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Journal ArticleDOI

Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica

01 Nov 2002-Geology (Geological Society of America)-Vol. 30, Iss: 11, pp 1043-1046

AbstractAn expanded Oligocene-Miocene boundary interval recovered in the Cape Roberts Project CRP-2A core from beneath the Ross Sea, Antarctica, has yielded a high-resolution integrated chrono stratigraphy that has, in turn, enabled a new, more direct, calibra tion of magnetic polarity and biostratigraphic events. The Oligocene-Miocene boundary interval in the CRP-2A core comprises three ∼60-m-thick, rapidly deposited (>0.5 m/k.y.) sedimentary sequences (sequences 9, 10, and 11). In sequences 10 and 11, single-crystal, laser-fusion 40Ar/39Ar analyses of anorthoclase phenocrysts from two tephra horizons independently calibrate the CRP-2A magnetic-polarity stratigraphy and age model. Sequences 10 and 11 encompass subchron C6Cn.3n, which is dated as 24.3 ± 0.1 to 24.16 ± 0.1 Ma. Sequence 9 is interpreted to encompass subchron C6Cn.2n and the Oligocene-Miocene boundary, which is dated as 24.0 ± 0.1 Ma. These ages are ∼0.2 m.y. older than those of the geomagnetic polarity time scale calibrated from seafloor-spreading ridges and ∼0.9–1.3 m.y. older than the newly proposed astronomically calibrated ages. We contend that the discrepancy with the astronomically calibrated ages arises from a mismatch of three 406 k.y. eccentricity cycles or a 1.2 m.y. modulation of obliquity amplitude in the astronomical calibration of the Oligocene–Miocene time scale.

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Citations
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Journal ArticleDOI
Abstract: New biostratigraphic investigations on deep sea cores and outcrop sections have revealed several shortcomings in currently used tropical to subtropical Eocene plank­ tonic foraminiferal zonal schemes in the form of: 1) mod­ ified taxonomic concepts, 2) modifiel:l/different ranges of taxa, and 3) improved calibrations with magnetostratig­ raphy. This new information provides us with an op­ portunity to make some necessary improvements to ex­ isting Eocene biostratigraphic schemes. At the same time, we provide an alphanumeric notation for Paleo­ gene zones using the prefix 'P' (for Paleocene), 'E' (for Eocene) and '0' (for Oligocene) to achieve consistency with recent short-hand notation for other Cenozoic zones (Miocene ['M'], Pliocene [PL] and Pleistocene [PTD. Sixteen Eocene (E) zones are introduced (or nomen­ claturally emended) to replace the 13 zones and subzones of Berggren and others (1995). This new zonation serves as a template for the taxonomic and phylogenetic studies in the forthcoming Atlas of Eocene Planktonic Forami­ nifera (Pearson and others, in press). The 10 zones and subzones of the Paleocene (Berggren and others, 1995) are retained and renamed and/or emended to reflect im­ proved taxonomy and an updated chronologic calibra­ tion to the Global Polarity Time Scale (GPTS) (Berggren and others, 2000).' The PaleocenelEocene boundary is correlated with the lowest occurrence (LO) of Acarinina sibaiyaensis (base of Zone El), at the top of the trun­ cated and redefined (former) Zone P5. The five-fold zonation of the Oligocene (Berggren and others, 1995) is modified to a six-fold zonation with the elevation of (former) Subzones P21a and P21b to zonal status. The Oligocene (0) zomil' components are re­ named and/or nomenclaturally emended.

517 citations


Journal ArticleDOI
Abstract: At Ocean Drilling Program (ODP) Site 1090 (subantarctic South Atlantic), benthic foraminiferal stable isotope data (from Cibicidoides and Oridorsalis) span the late Oligocene through early Miocene (f24-16 Ma) at a temporal resolution of f5 ky. Over the same interval, a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity time scale (GPTS), thereby providing direct correlation of the isotope record to the GPTS. In an initial age model, we use the newly derived age of the Oligocene/Miocene (O/M) boundary of 23.0 Ma of Shackleton et al. (Geology 28 (2000) 447), revised to the new astronomical calculation (La2003) of Laskar et al. (Icarus (in press)) to recalculate the spline ages of Cande and Kent (J. Geophys. Res. 100 (1995) 6093). We then tune the Site 1090 y 18 O record to obliquity using La2003. In this manner, we are able to refine the ages of polarity chrons C7n through C5Cn.1n. The new age model is consistent, within one obliquity cycle, with previously tuned ages for polarity chrons C7n through C6Bn from Shackleton et al. (Geology 28 447-450 (2000)) when rescaled to La2003. The results from Site 1090 provide independent evidence for the revised age of the Oligocene/Miocene boundary of 23.0 Ma. For early Miocene polarity chrons C6AAr through C5Cn, our obliquity-scale age model is the first to allow a direct calibration to the GPTS. The new ages are generally within one obliquity cycle of those obtained by rescaling the Cande and Kent (J. Geophys. Res. 100 (1995) 6093) interpolation using the new age of the O/M boundary (23.0 Ma) and the

119 citations


Journal ArticleDOI
Abstract: We extend existing high-resolution Oligocene–Miocene proxy records from Ocean Drilling Program (ODP) Leg 154. The extended record spans the time interval from ∼ 17.86 to 26.5 Ma. The data are age calibrated against a new astronomical solution that affords a re-evaluation of the intricate interaction between orbital (“Milankovitch”) forcing of the climate and ocean system, and the fidelity with which this forcing is recorded in oxygen and carbon stable isotope measurements from benthic foraminifera, and associated lithological proxy records of magnetic susceptibility, colour reflectance, and the measured sand fraction. Our records show a very strong continual imprint of the Earth's obliquity cycle, modulate in amplitude every ∼ 41 ka , a very strong eccentricity signal in the carbon isotope records, and a strong, but probably local, imprint of climatic precession on the coarse fraction and magnetic susceptibility records. Our data allowed us to evaluate how the interaction of long, multi-million year beats in the Earth's eccentricity and obliquity are implicated in the waxing and waning of ice-sheets, presumably on Antarctica. Our refined age model confirms the revised age of the Oligocene–Miocene boundary, previously established by analysis of the lithological data, and allows a strong correlation with the geomagnetic time scale by comparison with data from ODP Site 1090, Southern Ocean.

114 citations


Additional excerpts

  • ...H. Pälike et al. / Quaternary Science Reviews ] (]]]]) ]]]–]]] 3 Wilson et al. (2002)....

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Journal ArticleDOI
Abstract: The clay mineral assemblages of the ca. 1600 m thick Cenozoic sedimentary succession recovered at the CRP-1, CRP-2/2Aand CRP-3 drill sites off Cape Roberts on the McMurdo Sound shelf, Antarctica, were analysed in order to reconstruct thepalaeoclimate and the glacial history of this part of Antarctica. The sequence can be subdivided into seven clay mineral unitsthat reflect the transition from humid to subpolar and polar conditions. Unit I (35–33.6 Ma) is characterised by an almostmonomineralic assemblage consisting of well crystalline, authigenic smectite, and therefore does not allow a palaeoclimaticreconstruction. Unit II (33.6–33.1 Ma) has also a monomineralic clay mineral composition. However, the assemblage consistsof variably crystallized smectite that, at least in part, is of detrital origin and indicates chemical weathering under a humidclimate. The main source area for the clays was in the Transantarctic Mountains. Minor amounts of illite and chlorite appear forthe first time in Unit III (33.1–31 Ma) and suggest subordinate physical weathering. The sediments of Unit IV (31–30.5 Ma)have strongly variable smectite and illite concentrations indicating an alternation of chemical weathering periods and physicalweathering periods. Unit V (30.5–24.2 Ma) shows a further shift towards physical weathering. Unit VI (24.2–18.5 Ma)indicates strong physical weathering under a cold climate with persistent and intense illite formation. Unit VII (18.5 Ma topresent) documents an additional input of smectite derived from the McMurdo Volcanic Group in the south.D 2005 Elsevier B.V. All rights reserved.

89 citations



References
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Journal ArticleDOI
Abstract: Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic. The age of 66 Ma for the Cretaceous/Paleogene (K/P) boundary used for calibration in the geomagnetic polarity timescale of Cande and Kent (1992) (hereinafter referred to as CK92) was supported by high precision laser fusion Ar/Ar sanidine single crystal dates from nonmarine strata in Montana. However, these age determinations are now

3,475 citations


"Integrated chronostratigraphic cali..." refers background or methods in this paper

  • ...…that the geomagnetic polarity time scale in the vicinity of the Oligocene-Miocene boundary was ;0.2 m.y. older than the conventional calibration of the geomagnetic polarity time scale (Cande and Kent, 1995) and 0.9–1.3 m.y. older than the astronomical calibration of Shackleton et al. (2000)....

    [...]

  • ...We conclude that it is not possible to resolve *E-mail: Channell—jetc@ufl.edu; Martin—emartin@geology.ufl.edu. ages in the 23.5 to 25 Ma (C7–C6C) interval of the CK95 time scale (Cande and Kent, 1995) using strontium isotopes....

    [...]

  • ...Ages are reported with respect to the time scale of Cande and Kent (1995)....

    [...]


Book ChapterDOI
01 Jan 1995
Abstract: Since the publication of our previous time scale (Berggren and others, 1985c = BKFV85) a large amount of new magneto- and biostratigraphic data and radioisotopic ages have become available. An evaluation of some of the key magnetobiostratigraphic calibration points used in BKFV85, as suggested by high precision 40 Ar/ 39 Ar dating (e.g., Montanari and others, 1988; Swisher and Prothero, 1990; Prothero and Swisher, 1992; Prothero, 1994), has served as a catalyst for us in developing a revised Cenozoic time scale. For the Neogene Period, astrochron- ologic data (Shackleton and others, 1990; Hilgen, 1991) required re-evaluation of the calibration of the Pliocene and Pleistocene Epochs. The significantly older ages for the Pliocene-Pleistocene Epochs predicted by astronomical calibrations were soon corroborated by high precision 40 Ar/ 39 Ar dating (e.g., Baksi and others, 1992; McDougall and others, 1992; Tauxe and others, 1992; Walter and others, 1991; Renne and others, 1993). At the same time, a new and improved definition of the Late Cretaceous and Cenozoic polarity sequence was achieved based on a comprehensive evaluation of global sea-floor magnetic anomaly profiles (Cande and Kent, 1992). This, in turn, led to a revised Cenozoic geomagnetic polarity time scale (GPTS) based on standardization to a model of South Atlantic spreading history (Cande and Kent, 1992/1995 = CK92/95). This paper presents a revised (integrated magnetobiochronologic) Cenozoic time scale (IMBTS) based on an assessment and integration of data from several sources. Biostratigraphic events are correlated to the recently revised global polarity time scale (CK95). The construction of the new GPTS is outlined with emphasis on methodology and newly developed polarity history nomenclature. The radioisotopic calibration points (as well as other relevant data) used to constrain the GPTS are reviewed in their (bio)stratigraphic context. An updated magnetobiostratigraphic (re)assessment of about 150 pre-Pliocene planktonic foraminiferal datum events (including recently avail- able high southern (austral) latitude data) and a new/modified zonal biostratigraphy provides an essentially global biostratigraphic correlation framework. This is complemented by a (re)assessment of nearly 100 calcareous nannofossil datum events. Unrecognized unconformities in the stratigraphic record (and to a lesser extent differences in taxonomic concepts), rather than latitudinal diachrony, is shown to account for discrep- ancies in magnetobiostratigraphic correlations in many instances, particularly in the Paleogene Period. Claims of diachrony of low amplitude (<2 my) are poorly substantiated, at least in the Paleocene and Eocene Epochs. Finally, we (re)assess the current status of Cenozoic chronostratigraphy and present estimates of the chronology of lower (stage) and higher (system) level units. Although the numerical values of chronostratigraphic units (and their boundaries) have changed in the decade since the previous version of the Cenozoic time scale, the relative duration of these units has remained essentially the same. This is particularly true of the Paleogene Period, where the Paleocene/Eocene and Eocene/Oligocene boundaries have been shifted ~2 my younger and the Cretaceous/Paleogene boundary ~1 my younger. Changes in the Neogene time scale are relatively minor and reflect primarily improved magnetobiostratigraphic calibrations, better understanding of chronostratigraphic and magnetobiostratigraphic relationships, and the introduction of a congruent astronom- ical/paleomagnetic chronology for the past 6 my (and concomitant adjustments to magnetochron age estimates).

3,063 citations


Journal ArticleDOI
Derek York1
Abstract: Earlier least squares treatments of the fitting of a straight line when both variables are subject to crrors are generalized to allow for correlation of the z and y errors. The method is illustrated by reference to lead isochron fitting.

2,181 citations


Journal ArticleDOI
Abstract: We have constructed a magnetic polarity time scale for the Late Cretaceous and Cenozoic based on an analysis of marine magnetic profiles from the world's ocean basins. This is the first time, since Heirtzler et al. (1968) published their time scale, that the relative widths of the magnetic polarity intervals for the entire Late Cretaceous and Cenozoic have been systematically determined from magnetic profiles. A composite geomagnetic polarity sequence was derived based primarily on data from the South Atlantic. Anomaly spacings in the South Atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles. Fine-scale information was derived from magnetic profiles on faster spreading ridges in the Pacific and Indian Oceans and inserted into the South Ariantic sequence. Based on the assumption that spreading rates in the South Atlantic were smoothly varying but not necessarily constant, a time scale was generated by using a spline function to fit a set of nine age calibration points

1,381 citations


"Integrated chronostratigraphic cali..." refers background or methods in this paper

  • ...…that the geomagnetic polarity time scale in the vicinity of the Oligocene-Miocene boundary was ;0.2 m.y. older than the conventional calibration of the geomagnetic polarity time scale (Cande and Kent, 1995) and 0.9–1.3 m.y. older than the astronomical calibration of Shackleton et al. (2000)....

    [...]

  • ...We conclude that it is not possible to resolve *E-mail: Channell—jetc@ufl.edu; Martin—emartin@geology.ufl.edu. ages in the 23.5 to 25 Ma (C7–C6C) interval of the CK95 time scale (Cande and Kent, 1995) using strontium isotopes....

    [...]

  • ...Ages are reported with respect to the time scale of Cande and Kent (1995)....

    [...]


Journal ArticleDOI
Abstract: An improved and updated version of the statistical LOWESS fit to the marine 87Sr/86Sr record and a revised look-up table (V3:10/99; available from j.mcarthur@ucl.ac.uk) based upon it enables straightforward conversion of 87Sr/86Sr to numerical age, and vice versa, for use in strontium isotope stratigraphy (SIS). The table includes 95% confidence intervals on predictions of numerical age from 87Sr/86Sr. This version includes the Triassic and Paleozoic record (0509 Ma) omitted from previous versions because of the paucity of adequate data at the time of preparation. We highlight differences between the previous versions of the table and the current version and discuss some aspects of the 87Sr/86Sr record that may have geological significance. We give examples of how the table can be used and where it has proven useful.

1,174 citations


"Integrated chronostratigraphic cali..." refers background in this paper

  • ...* 87Sr/86Sr age errors include the 2s measurement error, a 2s long-term laboratory error for standard determination (NIST-987 5 0.710249) and error in the LOWESS fit to the marine Sr curve of McArthur et al. (2001)....

    [...]

  • ...The 87Sr/86Sr ages given for core CRP-2A (Lavelle, 2000; Wilson et al., 2002) are based on the 87Sr/86Sr age tables of McArthur et al. (2001)....

    [...]


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