SYNCHROTRON-BASED TECHNIQUES: THE MOLECULAR TAPHONOMY OF INSECTS TRAPPED IN AMBER FROM THE EARLY MIOCENE CHIAPAS LAGERSTÄTTE

The unusual deposits of well-preserved fossil material, which may represent complete exceptionally preserved biotas, are called Konservat-Lagerstätten (KL). At the present time, the KL are the focus of the studies related to the evolution of Earth's ecosystems and the exceptionally preservation of organic material. Here soft tissues of the fossil specimens are preserved intact at the cellular and subcellular level.

There is an amber KL in southern Mexico: the Chiapas Lagerstätte (ca. 23 Myr), this is part of a large known accumulation of fossil resin that preserves a rich fossil assemblages of plants and insects from an ancient subtropical forest biome.

The preservation of hard/soft tissues on insects can be inferred by the molecular and biogeochemical composition. Such small-scale analyses are enclosed in the molecular taphonomy research. The use of synchrotron-based techniques provides novel insights regarding chemical transformation of the ancient organic material.

This work shows the results of the ultrastructural and biogeochemical studies based on the following combined analytical techniques: Extended X-ray Absorption Fine Structure spectroscopy (EXAFS), Small Angle X-ray Scattering (SAXS), Fourier Transform InfraRed spectroscopy (FTIR), and X-ray Fluorescence (XRF) microprobe. These studies were performed on three-dimensional body structures of insects, as well as the fossil resin from the Chiapas Lagerstätte.

The preserved insects display a wide range of organic structures from nearly intact to intense decay microbial-induced. SAXS analysis show the polymeric microfabric of nanometer fibers with semicrystalline phases associated with the fossilization process of the resin. EXAFS shows the sulfur and calcium speciation in amber linked to paleoenvironment and the complex interaction with sediments. µ-FTIR spectra show chemotaxonomy signals of the higher plant precursors of amber, and the maturation that have occurred after burial. Finally, µ-XRF detected biogeochemical traces, including elements like iron, calcium, and phosphorus that are long-lived biomarkers of exoskeletons in fossil insects, also small-scale patterns of their molecular transformation are evident.

Additional co-authors: M.A. Coutiño, & G. Carbot. Museo de Paleontología "Eliseo Palacios Aguilera," Chis. Mex.