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Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processesPatterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.
Document ID
20040089337
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Hayes, J. M.
(Indiana University Bloomington 47405, United States)
Freeman, K. H.
Popp, B. N.
Hoham, C. H.
Date Acquired
August 21, 2013
Publication Date
January 1, 1990
Publication Information
Publication: Organic geochemistry
Volume: 16
Issue: 6-Apr
ISSN: 0146-6380
Subject Category
Exobiology
Funding Number(s)
CONTRACT_GRANT: NGR15003-118
CONTRACT_GRANT: 20107-AC2
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Exobiology

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