RESULTS

Values for ¹³C and ¹⁸O range between 0 and 2 (average = 1.1 ± 0.4, 1) for carbon and largely between –2 and –3 (average = –2.3 ± 0.3, 1) for oxygen (Table T1). For Sites 1258, 1259, 1260, and 1261, where stratigraphic coverage was good for some or all of the upper Campanian–Maastrichtian interval, ¹³C values show no apparent temporal trends with the exception of Site 1259 where ¹³C values <1 were only measured in lowest 15 m of section (Fig. F1). Site 1259 also exhibited the least amount of scatter in ¹³C values, whereas at the other three sites adjacent samples commonly differ by >1. The average ¹³C value is less than those values seen in correlative samples from Blake Nose (e.g., MacLeod et al., 2005), suggesting secondary calcite with a contribution from remineralized organic carbon was present in most, if not all, samples.

Variation in ¹⁸O values among adjacent samples within each section is generally <0.5, and paleotemperatures calculated assuming an ice-free Earth are ~25°C (Erez and Luz, 1983; _w = –1). This value is lower than expected for contemporary tropical sea-surface temperatures (e.g., Pearson et al., 2001), which is consistent with formation of secondary carbonate at the relatively shallow burial depths inferred for these samples. Assuming bottom water temperatures of ~10°C and an average geothermal temperature gradient, burial depths were shallow enough that diagenetic temperatures should not have exceeded surface water temperatures and alteration would have shifted values to cooler temperatures. At Sites 1258, 1259, and 1260, ¹⁸O values seem to decrease slightly in the middle portions of the record before increasing slightly toward the end of the Maastrichtian. The magnitude of any excursion, though, is small relative to between sample variation and apparent average diagenetic offsets. Further, when data from all four sections are projected onto a single age axis, the position of the minima do not correspond (Fig. F2).