Tsunemasa Saito

Pliocene-Pleistocene Sediments of the Equatorial Pacific: Their Paleomagnetic, Biostratigraphic, and Climatic Record

Magnetic stratigraphy of 15 oriented cores from the equatorial Pacific was determined as far back as the Gilbert reversed-polarity epoch. Ranges of selected species of four major microfossil groups (diatoms, silicoflagellates, foraminifers and Radiolaria) are compared with the record of geomagnetic reversals during the last 4.5 m. y. in eastern equatorial Pacific deep-sea cores. Characteristics of the fossil assemblages are used as criteria for recognition of most of the paleomagnetic reversals that occurred during this interval. Two zones of major paleontological change occur characterized by extinctions of several species and coiling direction changes in some foraminifers. The first change comes in the middle of the Gauss normal magnetic series (about 3 m.y. B.P.) and the second near the Olduvai magnetic event (about 2.0 m.y. B.P.). Seven equatorial foraminiferal species, two radiolarian species, and two diatom species become extinct near reversals. The establishment of the true chronostratigraphic relationships of these selected microfossil species allows us to date zonations of previous authors and provides absolute dates that can be used in worldwide correlation of marine sediments. The percentage of calcium carbonate was determined throughout the lengths of four cores. Eight distinct carbonate cycles are present in the Brunhes series, having periodicities of about 75,000 years in the upper Brunhes to over 100,000 years in the lower Brunhes. It is possible to correlate these carbonate cycles among our cores and also to correlate them with the previous work of Arrhenius who equated the carbonate peaks with glacial stages and the troughs with interglacial stages. This interpretation is supported by paleomagnetic and C14 dating of the last carbonate high which is synchronous with the Wisconsin glaciation (80,000 to 11,500 years B.P.). It, therefore, is probable that there were eight major glacial fluctuations during the last 700,000 years. During the last 400,000 years there is good correlation between the carbonate cycles of the Pacific and evidence of climatic fluctuations in the Atlantic established by Ericson and Wollin (1968) and Emiliani (1966) based on fossil abundances and oxygen isotope ratios, respectively. The rates of sedimentation during the Brunhes series range between 3.5 mm/1000 years for siliceous ooze to 17.5 mm/1000 years for highly calcareous sediment.

Pacific Pleistocene Sediments: Planktonic Foraminifera Dissolution Cycles and Geochronology

Late Pleistocene equatorial Pacific sediments can be correlated by the ratios of certain solution-susceptible versus solution-resistant planktonic foraminifera. These ratios fluctuate in a cyclic manner whose timing is in phase with glacial-interglacial fluctuations established by oxygen isotope geo-chronology. Glacial stages are characterized by less solution of foraminifera than interglacial stages.

Tertiary Sediment from the Mid-Atlantic Ridge

Lower Miocene microfossils occur in basaltic glass in two dredge hauls from the crestal area of the Mid-Atlantic Ridge near 30�N. From the ridge and adjoining abyssal hills 43 pre-Pleistocene cores were identified, including one Cretaceous and four Eocene. Dredgings and cores now available suggest that the upper layer of the crust of the ridge is constructed of layers of interbedded sediments and basalt flows. The data rule out the possibility of large-scale continental drifting or spreading of the ocean floor since the Lower Miocene.

Tertiary sediment from the East pacific rise.

More than 50 cores ranging in age from Pliocene to Lower Miocene have been recovered from the East Pacific Rise. Near the crestal regions the sediment cover is thin or lacking, and only Pleistocene sediments were recovered. On the flanks, the sediment thickness increases and pre-Pleistocene sediments are encountered. This pattern of increasing age and increasing sediment thickness away from the axis of the rise is in agreement with that predicted for spreading of the ocean floor.

A cretaceous (Turonian) core from the Naturaliste Plateau southeast indian ocean

Abstract An Upper Cretaceous (Turonian) sediment core was recovered from the northeastern s slope of the Naturaliste Plateau, eastern Indian Ocean. At the core site, coarse grained foraminiferal sand of Recent-Pleistocene age disconformably overlies a white Cretaceous chalk consisting largely of planktonic organisms. The pelagic nature of the sediment suggests that the water depth at this core site was approximately the same in both Cretaceous and Pleistocene time. Bottom photographs and seismic profile records were also taken across this feature. The seismic profile records show a rather thin sediment layer with some thicker sedimentary pockets, possibly due to faulting. The south side of the Plateau is marked by a steep scarp with a well developed sediment “ramp” at its base. This sediment “ramp” probably owes its origin to longshore currents which sweep around the southwest tip of Australia. The Naturaliste Plateau is similar to other plateaus marginal to continents in that: (a) they have more or less flat summits, (b) Pleistocene overburden is thin or lacking, and (c) steep scarps are present on at least one side.

Emendation of Riveroinella martinezpicoi Bermudez and Seiglie, 1967, and synonymy of Riveroinella with Cassigerinella Pokorny, 1955

The monotypic genus Riveroinella was erected by Bermudez and Seiglie in 1967 as belonging to the family Ceratobuliminidae, a group of benthonic foraminifera characteristically having an aragonitic shell. Examination of its type species, R. martinezpicoi, reveals that the genus Riveroinella is a junior synonym of the planktonic foraminiferal genus Cassigerinella Pokorny, 1955, not only because R. martinezpicoi has an enrolled biserial coil in the last whorl, but also because the shell of R. martinezpicoi is calcitic, not aragonitic as claimed in the original description. A detailed morphologic examination of the type species of the genus Cassigerinella, C. chipolensis (Cushman and Ponton), was made with the use of a scanning electron microscope (SEM), because some authors have assigned this species to the benthonic foraminiferal family Cassidulinidae in the belief that C. chipolensis has an internal tooth plate. Our SEM examination indicates that Cassigerinella possesses no tooth plate, but instead a distinct rimlike protruding apertural flange. Therefore, the genus is herein retained in the planktonic foraminiferal family Hantkeninidae. INTRODUCTION Bermudez and Seiglie (1967) erected the monotypic foraminiferal genus Riveroinella, with type species Riveroinella martinezpicoi, placing it in the family Ceratobuliminidae because they believed its shell to be made of aragonite. While studying the foraminifera from JOIDES Hole 3 on the Blake Plateau off northern Florida (Bunce et al., 1965), the senior author observed an apparently new species of Cassigerinella, associated with Globigerinoides sicanus de Stefani, Globorotalia peripheroronda Banner and Blow, and Praeorbulina glomerosa (Blow). In describing planktonic foraminifera recovered during DSDP (Deep Sea Drilling Project) Leg 34 from the eastern Pacific Ocean, Quilty (1 976, p. 651, pl. 19, figs. 13-14) figured a Cassigerinella closely resembling the Cassigerinella specimen that the senior author recognized from the Blake Plateau. In general morphology, both of these specimens of Cassigerinella are closely comparable with Riveroinella martinezpicoi Bermudez and Seiglie, and the question was posed as to whether R. martinezpicoi is indeed an independent genus characterized by a planispiral test and an aragonitic shell, as was originally contended by Bermudez and Seiglie (1967). Examination of the holotype (USNM 687203) and two paratypes (687204, 687205), on loan from the United States National Mseum of Natural History in Washington, D. C., indicates that the specimen from the Blake Plateau is taxonomically identical with the type specimens of R. martinezpicoi and that chambers in the last whorl of R. martinezpicoi are arranged in an enrolled biserial coil in the manner characteristic of the genus Cassigerinella (text-figure 1). The purpose of this paper is to demonstrate that Riveroinella is a junior synonym of Cassigerinella, not only because its type species has an enrolled biserial coil in the last whorl, but also because the shell of R. martinezpicoi is calcitic, not aragonitic as claimed in the original description given by BermOdez and Seiglie in 1967. SYSTEMATIC PALEONTOLOGY Superfamily GLOBIGERINACEA Carpenter, Parker and Jones, 1862 Family HANTKENINIDAE, Cushman, 1927 Subfamily CASSIGERINELLINAE Bolli, Loeblich and Tappan, 1957 Genus Cassigerinella Pokorny, 1955 Discussion: In the original description, Pokorny (1955) suggested merely that the genus Cassigerinella is closely related to the genus Globigerinella. Bolli, Loeblich and Tappan (1957) were the first to assign Cassigerinella to the superfamily Globigerinacea, which includes only taxa having a planktonic mode of life. This assignment has been micropaleontology, vol. 23, no. 3, pp. 319-329, pls. 1-2, july, 1977 319 This content downloaded from 207.46.13.51 on Tue, 21 Jun 2016 06:55:29 UTC All use subject to http://about.jstor.org/terms

The morphology and taxonomy of Globigerina mexicana Cushman, 1925

Systematic descriptions, Globigerapsis mexicana (Cushman), Orbulinoides n. gen., O. beckmanni (Saito), synonymies

Planktonic Foraminifera from the American Oligocene

Planktonic foraminiferal assemblages from the Vicksburg group of the Gulf Coast region comprise species comparable with those found in the Oligocene of Tanganyika and northern Europe. The fauna is transitional between typical Upper Eocene and Miocene; its intermediate position is indicative of an Oligocene age.

An eocene dredge haul from the Taumotu ridge

Abstract Middle- and Upper-Eocene boulders representing shallow- and deep-water facies were dredged from the southwest flank of the Tuamotu Ridge at 14° 29°S and 150° 10′W. The dredging suggests that rapid subsidence occurred during upper Middle Eocene time in this portion of the Ridge. Lithification and the presence of bore holes caused by littoral organism in the Upper-Eocene boulders further indicate that uplift took place in post-Eocene time.