Global bioevents and the Cretaceous/Paleogene boundary in Texas and Alabama: Stratigraphy, correlation and ocean acidification

Abstract

With increasing levels of atmospheric pCO 2 the oceans are becoming progressively more acidic, with the impact of a lowered pH beginning to affect the calcification of numerous invertebrate groups, including foraminifers, pteropods, heteropods and calcareous nannoplankton. Research on the ecology of foraminifera in the Mediterranean Sea, Gulf of California, Caribbean Sea and elsewhere has shown how modern assemblages are responding to acidification. Experimental work in mesocosms and laboratory cultures are also adding to our knowledge of the response to pH changes. Near Ischia (Italy), natural CO 2 vents amongst sea grass meadows are creating low pH environments in which it is possible to observe the response of benthic foraminifera. At a pH of 7.8 the foraminiferal assemblages are already becoming less diverse and below pH 7.6 there are often no calcite-secreting benthic foraminifera. In the Gulf of California, in a deeper-water setting, natural CO 2 (and methane) vents are also lowering sea floor pH. The foraminifera show the impact of this change, although the relatively high carbonate saturation ensures that calcite-secreting foraminifers are able to live and reproduce in these relatively low pH environments, only becoming impacted by dissolution effects once dead. Using data from the Cretaceous-Paleogene boundary in Texas, Alabama and northwest Europe it is clear that the plankton was severely impacted by surface water acidification

Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact

“…This measured pH drop may be a conservative estimate of the full magnitude of impact-induced acidification, as the earliest Ir-rich ejecta layer at Geulhemmerberg is thought to have been eroded within ∼100 y of the impact (6). A geologically rapid 0.2 to 0.3 pH unit change would have disadvantaged calcifying plankton vs. noncalcifiers (9) and could therefore explain the selective extinction of calcifying pelagic organisms during the K-Pg mass extinction (10–13) compared to noncalcareous groups such as dinoflagellates (e.g., ref. 14) and radiolarians (e.g., ref.…”

Cephalopods from the Cretaceous-Paleogene (K-Pg) Boundary Interval on the Brazos River, Texas, and Extinction of the Ammonites

“…In this latter hypothesis, the K-Pg boundary was placed at the top of the event deposit, coincident with the highest occurrence of identifiably Cretaceous microfossils. This hypothesis is not well supported on either sedimentological or paleontological grounds (see discussions in Bralower et al, 2010;Hart et al, 2012Hart et al, , 2019Yancey and Liu, 2013).…”

“…3). The lithostratigraphic contact, an irregular surface with up to 2 m relief across the Brazos outcrop belt, marks the K-Pg boundary (Hansen et al, 1993;Hart et al, 2012;Yancey and Liu, 2013;Hart et al, 2019; fig. 2A, C).…”

“…This has included (mis)interpretation of volcanic ash beds (referred to as "yellow clay" in some papers) in the Corsicana Formation as impact ejecta layers and evidence for a pre-K-Pg timing of the Chicxulub impact event (e.g., Keller et al, 2007;. Recent work has sought to resolve these issues and develop a stratigraphic framework that can be accurately correlated to the international timescale (e.g., Hart et al, 2012Hart et al, , 2019Yancey and Liu, 2013;Leighton et al, 2017). Additional research has also better defined the K-Pg boundary based on the GSSP at El Kef, Tunisia, and elsewhere (Molina et al, 2006;2009).…”

Longer-term terrestrial responses in the aftermath of the end-Cretaceous mass extinction

“…Consequently, transient (< ~1 Kyr, millennia years) deterioration and recovery of ecosystem, environment and climate immediately following the Cretaceous/Paleogene boundary (K/PgB) have been well illustrated in marine environment anomalies in temperature (e.g., Vellekoop et al, 2016;Woelders et al, 2017;Barnet et al, 2018), bioproductivity (e.g., Donovan et al, 2016;Henehan et al, 2016), surface ocean acidification (D'Hondt et al, 1994;Kring, 2007;Ohno et al, 2014;Tyrrell et al, 2015;Hart et al , 2019;Henehan et al 2019), methane emission (Beerling et al 2002), extinction of pelagic calcifiers (e.g., D'Hondt and Keller, 1991;Bown, 2005), food web collapse (Coccioni and Marsili, 2007), carbonate dissolution (Coccioni et al, 2012;Henehan et al, 2016); and also in the terrestrial realm by biota (e.g., Vajda et al, 2001;Wilf et al, 2003;Coccioni and Marsili, 2007), geochemistry (e.g., Sepúlveda e al., 2009;Nordt et al, 2011;Gao et al, 2021), carbon and oxygen isotopes (Nordt et al, 2002(Nordt et al, , 2003Gao et al, 2015;Zhang et al, 2018), subaerial temperature (Nordt et al, 2003;Dworkin et al, 2005;Zhang et al, 2018), atmospheric CO 2 concentrations (i.e. the partial pressure, pCO 2 ; e.g., Nordt et al, 2002Nordt et al, , 2003Gao et al, 2015), magnetic susceptibility (Ma et al, 2018), total Hg/TOC ratios (e.g., Keller et al, 2020;…”