it just looks like those principles don't apply to unconformities.
the reason the
law of superposition is a
law instead of a
hypothesis is because of angular unconformities. they are what prove it beyond any shadow of doubt.
in order for an angular unconformity to exist, that layer and all below it need to be solidified before they are turned on their sides. the layers on top then
must be formed after this occurence, with time for weathering in between.
because angular unconformities are
local and happen at many different levels, it tells us that the geologic column must have been laid down sequentially. we can talk about
time later, but this is not the sort of event we see in a
flood plain. floods always make very disturbed-looking, semi-homogenous single layers. they do not separate, sediment, turn over, sediment some more, and repeat. they make
one layer.