BIOMARKER CHARACTERIZATION OF TERRESTRIAL ORGANIC MATTER IN APTIAN ARUNDEL FORMATION, POTOMAC GROUP, EASTERN USA

The Aptian Arundel Clay of the Cretaceous Potomac Group contains abundant theropod and plant remains, in addition to other fossil assemblage characteristic of fluvio-deltaic environments such as swamps and oxbow lakes. In this study, the biomarker composition of the aliphatic and aromatic organic matter extracted from Arundel Clay samples was examined using gas-chromatography/mass spectrometry (GC/MS). Samples were collected from stratigraphic sections measured near Baltimore, Maryland, and are described as thin- to medium-bedded, grayish black mudstone containing abundant remains of vascular plants. Our preliminary GC/MS results reflect both plant and bacterial inputs. The aliphatic compounds are dominated by high molecular weight n-alkanes (C23 to C33) having high odd/even carbon number predominance reflecting contributions from leaf waxes, and relatively lower abundance of aliphatic diterpenoids derived from conifer resins. Hopanes are also abundant in the aliphatic fraction, and are dominated by C30-hop-17(21)-ene, C30-nor-hopane, and C31-ββ-hopane derived from bacteria. The aromatic fraction contains sesquiterpenoids and diterpenoids (eg. simonellite) derived from conifer resins, including a functionalized diterpenoid tentatively identified as totarol or ferruginol. The aromatic diterpenoids are most abundant in the extract of a wood fragment collected from the same exposure. These findings are consistent with published palynological studies indicating the predominance of gymnosperm pollen and lack (or low abundance) of angiosperm pollen in the Arundel Clay at this location. The presence of functionalized diterpenoids such as totarol or ferruginol is noteworthy because they occur in the Taxodiaceae, Cupressaceae, and Podocarpaceae conifer families.