Taylor, David , Zinniker, David , McCorkle, Erin , Hu, Shusheng , Barbanti, Silvana , Moldowan, J. Michael .
Molecular paleoecological study of the Aptian (Early Cretaceous) Dutch Gap locality, Virginia, USA.
Biogeochemical studies are refining the understanding of sedimentology, and the spatial and temporal distribution of living group to improve understanding of paleoecology. Molecular fossils are common and abundant in many Cretaceous and Tertiary sediments, butrare in older sediments. The observed spatial and temporal distribution of the biomarker oleanane and des-A-oleanane(a putative byproduct of oleanane) has led to their use as a qualitative indicator of angiosperm input in sediments. All plants produce diterpenoids, but conifers tend to accumulate them more abundantly than most angiosperms. Thus, diterpanes are much less specific indicators for conifers, in a qualitative sense, than oleanane is for angiosperms. We have confirmed the natural sources of these angiosperm molecular fossils by sampling species from all the basal angiosperm orders as well as the basal orders of the monocots and eudicot clades. The samples were subjected to hydrouspyrolysis, extracted, hydrogenated using an ionic reduction procedure, and separated into saturate and aromatic fractions. The presence of appropriate functionalized natural products was tested using GCMS and GC-MRM-MS techniques. This mimics the conditions of diagenesis and burial that transform diverse functionalized natural products into a limited number of identifiable molecular fossils. A parsimony reconstruction the oleanoid distribution supports the hypothesis that they are ancestral in angiosperms. The two diagenetic transformation products, oleanane and des-A-oleanane, have similar distributions but des-A-oleanane is more easily measured in plant pyrolysates. We examined the paleoecology of Dutch Gap locality to test hypotheses that the early angiosperms were restricted to the levee based on mega- and microfossils. We sampled three facies: levee, backswamp, red clayballs in channels presumably from surrounding floodplain terraces. The abundance of the molecular fossils appears dependent on the depositional environment. Although this may be related to diagenesis including oxidation, relative comparison based on ratios to hopane (a bacterial biomarker) appears to show where angiosperms were dominant. We found the red clayballs more oxidized than other facies, had a complex signature, possible two stage diagenesis, and had the highest oleanane index and des-A oleanane to diterpenoids ratio. Comparisons between the levee and backswamp, show higher oleanane index and des-A oleanane to diterpenoids ratio in the levee and lower oleanane index and des-A oleanane to diterpenoids ratio in the backswamp. This would indicate that the red clayballs were preserved in a more oxidizing environment, angiosperm input was highest in the floodplain terraces and levee, and conifer input was higher in the backswamp.
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1 - INDIANA UNIVERSITY SOUTHEAST, Department Of Biology, 4201 GRANT LINE ROAD, NEW ALBANY, IN, 47150, USA
2 - Stanford University, Stanford, CA
3 - Indiana University Southeast, Biology, New Albany, IN
4 - Yale University, New Haven, CT
5 - Integrated Petroleum Expertise Company IPEXCo, , Rio de Janeiro, RJ, Brazil
6 - Stanford University, Stanford, CA
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Tuesday, July 10th, 2012
Time: 4:15 PM