ZINNIKER, D., J. M. MOLDOWAN*, J. DAHL, F. J. FAGO, H. LI, L. J. HICKEY, G. W. ROTHWELL, AND D. W. TAYLOR. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305; Department of Biology, Indiana University Southeast, New Albany, IN 47150; Department of Geology and Geophysics, Yale University, New Haven, CT 06511; Department of Environmental and Plant Biology, Ohio University, Athens, OH 45701. - Techniques and advances in molecular paleobotany: Methods for evaluating hypotheses of plant evolution and phylogeny by molecular fossils.
Advances in geochemistry have resulted in new analytical techniques
for the isolation and identification of ancient molecules or their
diageneic products. Sediments or fossils themselves, carefully
selected to prevent recent contamination, are first solvent extracted
with a Soxhlet apparatus. Extracts are separated into saturates and
aromatic fractions through the use of high-performance liquid
chromatography. The extracts are analyzed using gas
chromatography-mass spectrometry (GC-MS) and metastable reaction
monitoring GC-MS (MRM-GC-MS) to confirm the presence of specific
molecular fossils, that demonstrate the occurrence of several groups
of organisms geologically earlier than their first documented
micro-/megafossils. These techniques are now beginning to be applied
to plant groups. For example, molecular fossils linked to particular
dinoflagellates, diatoms, and chrysophytes have been documented in
many sedimentary rocks and petroleum. The use of polycyclic diterpanes
as higher plant markers is only beginning. We present preliminary data
from Carboniferous coals of eastern North America. The existence of a
widespread and unique tetracyclic diterpane signature in
Late-Carboniferous coals from Germany, Turkey, and the North America
is evidence of a stable and cosmopolitan vegetation community
inhabiting these coal swamps. Variations in diterpane abundance appear
to track variations in marine influence and dramatically separate
paleo-mid latitude coals of Nigeria from paleo-equatorial coals of
Europe and North America. A sample set of monospecific coal balls,
heterogeneous coals, and fossilized woods is being analyzed to
determine which plants are contributing to the diterpane signature.
Although individual contributors remain elusive, several microbially
produced diterpanes have been identified, and it appears that the
higher plant diterpane precursors originated as components of leaf
waxes and resinous exudates. Our future goal is ultimately to set up a
molecular stratigraphy that will allow the crude dating of petroleum
and source rocks that have significant higher plant input.
Key words: Carboniferous, Geochemistry, molecular fossil, MRM-GC-MS.