COMPARATIVE BENTHIC PALEOECOLOGY OF TWO LARGE BOLIDE IMPACT EVENTS: CHICXULUB AND MANICOUAGAN

Large bolide impact events have occurred throughout the Phanerozoic, but only the Late Cretaceous Chicxulub impact is associated with catastrophic global extinctions. Numerous parameters contributed to the degree of biotic response to the Chicxulub event, and these characteristics may be directly compared to those of other large impact events. An integrated examination of the physical and ecological traits of these large impact events illustrates the resilience of some paleocommunities, and not others, to catastrophic environmental perturbations.

The Chicxulub crater (180 km diameter) may be compared to the Manicouagan impact crater in Quebec, originally 100 km in diameter and dated to 214 ± 1 Ma (mid-Late Triassic) using U-Pb from zircons. This impact event is not associated with extensive extinction, despite having been one of the largest impact events of the Phanerozoic. This disparity in biotic response to comparably-sized impact events can only be partly explained by differences in the physical parameters of the two events, such as host material and location.

Paleoecological analyses of shallow marine communities from the latest Cretaceous and mid-Late Triassic reveal differences in ecological structure preceding the impact events that contributed to the degree of biotic response. During the Norian stage, at the time of the Manicouagan impact, shallow marine communities were primarily composed of wide-ranging generalist taxa that created homogenous niches, with the notable exception of the suspension-feeding epifauna. This life-habit was utilized by a variety of groups that oscillated in abundance throughout the period, but retained the same proportion of the community overall. End-Cretaceous communities were composed of more niches that were filled with greater numbers of groups that had more complex ecological relationships. Survivors of the K/T impact event could opportunistically exploit multiple ecological relationships or were specialized for niches that tended to require fewer ecological interactions, such as deposit-feeding infauna.

Previous research has shown that paleoecological trends in survivorship are evident through the K-T boundary. During catastrophic events, biotic resistance to extinction may extend beyond specific morphologies to community-level attributes.