CRETACEOUS- TERTIARY EXTINCTION EVENT

1. TOPIC- K-T BOUNDARY PROBLEM
PRESENTED BY GUIDED BY
KOMAL DAWAR Dr.VISHNU GADGIL
CLASS- M.Sc (1st SEM)

2. INDEX
PURPOSE OF STUDY
INTRODUCTION
CAUSES
EXTINCTION OF DINOSAURS
LITHOLOGY
FOSSILS
PROBLEMS
REFERENCES

3. PURPOSE OF STUDY
Of all the ‘Boundary Problem’ in the study of
Stratigraphy, the one that has attracted the largest
amount of interest and attention in recent years is
that connected with the Cretaceous-Tertiary
boundary. There was a huge change on earth after
the K-T BOUNDARY event. About 75% of life on
earth including non-avian dinosaurs, marine reptiles
like mosasaurs and plesiosaurs and ammonites
were extinct except birds.

4. INTRODUCTION
The full name of K-T Boundary is CRETACEOUS –TERTIARY Boundary.
According to the latest version of the International Stratigraphic
Scale ,the proper name for the K-T Boundary is Cretaceous –
Palaeogene Boundary (K-Pg). The term Tertiary is now
considered unofficial.
The K-T Boundary is a geological signature , usually a thin band of
rock dated on 66 million years ago. K the first letter of German
word Kreide is the traditional abbreviation for the Cretaceous
Period and T is the abbreviation for the Tertiary Period.The
boundary marks the end of the Creataceous Period , the last
period of Mesozoic Era and marks the beginning of Tertiary
Period , the first period of the Cenozoic Era as well as between
the Maastrichtiam and Danian Stages and is assoicated with the
Cretaceous- Tertiary extinction event, a mass extinction.

5. It coincides with one of the five mass extinction
in Earth’s history which affected many groups
of organisms both marine and continental ,
including all dinosaurs except for birds.
Strong evidence exists that the extinction
coincided with a large asteroid impact at the
Chicxulub Crater and the generally accepted
scientific theory is that this impact triggered
the extinction event .

7. CAUSES
There are six possible causes for this mass
extinction. They are :
Alvarez impact hypothesis
Chicxulub Crater
Deccan Traps
Multiple impact event
Maastrichtian sea-level regression
Supernova hypothesis

8. ALVAREZ IMPACT HYPOTHESIS
In 1980 , a team of researchers consisting of Noble Prize
winning Physicist Luis Alvarez , his son Walter Alvarez
and his team discovered that sedimentary layers found
all over the world at the K-T Boundary contain a
concentration of Iridium near Gubbio, Italy which was
many times greater than normal. Iridium is extremely
rare in the Earth’s crust because it is a siderophile and
therefore most of it travelled with the iron as it sank into
the Earth’s core during planetary differentiation. The
Alvarez team suggested that an asteroid struck the Earth
at the time of K-T Boundary. There were other earlier
speculations on the possibility of an impact event, but
no evidence had been uncovered it at that time.

9. • The EVIDENCE for the Alvarez impact theory
is supported by chondritic asteroid and
comets which have an Iridium concentration
of 455 parts per billion much higher than the
Earth’s crust. Chromium isotopic anomalies
found in K-T Boundary sediments are similar
to that of an asteroid or comet composed of
carbonaceous chondrites .

11. CHICXULUB CRATER
The Chicxulub Crater is an impact crater buried
under the Yucatan Peninsula in Mexico. Its centre
located near the town of Chicxulub, after which
the crater is named. It was formed by a large
asteroid or comet about 10-15 kilometres, the
Chicxulub impactor , striking the Earth.
The crater was discovered by Antonio Camargo and
Glen Penfield, geophysicist who had been looking
for petroleum in the Yucatan Peninsula during the
late 1970, this crater is oval with an average
diameter of 180 kilometres, about the size
calculated by Alvarez team.

12. A mass extinction in which 75% of plant and animal species
on Earth suddenly became extinct, including all non
avian dinosaurs.
EVIDENCE for the impact origin of the crater included
shocked quartz, a gravity anomaly and tektites in
surrounding areas.
The asteroid landed in a bed of anhydrite (CaSO4) and
gypsum[CaSO4.2(H2O)] which would have ejected large
quantities of sulphur trioxide SO3 they combine with
water to produce a sulphuric acid aerosol. This would
have further reduced the sunlight reaching the Earth’s
surface and then over several days, precipitated planet
wide as acid rain, killing vegetation, plankton and
organisms which build shells from calcium carbonate.

14. DECCAN TRAPS
Before 2000, arguments that the Deccan Traps flood basalts
caused the extinction thorugh several mechanisms,
including the release of dust and sulphuric aerosols into the
air which might have blocked sunlight and thereby reduced
photosynthesis in plants. In addition , Deccan Trap
volcanism might have resulted in carbon dioxide emissions
which would have increased the Greenhouse Effect when
the dust and aerosols cleared from the atmosphere.
However even Walter Alvarez acknowledge that there were
other major changes on Earth even before the impact such
as drop in sea level and massive volcanic eruptions that
produced the Indian Deccan Traps and these may hve
contributed to the extinctions.

15. EXTINCTION OF DINOSAURS
During their heyday in the Triassic, Jurassic and
Cretaceous periods dinosaurs evolved to fill
niches in most ecosystems. Mass extinction
often come to mind when the term extinction
is mentioned but the normal background
extinctions that occur throughout geologic
time probably account most for biodiversity, it
is rare to any particular type of dinosaur
survived from one geologic formation into the
next.

19. LITHOLOGY
Claystone
Mudstone
Sandstone massive
Siltstone
Conglomerate
Limestone

20. FOSSILS
Palaeocene Sediments
Pieces of Dinosaurs
Crocodile Fossil
Fossils of Fish
Some fossils of Leaves
Trace Fossils

21. K-T BOUNDARY IN INDIA
There are three regions in Indian subcontinent which have
exposed “Passage Beds”(Rama Rao, 1956). They are the Sind
area in Pakistan , the Tiruchchirappalli area in south India and
the Assam region in the north-eastern India.
The geology of the Sind area was first discribed by Blanford
(1880) which was later improved by Vredenberg (1909). The
basic divisions of the stratigraphic units representing the
Cretaceous Tertiary transition.
The Upper Cretaceous rocks of the Tiruchchirappalli area have
been classified into Uttatur , Trichinapoly and Ariyalur
formations.
The Upper Cretaceous rocks of Assam region comprising the
Mahadek Formation is conformably overlain by a marine
succession known as Langpar Formation.

22. PROBLEMS
Of all the ‘Boundary Problem’ in the study of Stratigraphy, the
one that has attracted the largest amount of interest and
attention in recent years is that connected with the
Cretaceous-Tertiary boundary. Several important
contributions dealing with this subject has been made in and
outside India; and this paper is to give a critical review of
these studies and discuss some aspects of fundamental
interest in the further elucidation of this problem.
Our starting point in this study is the old view prevalent for quite
a long time that between the Danian which represents the
youngest subdivision of the Cretaceous, and the Palaeocene
which constitutes the oldest part of the Tertiary, there is a
distinct break in the European Stratigraphical Scale , and this
break must be considered as making the Cretaceous-Tertiary
Boundary.

23. It is however important to note that even in the early days
when this conclusion was put forward in Europe, there
were some doubts as to the exact ‘definition’ of the
‘Danian’ and its placement in the Cretaceous –Tertiary
succession (Rama Rao 1953). The views of the earlier
geologist in this matter were based mostly on field
observations, together with the evidence of some
macrofossils like Molluscs. Now a days the problem has
been looked at from all possible points of view- structural,
straitgraphical, and palaeontological; of these
micropalaeontological studies have come to play an
increasingly part, and it is currently believed by many
stratigrapher that the attack from this side is the most
effective and reliable way of dealing with this problem.

24. REFERENCES
BOOK
Ravindra Kumar- Fundamentals of Historical
Geology and Stratigraphy of India.(Page no.
201-203)
WEBSITE
https://www.britannica.com
https://en.m.wikipedia.org
https://www.sciencetheearth.com