Miocene to Pliocene deep-sea sediments recovered during Ocean Drilling Program Leg 151 in Hole 909C in the Fram Strait (North Atlantic-Arctic Gateway) contain between 0.5% and 1.6% organic carbon, which is mostly of terrigenous origin as far as it is represented by the nonaromatic hydrocarbons in the solvent extractable fraction. This is illustrated, for example, by the occurrence of pentacyclic triterpenes of higher plant origin and the dominance of C29 steroid hydrocarbons. Molecular indicators show some variation in the supply of the organic material, for example, by the specific occurrence of two isomeric 24,28-dinor-lupanes in two Miocene horizons. Diagenetic evolution of the organic matter is obvious in the nonaromatic hydrocarbon fractions by the disappearance of regular sterenes, isomerization of diasterenes at C-20, appearance of regular and rearranged steranes, and the increase of the neo-hop-13(18)-ene/hop-17(21)-ene ratio in the deeper part of the section. Despite the apparently high geothermal gradient, the zone of thermal cracking according to biomarker analysis has not been reached by drilling. The low maturity of the organic matter, observed by bulk and molecular organic geochemical parameters, indicates that the sudden increase of low-molecular-weight hydrocarbon (C4-C7) concentrations at the bottom of Hole 909C is due to migration of these compounds from deeper sediments with more mature organic matter.
Date of initial receipt: 4 August 1995
Date of acceptance: 20 November 1995
Return to Contents of Leg 151
Return to Contents of Scientific Results