Cretaceous Periods


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Cretaceous: Tectonics and Paleoclimate, Flora, Fauna, Orogeny

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Cretaceous Periods

  1. 1. • 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, Turkey • 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.  Facies: • 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
  2. 2. Astroblemes • 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 
  3. 3. • tons of substrate. The dust entered the atmosphere, presumably blocking out sunlight for an extended time (perhaps 6 months). • 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
  4. 4. Special Events  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 Coast.  Mass Extinction • 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 representatives.
  5. 5. Cretaceous Graphics Cretaceous Sea Belemnites 
  6. 6.  Pteranodon Tyrannosaurus
  7. 7. Baculites  Placenticera s
  8. 8. Ammonite  Helioceras 
  9. 9.  Tyrannosaurus Skull  Tyrannosaurus Teeth
  10. 10.  Mosasaur Mosasaur Skull
  11. 11. The Cretaceous Period 144 to 65 Million Years Ago • 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 plants. • 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 came together.
  12. 12. 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 and Turonian. 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 Mesozoic Era .  -  Maastrichtian - Campanian - Santonian - Coniacian = Late Cretaceous   - Turonian - Cenomanian -------------------------- - Albine - Aptian =Early Cretaceous - Barremian - Neocomain   ---------------------    Subdivisions of the Cretaceous:
  13. 13. Cretaceous Period: Stratigraphy 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 and Turonian. 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 Mesozoic Era.
  14. 14. 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 Anthophyta. • 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 flowering plants. • 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  Flora Ficus stavina  :Fauna
  15. 15. 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 vegetation. 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 Nannoplankton( Nannofossils)  Fauna  Foraminifera: exceedingly abundant as rock builders of chalk and other calcareous rocks.  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 Jurassic.Echinoides very important e.g. Cidris, Cassidulus, Hemiaster.  Brachiopods : shown gradual declination, numerous only in restricted regions.  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.
  16. 16. Cretaceous Life Small Stuff: Plankton &Microorganisms
  17. 17. 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 Cretaceous site. • Hell Creek, Montana • Pt. Loma Formation - This California locality has yielded inportant fossils for understanding western North American dinosaurs • Cretaceous in Egypt • The Cretaceous rocks covers about 2/5 of Egypt's surface. • In Sinai • Gebel Shabraweat • Gebel Ataqa and along the Red Sea Coast
  18. 18. 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
  19. 19. • 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 .
  20. 20. 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 ammonites. • 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. Fast Facts -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 Mass Extinctions 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 entitled, Extinction The End-Cretaceous (K-T) Extinction
  21. 21. Geological Setting • 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
  22. 22.  Extinction Processes • 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 mass extinctions. • 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 showers, • 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
  23. 23. 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 Cenozoic. 5- Many taxononmic groups declined before the end of the Cretaceous period, but other taxa died out abruptly right at the end. 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:
  24. 24. 1- Early in late Cretaceous time, about 65 million years ago, a moderately severe extinction eliminated many species in the marine realm.   2- During the past few years, this biotic crisis , which brough the Mesozoic 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 meteorites 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 predict. 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
  25. 25. 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 extinction occurred. • 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.
  26. 26. Meteorite Impact • 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 boundary layer. • Recent research suggests that the impact site may have been in the Yucatan Peninsula of Mexico.
  27. 27. Volcanic Eruptions • 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
  28. 28. 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 fossils; In the upper Cretaceous beds , abundant remains of land plants now restricted to temperates or sub-tropical region are recorded. 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.  Cretaceous: Orogeny • 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” Revolution. • 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
  29. 29. All fossils in the Cretaceous Gryphaea sp. © 2006 Exogyra ponderosa © 2006
  30. 30. Exogyra costata Inoceramus © 2003
  31. 31. Pterotrigoni a thoracica © 2004 Pycnodonte (Gryphaea) convexa
  32. 32. Collignoniceratidae © 2005 Discoscaphites conradi © 2005
  33. 33. Exiteloceras jennyi © 1998 Hoploscaphites nicolletti © 2005
  34. 34. Pachydesmoceras colusaense © 2004 Placenticeras placenta © 2006
  35. 35. Prionocyclus Scaphites
  36. 36. Scaphites nodosus © 1998 Shenodiscus lenticulares © 2005
  37. 37. Maiasaura peeblesorum © 2005 Tyrannosauru s rex © 2005
  38. 38. Epiaster whitei © 1998 Anomalina popenoei © 1999
  39. 39. Anchura substriata © 2006 Pyropsis proxim © 2006
  40. 40. Gyrodes crenata Chondrichthy es © 2003
  41. 41. Squalicorax pristodontus © 2005 Ptychodus polygyrus © 2004