Leg 208 synthesis: Cenozoic climate cycles and excursions

Abstract

During Ocean Drilling Program Leg 208, six sites were drilled at water depths between 2500 and 4770 m to recover Cenozoic sediments on the northeastern flank of Walvis Ridge. Previous drilling in this region (Deep Sea Drilling Project [DSDP] Leg 74) recovered pelagic oozes and chalk spanning the Cretaceous/Paleogene (K/Pg), Paleocene/Eocene, and Eocene/Oligocene boundaries. The composite sections, recovered via double and triple coring, provide a detailed history of paleoceanographic variation associated with several prominent episodes of early Cenozoic climate change, including the K/Pg boundary, Paleocene/ Eocene Thermal Maximum (PETM), early Eocene Climatic Optimum, and early Oligocene Glacial Maximum. The PETM interval, the main target of Leg 208, was recovered at five sites along a depth transect of 2.2 km. A prominent red clay layer marks the boundary sequence at all sites. Additionally, two as-yet undocumented early Eocene hyperthermal events were recovered: Elmo and X, dated at ~53.5 and ~52 Ma, respectively. A number of postcruise investigations were undertaken on these critical intervals, principally to improve stratigraphic control and the resolution of proxy records of climate and ocean chemistry, and to better understand the regional impacts of these events on biota. The major contributions of Leg 208 include (1) development of new orbitally tuned chronologies for the Paleocene and lower Eocene, (2) high-resolution characterization of Paleocene/Eocene boundary carbonate dissolution horizons and correlation to the carbon isotope excursion and PETM, (3) development of the first marine-based carbon isotope record of terrestrial n-alkanes for the PETM, (4) documentation of the ecological impacts of the PETM on calcareous algae, (5) resolving the full magnitude of the

Late Paleocene–early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change

“…The prominent event during this interval was the PETM hyperthermal at which substantial changes happened (transition from platform stage II to platform stage III). Recent investigations from ODP and IODP drilling sites on the Shatsky Rise (Western Pacific Ocean; Bralower et al, 2002), Demerara Rise (Northern Atlantic; Sexton et al, 2006b) and Walvis Ridge (Southern Atlantic; Kroon et al, 2007) revealed the occurrence of further possible hyperthermals in the deep ocean (Kroon et al, 2007). These deep marine hyperthermal findings were supported by similar CIE's in shallow-marine sediments from the continental margin of New Zealand (Nicolo et al, 2007).…”

“…The carbon isotopic excursion of the Elmo horizon measures roughly 1.5‰-2‰, while the carbon isotopic excursion for the X-event lies between 0.6‰ and 1.0‰. The Elmo horizon at 53.5 Ma is linked with a rise in sea-surface temperature of about 3°-4°C Dutton et al, 2005) and a rise in deep-sea temperature of 2°-3° (Kroon et al, 2007). As the investigations on the X-event (52 Ma) are still ongoing , no further results can be presented so far.…”

“…Evidence for a first transient climatic warming was found in the early late Paleocene at ca. 58.4 Ma Kroon et al, 2007).…”

Deep water temperature, carbonate ion, and ice volume changes across the Eocene‐Oligocene climate transition

“…Isotope values are reported relative to the VPDB (Vienna PeeDee belemnite) standard. (b) Site 1265 benthic foraminiferal Mg/Ca ratios (red diamonds; C. praemundulus ) in mmol/mol plotted with weight percent carbonate (black line) from Kroon et al [2006]. (c) Site 1090 benthic foraminiferal δ 18 O values (blue circles; Cibicidoides spp.).…”

“…(b) ODP Site 1090 Cibicidoides grimsdalei SEM image at 10 μ ms from 228.24 mcd with 30 weight percent CaCO 3 [ Latimer and Filippelli , 2002]. (c) ODP Site 1265 Cibicidoides praemundulus SEM image at 400 μ ms showing spiral side of foraminifera from 186.58 mcd with 85 weight percent CaCO 3 [ Kroon et al , 2006]. (d) ODP Site 1265 Cibicidoides praemundulus SEM image at 400 μ ms showing umbilical side of foraminifera from 186.58 mcd with 85 weight percent CaCO 3 [ Kroon et al , 2006].…”