Chemical Signatures of Fossilized Resins and Recent Plant Exudates

Abstract

Amber is one of the few gemstones based on an organic structure. Found over most of the world, it is the fossil form of sticky plant exudates called resins. Investigation of amber by modern analytical techniques provides structural information and insight into the identity of the ancient plants that produced the source resin. Mass spectrometric analysis of materials separated by gas chromatography has identified specific compounds that are the basis of a reliable classification of the different types of amber. NMR spectroscopy of bulk, solid amber provides a complementary classification. NMR spectroscopy also can be used to characterize modern resins as well as other types of plant exudates such as gums, gum resins, and kinos, which strongly resemble resins in appearance but have very different molecular constitutions.

Nuclear Magnetic Resonance (NMR) Examination of Fossilized, Semi-fossilized, and Modern Resins from the Caribbean Basin and Surrounding Regions

“…Samples from other parts of the United States, from California to the East Coast, have proved to be Group A for the most part and occasionally Group B (Lambert et al 2008). We have analyzed two previously unreported samples from the state of Texas (TX) and one from Mississippi (MS).…”

“…Since there are no known amber sources in northeastern Venezuela and the Lesser Antilles, the trans-Caribbean circulation of this material from Mexico, Colombia, and northwest and north central Venezuela must be evaluated in addition to traditional concepts of trade from the South American mainland via island-hopping to the north (Rouse 1992). Amber is particularly amenable to interaction studies in archaeology, as it can be characterized by various physical methods, including nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) (Labandeira 2014;Lambert et al 1995Lambert et al , 2002Lambert et al , 2008Lambert et al , 2014. This process of analysis potentially can distinguish not only paleobotanical sources, but also geographical provenance and degrees of maturity of the resin.…”

“…Examination of fossilized resins by molecular spectroscopic methods has yielded five categories, which differ in their molecular constituency (Lambert et al 2008). Whereas MS identifies specific molecules to realize these distinctions, NMR spectroscopy examines the overall spectral pattern of either the carbon atoms or the hydrogen atoms that constitute the bulk.…”

“…This categorization was derived from the NMR experiments. The MS experiments generated parallel groupings, in which, for example, Group B is known as Class Ic (Lambert et al 2008).…”

“…Unlike other natural organic materials, like leaves, bark, and wood, resins (particularly when buried) do not decay rapidly into soil humus. Through processes of polymerization, cross-linking, and oxidation, the original di-and triterpenes become a massively interlinked molecular mass that resembles a rock (Lambert et al 2008). Such processes require geological times, most typically cited as millions of years (Schlee and Glöckner 1978) but as little as 40,000 years (Vávra 2009).…”