Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
6 online now:
Newest Member: popoi
Post Volume: Total: 915,809 Year: 3,066/9,624 Month: 911/1,588 Week: 94/223 Day: 5/17 Hour: 1/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Growing the Geologic Column
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 210 of 740 (734238)
07-27-2014 6:57 AM
Reply to: Message 184 by Faith
07-26-2014 5:20 PM


Re: Layer / Sill
Faith writes:
Well, OK, but nost sills don't even look like layers. But OK, yes, thanks, you are correct. I keep calling it a sill which I would have thought made the point. So shall I now call it an "intrusive layer" as HBD suggests?
Acceptable terms would be "sill", "intrusion" and "intrusive layer", and there may even be other synonyms. It only gets confusing when you say it's not a layer.
I think both HDB and I are a bit unsatisfied with the geological terminology here. To us it just feels right that the geologic column should be everything in the column of rock beneath your feet, but we have to accept the definitions as they are, and an intrusion is not considered part of the geologic column. I think the reason for this is that the intrusion isn't part of a time sequential sequence of layers and so is out of order with the geologic timescale, and by this reasoning it makes sense that an intrusion represents an intrusion into the geologic column and so is not part of the geologic column.
If you look at the definition of "stratigraphic column" over at Wikipedia you can see that there's a subtle difference between it and the definition of "geologic column". "Stratigraphic column" has two definitions. One is the same as "geologic column", that definition calls it a "time column", but the other calls it a "structural column", meaning the rocks just as they are without regard to how or when they got there. I think this second definition of "stratigraphic column" is the definition that feels best to HBD and myself.
As Edge once commented, all during his education there was barely a nit of a attention paid to the definition of "geologic column". Like any word it's just a label, and the details of what any specific use of the word actually refers to are what's important. For example, if in a conversation among geologists someone were to refer to an upside down rock sequence (where the order of layers is completely backwards to the timescale) as a "geologic column", no one would bat an eyelash because they understand what it is he's referring to. No one would say anything like, "You're claims about this rock sequence are completely wrong because that's not a geologic column." For your "argument via definition" approach to have any chance of success it would have to be true that if you don't call a rose a rose then it doesn't smell as sweet.
That words are just labels means you can't use definitions to infer how the world really works, which is what you're trying to do with the term "geologic column". You're insisting that the definition of "geologic column" excludes the possibility of adding to it, as if geologic columns could only be constructed during global floods. But what we observe happening in all low lying regions around the world today (mostly sea floor) is the creation of a time ordered sequence of sedimentary and igneous layers, the very definition of a geologic column.
--Percy
Edited by Percy, : Wordsmithing in next to last para.

This message is a reply to:
 Message 184 by Faith, posted 07-26-2014 5:20 PM Faith has not replied

Replies to this message:
 Message 213 by herebedragons, posted 07-27-2014 8:28 AM Percy has seen this message but not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 211 of 740 (734239)
07-27-2014 7:20 AM
Reply to: Message 178 by herebedragons
07-26-2014 2:09 PM


I touched on this in Message 210, see if you agree.
--Percy

This message is a reply to:
 Message 178 by herebedragons, posted 07-26-2014 2:09 PM herebedragons has not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 212 of 740 (734240)
07-27-2014 8:26 AM
Reply to: Message 193 by Faith
07-26-2014 7:00 PM


Interspersed Volcanic and Sedimentary Layers
Hi Faith,
The Columbia River Basalt Group in the western US (mostly Washington state) consists of basalt layers from volcanic lava flows interspersed with sedimentary layers. Here's a diagram of the layers at Hanford Reach along the Columbia River. It shows basalt layers from lava flows interspersed with sedimentary layers:
Here's a good description of how these layers formed from The Columbia River Basalt Group - Exposed by the Ice Age Floods :
Hundreds of eruptions--each separated by thousands of years--leave us with a unique record of conditions millions of years ago. During periods of volcanic inactivity, water would accumulate in depressions, sediment would accumulate in valleys, and wind would deposit dust. Soil layers would develop and forests and grasslands would flourish. Plants and animals would appear. The next cycle of lava flows would would abruptly terminate their existence, but preserve a fossil record.
Here's a couple images - unfortunately the websites didn't note which specific layers these are. I did dig a little trying to find images with some labeling, but no luck. Maybe someone else can find some labeled images:
But the bottom line question for you is why you wouldn't expect volcanic lava (basalt) and tuff layers (both igneous layers) between sedimentary layers. What is to prevent a volcanic eruption in a region where sediments are being deposited? Even in a global flood a volcanic eruption could occur, leaving behind pillow lava, something I mentioned before that also occurs in the geologic column.
--Percy

This message is a reply to:
 Message 193 by Faith, posted 07-26-2014 7:00 PM Faith has not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 232 of 740 (734271)
07-27-2014 4:43 PM
Reply to: Message 222 by Faith
07-27-2014 3:38 PM


Re: Blackrock Escarpment is all volcanic
Faith writes:
I've read this through a number of times, and I know you've posted on it many times before, but right now I can't figure out why it can't be a sill.
Here's a diagram of the eastern Grand Canyon region. At the top is a cross section showing the layers of the Grand Canyon supergroup, which includes the Cardenas Basalt (the diagram refers to it as the Cardenas Lava). At the bottom left is a map with a line showing the location of the cross section, and at the bottom right is a color key for all the layers:
The Cardenas Basalt overlies the Dox Formation (mostly sandstone) and underlies the Nankoweap Formation (lower portion is sandstone and siltstone). The Cardenas Basalt's boundary with the overlying Nankoweap is an unconformity, meaning that the Cardenas Basalt layer was eroded before the Nankoweap was deposited. The upper part of the the Cardenas Basalt contains eroded fragments of basalt and shows evidence of contact metamorphism by overlying lava flows that are no longer there, having eroded away.
The upper couple feet of the underlying Dox Formation also shows evidence of contact metamorphism by the heat of the lava layers deposited on top of it, a characteristic completely missing from the Nankoweap's contact with the Cardenas's upper boundary.
The contact metamorphism evident in the underlying layer and the absence of contact metamorphism in the overlying layer is an identifying characteristic of a basaltic layer deposited by lava flows, as opposed to a sill where both the underlying and overlying layers display the effects of contact metamorphism. The Wikipedia article on sills explains the difference between a sill and a lava layer like this:
Wikipedia writes:
Sills can be confused with solidified lava flows; however, there are several differences between them. Intruded sills will show partial melting and incorporation of the surrounding country rock. On both contact surfaces of the country rock into which the sill has intruded, evidence of heating will be observed (contact metamorphism). Lava flows will show this evidence only on the lower side of the flow. In addition, lava flows will typically show evidence of vesicles (bubbles) where gases escaped into the atmosphere. Because sills generally form at shallow depths (up to many kilometers) below the surface, the pressure of overlying rock prevents this from happening much, if at all. Lava flows will also typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not.
You go on to ask:
Or, since volcanic ash has been coming up, could it be that?
Just as it is very easy to tell the difference between lava and volcanic ash lying on the surface, it is also very easy to tell the difference between cooled lava (basalt) and volcanic ash that has been deeply buried and compacted. One could never be mistaken for the other. But lava and ash can certainly be interbedded, since they are produced at the same time by the same event.
--Percy

This message is a reply to:
 Message 222 by Faith, posted 07-27-2014 3:38 PM Faith has not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 238 of 740 (734279)
07-27-2014 4:59 PM
Reply to: Message 233 by Faith
07-27-2014 4:44 PM


Re: Layer / Sill
Faith writes:
I didn't mean it ALWAYS has to be dikes and sills, of course it CAN just flow and deposit wherever. I was answering HBD's apparent idea that it isn't an intrusive when you find it as a layer.
Both sills and lava layers are layers. As the Wikipedia article I quoted in my previous message says, it can sometimes be difficult to tell the difference between a sill layer and a lava layer, but it goes on to describe their unique characteristics by which we tell them apart.
--Percy

This message is a reply to:
 Message 233 by Faith, posted 07-27-2014 4:44 PM Faith has not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 242 of 740 (734284)
07-27-2014 5:13 PM
Reply to: Message 237 by Faith
07-27-2014 4:54 PM


Re: Layer / Sill
Faith writes:
In her defense, I think that what we observe happening today DOES look strangely different than what we see in the rock record.
YES! Thanks for that much. It looks really strangely weirdly dramatically different. There is NO way there's ever going to be another Redwall limestone or Coconino sandstone. That's the way it just plain LOOKS when you compare those formations with the paltry depositions that are offered up as the equivalent today.
I don't know why HBD said such a thing. Buried geologic layers are made up of or include many of the same things we see on and near the surface today, such as lava basalt, volcanic ash, sand, silt, mud, clay, burrows, tracks, life (in the form of fossils), even things like entire oyster beds. To me the majority of geologic layers look like lithified ancestors of the layers forming today.
Yeah, Time, the Magic Ingredient that turns a delta or continental shelf into the Grand Canyon.
You make it sound like an ancient Earth is just something geologists made up, instead of something that is supported by literally mountains of evidence. The side in this debate who is making things up left and right is you.
--Percy

This message is a reply to:
 Message 237 by Faith, posted 07-27-2014 4:54 PM Faith has replied

Replies to this message:
 Message 246 by herebedragons, posted 07-27-2014 5:31 PM Percy has seen this message but not replied
 Message 259 by Faith, posted 07-27-2014 11:26 PM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 245 of 740 (734287)
07-27-2014 5:22 PM
Reply to: Message 240 by herebedragons
07-27-2014 5:05 PM


Re: Layer / Sill
herebedragons writes:
When a rock is referred to as Basalt, it can be assumed to be extrusive, unless there are reasons to think otherwise. Are there reasons why you think those examples are intrusions?
You're right, but if you do a Google search for "intrusive basalt" (including the quotes) you'll get thousands of results. During the discussion while poking around on the web it seemed to me like there are many articles out there that aren't careful in their terminology and refer to sills and dikes as just "basalt" without the "intrusive" modifier.
So I wonder if it might be better to not belabor the point about correct usage of the word "basalt" and instead just always be clear about whether we're talking about extrusive or intrusive, or about lava or magma, or about sills or lava layers.
--Percy

This message is a reply to:
 Message 240 by herebedragons, posted 07-27-2014 5:05 PM herebedragons has replied

Replies to this message:
 Message 249 by herebedragons, posted 07-27-2014 5:43 PM Percy has seen this message but not replied
 Message 250 by Minnemooseus, posted 07-27-2014 5:52 PM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 251 of 740 (734295)
07-27-2014 5:54 PM
Reply to: Message 244 by Faith
07-27-2014 5:16 PM


Re: Layer / Sill
Faith writes:
According to Old Earth assumptions, but they are just assumptions, something you take for granted,...
There are no assumptions. The amount of evidence for an ancient Earth is massive across many fields of science, not just geology. You're just tossing grenades into the discussion. Let's keep the focus on the topic.
...but if a worldwide Flood DID occur that would provide the very situation of changing sea levels where Walther's Law operates, but much faster.
The tsunami wave that flowed over Japan did not leave behind anything resembling Walther's Law. That's because Walther's Law requires geologic time in order to operate. Waves have to pound shorelines day after day and year after year for eons while runoff from land feeds the process as a source of the sedimentary material laid down by Walther's Law. A flood, no matter how large, cannot leave behind this kind of sedimentary sequence nor even these kinds of sedimentary layers to any significant extent.
If the Atlantic Ocean transgressed across New Jersey and into the mid-west, you'd see layers precursive to those Faith is talking about.
Yes, that's the idea. And so much the more if the Pacific wandered up to meet the Atlantic in the Midwest.
If Edge was describing a situation where in just a few months the Atlantic Ocean transgressed all the way to the mid-west, then no, we wouldn't observe anything like the flood layers you keep describing, not even precursors.
If Edge was instead describing a situation where in geologic time the Atlantic Ocean transgressed all the way to the mid-west, then yes, we would observe the beginnings of the types of layers normally seen in the geologic record.
--Percy

This message is a reply to:
 Message 244 by Faith, posted 07-27-2014 5:16 PM Faith has replied

Replies to this message:
 Message 260 by Faith, posted 07-28-2014 12:52 AM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 253 of 740 (734297)
07-27-2014 6:06 PM
Reply to: Message 250 by Minnemooseus
07-27-2014 5:52 PM


Re: Layer / Sill
Minnemooseus writes:
That they are sills or dikes automatically means "intrusive". Intrusive dike would be a redundancy.
Well, sure, but misuses like that are what you find on the Internet, and the Internet is where Faith finds most of the raw material from which she constructs her misimpressions. The first result of a Google search for "intrusive basalt" is a website with the phrase "intrusive basalt dike".
But my main concern is when "basalt" is used without a modifier. We could insist that it always means extrusive, but we'd be fighting Faith forever on that definition because half the Internet uses it to also refer to sills, plugs and dikes.
--Percy

This message is a reply to:
 Message 250 by Minnemooseus, posted 07-27-2014 5:52 PM Minnemooseus has seen this message but not replied

Replies to this message:
 Message 261 by Faith, posted 07-28-2014 12:55 AM Percy has seen this message but not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 369 of 740 (734449)
07-29-2014 11:57 AM
Reply to: Message 259 by Faith
07-27-2014 11:26 PM


Re: New depositions strangely different from old strata
Faith writes:
And one thing that's different is the scale, those thick thick rocks that span whole continents, and originally piled three miles deep as well. That's why I said there will never be another Redwall Limestone or Coconino Sandstone, could add never another Dover Cliffs or that gigantic wall of rock somebody posted from South America a while back, sorry don't remember the name of it.
There are layers on the same scale forming today. Here's a diagram of sedimentary layers that begin on land near the Texas/Lousiana coastline and then extend out into the Gulf of Mexico. These layers are kilometers thick, and they are still being added to today:
Also note the faults that extend only partway through the layers. For example, look at the fault roughly in the image's center that extends from just above the top of the basement rock all the way up to the bottom of the Milocene layer, meaning the fault occurred around 20 million years ago. Sediments continued to accumulate after the fault occurred to a depth of an additional 5 kilometers.
ABE: Looking for that picture of the South American formation, found "tepui" and Mt. Roraima which may be what I'm remembering but the picture that was posted here didn't show up. This one is maybe the closest:
Such enormous slabs of rock that originally had to have been strata suggest the Flood to my mind, and certainly not slow deposition over millions of years.
As has been pointed out to you countless times, the strata we see the world over bear no resemblance to flood layers. Those particular strata will have the same characteristics as all other layers indicating slow deposition over millions of year, including fine-grained sediments, different compositions of different layers, increasing differences of fossils from modern forms with increasing depth, the presence of footprints, burrows and nests, increasing levels of radiometric decay products with increasing depth, and unconformities.
And besides such gigantic flat slabs of rock there are all kinds of strange/ weird/ bizarre geological formations all over the world that I can't see ever getting reproduced on the Old Earth model, that all suggest the Flood to me.
Everything suggests the Flood to you. Your problem is that no evidence suggests the Flood.
Well, there's no point in arguing this out for the zillionth time but in a sense BOTH sides are making things up because that's pretty much all you can do with the prehistoric past.
No, both sides are not making things up. Only you are making things up and making assumptions. The only assumptions of science are that the same physical laws we observe in the universe today have been at work throughout its history. We know how those physical laws affect the Earth because we can see those forces and what they do on the Earth today. The present is the key to the past, and we can find the same types of structures that are forming today buried within sedimentary layers.
--Percy

This message is a reply to:
 Message 259 by Faith, posted 07-27-2014 11:26 PM Faith has replied

Replies to this message:
 Message 414 by Faith, posted 07-30-2014 7:45 AM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 442 of 740 (734545)
07-30-2014 2:42 PM
Reply to: Message 260 by Faith
07-28-2014 12:52 AM


Re: Layer / Sill
Hi Faith,
I seem to be in catch up mode. I'm replying to a message from only the day before yesterday and yet am 160 messages behind.
All that evidence for the Old Earth in all the sciences is mostly just plausibilities, interpretations of observations, suppositions, assumptions, hypotheses and so on. There's a lot of it so it looks like a lot of *evidence* -- which it is of course if you count plausibilities, interpretations of observations, assumptions, hypotheses and so on as evidence. Which again, is all anyone's got for the prehistoric past.
What we actually have is evidence, and interpretation and analysis of evidence. The "plausibilities,...,suppositions, assumptions, hypotheses" stuff is all on your side of the fence.
For example, we know how sand is deposited in deserts and along coastlines because we observe it happening today. And we know that the sandstone in geological layers was deposited in the same way because analysis reveals it has the same composition, structure and types of fossils as sedimentary sand deposits forming today.
You, on the other hand, claim a Flood that does things that no flood anywhere has ever done, and that no one can conceive could happen using natural processes. You claim this is a Flood as has never been seen before and that it could nonetheless do these things, but now you are way beyond even "plausibilities, suppositions, assumptions, hypotheses" and into the realm of fiction.
Walther's Law is about rising sea level, not waves, tsunami-sized or not.
You still misunderstand Walther's Law. Walther's Law is about a depositional environment moving across a landscape. It could be the riverbank of a meandering river or the coastline of a transgressing/regressing sea. Both are examples of Walther's Law in action.
If you read the Wikipedia Section on Walther's Law you'll see that it describes it as "when a depositional environment 'migrates' laterally". This could refer to a coastline that moves inland or out to sea with the depositional environments of that coastline moving with it, or to the banks of a meandering river whose depositional environments moves back and forth across the landscape with the changing course of the river.
It order for a depositional environment to deposit the significant amounts of sand, silt, mud, clay, calcium carbonate remains and mid-ocean ooze that we see in the sedimentary record, that environment has to persist in one place for quite some time. That's why the transgression onto or regression from a landscape has to be gradual, otherwise there's no time for significant deposits to form. The runoff from land has to feed the depositional environments with the raw material that it sorts by density and grain size. The heaviest material, sand, can fall out of suspension in the active water of waves, and so we find sand at the interface between between land and ocean, and the activity of the waves provides additional weathering that produces more sand. A little further off the coast we find mud, silt and clay sediments that consist of smaller and lighter particles and that require quieter water to fall out of suspension. Further off the coast if the environment is suitable the carbonate skeletons of microorganisms will accumulate, and otherwise there will be only mid-ocean ooze.
Walther's Law is definitely not about a flood moving across a landscape, even a global flood. Once the world is flooded no water is moving in any significant way and there are no higher elevations from which sediments can be supplied. You think the sediments would come from the scoured landscape, but floods do not scour landscapes, only fast flowing water does that, and fast flowing water only occurs in confined waterways. Floods spread out across landscapes and move slowly. But even a fast flowing tsunami does not scour a landscape, as we saw when the tsunami flooded across the Japanese landscape. About the best it did in the way of scouring was pick up a little beach sand and carry it a little bit inland.
YOu think it would have taken "geologic time" in the millions of years to lay down the sediments we see in the strata, I don't. Matter of plausibilities.
No, it is not a "matter of plausibilities. There is nothing plausible about a global flood that has no source of sediment yet not only produces copious sedimentary layers into which it inserts undisturbed footprints, burrows and nests, it sorts them by type (but without regard to density and size), by degree of difference of fossils from modern forms, and by amount of radiometric decay products. Your ideas about the Flood fail on the simplest and most fundamental levels.
You can't prove how long it would have taken and neither can I,...
Au contraire, we *can* prove (that's "prove" in the scientific sense of providing evidence for one's theories) how long it would have taken because we can observe how slowly the same processes are happening today while building sedimentary layers identical in character to their lithified cousins deeper in the geologic column. In addition we have the radiometric data, and we have the fossils.
...but five months up and five months back seems like plenty of time to carry and dump sediments.
Here's yet another reason you're mistaken. Sedimentary layers are everywhere around the world. If the flood had truly carried sediments from one place to be deposited in another, then the places where the sediments came from should have no material left. Yet, as I said, sedimentary layers are everywhere. There is nowhere in your scenario from which the sediments could come.
Oceans cover 3/4 of the globe, which is 3/4 of a global flood. There's nothing in today's oceans remotely similar to your claim of cubic miles and miles sediments being carried from one set of places hither and yon to another set of places in short periods of time.
--Percy

This message is a reply to:
 Message 260 by Faith, posted 07-28-2014 12:52 AM Faith has replied

Replies to this message:
 Message 455 by Faith, posted 07-30-2014 5:28 PM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 443 of 740 (734546)
07-30-2014 3:01 PM
Reply to: Message 270 by Faith
07-28-2014 2:11 AM


Re: Cardenas
Faith writes:
You have been given abundant evidence that the Cardenas is extrusive. Why do you simply deny?
Why do you assume that there is only one intrusive/extrusive event?
I'm not so much assuming it as looking for evidence for it. Because I did get convinced that all this occurred after the strata were laid down so I continue to look for how that could be evidenced.
This is a puzzling approach. Since you're only now seeking evidence of a single event, you must have become convinced of a single event before you had evidence.
One might find it a better practice to allow one's mind to become convinced of things only after evidence is identified, not before.
--Percy

This message is a reply to:
 Message 270 by Faith, posted 07-28-2014 2:11 AM Faith has replied

Replies to this message:
 Message 446 by Faith, posted 07-30-2014 3:39 PM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 445 of 740 (734548)
07-30-2014 3:39 PM
Reply to: Message 272 by Faith
07-28-2014 2:25 AM


Re: New depositions strangely different from old strata
Faith writes:
Yes, eroded out of an incredibly thick and extensive metamorphized sandstone LAYER, that covered some enormous amount of geography. Yes, I know that. Suggests the Flood to me.
But everything suggests the Flood to you. To someone else that image might suggest ancient aliens, and you have no more evidence for your Flood then they'd have for aliens.
If a rapid flow had created that plateau while its sedimentary layers were in a softer state then it would be teardrop shaped. Also, as you've been informed many times, rocks do not harden by drying. Once the pressure of compaction is removed, lithification ceases.
It's their hugeness, like the Coconino, the Redwall, the Dover Cliffs and other similar formations, their depth and breadth, that suggests they'll never be repeated on this planet, not their age, which of course is only about 4300 years on my reckoning anyway.
Well, since you've said this again, it bears repeating again that this is not true. This is the image of the kilometers-deep layers that have formed and still forming today in the Gulf of Mexico off the coast of Louisiana and Texas:
--Percy

This message is a reply to:
 Message 272 by Faith, posted 07-28-2014 2:25 AM Faith has replied

Replies to this message:
 Message 447 by Faith, posted 07-30-2014 4:07 PM Percy has replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


(1)
Message 454 of 740 (734558)
07-30-2014 4:49 PM
Reply to: Message 284 by Faith
07-28-2014 4:02 AM


Re: New depositions strangely different from old strata
Faith writes:
I would think it would be a lot harder to accumulate that much sand in one place on the Old Earth model than on the Flood model. In the Flood the water would do a lot of pulverizing as well as transporting and depositing. Where's all that sand going to come from over hundreds of millions of years? Can you identify a source on the South American continent and a method for its deposition and compression to such a huge depth and breadth?
The processes that produces the sedimentary layers found around the world have been described before, but it doesn't hurt to describe them again. This isn't any great mystery, because we see these processes happening today. The runoff from land reaches the coastline via wind and rivers and water flow from rain, and this runoff carries the products of all the weathering from the landmass in the form of rocks, pebbles, grains and particles of minerals.
At the coastline a sorting process is performed on this sediment laden runoff from land. Because the most energetic water is nearest shore, that is where the largest and densest material will fall out of suspension. This is why the biggest and heaviest sediments, namely sand and pebbles, are found along beaches and not further out.
A little further from shore the water is much more still, and so silt and mud and clay will fall out of suspension there.
Even further from shore, too far off shore for the sediment-laden runoff from land to reach very effectively, will be mid-ocean ooze and, if conditions are right, carbonate skeletons of dead microorganisms.
As the sediments accumulate their weight causes isostatic subsidence, so more sediments accumulate, adding more weight and causing more subsidence. Even with stable sea levels there will always be coastline erosion, so depending upon the amount of runoff from land the natural state of a coastline is not stationary but is one of gradual transgression inland or regression out to sea. It depends upon whether sediments are delivered to a coastline faster than oceans are eroding the coastline away. So the sedimentary depth gradually builds up over thousands of years as the coastline moves gradually inland. The layers will not be horizontal both because of gradual isostatic subsidence and because the transgressions are climbing higher on the landscape while regressions are receding lower.
The Mississippi River Delta is a good example of sediments being delivered to the coast faster than oceans are eroding them away. The Beaufort Sea in Alaska, where in some years as much as a hundred feet of coast can disappear, is an example of a coastline eroding faster than sediments are being delivered. Happisburgh in Norfolk, Great Britain, is another good example:
Of course, if seas are rising or falling, or even alternately rising and falling, then coastlines will move back and forth across a landscape, generating complex and interesting sequences of sedimentary layers. Also note that when seas retreat then the sedimentary layers just deposited will be exposed to the forces of weathering and will be eroded, creating an unconformity surface the next time the sea transgresses and begins depositing more sediments.
--Percy
Edited by Percy, : Typo.

This message is a reply to:
 Message 284 by Faith, posted 07-28-2014 4:02 AM Faith has not replied

  
Percy
Member
Posts: 22390
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 471 of 740 (734587)
07-31-2014 8:49 AM
Reply to: Message 312 by Faith
07-28-2014 3:51 PM


Re: New depositions strangely different from old strata
Hi Faith,
Obviously I'm still around 150 messages behind, but I wanted to comment on this:
Faith writes:
Just because I'm talking about the great sedimentary rocks doesn't mean I'm ignoring anything, I'm simply talking about the great sedimentary rocks.
I hope you're talking about "the great sedimentary rocks" to make a point that will lead back to the topic about growing the geological column. I thought this diagram from JonF made the point especially well that not only are volcanic deposits of basalt and tuff interspersed with sedimentary layers, this process has been continuous for a long time right up to the present day:
By the way, "great sedimentary rocks" is not an actual term within geology so far as I am aware, and as I pointed out in previous posts, layers just as "great" are still in the process of formation today.
As others have mentioned before, you've mistakenly cast the Grand Canyon region as telling the full story of geology around the world, as if the Grand Canyon layers were the definition of "typical" and anything different is an exception. It's easy to make this mistake because there is far more information about the layers of the Grand Canyon region than most other regions of the world, but that's only because the Grand Canyon makes those layers so easy to study. We can't study layers currently being formed because since they're in regions of net deposition there can be no canyons cut through them. The only way we can know the inner details of new sedimentary layers forming on sea and lake bottoms is to drill cores. It isn't like at the Grand Canyon where you can literally see all the layers before your very eyes. And most geological layers do not have canyons cut through them. We can't show you images of sedimentary layers interspersed with volcanic layers if no canyon has been cut to expose the layers.
You're taking this lack of data about non-exposed layers as compared to the copious data available about the Grand Canyon layers to draw the conclusion that what happened at the Grand Canyon is what happened everywhere. That conclusion is wrong. In particular, both tectonic and volcanic activity have never been absent during the entire history of the Earth. But much of that activity is concentrated at plate boundaries, and the Grand Canyon region isn't remotely close to any plate boundary.
--Percy
Edited by Percy, : Typo.

This message is a reply to:
 Message 312 by Faith, posted 07-28-2014 3:51 PM Faith has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024