Table 2.
Sr isotopic ratios and the corresponding numerical ages of calcite and aragonite fractions in the carbonate concretions.
| Sample | fraction | 87Sr/86Srmeasured*,a | 87Sr/86Srcorrected*,b | age (Ma)*,c |
|---|---|---|---|---|
| tusk-shell concretion | ||||
| 111401 | calcite | 0.708664 +/− 0.000013 | 0.708651 | |
| 111403 | calcite | 0.708662 +/− 0.000013 | 0.708648 | |
| 111404 | calcite | 0.708670 +/− 0.000014 | 0.708657 | |
| 111405 | calcite | 0.708678 +/− 0.000011 | 0.708665 | |
| 111406 | calcite | 0.708685 +/− 0.000013 | 0.708671 | |
| 111409 | calcite | 0.708664 +/− 0.000014 | 0.708651 | |
| average | 0.708657 +/− 0.000009 | 17.08 (+0.27, −0.28) | ||
| concretion without fossil | ||||
| 0708-01 | calcite | 0.708670 +/− 0.000011 | 0.708657 | |
| 0708-02 | calcite | 0.708657 +/− 0.000014 | 0.708645 | |
| 0708-03 | calcite | 0.708694 +/− 0.000013 | 0.708682 | |
| 0708-04 | calcite | 0.708689 +/− 0.000011 | 0.708676 | |
| 0708-05 | calcite | 0.708676 +/− 0.000011 | 0.708664 | |
| average | 0.708665 +/− 0.000014 | 16.95 (+0.36, −0.37) | ||
| average of concretions with tusk shell and without fossil | 0.708661 +/− 0.000009 | 17.02 (+0.27, −0.27) | ||
| tusk-shell | ||||
| a1 | aragonite | 0.708694 +/− 0.000014 | 0.708680 | |
| 1996-01 | aragonite | 0.708667 +/− 0.000014 | 0.708654 | |
| 2014-01 | aragonite | 0.708682 +/− 0.000013 | 0.708669 | |
| 2015-01 | aragonite | 0.708687 +/− 0.000013 | 0.708675 | |
| average | 0.708670 +/− 0.000012 | 16.86 (+0.34, −0.34) | ||
| matrix | ||||
| 111407 | calcite | 0.709135 +/− 0.000013 | 0.709121 | |
| 111408 | calcite | 0.708639 +/− 0.000014 | 0.708626 | |
| 111410 | calcite | 0.708706 +/− 0.000011 | 0.708693 | |
Strontium isotopic ratios, 87Sr/86Sr, of calcite or aragonite fractions from the tusk-shell concretions, concretions without fossil, host rock matrices and tusk-shells from the Yatsuo Group are shown. Based on the Sr isotopic stratigraphy, the numerical ages for the tusk-shell concretions, concretions without fossils, and tusk-shells are determined to be 17.08 (+0.27, −0.28) Ma, 16.95 (+0.36, −0.37) Ma and 16.86 ± 0.34 Ma and are fairly consistent with each other. An averaged age of concretions with tusk-shell and without fossil is 17.02 ± 0.27 Ma.
*,aThe errors are 2 SE level on single measurements.
*,bThe repeated analysis of NIST-SRM987 during this study gives the value of 0.710261 ± 0.000005 (2 SE, n = 14). 87Sr/86Sr ratio is normalized to NIST Standard Reference Material (SRM) 987 value (=0.710248). Averaged 87Sr/86Sr ratios for calcite fractions in concretions with tusk-shell, those without fossils, both of the calcites, and aragonite fractions of tusk-shells are presented with 2 SE. Each error of the 87Sr/86Sr ratio includes both error for repeated analysis of the samples and that of NIST-SRM987, that is error propagation. See “METHOD SUMMARY” in detail.
*,cAges are determined by the method of McArthur et al.13. The age error for each calcite/aragonite sample is based on 2 SE for the repeated analysis of multiple samples and that of NIST-SRM987.