North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy
Upper Miocene foraminiferal nannofossil ooze and chalk from DSDP Hole 552A in the northeast Atlantic Ocean have been closely sampled for biostratigraphic, paleomagnetic, and stable-isotopic studies. Sampling at 10-cm intervals resulted in an uppermost Miocene isotope stratigraphy with a 1000- to 300...
Main Authors: | , , |
---|---|
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
1987
|
Subjects: | |
Online Access: | https://doi.org/10.7916/D8ZG72RW |
id |
ftcolumbiauniv:oai:academiccommons.columbia.edu:10.7916/D8ZG72RW |
---|---|
record_format |
openpolar |
spelling |
ftcolumbiauniv:oai:academiccommons.columbia.edu:10.7916/D8ZG72RW 2024-09-09T19:56:16+00:00 North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy Keigwin, L. D. Aubry, Marie-Pierre Kent, Dennis V. 1987 https://doi.org/10.7916/D8ZG72RW English eng https://doi.org/10.7916/D8ZG72RW Geophysics Articles 1987 ftcolumbiauniv https://doi.org/10.7916/D8ZG72RW 2024-08-23T04:10:25Z Upper Miocene foraminiferal nannofossil ooze and chalk from DSDP Hole 552A in the northeast Atlantic Ocean have been closely sampled for biostratigraphic, paleomagnetic, and stable-isotopic studies. Sampling at 10-cm intervals resulted in an uppermost Miocene isotope stratigraphy with a 1000- to 3000-yr. resolution. Covariance in benthic (Planulina wuellerstorfi) and planktonic (Globigerina bulloides) foraminiferal δ^O¸ records is taken as evidence for variability in continental ice volume. Our best estimate is that glacial maxima occurred at ~ 5.0 and ~ 5.5 Ma and lasted no more than 20,000 yrs. These events probably lowered sea level by 60 m below the latest Miocene average. There is little oxygen-isotope evidence, however, for a prolonged glaciation during the last 2 m.y. of the late Miocene. High- and low-frequency variability in the δ^13C record of foraminifers is useful for correlation among North Atlantic DSDP Sites 408, 410, 522, 610, and 611, and for correlation with sites in other oceans. Similar δ^13C changes are seen in P. wuellerstorfi and G. bulloides, but the amplitude of the signal is always greater in G. bulloides. Variability in δ^13C common to both species probably reflects variability in the δ^13C of total CO2 in seawater. Major long-term features in the δ^13C record include a latest Miocene maximum (P. wuellerstorfi = 1.5‰) in paleomagnetic Chron 7, an abrupt decrease in δ^13C at -6.2 Ma, and a slight increase at -5.5 Ma. The decrease in δ^13C at -6.2 Ma, which has been paleomagnetically dated only twice before, occurs in the upper reversed part of Chronozone 6 at Holes 552A and 611C, in excellent agreement with earlier studies. Cycles in δ^13C with a period of ~ 104 yrs. are interpreted as changes in seawater chemistry, which may have resulted from orbitally induced variability in continental biomass. Samples of P. wuellerstorfi younger than 6 Ma from throughout the North Atlantic have δ^13C near 1‰, on average ~ 1‰ greater than samples of the same age in the Pacific Ocean. Thus, there is ... Article in Journal/Newspaper North Atlantic Northeast Atlantic Columbia University: Academic Commons Pacific |
institution |
Open Polar |
collection |
Columbia University: Academic Commons |
op_collection_id |
ftcolumbiauniv |
language |
English |
topic |
Geophysics |
spellingShingle |
Geophysics Keigwin, L. D. Aubry, Marie-Pierre Kent, Dennis V. North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
topic_facet |
Geophysics |
description |
Upper Miocene foraminiferal nannofossil ooze and chalk from DSDP Hole 552A in the northeast Atlantic Ocean have been closely sampled for biostratigraphic, paleomagnetic, and stable-isotopic studies. Sampling at 10-cm intervals resulted in an uppermost Miocene isotope stratigraphy with a 1000- to 3000-yr. resolution. Covariance in benthic (Planulina wuellerstorfi) and planktonic (Globigerina bulloides) foraminiferal δ^O¸ records is taken as evidence for variability in continental ice volume. Our best estimate is that glacial maxima occurred at ~ 5.0 and ~ 5.5 Ma and lasted no more than 20,000 yrs. These events probably lowered sea level by 60 m below the latest Miocene average. There is little oxygen-isotope evidence, however, for a prolonged glaciation during the last 2 m.y. of the late Miocene. High- and low-frequency variability in the δ^13C record of foraminifers is useful for correlation among North Atlantic DSDP Sites 408, 410, 522, 610, and 611, and for correlation with sites in other oceans. Similar δ^13C changes are seen in P. wuellerstorfi and G. bulloides, but the amplitude of the signal is always greater in G. bulloides. Variability in δ^13C common to both species probably reflects variability in the δ^13C of total CO2 in seawater. Major long-term features in the δ^13C record include a latest Miocene maximum (P. wuellerstorfi = 1.5‰) in paleomagnetic Chron 7, an abrupt decrease in δ^13C at -6.2 Ma, and a slight increase at -5.5 Ma. The decrease in δ^13C at -6.2 Ma, which has been paleomagnetically dated only twice before, occurs in the upper reversed part of Chronozone 6 at Holes 552A and 611C, in excellent agreement with earlier studies. Cycles in δ^13C with a period of ~ 104 yrs. are interpreted as changes in seawater chemistry, which may have resulted from orbitally induced variability in continental biomass. Samples of P. wuellerstorfi younger than 6 Ma from throughout the North Atlantic have δ^13C near 1‰, on average ~ 1‰ greater than samples of the same age in the Pacific Ocean. Thus, there is ... |
format |
Article in Journal/Newspaper |
author |
Keigwin, L. D. Aubry, Marie-Pierre Kent, Dennis V. |
author_facet |
Keigwin, L. D. Aubry, Marie-Pierre Kent, Dennis V. |
author_sort |
Keigwin, L. D. |
title |
North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
title_short |
North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
title_full |
North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
title_fullStr |
North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
title_full_unstemmed |
North Atlantic Late Miocene Stable-Isotope Stratigraphy, Biostratigraphy, and Magnetostratigraphy |
title_sort |
north atlantic late miocene stable-isotope stratigraphy, biostratigraphy, and magnetostratigraphy |
publishDate |
1987 |
url |
https://doi.org/10.7916/D8ZG72RW |
geographic |
Pacific |
geographic_facet |
Pacific |
genre |
North Atlantic Northeast Atlantic |
genre_facet |
North Atlantic Northeast Atlantic |
op_relation |
https://doi.org/10.7916/D8ZG72RW |
op_doi |
https://doi.org/10.7916/D8ZG72RW |
_version_ |
1809926920398176256 |