@farmerman,
HAd a chance , as a result of a field trip this week, to view a possible Ediacaran (type) fossil assemblage that is correlated to a similar formation from early Ediacaran age (near the base of the EDiacara) from the HAywood Fm of western Canada. This lies as an allochthanous ("Slid over the top of") block of precambrian sedimentary material from the Appalachians.
The argument is that this ancient allocthanous block, and its early "Hard shell" life , is important from two standpoints.
1. It shows a growing worldwide assemblage of more complex life forms that predate the "Cambrian Explosion" that occured 45 MY later. ( It Makes the CAmbrian "Explosion" appear to be more of a post Cryogenian continuation of life already becoming more complex due more to chemical-environmental reasons and not some unknown basal oddity that heretofore had defined the Paleozoic basal rocks).Ie, the "Cambrian Explosion" now seems to have been a worldwide environmental adjsutment that lasted more than 60 million years from the top of the "Cryogenian" to the base of the Cambrian, and these terms have been officially added to the world stratigraphic column)
2 More important to geologists is the fact that this allocthanous block, is showing us major extensional features(like big cracks in the rocks that were infilled with quartz and calcite) that correlate well with an opening ocean basin that later became the Iapetan Sea. The environmental issues from this post Cryogenian ("Snowball earth age") show that several environmental things were happening
A. The proto Appalachia forelands (continents) were breaking up thus allowing free exchange of seaways and gradual warming due to "gulf stream" like streams.
B Sea loevels were rising, giving birth to shallow warm seas and seaways that are now becoming better understood as "birth placese of several unique assemblages of index type fossils"
C. "Contaminants" in the sea chemistry , such as the rise of "contaminants" like CO2 and free O2, as well as the declining acidity of the seas,gave rise to the new "Biodepositinal life forms" that could deposit free calcium carbonate as shell material .These life forms were subsequent colonizers that arose after the stromatolites and blue green algaes filled the oceans with lovely oxygen)
(The life forms of the EDiacaran were, where hard parts did exist, were mostly chitenous and not CaCO3 shells.
Im sure we are gonna see even more locations of Worldwide Ediacaran age life as more complex forms become recognized as common. We now have sites from at least 7 newer (Ediacaran) locations worldwide where PreCambrian complex life is being noted.(Not just the Type section of the Ediacara from Flinders Hills in Australia).
The puzzle of the rise of life and the shape of the earth is being filled in with new pieces , and many of these pieces are just the result of re-examination of previously "settled" geology from the Appalachians or the CAnadian Shield (as well as several other peri-Shield areas from around the world).
Thought Id let ya in on what I was doing this past weekend. It was a lotta fun, almost as much fun as a recent sailing trip to Nova SCotia