Widespread mineralization of soft‐bodied insects in Cretaceous amber

Abstract

Fossilized tree resin, or amber, commonly contains fossils of animals, plants and microorganisms. These inclusions have generally been interpreted as hollow moulds or mummified remains coated or filled with carbonaceous material. Here, we provide the first report of calcified and silicified insects in amber from the mid‐Cretaceous Kachin (Burmese) amber. Data from light microscopy, scanning electron microscopy (SEM), energy‐dispersive and wavelength‐dispersive X‐ray spectroscopy (EDX and WDX), X‐ray micro‐computed tomography (Micro‐CT) and Raman spectroscopy show that these Kachin fossils owe their preservation to multiple diagenetic mineralization processes. The labile tissues (e.g. eyes, wings and trachea) mainly consist of calcite, chalcedony and quartz with minor amounts of carbonaceous material, pyrite, iron oxide and phyllosilicate minerals. Calcite, quartz and chalcedony also occur in cracks as void‐filling cements, indicating that the minerals formed from chemical species that entered the fossil inclusions through cracks in the resin. The results demonstrate that resin and amber are not always closed systems. Fluids (e.g. sediment pore water, diagenetic fluid and ground water) at different burial stages have chances to interact with amber throughout its geological history and affect the preservational quality and morphological fidelity of its fossil inclusions.

Unparalleled details of soft tissues in a Cretaceous ant

“…Recently, the mineralization process of insects preserved in Kachin amber has been investigated and hypothesized -the resin prevented the degradation of the insects until it was cracked when buried in marine sediment (Jiang et al, 2022). Pore water with reactive chemical species of diagenesis then in ltrated the amber pieces through the cracks, which resulted in the cali cation or sili cation of the insect bodies (Jiang et al, 2022). On the one hand, this hypothesis explains why a great proportion of known amber inclusions are preserved in a solid state lled with minerals (Henwood, 1992b;.…”

“…Fossils with soft-tissue preservation are rare, and often with only a certain part of the internal structures such as the muscular (Kornilowitsch, 1903;Petrunkevitch, 1935;Henwood, 1992a Liu et al, 2018). Recently, the mineralization process of insects preserved in Kachin amber has been investigated and hypothesized -the resin prevented the degradation of the insects until it was cracked when buried in marine sediment (Jiang et al, 2022). Pore water with reactive chemical species of diagenesis then in ltrated the amber pieces through the cracks, which resulted in the cali cation or sili cation of the insect bodies (Jiang et al, 2022).…”

Morphological and organic spectroscopic studies of a 44-million-year-old leaf beetle (Coleoptera: Chrysomelidae) with preserved α-chitin

“…The effects of weathering and diagenesis, along with possibility of exogenous organic material as contaminants make spectral interpretation more difficult 2 . Fortunately, amber as a preservational medium provides a relatively closed system (except for exceptional circumstances 22 ), so that inorganic and organic contributions from sediment are expected to be minimal.…”

The largest amber-preserved flower revisited

“…The exceptional preservation of amber inclusions like S. kowalewskii is possibly caused by the biocidal properties of the embedding resin, which inhibits degradation processes 79,80 . In many plant inclusions, internal and external structures are three-dimensionally preserved 13 , similar to mummifications 16 ; however, it is unknown as to which processes are involved in the preservation of plants in amber.…”

“…In many plant inclusions, internal and external structures are three-dimensionally preserved 13 , similar to mummifications 16 ; however, it is unknown as to which processes are involved in the preservation of plants in amber. In contrast, the taphonomy of animal inclusions has been studied in detail, showing numerous factors that control their preservation, such as size of the organism, resin viscosity and stickiness [80][81][82][83] . Some of these factors could be similarly important for plant inclusions.…”