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The same picture through different lenses; quantifying the effects of two preservation pathways on Green River Formation insects

Evan P. Anderson and Dena M. Smith
The same picture through different lenses; quantifying the effects of two preservation pathways on Green River Formation insects
Paleobiology (May 2017) 43 (2): 224-247

Abstract

Insects in the fossil record are generally preserved in lacustrine shales or in amber. For those in lacustrine shales, preservation is usually via keroginization or mineralization. Given the extended period of microbial decay required to generate ions for mineralization, there is a predicted inherent bias toward lower preservation quality for this pathway by most taphonomic indices compared with keroginization. This study tests this hypothesis by comparing multiple measures of preservation quality between sites with similar sedimentology in the Eocene Green River Formation of Colorado. Here, insects are either mineralized in iron oxides (likely after pyrite) at the Paleoburn site or keroginized at the Anvil Points site.Generally, the prediction that keroginization preserves soft-bodied fossils with higher preservational quality than mineralization is affirmed, but with some caveats. Beetles, known for their robust cuticles, are proportionately more abundant at the Paleoburn site, but eight of the nine orders recorded are shared between sites. As predicted, insects show lower preservation fidelity at th Paleoburn site, but they also show higher degrees of disarticulation. This second bias should be acquired primarily during the biostratinomy stage, and not early diagenesis. Nonetheless, higher-energy biostratinomic conditions may be compatible with taphonomic conditions that promote mineralization over keroginization. Comparing the inherent taphonomic bias of different preservation pathways is often difficult, since fossil deposits may be preserved millions of years or thousands of kilometers apart. By studying two different preservation pathways of insects within the same formation, we can affirm that keroginization does indeed preserve recalcitrant organic matter with higher quality than pyritization or iron-oxide mineralization. Additionally, some guidelines can be proposed concerning the body parts and taxa that can be compared, and for what purpose, when contrasting mineralized and keroginized soft-bodied deposits.


ISSN: 0094-8373
EISSN: 1938-5331
Coden: PALBBM
Serial Title: Paleobiology
Serial Volume: 43
Serial Issue: 2
Title: The same picture through different lenses; quantifying the effects of two preservation pathways on Green River Formation insects
Affiliation: University of Colorado at Boulder, Department of Geological Sciences, Boulder, CO, United States
Pages: 224-247
Published: 201705
Text Language: English
Publisher: Paleontological Society, Lawrence, KS, United States
References: 90
Accession Number: 2017-046228
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF grants EF-1305066 and EAR-1123802
Illustration Description: illus. incl. strat. col., 6 tables, geol. sketch map
N39°30'00" - N39°30'00", W108°00'00" - W108°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, The Paleontological Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201725
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