Jurassic to Paleogene: Part 2 Paleogene geochronology and chronostratigraphy

Abstract

S U M M A R Y :We present a revised Paleogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chronostratigraphic boundaries: Cretaceous-Tertiary boundary (Chron C29R), 66.4 Ma; Paleocene-Eocene (Chron C24R), 57.8 Ma; Eocene-Oligocene (Chron C13R), 36.6 Ma; Oligocene-Miocene (Chron C6CN), 23.7 Ma.The Eocene is seen to have expanded chronologically (-21 m.y.) at the expense of the Paleocene (-9 m.y.) and is indeed the longest of the Cenozoic epochs. In addition, magnetobiostratigraphic correlations require adjustments in apparent correlations with standard marine stage boundaries in some cases (particularly in the Oligocene). Finally, we present a correlation between standard Paleogene marine and terrestrial stratigraphies.It is nearly 20 years since Brian Funnell prepared the first relatively precise Cenozoic time-scale based on an assessment of palaeontologically controlled radiometric data in connection with the symposium on the Phanerozoic timescale sponsored by the London Geological Society, and 10 years since one of us (WAB) presented the first in a series of attempts to further refine Cenozoic geochronology. During the past decade several revisions to the Cenozoic time-scale have appeared and here, at this, the second symposium on the Phanerozoic time-scale sponsored by the Geological Society of London, it is appropriate to present an updated and, hopefully, improved version of the Cenozoic time-scale.It is opportune that over the past decade direct correlation has been achieved between plankton biostratigraphy in some of the standard European continental marine sections and North American terrestrial vertebrate biochronology and magnetic polarity stratigraphy over much of the Cenozoic Era. The recent improvement in deep sea coring techniques has further extended these correlations on a global scale. It is now possible to make age estimates of epoch boundaries and the extent of time-stratigraphic (standard ages) units in terms of plankton biostratigraphy and magnetic polarity chrons and/or anomalies.Finally a critical evaluation must be made within a geohistorical context of biostratigraphically controlled radiometric dates and radiometrically dated polarity stratigraphy in order to provide constraints on an internally consistent geologic time-scale.The revised Cenozoic geochronology has been prepared in two parts: (a) Paleogene; (b) Neogene. In this paper dealing with the Paleogene we first discuss the development of geomagnetic polarity history of the late Cretaceous and Cenozoic. A revised geochronology is then presented which is based upon a best fit to selected high temperature radiometric dates on a number of identifi...

Paleogene Benthic Foraminifers from the Southern Indian Ocean (Kerguelen Plateau): Biostratigraphy and Paleoecology

“…The geochronology is according to Berggren et al (1985) and Aubry et al (1988). At Site 748, the Paleogene sedimentary record starts in the lower upper Paleocene above a hiatus spanning the Cretaceous/Paleocene boundary.…”

Explanatory Notes

“…The Leg 129 paleontologists chose the following chronostratigraphy for use during the cruise: the time scale of Berggren et al (1985aBerggren et al ( , 1985b for the Cenozoic and the chronostratigraphy and geochronology of Kent and Gradstein (1985), with modifications, for the Early Cretaceous and the Jurassic (Fig. 9).…”

“…Calibration of nannofossil zonation with geochronology follows Berggren et al (1985aBerggren et al ( , 1985b. …”

“…For the Cretaceous the zonations reported by Caron (1985), Kent and Gradstein (1985), and Monechi and Thierstein (1985) were followed. Calibration of planktonic foraminiferal zonation with chronostratigraphy and geochronology followed Berggren et al (1985aBerggren et al ( , 1985b for the Cenozoic and Kent and Gradstein (1985) for the Cretaceous (Fig. 9).…”

“…The zonation of Matsuoka andYao (1985, 1986) was not originally assigned to stages. ogy of Berggren et al (1985aBerggren et al ( , 1985b for the Cenozoic and to the time scale of Kent and Gradstein (1985) for the Mesozoic (Fig. 9).…”