Rotation of the iberian peninsula.

Jones and Ewing (1) have presented seismic profiler data from the Bay of Biscay which allows a 120 anticlockwise rotation of the Iberian peninsula between Eocene and Middle to Upper Miocene times. They refer several times to the fact that this va'ue is appreciably less than a rotation of 220, which they believe resulted from our paleomagnetic study of the Lisbon Volcanics (2). We must point out that in our paper (2) a post-Eocene rotation of 220 was not our unequivocal interpretation of the paleomagnetic data (3). As emphasized several times (2, 3), both graphically and otherwise, the accuracy of the paleomagnetic method is inherently limited. Therefore such precise interpretation (1) of our data is unwarranted. As stated in our abstract (2) and elsewhere, our conclusion is restricted to a belief that the rotation of the Iberian peninsula, which had previously been proposed by several authors using totally independent reasoning, may have occurrcd in part in post-Eocene times. This conclusion has been strongly challenged by Van der Voo (4), whose position is based on a large amount of paleomagnetic data from Paleozoic and Mesozoic rocks from Spain and Portugal. He and others prefer to think that the rotation ceased at the end of the Cretaceous period. We have reaffirmed our belief in the possibility of some post-Eocene rotation (5), but this has been repeatedly dismissed by Van der Voo (6). It would, therefore, appear to be more appropriate at this time to emphasize the relevance of Jones and Ewing's result (1) to resolution of the above controversy rather than to attribute, prior to its comparison with the seismic implications, a precision to our paleomagnetic work, which is unfortunately both unfounded and misleading. As we have suggested (5, p. 551), marine geophysics of the Bay of Biscay has contributed to a resolution of our debate with Van der Voo: The 120 wedge of crust, which is possibly younger than Cretaceous but older than Upper Miocene (1), is quite consistent with our Eocene paleomagnetic data. Finally, it appears that our prediction (7) of a fan-shaped anomaly pattern reflecting in part a post-Eocene rotation and a history of geomagnetic polarity existing in the Bay of Biscay is now quite feasible. Matthews and Williams