Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 86 (8915 total)
Current session began: 
Page Loaded: 07-21-2019 1:33 AM
23 online now:
AZPaul3 (1 member, 22 visitors)
Chatting now:  Chat room empty
Newest Member: 4petdinos
Upcoming Birthdays: anglagard
Post Volume:
Total: 857,228 Year: 12,264/19,786 Month: 2,045/2,641 Week: 0/554 Day: 0/113 Hour: 0/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Introduction To Geology
petrophysics1
Inactive Member


(1)
Message 173 of 293 (675137)
10-06-2012 5:01 PM
Reply to: Message 172 by Dr Adequate
10-06-2012 2:16 PM


Re: Unconformities
Why don't you go and rewrite this. Begin by explaining and defining AN UNCONFORMITY. Then everyone will see that an angular unconformity, a disconformity, a nonconformity, and a paraconformity are all types of an unconformity.

Nonconformity is rarely used outside of a classroom and the British do not recognize "disconformity" or "paraconformity".

By what you've said, about any bedding boundary can be called a paraconformity (basically a useless word, and what are the chances of NOTHING happening, no deposition, no erosion, no rain, no wind, no plants growing, no creature walking across it, shiting or pissing on it or any one of a thousand things which would leave a mark).

BTW you can not see a jump in fauna across a noncomformity.....because there aren't any fossils in igneous or metamorphic rocks.

While you're at it fix this too.

Dr.A writes:

The picture below shows large-scale cross-bedding in sandstone. (To give you an idea of the scale, the small patches of green visible in the top right corner are not moss, as you might guess, but bushes.)


The scale of the cross-bedding depends on the process that produced it: this was produced by wind; smaller-scale cross-bedding would be produced by the formation of tidal ripples.

This was not deposited by wind.

Edited by petrophysics1, : add ,

Edited by petrophysics1, : remove nd

Edited by petrophysics1, : No reason given.


This message is a reply to:
 Message 172 by Dr Adequate, posted 10-06-2012 2:16 PM Dr Adequate has responded

Replies to this message:
 Message 174 by Dr Adequate, posted 10-06-2012 6:44 PM petrophysics1 has not yet responded
 Message 175 by Dr Adequate, posted 10-08-2012 2:23 PM petrophysics1 has responded
 Message 183 by TrueCreation, posted 10-12-2012 10:43 AM petrophysics1 has not yet responded

  
petrophysics1
Inactive Member


(1)
Message 177 of 293 (675280)
10-09-2012 6:05 PM
Reply to: Message 175 by Dr Adequate
10-08-2012 2:23 PM


Re: Petrophysics
Dr.A. writes:

Except that if the period of non-deposition lasted for any significant amount of time we would see a sudden jump in the faunal succession: where the geological column shows fossils in order (for example) P, Q, R, S, T, U, then at the location of the nonconformity we would see P, Q, T, U, where P and Q correspond to the first episode of deposition, T and U correspond to the second episode of deposition, and the missing fossils R and S correspond to the time at which no deposition was taking place.

Get rid of "nonconformity" in this sentence. It makes no sense.

Paraconformity= "A term introduced by Dunbar & Rodgers(1957, p.119)* for an obscure or uncertain uncomformity in which no erosion surface is discernable or in which the contact is a simple bedding plane, and in which the beds above and below are parallel"(Glossary of Geology 4th ed, p.464, Julia A. Jackson).

In your example above you have a break in the fauna. Now I don't consider that to be either "obscure" or "uncertain", so it doesn't match the definition. I'd call it an unconformity.

HOWEVER, do you FEEL it's obscure or do you FEEL uncertain about it? If you do and also think that the geologists feelings have a place in geologic descriptions by all means call it a paraconformity.

Most (but not all) unconformities are angular unconformities. If you call something a disconformity make sure you have measured the strike and dip of the beds above and below and that they are parallel. Don't do this by eyeball, if you don't, just call it an unconformity since otherwise you are claiming something you actually don't know.

Your example of a disconformity is poor. If that structure is an anticline the beds above and below are not parallel anywhere. If it's a fold there is a line along the crest which can be said to be parallel to the beds above. I've never seen anyone do that. I suggest a drawing with parallel beds and an erosion surface or a paleosol. Something simple and to the point.

Unconformity= A substantantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratagraphic succession, such as an interruption in the continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedmentary strata. It results from a change that caused deposition to cease for a considerably span of time, and it normally implies uplift and erosion with loss of the previously formed record. An unconformity is of longer duration than a diastem. ..........Local, contemporaneous erosion and deposition associated with geological processes such as point-bar development or aeolian dune migration are excluded from the definition of unconformity. (same ref. as above, p.689)

I'll be back in a bit to talk about that picture.

*Dunbar, C.O., and Rodgers, John(1957) Principles of Stratigraphy. New York: Wiley.

Edited by petrophysics1, : typos & insert spaces

Edited by petrophysics1, : Waste time, adding a ref.

Edited by petrophysics1, : typo

Edited by petrophysics1, : insert spaces

Edited by petrophysics1, : No reason given.

Edited by petrophysics1, : No reason given.


This message is a reply to:
 Message 175 by Dr Adequate, posted 10-08-2012 2:23 PM Dr Adequate has responded

Replies to this message:
 Message 178 by Dr Adequate, posted 10-09-2012 9:00 PM petrophysics1 has not yet responded
 Message 179 by Pressie, posted 10-10-2012 12:40 AM petrophysics1 has not yet responded
 Message 182 by Dr Adequate, posted 10-11-2012 3:18 PM petrophysics1 has not yet responded

  
petrophysics1
Inactive Member


(1)
Message 245 of 293 (687907)
01-17-2013 5:02 PM


Try Looking
Dr.A writes:

The picture below shows large-scale cross-bedding in sandstone. (To give you an idea of the scale, the small patches of green visible in the top right corner are not moss, as you might guess, but bushes.)


The scale of the cross-bedding depends on the process that produced it: this was produced by wind; smaller-scale cross-bedding would be produced by the formation of tidal ripples.

Source of the above quoted

This was not deposited by wind.

Take your cursor/arrow and put it in the lower left corner of the picture. Now slide it up the left side of the picture to the base of the reddish brown conglomerate. Look at the size of the rocks just above your cursor/arrow. Do you really think the wind blew those in there?

Move about 20% to the right, see those holes. Well rocks like the ones on the left used to be there but fell out.

Go to the center, does that stuff look well sorted to you? It looks poorly sorted to me which means there is no way this is wind blown.

See the cross-beds along the bottom, those are trough cross-beds. They form in fluvial deposits.

Geology is about the careful, accurate, objective (unbiased) description and identification of minerals, rocks and fossils and their position in 3 dimensional space. Without this nothing else is possible in geology. If you understood that you would have looked at the photo, instead of believing an interpretation.

Rock descriptions are reproducible scientific data, they never include someone's interpretation of how it was deposited.

Edited by Adminnemooseus, : Added source for quoted material, since the "reply to message" was not used.


Replies to this message:
 Message 246 by Dr Adequate, posted 01-18-2013 2:41 AM petrophysics1 has not yet responded

  
petrophysics1
Inactive Member


Message 279 of 293 (697126)
04-21-2013 7:21 PM


Quiz?
So are you going to do a Quiz or would you like me to make one?

You probably will not like mine, since it will be about doing geology instead of reading about it, but it could be enlightening.


  
petrophysics1
Inactive Member


Message 281 of 293 (697868)
05-01-2013 9:43 AM


General Quiz
So here is a rather good quiz that you should do well on if you have read and understand what Dr.A has written here.

19 topics with 10 questions each about geology. I regard a test/quiz not as a test to see what you know but as a way to point you to what you don't understand so you can find out about it.

http://homepage.smc.edu/...richard/rocktest/physical_geology

I think this quiz is good and covers a lot of what Dr.A has talked about. It is, from my viewpoint as a working geologist, very simple, but I think if you can get around 70% on the quizes Dr.A has done a good job.

What do you think?

{I have taken this message and created a new topic with it. Please do any responses to the message at that new topic - "Introduction To Geology quiz".- Adminnemooseus}

Edited by Adminnemooseus, : Note in red.


  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019