The sedimentary record recovered over the course of several decades of deep-sea drilling has yielded a wealth of information on Earth's climate system. Pelagic sedimentary sections provide some of the most faithful time series of climate states from the Middle Jurassic to the Holocene. Potentially more significant, however, are the clues within the sedimentary archives of the mechanisms and processes that drive climate change and the effect of that change on biotic evolution and geochemical cycling (e.g., Schlanger et al., 1987; Dickens et al., 1995; Leckie et al., 2002).
The early decades of deep-sea drilling, largely associated with the Deep Sea Drilling Project (DSDP), involved a great deal of exploratory coring in locations where the stratigraphy of the sedimentary section was undocumented and poorly constrained. More recently, however, knowledge from previous drilling expeditions combined with the availability of high-resolution multichannel seismic reflection data have allowed us to target particular time slices at locations where the sedimentary section looks essentially complete. In addition, hydraulic piston coring technology developed during the Ocean Drilling Program (ODP) allows us to obtain high-quality records when these locations are revisited.
Shatsky Rise, a medium-sized large igneous province (LIP) in the west-central Pacific (Fig. F1) was the target of three DSDP expeditions, Legs 6, 32, and 86, and ODP Leg 132 (Fischer, Heezen et al., 1971; Larson, Moberly, et al., 1975; Heath, Burkle, et al., 1985; Natland, Storms, et al., 1993). The quality of the records from the older legs was hampered by rotary and spot-coring as well as low recovery in the Cretaceous because of the presence of persistent chert. Yet these legs revealed the potential of Shatsky Rise sediments to provide high-quality records of Cretaceous and Paleogene climate. This interval is located at shallow burial depths on the rise and thus is relatively unaltered by burial diagenesis (e.g., Schlanger and Douglas, 1974). Leg 198 was designed to recover high-quality sedimentary records of this age along a depth transect (Bralower, Premoli Silva, Malone, et al., 2002). The transect has the potential to provide two-dimensional reconstructions of ocean temperature, chemistry (i.e., carbonate solubility and oxygenation), circulation, and biology through some of the most fundamentally interesting intervals of climate change during the entire Phanerozoic.
The mid-Cretaceous (~120–80 Ma) and early Paleogene (~60–45 Ma) were characterized by equable climates including low latitudinal thermal gradients, lack of extensive cryosphere, a relatively warm deep ocean, and high atmospheric pCO2 levels (Fig. F2) (e.g., Barron and Washington, 1985; Berner, 1994). These "greenhouse" intervals also contain significant abrupt and transient warming events that led to major changes in oceanic environments, profound turnovers in marine communities including extinctions, and perturbations to global chemical cycles. Examples include the Paleocene/Eocene Thermal Maximum (PETM) (e.g., Kennett and Stott, 1991; Dickens et al., 1995; Katz et al., 1999; Norris and Röhl, 1999) and Cretaceous Oceanic Anoxic Events (OAEs) (e.g., Schlanger and Jenkyns, 1976; Jenkyns, 1980; Arthur et al., 1985, 1988). Leg 198 was designed to understand the causes, nature, and mechanics of the long-term Cretaceous and Paleogene "greenhouse" as well as of the transient events during this period. The location of Shatsky Rise in the tropical Pacific during the interval of interest is fundamentally significant—the aerial extent and importance of the Pacific in global circulation make this a critical target for investigation of warm climatic intervals. Yet, this ocean basin contains far less complete records than the Atlantic, Indian, and Tethyan Oceans. During Leg 198, one site was drilled on each of the North and Central Highs of Shatsky Rise (Sites 1207 and 1208, respectively) and six sites were drilled on the Southern High (Sites 1209–1214) (Bralower, Premoli Silva, Malone, et al., 2002).
An impressive 140-m.y. package of pelagic sediment was recovered at the eight sites (Figs. F3, F4, F5, F6, F7, F8, F9). In addition, the first cores from the basement of Shatsky Rise were recovered at Site 1213. Detailed descriptions and preliminary interpretations of the cores are provided in Bralower, Premoli Silva, Malone, et al. (2002) and Bralower et al. (2002). A broad array of exciting investigations have been conducted on the Leg 198 cores, resulting in a number of publications in the open literature and in this volume. This summary is organized in terms of the chronological history of Shatsky Rise, beginning with eruption of its basement foundation and followed by the progressive deposition of its sedimentary carapace.