INTRODUCTION

One of the principal objectives of Ocean Drilling Program (ODP) Leg 207 was to recover Cretaceous and Paleogene strata to reconstruct the history of low-latitude sea-surface temperatures. Studies of well-preserved Cenomanian and Turonian planktonic foraminifers from Deep Sea Drilling Project (DSDP) Site 144 (redrilled as Site 1257 during Leg 207) can be interpreted as evidence for unusually warm surface ocean temperatures, conservatively calculated between 30°C and 35°C (Norris et al., 2002; Wilson et al. 2002). However, the absence of continuously cored sequences at DSDP Site 144 prevented determination of the long-term record of tropical planktonic ¹⁸O, particularly in the Turonian–Campanian. Accordingly, we report a low-resolution record from Leg 207 sites of the tropical Atlantic Ocean through the Cretaceous and Paleogene.

The combination of poor preservation of carbonates and the ubiquitous occurrence of several hiatuses prevented us from analyzing a complete isotopic record of Cenomanian–Eocene sediments. Nonetheless, during Leg 207 an expanded sequence of Eocene and Paleocene carbonates, as well as Cenomanian–Santonian black shales were recovered. Campanian and Maastrichtian sections were also recovered, but poor preservation of calcareous microfossils restricts their utility for studies of ancient seawater properties. Fortunately, very well preserved to excellently preserved microfossils could be obtained from the black shales and Paleogene. The only major impediment to producing the Cretaceous part of this record is the difficulty extracting well-preserved fossils from the organic-rich black shales. Conventional processing techniques of drying and crushing samples and soaking in deionized water prior to sieving proved to produce foraminifers coated with bits of clay and organic matrix. Therefore, we experimented with a variety of cleaning techniques and tested the cleaned foraminifers to determine whether these cleaning methods had any effect on our stable isotope results.