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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 52 (1968)

Issue: 3. (March)

First Page: 559

Last Page: 560

Title: Planktonic Foraminifera as Indices of Paleoceanography: ABSTRACT

Author(s): Orville L. Bandy

Article Type: Meeting abstract

Abstract:

Each major oceanic water mass today is characterized by its own peculiar planktonic foraminiferal indices. These indices may be totally different groups of species, differently coiled populations of the same species, differences in abundance, differences in form, or some combination of these criteria. Furthermore, selective elimination of planktonic species occurs toward inshore areas, especially toward deltas. It is also known that forms with a calcite crust covering the normal wall of the test develop this crust in bathyal depths, providing in this way a useful index to depth of deposition.

Using some of the above criteria it is now known that cold-water planktonic faunas (Globigerina pachyderma sinistral populations), identified with summer surface water temperatures of less than about 5°C, expanded into the temperate areas during colder periods of the Pleistocene, during the middle Pliocene, and during a part of the late Miocene. In contrast, the warmer intervals of the early Pliocene, the late Pliocene, the Pleistocene, and the present are identified by the warmer water types of planktonic faunas (G. pachyderma dextral populations) indicating summer surface water temperatures of about 15° to 18°C, or possibly slightly higher. Eustatic changes in sea level, associated with these cold and warm paleoclimatic alternations in the Pleistocene, brought marked egressive-transgressive cycles in shallow-marine deposits; similar cycles are indicated for the Pliocene and the later Miocene. Thus, in the absence of complications due to variable rates of sedimentation and tectonism, shallow-water depositional sites may reflect a late Miocene nonmarine phase or an unconformity, an early Pliocene marine phase, a middle Pliocene nonmarine phase or an unconformity, a late Pliocene marine phase, and a major regression at the base of the Pleistocene.

Other criteria can be used to show former oceanic connections with marine basins by abundance patterns of planktonic Foraminifera. These patterns also may suggest current patterns of the past. For example, the Miocene planktonic foraminiferal facies of the San Joaquin Valley indicate that the major marine connection

End_Page 559------------------------------

was across the San Andreas fault zone at the southwestern edge of the valley and that the primary marine current was counterclockwise around the southern end of the basin.

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