Lower Eocene Crustacean Burrows (Israel) Reflect a Change from K- to r-Type Mode of Breeding Across the K-T Boundary Clarifying the Process of the End-Cretaceous Biological Crisis - Advances in Data, Methods, Models and Their Applications in Geoscience - page 322

ice cover most of the year (Hay, 2008). High sea-levels with their peak during the Turonian
characterized the general transgressive trend of the oceans throughout the Upper
Cretaceous and the Lower Tertiary. The continental plates continued to move toward their
present-day position whereby the Atlantic Ocean further opened perpendicular to the
Tethys Ocean improving the north-south water circulation. This global plate movement
triggered local tectonic movements which differentiated plate margins and intensified the
reduction of the previous Albian-Cenomanian-Turonian broad (50-300 km wide) shelves,
where rudistid bivalves thrived together with sessile ostreids and chondrodentids. These
could survive temporary exposure or cover by sediment, in contrast to hermatypic corals
which occupied protected regions in this shallow marine ecosystem. A broad intertidal flat
extended landward of this rudistid reefal belt, where calcareous detritus (bioclasts)
accumulated and was partly dolomitized under the high salinity of the lagoon and sabkha
settings. The abundance of calcitic mollusk conchs highly increased during the middle part
of the Cretaceous Period, represented by the shallow marine rudists, oysters and
chondrodonts, with Inoceramidae inhabiting the deeper water. The expansion of pelagic
environments during the Upper Cretaceous was associated with an increase in the
diversity and abundance of planktonic foraminifera and calcareous nannoplankton
(Coccolithophorida) all having calcitic endoskeletons. This abundance of biologically
precipitated calcite suggested a very low Mg/Ca ratio in Cretaceous seawater (MacLeod,
2005). Keeled planktonic foraminifera diversified from the uppermost part of the Lower
Cretaceous (Albian) onward throughout the Late Cretaceous, and were associated with
globular forms. Their calcitic tests accumulated as foraminiferal ooze in the outer shelf and
deeper marine bottoms forming chalk characterizing the Upper Cretaceous, such as the
Lower and Upper Chalk in northwest Europe. The gradual increase in the plankton bloom
in the broad oceans triggered a gradual rise in marine productivity evidenced in the later
Upper Cretaceous (Campanian-Maastrichtian) by extensive accumulations of organic-rich
('bituminous') chalk with chert (from dissolved diatoms and radiolarians) and phosphorite
beds mainly in the Tethys ocean (Lucas & Prévot-Lucas, 1996). These optimal living
conditions are corroborated by the increasing diversity of the marine fauna and the
development of gigantic organisms. The largest ammonite Parapuzosia seppenradensis
(Landois) with a diameter of about 2.50 m (Summesberger, 1979) and P. bradyi Miller &
Yongquist (D=1.37 m) from Wyoming, USA (Larson et al., 1997) are from the Lower
Campanian. Large inoceramid bivalves with an axial length of 1 m, and occasionally over 2-
3 m in size of the genus Platyceramus, occur in the Santonian-Lower Campanian of Colorado
(USA) (Kauffman et al., 2007). Marine reptiles related to plesiosaurs and mosasaurs grew to
a length of 9-15 m (MacLeod et al., 1997). Their flying relatives (Pterosauria) reached in
latest Cretaceous time wide wing spans up to 11-12 m in Quetzalcoatlus (Langston, 1981). The
marine high productivity extended into early Cenozoic times (Lower Eocene) despite the
profound change in zoo- and phytoplankton composition, suggesting that the Late
Cretaceous marine physical and chemical properties were neither affected by the Deccan
volcanism (India) nor by the asteroid impact. These marine conditions were controlled by
the continuing movement of the plates and the general transgressive trend of the widening
oceans during the Late Cretaceous and Early Tertiary. Thereby the size of the shelves and
the neritic habitats were considerably reduced. Organisms living within the 'reefal' habitat
of the rudistid and ostreid buildups decreased in abundance and disappeared from many
shrinking shallow marine environments, surviving only in restricted regions. The expansion
of the pelagic habitats increased the abundance of the nektonic organisms which comprised