61st Annual Report on Research 2016

The primary focus of this PRF DNI research is to examine first-order controls of Burgess Shale-type fossil preservation. To do so, my laboratory group is using two complementary approaches: (1) analysis of Burgess Shale-type fossil materials, and (2) controlled laboratory- and field-based decay experimentation. Burgess Shale-type preservation, named for the famed Cambrian fossil locality, reveals exceptional glimpses of the aftermath of the first major diversification of animals—the Cambrian Explosion—captured as carbonaceous compressions of labile tissues, though commonly associated with pyritization and aluminosilicification. Each case of soft-tissue preservation may be viewed as a race between destructive and constructive processes; in order for labile tissues to be preserved, the degradable organic carbon framework must be stabilized through replacive mineralization or geopolymerization processes in order to enter the fossil record. In the broadest sense, generally similar in focus to understanding the formation of petroleum or other carbon-bearing resources, the overarching goal of this research effort is to evaluate the diagenetic, biological, and paleoenvironmental factors responsible for generating carbonaceous compression fossils.

1.      Fossil materials—

Over the last grant period, PRF DNI funding was utilized for scanning electron microscopy-based microchemical analyses of fossil materials—with numerous successes to report. Thus far, we have published two papers in the Journal of Paleontology on macroalgal and comparable Burgess Shale-type materials (LoDuca et al., 2015a, b). While the first was a result of the pilot data collected for this proposal, the latter of these papers (LoDuca et al., 2015b) was directly supported by PRF DNI funding and provides the first report of Yuknessia simplex (a hemichordate originally interpreted as a macroalga; LoDuca et al., 2015a) in China, and the first report of the macroalga Fuxianospira in North America (see Figure 1, from LoDuca et al., 2015b). The findings have been presented at several conferences by my laboratory group and collaborators, and directly address the research goal of better understanding biological expression of the fossil materials in question. We have additionally continued with comparative microchemical analyses on animal fossils (predominantly vermiform and arthropod fossils) preserved through the same taphonomic pathways and from the same localities. Both target taxonomic groupings, worms and arthropods, have comprised the bulk of two student theses (a PhD and a MS student, respectively) and are currently in preparation for publication. This work, in sum, has contributed greatly to the design of laboratory- and field-based decay experimentation, as briefly described below.

2.      Laboratory- and field-based decay experimentation—

This grant has additionally supported the operation and maintenance of an anoxic glove-box in my decay laboratory, in which modern analogs of the analyzed fossil materials are currently undergoing decay experiments to observe early stages of “preservation” on laboratory timescales. Although impossible to replicate geologic time, this protocol allows for actualistic observation of the pace of decay under conditions designed to mimic the Cambrian seafloor where their fossil counterparts were preserved. At present, we are conducting decay experiments on waxworms (caterpillar larvae of the wax moth) and shrimp, and have recently finished field-based decay experimentation of crabs, conducted in a natural coastal environment at the Gerace Research Center, San Salvador, Bahamas. For the latter, analyses of collected sediments and chitinous materials is currently underway. Together, the lab- and field-based work has resulted in several graduate student-led presentations at national meetings. For the laboratory-based decay experimentation, artificial seawater and sterilized quartz sand and clay media were used to house the decay replicates, and each replicate was inoculated with Desulfovibrio salixigens sulfate-reducing microbes. Thus far, with several experiments still on-going, we have recovered lightly pyritized materials, or more appropriately, iron sulfides associated with morphological features of the decay organisms (see Figure 2).  

3.   Summary—

Nearing conclusion of this project (an extension of analytical funds has been approved), we have made significant strides in fossil material analyses, which have yielded contributions to our understanding of Burgess Shale-type preservation, and have begun to assimilate results of decay experimentation to best-approximate the earliest stages of this taphonomic window. The results obtained thus far have yielded: (1) one publication directly from the research proposed herein as well as publication of the pilot study; (2) a second publication from a side project initiated while collecting materials for this project (Selly et al., 2016); and (3) several national and regional meeting presentations (n=17). More importantly, this PRF DNI funding has built firm foundations that will help in procuring long-term research funding, and has directly supported the research endeavors of three graduate students and one undergraduate researcher in my laboratory.           

4.   References—

LoDuca, S.T., Caron, J.-B., Schiffbauer, J.D., Xiao, S., and Kramer, A. 2015a. A reexamination of Yuknessia from the Cambrian of British Columbia and Utah. Journal of Paleontology 89: 82–95.

LoDuca, S.T., Wu, M., Zhao, Y., Xiao, S., Schiffbauer, J.D., Caron, J.-B, and Babcock, L.E. 2015b. Reexamination of Yuknessia from the Cambrian of China and first report of Fuxianospira from North America. Journal of Paleontology 89: 899–911.

Selly, T., Huntley, J.W., Shelton, K.L., and Schiffbauer, J.D. 2016. Ichnofossil record of selective predation by Cambrian trilobites. Palaeogeography, Palaeoclimatology, Palaeoecology 444: 28–38.

5.   Figures and captions—

Figure 1: (from LoDuca et al., 2015b) Reflected light and SEM images of Fuxianospira gyrata from the Marjum Formation, House Range, Utah. (1) KUMIP 373593, reflected light; (2) Backscattered electron image mosaic of specimen in (1); (3–5) Energy dispersive X-ray spectroscopic elemental maps for calcium, iron, and silicon, respectively, for the white rectangle in (2); (6) KUMIP 373594, reflected light; (7) Backscattered electron image mosaic of specimen in (6); (8) higher magnification of area marked by white arrow in (7), showing fossil surface with iron oxide framboids (pseudomorphs after pyrite weathering); (9–11) Energy dispersive X-ray spectroscopic elemental maps for calcium, iron, and silicon, respectively, for the white rectangle in (7).

Figure 2: Hexagonal surface ornamentation on waxworm (left; backscattered electron image in low vacuum mode), and hexagonal molds in iron sulfide minerals (bright hexagonal shapes) from recovered from decay environment (right; secondary electron image in low vacuum mode).