Lepidodendron dawsonii: functional groups and pyrolysates of compression and fossilized-cuticle (Late Asturian, Canada)

Erwin L Zodrow,Robert Helleur,Maria Mastalerz

doi:10.4154/gc.2012.26

Abstract

Lepidodendron dawsonii BELL 1938 is an endemic species of Late Asturian age in the Canadian Sydney Coalfield, with conspicuous elongate leaf cushions. The study specimen, 35 cm long and 10 cm wide, represents a dichotomous bough from the tree crown in which the inner part of one side is black and compression-preserved, whereas the one in contact with the entombing rock matrix is dark-amber in colour and fossilized-cuticle preserved. Only stomatal pits and cuticular details are preserved. Comparison of these preservation states, based on Fourier transform infrared (FTIR) spectrometry, and flash pyrolysis gas chromatography mass spectroscopy (Py-GC/MS), demonstrate sufficient differences in chemistry to be able to link the two preservation states with differing pathways of organic matter transformation (diagenesis). The aliphatic-hydrocarbon chains of the cuticles are comparatively shorter and more branched than the longer chains of the compressions. Py-GC/MS results support the presence of hydrocarbon markers of plant cuticles. The high abundances of C1 and -C2 alkylphenols and C1 and -C2 alkylbenzenes in pyrolysates are likely derived from maturing lignin or lignin-like biomacromolecules. We suggest comparison of L. dawsonii’s cuticles with Lepidodendron coal macerals in Chinese Permian Leping coal, and with suberinite.

Highlights

Lepidodendron dawsonii BELL 1938 is a fairly common lepidophyte component in the Late Asturian of Sydney Coalfield, Canada (Fig. 1A & B), and ranges from the Emery Seam to the highest strata at Point Aconi (Fig. 1C)
The focus is on the two preservation states in one contiguous specimen of L. dawsonii. as each is capable of providing its own spectrochemical information as a consequence of its fossilization history, i.e., coalification and natural maceration (ZODROW & MASTALERZ, 2009)
The leaf scars are rhomboidal in shape, and BELL (1938) compared older stems of L. dawsonii with L. rimosum

Summary

INTRODUCTION

Lepidodendron dawsonii BELL 1938 is a fairly common lepidophyte component in the Late Asturian of Sydney Coalfield, Canada (Fig. 1A & B), and ranges from the Emery Seam to the highest strata at Point Aconi (Fig. 1C). The specimen is significant (Pl. 1A) because of the dual preservation as 1) a coalified compression, typical of fossil plants in the Sydney Coalfield (Pls. 1B & C), and 2) as rare fossilized-cuticle C Lose compressed leaf-cushion material after 30-min HF treatment. PLATE 2 Lepidodendron dawsonii A Amber-coloured fossilized-leaf cushions in situ. B Fossilized-leaf cushions after 20-min HF treatment. Zodrow et al.: Lepidodendron dawsonii: functional groups and pyrolysates of compression and fossilized-cuticle (Late Asturian, Canada)

PRESERVATIONS AND CUTICULAR MORPHOLOGY

MATERIAL AND METHODS

Findings

OF RESULTS