Calcareous Nannofossil Age Determinations: Leg 7, Deep Sea Drilling Project

Abstract

The data presented here represent age determinations made by means of calcareous nannofossils on sediment cores recovered in the Pacific Ocean during Leg 7 of the Deep Sea Drilling Project. All determinations were made with a light microscope on smear slides prepared from unprocessed samples. The accuracy of the age determination differs from one sample to the next, owing largely to the differences in assemblages. Assemblages containing age diagnostic species may be assigned to a zone. Some samples, however , contain few or no age diagnostic species; in which case, relatively broader age assignments are made that are commonly equivalent to the interval represented by a stage. Stage terms are avoided (except in the late Miocene), as it seems more reasonable to use such terms as early Miocene or middle Eocene, than to refer to one or another stage term used for the respective intervals. In no case is an exhaustive species list given for a sample. For the most part only those species are recorded which actually aid in the age determination of a sample. It should be stressed that these results are preliminary, and will be subject to minor revisions as more detailed studies are made. Hole 62.0 Sample 7-62.0-1-1, 8-9 cm: Discoaster brouweri, Discoaster pentaradiatus, Pseudo-emiliania lacunosa, Reticulofenestra pseudoumbilica, Sphenolithus abies, Helicopontosphaera kamptneri. Age: Middle Pliocene (possibly mixed). Sample 7-62.0-1-6, 8-9 cm: Sphenolithus abies, Discoaster pentaradiatus, Reticulo-fenestra pseudoumbilica, Discoaster brouweri, Helico-pontosphaera kamptneri, Helicopontosphaera sellii. Age: Probably early Pliocene. Sample 7-62.0-2-1, 92-93 cm: Cyclococcolithina leptopora, Coccolithus pelagicus, Discoaster brouweri, Sphenolithus abies, Discoaster quinqueramus. Age: Late Miocene (probably Discoaster quinqueramus Zone). Sample 7-62.0-2-6, 12-13 cm: Discoaster neohamatus, Sphenolithus abies, Discoaster quinqueramus. Age: Late Miocene. Sample 7-62.0-3-1, 8-9 cm: Sphenolithus abies, Cyclococcolithina leptopora, Dis-coaster variabilis, Discoaster calcaris, Discoaster quin-queramus, Discoaster hamatus (5 rays), Catinaster coalitus, Reticulofenestra pseudoumbilica. Age: Late Middle Miocene (Tortonian). Sample 7-62.0-3-6, 7-8 cm: As above. Sample 7-62.0-4-1, 11-12 cm: Sphenolithus heteromorphus, Coccolithus floridanus. Age: Early Middle Miocene (probably Helicoponto-sphaera ampliaperta Zone). Sample 7-62.0-4-6, 9-10 cm: As above. Sample 7-62.0-5-2, 11-12 cm: Coccolithus floridanus, Sphenolithus moriformis. Age: Probably Oligocene (assemblage not age diagnostic). Sample 7-62.0-5-4, 9-10 cm: As above.