Interpretation of preliminary paleomagnetic (a.f. demagnetized) and biostratigraphic data from Upper Cretaceous deposits suggests that the Nacatoch Sand (Navarroan) and the Brownstown Marl (Austinian) of southwestern Arkansas correlate with Guffio (Italy) reversed polarity zones E- and A-, respectively. Other Austinian, Tayloran, and Navarroan Upper Cretaceous deposits (Tokio Formation, Ozan Formation, Annona Chalk, Marlbrook Marl, Saratoga Chalk, Arkadelphia Marl, Gober Chalk, Sprinkle Formation) possess a weak remanent magnetization of normal paleomagnetic polarity. We assume the normal polarity to be primary magnetization, and interpret deposition of the Tokio Formation during the Gubbio long normal zone (Santonian and older), and that of the other units in Gubbio norm l polarity zone B+ (Campanian to early Maestrichtian); this is consistent with previous assignments of the units to stages on the basis of biostratigraphic data.

We conclude that the boundary between the Austinian and Tayloran provincial stages approximates the boundary between the Gubbio reverse polarity zone A and the Gubbio normal polarity zone B+. The Tayloran-Navarroan boundary is probably within the upper part of Gubbio normal polarity zone B+.

The magnetostratigraphic approach for refinement of the

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geochronology for Upper Cretaceous deposits in Arkansas and Texas offers another method of dating geologic events in these areas and relating them to events elsewhere.

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