Friday, September 16, 2016

What Is That Gunk on My Rock? from Shadows on the Trail Quadrilogy

Figure One. The artifact inspiring the SHADOWS ON THE TRAIL QUADRILOGY.
Side B of 4.1 inch long discoidal biface made from Alibates Chert. The original
"down" position for this artifact. 
For those of you who are not aware, the seed for the SHADOWS ON THE TRAIL QUADRILOGY sprouted on an early summer morning in 2010 on a northern Colorado ranch when I found a prehistoric stone tool made from a red and gray striped rock only found in a prehistoric rock quarry in Texas (Figures One and Two). I believe that the mysterious Folsom People made this prehistoric stone tool sometime between 10,900 and 10,200 years ago.

Figure Two. The artifact inspiring the SHADOWS ON THE TRAIL
QUADRILOGY. Side A not showing much pedogenic carbonate.
The original "up" position of this artifact. 

When I found this prehistoric tool, I stared at it for some time, wondering about the ancient people who made it. How did this stone tool end up all the way to a prehistoric campsite in northern Colorado, five hundred miles to the north of the prehistoric rock quarry? Who actually made it? What was he or she like? What happened on its journey from Texas to northern Colorado? Since it was impossible for me to ask the person who made it, I wrote my own version of the journey in the SHADOWS ON THE TRAIL QUADRILOGY.

Figure Three. The Exciting Conclusion. CLICK to ORDER.

What happened to the stone tool between the time it was lost around plus 10,700 years ago and the time I recovered it in 2010? Obviously, it spent some time buried, otherwise, someone else or a cow or horse hoof would have found it and shattered it into ten thousand pieces. But, what is that white stuff covering the top of it in Figure one?

Figure Four. Side A of 6.5 inch long ultrathin knife form, made
from obsidian. Side A shows little pedogenic carbonate.  
That white stuff is called pedogenic (secondary) carbonate and I will explain the process to you.

Pedogenic carbonation occurs when rainwater and carbon dioxide in the atmosphere mix to form diluted carbonic acid in the soil. This weak acidic water dissolves minerals in the soil, yielding water-soluble calcium carbonate, bicarbonate, and other salts capable of precipitating onto other rocks and minerals if the ground water conditions are suitable. See Figures Four and Five.

Figure Five. Side B of 6.5 inch long ultrathin knife form
showing extensive pedogenic carbonate. This indicates the
original down position of the artifact.

Pedogenic carbonate accumulates on or between sediment grains, occluding and cementing the sediment as a result. Pedogenic carbonate forms a geopetal structure that accumulates first on the lowest part of the buried artifact. As time goes on and the process continues, pedogenic carbonation coats more elevated areas of the buried artifact. A geopetal indicator is a characteristic observed on a rock, or sequence of rocks, that makes it possible to determine whether they are right side up (i.e. the attitude originally deposited, also known as "stratigraphic up") or have been overturned by subsequent structural movement.

As far as prehistoric artifacts, regardless of the position the artifact was found, the presence of pedogenic carbonate establishes the original up and down surfaces of that artifact.  

Low rainfall is the single most important factor for the development of pedogenic carbonate. Low rainfall allows the formation of pedogenic carbonates near the surface of the ground. High rainfall washes the water-soluble salts into the ground’s water table, removing them from the sediments where we find most prehistoric artifacts.

My newest book in the prehistoric adventure series CROW and the CAVE and
the original book where it all began, SHADOWS on the TRAIL.   
Where It All Began - CLICK TO ORDER