Discovery of fish mortality horizon at the K-T Boundary on Seymour Island: Re-evaluation of events at the end of the Cretaceous

Abstract

The discovery of a fish bone layer immediately overlying the K-T iridium anomaly on Seymour Island, Antarctic Peninsula, which may represent the first documented mass kill associated with the impact event, together with new faunal data across the boundary has provided new insight into events at the end of the Cretaceous. The utilization of a geographical approach and a new graphical representation of range data has revealed that events at the end of the Cretaceous were not instantaneous, but occurred over a finite period of time. Although the fish bone layer may contain victims of the impact event, the absence of ammonites in either the iridiumbearing layer or the overlying fish layer suggests that the extinction event at the end of the Cretaceous was the culmination of several processes beginning in the late Campanian. The impact was the proverbial “straw that broke the camel's back,” leading to the extinction of many others forms of life that might have survived the period of global biotic stress during the waning stages of the Mesozoic if there had not been an impact. The absence of mass extinction following catastrophic geologic events in a biotic robust world, such as the Middle Ordovician Millbrig-Big Bentonite volcanic event suggests that the biosphere is remarkably resilient to major geologic catastrophes with mass extinction events occurring only when there is a conjunction of geologic events none of which might be capable of producing a global mass extinction by itself.

Evolution and extinction of Maastrichtian (Late Cretaceous) cephalopods from the López de Bertodano Formation, Seymour Island, Antarctica

“…4) et al, 2012). The highest ammonite occurrence is less than 50 cm below the base of the glauconite 359 sandstone containing the iridium anomaly and K-Pg boundary (Zinsmeister, 1998). 360…”

“…Previous authors have suggested that this upper portion of the succession across the K-Pg 126 boundary represents a regressive phase and loss of accommodation space (Macellari, 1988; Crame et 127 al., 2004;Olivero, 2012a). The base of a prominent series of glauconite horizons~1000 m above the 128 base of the sequence coincides with a distinct change in both macro and microfossil faunas and floras 129 (Elliot et al, 1994;Zinsmeister, 1998; Crame et al, 2004;Stilwell et al, 2004; Bowman et al, 2012), 130 and is interpreted as being equivalent to the 'K-T glauconite' succession of Zinsmeister (1998) (Fig. 131 2).…”

“…298 No definitively in situ cephalopod fossils were found above the K-Pg boundary, although 299 poorly preserved ammonites have been previously reported from this interval on Seymour Island 300 (Sadler, 1988;Zinsmeister et al, 1989). Zinsmeister (1998) considered these to be the result of local 301 inliers of Cretaceous-aged sediment in the broad dip-slopes of the Paleocene unit 'Klb10' but our 302 recent observations indicate that their positions may be the result of recent transport due to glacial 303 action, and they are therefore considered reworked. 304…”

“…Whilst previous studies (e.g. Macellari, 1986;Zinsmeister, 1998; Zinsmeister, 85 2001) have also illustrated cephalopod range data from this succession, our study involves systematic 86 high-resolution sampling tied to measured sedimentary sections in the field, allowing for accurate 87 5 stratigraphic location of individual fossils. In addition, we have undertaken a taxonomic review of the 88 fauna (see Appendix 1) and compared our data to newly developed age models (e.g.…”

Ammonites on the Brink of Extinction: Diversity, Abundance, and Ecology of the Order Ammonoidea at the Cretaceous/Paleogene (K/Pg) Boundary

“…(Site 29). The section at Seymour Island has been extensively studied (Macellari 1986(Macellari , 1988Elliot et al 1994;Zinsmeister and Feldmann 1996;Zinsmeister 1998;Zinsmeister et al 1989;Tobin et al 2012). The sequence consists of mid-shelf clastic to inner-shelf concretionary siltstones and silty sandstones of the López de Bertodano Formation.…”