--> Abstract: Terrestrial Organic Matter Contributions to the Hydrocarbon Geochemistry of Mudrocks, by Amelia C. Robinson, Isabel P. Montanez, and Peter J. Hernes; #90039 (2005)

Datapages, Inc.Print this page

Terrestrial Organic Matter Contributions to the Hydrocarbon Geochemistry of Mudrocks

Amelia C. Robinson, Isabel P. Montañez, and Peter J. Hernes
University of California-Davis, Davis, CA

The organic geochemistry of mudrocks deposited along continental margins is controlled by the balance of terrestrial and marine organic matter (OM) deposition and its mineral sorption, transformation and sequestration. Such studies typically ignore the terrestrial OM contribution considering it an insignificant contributor. However, recent studies of modern continental margin sediments suggest that existing models of the partitioning of OM are overly simplistic resulting in the underestimation of the terrestrial contribution to marine sediment bulk OM. Furthermore, mudrock geochemical compositions and the quality and composition of derived hydrocarbons are greatly influenced by the original composition of their source OM (e.g., amino acids and lignin) and their propensity to sorb to mineral surfaces. Thus, mudrock δ13C compositions may be more ambiguous indicators of OM source than initially considered without quantitative analyses of OM sources and end-member compositions. This study utilizes an experimental and empirical (continental margin coretop samples) multi-biomarker approach for constraining the sorption-desorption history of hydrocarbon precursors. Sorption-desorption experiments using lignin phenols and amino acids allow for differentiating preferential sorption trends from variations in OM source and/or diagenetic history. Acid-aldehyde ratios in lignin phenolic compounds and total hydrolyzable amino acids can be used as proxies for extent of diagenetic transformations. Lignin phenols are exclusively terrestrial biomarkers and provide a diagnostic indicator of the terrestrial contribution to bulk organic properties. In summary, this approach provides a framework for constraining what types of compounds are actively being preserved and sequestered in fine-grained marine sediments and thereby making better models for delineating potential subsurface OM transformations.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005