Miocene Deposits in the Amazonian Foreland Basin

Abstract

In their report, Matti E. Rasanen et al. state that there is a tidal origin for the sedimentary sequences they studied in the western Amazon region (1). Their interpretation of these sequences in Acre, Brazil, as tidal, on the basis of a relatively small data set, implies the existence of a marine connection between the Caribbean Sea and the southern Atlantic Ocean. Background information and earlier work suggests that this conclusion is not the best explanation of the sediments in Acre. The sedimentary history and paleogeography of this area are more complex than Rasanen et al. or S. David Webb, in his Perspective (2), suggest.