Gansserina

Abstract: A new chronostratigraphic framework is presented for upper Campanian-Maastrichtian pelagic sediments cored at DSDP/ODP Sites 390A/1049, 1050, and 1052, which were drilled across a 1300-m depth transect on the Blake Nose (subtropical western Atlantic Ocean). The planktonic foraminiferal zonation is based on standard global biozones for this interval, but rare and sporadic occurrence of two zonal biomarkers, Gansserina gansseri and Globotruncana aegyptiaca , precludes reliable identification of the nominate zones for those species. The Pseudoguembelina palpebra Partial-range Zone is defined as a means of subdividing this upper Campanian biostratigraphic interval. Planktonic foraminiferal, calcareous nannofossil and paleomagnetic datums are integrated to construct reliable age-depth curves for each of the Blake Nose drill sites. These age models are largely confirmed by Sr-isotopic data and suggest significant unconformities at various positions within the sections. Compilation of stable isotope datasets for this time interval from the Blake Nose sites reveals no significant shifts in δ 18O and δ 13C at the time of the inoceramid bivalve extinction (now dated as 68.5–68.7 Ma in the Blake Nose sections) and no correlation with proposed Campanian-Maastrichtian glacial intervals. However, benthic warming associated with Deccan volcanism during the late Maastrichtian is supported.

Abstract: An outer shelf–upper slope tropical Tethyan pelagic environment existed over southern Israel during Maastrichtian time. Planktic foraminifera in the >63 and >149 µm size fractions from four sections in this area were studied quantitatively for a high-resolution ecostratigraphic analysis of the pre–Cretaceous-Tertiary (K-T) paleoenvironment. During the Maastrichtian, 41% of the planktic foraminifera species became extinct, mostly keeled Globotruncanidae , which also became quantitatively reduced near the end of the Maastrichtian from as much as 35% to only 5% of the planktic foraminifera population. Evolutionary replacement of extinct species by new forms nearly ceased in that interval. Two major opportunistic blooms of Guembelitria took place, associated with reduced abundances of keeled forms and the dominant species Heterohelix globulosa . The first bloom occurred within the upper Gansserina gansseri to lower Abathomphalus mayaroensis Zones and the second within the Plummerita hantkeninoides Zone. The extinctions, concomitant changes in faunal dominance, and opportunist blooms indicate that the pelagic ecosystem in the Negev area experienced multiple stresses during the Maastrichtian. The planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the K-T boundary crisis.