oa Biomarker Signatures of Oligocene Sediments from IODP Expedition 378 Site U1553, Campbell Plateau, Southern Pacific Ocean

42 samples from IODP Hole U1553A on the Campbell Plateau, New Zealand were selected to investigate the Oligocene environment using gas chromatography–mass spectrometry (GC–MS) and gas chromatography–triple quadrupole mass spectrometry (GC–MS/MS). Abundant biomarkers were detected in the Oligocene sediments including tricyclic terpanes, hopanes, steranes, and diasteranes. The total ion chromatograms of the samples are characterized by an unresolved complex mixture, which is a signature of biodegradation. Based on the absence of most of the n-alkanes, isoprenoids, and the occurrence of 25-norhopanes, the samples are interpreted to have undergone about level 5-6 biodegradation. The hopanoids and steroids do not appear to be affected by biodegradation, except for some alteration of hopanes to 25-norhopanes. The biomarker distribution and associated ratios suggest that the organic matter (OM) in the Oligocene samples is at a thermally mature stage. Given the shallow depth of the Oligocene at Site U1553, and the immature nature of the underlying Palaeocene at the same site, this likely indicates the reworking of mature OM during the Oligocene. The OM is interpreted to have been biodegraded at this time, during transport in the marine environment. The OM source is diverse, including higher plants, bacteria, and marine algae.