Abstract
During Integrated Ocean Drilling Program Expedition 302 (Arctic Coring Expedition (ACEX)) a more than 200 m thick sequence of Paleogene organic carbon (OC)‐rich (black shale type) sediments was drilled. Here we present new biomarker data determined in ACEX sediment samples to decipher processes controlling OC accumulation and their paleoenvironmental significance during periods of Paleogene global warmth and proposed increased freshwater discharge in the early Cenozoic. Specific source‐related biomarkers includingn‐alkanes, fatty acids, isoprenoids, carotenoids, hopanes/hopenes, hopanoic acids, aromatic terpenoids, and long‐chain alkenones show a high variability of components, derived from marine and terrestrial origin. The distribution of hopanoic acid isomers is dominated by compounds with the biological 17β(H), 21β(H) configuration indicating a low level of maturity. On the basis of the biomarker data the terrestrial OC supply was significantly enriched during the late Paleocene and part of the earliest Eocene, whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the Paleocene‐Eocene thermal maximum and Eocene thermal maximum 2 events as well as the middle Eocene time interval. Furthermore, samples from the middle Eocene are characterized by the occurrence of long‐chain alkenones, high proportions of lycopane, and high ratios (>0.6) of (n‐C35+ lycopane)/n‐C31. The occurrence of C37‐alkenenones, which were first determined toward the end of theAzollafreshwater event, indicates that the OC becomes more marine in origin during the middle Eocene. Preliminary U37K′‐based sea surface temperature (SST) values display a long‐term temperature decrease of about 15°C during the time interval 49–44.5 Ma (25° to 10°C), coinciding with the global benthicδ18O cooling trend after the early Eocene climatic optimum. At about 46 Ma, parallel with onset of ice‐rafted debris, SST (interpreted as summer temperatures) decreased to values <15°C. For the late early Miocene a SST of 11°–15°C was determined. Most of the middle Eocene ACEX sediments are characterized by a smooth short‐chainn‐alkane distribution, which may point to natural oil‐type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition.
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