This brings back memories of my first professional job, summer field assistant after my sophomore year, about 1967. I was the assistant to a USGS geologist who was mapping several quadrangles in NW Wyoming, mainly to map out the extent and lithology of the Phosphoria. It was a great learning experience. Thank you for your posts.
I recently watched a YouTube (Permian-Triasic Mayhem: Earth's Largest Mass Extinction - https://www.youtube.com/watch?v=VnUq33HCLzU&ab_channel=RoyalTyrrellMuseumofPalaeontology) from 2013. Beauchamp, studying Late Permian rocks in the Sverdrup Basin (Canadian Arctic), has bedded chert composed of predominately sponge spicules in a shallow marine shelf depositional setting as evidence of a shallowing of the carbonate compensation depth and the acidification of the Late Permian oceans (at least locally). Perhaps a mechanism for the banded cherts observed in the Phosphoria? Just a passing thought.
Thanks for that -- I definitely think the position of the carbonate compensation depth must have had a role, and its fluctuations (due to tectonics, glaciers, or changes due to water chemistry like acidification as you suggest) might well have contributed to the formation of chert (perhaps partly through the exclusion of carbonate?) and the rapid variations in lithologies. I'm just not a good enough geochemist to really grasp the details. (For readers who don't know, the carbonate compensation depth is the position in the sea below which carbonates (calcite, limestone) cannot deposit because the rate of dissolution is greater than precipitation. It depends on temperature, pressure, salinity, carbonate saturation, and other chemical parameters.)
I don't think that Beauchamp expressively states that carbonate shelf deposition was unlikely but that with such a shallow CCD any carbonate was unlikely to be preserved. And that might account for both the abundance of sponges (less ecologic competition?) and thick chert deposition. Ocean chemistry in the Late Permian was very odd.
This brings back memories of my first professional job, summer field assistant after my sophomore year, about 1967. I was the assistant to a USGS geologist who was mapping several quadrangles in NW Wyoming, mainly to map out the extent and lithology of the Phosphoria. It was a great learning experience. Thank you for your posts.
That's cool. I think indeed that mapping (and understanding) the Phosphoria was a major push in the '50s and '60s.
I recently watched a YouTube (Permian-Triasic Mayhem: Earth's Largest Mass Extinction - https://www.youtube.com/watch?v=VnUq33HCLzU&ab_channel=RoyalTyrrellMuseumofPalaeontology) from 2013. Beauchamp, studying Late Permian rocks in the Sverdrup Basin (Canadian Arctic), has bedded chert composed of predominately sponge spicules in a shallow marine shelf depositional setting as evidence of a shallowing of the carbonate compensation depth and the acidification of the Late Permian oceans (at least locally). Perhaps a mechanism for the banded cherts observed in the Phosphoria? Just a passing thought.
Thanks for that -- I definitely think the position of the carbonate compensation depth must have had a role, and its fluctuations (due to tectonics, glaciers, or changes due to water chemistry like acidification as you suggest) might well have contributed to the formation of chert (perhaps partly through the exclusion of carbonate?) and the rapid variations in lithologies. I'm just not a good enough geochemist to really grasp the details. (For readers who don't know, the carbonate compensation depth is the position in the sea below which carbonates (calcite, limestone) cannot deposit because the rate of dissolution is greater than precipitation. It depends on temperature, pressure, salinity, carbonate saturation, and other chemical parameters.)
I don't think that Beauchamp expressively states that carbonate shelf deposition was unlikely but that with such a shallow CCD any carbonate was unlikely to be preserved. And that might account for both the abundance of sponges (less ecologic competition?) and thick chert deposition. Ocean chemistry in the Late Permian was very odd.
I like that as an explanation for abundance of sponges. "Ocean chemistry in the Late Permian was very odd." -- For sure!!