Sea Grass Meadow and Foraminifera Relationship may Predate the Cretaceous-Paleogene Mass Extinction

The Cretaceous/Paleogene boundary: Foraminifera, sea grasses, sea level change and sequence stratigraphy

Authors:

Hart et al

Abstract:

The tsunami generated by the Chicxulub impact eroded the uppermost Cretaceous surface of the Gulf Coast region (U.S.A.) forming a distinctive topography that was previously interpreted as a sequence boundary. At more distal sites, such as Stevns Klint (Denmark), there appears to be no sequence boundary at the Cretaceous/Paleogene boundary but there is one within the uppermost Maastrichtian, between the Sigerslev and Højerup members, and another in the lowermost Paleocene (top of Zone P1a). Both of these surfaces are identified by distinctive, phosphatized, and incipient hardgrounds. The changes in sea level involved in the generation of uppermost Cretaceous sequences are thought to have been minimal as, in the Gulpen and Maastricht formations of the Maastricht area (Netherlands), the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis (less than 20 m), even across the postulated sequence boundaries. The assemblages of foraminifera associated with sea grasses in the uppermost Maastrichtian are comparable in morphology with those associated with modern sea grass meadows and indicate a relationship that may have existed since, at least, the latest Cretaceous.

Gerta Keller Strikes Back: Maastrichtian Cretaceous a High Stress Environment due to Deccan Vulcanism

Late Maastrichtian–early Danian high-stress environments and delayed recovery linked to Deccan volcanism

Authors:

Punekar et al

Abstract:

Deccan volcanism occurred in three intense phases of relatively short duration: phase 1 spanning the paleomagnetic chron C30r/C30n boundary (planktic foraminiferal CF4), phase 2 in the latest Maastrichtian C29r (zones CF1–CF2), and phase 3 in the early Danian C29n (P1b). This study explores the nature of paleoenvironmental changes correlative with the three volcanic phases in central Egypt and the Sinai based on planktic foraminifers, stable carbon and oxygen isotopes.

Results show that high-stress assemblages dominated by Guembelitria blooms are prominent in, but not exclusive to, all three volcanic phases. These blooms are well known from the aftermath of this mass extinction in zones P0–P1a, the intertrappean interval between volcanic phases 2 and 3. Guembelitria blooms in CF4 (phase 1) are relatively minor (less than 45% ) although they comprise a substantial component of the planktic foraminiferal assemblages. Maximum Guembelitria blooms (greater than 80% of the total assemblage) are observed in CF1, which spans the last 160 ka of the Maastrichtian marked by rapid global climatic warming and cooling correlative with phase 2. Major Guembelitria blooms (50–75%) are also observed in P1b, which is marked by climate warming (Dan-C2 event) and a major negative carbon isotope excursion correlative with phase 3. This high-stress event precedes full marine biotic recovery after the mass extinction.

Toarcian Jurassic Oceanic Anoxic Event Evidence From Foraminifera and Ostracods Isotopic Evidence

Stable isotopes on foraminifera and ostracods for interpreting incidence of the Toarcian Oceanic Anoxic Event in Westernmost Tethys: Role of water stagnation and productivity

Author:

Matías Reolid

Abstract:

The analysis of δ13C and δ18O from whole rock and the shells of selected foraminifera (Lenticulina and Dentalina) and bairdioid ostracods from Lower Toarcian of the South Iberian Palaeomargin (Western Tethys) is presented with the aim of improving knowledge of the processes and the environmental effects of the Toarcian Oceanic Anoxic Event. In addition, isotopic data are compared with geochemical redox and palaeoproductivity proxies. The microhabitat affected δ13C values, δ13CLenticulina generally being lower than δ13CDentalina due to more depleted 13C values for sediment pore-water in the deep infaunal microhabitat. The lowest values of δ13C (lower part of Serpentinum Zone) happen during suboxic conditions, as indicated by redox proxies, low diversity and abundance of foraminifera and higher TOC values. The fine-grained, organic rich sediments allow for conditions favouring pore-water dissolved inorganic carbon that is depleted in 13C with respect to that of the bottom sea-water, particularly during the suboxic conditions. The δ13C of potential deep infauna (Lenticulina) reflects the oxygen restricted conditions better than shallow infauna (Dentalina) and whole sediment. Regarding δ18O, values from bulk rock present stronger fluctuations and lower values than δ18ODentalina and δ18OLenticulina. The stratigraphic differences between δ18ODentalina and δ18OLenticulina correspond to vital effects, since no important fluctuations in temperature occurred in the bottom sea-water, as deduced from the absence of peaks and stratigraphic trends in the interval studied. The δ18O values do not allow us to infer temperature changes related to the Toarcian Oceanic Anoxic Event in this part of the palaeomargin.