The age of the Aptian Stage and its magnetic events: New Ar-Ar ages and palaeomagnetic data from the Negev, Israel

An early Aptian fossiliferous marine bed was recently discovered intercalating the lowermost part of the terrestrial Hatira Formation in the Makhtesh Ramon erosional cirque of the Negev, Israel. A basaltic unit that overlies this marine intercalation has yielded a Ar-40-Ar-39 age of 118.0+/-1.5 Ma. A magnetic polarity inversion from reverse to normal was detected near the base of the basaltic unit. This reversal is correlated with the end of the ISEA reverse polarity subchron, within the early part of the Cretaceous Normal Polarity Superchron. The first appearance of tricolpate palynomorphs, found below the early Aptian marine unit, represents the earliest stage in tricolpate angiosperm evolution in the northern Gondwana palaeoequatorial palynoprovince. From the co-occurrence of the biostratigraphic age, isotopic age, and magnetic reversal at the same site in the Negev we deduce that: (a) the age of the ISEA reverse polarity subchron within the Cretaceous Normal Polarity Superchron is 118.0+/-1.5 Ma; (b) the Barremian-Aptian stage boundary must be significantly older than 118.0+/-1.5 Ma; (c) our results better fit numerical time scales whose calculations exclude ages obtained from Early Cretaceous glauconites; and (d) the first appearance of the tricolpate angiosperms is earlier than 118.0+/-1.5 Ma. (C) 1996 Academic Press Limited.