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Geological deposits

Posted by Heath Barnes  
Geological deposits
May 11, 2012 11:45PM
These pics show an area where ive managed to get a very clear picture of laters that are usualy hidden beneath the water line, the gravel bed can be seen above the riot of colourfull clay layers and believe me the pictures do not show the true richness of colour
Attachments:
open | download - DSCF0216-001.JPG (110.9 KB)
open | download - DSCF0210-001.JPG (117 KB)
open | download - DSCF0214-001.JPG (135.2 KB)
avatar Re: Geological deposits
May 12, 2012 01:00AM
I don't know how it is elsewhere, but around here and in NC, there can be good gold associated with blue clay. I have a couple ancient stream bed deposits I work, and the clay is usually only blue when first exposed. After a bit of time in contact with the air, it seems to oxidize to a more gray color. If I were you I would definitely get a pan and see if there's any gold there.
avatar Re: Geological deposits
May 12, 2012 02:48AM
us    
Heath,

The photos are great! Thanks.

To me, the upper reddish brown, thick layer looks somewhat like till, but it is overwhelmingly clay with only scattered larger gravel clasts. It might be a lacustrine clay containing dropstones (dropped from the bottom of glacial ice as the ice melted at the contact with water) derived locally from volcanic or igneous dike materials. The bright red layer is hematite-rich clay. The hematite probably was washed down from the overlying, reddish brown lacustrine clay (if my idea is correct), concentrating there because it could not penetrate into less permeable bluish clay below. The bluish clay would be a weathered zone consisting of of pure clay (that you can probably roll up and tie in knots, like modelling clay--right?). Below that (bottom of the excavation) is the same reddish brown material containing possible dropstones as in the upper layer.

If my explanation is correct, the geological report you have would not seem to be incorrect.

This is all very interesting, IMHO!

Anybody else want to take a stab at it?
Re: Geological deposits
May 12, 2012 03:21AM
Norman,
What makes for the blue color? when the hematite leaches out all the way, clays are usually white, right? would the blue be of organic origin?
Heath, that is a striking color change, and nice photos, esp. the third one, thanks!
Jeff, i would pan that in a heartbeat too, curious about any heavy minerals in the pan...
Re: Geological deposits
May 12, 2012 11:15AM
Norman King Wrote:
-------------------------------------------------------
> Heath,
>
> The photos are great! Thanks.
>
> To me, the upper reddish brown, thick layer looks
> somewhat like till, but it is overwhelmingly clay
> with only scattered larger gravel clasts. It might
> be a lacustrine clay containing dropstones
> (dropped from the bottom of glacial ice as the ice
> melted at the contact with water) derived locally
> from volcanic or igneous dike materials. The
> bright red layer is hematite-rich clay. The
> hematite probably was washed down from the
> overlying, reddish brown lacustrine clay (if my
> idea is correct), concentrating there because it
> could not penetrate into less permeable bluish
> clay below. The bluish clay would be a weathered
> zone consisting of of pure clay (that you can
> probably roll up and tie in knots, like modelling
> clay--right?). Below that (bottom of the
> excavation) is the same reddish brown material
> containing possible dropstones as in the upper
> layer.
>
> If my explanation is correct, the geological
> report you have would not seem to be incorrect.
>
> This is all very interesting, IMHO!
>
> Anybody else want to take a stab at it?
Thanks for that Norman we ( Me and the two local Geologists helping me with this work have not been able to find even the finest laminations in any of the layers, the bright blue clay is plastic but so is the red- brown above, and the red below the gravel bed The overlying and thickest deposits that cover the entier area ime working, is made up of a very dry, friable red brown loamy clay with minor pebbles, below that i usually find an at first blue sandy clay containing organic materal mostly what looks to be shiny very bright coal, this layer does change to a bland grayish coulor after being exposed for a while, this layer as well as the gravel bed must be related as ive excavated mammal bones that were tightly encased in both layers, ie half in the packed gravel the other in the packed clay above.
The area north of here( about 3 miles) is stated as once being the location of a large ice damed lake, this might give us the water to create these individual layers, ie slow melting and escape to the south, but does not explain the bone and organic material in the gravel bed, nor the basaltic andersite that lays to the north and south of its place of origin the almost straight line of the Cleveland dyke running in a south east north west direction.
The 3 new images show the gravel bed at 2 different locations and the related blue gray layer above, i have found mineralized bone and organic material incuding hazel shells and beech mast. The pic showing the bright veins in the lower red clay under the water line i believe is related to the same event that caused the bright layers at the location in the erlier post.
Attachments:
open | download - DSCF0371-001.JPG (133.4 KB)
open | download - IMG_8115-001.jpg (126.6 KB)
avatar Re: Geological deposits
May 12, 2012 11:24AM
us    
Mike,

The blue color is reduced iron. Iron in sedimentary deposits is well-known for ease of reversal in oxized and reduced states. I should not have referred to it as weathered. Altered, maybe, but not weathered.

Lake bottoms are prime places for reduction of iron. It would happen in stagnant conditions where organic matter also escapes oxidation due to inadequate circulation of water that has been in contact with the atmosphere. It is common for only the bottom sediment to be reduced (because, of course, that does not circulate), but the overlying water to be oxygen rich (because it can circulate). The reduced layer here is striking in the contrast and sharp contacts with overlying and underlying oxidized zones. I attribute that to poor permeability of the clay, but it is unusual.

I'd still like to hear alternative interpretations. In a case like this, two heads may be better than one.
avatar Re: Geological deposits
May 12, 2012 12:43PM
us    
Bones being found across the contacts, buried half-in-half in the layers, suggest those layers are of secondary origin. That is, diagenetic (the right term to use in place of “altered” or “weathered”).

The lower conglomeratic zone in these photos suggest debris flow deposit to me, rather than alluvium. You might think about a catastrophic glacial lake outburst deposit, rather than slow melting--like the Glacial Lake Missoula flood in the States. There is information on-line about the kinds of deposits formed by such events.

The Gowganda Formation in northern Ontario Province, Canada is full of glacial dropstone deposits. You could look those up also. The texture is similar to that in your upper layer.

The two most recent photos (DSCF0371.001 and IMG_8115-001) don’t show such sharp contacts, and are more typical of contacts between oxidized and reduced zones in sedimentary strata that I have seen in the field (I’ll see if I can get some together to post, but I have a job to do today that will keep me away for several hours).
avatar Re: Geological deposits
May 12, 2012 01:17PM
I sometimes wonder if the blue colour is at least partly due to microcrystalline vivianite? - its more common in freshwater deposits, in marine environments its usually grey. But you can get clays with an intrinsic blue colour too, especially smectites.

Regards,
Ralph
Re: Geological deposits
May 12, 2012 06:46PM
That blue is very similar to what I see underground in mines! but there it is copper staining of the rocks. How come that is like it is above ground... mmm

Great photos Heath! Are there any mines up with you? ones that I can go down into?

Claire
Re: Geological deposits
May 12, 2012 07:53PM
Thanks to everyone as Norman said more heads are definatly better, Norman the biggy here is that if these layers are of late devension were did the organic matereal and bone come from as this area was supposed to have been under mountains of ice, a gravel bed containing very well preserved organic material dose not fit into that picture, does it ?
ps anything you have i can use as a comparison would be most welcome as this is a big problem for me ie stuff i can trust!

The following images show a days work on my main excavation and shows me uncover a set of ribs burried in the layer above the gravel bed, ive found a lot of bone from this dig all from either the gravel bed or layer above, the layers above that are so far lifeless both in bone and stone fossils.
Attachments:
open | download - DV000263-001.JPG (159.8 KB)
open | download - DV000264-001.JPG (127.7 KB)
open | download - DV000269-001.JPG (141.9 KB)
Re: Geological deposits
May 12, 2012 08:01PM
Thanks to everyone as Norman said more heads are definatly better, Norman the biggy here is that if these layers are of late devension were did the organic matereal and bone come from as this area was supposed to have been under mountains of ice, a gravel bed containing very well preserved organic material dose not fit into that picture, does it ?
ps anything you have i can use as a comparison would be most welcome as this is a big problem for me ie stuff i can trust!

The following images show a days work on my main excavation and shows me uncover a set of ribs burried in the layer above the gravel bed, ive found a lot of bone from this dig all from either the gravel bed or layer above, the layers above that are so far lifeless both in bone and stone fossils.
Attachments:
open | download - DV000263-001.JPG (159.8 KB)
open | download - DV000264-001.JPG (127.7 KB)
open | download - DV000269-001.JPG (141.9 KB)
Re: Geological deposits
May 12, 2012 08:15PM
Rest of images
Attachments:
open | download - DV000280-001.JPG (114.9 KB)
open | download - DV000285-001.JPG (114.8 KB)
open | download - DV000290-001.JPG (114.5 KB)
Re: Geological deposits
May 12, 2012 08:18PM
And the last
Attachments:
open | download - DV000291-001.JPG (155.9 KB)
avatar Re: Geological deposits
May 12, 2012 11:55PM
us    
I am going to divide this into a couple of separate postings in order to keep you all with me, and with three photos per page.

My analogies are mostly from the Gowganda Formation of the Huronian Supergroup in Ontario, Canada. These photos are from near Elliot Lake, 10 or so km north of the north shore of Lake Huron. These beds were deposited about 2.35 billion years ago under glacial influences. Some are claimed to be tillites, others are laminated and were apparently glacial varves, and some are muddy sediments containing dropstones. These beds are all metamorphosed, and are now very hard argillites and quartzites. There are places where some of my group banged on them with a sedge hammer until their arms almost fell off, and they could not break off a sample (on the other hand, I just walked along and picked up pieces from the ditch–that’s the wisdom we get with age!).

One photo is of Upper Carboniferous (Pennsylvanian) beds in St. Louis, Missouri, and is not very glacial. It shows a portion of a cyclothem with an iron-oxide rich clay layer and bluish mudstone beneath it. Cyclothems were deposited during glacially controlled sea-level fluctuations resulting from variable amounts of former sea water locked up on land due to glacial advances and retreats in Gondwana, so there actually is a glacial connection, but that’s another story.

I’ll show that photo first. The red layer is clear. Ignore the strata above it, because it is nothing like your situation (it’s gray shale and then limestone with marine fossils). The claystone below it is largely yellowish and greenish gray just below the iron oxide layer, and is bluer below. Such bluish clay does occur here and there, but is not really common. Ralph Bottrill could be right about the vivianite, but I don’t think the clay in that zone could be pure enough montmorillonite for that to be the source of the color. I wouldn’t hang any interpretation on that color. The red layer isn’t very important, either–it’s a secondary (diagenetic) feature.





The photo below is the Gowganda Formation that shows muddy layers in the lower half with discontinuous thick lenses of gravel. The upper half is sand with continuous thin gravel layers. My interpretation is that this was a glacial outwash plain having scattered ponds (the mudstone) and crossed by streams (the sandstone), where there were occasional debris flows, some confined to channels (thick conglomerate lenses) and others spreading out over the plain (thin conglomerate beds). The presence of ponds and apparent debris flow deposits are similar to the situation you may be studying.





(Continued in my next posting.)



Edited 1 time(s). Last edit at 05/13/2012 01:23AM by Norman King.
avatar Re: Geological deposits
May 13, 2012 12:18AM
us    
This photo shows dropstones. I mentioned those in an earlier post. This is marine mudstone showing episodic deposition (thin bedding). The area was at least occasionally covered by glacial ice advancing from a near-by landmass. The ice contained pebbles and other sizes of lithic debris that fell onto the sea floor, the larger ones making little “craters” like you see here, as the ice melted underneath.





The next photo is a larger view of mudstone containing scattered dropstones and an interbedded debris flow (where the hammer is).





This is the last photo. It shows gradation from coarse conglomerate deposited by very energetic mass movement (debris flow) at the base, upward to pebbly mudstone. Not shown here is the overlying layer of mudstone with scattered dropstones. That was in the next photo above.

This could be very similar to what you are working with in the Pleistocene deposits there. Possibly a glacially-dammed lake broke, with the initial torrent transporting the larger clasts. As the current diminished, there were fewer and smaller clasts, becoming more widely spaced in the mud. Bones might have been deposited then, except these are Precambrian deposits that predate multi-celled life. The overlying layers (see next photo above) show the usual quiet-water lake muds with dropstones–analogous to your overlying reddish clay with pebbles but no bones.




I hope this makes sense.
avatar Re: Geological deposits
May 13, 2012 03:16AM
us    
Heath,

I think your photos DV000269-001 and DV000291-001 are most similar to the Gowganda Formation analogs that I sent. Any two groups of photos of different formations in different parts of the world are going to be different. But the basics of these are quite similar, and considering that one set is Pleistocene and the other Precambrian, that's impressive!
avatar Re: Geological deposits
May 13, 2012 05:13AM
Classic outcrops and good discussion thanks Norman. We have very similar geology outside my door here: hornfelsed late Carboniferous to Permian mudstones with lots of drop stones and some pebbly horizons that probably form as described, grading up into Limey fossiliferous sediments too. It indicates how pervasive that ice age was, but life bounced back rapidly!

Regards,
Ralph
Re: Geological deposits
May 13, 2012 11:59AM
Hi Clair no mines in the area ime working in since they mined the dyke for road surfacing, also the sandstone the dyke intruded, the wider area has been mined extensivly for pot ash of the coast, iron ore in the hills just west of here ( huge mines) now i think inaccesible and there are very large brine tunnels not far to the north of my area, under Bllingham
Re: Geological deposits
May 13, 2012 12:31PM
Norman King Wrote:
-------------------------------------------------------
> This photo shows dropstones. I mentioned those in
> an earlier post. This is marine mudstone showing
> episodic deposition (thin bedding). The area was
> at least occasionally covered by glacial ice
> advancing from a near-by landmass. The ice
> contained pebbles and other sizes of lithic debris
> that fell onto the sea floor, the larger ones
> making little “craters” like you see here, as
> the ice melted underneath.




> Norman thanks for that ive got my head round most of it and its fascinating me, as i can see simmalaritys with my softer stuff, and it makes sence yet if ime to believe the explanations ive had from the people over here who have kindly tried to help me over here the deposits they say can not be pliectocene! becouse they say them deposits would have been bulldozed by the last devension ice flows?

But with all that said they can not yet give me an explanation of the laters ime excavating and what it contains, the area has been studied in the past but as far as i can see it was limited to sparadic bore holes and surface views in the deep beck valleys, ive tried to explain in my blog that the bore holes would have quite easily not picked up on the 3 to 400mm gravel bed and the thin bright coloured clay layers, and that a surface view of the beck valleys would indeed look like boulder clay as each individual layer would as i still observe it doing, fold into each other as each one gradually collapses.


These pics are of an outcrop i uncovered just to the south of my main excavation, we have aurgered this deposit it sits directly below the dry red brown loamy clay that covers this area, it apears to be alluvial in origin with occasional minor angular and sub angular and rounded pebbles along with intermittent specks of mica, jurassic fossils are also present in very good condition, i was informed by the geologists present that after a test with dilute HCL it indicated a high calcium carbonate content. this stuff is real tuff i was informed by the geologists this blue red clay along with the upper red brown clay this was the hardest clay deposits they had encountered.

Three more images in next post.



>
>
>
>
> The next photo is a larger view of mudstone
> containing scattered dropstones and an interbedded
> debris flow (where the hammer is).
>
>
>
>
>
> This is the last photo. It shows gradation from
> coarse conglomerate deposited by very energetic
> mass movement (debris flow) at the base, upward to
> pebbly mudstone. Not shown here is the overlying
> layer of mudstone with scattered dropstones. That
> was in the next photo above.
>
> This could be very similar to what you are working
> with in the Pleistocene deposits there. Possibly a
> glacially-dammed lake broke, with the initial
> torrent transporting the larger clasts. As the
> current diminished, there were fewer and smaller
> clasts, becoming more widely spaced in the mud.
> Bones might have been deposited then, except these
> are Precambrian deposits that predate multi-celled
> life. The overlying layers (see next photo above)
> show the usual quiet-water lake muds with
> dropstones–analogous to your overlying reddish
> clay with pebbles but no bones.
>
>
>
>
> I hope this makes sense.



Edited 1 time(s). Last edit at 05/13/2012 02:44PM by Heath Barnes.
Attachments:
open | download - DSCF0155-001.JPG (122.8 KB)
open | download - DSCF0158-001.JPG (129.7 KB)
open | download - DSCF0163-001.JPG (132.6 KB)
avatar Re: Geological deposits
May 13, 2012 01:48PM
us    
Remember, Heath, that the deposits left by the most recent glacier, as it retreated, would not have been bulldozed. Each glacier does, indeed, destroy most of the deposits left by the previous one, but here hasn't been a new glacier yet to destroy what you are digging up.
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