Diatom Samples from Ocean Drilling Program Leg 112, Holes 682A and 688E from Offshore Peru

The diatom biochronology of ODP Holes 682A and 688E provides a nearly complete offshore reference section to correspond with onshore studies of the Miocene age materials of the East Pisco Basin of Southern Peru, which is known for its excellent preservation of fossil vertebrates. From these holes a nearly complete sequence of low latitude and northeastern Pacific diatoms has been recognized. The missing intervals of this sequence are from ~17 to 14 Ma, caused by dissolution and/or a hiatus, and 23.4 to 21.8 Ma, likely caused by an Early Miocene hiatus. Whereas eastern equatorial Pacific diatom zones are applicable to materials deposited during the Oligocene through Early Miocene, during the Middle to Late Miocene an increase of diatoms associated with cooler water resulted in a transition towards greater applicability of northeast Pacific diatom zones. However, an exception to this cooling trend is noted from material deposited during the 7 to 6 Ma Messinian interval of the latest Miocene, which is dominated by warm water diatoms.