ABSTRACT: Middle to Late Miocene Paleo-oceanography of Deep Sea Drilling Project (DSDP) Leg 5, Site 36: Northeast Pacific Ocean

Elmira Wan, Scott W. Starratt

The late Neogene planktonic foraminiferal record at DSDP Site 36 in the northeast Pacific has been reexamined, resulting in a modern biostratigraphic and paleo-oceanographic interpretation of this site. Tephrachronology at Site 36 constrains the ages of the microfossil datums. An age of middle Miocene to Pleistocene (zone N15-N22) is reported for this section. A hiatus is present at zones N15/N17B beneath the Miocene-Pliocene boundary (N17B/N18 zonal boundary). This hiatus corresponds to Neogene hiatuses NH4-NH6. The biostratigraphy and paleo-oceanography of the revised report has been correlated with that of the preliminary report.

Sedimentation rates were calculated using both radiometric (K-Ar) dates and microfossil data. The three radiometric dates (0.4, 2.0, and 4.8 Ma) yield a uniform sedimentation rate of approximately 18 m/106 years. Using planktonic foraminiferal data yields a similar rate for the upper half of zone N21 and the lower portion of N22. In the lower part of zone N21, the sedimentation rate is reduced to about 9 m/106 yr. Zones N19-N20 are characterized by an increased sedimentation rate (28 m/106 yr). Coincident with a major period of dissolution near the zone N18-N19 boundary, the sedimentation rate is 8 m/106 yr.

Analysis of the planktonic foraminiferal faunas indicates that fluctuations in the characteristics of the overlying surface water mass have taken place. These variations may at least in part be the result of the reorganization of the California Current. Species number increases gradually through the late Miocene and early Pliocene, reaching its zenith in zone N19. Species number is gradually reduced through the remainder of the Pliocene and the Pleistocene.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990