Abstract Detail

Paleobotany

Gensel, Patricia [1], Smith, Selena [2].

A preliminary study of Early Devonian pyrite permineralized stems by Micro-CT scanning.

Several approaches to studying the anatomy of Devonian plants from pyritized specimens exist, with results from each depending on extent of plant cell wall and pyrite formation. Etched and polished thin sections usually provide considerable information but even better are peels – less material is lost between sections, more detailed structures are shown – as was done for Armoricaphyton (e.g., Gerrienne and Gensel 2016). Critical to this appears to be both a comparatively small degree of cell wall degradation or destruction and how the permineralization occurred; in particular, in specimens with more details, the pyrite appears more cohesive and perhaps with a smaller crystal size. Attempts to generate informative peels from several taxa from the Early Devonian of Canada (New Brunswick and Gaspé) were inconsistent or unsuccessful. It appears cell walls are less well preserved and much of the pyrite is less intact. Etched and polished sections yield considerable information, but the small axis size (2-5 mm) makes it difficult to cut in desired planes. We therefore examined examples of 4 different plant types of trimerophyte grade organization, with micro-CT scanning to see if more can be learned. Specimens were scanned on a Nikon XTH 225ST industrial microCT scanner at the University of Michigan yielding tomograms with voxel sizes of 7.1 to 11.7 µm. Scan data were processed using Avizo computer software to visualize the data. The Gaspé specimens included axes from two plants tentatively attributable to Psilophyton and an unnamed new genus: the New Brunswick specimens are from the new plant with secondary xylem. Results are informative, most particularly concerning isotomous branching or lateral trace formation. Locating intact protoxylem or rays in secondary xylem was not accomplished, and in many cases it is concluded that those cells were not preserved. Most interesting thus far are aspects of taphonomy that are revealed from the stack of 2000 tomograms. Major areas of degradation are more prominent than when going through series of sections. Some axes that appeared as part of a single branching system were found, when observed in 3D, to be unrelated. Other interesting aspects of orientation of axes and of taphonomic effects also were observed and can be compared to better understand features observed by thin section techniques. Micro-CT scanning, in conjunction with standard thin sections, promises to provide a more multidimensional and accurate view of anatomical changes in critical regions of these early plants.

1 - University Of North Carolina, Department Of Biology, CB# 3280, Coker Hall, Chapel Hill, NC, 27599, United States
2 - Department Of Earth & Environmental Sciences, 1100 North University Avenue, Room 2534, NUB, Ann Arbor, MI, 48109, United States

Keywords:
Micro-CT
Devonian
pyritized axes.

Presentation Type: Oral Paper
Session: PAL2, Paleobotany II: Paleozoic and Mesozoic Paleobotany
Location: Tucson G/Starr Pass
Date: Monday, July 29th, 2019
Time: 3:45 PM
Number: PAL2001
Abstract ID:613
Candidate for Awards:None