Cretaceous-Paleogene (K-Pg/KT) Mass Extinction:
The Chicxulub Impact Crater will be drilled. Some are saying for the first time, but I do believe the original oil workers who reported it back in the 80s (?) did so before.
There was a partial collapse of the marine carbon pump at the K-Pg boundary.marine
Permian Triassic Mass Extinction:
There is contrary evidence from conondont tooth oxygen isotopes suggesting a sharp temperature drop right at the PT Extinction. This is contrary to the global cooking scenario.
The Permian ocean bottom waters in China were not anoxic at the time of the PT Extinction.
In South China, the redox conditions were fluctuating at the PT Boundary.
The Kayitou Formation in China appears to have the terrestrial record of the PT Extinction.
There is also evidence of cyanobacteria blooms from China as well across the PT.
Devonian Mass Extinctions:
Here's evidence of what happened during the Famenian-Frasnian Event (aka mass extinction) in Devonian in China.
There was a disruption in the nitrogen cycle at the end Devonian Mass Extinction.
Here's some more interesting evidence of what was going on during the end Devonian Mass Extinction.