UPDATED CENOZOIC NANNOFOSSIL MAGNETOBIOCHRONOLOGY
Wuchang Wei and Alyssa Peleo-Alampay
Scripps Institution of Oceanography, University of California, San Diego, USA
The Cenozoic magnetobiochronology of Berggren et al. (1985a, b, c) has been essential intranslating biostratigraphic information into numerical age information and widely used instudies of Cenozoic marine sediments. However, a significantly improved geomagnetic polarity
time scale has recently been published (Cande and Kent, 1992) and the age differences between
the new time scale and that of Berggren et al. (1985) are up to 2.9 m.y. It is thus necessary toconvert the magnetobiochronologic ages of Berggren et al. (1985) to the new time scale. Here werecalculate the nannofossil datum ages given in table 4 of Berggren et al. (1985a) and table 7 of
Berggren et al. (1985b) and graphically present them in the new time scale (Fig. 1).
Each new datum age is calculated based on:(A 0 - T 0 )/(Bo- A0 ) = (An- Tn)/(Bn- An) or:
An= CTn-Ao- Ao·Bn+To·Bn- Tn·Bo)/(To- Bo)
where A is the age of the datum, T and B are the ages for the top and bottom, respectively, of themagnetic subchron in which the datum is located, and the subscripts " 0 " and "n" indicate oldand new time scales, respectively.
A few of the datum ages given in Berggren et al. (1985a, b) are inappropriate even in theold time scale. These problems are corrected and briefly outlined below:
The age for the first occurrence (FO) of Catinaster calyculus was given the same age asthat of Discoaster hamatus (Berggren et al., 1985b) and thus subzone CN7a does not exist,
although Berggren et al. (1985b, c) inferred its existence. The last occurrence (LO) of Sphenolithus belemnos, the marker for the NN3/NN4 boundary, has an age of 17.4 Ma in Berggren et al.
(1985b) based on DSDP Site 516, 18.8 Main Backman et al. (1990) based on ODP Site 710, and18.7 Ma in Gartner (1992) based on DSDP Site 608. We adopt the age of 18.8 Ma, whichtranslates to 18.5 Main the new time scale. The FO of S. belemnos was assigned an age of 21.5
Ma in Berggren et al. (1985b), who cited Miller et al. (1985) as the data source. However, thelatter study gave an age of about 20.8 Ma, which is virtually the same as that determined byTakayama and Sato (1987). We use the latter age, which translates to 20.5 Ma in the new timescale. The FO of lsthmolithus recurvus has an age of 37.8 Ma in Berggren et al. (1985a). Thisage was revised to about 39.0 Ma based on data from the Massignano section (Italy) and ODP
Sites 744, 689, and 690 (Wei, 1992). The latter age translates to 36.2 Ma in the new time scale.
REFERENCES
Backman J., Schneider D.A., Rio D. & Okada H. 1990: Neogene low-latitude magnetostratigraphy from Site 710 andrevised age estimates of Miocene nannofossil datum events. Proc. ODP Sci. Res., 115, 271-276.
Berggren W.A., Kent D.V. & Flynn J.J. 1985a: Palaeogene geochronology and chronostratigraphy. In, Snelling N.J.
(ed) "The Chronology of the Geological Record", Blackwell, p. 141-195.
Berggren W.A., Kent D.V. & van Couvering J.A. 1985b: Neogene geochronology and chronostratigraphy. In,Snelling N.J. (ed) "The Chronology of the Geological Record", Blackwell, p. 211-260.
Berggren W.A., Kent D.V. Flynn J.J. & van Couvering J.A. 1985c: Cenozoic geochronology. Geol. Soc. Am. Bull.,96, 1407-1418.
Cande S. & Kent D.V. 1992: A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. J Geophys.
Res., 97, 13917-13951.
Gartner S. 1992: Miocene nannofossil chronology in the North Atlantic, DSDP Site 608. Mar. Micropaleont., 18,307-331.
Martini, E. 1971: Standard Tertiary and Quaternary calcareous nannoplankton zonation. In, Farinacci A. (ed),Proceedings 11 Planktonic Conference, Roma1970, 2, 739-785.
Miller K.G., Aubry M-P., Khan M.J., Melilo A.J., Kent D.V. & Berggren W.A. 1985: Oligocene-Miocene
biostratigraphy, magnetostratigraphy and isotope stratigraphy of western North Atlantic. Geology, 13, 257261.
Okada H. & Bukry D. 1980: Supplementary modification and introduction of code numbers to the low-latitude coccolith
biostratigraphic zonation (Bukry 1973, 1975). Mar. Micropaleont., 5, 321-325.
Takayama T. & Sato T. 1987: Coccolith biostratigraphy of the North Atlantic Ocean, Deep Sea Drilling Project Leg
94. IRDSDP, 94, 651-702.
Wei W. 1992: Updated nannofossil stratigraphy of the CIROS-1 core from McMurdo Sound (Ross Sea). ODP Sci. Res.,
120, 1105-1117.

INA Newsletter 15/1 - 1993

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---

2_s .... ·s"'~"'-r--.>4 '-''26"'s::0uIU-~<~bl)00\'2'-'0].s::"'0 ;:l~~60~ ·~~ ~§N:S--2_s -"'8'1:)00"'0\.>4:::::,---''1:l 0\IUbl)

Nannofossil datums (Ma)

<r--

....

"'s::.s::"'0u

Jt N a-~~]g0\'-'o ·s00 ;:l~~§'1:l"'~ ·~t:0 "'
N:S10
E. huxleyi (0.294)
P. lacunosa (0.506)

C. calyculus (10.5)
D. hamatus (10.5)

11-'-C. coalitus ( 11.2)

12
H. sellii ( 1.46)
C. macintyrei (1.54)
G. oceamca (1.781
G. caribbeanica ~ .84)
D. brouweri (2.02b13NN7

CN5-'-D. kugleri (13.2)a

14
D. pentaradiatus (2.4)
D. surculus (2.5)
D. tamalis (2. 7)

Nannofossil datums (Ma)

NN6-r-S. heteromorphus (14.4)

15CN4NN53-r-H. ampliaperta (16.0)

16~-r- R. pseudoumbilicus (3.7)-r- A. tricorniculatus (3.9)

.9
i:i:

4

D. asymmetricus (4.3)
A. primus (4.61
C. rugosus (4. )5-'-S. heteromorphus (16.9)

17NN4

18-r-S. belemnos ~18.5~-r-T. carinatus 18.7

CN21920a...J...S. belemnos (20.5)-r- D. quinqueramus (6.0)

6NN2

21bc

22-'-A. primus (6.9)

723CN1...J...D. druggii (23.2)

NNllCN9b24aa8

NN1.....s. ciperoensis (24.6)

259CN8CN7-'-D. quinqueramus (8.9)

26-r- D. hamatus (9.5)

27bNP25NN10NN928.,..s. distentus (27.0)
a NP24...l..S. ciperoensis (28.6)

29-'- First occurrence....
Last occurrence

CP18NP2330

Fig. 1. Updated Cenozoic nannofossil magnetobiochronology. The magnetic polarity
time scale is that of Cande and Kent (1992). The datum ages are converted fromBerggren et al. (1985a,b) except for a few as discussed in the text.

16INA Newsletter 15/1 - 1993

Fig. 1 (continued)

INA Newsletter 15/1 - 199317