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Asking braided stream & meandering 
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Joined: Mon Mar 28, 2011 7:55 am
Posts: 5
Post Asking braided stream & meandering
what is the characteristic of braided stream and meandering,
1. characteristic in wireline log curve
2. structure sedimen
3. mineralogy (if any)

if braided mostly in river, how can it be calcareous, where from clacareous ?

Thanks


Wed Feb 22, 2012 2:36 am

Joined: Wed May 02, 2012 3:45 pm
Posts: 18
Post Re: Asking braided stream & meandering
Hello,

I just joined the group today and see that no one has responded to your question.

I have only a few minutes and discussing the characteristics of braided and meandering rivers will take longer than I have but I promise to get back to the question in a few days as it is one of my favorite topics.

In the time I have, I offer the following 3 suggestions for ways of getting calcereous cement in braided river sands.

1) As occurs locally, microscopic limestone can be picked up by the wind and scattered over distances of 10's to 100's of km. Along the way it will be deposited as dust on the ground and the dry bed or water surface of any river it encounteres. From there it can be incorperated directlyl into the sediment or dissolved and carried down into the sands.

2) The tributaries to the braided river can be eroding limestone fragments from outcrops and/ or picking it up in solution before emptying into the braided river channel.

3) Assuming you are dealing with a subsurface braided stream deposit, the calcium could be dissolved anyplace and then precipitated in the sands long after the sands were buried.

This does not pertain strictly to braided or meandering streams but I have seen extreme examples where the question I had to answer was "Is this a sand that had the matrix dissolved out and then replaced with limestone or is it a limestone that received the clastic particles from the wind or (?) while being precipitated. I did not have a petrographic microscope to examine thin sections so the question remained unanswered.

More later.

Darryl


Wed May 02, 2012 11:27 pm

Joined: Wed May 02, 2012 3:45 pm
Posts: 18
Post Re: Asking braided stream & meandering
hestu wrote:
what is the characteristic of braided stream and meandering,
1. characteristic in wireline log curve

I don't remember the answer to the question but if you look around or do an internet search you may be able to find a wall chart of SP log characteristics for various depositional environments. I have mine at home but not in the trailer so I can't tell you the publisher. I think it was IHRDC but I don't think they are in business now. It may have been Penwell of Tulsa Oklahoma. You may be able to find one at USGEO SUPPLY, I just bought another wall chart of elog characteristics from them a few weeks ago.

2. structure sedimen {color=#0000FF][/color]

Again, I don't have a direct answer to the differences in sedimentary structures or the vertical or horizontal sequence of such structures but if you have access to a library you might compile a usable set of criteria from the following books: Fluvial Sedimentology, edited by A. D. Miall, 1978, Canadian Society of Petroleum Geologists; Sedimentary Environments and Facies, Edited by H. G. Reading, pub by Elsevier OR Balckwell Scientific Publishing - 1978 and Sands and Sandstones by Pettijohn, Potter & Siever, pub by Springer-Verlag,1973. These are old books but I am an old geologist.

3. mineralogy (if any)

[color=#0000FF[/color]While this is a good question, I don't think there is going to be a good answer but the following may help.

A) the minerals in a river bed at any particular point are those that have been put in minus that that have been taken out
A1) the minerals put in come from the source area of the tributaries
A2) the minerals taken out include those that have been chemically altered to clay, those that have abraided to an average size less than the minimum size preserved through out the gathering, cleaning, seiving and maybe other lab and field processes.


B) Streams tend to be braided near their source and meandering near their terminus - this may be to generallized to be of much value but it is true for a long enough river.

C) Many of the rivers long enough for statement B to be true originate in mountains or other high areas where igneous and metamorphic rocks are prevalent - an obvious exception would be those originating in the foot hills of major mountain chains because the outcrops there are frequently dominated by sedimentary rocks uplifted by the rising mountain chain.

D) braided streams are characteristic of areas with a higher slope and a more intermittent or periodic moisture input than meandering streams.

E) combining A, B, C, and D and hoping the exception noted in C doesn't cause a problem: - Braided streams may have:
E1) a higher ratio of pyroxenes, amphiboles and plagioclase to quartz and or orthoclase
E2) a higher ratio of large grains to small grains
E3) a higher ratio of quartz grains with a high angularity to those with low angularity
E4) a higher variability of grain size - look up Visher Plots or grain size historgrams for more information on this idea.
E5) a higher variability in paleo current direciton as indicated by the orientation of the long axes of individual minerals or grains.
E6) a higher number of individual fining upward sequences per unit length of core examined or vertical distance of outcrop examined.

Note that the items in the above list are qualitative and or relative and they are trends or tendencies. I doubt there is much or even anything quantitative about any of them.

You might also look up topics related to stream geometry etc put out by civil or hydraulic engineers, governamental agencies etc. This is a VERY LARGE topic and I suspect you could spend years studying it.


if braided mostly in river, how can it be calcareous, where from clacareous ?

I don't have any new information on this question.



Thanks


Wed May 16, 2012 2:11 pm

Joined: Wed Jun 09, 2010 11:05 pm
Posts: 14
Post Re: Asking braided stream & meandering
Darryl,

Fantastic information here! Very much appreciated eventhough I did not ask the questions. I feel you tackled most aspects but feel that the following can also be explained differently:

Darryl wrote:
B) Streams tend to be braided near their source and meandering near their terminus - this may be to generallized to be of much value but it is true for a long enough river.

C) Many of the rivers long enough for statement B to be true originate in mountains or other high areas where igneous and metamorphic rocks are prevalent - an obvious exception would be those originating in the foot hills of major mountain chains because the outcrops there are frequently dominated by sedimentary rocks uplifted by the rising mountain chain.

D) braided streams are characteristic of areas with a higher slope and a more intermittent or periodic moisture input than meandering streams.


To my knowledge formation of braided streams is mostly related to the rate of avulsion, generally an aspect of sediment load. True, in areas with higher slopes, flow rates are often higher and coupled to higher erosion rates sediment load is often higher too. Also, high variability in precipitation generally causes flash floods and adds to that effect.

If rivers carry a lot of sediment (predominantly bed load) they will deposit this at any point where flow rate decreases, which is usually just behind interchannel bars, causing them to grow. These bars are later cut through again as new bars form. In high discharge and not so steep systems this can also occur. In some incised valleys of delta's (near their terminus) braided systems are found as sediment is not lithified yet and sediment load is high, while slopes quickly achieve equilibrium which may not be very steep.

Sorry for babbling on here and I realize you were giving the short answer. Just something I wanted to get of my chest.


Wed May 16, 2012 9:52 pm

Joined: Wed May 02, 2012 3:45 pm
Posts: 18
Post Re: Asking braided stream & meandering
DKarlstadt wrote:
Darryl,

Fantastic information here! Very much appreciated eventhough I did not ask the questions. I feel you tackled most aspects but feel that the following can also be explained differently:

Thanks :D

Darryl wrote:
B) Streams tend to be braided near their source and meandering near their terminus - this may be to generallized to be of much value but it is true for a long enough river.

C) Many of the rivers long enough for statement B to be true originate in mountains or other high areas where igneous and metamorphic rocks are prevalent - an obvious exception would be those originating in the foot hills of major mountain chains because the outcrops there are frequently dominated by sedimentary rocks uplifted by the rising mountain chain.

D) braided streams are characteristic of areas with a higher slope and a more intermittent or periodic moisture input than meandering streams.


To my knowledge formation of braided streams is mostly related to the rate of avulsion, generally an aspect of sediment load.

Sounds good to me.


True, in areas with higher slopes, flow rates are often higher and coupled to higher erosion rates sediment load is often higher too. Also, high variability in precipitation generally causes flash floods and adds to that effect.

If rivers carry a lot of sediment (predominantly bed load) they will deposit this at any point where flow rate decreases, which is usually just behind interchannel bars, causing them to grow. These bars are later cut through again as new bars form. In high discharge and not so steep systems this can also occur. In some incised valleys of delta's (near their terminus) braided systems are found as sediment is not lithified yet and sediment load is high, while slopes quickly achieve equilibrium which may not be very steep.

Sorry for babbling on here and I realize you were giving the short answer. Just something I wanted to get of my chest.




Well I for one certainly appreciate it. Your answer was more specific than mine but that is because I didn't know what you so obviously do. Or least if I did it's been too long since I though about it to be that specific. Thanks for the input!

Darryl


Wed May 16, 2012 10:23 pm

Joined: Mon Mar 28, 2011 7:55 am
Posts: 5
Post Re: Asking braided stream & meandering
thank you very much for all contributor to my topics it valuable info for me.


Wed Jun 27, 2012 2:08 am
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