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While the correlation of mag reversals with major extinctions or the formation
of new species seems attractive it has not stood up to close scrutiny and the
idea has been discarded by mainstream geologists. ...
Ice ages and mag reversals don't correlate at all. ...
... . Models of the impact
at Ch.... in the Yucatan suggest that the meteor was not big enough to create
such an effect just form inert dust thrown into the air (I've also heard that
early models of the nuclear winter greatly exaggerated the effect). The
answer appears to be that the rocks in the area contain a lot of sulfur and
that along with the cold and the dark there was a severe case of acid rain.
In fact the acid may have been the main killer. This fits nicely with the
observation that land species were hurt the worst, deep water species hurt the
least and shallow water species experienced intermediate losses.
The difference in rotation rate between crust and core is a recent discovery
and at this point correlation with ice ages, meteor impacts, etc. is pretty
much speculation.
While a record of the paleo magnetic field is preserved in
igneous rocks, I can think of no way that this spin mismatch would be recorded
and thus no way to test or verify the speculation.
Conventional wisdom (most geology texts) states that during a reversal the
earth's mag. field is reduced to a fraction of its normal strength and then
rebuilds in a reversed polarity, with the reversal taking place over a thousand
years or so.
As mentioned Understanding Earth is an excellent intro text and
general reference for things geological. For geophysics P.V. Sharma writes
a book that I like. It is more earth physics and less oil and mineral
exploration than most geophysics texts.