INFLUENCE OF IMPACT SITE PROXIMITY TO K/PG RECOVERY OF ECOSYSTEM STRUCTURE AND DIVERSITY: NEW INSIGHT FROM THE GULF COASTAL PLAIN AND ATLANTIC COASTAL PLAIN

The Cretaceous/Paleogene (K/Pg) boundary outcrops throughout the Atlantic Coastal Plain (ACP) and Gulf Coastal Plain (GCP). This boundary represents the last major mass extinction event where more than 70% of marine species died out. Although the cause of the extinction has been widely studied and debated, the post-extinction recovery period has received much less attention. Recently, new K/Pg boundary exposures have been discovered in both the ACP and GCP, providing new insight into how marine invertebrate fauna were affected by the impact, and how ecosystems were restructured once the environment stabilized. These sections reveal patterns of survivorship and recovery in both distal and proximal settings to the impact site in Chixculub, Mexico. Lower Agony Creek (Monmouth Co. NJ) represents a distal site in the ACP, whereas Starkville (Oktibbeha Co. MS), Prairie Bluff Landfill (Chickasaw Co. MS), Moscow Landing (Marengo Co. AL) and Mooseland (Wilcox Co. AL) represent proximal sites in the GCP. The ACP site is dominated by suspension feeders, suggesting a fast recovery or diminished effects from the impact compared to previous investigations by Gallagher (2002). GCP sites mostly match the two-phase model of Hansen (1989): during the initial “ecological recovery phase” surviving taxa are dominated by scavenger-carnivores. These taxa are likely abundant due to diminished primary production that limited resources for suspension feeders in perturbed post-impact ecosystems. The later “radiation phase” shows a reappearance and dominance of suspension feeders, suggesting a return of primary production providing resources for these taxa to thrive. A third phase preceding Hansen’s “ecological recovery phase” is observed in some GCP sites, where recovery ecosystems are composed of rare occurrences of a single taxa of suspension feeding bivalves. This likely reflects the extremely perturbed environment proximal to the impact site that is only able to support few, specific taxa. Comparing patterns of survivorship and recovery shows a strong correlation between later stages of recovery in the GCP to earlier stages of recovery in the ACP, suggesting diminished effects from the impact or more time missing in the ACP. This is congruent with an asteroid impact extinction mechanism proximal to the GCP and more distal to the ACP.