Constraining mass accumulation rates across the Cretaceous-Paleogene boundary clay layer using extraterrestrial helium-3

The extended duration of the negative δ¹³C excursion observed in marine carbonates spanning the Cretaceous-Paleogene (K-Pg) mass extinction event has lead to two main hypothesized post-extinction models ("Strangelove" and "Living Ocean";[1, 2]) for the status of marine primary productivity and the global carbon cycle. However, these models are largely inconsistent with recent paleontological and geochemical evidence suggesting heterogeneous changes in marine productivity and carbon export [3, 4]. While the analysis of lipid biomarkers in the cosmopolitan boundary clay layer allows us to assess changes in primary production by non-calcifying organisms in the immediate aftermath of the mass extinction [4], our poor understanding of the deposition of the clay layer precludes a more detailed reconstruction of short-term variations in marine ecosystem resilience. Here, we present data on extraterrestrial ³He derived from interplanetary dust particles used as a constant flux proxy to constrain fluctuations in mass accumulation rates (MARs) [5] and the duration of the boundary clay deposition in three classic and expanded K-Pg boundary sections: El Kef (Tunisia), Caravaca (Spain), and Kulstirenden (Denmark). Our results from different depositional environments indicate average durations for the sedimentation of the clay layer that are comparable (~10 kyr) to other localities [5], thus confirming its globally brief deposition. Early Paleogene MARs vary among locations when compared to background Late Cretaceous values and do not strictly follow carbonate content as traditionally assumed, thus suggesting variable depositional conditions at different locations. Changes in sediment MARs across the K-Pg will be used to calculate MARs of algal- and bacterial-derived biomarkers, as well as benthic foraminifera, in order to assess the timing and global nature of the recovery of marine primary production and carbon export. 1. Hsu, K.J., He, Q., Mckenzie, J.A., Weissert, H., Perchnielsen, K., Oberhansli, H., Kelts, K., Labrecque, J., Tauxe, L., Krahenbuhl, U., et al. (1982). Mass Mortality and Its Environmental and Evolutionary Consequences. Science 216, 249-256. 2. D'hondt, S. (1998). Organic carbon fluxes and ecological recovery from the Cretaceous-Tertiary mass extinction (vol 282, pg 276, 1998). Science 282, 1051-1051. 3. Alegret, L., Thomas, E., and Lohmann, K.C. (2012). End-Cretaceous marine mass extinction not caused by productivity collapse. P Natl Acad Sci USA 109, 728-732. 4. Sepulveda, J., Wendler, J.E., Summons, R.E., and Hinrichs, K.U. (2009). Rapid Resurgence of Marine Productivity After the Cretaceous-Paleogene Mass Extinction. Science 326, 129-132. 5. Mukhopadhyay, S., Farley, K.A., and Montanari, A. (2001). A short duration of the Cretaceous-Tertiary boundary event: Evidence from extraterrestrial helium-3. Science 291, 1952-1955.