Organic carbon concentrations in ODP Hole 105-645E

The aliphatic hydrocarbon fractions of eight early Miocene to Pliocene sediment samples from Hole 645E (Baffin Bay; ODP Leg 105) were investigated by gas chromatography and gas chromatography/mass spectrometry. Long, straight-chain alkanes of terrigenous origin are often present as major compounds. Other terrigenous biological markers include three oleanenes with a double bond at positions 12, 13(18), or 18, and taraxer-14-ene. Urs-12-ene is identified tentatively. In the three deepest samples, 17a(H), 18a(H), and 210(H)-28, 30-bisnorhopane is the most abundant compound. Several new compounds were detected, some of which are tentatively identified. The identification and possible significance of 23-norlupane, three A/B-ring nuclear demethylated (or A-nor-) oleanenes, and an A/B-ring nuclear demethylated (or A-nor-) urs-12-ene are discussed. The authors postulate that taraxer-14-ene isomerizes to olean-12-ene with increasing burial depth.