The impact of the Maastrichtian cooling on the marine nutrient regime—Evidence from midlatitudinal calcareous nannofossils

Abstract

The latest Campanian-earliest Maastrichtian interval is well known as a period of intense climate cooling. This cooling caused a distinctive bipolar biogeographic distribution of calcareous nannofossil assemblages: High-latitude settings were dominated by newly evolving endemic taxa, former cosmopolitan species disappeared at the same time, and equatorial communities experienced an invasion of cool water taxa. The impact of this cooling on northern midlatitude assemblages is, however, less well known. In order to overcome this gap we studied the Kronsmoor section (northwest Germany). This section provides a continuous upper Campanian-lower Maastrichtian succession with moderately to well preserved nannofossils. Uppermost Campanian assemblages are dominated by Prediscosphaera cretacea; other common taxa include Prediscosphaera stoveri, Watznaueria barnesiae, and Micula staurophora. The lower Maastrichtian is characterized by lower numbers of P. cretacea and frequent Kamptnerius magnificus, Arkhangelskiella cymbiformis, and Cribrosphaerella ehrenbergii. These changes reflect, in part, the Campanian-Maastrichtian boundary cooling since some successful taxa (e.g., K. magnificus) are related to cool surface waters. Other shifts in the nannofossil communities were perhaps the result of a changing nutrient regime. Stronger latitudinal gradients may have increased wind velocities and thus the eolian input of ferruginous dust required by N-fixing bacteria. The enhanced high-latitude deep water formation probably changed the bottom water environment in disfavor of denitrificating organisms. A decline of chemical weathering and fluviatile transport may have reduced the amount of bioavailable phosphate. These processes led to an increased nitrate and a decreased phosphate content shifting the nutrient regime from nitrate toward phosphate limitation.

Global ecomorphological restructuring of dominant marine reptiles prior to the Cretaceous–Palaeogene mass extinction

“…The cause behind the abrupt shift in mosasaurid community composition across the ‘Niobraran–Navesinkan’ is as yet unclear. A decrease in global oceanic temperature between the mid- and late Campanian is coincident with the turnover [6,50] . Such a shift in temperatures would have affected multiple habitats, potentially driving a pre-Maastrichtian restructuring of marine reptile communities in deep- and shallow-water biomes [11].…”

Global ecomorphological restructuring of dominant marine reptiles prior to the K/Pg mass extinction

“…The cause behind the abrupt shift in mosasaurid community composition across the ‘Niobraran-Navesinkan’ is as yet unclear. A decrease in oceanic temperature between the mid- and late-Campanian is coincident with the turnover (Polcyn et al 2014; Linnert et al 2016), which essentially removed smaller species within multiple clades (e.g. Selmasaurus, Plesioplatecarpus, Tylosaurus kansasensis ).…”

Calcareous nannofossil assemblages of the Late Cretaceous Fiqa Formation, north Oman

“…This basin formed as a result of crustal loading associated with over-thrusting and emplacement of oceanic crust known as the Sumail ophiolite and other associated sheets onto the eastern margin of the Arabian Peninsula (Bechennec et al, 1990). This occurred as a result of a major compressional tectonic phase associated with the closure of the Neotethys Ocean (Lippard et al, 1986). The basin was deeper proximal to the thrusted sheets in the north and west of Oman and shallowed toward the southeast as seen from seismic and well data (Forbes et al, 2010).…”