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Lebanese Jurassic versus Cretaceous amber: Chemical characterization

Abstract : About 400 different amber outcrops have been found in Lebanon, which are dated as Early Cretaceous ("Neocomian", about 140-120 Ma).Lebanese Cretaceous amber is recognized as being one of the most fossiliferous in the world, with a large variety of arthropods (insects, arachnids) and botanical remains found preserved in the fossilized tree resin [1]. These fossils provide information on a vanished ecosystem that existed at the time of the resin secretion by a certain botanical family. Plant remains found in some amber pieces are assignable to two potential families of conifers, the still extant Araucariaceae and the exclusively extinct Cheirolepidiaceae. More recently, we added 19 further amber outcrops which we dated as Late Jurassic (Basaltic Kimmeridgian age circa 150 Ma), and in which we found fungal inclusions but no plant or insect inclusions to date [2, 3]. The high number of outcrops and the different ages are a great potential to reconstruct the evolution of past forest environments. But biological inclusions are not sufficient and the chemical characterization of amber itself allows us to shed light on the potential tree source of the resins through different chemical biomarkers which are characteristic of different families of plants. A more complete reconstruction of these ancient ecosystems is thus possible by combining the chemical and biological studies. To investigate the respective botanical sources of Cretaceous and Jurassic Lebanese ambers, we conducted a comparative chemical characterization using both Fourier Transform Infrared spectroscopy (FTIR) and Pyrolysis-Gas Chromatography-Mass Spectroscopy (Py-GC-MS) analyses. The latter reveals that both Jurassic and Cretaceous ambers belong in the Class Ib amber (a classification based on Polylabdanoides skeleton) along with a potential presence of Abietane and Pimarane skeleton. The FTIR analysis, shows a high resemblance between both ambers which present some affinities with modern resins of the conifer families Araucariaceae and Cupressaceae, though the extinct family Cheirolepidiaceae cannot be excluded as a potential source. Finally these results suggest a rather stable forest paleoenvironment in Lebanon during these two geological ages, as both Cretaceous and Jurassic ambers have probably the same botanical origin.
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Submitted on : Thursday, September 25, 2014 - 10:48:43 AM
Last modification on : Wednesday, July 15, 2020 - 11:52:04 AM

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Youssef Nohra, Vincent Perrichot, Laurent Jeanneau, Raymond Gèze, Dany Azar. Lebanese Jurassic versus Cretaceous amber: Chemical characterization. 20th LAAS International Science Conference, Mar 2014, Hadath, Lebanon. pp.865-866. ⟨insu-01068166⟩

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