Abstract
The southernmost Cretaceous – Paleogene (K-Pg) outcrop exposure is the well-studied exposure on Seymour Island, Antarctica. Deposition across the K-Pg boundary there is uninterrupted, and as a consequence the ammonite fossil record is commonly used to test statistical methods of evaluating mass extinctions to account for the incompleteness of the fossil record. Numerous detailed fossil data sets from Seymour Island, comprised dominantly of mollusks, have been published over the last 30 years, but in most cases have not received statistical treatment. Here a previously published statistical technique is modified, automated, and applied to all published macrofossil data sets available from Seymour Island. All data sets reveal likely evidence of two separate multi-species extinctions, one synchronous with bolide impact evidence at the K-Pg boundary, and another 45 ± 15 meters (~140–290 ky) below the boundary. The apparent earlier extinction primarily affects benthic mollusks, while the boundary extinction primarily affects ammonites. While there is no unique sedimentological change over the interval where the earlier extinction is identified, it is impossible to exclude the possibility that this pattern is stratigraphically controlled. The automation of this technique allows it to be applied easily to other large fossil data sets.
Highlights
The End Cretaceous, or Cretaceous – Paleogene, Mass Extinction, is the most recent of the major mass extinctions of the Phanerozoic, and has drawn significant research interest
This data has been used previously in assessing the rapidity of the K-Pg mass extinction[26,28,29], generally with the conclusion that the extinction of ammonites on Seymour Island (SI) was consistent with a sudden rapid extinction like that caused by a bolide impact
The multi-taxon confidence interval (MTCI) width pattern is smaller than the 2.5% percentile window only at the K-Pg boundary, indicative of a single phase extinction for ammonites, as found in previous studies
Summary
The End Cretaceous, or Cretaceous – Paleogene, Mass Extinction, is the most recent of the major mass extinctions of the Phanerozoic, and has drawn significant research interest. Independent data sets of molluscan fossils from SI have been used to argue for both a multi-phase[17] and single phase[25] extinction across the K-Pg boundary To resolve this discrepancy, I have modified a previously published approach to estimating the confidence interval (in terms of stratigraphic width) of a multi-species extinction[27], and applied it to every available macro-fossil data set from SI25,33–35. Seymour Island (SI) is part of the James Ross Island Group located off the northeastern tip of the Antarctic Peninsula (Fig. 1) It has experienced little tectonic activity and has not appreciably changed its latitude since deposition[17], and the lack of alteration or significant burial has resulted in exceptional fossil preservation in terms of absolute numbers, three-dimensional morphology, and skeletal geochemistry. The basin preserves sediment from the Aptian-Albian through the Eocene, but the Maastrichtian through Danian interval on SI (López de Bertodano Formation – LBF) is probably the most well-studied due to preservation of uninterrupted deposition across the K-Pg boundary[39,40,41,42,43]
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