Comparison s o f microfossils fro m deep-sea cores, fro m sample s o f an explorator y drill hole, and fro m dredged rocks o f the Gulf o f Alaska, with coeval microfossil assemblage s on the Nort h America n continent, provide constraints on the northwar d migratio n o f the Yakuta t block and the Princ e William terran e during Tertiary time. The estimated paleolatitudes of microfauna and flora indicate that: (1 ) the Prince William terran e wa s attache d to North Americ a in its present position by middl e Eocen e time (40 to 42 Ma) , consistent with models derived fro m paleomagneti c data , and (2) the adjacent Yakuta t block was 30 ± 5 ° south o f its present position in earl y Eocen e (50 Ma) , 20 ± 5 ° south in middl e Eocen e (40 to 44 Ma) , and 15 ± 5 ° south in lat e Eocen e tim e (37 to 40 Ma) , thus requiring a northwar d motion o f about 30 ° since 50 Ma . Moreover , the Yakuta t block wa s at least 10° south o f the Princ e William terran e during Eocen e time . Thes e dat a ar e consistent with migratio n o f the Yakuta t block with the Pacifi c and Kul a plate s for a t least the last 50 Ma . T h e collision o f the Yakuta t block with Nort h Americ a resulted in subduction o f the block coincident with uplift o f the Kena i Mountains. Th e extension o f the Kena i Mountains into the Kodiak are a suggests tha t a southwest extension o f the Yakuta t block collided with the Kodiak margi n and was completely subducted. Th e subducted extension o f the Yakuta t block could have connected the now subducting head o f Zodiak deep-sea fan to a Nort h America n sourc e o f sediment during deposition o f the fan.  PDF