Chert! Extensive Preservation of Glass Meadows
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- Опубликовано: 8 янв 2023
- Presented by Dr. Leif Tapanila
Idaho State University
The Phosphoria Sea was centered in Idaho during the Permian time period, 280 million years ago, and its seafloor rocks extend today from Nevada north through Utah, Idaho, Wyoming, and Montana. Recent studies mapping environments and fossils show that the Phosphoria Sea supported a diverse marine ecosystem including the top predator on the planet, the buzzsaw shark Helicoprion.
The Phosphoria Formation is perhaps best known for its rich deposits of phosphate ore that have been mined for over a century in eastern Idaho. However, this formation contains abundant chert deposits that alternate with carbonate and phosphate units. In places, the chert comprises the bulk of the Phosphoria Formation. Where are all these cherts coming from? Early researchers recognized sponge spicules in thin section, suggesting a sponge origin of the silica. But only recently has the source of chert been found in place... and it's spectacular. Two research groups, working independently, converged on the same finding on opposite sides of the Phosphoria Sea, revealing the Glass Factory.
The Glass Factory is analogous to the carbonate factory, a place where large volumes of biogenic silica (rather than carbonate) are produced and later mobilized as the biogenic opaline silica dissolves and reprecipitates to form chert. Preserving meadows of glass-forming sponges is very unusual (unprecedented, perhaps), but they are extensive along the margins of the Phosphoria Sea deposits. These tubular cherts have been described for decades, but misinterpreted as burrows or inorganic concretions, leading us to suspect more Glass Factories are out there to be discovered.
Brilliant presentation!
Just one kind of video I’m glad I found this one great work guys and gals thank you bye-bye
Incredibly interesting talk and subject!
Were these really hexactinellids, though? Modern hexactinellids live in much, much deeper water, as deep as 1000m. Some demosponges, on the other hand, also produce siliceous spicules, live at much shallower depth, and live in and among carbonate reef communities. One would expect that the sponges of the glass meadows also lived among carbonate reefs, given the limestone in which they were encased and upon which they grew.
It’s worth noting that the “chert is only secondary” axiom only applies to chert and flint nodules and concretions found in carbonates. I don’t think many geologists would say that about the other kinds of marine and lacustrine cherts, which form in large part as primary deposits from the collection of siliceous diatoms on the seafloor.
I’m curious: what relation did the Phosphoria Basin/Sea have to the Pennsylvanian-Permian Slide/Mountain/Havallah back-arc basin, which existed off the NW coast of Pangea at the time? Would I have been an epicontinental embayment of the larger Slide Mountain/Havallah Sea?
On Fort Peck I constantly saw ammonites that are cylindrical in form, too.
Elaine Benes would indubitably find this man sponge worthy.
The upwelling water might also bring silica rich water to the surface, which would be that way because of dead phytoplankton.
I hope the female student was intrigued enough to pursue a degree and career in the field.