Hydrocarbons as Indicators for Provenance and Thermal History of Organic Matter in Late Cenozoic Sediments from Hole 909C, Fram Strait

Abstract

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 C 29 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-<imor-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 «eo-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 (C 4 -C 7 ) concentrations at the bottom of Hole 909C is due to migration of these compounds from deeper sediments with more mature organic matter.

Geochemical characterisation of Early Cretaceous lacustrine sediments of Bima Formation, Yola Sub-basin, Northern Benue Trough, NE Nigeria: Organic matter input, preservation, paleoenvironment and palaeoclimatic conditions

“…The presence of C 29 norhopane in some samples (Fig. 6) may also be associated with land plant input (Rinna et al, 1996).…”

Geochemistry of the Cretaceous coals from Lamja Formation, Yola Sub-basin, Northern Benue Trough, NE Nigeria: Implications for paleoenvironment, paleoclimate and tectonic setting

“…The relative abundance of C 29 to C 30 hopane is generally similar in most of the studied coal samples with C 29 /C 30 ratios ranging from 0.8 to 1.0 ( Table 1). The predominance of C 29 hopane is frequently associated with carbonate-rich, but this is not always the case (Waples and Machihara, 1991), and the enhanced norhopane input may also be associated with land plant input (Rinna et al, 1996). The carbonate character of the coal samples is consistent with the mineral composition with CaO element in the range of 7.8-31.9% (Table 2).…”

Organic Geochemistry and Thermal Maturity Assessment of Cretaceous Balambo Formation from Selected Sites, Kurdistan, NE Iraq

“…C 29 /C 30 ratio of higher than 1 is commonly associated with carbonate source rocks, but this is not always the case [34]. The enhanced C 29 -norhopane input may also be associated with land plant input [35]. In this study, the C 29 /C 30 ratio ranges from 0.81 to 1.13, this indicates a mixed carbonate and clay rock (shale).…”