Abstract The Jenkyns Event or Toarcian Oceanic Anoxic Event was an episode of severe environmental perturbations reflected in carbon isotope and other geochemical anomalies. Although well studied in the epicontinental basins in NW Europe, its effects are less understood in open marine environments. Here we present new geochemical (carbon isotope, CaCO 3 , [Mn]) and nannofossil biostratigraphic data from the Tölgyhát and Kisgerecse sections in the Gerecse Hills (Hungary). These sections record pelagic carbonate sedimentation near the margin of the Tethys Ocean. A negative carbon isotope excursion of c. 6‰ is observed in the Tölgyhát section, in a condensed clay and black shale layer where the CaCO 3 content drops in association with the Jenkyns Event. At Kisgerecse, bio- and chemostratigraphic data suggest a gap in the lower Toarcian. The presence of an uppermost Pliensbachian hardground, the absence of the lowermost Toarcian Tenuicostatum ammonite zone and the condensed record of the Jenkyns Event at Tölgyhát, together with a condensed Tenuicostatum Zone and the missing negative carbon isotope anomaly at Kisgerecse, imply arrested carbonate sedimentation. A calcification crisis and sea-level rise together led to a decrease in carbonate production and terrigenous input, suggesting that volcanogenic CO 2 -driven global warming may have been their common cause.

Abstract The benthic foraminifera have been studied from a large number of samples collected from successions both in, and close to, the Brazos River (Falls County, Texas, U.S.A.) and from the cliffs of Stevns Klint (south of Copenhagen, Denmark). The sections from the Brazos River contain extensive and nearly continuous outcrops, recording the so-called “event” deposits and the Cretaceous–Paleogene boundary. Micropaleontological analysis of samples taken from the Mullinax-1 core, and some of the exposures in the Brazos River (and tributaries), have been investigated for benthic and planktic foraminifera, all of which are indicative of relatively shallow shelf conditions. The benthic foraminifera suffer a significant loss of diversity at the level of the “event” deposits, which appear to predate the micropaleontological Cretaceous–Paleogene boundary, but no mass extinction is recorded. The agglutinated taxa almost disappear at this level, and the faunal changes indicate that there may have been a shallowing at that time. The benthic foraminifera from Stevns Klint are very different from those recorded in Texas, being typical of assemblages in the chalk facies of northwestern Europe. At the base of the Højerup Member (previously known as the Grey Chalk) there are significant changes in the benthic assemblage, again suggestive of a shallowing event at the level of two closely spaced hardgrounds, which often merge into a single horizon. The “event” deposits of the Brazos River successions may, therefore, be related to events associated with the hardground horizon at Stevns Klint, and the evidence for this interpretation is presented. This, and other, correlations provide data for the construction of a sequence stratigraphy for the Cretaceous–Paleogene boundary interval.