A Lot Happening In This Shale Outcrop. I Don't Understand Much Of It!

 Welcome to Some ancient mud, much travelled through time and heavily vexed.

 

It's been turned into Shale, a rock.  The clay minerals in the transformed mud make it crumbly.  If it is compressed consistantly in a certain direction, the platy clay minerals will align perpendicular to that direction and make the rock fracture in plates.  But our rock is not there yet. Here are some fractures.

into little cubical blocks.

 

But WHOAH! what is happening here?

 

 

 

So swirly! Clearly some regions are more crumbly than others.  Different sand/clay content?  And then there are what look like uncrumbled concretions/pebbles.  Are they higher sand content that fell in the mudd.  But why does the shale fracture in swirls around them?  I do not understand.  Does the structure form when the mud is layed down or after it turns to stone and is stressed?

There are more interesting things happening:


 

Some layers are much less crumbly!

Chemistry happens. Some layers and splotches are reddish (oxidized iron?) and at the surface they turn orange (iron hydroxide?)

 

Perhaps the burgundy is an Iron Oxide and the orange is an iron hydroxide? (rust).  the oxidation can happen when the minerals are exposed to the atmosphere and hydroxide, if they are exposed to moisture?