• The Cretaceous Period (meaning "chalk," from the many chalk deposits of
this age [the White Cliffs of Dover, to name one]) easily stands as one of the
most popular times among the general populus. The period extends from
about 141 million years ago until 65 million years ago.
• Duration :71 million years
• The name Cretaceous was derived from chalk (Crai, Kreides, Latin Creta)
known in England, France, Germany. This chalk is a facies which changed
laterally into sandstone in other places on the border of the Cretaceous
basin in Europe.
• It show a wider extension than in the Jurassic.
• It is found in most of the Europian countries, North Africa, Egypy, Arabia,
• The Cretaceous was also punctuated and concluded by one of the greatest
mass extinctions of all time. About half of all animal families did not make
the transition to the Tertiary Period.
• They exhibit considerable local variation, generally:
The Lower Cretaceous formations are all non-marine being
of terrestrial and estuarine origin, the lower member begins with
basal sands that are coarse and gravelly, commonly arkose and
generally cross –bedded. Sands and clays alternate and also grade
laterally on into another.
The Upper Cretaceous beds rest unconformably upon the lower
• Eleven major impact structures are known
from the Cretaceous, but none rival the
terminal event in Cretaceous existence.
Some 65 million years ago a massive
asteroid, 10-20 km in diameter struck the
Earth north of the Yucatan Peninsula in
what is now the Gulf of Mexico. The
resulting crater approaches 300 km in
diameter, and is the second-largest
craterform structure known.
• The asteroid would have been travelling at a
speed between 10 and 20 km per second
when it entered Earth's atmosphere and a
relatively oblique angle from the south.
• Both the air and any water would have
provided negligible resistance, and the
resulting impact with the Earth's surface
would have kicked up billions of
• tons of substrate. The dust
entered the atmosphere,
presumably blocking out sunlight
for an extended time (perhaps 6
• Models suggest that a global
cooling would have resulted for
about 10 years due to a 10-20%
reduction in solar transmission
through the atmosphere. This, in
turn, would be followed by a
warming trend for about 100
years due to a greenhouse effect
Rise of the Rocky Mountains
• During the Cretaceous, severe compressional forces were
in play throughout Idaho, Wyoming, and Utah, causing
masses of rock to be moved horizontally and folded
upward. During the Middle Cretaceous, this uplift was
further aided by plutonic and volcanic action on the West
• The close of the Cretaceous also marks a time of mass
extinction, certainly in part due to impact by an
extraterrestrial body. This was the second-greatest
extinction of all time, with about half of all animal families
not making the transition to the Paleocene.
• All of the dinosaurs became extinct, and marine reptiles
and flying pterosaurs vanished as well. Among the
invertebrates, the ammonoids and belemnoids were wiped
out, and many families of clams and snails were
eliminated. Corals lost two-thirds of their members.
• A few groups, such as land plants, mammals, fishes,
brachiopods, and amphibians, lost relatively few
The Cretaceous Period 144 to 65 Million Years
• The Cretaceous is usually noted for being the last portion
of the "Age of Dinosaurs", but that does not mean that new
kinds of dinosaurs did not appear then.
• It is during the Cretaceous that the first ceratopsian and
pachycepalosaurid dinosaurs appeared. Also during this
time, we find the first fossils of many insect groups,
modern mammal and bird groups, and the first flowering
• The breakup of the world-continent Pangaea, which began
to disperse during the Jurassic, continued. This led to
increased regional differences in floras and faunas
between the northern and southern continents.
• The end of the Cretaceous brought the end of many
previously successful and diverse groups of organisms,
such as non-avian dinosaurs and ammonites. This laid open
the stage for those groups which had previously taken
secondary roles to come to the forefront. The Cretaceous
was thus the time in which life as it now exists on Earth
Subdivisions of the Cretaceous:
The chart at left shows the major
subdivisions of the Cretaceous Period. The
Coniacian Age is not labelled here, because
it is too short to allow this -- you will notice
it as a narrow strip between the Santonian
This chart is mapped, to allow you to travel
back to the Jurassic, or forward into the
Paleogene (in the Cenozoic Era). The
Cretaceous Period is part of the
- Coniacian = Late Cretaceous
- Aptian =Early Cretaceous
Subdivisions of the Cretaceous:
Cretaceous Period: Stratigraphy
Subdivisions of the
The chart at left shows the major
subdivisions of the Cretaceous
Period. The Coniacian Age is not
labelled here, because it is too short
to allow this -- you will notice it as a
narrow strip between the Santonian
This chart is mapped, to allow you to
travel back to the Jurassic, or
forward into the Paleogene (in the
The Cretaceous Period is part of the
Cretaceous Period: Life
• No great extinction or burst of diversity separated the Cretaceous from the
Jurassic Period that had preceded it.
• In some ways, things went on as they had. Dinosaurs both great and small
moved through forests of ferns, cycads, and conifers.
• Ammonites, belemnites, other molluscs, and fish were hunted by great
"marine reptiles," and pterosaurs and birds flapped and soared in the air
above. Yet the Cretaceous saw the first appearance of many lifeforms that
would go on to play key roles in the coming Cenozoic world.
• Perhaps the most important of these events, at least for terrestrial life, was
the first appearance of the flowering plants, also called the angiosperms or
• appearing in the Lower Cretaceous around 125 million years ago, the
flowering plants first radiated in the middle Cretaceous, about 100 million
years ago. By the close of the Cretaceous, a number of forms had evolved
that any modern botanist would recognize.
• At about the same time, many modern groups of insects were beginning to
diversify, and we find the oldest known ants and butterflies. Aphids,
grasshoppers, and gall wasps appear in the Cretaceous, as well as termites
and ants in the later part of this period. Another important insect to evolve
was the eusocial bee, which was integral to the ecology and evolution of
• The Cretaceous also saw the first radiation of the diatoms in the oceans
(freshwater diatoms did not appear until the Miocene).
Life of the Cretaceous
Life of the Cretaceous
Many of the Jurassic genera still exist in the Cretaceous together with the
apprearance of new forms. Sudden disappearance of most of the
characteristic Cretaceous genera
before coming of the Eocene ones.
Flora: Ferns, Cycads and Coniferse are still the most important tribs of
Cycads were exceedingly developed and widely spread and the
Mesozoic sometimes called the, age of Cycads .
Development and spead of Angiosperms (true flowering plant). Calcareous
Foraminifera: exceedingly abundant as rock builders of chalk and other
Corals and Sponges: locally abundant, reef builders developed in few
localities.Solitary corals e.g. Cyclolites were soread widely.
Echinoderms: Crinoids do not play important part as in the
important e.g. Cidris, Cassidulus, Hemiaster.
Brachiopods : shown gradual declination, numerous only in restricted
Pelecypods and Gastropods:abundant of many kinds and essentially of moden
appearance e.g. Oysters, Exogyra….etc.Rudists were distinctive builders of bioherms and
associated with acteonillids.
Cephalopods: mainly Ammonites and Belemnites both were on a decline
numerically although the Ammonites still played a
conspicuous role until the end of the period.
Small Stuff: Plankton
Cretaceous Period: Localities
• Cretaceous localities on this
server: (see map above)
• Clayton Lake, New Mexico - One of
the most extensive and best
preserved dinosaur trackways in
the United States is this
• Hell Creek, Montana
• Pt. Loma Formation - This
California locality has yielded
inportant fossils for understanding
western North American dinosaurs
• Cretaceous in
• The Cretaceous rocks
covers about 2/5 of
• In Sinai
• Gebel Shabraweat
• Gebel Ataqa and along the
Red Sea Coast
Cretaceous: Tectonics and Paleoclimate
• The Cretaceous is defined as the period between 144 and 65 million years ago, the last
period of the Mesozoic Era, following the Jurassic and ending with the extinction of the
dinosaurs. By the beginning of the Cretaceous, the supercontinent Pangea was already
rifting apart, and by the mid-Cretaceous, it had split into several smaller continents.
This crested large-scale geographic isolation, causing a divergence in evolution of all
land-based life for the two new land masses.
• The rifting apart also generated extensive new coastlines, and a corresponding increase
in the available near-shore habitat. Additionally, seasons began to grow more
pronounced as the global climate became cooler. Forests evolved to look similar to
present day forests, with oaks, hickories, and magnolias becoming common in North
America by the end of the Cretaceous.
• At the end of the Cretaceous period, 65 million years ago, an asteroid hit Earth in the
Yucatán Peninsula, Mexico, forming what is today called the Chicxulub impact crater.
It has been estimated that half of the world's species went extinct at about this time, but
no accurate species count exists for all groups of organisms. Some have argued that
many of the species to go extinct did so before the impact, perhaps because of
environmental changes occuring at this time. Whatever its cause, this extinction event
marks the end of the Cretaceous and of the Mesozoic Era
• The appearance and diversification of angiosperms characterizes this period. Flowering plants
invaded more varied environments and created a niche for themselves in the damper climates
which began to emerge. Although these angiosperms did not develop shrub or tree like
morphologies, by the Cenomanian age they had radiated into a new habitat: disturbed riparian
areas. Ferns dominated open, dry and/or low-nutrient lands.
• Typical Jurassic vegetation, including conifers, cycads, and other gymnosperms, continued on into
the Early Cretaceous without significant changes. At the beginning of this period, conifer diversity
was fairly low in the higher latitudes of the Northern Hemisphere, but by the middle of this period,
species diversification was increasing exponentially.
• Ferns dominated open, dry and / or low-nutrient land. However, the up-and-coming angiosperms
took over cycad and cycadeoid habitats. High southern latitudes were not invaded by angiosperms
until the end of the Cretaceous.
• Swamps were dominated by conifers and angiosperm dicots .
The Cretaceous-Tertiary Extinction
• The most famous, if not the largest, of all mass extinctions marks the end of
the Cretaceous Period, 65 million years ago. As everyone knows, this was the
great extinction in which the dinosaurs died out. (Except for the birds, of
course.) The other lineages of "marine reptiles", such as the ichthyosaurs,
plesiosaurs, and mosasaurs, also were extinct by the end of the Cretaceous, as
did the flying pterosaurs -- although some, like the ichthyosaurs, were probably
extinct a little before the end of the Cretaceous. Many species of
foraminiferans went extinct at the end of the Cretaceous, as did the
• But many groups of organisms, such as flowering plants, gastropods and
pelecypods (snails and clams), amphibians, lizards and snakes, crocodilians,
and mammals "sailed through" the Cretaceous-Tertiary boundary, with few or
no apparent extinctions at all.
-Numerous evolutionary radiations occurred during the Cretaceous
(144-65 million years ago)
- A major extinction occurred at the end of the period.
- 85% of all species died in the End-Cretaceous (K-T) extinction
Several mass extinctions are recorded in the fossil record.
Paleontologists have been able to recognize patterns within and
between extinction events. Currently, there are five major extinction
patterns recognized. Steven M. Stanley, has outlined them in his book
The End-Cretaceous (K-T) Extinction
• Following the Permian mass extinction, life was abundant but there was a low diversity
of species. However, through the Triassic, Jurassic, and Cretaceous, major faunal
radiations resulted in a large number of new species and forms. New terrestrial fauna
that made their first appearance in the Triassic included the dinosaurs, mammals,
pterosaurs (flying reptiles), amphibians (including frogs and turtles). In addition, the
first birds appeared in the Jurassic. Among the terrestrial flora, the gymnosperms of
the Permian remained dominant until the evolution of the angiosperms (flowering
plants) in the Cretaceous.
• In the Cretaceous there was also major radiations occurring in several esablished
grounps including the the marine reptiles, rudist bivalves, ammonoids, belemnoids, and
scleractinian corals. Bivalves, and brachiopods. Marine groups that were present but
did not undergo major evolutionary expansion in the period included the gastropods,
bryozoans, crinoids, sea urchins, and sponges.
• Species Affected
• During the End-Cretaceous (K-T) extinction (65 million years ago) eighty-five percent of all species
disappeared, making it the second largest mass extinction event in geological history.
• This mass mass extinction, extinction event has generated considerable public interest, primarily
because of its role in the demise of the dinosaurs. Although dinosaurs were among the unfortunate
victims to perish in the K-T extinction, several other terrestrial and marine biotic groups were also
severely affected or eliminated in the crisis. Among those that perished were the pterosaurs,
belemnoids, many species of plants (except amongst the ferns and seed-producing plants),
ammonoids, marine reptiles, and rudist bivalves
• Organisms which were severly affected included planktic foraminifera, calcareous nannoplankton,
diatoms, dinoflagellates, brachiopods, molluscs, echinoids, and fish.
• Remarkably, most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians were
primarily unaffected by the End-Cretaceous mass extinction
• Extinction strikes in both the land and the sea.
• On the land, while animals suffer repeatedly, plants tend to
be highly resistant to mass extinctions.
• Preferential disappearance of tropical forms of life during
• Tendency of certain groups of animals to experience them
repeatedly (for example, trilobites and ammonoids).
• Alleged equal spacing, or periodicity in geological time
(occurring about every 26 million years.
• These similarities between distinct extinction
occurrences aid paleontologists in determining the agents
the agents that perpetuated the disappearances of species
in each extinction event. Such agents are currently divided
into two types:
• Catastrophic Agents- such as meteorite impacts and comet
• Earth Agents- such as volcanism, glaciation, variations in
sea level, global climatic changes, and changes in ocean
levels of oxygen or salinity
Although these agents can explain mass extinction, the
causes of mass extinction events remains relatively
1- On the land, the Dinosaures were the primary victims of
the terminal crisis.
2- In the seas . Ammonoides, which had flourished with
only temporary set beach through Mesozoic time
and huge Swimming Reptiles failed to make the transition
into the Cenozoic.
3- The Reef building rudists also died out along with
certain other groups of bivalve.
4- Calcareous nannoplanktonand planktonic foraminifera
suffered heavy losses , but they recovered during the
5- Many taxononmic groups declined before the end of the
Cretaceous period, but other taxa died out abruptly right at
6- Extinction was heaviest in tropical regions and another
important group of Mesozoic bivalves the Inoceramids also
decline and perhaps disappeared.
7- Rudists reef that formed within 1 or 2 millions years of
the end of the Maastrichtian age . the final age of the
Cretaceous period were weakly developed and the number
of species was depleted.
Nature of the terminal Cretaceous:
1- Early in late Cretaceous time, about 65 million years ago, a
moderately severe extinction eliminated many species in the
2- During the past few years, this biotic crisis , which brough the
Era to close, has been attracted special Attention because of
intriguing suggestion that the cause was the impact on earth of
large bolide(meteorite or comet).
3- The primary evidence for such an event is the presence of so-
called Irridium anomaly at the Cretaceous – Paleogene boundary in
many areas of the world (Irridium is an element that is generally
very rare in the earth's crust). But it is abundant in stony
4- A meteorite or Comet, about 10 km, in diameter, exploding on
impact cloud have released the total amount of excessive iridium
observed in the rock record .
5- The biotic consequence of such colloision are difficult to
6- On likely, would be that a huge volume of dust and smoke would
be thrown up into the atmosphere to circle the earth
7- Blocking out a large percentage of sunlight, this global cloud
CRETACEOUS MASS EXTINCTION
Speculated Causes of the End-Cretaceous
Extinction• The End-Cretaceous mass extinction has generated considerable
public interest in recent years, in response to the controversial
debates in the scientific community over its cause.
• The more prominent of these new hypoteses invoke extra-
terrestrial forces, such as meteorite impacts or comet showers as
the causative extinction agent.
• Older hypotheses cite earthly mechanisms such as volcanism or
glaciation as the primary agent behind this mass extinction.
The K-T Boundary
• Evidence for catastrophism at the Cretaceous-Tertiary boundary is found in
a layer of sediment which was deposited at the same time that the
• This layer contains unusually high concentrations of Iridium, found only in
the earth's mantle, and in extra-terrestrial meteors and comets.
• This layer has been found found in both marine and terrestrial sediments, at
numerous boundary sites around the world.
• Some paleontologists believe that the widespread
distribution of this Iridium layer could have only been
caused by meteorite impact. Further, these researchers
cite the abundance of small droplets of basalt, called
spherules, in the boundary layer as evidence that basalt
from the earth's crust that were melted and flung into the
air upon impact.
• The presence of shocked quartz - tiny grains of quartz that
show features diagnostic of the high pressure of impact -
found in the boundary layer provides additional evidence of
an extra- terrestrial impact at the Cretaceous-Tertiary
• Recent research suggests that the impact site may have
been in the Yucatan Peninsula of Mexico.
• The high concentrations of Iridium in the boundary layer has also
been attributed to another source, the mantle of the earth.
• It has been speculated by some scientists that the Iridium layer
may be the result of a massive volcanic eruption, as evidenced by
the Deccan Traps - extensive volcanic deposits laid down at the
Cretaceous-Tertiary boundary - of India and Pakistan.
• These lava flows came about when India moved over a "hot spot"
in the Indian Ocean, producing flows that exceeded one hundred
thousand square kilometers in area and one hundred and fifty
meters in thickness.
• Such flows would have produced enormous amounts of ash,
altering global climatic conditions and changing ocean chemistry.
Evidence that volcanism was a primary extinction agent at this
boundary is also relatively strong.
• In addition, and the presence of spherules and shocked quartz
worldwide in the boundary layer may also have been the result of
such explosive volcanism.
• Thus at present, both the volcanic and meteorite impact
hypotheses are both viable mechanisms for producing the
Cretaceous mass extinction, although the latter is more popular
Cretaceous: ClimateClimate warm. In the early Cretaceous time , the
temperature was generally below normal. Similar lower
temperature were prevalent in many other parts of the
world as shown by the distribution of plants and animal
In the upper Cretaceous beds , abundant remains of land
plants now restricted to temperates or sub-tropical region
By the close of the Cretaceous, the general temperature
dropped because the continent stood higher than usual due
to the great mountain formed at the time of the Rocky
Mountains- Great Alpine Revolution.
• Towards the close of the Cretaceous , there was vigerous crustal
deformation including both folding of strata.This great crustal
disturbance has been called ‘ Rocky Mountain” or “Laramide”
• A number of great , elongate, dome –like anticline with cores of
Pre-Cambrian granite were found. The Rocky Mountain orogeny “”
Great Alpine Tectonic disturbance of Europe “ began well before
the close of Cretaceous and continued with more or less intensity
into the Early Tertiary