Establishing geochemical constraints on mass accumulation rates across the Cretaceous-Paleogene boundary with extraterrestrial Helium-3

Abstract

Records of ocean biogeochemistry in marine sediments show shifts across the Cretaceous-Paleogene boundary (K-Pg) that are simultaneous with the extinction event and onset of the boundary clay deposition. However, the timescale of these records is difficult to determine near the boundary because of fluctuating sedimentation rates and the short duration of the event. In this study, we have used extraterrestrial helium-3 as a constant flux proxy for instantaneous mass accumulation rates in four marine sections: Caravaca, Spain; El Kef, Tunisia; and Hojerup and Kulstirenden, Denmark. These sections are characterized by a thick boundary clay layer and, therefore, are more suitable than many other proxies for high-resolutions studies. In order to better understand the extent of the impact-related perturbations in different paleoenvironments, we performed a high-resolution analysis at Caravaca and lower-resolution analyses at the other three sections. We find that Hojerup and Kulstirenden are not suitable for this analysis due to the probable variation in the flux of extraterrestrial helium-3 as a result of lateral changes in sedimentation rate. Our results suggest that carbonate burial, and likely carbonate production, were more severely affected with increasing paleolatitude. However, the unique depositional environments are probably much more important than just paleolatitude alone. We calculate boundary clay durations of Caravaca and El Kef of 6.45 (h 0.86) kyr and 6.28 (± 1.03) kyr, respectively. These results are consistent with other studies and indicate a uniform, global deposition of the boundary clay and a rapid recovery of carbonate burial in the marine ecosystem after the Cretaceous-Paleogene extinction event.