The Naked Scientists

The Naked Scientists Forum

Author Topic: Angular Sand?  (Read 7994 times)

Offline OokieWonderslug

  • Full Member
  • ***
  • Posts: 93
    • View Profile
Angular Sand?
« on: 04/05/2011 19:07:48 »
The other day I went to place called "Sugarloaf Mtn" SC. It is an odd outcrop of iron cemented sandstone that protected a sand dune from eroding thus leaving a hill in it's place topped with this sandstone.

This site is confusing to me. Supposedly the Carolina Sandhills are a result of sand blown westward by winds forming a dune area that subsequently had vegetation grow over it and stabilized the dunes into hills.

If that is so, then where did the sandstone come from on top of the dune? How did it get blown there? And what caused it to cement together with iron in only that one spot?

And this is the biggie, how in the world did sand get anywhere and be so angular as this sand in the sandstone? It isn't the least bit rounded in any way. It is rough like it came straight out of a crusher. How does sand form without any weathering? Doesn't sand form when large rocks are broken unto smaller rocks through erosion (wind, water)? Doesn't this process tumble the sand until it is fairly smooth?

The sand under the rocks is smooth like it could be windblown or at least eroded out of some form of sea bed or whatever. But the sand in the stone is as rough as it can be. I can't figure it.

What I see when I look at the scene there is apparently impossible. What I see is a fossil sea bed and a completely rusted and decomposed ship that has had it's iron from it's hull slowly cement the sea sand together and then the sea went away, all the surrounding sand washed away leaving the remains of this ship (and it is a ship sized outcrop. About 1,000ft long, 200ft wide, and apparently about 50ft thick at it's thickest.) There are empty pockets in the rock and what looks like impressions of broken timbers and also places that look like it was crumpled steel at one point.

We all know this is impossible. The sea hasn't been there since the cretaceous period and there weren't any supertanker sized ships back then at any rate. But if that's so impossible, what other way is there to explain this outcrop? It is all alone out there in a sea of sand dunes.

But even if it was a ship, that still doesn't explain the roughness of the sand grains. How does that happen? The only thing I can come up with is the ship was carrying a cargo of crushed quartz and mica flakes when it sunk. But that's impossible.

So what's the deal with the sand and the lonely iron cemented stone all alone in the middle of nothing else?


 

Offline Airthumbs

  • Hero Member
  • *****
  • Posts: 958
  • Personal Text
    • View Profile
Re: Angular Sand?
« Reply #1 on: 05/05/2011 00:46:58 »
I don't suppose you found any name plaques did you like USS Eldridge for example?
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Re: Angular Sand?
« Reply #2 on: 05/05/2011 03:55:31 »
First, I am assuming that the Sugar Loaf Mt you are referring to is close to US Highway 1 northwest of Florence, SC. There is a Sugar Land Mountain in the Thrust Section of the interior Piedmont that is a lot more interesting.

The more angular a sand grain the YOUNGER it is. These sand grains  had just eroded from fine grained granite or diorite (probably - possibly could have been some other rock type.) These sand grains just came from a fine to very fine grained igneous source. So they didn't get transported very far or they would have been more rounded.

Secondly, the flatness of the formation or geologic unit under it doesn't really have much to do with the formation over it or the sand grain unit itself. The were laid down sequentailly, one on top of each other.

Since the geologic map of S. Carolina shows the area of the park to be in the Cretaceous, the area we are talking about was having very rapid erosion and deposition from the west. There were large deltas spewing sand all over the place out in front them that were then much higher than the Appalachian Mountains are now. The layered water-placed deposits were covered up as fast as they were put down.
As the depositional center moved from one area to another, as the mouth of the Mississippi is now try to do by pouring its water out through the Atchafalaya River Basin, Erosion takes place and the sands are transported along shore, sorted in size, and re-deposited into sand dunes. These then get blown in-land as dunes in specific areas. They get covered with mud and become the perfect place to allow water to flow through. As the iron rich water flowing through the sand gets closer to the sea, the amount of iron it can carry diminishes, the iron is deposited on the sand grains and the grains are eventually cemented together.

Reverse the process of erosion 50 million or more years later and you get Sugar Loaf Mountain.


REMEMBER: Sand is very hard, It takes a very long time to go from an angular grain to a rounded grain. Usually it takes 4 to 8 erosional cycles for the round grains to be formed
« Last Edit: 05/05/2011 03:58:28 by JimBob »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Angular Sand?
« Reply #3 on: 05/05/2011 18:33:59 »
Very cool JB, I can see how such a formation sets the imagination working though.
I would really have liked a photo of it :) Just to see what people think it could be, not knowing this.
 

Offline OokieWonderslug

  • Full Member
  • ***
  • Posts: 93
    • View Profile
Re: Angular Sand?
« Reply #4 on: 06/05/2011 00:57:59 »
First, I am assuming that the Sugar Loaf Mt you are referring to is close to US Highway 1 northwest of Florence, SC. There is a Sugar Land Mountain in the Thrust Section of the interior Piedmont that is a lot more interesting.

The one in SC is what I was referring to.

The more angular a sand grain the YOUNGER it is. These sand grains  had just eroded from fine grained granite or diorite (probably - possibly could have been some other rock type.) These sand grains just came from a fine to very fine grained igneous source. So they didn't get transported very far or they would have been more rounded.

I understand that. It's why I was wondering. The sand all around is much smaller and is rounded. The sand in the rock is massive and very sharp.

Secondly, the flatness of the formation or geologic unit under it doesn't really have much to do with the formation over it or the sand grain unit itself. The were laid down sequentailly, one on top of each other.

Is that true for a dune field? From what I have read, the Sandhills are supposed to be the result of wind blown sand. The Ocean level fell and exposed the coastal plain and the sand then blew into dunes and traveled northwest until vegetation stopped their progress. I know the sands of the coastal plain are the result of river effluent. But the sands of the Sandhills are supposed to have been blown there. How can angular sand be blown anywhere and then cemented together at the top of a dune?


Since the geologic map of S. Carolina shows the area of the park to be in the Cretaceous, the area we are talking about was having very rapid erosion and deposition from the west. There were large deltas spewing sand all over the place out in front them that were then much higher than the Appalachian Mountains are now. The layered water-placed deposits were covered up as fast as they were put down.

So there was a 4000ft cliff face at the ocean? I had no idea the Fall Line was that pronounced at any point. I have read the ocean was 800ft higher than it is today, but not that the very edge of the piedmont was so tall. Well, I did read that it was at one time, but when Africa broke away didn't it pull the piedmont and thin it out and that was when the mountains that were here went away? Didn't Africa leave 200 million years ago? The cretaceous was 65 million years ago. Weren't the mountains long gone by then? I had been given the impression that the topography of today's piedmont is not much different than it was 65 million years ago other than the ocean being at the Fall line and the hills being a little more pronounced than they are today.

I think my timeline is skewed or I have read the wrong articles about geology. 


As the depositional center moved from one area to another, as the mouth of the Mississippi is now try to do by pouring its water out through the Atchafalaya River Basin, Erosion takes place and the sands are transported along shore, sorted in size, and re-deposited into sand dunes. These then get blown in-land as dunes in specific areas. They get covered with mud and become the perfect place to allow water to flow through. As the iron rich water flowing through the sand gets closer to the sea, the amount of iron it can carry diminishes, the iron is deposited on the sand grains and the grains are eventually cemented together.

Let me see if I got my head around this correctly. 65 million years ago, the mountains of the piedmont were like the Appalachians are today. There were short rivers running into the sea. These rivers deposited sand where the Sandhills are today. The fossil dunes are not the remnants of wind blown dunes, but water formed dunes under the ocean in a continental shelf type environment. As the water receded the rivers cut new channels and eventually there was an oxbow lake or something of the sort and bacteria managed to stay there long enough for it's secretions to cement the sand together into sandstone. The areas that look like folded rusted metal are bacteria mats that have sunk and collapsed on the bottom and then were covered in sand. The sand washed away and the river dried up or moved two miles west and then erosion took away all the surrounding sands and left this "fossil oxbow" sitting high and dry.

Is this right? How did the piedmont sink so far so fast? I thought the crust was under compression in this area since we are locked into the spreading ridge in the Mid Atlantic. How would it sink? I thought also that the land slowly rose as erosion removed the overburden. How did it rise and fall at the same time?

Why do they say the Sandhills are the result of wind and not water?


Reverse the process of erosion 50 million or more years later and you get Sugar Loaf Mountain.


REMEMBER: Sand is very hard, It takes a very long time to go from an angular grain to a rounded grain. Usually it takes 4 to 8 erosional cycles for the round grains to be formed
« Last Edit: 06/05/2011 02:00:18 by OokieWonderslug »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Angular Sand?
« Reply #5 on: 06/05/2011 05:02:21 »
Oakie can't you also post some photos of it? It's so much nicer to see what we're talking about, and maybe some close in photos of the texture?
 

Offline OokieWonderslug

  • Full Member
  • ***
  • Posts: 93
    • View Profile
Angular Sand?
« Reply #6 on: 06/05/2011 23:38:50 »
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Angular Sand?
« Reply #7 on: 09/05/2011 00:55:17 »
First, I am assuming that the Sugar Loaf Mt you are referring to is close to US Highway 1 northwest of Florence, SC. There is a Sugar Land Mountain in the Thrust Section of the interior Piedmont that is a lot more interesting.

The one in SC is what I was referring to.

The more angular a sand grain the YOUNGER it is. These sand grains  had just eroded from fine grained granite or diorite (probably - possibly could have been some other rock type.) These sand grains just came from a fine to very fine grained igneous source. So they didn't get transported very far or they would have been more rounded.

I understand that. It's why I was wondering. The sand all around is much smaller and is rounded. The sand in the rock is massive and very sharp.
They are from two different sources and deposited at two different times - that is all.


Secondly, the flatness of the formation or geologic unit under it doesn't really have much to do with the formation over it or the sand grain unit itself. The were laid down sequentially, one on top of each other.

Is that true for a dune field? No From what I have read, the Sandhills are supposed to be the result of wind blown sand. they are The Ocean level fell and exposed the coastal plain (sea level does not need to change. All that need happen is that enough sand is deposited to get some of it above sea level at high tide) ... and the sand then blew into dunes and traveled northwest a VERY short difference - see picture belowuntil vegetation stopped their progress. I know the sands of the coastal plain are the result of river effluent. But the sands of the Sandhills are supposed to have been blown there. How can angular sand be blown anywhere and then cemented together at the top of a dune?

Angular sand is just angular sand. It behaves in every way as other sand - there is nothing magic about it being angular.

Also,you are assuming that not much else was going on.

MOST IMPORTANTLY - You are thinking of the area as if it has not changed much since the angular sandstone was deposited and then left as we see it today.

It didn't happen that way. The cemented Cretaceous sand was deeply buried before being exposed again.
 


Since the geologic map of S. Carolina shows the area of the park to be in the Cretaceous, the area we are talking about was having very rapid erosion and deposition from the west. There were large deltas spewing sand all over the place out in front them that were then much higher than the Appalachian Mountains are now. The layered water-placed deposits were covered up as fast as they were put down.

So there was a 4000ft cliff face at the ocean?

NO

I had no idea the Fall Line was that pronounced at any point. I have read the ocean was 800ft higher than it is today, but not that the very edge of the piedmont was so tall.

The Piedmont we see today was deep;ly burried at the time the sand was deposited.

Well, I did read that it was at one time, but when Africa broke away didn't it pull the piedmont and thin it out and that was when the mountains that were here went away? Didn't Africa leave 200 million years ago?

It has begun to separate in some places but was still attached in the south Atlantic

The cretaceous was 65 million years ago. Weren't the mountains long gone by then? 
No  The Cretaceous deposits were at the shoreline or just off-shore

I had been given the impression that the topography of today's piedmont is not much different than it was 65 million years ago other than the ocean being at the Fall line and the hills being a little more pronounced than they are today.

I think my timeline is skewed or I have read the wrong articles about geology. 


Time line fairly accurate - visualization of the respective heights and their relationship is the main problem.


As the depositional center moved from one area to another, as the mouth of the Mississippi is now try to do by pouring its water out through the Atchafalaya River Basin, Erosion takes place and the sands are transported along shore, sorted in size, and re-deposited into sand dunes. These then get blown in-land as dunes in specific areas. They get covered with mud and become the perfect place to allow water to flow through. As the iron rich water flowing through the sand gets closer to the sea, the amount of iron it can carry diminishes, the iron is deposited on the sand grains and the grains are eventually cemented together.

Let me see if I got my head around this correctly. 65 million years ago, the mountains of the piedmont were like the Appalachians are today. There were short rivers running into the sea. These rivers deposited sand where the Sandhills are today. The fossil dunes are not the remnants of wind blown dunes,   Yes, they are but water formed dunes under the ocean in a continental shelf type environment. As the water receded the rivers cut new channels and eventually there was an oxbow lake or something of the sort and bacteria managed to stay there long enough for it's secretions to cement the sand together into sandstone. The areas that look like folded rusted metal are bacteria mats that have sunk and collapsed on the bottom and then were covered in sand. The sand washed away and the river dried up or moved two miles west and then erosion took away all the surrounding sands and left this "fossil oxbow" sitting high and dry.

Is this right? How did the piedmont sink so far so fast? It didn'tI thought the crust was under compression in this area It hasn't ben for quite a while. The Charelston Earthquake of 1886 was the result of crustal relaxation - the opposite of what you are theorizing since we are locked into the spreading ridge in the Mid Atlantic. How would it sink? I thought also that the land slowly rose as erosion removed the overburden. How did it rise and fall at the same time?

Why do they say the Sandhills are the result of wind and not water? Simple - because the wind blew the sand into dunes.


Reverse the process of erosion 50 million or more years later and you get Sugar Loaf Mountain.


REMEMBER: Sand is very hard, It takes a very long time to go from an angular grain to a rounded grain. Usually it takes 4 to 8 erosional cycles for the round grains to be formed

This is what the area MAY have looked like: The cliffs in the far distant are probably only 50 feet high and the Welch mountains behind them are only a 1000 feet or so high.



CREDIT - http://www.homedesignfind.com/green/an-airy-underground-home-high-above-the-welsh-coast/


Sand dunes such as these get the sea grass solidifying them, are subsequently drowned and cemeted - not by biological action but by the chemistry of the water with the iron in it changing and the iron precipitating out in rust coatings on the sand grains binding them together.




CREDIT - The Guardian - http://www.guardian.co.uk/environment/2007/feb/13/frontpagenews.ruralaffairs 
 

Offline OokieWonderslug

  • Full Member
  • ***
  • Posts: 93
    • View Profile
Angular Sand?
« Reply #8 on: 09/05/2011 01:43:35 »
Thank you for your reply. I guess what threw me off what when you said there was a 4000ft altitude (the average height of the Appalachians) difference between then and now. I have read that 5 miles of sediment has washed away from over the piedmont. But I assumed it was always the same altitude above sea level the entire time and the ground rebounded and raised as the weight of the land was removed. The real story is confusing though.

There were mountains here, they eroded away, there came more mountains, they eroded away, and again there came more, they fell and are about eroded away yet again. The ocean comes and goes, the land here used to be another version of Japan, it is hard to keep it all straight.

So, what we see today was deeply buried and has been exposed through erosion. There are no fossil sea beds as what we see today is merely random deposits eroded out of a bed with no hint of past topography.

I had the impression that the surface we see today was pretty much what was exposed when the ocean receded. That sand had blown off of the exposed sea bed and collected into dunes and then froze. You're saying that happened, it was all buried and then re exposed.

I had no idea that bb size sharp quartz grains could be blown into dunes. ALL of the sandstone deposits that are wind created I have ever seen were made of small rounded grains. That is why I questioned it. It's out of the realm of my past observations. The sand everywhere except the rock is typical of the wind blown deposits I have seen in the past. That is why it stood out so much.

One of these days I may fully understand the geologic history of the Carolinas. But not today apparently.
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Angular Sand?
« Reply #9 on: 09/05/2011 21:08:21 »
You got it - the earth is constantly changing shape - 500 years from now you wouldn't recognize the place your house sits on.

 

Offline Bass

  • Neilep Level Member
  • ******
  • Posts: 1340
  • Thanked: 5 times
    • View Profile
Angular Sand?
« Reply #10 on: 09/05/2011 23:22:46 »
 
You got it - the earth is constantly changing shape - 500 years from now you wouldn't recognize the place your house sits on.



I hope to live so long...

anyway, my house will probably be under 300' of water in Lake Missoula [:0]
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Angular Sand?
« Reply #11 on: 10/05/2011 19:42:48 »
But ..... well, your a fish. Why should that make a difference?
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
Angular Sand?
« Reply #12 on: 10/05/2011 22:55:22 »

 anyway, my house will probably be under 300' of water in Lake Missoula [:0]


Bummer! That means mine will get washed away when the friggin dam breaks.

Anyway, I wouldn't worry too much about it. Jellystone will probably blow its top first.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Angular Sand?
« Reply #13 on: 11/05/2011 05:42:54 »
Thanks for the photos Oakie :)
Made it easier to see.
=

And a sweet bike.
« Last Edit: 11/05/2011 05:51:27 by yor_on »
 

Offline OokieWonderslug

  • Full Member
  • ***
  • Posts: 93
    • View Profile
Angular Sand?
« Reply #14 on: 13/05/2011 01:13:43 »
Thanks. Ride it everywhere I go. My pride and joy.
 

The Naked Scientists Forum

Angular Sand?
« Reply #14 on: 13/05/2011 01:13:43 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums