental collision at one or more points in time, when the Atlantic Ocean basin closed.

Moose

Message 1174 of 1255 (860501) 08-08-2019 2:33 AM

Reply to: Message 1173 by PaulK 08-08-2019 12:14 AM

If by "sea bed" you mean oceans that are over the continental shelf or seas that were from a greater sea transgression onto the continents, then I would agree with you. If by "sea bed" you mean oceanic crust and sediments, then there is a big difference - The continents have a general specific gravity ("density") of 2.7 while the oceanic crust is 3.0.

Again, significant density difference. See isostasy.

Moose

Message 1205 of 1255 (860603) 08-09-2019 12:11 AM

Reply to: Message 1176 by PaulK 08-08-2019 7:53 AM

Actually, an at least partial reason for the height of the mid-oceanic ridges is that the relatively hot rock at the spreading center is slightly less dense than the cooler rock further from the spreading center. Less dense floats higher.

quote:

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At the spreading center on a mid-ocean ridge the depth of the seafloor is approximately 2,600 meters (8,500 ft).[1][2] On the ridge flanks the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is closely correlated with its age (age of the lithosphere where depth is measured). The age-depth relation can be modeled by the cooling of a lithosphere plate[3][4] or mantle half-space.[5] A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge proportional to the square root of the age of the seafloor.[5] The overall shape of ridges results from Pratt isostacy: close to the ridge axis there is hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens and the density increases. Thus older seafloor is underlain by denser material and is deeper.[3][4]

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https://en.wikipedia.org/wiki/Mid-ocean_ridge#Morphology

Links and much more reading at source page.

May want to also look at https://en.wikipedia.org/wiki/Guyot

All this is pretty irrelevant to continental deposition and deformation considerations. But someones got to put something interesting into the topic.

Moose

Edited by Minnemooseus, : Clean up formatting a bit.

Message 1206 of 1255 (860605) 08-09-2019 12:43 AM

Reply to: Message 1201 by Percy 08-08-2019 6:53 PM

...

quote:

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During the Late Jurassic, continued rifting widened the Gulf of Mexico and progressed to the point that sea-floor spreading and formation of oceanic crust occurred.

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quote:

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Increasingly, the Gulf of Mexico is regarded as a backarc basin behind the Jurassic Nazas Arc of Mexico.

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https://en.wikipedia.org/wiki/Gulf_of_Mexico#Geology

quote:

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Back-arc basins are geologic basins, submarine features associated with island arcs and subduction zones. They are found at some convergent plate boundaries, presently concentrated in the western Pacific Ocean. Most of them result from tensional forces caused by oceanic trench rollback (the oceanic trench is wandering in the seafloor direction) and the collapse of the edge of the continent. The arc crust is under extension or rifting as a result of the sinking of the subducting slab. Back-arc basins were initially a surprising result for plate tectonics theorists, who expected convergent boundaries to be zones of compression, rather than major extension. However, they are now recognized as consistent with this model in explaining how the interior of Earth loses heat.

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https://en.wikipedia.org/wiki/Back-arc_basin

Another interesting tidbit (or two) I encountered:

quote:

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Western and central Cuba are a deformed orogen, that came about due to the collision of an island arc in the Cretaceous with the Florida-Bahamas platform. As a result, the Cuban ophiolite zone became obducted and a northward verging fold and thrust belt formed.

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https://en.wikipedia.org/wiki/Geology_of_Cuba

quote:

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An ophiolite is a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. Ophis is Greek for "snake", and lite (from Greek lithos) means "stone", after the green-color rocks that make up many ophiolites.

Their great significance relates to their occurrence within mountain belts such as the Alps and the Himalayas, where they document the existence of former ocean basins that have now been consumed by subduction. This insight was one of the founding pillars of plate tectonics, and ophiolites have always played a central role in plate tectonic theory and the interpretation of ancient mountain belts.

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My "bolding".

https://en.wikipedia.org/wiki/Ophiolite

Tectonics seem to be pretty damn complicated.

I seem to be turning into a geo-LamarkNewAge. Oh Flying Spaghetti Monster, save me!

Moose

Message 1236 of 1255 (860898) 08-13-2019 4:08 AM

Reply to: Message 1233 by PaulK 08-13-2019 1:36 AM

First of all, one shouldn't assume that deposition, deformation, and erosion are sequential processes operating independent of each other. It's not deposition, then deformation, then erosion. Deformation may well be happening while deposition is ongoing, and there certainly is going to be erosion and redeposition of the eroded material while deformation is ongoing.

PaulK's first sentence of the first paragraph really gave me a "there's some weird syntax doing on here" feeling. I repeat it:

Any deformation isn't going to happen to any strata before the strata was laid down. So that sentence would be better stated as:

At the Siccar Point angular unconformity, there was most likely erosion and redeposition while the older Silurian rocks were being folded and tilted. I don't offhand have the petrology down, but the upper Devonian rocks were at least in part derived from the erosion of the Silurian - There are clasts of the Silurian now part of the Devonian rocks.

Anyway, the deformed Silurian rocks were later further deformed at the same time the Devonian rocks were.

As a side note, a perhaps odd situation in one pre-Cambrian rock unit in northern Minnesota. There is a large unit called the Knife Lake Group (or is it Supergroup?). Anyway, a pretty thick stack of sediments. The lower part of the Knife Lake is intruded by the Saganaga "Granite" (actually a tonalite, IIRC). Anyway, a generally granitic type intrusion. The Knife Lake is contact metamorphosed by the Saganaga and both the Knife Lake and the Saganaga are deformed, with the Saganaga crystal structure showing pronounced stretching. But the kicker of this situation is that distinctive cobbles of the stretched Saganaga are found deposited in the more upper part of the Knife Lake.

So, the general sequence would be, deposition of Knife Lake sediments, then intrusion by the Saganaga while deposition of the Knife Lake continued, then deformation of the Knife Lake and the Saganaga while the deposition of the Knife Lake continued, then erosion of the Knife Lake and Saganaga in one area while the deposition of the Knife Lake continued in another area.

Nutshell - You have the same intrusion intruding and metamorphising a thick sedimentary unit, and later have that same intrusion supplying sediment to a later part of that thick sedimentary unit. Sedimentation, intrusion, metamorphism, deformation, erosion all happened while deposition was ongoing. Or something like that. I don't have time span information for how long that all took.

Critiques of my reasonings certainly welcome.

Moose

Added by edit - A couple of Saganaga Granite links:

https://www.jstor.org/stable/30056034?seq=1#page_scan_tab...
https://www.nrcresearchpress.com/...139/e71-097#.XVJwamR7nIU

Edited by Minnemooseus, : Added by edit.