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Application of an eutrophic lake model to the origin of ancient organic‐carbon‐rich sediments
Author(s) -
Hollander David J.,
McKenzie Judith A.,
Hsu Kenneth J.,
Huc Alain Y.
Publication year - 1993
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/92gb02831
Subject(s) - organic matter , carbonate , total organic carbon , water column , eutrophication , anoxic waters , productivity , sedimentary organic matter , geology , environmental chemistry , sediment , environmental science , nutrient , chemistry , oceanography , paleontology , organic chemistry , economics , macroeconomics
In this paper we approach the problem of the origin of organic‐carbon‐rich sediments by using an integrated isotopic and organic geochemical study of the annual productivity/eutrophication cycle in the water column of Lake Greifen (Switzerland) and the historical expression of such cycles as found in the sediments. The Lake Greifen water column and sediment studies reveal that Δδ 13 C carbonate‐organic matter is correlated with the hydrogen indices (HI) of kerogens, explicable in terms of changing productivity and preservation of the organic matter, and the CO 2 budget of the water body. The lake model implies that, if high productivity in CO 2 limited surface waters (high nutrient/CO 2 ratio) was controlling the preservation of organic matter, a correlation between decreasing Δδ 13 C carbonate ‐organic matter and increasing HI values may be observed. In contrast, if low to moderate productivity in CO 2 unlimited surface waters (low nutrient/CO 2 ratio) where bottom water anoxia promotes the preservation of organic matter, a correlation between increasing Δδ 13 C carbonate‐organic matter and increasing HI values may be observed. Application of this model to two well known Jurassic sequences, gave a correlation of increasing HI values with decreasing Δδ 13 C carbonate‐organic matter for the Kimmeridge Clay Formation (United Kingdom), and increasing HI values with increasing Δδ 13 C carbonate organic matter for the early Toarcian shales (France). This suggests that the controlling factor of the former deposit was high primary bioproductivity and of the latter deposit anoxic bottom water conditions.