58th Annual Report on Research 2013 Under Sponsorship of the ACS Petroleum Research Fund

The relative abundance of plant-derived terpenoids in geologic sediments provides unique information on depositional environment, organic matter provenance, and source rock ages. Terpenoids are diverse in structure and provide plant group specificity. For example, non-hopanoid pentacyclic triterpenoids are almost exclusively synthesized by angiosperms and tricyclic diterpenoids are produced by gymnosperms. Terpenoids have been used extensively in geologic and modern applications, but interpretations of their abundance in geologic samples are highly uncertain because little is known about terpenoid alteration as terpenoids are transferred from plants to depositional environments. To address these issues, we had the following aims: 1) quantify di- and triterpenoid concentrations in plants, sediments, and particulate and dissolved organic matter in a small river catchment to (a) determine if the contribution of terpenoids from source vegetation is reflected in forested soil and river sediments, and (b) constrain the dispersal of these compounds in fluvial systems; 2) investigate the diversity of terpenoid compounds among conifer species; and 3) investigate degradation biases between di- and triterpenoids with hydrous pyrolysis. This research is entering the second year of funding and we are excited to continue working on this project. A brief description of each aim is provided below and a report on our current progress.

Aim 1) Evaluating the use of modern plant biomarkers in river systems

For this aim, we focused on the Miners River watershed in the Upper Peninsula of Michigan that has a mixed plant-community of conifer and angiosperm species. One of the most notable components of this work has been the development of a new method to analyze molecular biomarkers in dissolved organic matter from river water. Until now, few studies have investigated dissolved biomarkers in river waters, primarily because biomarkers are at very low concentration in surface waters and complicated by complex environmental samples (matrix effects). Our method uses solid-phase extraction to isolate and quantitatively remove the dissolved biomarkers from river water in combination with gas chromatography mass-selective ion-monitoring mass spectrometry. Excitingly, we found both di- and triterpenoids in dissolved organic matter fractions. This has interesting implications for thinking about terpenoids in sedimentary archives. Within the Miners River drainage basin, we found that evergreen conifers are less abundant than deciduous angiosperms, yet contribute 4.5 times more terpenoids to sediments, even when scaled for leaf litter production and present vegetation cover. This was surprising and may suggest regional differences in production levels by various plant communities. The di- to triterpenoid ratios in modern plants do not match that in found in river sediments, suggesting that processes, or combination of processes, preferentially remove diterpenoids. Despite a preservation bias, we found that sediment terpenoid concentrations can be used to predict the present plant community composition (based on plant community counts) within 10-15%. This work was completed as part of my graduate student Sharmila Giri’s M.S. Thesis and we are in the process of submitting this work for publication. We presented the results of this work at three conferences. In addition, two undergraduate students, Mr. Marsh (Miami Univ. of Ohio) and Ms. Hassan (UC Geology), have worked on this project.

Aim 2) Modern conifer biomarker distributions for interpreting ancient environments

Previous research indicates that molecular biomarkers are not evenly distributed among conifer plant species and was clear from work completed in Aim 1 above. Previous diterpenoids research was primarily limited to conifer families that grow in North America today. This unfortunately ignores several southern hemisphere conifer families (i.e. Podocarpaceae, Araucariaceae) that were present in North America in the early Paleogene. To address this sampling bias, we collected leaves from ~50 species of conifers at the University of California Botanical Garden at Berkeley (UCBGB) with the help and support of curator Holly Forbes. The UCBGB was the ideal location to do this study as this garden has the most diverse collection of conifer species anywhere in the world. We are currently completing the laboratory analyses of the samples and anticipate completion of the project in the coming year. Several undergraduate students have been involved in this project.

Aim 3) Characterization of terpenoid alteration as a function of digenesis with hydrous pyrolysis

While completing Aim 1, we identified that early alteration and mineralization of terpenoids is not consistent among terpenoid classes. Interestingly, geologic studies indicate that diterpenoids are preferentially preserved in contrast to the observations discovered during completion of Aim 1. These conflicting results may suggest other processes are responsible during later stages of preservation/mineralization. Therefore, we are investigating alteration and decomposition of di- and triterpenoids with hydrous pyrolysis to mimic geologic conditions using a suite of temperatures. This project is part of Doug Sberna’s (UC Geology) senior research project and anticipate completion in the upcoming year.