David Winship Taylor
, Indiana University (Southeast)
The final goal of this project is to describe the distribution of oleanoid molecular fossils from a single formation known to have oleanane. Our earlier work show the observed spatial and temporal distribution of the biomarker oleanane and des-A-oleanane (and the widespread occurrence of functionalized oleanoids in living basal angiosperms, monocots and eudicots) has led to oleanane’s use as a qualitative indicator of angiosperm input in sediments. Oleanoids were found in the most basal orders of living angiosperms and a parsimony reconstruction supports the hypothesis that they are ancestral to angiosperms. The two diagenetic transformation products, oleanane and des-A-oleanane, have similar distributions but des-A-oleanane is more easily measured in extracts. The sediment samples were extracted, hydrogenated using an ionic reduction procedure, and separated into saturate and aromatic fractions. The presence of appropriate molecular fossils was tested using GCMS and GC-MRM-MS techniques. Although this may be related to diagenesis including oxidation, relative comparison based on ratios to hopane (a bacterial biomarker) may show where angiosperms were dominant. Presumed molecular fossils of conifers (diterpanoids) were also examined. Molecular fossil relative abundances are correlated to detailed macrofossil study of the depositional environment at the Aptian Dutch Gap locality in VA, USA. The locality is Pollen Zone 1 and oldest well-studied Aptian site in North America with angiosperms. Three facies were sampled: levee, backswamp, clayballs in channels presumably from surrounding flood plain terraces. The megafossil studies suggest angiosperms were confined to the levee deposits and not a significant contributor to the more diverse flora in the backswamp. The pollen studies show angiosperms grains are found in all facies. Examination of different sediments show the abundance of the molecular fossils appears dependent on the depositional environment. The clayballs are more oxidized than other facies, have a complex signature, and possibly a two stage diagenesis. They also have the highest oleanane index, and des-A oleanane to diterpenoids ratio, but these may not be comparable to the other facies because of high oxidation. Comparison between the less oxidized levee and backswamp facies, show higher levels of angiosperm input in the levee, and higher levels of conifer input in the backswamp. In summary, angiosperms are found in all facies, input and dominance over conifers appears highest in the clayballs with conifer input highest in the backswamp. This project has involved colleagues at Stanford University as well as an undergraduate. The undergraduate was involved by looking at the biochemical literature of living organisms to attempt to find other potential biomarkers. She gave a presentation at the campus research conference. She has graduated with a degree in Biology and a Plant Sciences minor and has applied to graduate school. The funding was important for me as a provided me with the ability to have samples analyzed and to continue a long term collaboration on plant molecular fossils. The project has made excellent progress in it third of three reporting periods. At this stage analysis is almost completed and we have begun to outline two manuscripts that will be written over the next year, during the time the grant was extended. A new undergraduate is involved with the data analysis.