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Abstract Recent experiments and field observations have indicated that biomarker molecules can react over short timescales relevant to seismic slip, thereby making these compounds a useful tool in studying temperature rise in fault zones. However, short‐timescale biomarker reaction kinetics studies have previously focused on compounds that have already experienced burial heating. Here, we present a set of hydrous pyrolysis experiments on Pleistocene‐aged shallow marine sediment to develop the reaction kinetics of long‐chain alkenone destruction, change in the alkenone unsaturation ratio (), and change in then‐alkane chain length distribution. Our results show that biomarker thermal maturity provides a useful method for detecting temperature rise in the shallow reaches of faults, such as subduction zone trench environments. Through the course of our work, we also noted the alteration of total alkenone concentrations andvalues in crushed sediments stored dry at room temperature for durations of months to years but not in the solvent extracts of these materials. This result, though parenthetical for our work in fault zones, has important implications for proper storage of sedimentary samples to be used for alkenone paleotemperature and productivity analysis.
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Organic thermal maturity as a proxy for frictional fault heating: Experimental constraints on methylphenanthrene kinetics at earthquake timescales
Biomarker thermal maturity is widely used to study burial heating of sediments over millions of years. Heating over short timescales such as during earthquakes should also result in measurable increases in biomarker thermal maturity. However, the sensitivity of biomarker thermal maturity reactions to short, higher-temperature heating has not been established. We report on hydrous pyrolysis experiments that determine the kinetic parameters of methylphenanthrene maturation at timescales and temperatures relevant to earthquake heating. Samples of Woodford Shale were heated at temperatures up to 343 °C over 15–150 min. The thermal maturity of the samples as measured by the methylphenanthrene index-1 (MPI-1) increased with heating time and temperature. We find that MPI-1 increases with time and temperature consistent with a first-order kinetic model and Arrhenius temperature relationship. Over the timescales tested here, MPI-1 is strongly affected by maximum temperature and less sensitive to heating duration. Production of new phenanthrene isomers and expulsion of a liquid pyrolyzate also occurred. Differential expulsion of methylphenanthrene isomers affected the apparent maturity of the rock at lower temperatures and may need to be considered for organic-rich fault rocks. Our results demonstrate that the overall MPI-1 reaction extent in both the rock and pyrolyzate are a useful measure of thermal maturity and reflect temperature history during rapid heating.
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- Award ID(s):
- 1219488
- PAR ID:
- 10616616
- Publisher / Repository:
- Geochimica et Cosmochimica Acta
- Date Published:
- Journal Name:
- Geochimica et Cosmochimica Acta
- Volume:
- 151
- Issue:
- C
- ISSN:
- 0016-7037
- Page Range / eLocation ID:
- 103-116
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.gca.2014.11.020
