Lower Ordovician Fossils in Undocumented Silicate Stone Formation

[FranzBernhard]

9 hours ago, Philip Rutter 2 said:

And probably best, 3 - not common information (1) but quartz is transparent to x-rays; (2) quartz tubes are regularly used to contain material being subjected to x-ray analysis - as they don't interact.  And why I knew that, I don't know.   :-)

(1) Not particularly. X-rays energetic enough will go through a given sheet of silica. X-rays not energetic enough will the absorbed by the same sheet of silica.

 

(2) Are you talking about glass capillaries for X-ray diffraction?

 

Franz Bernhard

 

 

Edited September 7 by FranzBernhard

[Isotelus2883]

This might answer:

https://www.usgs.gov/publications/origin-jasperoid-limestone#:~:text=As limestone dissolves%2C Ca ions,the precipitation of colloidal silica.

I don’t think it is stromatolite. You can easily test this by testing another fossil to see what the silica content is. 

[ynot]

On 9/5/2024 at 6:20 PM, Philip Rutter 2 said:

But - known geology below; Oneota dolostone; and above; New Richmond sandstone - are both reasonably well studied and characterized, and a pure silicate layer, which after 3 years and one broken wrist of surveying I estimate as varying from 3 m to 8 m thick - is just not mentioned anywhere.

 

My 7 year educated guess is that the silicate is IN the unconformity known to lie between the Oneota and the New Richmond.  Ain't that interesting?

 

Seems to be mentioned here....

On 9/5/2024 at 8:28 PM, Philip Rutter 2 said:

Their description of chert in the Oneota agrees with my own; there is an abundance of oolitic chert, as well as other oolites.  They refer to bands of chert some meters thick- that's new to my info, and I wanna see them.  :-)

From your description I think you are digging in one of the bands of "chert" .

 

Have you considered stress fracturing? I have seen silicate rocks that have been subjected to high stress that will have pseudo rhombohedral fracture. A mile thick ice sheet did cover that area.

Also there is the possibility of temperature change fracturing (like marbles in boiling water)

 

Regarding the "label"  put on it, at 95% silica it is a silicate rock.

Because of the environment in which it formed it is clearly not agate or chalidone. It is also clearly not jasper, chrysoprase, quartzite or keystone..

This leaves either flint or chert, take your pick.

I know of no other silicate rocks that would fit this type deposit.

 

 

 

 

 

 

 

 

[Diomedia]

Welcome Philip!  I am following this thread with much interest. The advisor on the Carleton paper is, I believe, a sedimentologist and may be able to offer an opinion on the chert controversy. (I have not read the paper). Question - would making a thin section of this rock to discern any relict structure be a possibility?  Also, isn’t chert a deep water pelagic ooze deposit? The Ordovician rocks in SE Minnesota are, I think, mostly shallow epeiric seas.

[Philip Rutter 2]

Lower Ordovician Silicate bed, post 3; Sept. 17

 

Sorry it's been ten days! Non-silicate life keeps intruding.  :-)

I'm working on learning to communicate here; this is a wonderful collection of people- and a little different from my recent experiences.  

Always start at the beginning is great advice - the trick is finding the actual beginning.  In my case, this particular conversation, the "beginning" is not at "fossil", nor "geology", I think.

 

What I very much want to share here is - a Puzzle.  All fossils are puzzles of course; but the situation I am in is a puzzle at a yet deeper level; I need your help with this puzzle, which means I need to clearly show you what the puzzle consists of.  

 

All fossil collectors have to deal with these puzzle factors, but in many, perhaps most cases, some predecessor worked out the basic details - What age are these stones?  What is their chemistry?  What has their history been?  What kinds of fossils might one find here?

In the case of my silicate rock bed, it has apparently gone unnoticed by professional geologists working in this region.  And it's in an unusual place; at the top of the Oneota dolostone, below the New Richmond Sandstone; approximately right in the unconfomity between them.  Perhaps.  The only geology work I can find looking at this juncture did not find a silicate bed in any of the exposed situations they were able to examine.    https://www.carleton.edu/departments/geol/Resources/comps/CompsPDFfiles/2005/Robins2005.pdf   That's not a huge surprise, there are many ways such a bed could be present here, and not there.

 

There doesn't appear to be any previous scholarly examination of this bed, so - some basic information needs to be generated.  Like- how old is this stuff, really?   I am an evolutionary ecologist, mostly- which does mean I am interested in the whole ecology of the world that created this silicate stone- all maybe 10 meters of it, when below is ~ 100 m of dolostone, and just above is highly variable depths of sandstone which often borders on quartzite; both generally assigned to "Lower Ordovician".  And when did it happen?  The Ordovician had some astonishing climate excursions, far out of our experiences or expectations- but - life was there, thriving; the silicate rocks are all the product of living processes at first, even if transformed later by geology- this stuff was salt water ocean bottom - muck, with body parts from predation; and/ or reef organisms.  

 

Confession; I am completely fascinated by that world, those creatures.

 

The puzzle!  First, here is the resource I'm working on; the site.  The location, no surprise, I'm not at liberty to disclose.  It is "not far" from my home, i.e. it is also in Fillmore County, Minnesota; the portion overlain with New Richmond Sandstone.  I have the owners permission to dig, excavate, and collect there, but not permission to publicize the location.

 

The site consists of a substantial steep sided water course, and its tributaries.  The terrain is unusual - we are in the "Driftless Region", which means my hills did not get smashed by the Pleistocene glaciations (though some glaciologists think one of the earliest of those might have been here...)  So it's possible that my forest soils, terrain, and rock formations, last saw glaciers around 300 million years ago; in the Permian.  Give or take 50 million years.  There's a pretty fair chance my current topography was formed mostly by the melt waters from the Pleistocene glaciation ending- pretty recent cuts through long undisturbed lands.   Here is my schematic of the site:  

 

 

The silicate bed is cut through by the main stream bed, and by all of the tributary "feeder" ravines; all of them steep, average inclines of side walls being around 60°, varying from 45° to 90°.   My surveys over 7 years show the bed is present in all possible places, but the glaring white silicate that caught my attention in the first place, when it is newly eroded - escaped from the bed, is very rapidly colonized with moss, algae, and lichens, then subsumed in the forest soil of the hillside, where erosion is slow.   In all places on the site, there are fossls and bed breakage in the stream bottom deposits, both just at the bottom of the hillsides, and in larger mini-deltas, and in the bottoms of the water course.  My impression, though I have not broken enough boulders, is that the major rocks in the main water course are about 80% dolostone, 5% sandstone-quartzite,  14% local silicates, with the remaining 1% being apparent glacial erratics - from the Permian (?).  All pretty hard stone, serving to pound each other into sand and soil during "flood" flows, which need only a 10 cm rain event.

 

There is a very large amount of shallowly buried specimen material available.  I have examined material from all the drainages- so far it appears to show some consistent differences, site to site.  Which could just be sample error, or actually reflect differences over this small scale in deeper vs shallower places in the original "tidal estuary" - ? 

 

The diversity in the specimens is so high I am, literally afraid to go hunting for more.  At around 90% of the time- I find...  new puzzles.  I love the puzzles, don't get me wrong- but!  I'm getting antsy to have some answers.

 

Which brings me to the second "starting point" for today.  I didn't manage to explain this at all previously- sorry.  My "not chert" white 95% SiO2 rock - is variable as all get out- often within a single 2-hands-full specimen.  The specific choice of silicate crystal lattice - is visibly different, across the stone; opaque snow white here, to chalcedony gray, to glittering just plain quartz (not druzy) to... everything else.  Oh, with fossils, included- probably-  

 

AND - to make it all more of a pain to decipher the ecosystem - not infrequently a specimen will include edges or components that grade off into - what is known professionally to petroleum engineers as tripolitic chert.  AKA, for me- "composted quartz".  Here's the specimen for this conversation, before we go further ; this stone is "as-is", coming out of 15 cm deep forest soil, washed with soap and hydrogen peroxide -

 

 

I apologize for the inch scale, and the ultimate resolution of the photo; I'm in camera hell at the moment, by top lens got rained on a month ago- and will no longer focus when asked; going to have to replace it.

 

But; this should suffice for you to understand several points; the bloody "white" is so white as to be blinding in almost any light; the exact apparent "color" of the stone varies a good deal; both top and bottom edge turns into brown non- hard material; fossils not infrequently extend from hard into non-hard areas.  Not visible facts; the brown material - is dissolved by acid cleaners like peroxide, and will disappear, while the hard white silicate is virtually immune to any acid; there are abundant fossils in the brown stuff that will be washed away during acid cleaning, and, it is very common for fossil details in the white stone to be visible only under specific circumstances, which vary; angle of incident ligth and wetness being most common factors, but combinations of those (e.g. "half-wet") are common.

 

Which makes the eternal question "is what I'm looking at real?" - extraordinarily elusive.   I think mostly- what I'm seeing is real, because; the "half-wet" visibility sort of thing is quite consistently reproducible; and- at the edges with the brown tripolitic material- the 'possibly imaginary" stuff in the semi-translucent hard silicate- OFTEN - will be revealed by acid dissolving of less resistant material - to be a definite 3-dimensional unmistakeable fossil.

 

This photo should have good enough resolution for you to find most of those features if you blow it up and examine various figures.  Besides the obvious i/2 tripolitic nautiloid, there are 3 more definite nautiloid partials, a couple of suspects - and on the other side of the stone which I'm not showing here, a lovely certain gastropod.

 

I can, for my next post in this puzzle, provide both sides, images processed for beyond-human visibility, and fossils I see circled.  Should I do that?  

  

So it's all kind of like a 7-dimensional Rubik's Cube, to me.   Enough for now, yes?  :-)

 

 

 

 

Edited September 17 by Philip Rutter 2
multiple fixes

[Philip Rutter 2]

On 9/16/2024 at 9:41 AM, Diomedia said:

Question - would making a thin section of this rock to discern any relict structure be a possibility?  Also, isn’t chert a deep water pelagic ooze deposit? The Ordovician rocks in SE Minnesota are, I think, mostly shallow epeiric seas.

Thin sections would be highly desirable - but needs tools currently out of my reach.   The opinions I gleaned from 2 emeritus heads of geology departments is that "we don't really understand how chert forms... particularly nodules, but..."    Yes, all indications are my fossils are from shallow water, the expected "tidal estuary " sort of thing.  Ooze mucks though are also known to form in shallow situations - I can attest personally from hours in and out of a canoe in marshes... among other things.  :-)   I do find a lot of geological references which seem to have been published based mostly on 1 professor's personal opinions- can be easy to find contradictions.   I'm not blaming geologists - the world is just crazy complex and diverse- when you look at it hard.