RESULTS

Oxygen isotope ¹⁸O values in C. mundulus exhibit a series of 0.1–0.6 variations from 316.41 to 327.07 mcd in Core 202-1237B-31H (Fig. F4). Highest values reaching ~2.4 are recorded in upper Chron 9n. Lowest values reaching ~1.8 are recorded in upper Chron 8r. Superimposed upon the mean decrease of ~0.30 is a series of three steps from 323 to 321 mcd within Chron 8r (27.027–26.554 Ma in GTS 2004). The initial decrease at 322.9 mcd is closely associated with the last occurrence of Paragloborotalia opima (P21/P22 planktonic foraminifer zonal boundary) between Samples 202-1237B-31H-5, 10 cm, and 31H-5, 61 cm (322.51–322.76 mcd), in lowermost Chron 8r.

Carbon isotope ¹³C values exhibit a series of 0.1–0.6 variations, including a distinct positive excursion of ~0.5 between 321.6 and 318.4 mcd (Fig. F4). Lowest values reaching ~0.5 are recorded in upper Chron 8r, and highest values reaching ~1.1 are recorded in lower Chron 8n. The ¹³C maximum at 319.2 mcd occurs 2 m above the final decrease in C. mundulus ¹⁸O at 321 mcd.