K-T BOUNDARY PROBLEM

CRETACEOUS- TERTIARY EXTINCTION EVENT

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

6. 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

7. 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.

8. 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 .

9. 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.

10. 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.

11. 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.

12. 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.

13. LITHOLOGY Claystone Mudstone Sandstone massive Siltstone Conglomerate Limestone

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

15. 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.

16. 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.

17. 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.

18. 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