Milankovitch cycles

For the sake of argument, let's suppose macroevolution is true. Let's also suppose various parts of the world are fairly stable over time.

On those assumptions, the fossil record embedded in the geological column of a given region would be vertical snapshot of how local species evolved. Something approximating a control group. Based on the law of superposition, species lower down would be more primitive while species higher up would be more advanced. 

Now let's introduce Milankovitch cycles. Orbital eccentricity, axial precession, and axial tilt are cyclical variations which combine to affect the distance and position of the earth in relation to the sun. Solar variation is another factor. 

In theory, these cycles effect climate change. Because they are mutually independent, and have different durations, they intersect in complex ways.  

Assuming this is roughly correct, I assume it will affect biogeography and even biodiversity. Fauna and flora are sensitive to climate. If a wetter region becomes dryer, or vice versa, if a warmer region becomes cooler, and vice versa, that will impact local fauna and flora. 

Some species may adapt to new conditions. Some species may migrate out of the affected area while other species may migrate into the affected area. Some species may become extinct because they can't adapt and lack the mobility go migrate, or because natural barriers impede migration. 

Although we think of migration in terms of fauna rather than flora, since plants immobile, seeds are widely dispersible by various natural mechanisms. So it's possible for exotic flora to be transported to a new region. 

But consider how these factors would affect the fossil record. You'd no longer have a continuous record of species from the same area. Rather, that would be disrupted by preexisting and coexisting exotic species migrating into the area, to supplant previous occupants, which either migrated out of the area or went extinct. 

This, in turn, complicates the inference that the geological column charts the continuous evolution of local species. For the sequence no longer represents the history of a stable control group. Rather than a clean diachronic progression, you have synchronous species from different regions that relocate. It's horizontal as well as vertical. Change in place as well as time. 

Is a species higher up evolved from a species lower down? Or is this an exotic species which, due to climate change, migrated to a more hospital environment? A preexisting species that coexisted with species further down? 

I'm not qualified to assess these variables. But it's something I consider when Darwinians confidently appeal to the fossil record.