Origin and palaeoenvironmental significance of C25 and C27 n-alk-1-enes in a 25,000-year lake-sedimentary record from equatorial East Africa

Abstract

, J. van (2014).Origin and palaeoenvironmental significance of C25 and C27 n-alk-1-enes in a 25,000-year lake-sedimentary record from equatorial East Africa. AbstractWe studied the distribution of long-chain alkenes (n-C23 to n-C31) in well-dated sediments from Lake Challa, a deep crater lake near Mt. Kilimanjaro in equatorial East Africa, to reveal signatures of palaeo-environmental and palaeo-climatic changes affecting the production of these compounds during the last 25 kyr. The apolar fractions of organic sediment extracts dated to the last 16 kyr showed an unusual dominance of δ 13 C-depleted n-C25:1 and n-C27:1 alk-1-enes. These

Geochemical Evolution of Occluded Hydrocarbons inside Geomacromolecules: A Review

“…maturation stage, which can be illustrated with the chemical scheme as follows: 72,73 The even-carbon-numbered n-alk-1-enes are assumed to be degradation products of esters with even-carbon-numbered linear alkyl chains that are commonly present in organisms, 18 but are thermally unstable. 35,74,75 Actually, n-alk-1-enes are frequently found in modern sediments, 76 but reports of the presence of such compounds in crude oil have hitherto been scarce. Therefore, the n-alk-1-enes released from asphaltene and solid bitumen are not from the thermal cracking of geomacromolecule, but from the occluded fraction of kerogen.…”

Use of selected anthropogenic pesticides, nutrients, and biomarkers to spatially and temporally characterize eutrophication dynamics at a shallow lake (Lake Seeburg)

“…Lipid biomarkers reflecting characteristic precursor biota provide important information on the sources of organic matter or past biogeochemical processes . Therefore, sedimentary biomarkers have been widely used to reconstruct modern and ancient lake environments (Meyers, 2003;Naeher et al, 2012;van Bree et al, 2014). For instance, terrestrial organisms such as higher plants deliver different lipids into sediments than aquatic phytoplankton Volkman, 1986;Castañeda and Schouten, 2011); therefore, a shift from terrestrial to more aquatic dominated distributions may indicate increasing eutrophication of a lake system over time .…”