Mid-Miocene isotope stratigraphy in the deep sea; high-resolution correlations, paleoclimatic cycles, and sediment preservation

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doi: 10.1029/91PA02561
Author(s): Woodruff, Fay; Savin, Samuel M.
Author Affiliation(s): Primary:
Univ. South. Calif., Dep. Geol. Sci., Los Angeles, CA, United States
Case West. Reserve Univ., United States
Volume Title: Paleoceanography
Source: Paleoceanography, 6(6), p.755-806. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0883-8305 CODEN: POCGEP
Note: In English. 106 refs.; illus. incl. 11 table, sketch map
Summary: Mid-Miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera. Precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates, for example, Deep Sea Drilling Project sites 289 and 574. The mid-Miocene carbon isotope records are characterized by an interval of high δ13C values between 17 and 13.5 Ma (the Monterey Excursion of Vincent and Berger 1985) upon which are superimposed a series of periodic or quasi-periodic fluctuations in δ13C values. These fluctuations have a period of approximately 440 kyr, suggestive of the 413 kyr cycle predicted by Milankovitch theory. Vincent and Berger proposed that the Monterey Excursion was the result of increased organic carbon burial in continental margins sediments. The increased δ13C values (called 13C maxima) superimposed on the generally high mid-Miocene signal coincide with increases in δ18O values suggesting that periods of cooling and/or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric CO2 levels. It is likely that during the Monterey Excursion the ocean/atmosphere system became progressively more sensitive to small changes in insolation, ultimately leading to major cooling of deep water and expansion of continental ice. We have assigned an absolute chronology, based on biostratigraphic and magneto-biostratigraphic datum levels, to the isotope stratigraphy and have used that chronology to correlate unconformities, seismic reflectors, carbonate minima, and dissolution intervals. Intervals of sediment containing 13C maxima are usually better preserved than the overlying and underlying sediments, indicating that the δ13C values of TCO2 in deep water and the corrosiveness of seawater are inversely correlated. This again suggests that the 13C maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric CO2. The absolute chronology we have assigned to the isotopic record indicates that the major mid-Miocene deepwater cooling/ice volume expansion took 2 m.y. and was not abrupt as had been reported previously. The cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals. The cooling was not monotonic, and the 2 m.y. interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period. The increase in δ18O values of benthic foraminifera between 14.9 and 12.9 Ma was greatest at deeper water sites and at sites closest to Antarctica. The data suggest that the δ18O value of seawater increased by no more than about 1.1 per mil during this interval and that the remainder of the change in benthic δ18O values resulted from cooling in Antarctic regions of deepwater formation. Equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0.4 per mil steplike increases in δ13C values. Only one of these increases in planktonic δ13C is correlated with any of the features in the mid-Miocene benthic carbon isotope record. Copyright 1991 by the American Geophysical Union.
Year of Publication: 1991
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Benthic taxa; C-13/C-12; Carbon; Cenozoic; Correlation; DSDP Site 237; DSDP Site 289; DSDP Site 317; DSDP Site 366; DSDP Site 525; DSDP Site 563; DSDP Site 574; DSDP Site 588; Deep Sea Drilling Project; Deep-sea environment; Foraminifera; Global; IPOD; Invertebrata; Isotopes; Leg 108; Leg 115; Leg 119; Leg 120; Leg 121; Leg 24; Leg 30; Leg 33; Leg 41; Leg 74; Leg 82; Leg 85; Leg 90; Marine environment; Marine sediments; Microfossils; Middle Miocene; Miocene; Neogene; O-18/O-16; ODP Site 667; ODP Site 709; ODP Site 744; ODP Site 747; ODP Site 751; ODP Site 752; ODP Site 754; Ocean Drilling Program; Oxygen; Paleoclimatology; Protista; Ratios; Sediments; Stable isotopes; Stratigraphy; Tertiary; World ocean
Record ID: 1992011144
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.

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