Geochemistry of ambers

This work on the chemistry of ambers is based on a collaboration with Vincent Perrichot, a paleontologist specializing in ambers and was developed starting in 2012 thanks to Youssef Nohra. During his PhD thesis, Youssef Nohra analyzed the chemical composition of roughly 60 ambers using thermochemolysis coupled with GC-MS thereby creating a database that is particularly interesting for the reconstruction of terrestrial paleo-environments.

Paleo-environment - © Laurent Jeanneau

The extinct family Cheirolepidiaceae was very common in the Mesozoic and was probably a major contributor to the formation of coal and lignite. As a result, it is quite important to differentiate these plants from other conifers from a terrestrial paleo-environment reconstruction point of view.  The analysis of the chemical composition of amber, the polymerized fossil form of tree resins, which is often found in combination with coal and lignite deposits, has brought new information to light. Given that the Cheirolepidiaceae family is extinct, we do not have modern analogs at our disposal in order to directly determine the chemical biomarkers specific to this family.
 
The chemical analysis using thermochemolysis in the presence of TMAH coupled with GC-MS of about sixty ambers from different geographical origins, botanical origins and of different ages and having undergone different levels of diagenesis allowed to identify 25 samples from the Cretaceous from France and Lebanon. Compared with two samples from the
Italian Triassic and Spanish Cretaceous for which a botanical origin of Cheirolepidiaceae is suggested, a chemical imprint for this extinct coniferous family was proposed for the first time. Thus, the simultaneous presence of callistrisate, phenolic diterpenoids,labdanoic acids and their respective diagenetic products is considered indicative of resins produced by the extinct Cheirolepidiaceae family.

Biomarkers - © Laurent Jeanneau

This work has been partly published in the Journal of Natural Products: Nohra, Y. A., Perrichot, V., Jeanneau, L., Le Pollès, L. and Azar,D. : Chemical Characterization and Botanical Origin of French Ambers, J. Nat. Prod., 78(6), 1284–1293, 2015.