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Sylvie Derenne - One of the best experts on this subject based on the ideXlab platform.
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Occurrence of non-hydrolysable amides in the macromolecular constituent of Scenedesmus quadricauda cell wall as revealed by 15N NMR: Origin of n-Alkylnitriles in pyrolysates of ultralaminae-containing kerogens
Geochimica et Cosmochimica Acta, 1993Co-Authors: Sylvie Derenne, Claude Largeau, Francis TaulelleAbstract:Abstract New structures, termed ultralaminae, were recently shown to occur in kerogens from numerous oil shales and source rocks. Morphological and chemical studies revealed that ultralaminae originate from the selective preservation of the non-hydrolysable biomacromolecules (algaenans) building up the thin outer walls of several Chlorophyceae (green microalgae) including the cosmopolitan genera Scenedesmus and Chlorella . The chemical correlation between such algaenans and fossil ultralaminae was mainly based on the production, on pyrolysis, of nitrogen compounds, n -Alkylnitriles, with specific distributions depending on the lacustrine or marine origin of the considered samples. In addition, these bioand geopolymers were characterized by quite high N levels. Solid-state 15 N NMR was carried out on 15 N-enriched algaenan (isolated from Scenesdesmus quadricauda grown with 15 NO 3 − as sole nitrogen source) and revealed that amides are the most abundant nitrogen groups in this material. Minor amounts of two other nitrogen groups, amines and probably Nalkyl substituted pyrroles (indoles, carbazoles), are also observed. Amines are unlikely to contribute to the macromolecular structure but could simply correspond to trapped compounds. A part of the tentatively identified N-alkyl substituted pyrroles is released during pyrolysis, but a large fraction of these moieties is retained in the insoluble residue while their N-alkyl substituents are eliminated. The predominant amide groups associated with long polymethylenic chains, occurring in S. quadricauda algaenan, are eliminated during pyrolysis and lead, after a fast dehydration, to the formation of n -Alkylnitriles. This study provides, to our knowledge, the first example of non-hydrolysable amide moieties in a biomacromolecule. This unusual resistance is probably due to steric protection within the macromolecular network. Such a protection also allows amide groups in chlorophycean algaenans to survive diagenesis and accounts for the production of n -Alkylnitriles with typical distributions on pyrolysis of ultralaminae-containing kerogens.
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Formation of ultralaminae in marine kerogens via selective preservation of thin resistant outer walls of microalgae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, F. Le Berre, Claude Largeau, Patrick G. Hatcher, Jacques Connan, J.f. RaynaudAbstract:Abstract Transmission Electron Microscopy (TEM) observations recently revealed the common occurrence of very thin lamellar structures, termed ultralaminae, in kerogens from source rocks and oil shales so far considered as amorphous. Ultralaminae in lacustrine kerogens were shown to derive from the selective preservation of the algaenans occurring in the very thin outer walls of various freshwater Chlorophyceae. The chemical correlation between such algaenans and fossil lacustrine ultralaminae was chiefly based on the production on pyrolysis of n -Alkylnitriles with a typical distribution (bimodal, maxima at C 28 and C 16 ). The origin of marine ultralaminae is investigated in this work. To this end, spectroscopic and pyrolytic studies were carried out on (i) the algaenan forming the very thin outer walls of Nanochlorum eucaryotum (an extant marine Chlorophycea) and (ii) two ultralaminae-containing marine kerogens from the Lower Toarcian shales of Paris basin (Fecocourt and Bray). A high contribution of polymethylenic chains probably linked via ehter bridges was observed in these bio- and geopolymers. Furthermore, on pyrolysis they afforded the same n -Alkylnitriles with the same distribution (unimodal, maximum at C 13 , lack of C 17+ compounds). Fossil ultralaminae in marine kerogens therefore derive from the selective preservation of the algaenan-composed very thin outer walls of marine Chlorophyceae such as N . eucaryotum. Algaenans from marine and freshwater Chlorophyceae and, therefore, marine and lacustrine ultralaminae, should be characterized by sharply distinct n -Alkylnitrile distributions.
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Structure of Chlorella fusca algaenan: relationships with ultralaminae in lacustrine kerogens; species- and environment-dependent variations in the composition of fossil ultralaminae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, Claude Largeau, Patrick G. HatcherAbstract:Numerous kerogens from marine and lacustrine source rocks and oils shales, previously considered as amorphous, were recently shown to comprise very thin (10–30 nm thick) lamellar structures, termed ultralaminae. Comparative morphological and chemical studies of a lacustrine ultralaminae-rich kerogen and of the non-hydrolysable biopolymer (algaenan) isolated from the thin resistant outer walls of a freshwater microalga (Scenedesmus quadricauda) established a close relationship between these two materials. Chemical correlation was mainly based on the production upon pyrolysis of a series of n-Alkylnitriles with a bimodal distribution. The non-hydrolysable biopolymer isolated from the outer walls of the ubiquitous freshwater microalga, Chlorella fusca, exhibits the same morphologicalfeatures as those observed in S. quadricauda and in fossil ultralaminae. The investigation of C. fusca algaenan by solid-state 13C NMR and analysis of pyrolysis products revealed that the correlation previously established between S. quadricauda and lacustrine ultralaminae also holds for C. fusca since the same series of n-Alkylnitriles with the same distribution is formed upon pyrolysis (probably via cleavage of amide functions).This confirms that fossil ultralaminae in lacustrine kerogens derive from the algaenans building up the thin outer walls of freshwater microalgae via the selective preservation pathway. In addition, the analysis of the 2-n-alkanones generated on pyrolysis indicates that their distribution depends on the algal species considered. Accordingly, variations in ketone distributions in the pyrolysates of lacustrine ultralaminae-rich kerogens may reflect differences in populations of the source microalgae. On the contrary, changes in n-Alkylnitrile distribution would not be species-dependent but would reflect the lacustrine or marine origin of the considered material.
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Chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae: Origin of ultralaminae
Geochimica et Cosmochimica Acta, 1991Co-Authors: Sylvie Derenne, Claude Largeau, E. Casadevall, Claire Berkaloff, B. RousseauAbstract:Abstract New structures, termed ultralaminae, were recently observed by Transmission Electron Microscopy, usually in high amounts, in a number of kerogens from oil shales and source rocks. Morphological similarities were noted between ultralaminae and the thin (ca. 15 nm) resistant outer walls, composed of non-hydrolyzable macromolecules (algaenans), commonly occurring in extant Chlorophyceae, especially in the cosmopolitan genus Scenedesmus . Identification of the pyrolysis products of S. quadricauda algaenan showed (i) a highly aliphatic structure based on a macromolecular network of long (up to C 32 ) polymethylenic chains probably cross-linked by ether bridges, and (ii) a close correlation based on the formation of n- Alkylnitriles , between this algaenan and two ultralaminar kerogens, the Rundle Oil Shale (mainly composed of ultralamina accumulations) and the Green River Shale (ultralaminae dispersed within an amorphous matrix). These fossil ultralaminae, therefore, likely originated from the selective preservation of the thin, algaenan-containing, outer walls of Scenedesmus and/or of other Chlorophyceae containing outer walls of a similar morphology and composition. Relative distributions of n- Alkylnitriles and of n- alkanoic acids, in the pyrolysates of S. quadricauda algaenan and of the Rundle Oil Shale, indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions, likely amides. Previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens; the present results, added to ultralamina common occurrence and abundance, point to a wide involvement and to a large contribution of the selective preservation of algaenan-containing thin outer walls of Chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales. All the available information suggest that the three-way correlation (selective preservation of algaenans from thin resistant chlorophycean outer walls, formation of fossil ultralaminae, presence of n- Alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens) observed in this study might be of a general character.
Claude Largeau - One of the best experts on this subject based on the ideXlab platform.
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An improved method for the isolation of artifact-free algaenans from microalgae
Organic Geochemistry, 1998Co-Authors: Béatrice Allard, Joëlle Templier, Claude LargeauAbstract:Abstract A new process for the isolation of algaenans (insoluble non-hydrolysable, highly aliphatic biopolymers of microalga cell walls) which avoids their contamination with melanoidin-like polymer artifacts is presented and the algaenans of two species from the Chlorophyceae (Scenedesmus communis and Botryococcus braunii) are re-examined. Preliminary release of the polysaccharides from these microorganisms by trifluoroacetic acid hydrolysis affords a pure, or much less contaminated, algaenan for the two species. Re-examination of the pyrolysate of S. communis algaenan indicates that the long-chain n-Alkylnitriles, previously detected when the algaenan was isolated by the usual process ( Berkaloff et al., 1983 ), do not actually originate from this biopolymer. We suggest that some nitrogen-containing molecules present in S. communis (or in other Chlorophyceae species) are incorporated into the structure of the melanoidin-like polymers generated when the algaenan is isolated by the usual process which lead, upon pyrolysis, to nitriles. Consideration of previous data, on the pyrolysates of numerous kerogens, suggests that a similar process occurs under natural conditions during early diagenesis.
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Occurrence of non-hydrolysable amides in the macromolecular constituent of Scenedesmus quadricauda cell wall as revealed by 15N NMR: Origin of n-Alkylnitriles in pyrolysates of ultralaminae-containing kerogens
Geochimica et Cosmochimica Acta, 1993Co-Authors: Sylvie Derenne, Claude Largeau, Francis TaulelleAbstract:Abstract New structures, termed ultralaminae, were recently shown to occur in kerogens from numerous oil shales and source rocks. Morphological and chemical studies revealed that ultralaminae originate from the selective preservation of the non-hydrolysable biomacromolecules (algaenans) building up the thin outer walls of several Chlorophyceae (green microalgae) including the cosmopolitan genera Scenedesmus and Chlorella . The chemical correlation between such algaenans and fossil ultralaminae was mainly based on the production, on pyrolysis, of nitrogen compounds, n -Alkylnitriles, with specific distributions depending on the lacustrine or marine origin of the considered samples. In addition, these bioand geopolymers were characterized by quite high N levels. Solid-state 15 N NMR was carried out on 15 N-enriched algaenan (isolated from Scenesdesmus quadricauda grown with 15 NO 3 − as sole nitrogen source) and revealed that amides are the most abundant nitrogen groups in this material. Minor amounts of two other nitrogen groups, amines and probably Nalkyl substituted pyrroles (indoles, carbazoles), are also observed. Amines are unlikely to contribute to the macromolecular structure but could simply correspond to trapped compounds. A part of the tentatively identified N-alkyl substituted pyrroles is released during pyrolysis, but a large fraction of these moieties is retained in the insoluble residue while their N-alkyl substituents are eliminated. The predominant amide groups associated with long polymethylenic chains, occurring in S. quadricauda algaenan, are eliminated during pyrolysis and lead, after a fast dehydration, to the formation of n -Alkylnitriles. This study provides, to our knowledge, the first example of non-hydrolysable amide moieties in a biomacromolecule. This unusual resistance is probably due to steric protection within the macromolecular network. Such a protection also allows amide groups in chlorophycean algaenans to survive diagenesis and accounts for the production of n -Alkylnitriles with typical distributions on pyrolysis of ultralaminae-containing kerogens.
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Formation of ultralaminae in marine kerogens via selective preservation of thin resistant outer walls of microalgae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, F. Le Berre, Claude Largeau, Patrick G. Hatcher, Jacques Connan, J.f. RaynaudAbstract:Abstract Transmission Electron Microscopy (TEM) observations recently revealed the common occurrence of very thin lamellar structures, termed ultralaminae, in kerogens from source rocks and oil shales so far considered as amorphous. Ultralaminae in lacustrine kerogens were shown to derive from the selective preservation of the algaenans occurring in the very thin outer walls of various freshwater Chlorophyceae. The chemical correlation between such algaenans and fossil lacustrine ultralaminae was chiefly based on the production on pyrolysis of n -Alkylnitriles with a typical distribution (bimodal, maxima at C 28 and C 16 ). The origin of marine ultralaminae is investigated in this work. To this end, spectroscopic and pyrolytic studies were carried out on (i) the algaenan forming the very thin outer walls of Nanochlorum eucaryotum (an extant marine Chlorophycea) and (ii) two ultralaminae-containing marine kerogens from the Lower Toarcian shales of Paris basin (Fecocourt and Bray). A high contribution of polymethylenic chains probably linked via ehter bridges was observed in these bio- and geopolymers. Furthermore, on pyrolysis they afforded the same n -Alkylnitriles with the same distribution (unimodal, maximum at C 13 , lack of C 17+ compounds). Fossil ultralaminae in marine kerogens therefore derive from the selective preservation of the algaenan-composed very thin outer walls of marine Chlorophyceae such as N . eucaryotum. Algaenans from marine and freshwater Chlorophyceae and, therefore, marine and lacustrine ultralaminae, should be characterized by sharply distinct n -Alkylnitrile distributions.
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Structure of Chlorella fusca algaenan: relationships with ultralaminae in lacustrine kerogens; species- and environment-dependent variations in the composition of fossil ultralaminae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, Claude Largeau, Patrick G. HatcherAbstract:Numerous kerogens from marine and lacustrine source rocks and oils shales, previously considered as amorphous, were recently shown to comprise very thin (10–30 nm thick) lamellar structures, termed ultralaminae. Comparative morphological and chemical studies of a lacustrine ultralaminae-rich kerogen and of the non-hydrolysable biopolymer (algaenan) isolated from the thin resistant outer walls of a freshwater microalga (Scenedesmus quadricauda) established a close relationship between these two materials. Chemical correlation was mainly based on the production upon pyrolysis of a series of n-Alkylnitriles with a bimodal distribution. The non-hydrolysable biopolymer isolated from the outer walls of the ubiquitous freshwater microalga, Chlorella fusca, exhibits the same morphologicalfeatures as those observed in S. quadricauda and in fossil ultralaminae. The investigation of C. fusca algaenan by solid-state 13C NMR and analysis of pyrolysis products revealed that the correlation previously established between S. quadricauda and lacustrine ultralaminae also holds for C. fusca since the same series of n-Alkylnitriles with the same distribution is formed upon pyrolysis (probably via cleavage of amide functions).This confirms that fossil ultralaminae in lacustrine kerogens derive from the algaenans building up the thin outer walls of freshwater microalgae via the selective preservation pathway. In addition, the analysis of the 2-n-alkanones generated on pyrolysis indicates that their distribution depends on the algal species considered. Accordingly, variations in ketone distributions in the pyrolysates of lacustrine ultralaminae-rich kerogens may reflect differences in populations of the source microalgae. On the contrary, changes in n-Alkylnitrile distribution would not be species-dependent but would reflect the lacustrine or marine origin of the considered material.
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Chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae: Origin of ultralaminae
Geochimica et Cosmochimica Acta, 1991Co-Authors: Sylvie Derenne, Claude Largeau, E. Casadevall, Claire Berkaloff, B. RousseauAbstract:Abstract New structures, termed ultralaminae, were recently observed by Transmission Electron Microscopy, usually in high amounts, in a number of kerogens from oil shales and source rocks. Morphological similarities were noted between ultralaminae and the thin (ca. 15 nm) resistant outer walls, composed of non-hydrolyzable macromolecules (algaenans), commonly occurring in extant Chlorophyceae, especially in the cosmopolitan genus Scenedesmus . Identification of the pyrolysis products of S. quadricauda algaenan showed (i) a highly aliphatic structure based on a macromolecular network of long (up to C 32 ) polymethylenic chains probably cross-linked by ether bridges, and (ii) a close correlation based on the formation of n- Alkylnitriles , between this algaenan and two ultralaminar kerogens, the Rundle Oil Shale (mainly composed of ultralamina accumulations) and the Green River Shale (ultralaminae dispersed within an amorphous matrix). These fossil ultralaminae, therefore, likely originated from the selective preservation of the thin, algaenan-containing, outer walls of Scenedesmus and/or of other Chlorophyceae containing outer walls of a similar morphology and composition. Relative distributions of n- Alkylnitriles and of n- alkanoic acids, in the pyrolysates of S. quadricauda algaenan and of the Rundle Oil Shale, indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions, likely amides. Previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens; the present results, added to ultralamina common occurrence and abundance, point to a wide involvement and to a large contribution of the selective preservation of algaenan-containing thin outer walls of Chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales. All the available information suggest that the three-way correlation (selective preservation of algaenans from thin resistant chlorophycean outer walls, formation of fossil ultralaminae, presence of n- Alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens) observed in this study might be of a general character.
B. Rousseau - One of the best experts on this subject based on the ideXlab platform.
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Chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae: Origin of ultralaminae
Geochimica et Cosmochimica Acta, 1991Co-Authors: Sylvie Derenne, Claude Largeau, E. Casadevall, Claire Berkaloff, B. RousseauAbstract:Abstract New structures, termed ultralaminae, were recently observed by Transmission Electron Microscopy, usually in high amounts, in a number of kerogens from oil shales and source rocks. Morphological similarities were noted between ultralaminae and the thin (ca. 15 nm) resistant outer walls, composed of non-hydrolyzable macromolecules (algaenans), commonly occurring in extant Chlorophyceae, especially in the cosmopolitan genus Scenedesmus . Identification of the pyrolysis products of S. quadricauda algaenan showed (i) a highly aliphatic structure based on a macromolecular network of long (up to C 32 ) polymethylenic chains probably cross-linked by ether bridges, and (ii) a close correlation based on the formation of n- Alkylnitriles , between this algaenan and two ultralaminar kerogens, the Rundle Oil Shale (mainly composed of ultralamina accumulations) and the Green River Shale (ultralaminae dispersed within an amorphous matrix). These fossil ultralaminae, therefore, likely originated from the selective preservation of the thin, algaenan-containing, outer walls of Scenedesmus and/or of other Chlorophyceae containing outer walls of a similar morphology and composition. Relative distributions of n- Alkylnitriles and of n- alkanoic acids, in the pyrolysates of S. quadricauda algaenan and of the Rundle Oil Shale, indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions, likely amides. Previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens; the present results, added to ultralamina common occurrence and abundance, point to a wide involvement and to a large contribution of the selective preservation of algaenan-containing thin outer walls of Chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales. All the available information suggest that the three-way correlation (selective preservation of algaenans from thin resistant chlorophycean outer walls, formation of fossil ultralaminae, presence of n- Alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens) observed in this study might be of a general character.
Patrick G. Hatcher - One of the best experts on this subject based on the ideXlab platform.
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Formation of ultralaminae in marine kerogens via selective preservation of thin resistant outer walls of microalgae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, F. Le Berre, Claude Largeau, Patrick G. Hatcher, Jacques Connan, J.f. RaynaudAbstract:Abstract Transmission Electron Microscopy (TEM) observations recently revealed the common occurrence of very thin lamellar structures, termed ultralaminae, in kerogens from source rocks and oil shales so far considered as amorphous. Ultralaminae in lacustrine kerogens were shown to derive from the selective preservation of the algaenans occurring in the very thin outer walls of various freshwater Chlorophyceae. The chemical correlation between such algaenans and fossil lacustrine ultralaminae was chiefly based on the production on pyrolysis of n -Alkylnitriles with a typical distribution (bimodal, maxima at C 28 and C 16 ). The origin of marine ultralaminae is investigated in this work. To this end, spectroscopic and pyrolytic studies were carried out on (i) the algaenan forming the very thin outer walls of Nanochlorum eucaryotum (an extant marine Chlorophycea) and (ii) two ultralaminae-containing marine kerogens from the Lower Toarcian shales of Paris basin (Fecocourt and Bray). A high contribution of polymethylenic chains probably linked via ehter bridges was observed in these bio- and geopolymers. Furthermore, on pyrolysis they afforded the same n -Alkylnitriles with the same distribution (unimodal, maximum at C 13 , lack of C 17+ compounds). Fossil ultralaminae in marine kerogens therefore derive from the selective preservation of the algaenan-composed very thin outer walls of marine Chlorophyceae such as N . eucaryotum. Algaenans from marine and freshwater Chlorophyceae and, therefore, marine and lacustrine ultralaminae, should be characterized by sharply distinct n -Alkylnitrile distributions.
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Structure of Chlorella fusca algaenan: relationships with ultralaminae in lacustrine kerogens; species- and environment-dependent variations in the composition of fossil ultralaminae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, Claude Largeau, Patrick G. HatcherAbstract:Numerous kerogens from marine and lacustrine source rocks and oils shales, previously considered as amorphous, were recently shown to comprise very thin (10–30 nm thick) lamellar structures, termed ultralaminae. Comparative morphological and chemical studies of a lacustrine ultralaminae-rich kerogen and of the non-hydrolysable biopolymer (algaenan) isolated from the thin resistant outer walls of a freshwater microalga (Scenedesmus quadricauda) established a close relationship between these two materials. Chemical correlation was mainly based on the production upon pyrolysis of a series of n-Alkylnitriles with a bimodal distribution. The non-hydrolysable biopolymer isolated from the outer walls of the ubiquitous freshwater microalga, Chlorella fusca, exhibits the same morphologicalfeatures as those observed in S. quadricauda and in fossil ultralaminae. The investigation of C. fusca algaenan by solid-state 13C NMR and analysis of pyrolysis products revealed that the correlation previously established between S. quadricauda and lacustrine ultralaminae also holds for C. fusca since the same series of n-Alkylnitriles with the same distribution is formed upon pyrolysis (probably via cleavage of amide functions).This confirms that fossil ultralaminae in lacustrine kerogens derive from the algaenans building up the thin outer walls of freshwater microalgae via the selective preservation pathway. In addition, the analysis of the 2-n-alkanones generated on pyrolysis indicates that their distribution depends on the algal species considered. Accordingly, variations in ketone distributions in the pyrolysates of lacustrine ultralaminae-rich kerogens may reflect differences in populations of the source microalgae. On the contrary, changes in n-Alkylnitrile distribution would not be species-dependent but would reflect the lacustrine or marine origin of the considered material.
J.f. Raynaud - One of the best experts on this subject based on the ideXlab platform.
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Formation of ultralaminae in marine kerogens via selective preservation of thin resistant outer walls of microalgae
Organic Geochemistry, 1992Co-Authors: Sylvie Derenne, F. Le Berre, Claude Largeau, Patrick G. Hatcher, Jacques Connan, J.f. RaynaudAbstract:Abstract Transmission Electron Microscopy (TEM) observations recently revealed the common occurrence of very thin lamellar structures, termed ultralaminae, in kerogens from source rocks and oil shales so far considered as amorphous. Ultralaminae in lacustrine kerogens were shown to derive from the selective preservation of the algaenans occurring in the very thin outer walls of various freshwater Chlorophyceae. The chemical correlation between such algaenans and fossil lacustrine ultralaminae was chiefly based on the production on pyrolysis of n -Alkylnitriles with a typical distribution (bimodal, maxima at C 28 and C 16 ). The origin of marine ultralaminae is investigated in this work. To this end, spectroscopic and pyrolytic studies were carried out on (i) the algaenan forming the very thin outer walls of Nanochlorum eucaryotum (an extant marine Chlorophycea) and (ii) two ultralaminae-containing marine kerogens from the Lower Toarcian shales of Paris basin (Fecocourt and Bray). A high contribution of polymethylenic chains probably linked via ehter bridges was observed in these bio- and geopolymers. Furthermore, on pyrolysis they afforded the same n -Alkylnitriles with the same distribution (unimodal, maximum at C 13 , lack of C 17+ compounds). Fossil ultralaminae in marine kerogens therefore derive from the selective preservation of the algaenan-composed very thin outer walls of marine Chlorophyceae such as N . eucaryotum. Algaenans from marine and freshwater Chlorophyceae and, therefore, marine and lacustrine ultralaminae, should be characterized by sharply distinct n -Alkylnitrile distributions.
