GUIDO ROGHI, EUGENIO RAGAZZI, PIERO GIANOLLA
PALAIOS 21 (2), 143-154, (1 April 2006) https://doi.org/10.2110/palo.2005.p05-68
The Heiligkreuz-Santa Croce Formation (also known as Dürrenstein Formation, Upper Triassic) in the Dolomites contains one of the most ancient and substantial Triassic amber deposits in the world. The amber is found in sandstones and paleosols. It has an affinity to the conifer family Cheirolepidiaceae, and amber samples from the Julian and Carnic Alps (Southern Alps) also show an affinity to this family.
Physico-chemical investigations of the amber from the Dolomites by solid-state Fourier-transform infrared analysis (FTIR), nuclear magnetic resonance (NMR), pyrolysis-gas-chromatography/mass-spectrometry (pyr-GC/MS), thermogravimetry (TG), differential thermogravimetry (DTG), and automatized elemental analysis yielded a complete characterization of the amber, and allowed comparison with other ambers and younger resins (copals). FTIR revealed absorption bands typical of all fossil resins, and the spectrum region from 8–10 μm provided a fingerprint of the Triassic amber that differs from other known resins. The NMR spectrum also shows a typical pattern for fossil resins, but peculiar peak abundances permitted further characterization of the Triassic amber, both in the saturated (10–70 ppm) and unsaturated carbon region (100–160 ppm). The amber also lacks exomethylene resonances found in younger resins at 110 and 150 ppm. Pyrolysis-gas-chromatography/mass-spectrometry (pyr-GC/MS) experiments showed the amber was of class II, with some components of Class I. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses of combustion behavior of Triassic amber indicated a main exothermal event near 437°C, higher than that of other known resins. The elemental composition of Triassic amber is consistent with well-known constituents of natural resins, although the sulfur content was higher, likely due to high sulfur content in the embedding sediment. Triassic amber from the Dolomites appears to be a new kind of fossil resin with unique stratigraphical and physico-chemical characteristics.