PLEISTOCENE GLACIATION[2].pptx

1.Introduction
2.Major glacial phases
3.Pleistocene stages
3.Pleistocene glaciation
a.Causes b.Effects c.Pleistocene flora fauna , evolutionary megafaunal extinction changes and
d.Pleistocene fossils e.Evidences
4.Next glacial period
5.Conclusion
6.Reference

1. Pleistocene Glaciations BY NIKSHITA JENA II SEMESTER ROLL NO-22GEOL016

2. CONTENTS… 1.Introduction 2.Major glacial phases 3.Pleistocene stages 3.Pleistocene glaciation a.Causes b.Effects c.Pleistocene flora fauna , evolutionary changes and megafaunal extinction d.Pleistocene fossils e.Evidences 4.Next glacial period 5.Conclusion 6.Reference

3. INTRODUCTION Glaciation- A glaciation (Glacial period ) is an interval of time (thousand of years to million of years) which is marked by colder temp. and development of ice sheets in the continents (sub polar to sub tropical climates). A major glaciation phase consists of a number of glacial and interglacial periods. Their study and interpretation is of greatest importance since they are indicators of earth’s history prior to human evolution, future climate. Ice ages were first discovered in 1830 by Louis Agassiz in the Swiss Alps He identified that they had occurred all over Europe.He did this by seeing that certain areas had similar features. The Pleistocene glaciation:- Pleistocene Epoch: 2.58 million to 10,000 years ago During the Pleistocene, the earth experienced multiple periods of glacial-interglacial cycles .

4. Cont... The glaciers were enormous, often 2-3 km thick. At their maximum extent, they covered up to one third of the earth’s land surface. The glaciers were advanced up to the sub tropical regions. Glacial periods have left evidence in landscape in terms of erosional and depositional features More than a century ago, geologists determined using such evidence that at the coldest time of the Pleistocene, glaciers covered Edinburgh, Scotland; Moscow, Russia; and Detroit and Chicago in the US. From the glacial deposits alone, glaciologists had inferred several major advances and retreats of the two major ice sheets, the Laurentide in North America and the Fennoscandian in Europe and Asia.

5. Major glacial phases There have been five known glacial periods in the Earth’s history 1.Huronian glaciation – Paleoproterozoic (2500 my-2100my ago) 2.Cryogenian glaciation- Neoproterozoic (Snowball earth) (850my-635my ago ) 3.Andean Saharan glaciation- Ordovician and Silurian (450-420mya) 4.Karoo glaciation - Carboniferous and Permian (360-260mya) 5.Pleistocene glaciation- Neogene (2.58my-12500years ) ""

6. Last major glaciation- known as the Last Glacial Maximum. The last glacial maximum was the most recent glacial period which began about 110000 years ago and ended about 12500 ago. The glaciation that occurred during this period covered many areas of the northern hemisphere, ice sheets covered Chicago, Boston, Detroit, and Cleveland. It has different names depending upon its geographic distribution such as Wisconsin in North America, Devensian in Great Britain, etc. The glacial advance reached its maximum extent about 18000 BP. The last glacial maximum(LGM):

7. PLEISTOCENE STAGES The Pleistocene is subdivided into four ages and their corresponding rock units : the Gelasian (2.6 million to 1.8 million years ago) the Calabrian (1.8 million to 774,000 years ago) the Chibanian (774,000 to 129,000 years ago) Stage 4 (129,000 to 11,700 years ago) Stage 4 awaits naming and ratification by the ICS.

8. Causes of pleistocene glaciation… The causes of glaciation may be related to several simultaneously occurring factors, such as: Astronomical cycle Feedback mechanism Atmospheric composition Plate tectonics Ocean current Astronomical cycle(Milankovitch cycle): Milankovitch cycles deals with the periodic changes in: 1. ECCENTRICITY-Changes from elliptical to more circular –(Approximately 100000 years) 2.OBLIQUITY- the tilt of the earth’s axis to the plane of the ecliptic. (period of about 41,000 years) Tilt changes from 22.1 and 24.5 degrees with respect to Earth's orbital plane.Currently 23.5 degree. 3. PRECESSION-(wobble on its axis )   gradual shift in the orientation of  Earth 's axis of rotation in a cycle of approximately 26,000 years.

9. This factor affects the duration of seasons in both hemisphere.

10. Obliquity and contrast in insolation between the seasons less contrast between seasons more contrast between seasons

11. Axial Precession present

12. Atmospheric composition: Decrease in atmospheric CO 2 an important greenhouse gas started the long term cooling that eventually led to glaciation. Recent studies of CO 2 content in gas bubble preserved in the Greenland ice cores supports the theory. CaSiO 3 + 2CO 2 +2H 2 O= CaCO 3 + SiO 2 + CO 2 + 2H 2 O This reaction shows the consumption of CO 2 by silicate weathering.

13. Plate tectonics and oceanic currents: An important component in long term temp. drop may be related to the position of continents relative to pole.This controls the oceanic currents and the heat flow pattern from equator to pole. Ex. The development of Isthmus of Panama at the convergent plate margin about 3.5my ago causing the separation of pacific and Atlantic ocean which further led to development of Gulf stream. Due to these moistures are carried to the north pole and precipitated as snow flakes.

14. Feedback mechanisms must operate to amplify the insolation changes caused by the orbital parameters. Feedback mechanisms One of these is- albedo The reflectivity of Earth’s surface,increased snow cover in high-latitude areas would cause increased cooling. Another feedback mechanism is the decreased carbon dioxide content of the atmosphere during times of glaciation, as recorded in the bubbles of long ice cores.

15. Effects of pleistocene glaciation: The presence of so much ice upon the continents had a profound effect upon almost every aspect of earth’s hydrologic system. The major effects were that the continental landforms fashioned both by glacial erosion and deposition and the global sea level fall. It also affected the oceanic circulation pattern and atmospheric wind pattern. The sea level dropped down up to a depth of 130m below from present level during the LGM and reached the maximum drop down at 18000BP .

16. C0NT… More pronounced temperature changes in the high latitudes than the low latitudes. Temperature changes in high latitude regions are thought to be about 10oC between glacial and interglacial. Abrupt swings in atmospheric circulation with wind belts such as the Intertropical Convergence Zone (ITCZ) shifting latitudinally by several degrees. Rises and falls of sea level by up to 120 meters and advances and retreat of the shoreline across the continental shelves. Massive floods of freshwater down rivers such as the St. Lawrence and Mississippi rivers at times when the ice melted. Northward and southward movements of vegetation belts across the continent.

17. The dramatic fall in sea level may be caused due to following reasons… 1.Laurentide ice sheet in Hudson bay, North America. 2.Cordilleran ice sheet in Rockies mountain, Canada. 3.Alpine type of glaciers in Swiss Alps. 4.Increasing thickness of ice sheets in both poles .

18. axial

19. Pleistocene flora fauna , evolutionary changes and megafaunal extinction Changes in climate and environment caused large-scale migrations of both plants and animals, evolutionary adaptations, and in some cases extinction. particular importance is the evolution of the genus Homo and the extinction of large mammals at the end of the epoch. Evolutionary changes during the Pleistocene generally were minor because of the short interval of time involved. They were greatest among the mammals. Mammalian evolution included the development of large forms, many of which became adapted to Arctic conditions. Among these were the woolly mammoth, woolly rhinoceros, musk ox, moose, reindeer, and others that inhabited the cold periglacial areas. Large mammals that inhabited the more temperate zones included the elephant, mastodon, bison, hippopotamus, wild hog, deer, giant beaver, horse, and ground sloth. During episodes of glaciation, polar faunas extended south to about 45° N latitude, whereas during interglaciations these faunas occurred mostly north of 70° and subtropical faunas extended far to the north under the influence of the Gulf Stream.

20. The end of the Pleistocene was marked by the extinction of many genera of large mammals, including mammoths, mastodons, ground sloths. The extinction event is most distinct in North America.

21. Pleistocene fossils paranthropus robustus fossil pleistocene peccary fossil Bison_latifrons_fossil_buffalo _(Pleistocene;_ North_America )

22. Evidences of pleistocene glaciation I . Glacial deposits : 1 .Glacial striations 2. Glacial moraines 3. Till 4. Loess and 5. Drumlins

23. Glacial Erratic Boulder transported and deposited by a glacier having a lithology different than the bedrock upon which it is placed . Rouches Moutonnees Rock hills shaped by the passage of ice to give  a smooth up-ice side and a rough, plucked and cliffed surface on the down-ice side. The upstream surface is often marked with striations.

24. The skeletons of marine organisms record the 18 O content in the water (sediments) Marine organisms incorporate 18 O preferentially in cold water Ice sheets preferentially incorporate water with 16 O, leaving the water remaining in the ocean enriched in 18 O So the marine organisms show high 18 O/ 16 O ratio during glacial period. II. The Oxygen Isotope ( 18 O) Record Net transfer of 16 O from oceans to ice sheets, leaving behind ocean water rich in 18 O .

25. It is known that all interglacial periods are not of same duration. Based on the solar heating and the amount of CO 2 in the atmosphere some calculations of future temp. have been made. According to these the interglacial period the earth is in now may persists for another 50000 years if CO 2 level increase to 750ppm (present amount398ppm).If it decreases up to 210ppm then next glacial period may only be 15000 years away. Next glacial period

26. The ice ages and the inter glacial periods are not uniformly cold or warm respectively .They are interrupted by no. of interstadials and stadials respectively. Stadial- Short span of cold periods within an inter glacial periods. Interstadial- Short span of warm periods within an glacial period. Studies of sea floor sediments and ice core indicate that the climatic change is not smooth. The change from warm to a cold climate can occur in a decade or two.

27. Conclusion: The glacial and interglacial cycles indicate that earth climate is not smooth but dynamic. The northern hemisphere glaciation was established around 3mya and the Antarctic ice sheets were developed around 32mya. These north and south pole development of ice was due to the opening and closing of ocean continent gateways. More than 30% of the land area of the Earth was covered by glacial ice; during the interglacial stages, probably only about 10% was covered. The animals of the Pleistocene began to resemble those of today, and new groups of land mammals, including humans, appeared. At the end of the epoch, mass extinctions occurred: in North America more than 30 genera of large mammals became extinct within a span of roughly 2,000 years. The major effects of the glaciations are erosion and deposition of material over large part of continents, modification of river system, creation of pluvial lakes, abnormal winds , change in sea level. Thus we need to understand the dynamic glacial cycles on the Earth system.

28. Reference: Living with Earth, An introduction to Environmental Geology- By Hudson (2006) Earth’s climate, past and future by Willium F. Ruddiman . https://www.britannica.com/science/Pleistocene-Epoch/Megafaunal-extinctions https://www.e-education.psu.edu/earth103/node/636 https://slideplayer.com/slide/7556043 / https://www.slideshare.net/fozzie/lesson-1-history-of-glaciation