Strange banding in Knightia eocaena slab

[Sagebrush Steve]

I've been working through a number of Green River fish I caught from the split fish layer (now called the sandwich layer) at the Warfield Fossil Quarry about 10 years ago.  They have been stored away and I'm just now cleaning them up for display.  Here are two slabs that are the part and counterpart of a Knightia eocaena.  I split it out at the quarry, brought both halves home, sawed them into two rectangular slabs, then wrapped them up individually in two sheets of bubble wrap and put them away for all those years.  After pulling them out of storage today and running some water over them to wash off the dust, I noticed this strange purplish-blue band running diagonally through the fish.  It has very sharply defined edges and runs all the way through both slabs (you can see it on the sides and backs of both slabs).  I've never seen anything like this before.  Does anyone have any ideas what might have caused it?

[westcoast]

I don't  know but it does appear to have a banded appearance. But the fish is beautiful. I used to paint  fossil fish and this specimen has grabbed my attention....I may start again!

[fifbrindacier]

You did not notice it at the time you collected those halves and worked on them ?

[ynot]

Could it be from heat or moisture effecting the oil in the rock?

 

Maybe @FossilDudeCO will know. 

[jpc]

It is pretty common to have color bands like this in the Split Fish Layer.  (I refuse to change the name).  I have no idea what causes it.  

[FossilDudeCO]

Yup, lots of these bands all over the place. Sometimes grey/blue/orange/red/yellow/white.

 

It is caused mainly by minerals staining the grains within each layer of the deposited sediments.

 

You see it more commonly within the 18-inch quarries. There is one layer we have dubbed "The fire layer" that often times contains multiple Cockerellites!

 

Thanks for the poke @ynot just got home from a collecting trip!

[Sagebrush Steve]

6 minutes ago, fifbrindacier said:

You did not notice it at the time you collected those halves and worked on them ?

It's been 10 years since I last looked at it, and I don't really remember.  I do know that while you can see it when the slab is dry, it is much more noticeable when it is wet.  I should have noticed it when I was cutting the slabs, as I was using a tile saw lubricated with water.

 

3 minutes ago, ynot said:

Could it be from heat or moisture effecting the oil in the rock?

 

Maybe @FossilDudeCO will know. 

Possibly. Although the sharpness of the edges and the deepness of the band would tend to downplay the idea of diffusion being a major contributor.

3 hours ago, jpc said:

It is pretty common to have color bands like this in the Split Fish Layer.  (I refuse to change the name).  I have no idea what causes it.  

I guess I will check with Lance Grande to see what he may know about it.  I looked through my copy of his latest book on the fossils of Fossil Lake but didn't find anything about it.  And @jpc I'll make sure to point out to him that his quest to change the name from split fish layer to sandwich layer hasn't been received with universal enthusiasm.

[RLG]

I believe that the banding does not come from the bluish gray being laid in (which is the older color of the base rock) but rather from the orangish yellow, which is a faint iron oxide staining from later groundwater action sometime over the last 50 million years or so. It is common in the so called "split fish" layers, probably because they have less oily layers and are more conducive to water permeation. That's my guess anyway.  Cheers!   LG

[Sagebrush Steve]

24 minutes ago, RLG said:

I believe that the banding does not come from the bluish gray being laid in (which is the older color of the base rock) but rather from the orangish yellow, which is a faint iron oxide staining from later groundwater action sometime over the last 50 million years or so. It is common in the so called "split fish" layers, probably because they have less oily layers and are more conducive to water permeation. That's my guess anyway.  Cheers!   LG

Thanks, Lance, that makes a lot of sense.  I could imagine a streak of oil running across the base rock soon after it was laid down, keeping the water out of that localized area over the millions of years.  Over time the rest of the rock oxidized but the oily streak did not.  That would explain why the streak is so clearly defined and looks like something that flowed across the rock in a deliberate fashion.