Climate Change



Global Creatceous; A Brief Summary





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.


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Why couldn't the dinosaurs survive the changes? Take a closer look at steggy's body



Palaeo-environment of the Western Interior of America
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 palaeochannels.

Marine Fauna



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 and foraminifera.
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 Herman (1990)





Plants


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 (Roddy, 1990)


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.

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