MODIFYING CLIMATE PROXY RECORDS THROUGH AUTOGENIC SEDIMENTATION: MODELING AND EXAMPLES FROM THE PALEOCENE-EOCENE THERMAL MAXIMUM

The alluvial record of the Paleocene Eocene Thermal Maximum (PETM) can help us understand how river systems may respond to rapid global warming. Autogenic landscape dynamics can complicate interpretations of PETM deposits, particularly because processes like river avulsion impose a large degree of variability in local and regional sedimentation rates on alluvial landscapes. It is even unclear the degree to which geochemical proxy records – such as the carbon isotope excursion (CIE) that defines the PETM – can be obscured or modified due to autogenic dynamics in sedimentary systems. Different sedimentary systems have different inherent autogenic sedimentation fluctuations, which may control the preservation of geochemical proxy records within different alluvial systems. Currently, we lack the tools to quantitatively assess how autogenic sedimentation may have influenced any given PETM CIE record. Here we model the effect of autogenic sedimentation on the preservation of the PETM CIE in sedimentary environments characterized by different autogenic dynamics using a 1D stochastic sedimentation model, where we control the magnitude, frequency, and probability of sedimentation-rate variations to simulate proxy-records developed within different environments. We find that even with conservative estimates for the magnitude and frequency of autogenic variability in sedimentation, there is a significant probability that the apparent duration, magnitude, and overall shape of the PETM CIE has been significantly altered in fluvial settings. Our model results are consistent with differences between existing PETM CIE records found within alluvial records in the Bighorn Basin, Wyoming and Piceance Basin, Colorado. This suggests that variability in the shape and duration of the CIE recorded in alluvial settings may be due entirely to autogenic dynamics in fluvial depositional systems.