Abstract:
Late Cretaceous (100-73 Ma) pelagic limestones were measured for helium concentration and isotopic composition to characterize the interplanetary dust flux using (super 3) He as a tracer. In the Bottaccione section near Gubbio, Italy, three intervals of elevated (super 3) He concentration were detected: K1 in the Campanian stage at approximately 79 Ma, K2 in the Santonian stage at approximately 85 Ma, and K3 in the Turonian stage at approximately 91 Ma. All three of these episodes are associated with high (super 3) He/ (super 4) He and (super 3) He/non-carbonate ratios, consistent with their derivation from an enhanced extraterrestrial (super 3) He flux rather than decreased carbonate sedimentation or dissolution. While K2 is modest in magnitude and duration and thus is of limited significance, K1 and K3 are each identified by a few myr interval with an approximately 4-fold enhancement in mean (super 3) He flux compared with pre-event levels. Samples from ODP Hole 762C in the Indian Ocean spanning both K2 and K3 (93-83 Ma) confirm the presence of a peak in the Turonian stage, suggesting that K3 is a global event. The K1 and K3 (super 3) He events are similar in most respects to the two peaks previously detected in the Cenozoic, suggesting a similar origin. These have been attributed to a major asteroid collision in the Late Miocene and to a shower of either comets or asteroids in the Late Eocene. Based on the age and temporal evolution of K1, we suggest that it most likely records the collision which produced the Baptistina asteroid family independently dated at approximately 80 Ma. The K3 event is less easily explained. It is characterized by an unusually spiky and erratic temporal progression, suggesting an unusual abundance of very (super 3) He rich particles not previously seen in the sedimentary (super 3) He record. We suggest this episode arises either from a comet shower or from an asteroid shower possibly associated with dust-producing lunar impacts. Abstract Copyright (2012) Elsevier, B.V.