Global temperatures were warm and equable. Temperatures at the equator were
17-26 degrees celcius and 0-15 degrees at the poles, and so they were ice free.
Seasonality increased in the Late
Cretaceous i.e. became more extreme,(Officer and others,1987)
Changes in ocean circulation from equator-dominated, in the Cretaceous, to
polar-dominated of the Cenozoic, as indicated by carbon/oxygen isotopes
(Mount and others,1986 ), resulted in surface-water warming events and decreases
in primary producivity at the K-T boundary.
A substantial increase in volcanism over the last 10,000 yrs of the K-T. Resulting
from increased tectonic activity and the volume of spreading of ocean ridges.
Intense volcanism would lead to acid rain, a lower pH of surface waters and ozone
layer depleation. Cretaceous levels of mean absorbed radiation were thought to be higher
than today's level plus the build up of CO2 in the atmosphere would result in an effect
similar to the greenhouse.
Rock sequences of Montana and North Dakota were deposited in a fluvial environment
of floodplains, shown by palaeosols (fossilized soils), and river channels known as
Casualities of the K-T boundary were; marine reptiles, ammonites and numerous families of
scleractinian corals, bivalves such as inoceramids and rudists, gastropods and
echinoids. coccolithoporidae, planktonic foraminiferaforaminifera and belemnite suffered almost
complete extinction with only a few species surviving.
Photo : Perhaps the oceans of the Cretaceous looked like this
A complex series of extinctions was underway in the worlds oceans long before the end
of the Cretaceous,Ward (1990).Plankton and ammonitesammonites suffered a rapid extinction, but
deep sea benthic (bottom living) foramminiferal records, in the vicinity of the
Antartic, show no evidence of mass extinction, Thomas (1990).
Modern plankton foraminifera become inhibited below pH 7.6-7.8, changes in pH,
resulting from volcanism would lead to the extinction effects of both coccolithoporidae
Volitile (gas) emissions from massive volcanic eruptions would lower calcite nucleation
of surface-dwelling warm water plankton, thus accounting for the extinction of calcareous
phyto-and zooplankton. The extinction appears to have occured over severalthousand years
The northern Great Plains and Rocky Mountains, U.S.A. reflect megafloral changes
before and at the end of the Cretaceous, Johnson and Hickey (1990). An overall loss
at the boundary was large (79 percent) principally by anginosperms .
This was followed by a dramatic increase in fern spores, known as a fern spike , which
indicate a radical change in climatic conditions.
Megafloral changes were due to regional climate warming. For example,If a temperature
drop of 100 degrees occurs in early spring it would kill 50% of the trees in a few days
C-T Cretaceous extinction
Extinctions at the Cenomanian-Turonian (C-T) stage boundary follow the 26-Ma cyclic
extinction, as predicted by Raup and Sepkoski (1982). Believed to result from climatic
and oceanographic changes (Elder ,1987). This extinction occured just prior to a
peak in global tectono-eustatic sea-level rise. Dinosaur casualties were numerous and this
shows that large extinctions have previously occurred in the Cretaceous.