Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic

TL;DR: 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.

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

Summary

Summary

• Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident hat 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.
• These age determinations are now considered to be anomalously old due to problems with sample preparation [Swisher et al., 1992, 1993].
• The astronochronologic estimates for the Brunhes/Matuyama (0.78 Ma) and Matuyama/Gauss (2.60 Ma) boundaries were already used for calibration in CK92; thus the good agreement of CK92 with the astronomical timescale to the older end of chron C2A (Gauss/Gilbert boundary) is not unexpected.
• Ln, C3n.2n, C3n.3n, and C3n.4n, or Cochiti, Nunivak, Sidufjall, and Thvera subchrons, respectively) that are systematically 150 to 180 kyr older than the interpolated ages in CK92.
• This points to the magnetic anomaly spacings for this interval used for interpolation by Cande and Kent [1992] as the likely source of the discrepancy and suggests that the available astronochronology provides reliable ages for polarity chrons through the Pliocene (see also Renne et al., 1994).
• Copyfight 1995 by tho Amorican Ooophysical Union.
• Calibration data given in Table 1 are otherwise the same as by Cande and Kent [1992].
• The revised geomagnetic polarity timescale is listed in Tables 2 and 3.
• Other age calibration data from Cande and Kent [1992].

Full text

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. B4, PAGES 6093-6095, APRIL 10, 1995
Revised calibration of the geomagnetic polarity timescale
for the Late Cretaceous and Cenozoic
S. C. Cande
Scripps Institution of Oceanography, La Jolla, California
D. V. Kent
Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York
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
considered to be anomalously old due to problems with sample
preparation [Swisher et al., 1992, 1993]. A consensus is
developing for an age of 65 Ma for the K/P boundary as
recorded in marine [Swisher et al., 1992; Dalryrnple et al.,
1993] and nonmarine [Swisher et al., 1993] sediments, and
the 65 Ma age has been adopted, for example, as an anchor
point in the Mesozoic timescale of Gradstein et al. [1994].
Astrochronologic control for the geomagnetic polarity
timescale has been developed by Shackleton et al. [1990] and
Hilgen [1991] for the Pleistocene and Pliocene to the base of
the Thvera polarity subchron (subchron C3n.4n) and has been
confirmed to about 3.3 Ma using high-precision At/At dating
[Renne et al., 1993]. The astronochronologic estimates for
the Brunhes/Matuyama (0.78 Ma) and Matuyama/Gauss (2.60
Ma) boundaries were already used for calibration in CK92; thus
the good agreement of CK92 with the astronomical timescale
to the older end of chron C2A (Gauss/Gilbert boundary) is not
unexpected. An appreciable discrepancy, however, emerges in
the early Pliocene where the astronomical timescale gives ages
for the constituent polarity intervals of chron C3n (C3n. ln,
C3n.2n, C3n.3n, and C3n.4n, or Cochiti, Nunivak, Sidufjall,
and Thvera subchrons, respectively) that are systematically
150 to 180 kyr older than the interpolated ages in CK92.
Wilson [1993] showed that the astrochronology gives a more
consistent seafloor spreading history when applied to his
revised spacings of anomalies on several Pacific spreading
ridges. This points to the magnetic anomaly spacings for this
interval used for interpolation by Cande and Kent [1992] as
the likely source of the discrepancy and suggests that the
available astronochronology provides reliable ages for
polarity chrons through the Pliocene (see also Renne et al.,
1994).
Copyfight 1995 by tho Amorican Ooophysical Union.
Paper number 9411303098.
0148-0227/95/94JB-03098505.00
A revised geomagnetic polarity timescale was generated
with 65 Ma rather than 66 Ma for the K/P boundary and an
astronomical age of 5.23 Ma [Hilgen, 1991] for the older
boundary of subchron C3n.4n (the base of the Thvera
subchron), rather than 2.60 Ma for the younger boundary of
chron C2A (Matuyama/Gauss boundary) used in CK92, for the
cubic spline interpolation. Calibration data given in Table 1
are otherwise the same as by Cande and Kent [1992]. The
ages of Pleistocene and Pliocene polarity intervals,
corresponding to subchron C3n.4n and younger subchrons, are
then inserted from the astrochronology of Shackleton et al.
[1990] and Hilgen [1991] with a refined astronomical age
recently suggested for the Gauss/Matuyama boundary by
Langereis et al. [1994]. The revised geomagnetic polarity
timescale is listed in Tables 2 and 3. These tables supersede
Tables 5, 6, and 7, respectively, of Cande and Kent [1992].
Table 1. Revised Age Calibrations for Geomagnetic
Polarity Timescale
Polarity South Atlantic
Chron Distance, km Age, Ma
C3n.4n(o) 84.68 5.23*
C5Bn(y) 290.17 14.8
C6Cn.2r(y) 501.55 23.8
C13r(.14) 759.49 33.7
C21n(.33) 1071.62 46.8
C24r(.66) 1221.20 55.0
C29r(.3) 1364.37 65.0•'
C33n(.15) 1575.56 74.5
C34n(y) 1862.32 83.0
Position within polarity chron is given as either decimal
fraction from younger end, or (o) for older and (y) for younger
end of chron.
* Ages for polarity chron C3n.4n(o) and younger are made
equivalent to astronomical timescale of Shackleton et al.
[1990] and Hilgen [1991], with refinement of Langereis et
al. [1994].
•' Revised K/P boundary age, see text. Other age
calibration data from Cande and Kent [1992].
6093

6094 CANDE AND KEI•: REVISED GEOMAG•C POLARITY TIMESCALE
Table 2. Revised Normal Polarity Intervals
Normal Polarity
Interval, Ma
Polarity
Chron
0.000 - 0.780
0.990 - 1.070
1.770 - 1.950
2.140 - 2.150
2.581 - 3.040
3.110 - 3.220
3.330 - 3.580
4.180 - 4.290
4.480 - 4.620
4.800 - 4.890
4.980 - 5.230
5.894 - 6.137
6.269 - 6.567
6.935 - 7.091
7.135 - 7.170
7.341 - 7.375
7.432 - 7.562
7.650 - 8.072
8.225 - 8.257
8.699 - 9.025
9.230 - 9.308
9.580 - 9.642
9.740 - 9.880
9.920 - 10.949
11.052 - 11.099
11.476 - 11.531
11.935 - 12.078
12.184 - 12.401
12.678 - 12.708
12.775 - 12.819
12.991 - 13.139
13.302 - 13.510
13.703 - 14.076
14.178 - 14.612
14.800 - 14.888
15.034 - 15.155
16.014 - 16.293
16.327 - 16.488
16.556 - 16.726
17.277 - 17.615
18.281 - 18.781
19.048 - 20.131
20.518 - 20.725
20.996 - 21.320
21.768 - 21.859
22.151 - 22.248
22.459 - 22.493
22.588 - 22.750
22.804 - 23.069
23.353 - 23.535
23.677 - 23.800
23.999 - 24.118
24.730 - 24.781
24.835 - 25.183
25.496 - 25.648
25.823 - 25.951
25.992 - 26.554
27.027 - 27.972
28.283 - 28.512
28.578 - 28.745
29.401 - 29.662
29.765 - 30.098
30.479 - 30.939
Cln
Clr. ln
C2n
C2r. ln
C2An. ln
C2An.2n
C2An.3n
C3n. ln
C3n.2n
C3n.3n
C3n.4n
C3An. ln
C3An.2n
C3Bn
C3Br. ln
C3Br.2n
C4n. ln
C4n.2n
C4r. ln
C4An
C4Ar. ln
C4Ar.2n
C5n. ln
C5n.2n
C5r. ln
C5r.2n
C5An. ln
C5An.2n
C5Ar. ln
C5Ar.2n
C5AAn
C5ABn
C5ACn
C5ADn
C5Bn. ln
C5Bn.2n
C5Cn. ln
C5Cn.2n
C5Cn.3n
C5Dn
C5En
C6n
C6An. ln
C6An.2n
C6AAn
C6AAr. ln
C6AAr.2n
C6Bn. ln
C6Bn.2n
C6Cn. ln
C6Cn.2n
C6Cn.3n
C7n. ln
C7n.2n
C7An
C8n. ln
C8n.2n
C9n
C10n. ln
C10n.2n
Clln. ln
Clln.2n
C12n
Table 2. (continued)
Normal Polarity Polarity
Interval, Ma Chron
33.058 - 33.545 C13n
34.655 - 34.940 C15n
35.343 - 35.526 C16n. ln
35.685 - 36.341 C16n.2n
36.618 - 37.473 C17n. ln
37.604 - 37.848 C17n.2n
37.920 - 38.113 C17n.3n
38.426 - 39.552 C18n. ln
39.631 - 40.130 C18n.2n
41.257 - 41.521 C19n
42.536 - 43.789 C20n
46.264 - 47.906 C21n
49.037 - 49.714 C22n
50.778 - 50.946 C23n. ln
51.047 - 51.743 C23n.2n
52.364 - 52.663 C24n. ln
52.757 - 52.801 C24n.2n
52.903 - 53.347 C24n.3n
55.904 - 56.39I C25n
57.554 - 57.911 C26n
60.920 - 61.276 C27n
62.499 - 63.634 C28n
63.976 - 64.745 C29n
65.578 - 67.610 C30n
67.735 - 68.737 C31n
71.071 - 71.338 C32n. ln
71.587 - 73.004 C32n.2n
73.291 - 73.374 C32r. ln
73.619 - 79.075 C33n
83.000 -118.000 C34n
Table 3. Revised Cryptochrons Identified in Polarity
Chrons C1 to C13 and C24 to C28
Interval, Ma Cryptochron
0.493
1.201
2.420
8.635
10.197
10.446
10.710
17.825
24.475
25.338
26.347
27.389
27.616
28.118
29.023
29.186
30.278
31.224
31.473
31.844
32.018
32.187
32.446
32.602
32.772
33.266
- 0.504 Cln-1
- 1.211 *Clr. 2r-ln
- 2.441 C2r.2r- 1
- 8.651 C4r.2r-1
- 10.205 C5n.2n- 1
- 10.470 C5n.2n-2
- 10.726 C5n.2n-3
- 17.853 C5Dr-1
- 24.486 C6r-1
- 25.354 C7r- 1
- 26.359 C8n.2n- 1
- 27.407 C9n- 1
- 27.634 C9n-2
- 28.130 C9r- 1
- 29.037 C10r-1
- 29.193 C10r-2
- 30.292 Cllr-1
- 31.243 C12r-1
- 31.482 C12r-2
- 31.863 C12r-3
- 32.027 C12r-4
- 32.197 C12r-5
- 32.465 C12r-6
- 32.612 C12r-7
- 32.782 C12r-8
- 33.283 C13n-1

CANDE AND KENT: REVISED GEOMAGNETIC POLARITY TIMESCALE 6095
Table 3. (continued)
Interval, Ma Cryptochron
33.677 - 33 694
33.877 - 33 885
34.168 - 34 184
34.414 - 34 430
53.550 - 53 558
53.686 - 53 694
53.892 - 53 901
54.031 - 54.040
54.223 - 54.232
54.524 - 54.533
54.757 - 54.766
54.956 - 54.965
55.066 - 55.075
55.286 - 55.296
55.565 - 55.574
56.675 - 56.690
56.833 - 56.849
56.976 - 56.984
57.216 - 57.224
57.361 - 57.377
58.413 - 58.431
58.973 - 58.992
59.179 - 59.189
59.367 - 59.376
59.760 - 59.779
60.098 - 60.107
60.360 - 60.369
63.784 - 63.810
C13r-1
C13r-2
C13r-3
C13r-4
C24r-1
C24r-2
C24r-3
C24r-4
C24r-5
C24r-6
C24r-7
C24r-8
C24r-9
C24r-10
C24r-11
C25r-1
C25r-2
C25r-3
C25r-4
C25r-5
C26r-1
C26r-2
C26r-3
C26r-4
C26r-5
C26r-6
C26r-7
C28r-1
* Shackleton et al. [1990] give an age of 1.19 Ma for the
Cobb Mt. subchron.
There will undoubtedly be further refinements to the
geomagnetic polarity timescale as the results of high-
precision radiometric and astronomical dating methods
become more widely available in a magnetostratigraphic
context. There is already good agreement between the
geomagnetic polarity timescale and new radiometric dates at
around chron C5 [Baksi et al., 1993; Baksi, 1993], chrons
C10r and C13r [Mcintosh et al., 1992], and chron C33r
[Hicks et al., 1995].
Acknowledgments. Supported by NSF grant OCE91-04447. LDEO
contribution 5314.
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S.C. Cande, Scripps Institution of Oceanography, MC 0215, La Jolla,
CA 92091. (e-mail: cande@gauss.u½sd.edu)
D. V. Kent, Lamont-Doherty Earth Observatory, Palisades, NY 10964.
(e-mail: dvk@ldgo.columbia.edu)
(Received July 15, 1994; revised November 17, 1994;
accepted November 29, 1994.)