Tonemapping artefact ?

[hugeknot]

Jokulsarlon
This picture has a dark area on the top and bottom left. I think it is due to tonemapping (super contrast), but where did it originate and how could I fix it?

Thanks in advance.

 

[Garbz]

Super contrast is where.

tonemapping localises the contrast based on what is around the point. If those areas were even slightly darker than the rest of the surrounding area, the tonemapping would try to separate it from the surroundings, hence make it darker.