Middle Eocene–Early Pliocene Subantarctic planktic foraminiferal biostratigraphy of Site 1090, Agulhas Ridge
Introduction
ODP Site 1090 is located in the central part of the present-day Subantarctic Zone (Fig. 1). The water depth of Site 1090 (3703 m) places it near the boundary between the North Atlantic Deep Water and the underlying Circumpolar Deep Water (see Shipboard Scientific Party, 1999). Site 1090 represents an important tie-point in correlating lower latitude sequences to Antarctic ones and in calibrating the Southern Ocean Paleogene–Neogene biostratigraphic data to the geomagnetic polarity time scale. A 330-m-thick section previously dated as Middle Eocene–Early Miocene (see Shipboard Scientific Party, 1999) was recovered in multiple cores (Holes 1090B, D, and E; see Fig. 2) encompassing a time interval crucial to the long-term evolution of the Antarctic ocean-cryosphere system during the Cenozoic. In particular, the presence of a well-preserved Eocene–Oligocene transition permits a detailed study of the time interval when the emplacement of a major Antarctic ice-sheet took place.
In this paper we describe and interpret the distribution of planktic foraminiferal assemblages from Site 1090, calibrating the identified bioevents to the available magnetostratigraphic data (see Shipboard Scientific Party, 1999), and tentatively correlating them to the Berggren et al. (1995) time scale and biochronology. A single benthic foraminiferal event has been used to corroborate the biostratigraphic interpretation based on planktic foraminifera across the Middle–Late Eocene transition.
Section snippets
Materials and methods
A total of 230 samples have been studied from an interval spanning from the bottom of Core 1090B to 71.55 mcd (metres composite depth). Overall recovery at Site 1090 was 93.4% (Shipboard Scientific Party, 1999). A complete splice covers approximately the upper 242 m of the section. Below the splice in Hole 1090B, recovery averaged 92.3%.
For this study one sample per section (ca. 1.5 m) has been studied, for most of the surveyed interval. Forty-cc samples were soaked in tap water and washed
Results and discussion
Relatively rich planktic foraminiferal assemblages occur from the bottom of Core 1090B to 360 mcd where preservation varies from moderate to good. From here upward, the record of planktic foraminifera gradually becomes less continuous. Above 330 mcd assemblages are steadily rare to scattered and moderately to poorly preserved. Several extended barren intervals occur from 330 mcd to 90 mcd. This trend clearly reflects the sharp lithological change occurring at ca. 340 mcd where mud-bearing
Summary
The analysis of planktic foraminiferal assemblages from the Middle Eocene–Early Pliocene ODP Site 1090 allowed a biostratigraphic subdivision based on the AP Zonation of Stott and Kennett (1990) for the Middle–Late Eocene. A calibration to the tropical–subtropical P zonations of Blow (1969) and Berggren et al. (1995) is tentatively made for the whole surveyed interval.
The age/depth curve based on our magnetobiostratigraphic interpretation of polarity data given by Shipboard Scientific Party
Acknowledgements
We thank Brian Huber and an anonymous referee for their critical review that greatly improved the manuscript. Thanks are due to S. Iaccarino, I. Premoli Silva, and J.P. Kennett for their opinions on the identification of Globorotalia sphericomiozea. This paper benefitted from funds COFIN ’99 to S. Monechi. SG is grateful to the Alfred Wegener Institute for financial support during his stay in Bremerhaven.
References (50)
Late Neogene biostratigraphy and paleoceanography of DSDP Site 310, Central North Pacific and correlation with the south west Pacific
Mar. Micropaleontol.
(1978)Late Neogene planktonic foraminiferal biostratigraphy and paleoceanography of the northwest Pacific DSDP Site 296
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(1979)Late Neogene paleoceanography of the North Pacific DSDP Sites 173, 310 and 296
Mar. Micropaleontol.
(1979)Early Pliocene to Pleistocene planktonic foraminiferal datum levels in the North Pacific: DSDP Sites 173, 310, 296
Mar. Micropaleontol.
(1979)- Berggren, W.A., 1977. Late Neogene planktonic foraminiferal biostratigraphy of DSDP Site 357 (Rio Grande Rise). In:...
- Berggren, W.A., 1992. Paleogene planktonic foraminifer magnetobiostratigraphy of the Southern Kerguelan Plateau (Site...
- Berggren, W.A., 1992. Neogene planktonic foraminifer magnetobiostratigraphy of the Southern Kerguelan Plateau (Site...
- et al.
Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology
Micropaleontology
(1988) - et al.
Cenozoic bathyal and abyssal calcareous benthic foraminiferal zonation
Micropaleontology
(1989) - Berggren, W.A., Aubry, M.P., Hamilton, N., 1983. Neogene magnetobiostratigraphy of DSDP Site 516 (Rio Grande Rise,...
The Oligocene marine microfossil record: Age assessment using strontium isotopes
Paleoceanography
Manual of New Zealand Permian to Pleistocene Foraminiferal Biostratigraphy
N.Z. Geol. Surv. Paleontol. Bull.
New Zealand Cenozoic planktonic foraminifera
N.Z. Geol. Surv. Paleontol. Bull.
Cited by (16)
Late middle Eocene to early Oligocene radiolarian biostratigraphy in the Southern Ocean (Agulhas Ridge, ODP Leg 117, Site 1090)
2021, Marine MicropaleontologyCitation Excerpt :The subdivisions of the Eucyrtidium spinosum Zone into these new subzones could improve significantly the biostratigraphic resolution of this zone. The age-depth model based on paleomagnetic data (Channell et al., 2003), planktic foraminifers (Galeotti et al., 2002), and calcareous nannofossils (Marino and Flores, 2002), were used to estimate the ages of the radiolarian events (Table 2; Fig. 4). The geomagnetic time scale was adopted from Gradstein et al. (2012).
Malvinia escutiana, a new biostratigraphically important Oligocene dinoflagellate cyst from the Southern Ocean
2011, Review of Palaeobotany and PalynologyCovarying sedimentary and biotic fluctuations in Lower-Middle Eocene Pyrenean deep-sea deposits: Palaeoenvironmental implications
2006, Palaeogeography, Palaeoclimatology, PalaeoecologyAstronomic calibration of the late Oligocene through early Miocene geomagnetic polarity time scale
2004, Earth and Planetary Science LettersCitation Excerpt :Magnetic measurements on Eocene to Miocene sediments from Site 1090 are described in detail by Channell et al. [11] who have augmented the shipboard paleomagnetic record with u-channel measurements as well as discrete (7 cm3) samples. Aided by stable isotopic [11,14] and biostratigraphic [11,20–22] information, a polarity-zone pattern can be interpreted in terms of late Eocene through early Miocene polarity chrons [11]. GPTS ages in the Channell et al. [11] study are based on rescaling the ages of Cande and Kent [8,9] using the astronomically calibrated age of the O/M boundary of 22.9 Ma [10] as a revised calibration point.
Middle Eocene to early Oligocene calcareous nannofossil stratigraphy at Leg 177 Site 1090
2002, Marine Micropaleontology