There is a lot of information on drying up a Mediterranean sized depression. However, there is not a lot of information on drowning such a large area or what sort of habitats could exist before the flood. eg before the Zanclean flood drowned the previously dry Mediterranean region and ended the Messianian Salinity Crisis.
In most scenarios the region would have to originally be mostly below sea level before the flood.
Most of my research around the Zanclean flood and other similar flood events have mentioned that it is typically in semi-arid and arid regions (ie previously dry) that these below sea-level depressions naturally dry up in. ie little rainfall or incoming river water. Which does make sense, as the water has to have gone somewhere...else.
I'm not focussed on how the depression would have become separated or rejoined to the larger ocean body. Just what sort of habitats are feasible before the flood, other than arid deserts?
Currently I am heavily contemplating drowning a large Mediterranean sized grassland and forest region, between 0 and 30 degrees north of the equator (equatorial region, lots of rainfall but also lots of evaporation). With a large dry desert above that.
Is it possible to have any other habitat aside from arid desert in such a large-area depression?
Affirmative answers should also address if and how this would be possible near the equator. ie Discounting a very large area of land subsidence, what natural features or processes would allow for an environment other than an expected lake or inland sea (BEFORE the flooding event)?
This is based off world but the planet has mostly earthlike processes and weather conditions.
Just incase, my planet does have a fair number of medium sized meteorites crashing down on it in the past, it can be very cratery in places. Back in prehistory, these impacts did do some substantial geological reorganising. I can increase/decrease this as necessary.