Short-Term Survival of Ammonites in New Jersey After the End-Cretaceous Bolide Impact

Abstract

A section containing the Cretaceous/Paleogene (= Cretaceous/Tertiary) boundary in Monmouth County, New Jersey, preserves a record of ammonites extending from the end of the Cretaceous into possibly the beginning of the Danian. The section includes the upper part of the Tinton Formation and lower part of the Hornerstown Formation. The top of the Tinton Formation is represented by a richly fossiliferous unit (the Pinna Layer) that contains many bivalves in life position as well as ammonite jaws preserved inside body chambers. Ammonites include Pachydiscus (Neodesmoceras) mokotibensis, Sphenodiscus lobatus, Eubaculites carinatus, E. latecarinatus, Discoscaphites iris, D. sphaeroidalis, D. minardi, and D. jerseyensis. The Pinna Layer probably represents a relatively short interval of time lasting tens to hundreds of years; it is conformably overlain by the Burrowed Unit, which contains a single fragment of Discoscaphites sp. and several fragments of E. latecarinatus , as well as several isolated specimens of ammonite jaws including two of Eubaculites. Examination of the mode of preservation of the ammonites and jaws suggests that they were fossilized during deposition of the Burrowed Unit and were not reworked from older deposits. Based on the ammonites and dinoflagellates in the Pinna Layer and the Burrowed Unit, these strata traditionally would be assigned to the uppermost Maastrichtian, corresponding to calcareous nannofossil Subzone CC26b. However, a weak iridium anomaly (500-600 pg/g) is present at the base of the Pinna Layer, which presumably represents the record of the bolide impact. Correlation with the iridium layer at the Global Stratotype Section and Point at El Kef, Tunisia, would, therefore, imply that these assemblages are actually Danian, provided that the iridium anomaly is in place and the ammonites and dinoflagellates are not reworked. If the iridium anomaly is in place, or even if it has migrated downward from the top of the Pinna Layer, the ammonites would have survived the impact at this site for a brief interval of time lasting from a few days to hundreds of years.

Paleobiogeography of Late Cretaceous Ammonoids

“…Occasionally, ammonoids are recorded from the earliest Paleogene, among them Discoscaphites iris and Hoploscaphites constrictus (Wiedmann 1988;Kennedy 1989Kennedy , 1993Birkelund 1993;Surlyk and Nielsen 1999;Machalski 2002Machalski , 2005Machalski and Heinberg 2005;Landman et al 2012), and most findings are clearly not reworked. These last representatives of the Ammonoidea occurred only in middle to high latitudes, but not in low latitudes (Stinnesbeck et al 2012).…”

“…Some of them are from the conservative taxa that evolved during the Campanian. In addition, ecologically very resistant species evolved like Hoploscaphites constrictus (Machalski 2005;Salazar et al 2010;Machalski et al 2012), Discoscaphites iris (Landman et al 2010(Landman et al , 2012, or Sphenodiscus pleurisepta (Ifrim and Stinnesbeck 2010;Landman et al 2010). None of the last North American Ammonoidea belongs to the conservative taxa, which are present virtually anywhere else.…”

Cretaceous-Paleogene Dinoflagellate Biostratigraphy and the Age of the Clayton Formation, Southeastern Missouri, USA

“…Equally interesting is the fact that there are other locations around the periphery of the Mississippi Embayment, particularly on its eastern side, at which an End-Cretaceous impact signature is also missing and at which a Danian age erosional surface has been identified [83][84][85][86]. In addition, the Cretaceous-Paleogene sequence in New Jersey also contains evidence of hiatuses in the Danian [55,56,87]. We suggest that some Mississippi Embayment occurrences, and possibly one or more of those in New Jersey also, are linked in the sense that they were produced by the same sequence stratigraphic erosive event.…”

“…The effects of this event appear to vary geographically. At Starkville, Mississippi, the End-Cretaceous part of the sequence is obliterated [85,86]; at our site near Bloomfield, Missouri, some End-Cretaceous sedimentary features remain (e.g., the layered tektites); at sites in Monmouth County, NJ, End-Cretaceous events appear to be largely preserved undisturbed [87]. Local depositional and paleoenvironmental conditions seem to have played a guiding role in producing the disparate character with which the Late Cretaceous-Early Paleogene record is expressed in the sediments of the Atlantic and Gulf Coastal Plains and of the Mississippi Embayment.…”

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

“…However, the Pinna Layer occurs above a horizon with a weak iridium anomaly (520 pg/g). The crucial question is whether this iridium anomaly represents the record of the bolide impact and, if so, whether it is in place or has migrated downward (Landman et al 2007(Landman et al , 2012bMiller et al 2010; for additional discussion about the remobilization of iridium, see Racki et al 2011). For example, if the iridium anomaly is in place, then the ammonites in the Pinna Layer and the Burrowed Unit may have been short-term survivors of the bolide impact, possibly persisting into the earliest Danian.…”