Analytical approaches for studies of fossil resins

The overview of analytical methods for studying of fossil natural resins

The review presents methods that are used frequently for multi-analytical study of fossil resins. The preliminary characterization relies on physical methods such as microhardness, density and fluorescence in UV light measurements. The spectroscopic methods: infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy are also presented in the paper. Besides that, the review also contains examples of the application of chromatographic methods: gas chromatography, thin layer chromatography, high-performance liquid chromatography, two-dimensional gas chromatography coupled to time-of-flight mass spectrometry as well as sample preparation methods for chromatographic studies such as pyrolysis. Additionally, thermal methods such as thermogravimetric analysis and differential scanning calorimetry also are covered by the review. Beside the examples of application, a detailed description with development history and perspective for further improvement are presented for each method. Moreover, fit-for-purpose assessment of each method is illustrated based on many examples from literature. The paper also contains examples of the application of multivariate statistical analysis and chemometric methods for comparing multiple properties of different fossil resin specimens for differentiation and classification purposes.

Identification of treated Baltic amber by FTIR and FT-Raman - A feasibility study

Heat-treated succinite modified under air, oxygen or inert gas atmosphere to improve its colour and clarity, was studied with Fourier-Transform Infrared and Raman spectroscopy, and referenced to variously altered untreated samples. For treated amber, the macroscopic observations revealed diagnostic features such as (1) the presence of discoidal " sun sparkles" inside the crumbs; (2) unusual colours (e.g. dark red) for transparent specimens; (3) mottled colour patches in "beeswax" and "dragon's blood" amber; (4) luminescence quenching; and (5) significant reduction of pine-tree resinous smell. On FTIR spectra the heat treatment of succinite is mainly marked by: (1) the intensity decrease of 2932 cm^-1 band (>CH₂ and -CH₃), followed by the intensity increase of line at 1732 cm^-1; (2) the shifts of the band from ν(C = O) towards lower wavenumbers (from 1735 cm^-1 to 1714 cm^-1); (3) the decrease of intensity of the band at 888 cm^-1 ((=CH₂ or -CH = CH-); (4) some slight distortion of "Baltic shoulder" in the region 1100-1300 cm^-1. The Principal Component Analysis applied to FTIR spectra enabled to distinguish not only untreated amber from treated one, but also recognize the modifications made under oxygen conditions from the ones in an inert gas. On RS spectra of the treated Baltic amber, the heat modifications are indicated by: (1) slight value increase of the relative intensity ratio I_1650/1445 compared to untreated succinite; (2) the shift of bands near 1650 (C = C) and 1445 cm^-1 (CH₂, CH₃) towards higher wavenumbers.

The study of Dominican amber-bearing sediments from Siete Cañadas and La Cumbre with a discussion on their origin

The paper presents comprehensive mineralogical and geochemical characteristics of Dominican amber-bearing sediments from Siete Cañadas, Hato Mayor Province of the Eastern Mining District (EMD) in the Cordillera Oriental. The characteristics of rocks collected from the borehole in Siete Cañadas area (EMD) were compared with petrography of coaly shales from La Cumbre in the Northern Mining District (NMD). The mineralogy of the rocks was determined using transmitted and reflected light microscopy, scanning electron microscopy, Powder X-ray diffraction and Fourier Transform Raman Spectroscopy. Biomarker analyses by the gas chromatography–mass spectrometry were used to trace the genetic source and transformation stage of organic matter hosted in the core sediments. In this study, the characteristics of rocks from La Cumbre were supplemented with the petrographic data from our studies reported earlier. Based on the findings, it has been concluded that the basins in the investigated parts of the EMD and NMD regions were likely characterized by different, isolated palaeosettings. Transformation and maturation of terrigenous material were affected by locally occurring physicochemical conditions. In both amber deposits, the sedimentation of clastic and organic material proceeded in the presence of marine conditions. In case of the La Cumbre deposit (NMD area), the sedimentation underwent probably in the conditions of the lagoon environment, a shallow maritime lake or periodically flooded plain that facilitated organic matter decomposition and carbonation from meta-lignite to sub-bituminous coal (random reflectance of coal—R_r^o = 0.39%). In the Siete Cañadas (EMD region), the sedimentation took place in a shallow saltwater basin, where terrigenous material was likely mixed with material found in situ (fauna fossils, carbonate-group minerals) to form the mudstones enriched in bituminous substance of low maturity. The organic matter found in the rocks from both deposits is of mixed terrestrial/marine origin and was deposited in the presence of low oxygen concentration and reducing and/or dysoxic conditions.

Recent developments in using the molecular decay dating method: a review

The dating of organic findings is a fundamental task for many scientific fields. Radiocarbon dating is currently the most commonly used method. For wood, dendrochronology is another state‐of‐the‐art method. Both methods suffer from systematic restrictions, leading to samples that have not yet been able to be dated. Molecular changes over time are reported for many materials under different preservation conditions. Many of them are intrinsically monotonous. These monotonous molecular decay (MD) patterns can be understood as clocks that start at the time when a given molecule was formed. Factors that influence these clocks include input material composition and preservation conditions. Different wood species, degrees of pyrolysis, and pretreatments lead to different prediction models. Preservation conditions might change the speed of a given clock and lead to different prediction models. Currently published models for predicting the age of wood, paper, and parchment depend on infrared spectroscopy. In contrast to radiocarbon dating, dating via MD does not comprise a single methodology. Some clocks may deliver less precise results than the others. Ultimately, developing a completely different, new dating strategy‐such as MD dating–will help to bring to light a treasure trove of information hidden in the darkness of organic findings.

Chemical and spectroscopic signatures of resins from Sumatra (Sarolangun mine, Jambi Province) and Germany (Bitterfeld, Saxony-Anhalt)

Fossil resins from Miocene coal deposit (Sarolangun mine, Jambi Province, Sumatra, Indonesia) have been analysed using spectroscopic methods: Raman Spectroscopy (RS), Fourier Transform-Infrared Spectroscopy (FT-IR), ¹³C Nuclear Magnetic Resonance (¹³C NMR), Fluorescence Spectroscopy (FS), and Gas Chromatography-Mass Spectrometry (GC-MS) in order to describe their diagnostic features. Simultaneously, glessite, a fossil resin from Upper Oligocene Bitterfeld deposit (Saxony-Anhalt, Germany), originating from similar botanical sources (i.e. angiosperms) was tested with the same analytical methods in order to find similarities and differences between the resins. The resins differ in colour, transparency and amounts of inclusions (resins from Sumatra-yellow, and transparent with few inclusions; glessite-brown-red, translucent with wealth of inclusions). In general, the IR and RS spectra of these resins are very similar, probably because the glessite colour-changing additives can be very subtle and non-observable in the infrared region. The RS spectra revealed also a slight difference in intensity ratio of the 1650/1450 cm^-1 bands (0.56 and 0.68 for Sumatra and Germany resins, respectively), indicating a differences in their maturation process. The resins from Sumatra seem to be more mature than glessite from Germany. The excitation-emission (EM-EX) and synchronous spectra showed unique, chemical compositions of these resins, which are different one from another. The GC-MS data for Sumatran resins, dominated by sesquiterpenoids and triterpenoids (amyrin), confirmed their botanical origin (angiosperms as their biological affinities). The sesquiterpenoid biomarkers with cadine-structures suggested the glessite underwent more advanced polymerization processes, which does not correlate with its RS spectrum. The geological factors, the environmental conditions of resin deposition, and later various diagenesis processes may have influenced the maturation and crosslinking of compounds. Despite the genetic similarity of the resins from various part of the world, Sumatra and Germany, advanced techniques such as Gas Chromatography-Mass Spectrometry and Fluorescence Spectroscopy were the most useful to find the differences between them. These differences are predominantly a result of different diagenetic transformations of the resins.

Unravelling the mystery of "Madagascar copal": Age, origin and preservation of a Recent resin

The loss of biodiversity during the Anthropocene is a constant topic of discussion, especially in the top biodiversity hotspots, such as Madagascar. In this regard, the study of preserved organisms through time, like those included in "Madagascar copal", is of relevance. "Madagascar copal" originated from the leguminous tree Hymenaea verrucosa, which produced and produces resin abundantly. In the last 20 years, interest has focused on the scientific study of its biological inclusions, mainly arthropods, described in dozens of publications. The age and origin of the deposits of "Madagascar copal" have not yet been resolved. Our objectives are to determine its age and geographical origin, and thus increase its scientific value as a source of biological/palaeobiological information. Although Hymenaea was established in Madagascar during the Miocene, we did not find geological deposits of copal or amber in the island. It is plausible that the evolution of those deposits was negatively conditioned by the type of soil, by the climate, and by the development of soil/litter microorganisms, which inhibit preservation of the resin pieces in the litter and subsoil over 300 years. Our results indicate that "Madagascar copal" is a Recent resin, up to a few hundred years old, that originated from Hymenaea trees growing in the lowland coastal forests, one of the most endangered ecosystems in the world. The included and preserved biota is representative of that ecosystem today and during historical times. Inclusions in this Recent resin do not have the palaeontological significance that has been mistakenly attributed to them, but they do have relevant implications for studies regarding Anthropocene biodiversity loss in this hottest hotspot.

Fossil Resins–Constraints from Portable and Laboratory Near-infrared Raman Spectrometers

Comparative studies of fossil resins of various ages, botanical sources, geological environments, and provenience were provided via a handheld portable Near-Infrared (NIR)-Raman spectrometer and benchtop instrument both working with laser line 1064 nm. The recorded Raman spectra of individual fossil resins were found to be sufficiently similar irrespective to the device type applied, i.e., handheld or benchtop. Thus, the portable equipment was found to be a sufficient tool for the preliminary identification of resins based on botanical and geographical origin criteria. The observed height ratio of 1640/1440 cm−1 Raman bands did not correlate well with the ages of fossil resins. Hence, it may be assumed that geological conditions such as volcanic activity and/or hydrothermal heating are plausible factors accelerating the maturation of resins and cross-linking processes.

Quantitative Analysis of Terpenic Compounds in Microsamples of Resins by Capillary Liquid Chromatography

A method has been developed for the separation and quantification of terpenic compounds typically used as markers in the chemical characterization of resins based on capillary liquid chromatography coupled to UV detection. The sample treatment, separation and detection conditions have been optimized in order to analyze compounds of different polarities and volatilities in a single chromatographic run. The monoterpene limonene and the triterpenes lupeol, lupenone, β-amyrin, and α-amyrin have been selected as model compounds. The proposed method provides linear responses and precision (expressed as relative standard deviations) of 0.6% to 17%, within the 0.5–10.0 µg mL⁻¹ concentration interval; the limits of detection (LODs) and quantification (LOQs) were 0.1–0.25 µg mL⁻¹ and 0.4–0.8 µg mL⁻¹, respectively. The method has been applied to the quantification of the target compounds in microsamples. The reliability of the proposed conditions has been tested by analyzing three resins, white copal, copal in tears, and ocote tree resin. Percentages of the triterpenes in the range 0.010% to 0.16% were measured using sample amounts of 10–15 mg, whereas the most abundant compound limonene (≥0.93%) could be determined using 1 mg portions of the resins. The proposed method can be considered complementary to existing protocols aimed at establishing the chemical fingerprint of these kinds of samples.

Mid-infrared spectroscopy for characterization of Baltic amber (succinite)

Natural Baltic amber (succinite) is the most appreciated fossil resin of the rich cultural traditions dating back to prehistoric times. Its unequivocal identification is extremely important in many branches of science and trades including archeology, paleontology, chemistry and finally mineralogical and gemological societies. Current methods of modification of natural succinite are more and more sophisticated making the identification of natural Baltic amber often challenging. In article the systematic analytical approach for identification of natural and modified under different conditions succinite, using mid-infrared spectroscopy (transmission, Drifts and ATR techniques) is presented. The correlation between spectral characteristics and properties of succinite is discussed pointing that the understanding of the nature of changes is the key of identification of this precious material.