Synthesis of 26-methyl cholestane and identification of cryostanes in mid-Neoproterozoic sediments. (January 2018)

• Record Type: Journal Article
• Authors: Adam, Pierre; Schaeffer, Philippe; Brocks, Jochen J.
• Is Part Of: Organic geochemistry. Volume 115(2018)
• Page Start: 246
• Page End: 249
• Publication Date: 2018-01
• Subjects: Mid-Neoproterozoic -- Snowball Earth -- 26-Methyl cholestane -- Synthesis -- Cryostanes -- Sponges; Organic geochemistry -- Periodicals; Biogeochemistry -- Periodicals; Géochimie organique -- Périodiques; 553.205
• DOI: 10.1016/j.orggeochem.2017.11.006
• Languages: English
• ISSNs: 0146-6380

Abstract

Highlights: Unusual steranes (cryostanes) restricted to pre-Snowball Earth sediments. Identified as 26-methylcholestanes from comparison with a synthetic standard. Possibly related in origin to sterols in demosponges. Abstract: The biomarker distributions of mid-Neoproterozoic sediments (800–717 million yr, Ma) from various locations are characterized by the occurrence, besides cholestane isomers, of a novel series of C28 steranes, whereas classical C-24 alkylated steranes are absent. These unusual C28 steranes, termed cryostanes, seem to be restricted to pre-Snowball Earth sediments. We report their conclusive identification as 26-methyl cholestanes based on comparison of gas chromatographic (GC) behavior and mass spectrum of the last eluting cryostane isomer with those of a 26-methyl 5α(H), 14α(H), 17α(H), 20 R -cholestane standard obtained by way of synthesis. Sterols methylated at C-26 seem to be restricted to some demosponges and, based on molecular clock estimates, demosponges may have emerged in the time interval 800–700 Ma. A sponge origin of cryostanes is thereby conceivable, making cryostanes the oldest molecular markers for animals. However, other biological sources need to be explored, including the wide variety of eukaryotic protists.