Paleomagnetically

The paleomagnetically determined paleolatitude of the Rosemary paleosol during the middle Devonian was about 40° ± 14° (18 ).

It is based on the following observations: (i) different regions in the oceans subside like BL until different flattening ages, some as old as 170 Ma (49 ); (ii) depth and heat flow in some old basins behave like BL but with an effective thermal age t e, which is younger than the (paleomagnetically determined) actual age t m (50 ); (iii) effective elastic lithosphere thicknesses under some intraplate volcanoes suggest that hot spots produce a "thermal rejuvenation," reducing t e (51 ); (iv) the depths and subsidence of hot spot swells suggest that many swells reduce t e to the same value (52 ); and (v) on old lithosphere, it is hard to find areas that have not been near hot spots (53 ).

Numerical predictions based on realistic viscoelastic Earth models and paleomagnetically constrained polar motion yield global-scale, differential sea-level trends that can be as large as ~200 meters.

Estimates of this time interval are based on the assumption that the K-T clay was deposited at the same rate as the clay fraction in the surrounding paleomagnetically dated limestones [e.g., (8 )]; this assumption is questionable during such a turbulent period.