Ch13 Mesozoic Events Notes.docx

The Earth Through Time Chapter 13—Mesozoic Events CHAPTER OUTLINE FOR TEACHING I. Overview of Mesozoic (251 to 65.5 million years ago) A. Spans Three Periods 1. Triassic: spans 51 million years 2. Jurassic: spans 55 million years 3. Cretaceous: spans 80 million years B. Evolution 1. Many new families of plants and animals 2. Two new vertebrate classes (birds and mammals) C. Supercontinent of Pangaea: rifted apart over a span of 150 million years. II. Breakup of Pangaea: 4 stages (three of those 3 during Mesozoic) A. Stage One: Triassic 1. Rifting and volcanism, normal faulting a. tensional stresses separated North America from Gondwanaland b. similarly Mexico from South America c. similarly eastern North America from northern Africa 2. Sea-floor generation during opening of oceans (basaltic volcanism) B. Stage Two: Triassic-Jurassic 1. Rifting of narrow oceans between South Africa and Antarctica, Africa and India 2. Massive outpouring of basaltic lavas (covering 7 million km2) C. Stage Three: Jurassic-Cretaceous 1. Atlantic Ocean rift extended northward 2. Clockwise rotation of Eurasia (Europe) 3. Closing of eastern Tethys Sea (pre-Mediterranean) 4. South America-Africa split apart 5. Australia-Antarctica remained intact 6. Eastern North America-Greenland-Baltica remained intact D. Stage Four: post-Mesozoic 1. Complete North America-Eurasia (Laurentia-Baltica) split 2. Antarctica-Australia split III. Mesozoic History of North America A. Triassic and Jurassic (eastern and southern areas) 1. Normal fault-bounded basins developed due to rifting: Nova Scotia to North Carolina a. troughs filled with terrestrial sediments and volcanics b. Newark Group (Upper Triassic-Lower Jurassic) c. Palisades basalts of NJ and NY (190 million years ago) 2. Fall Line: boundary of rift-faulted rocks, a prominent physiographic feature 3. Development of Gulf of Mexico a. occupied areas opening south of Appalachian-Ouachita folded mountains b. filled with Upper Triassic-Lower Jurassic salts and evaporites (indicating aridity); over 1000 m deposited; origin of Gulf coast salt domes of today B. Cretaceous (eastern and southern areas) 1. Flooding of coastal lowlands due to high sea levels a. Atlantic and Gulf Coastal Plains inundated as they acted as subsiding shelves at this time b. thick deposits of deltas, barrier islands, shelves, reefs, etc. formed c. Florida: shallow submarine bank for limestones d. reefs made of rudistid bivalves rimmed Gulf Coastal area during Early Cretaceous e. extensive chalk deposits of Cretaceous sea due to massive production of microscopic calcareous plankton (coccoliths); creta = chalk 2. Rifting and ocean opening on eastern side led to closure and compression on the western side of continent; subduction resulted C. Triassic (western areas) 1. Accretionary tectonics - characteristic of west coast subduction at this time a. steeply dipping subduction zone b. volcanic arcs and micro-continents carried to western margin (displaced, exotic, or alien terrains—as many as 50 now known) c. massive accretion by subduction (including volcanism), obduction, and tectonic accretion of displaced terrains d. tectonic collage of displaced terrains may be 70% of total western accretion; termed accretionary tectonics 2. Cordilleran region divisions a. western belt: volcanics and siliceous deposits (800 m) b. eastern belt: stable interior sediments 3. Sonoma orogeny: Permian-Triassic, Nevada a. island arc collided with west coast b. then a west-dipping subduction zone c. added 300 km new area to west d. massive thrust faulting e. Sonoma terrain: additional rocks added during accretion 4. Eastern belt deposition a. sandstones and limestones (shallow marine, 1000 m in Idaho, Early Triassic) b. Lower Triassic continental red-bed facies farther east c. Upper Triassic sediments: from rivers flowed west across area d. Upper Triassic-Jurassic stratigraphy (Arizona): Moenkopi Fm. (oldest), Shinarup Fm., Chinle and Kayenta Fms., Navajo Sandstone, Wingate Sandstone D. Jurassic-Early Tertiary (western area) 1. Nevadan orogeny: eastward shift in orogenic effect a. formation of convergent mélange deposits b. Franciscan belt of California (classic mélange) c. great volumes of granodiorite intruded: Sierra Nevada, Idaho, and Coast Range batholiths 2. Sevier orogeny: Middle Jurassic-earliest Tertiary a. precedes batholith intrusion b. basement-involved tectonics: multiple imbricated thrust faults (low-angle décollement structures) c. mainly seen in NV and UT, also MT, BC, Alberta d. crustal shortening by 100 km 3. Jurassic sedimentation a. Navajo Sandstone (Lower Jurassic, MT, WY, NV, Alberta): clean recycled eolian sands deposited in coastal dune and shoreline environments; covers 50,000 km2 b. Sundance Formation (Middle) Jurassic, famous for fossil reptiles): deposits of the Sundance Sea c. Morrison Formation (Upper Jurassic, famous for dinosaurs): swampy plain deposits formed as Sundance Sea regressed upon rising of Cordilleran highlands to the west 4. Laramide orogeny: Cretaceous-Paleogene a. eastward shift in deformation b. high-angle reverse faults c. domes and anticlines d. Rocky Mountain structures 5. Cretaceous sedimentation a. foreland basin sedimentation b. Early Cretaceous Seaway: seas withdrew during Middle Cretaceous regression c. Late Cretaceous Seaway: greatest of marine intrusions (transgressions); flooded area = foreland basin (i) Dakota Group: transgressive-phase clastics (Great Plains area) (ii) Niobrara Formation: carbonates of high sea level (limestones and marls) d. bentonites: altered volcanic ash layers IV. Mesozoic History of Eurasia (Europe) and the Tethys Seaway History A. Triassic 1. Limestone deposition 2. Highlands developed to north (Vindelician arch) 3. New Red Sandstone deposited as clastic wedge B. Jurassic: period of quiet C. Cretaceous 1. Africa moves north toward Eurasia (Europe) 2. Compression during collision deforms Tethys sediments 3. Many great transgressions of the sea V. Gondwanaland’s Continents A. South America 1. Triassic: 3 depositional areas a. western tract: turbidites, conglomerates, and siliceous sediments b. eastern tract: deeper water carbonates and shales 2. Jurassic a. widening split of South America and Africa b. Andean belt deformation and volcanism c. great outpourings of andesite in volcanic chain d. emplacement of large batholiths B. Africa 1. Early Triassic: Africa still joined to South America 2. Triassic-Jurassic: Karoo basin filled with fossiliferous continental clastics, then 1000 m of basalt flows due to rifting 3. Jurassic-Cretaceous: Africa is a stable continent C. India 1. Triassic-Cretaceous: moved continually north 2. Jurassic: interior sedimentation (dinosaurs well represented) 3. Cretaceous: vast outpourings of basaltic lava in northern regions (Deccan Traps covering 500,000 km2, as much as 1 million km3 of basalt makes it Earth’s greatest known outpouring) Answers to Discussion Questions 1. Rifting generally precedes the separation of continental crustal segments. Examples of Mesozoic rifting include Triassic rifting of eastern North America and Gondwanaland and the Jurassic-Cretaceous rifting of South America and Africa. 2. The Triassic Newark Group of the east coast of North America was formed in a tensional stress environment that caused rifting with associated normal faulting and basaltic volcanism. The rifts filled with alluvial and lacustrine sediments shed from adjacent fault-block mountains. The normal faults originated from gravity effects after crustal stretching and fracturing. Reverse faults were not produced for lack of requisite compression. Older lateral strike-slip faults and reverse faults provided sites for reactivation of crustal movement during rifting. 3. The Sevier orogeny involved basement crystalline rocks which were displaced laterally along imbricate thrust faults. These low-angle features represent a décollement where extensive amounts of crust become “unstuck” and are displaced laterally many kilometers. The most well known structure is the Lewis Thrust with over 65 km displacement. 4. Arid conditions are accountable for producing extensive evaporation to produce 1000 m of salt and gypsum. The tectonic setting also contributed such that a limited amount of seawater could enter the basin, evaporate, and then be recharged by another influx of seawater. The lighter specific gravity (density) of salt and gypsum and salt’s tendency to be plastically deformed under great pressure help create conditions so that deeply buried salt flows upward in the form of salt domes. Gulf Coast salt domes deform overlying strata as they migrate upward and thus create structural conditions for accumulation of migrating hydrocarbons in “petroleum traps.” 5. Accretionary tectonics probably accounts for most of the increase in size of North America during Mesozoic. Accretionary tectonics encompasses all active margin processes which add continental crust via subduction (including volcanism), obduction (including mélange accretion), and welding of displaced terrains (both micro-continents and island arcs). In North America during Mesozoic, accretionary tectonics characterizes the western belt of the Cordilleran area during Triassic. The Sonoma Orogeny specifically is an example of such tectonics. Likewise, with Jurassic the Nevadan Orogeny represents accretionary tectonics of western North America. Allochthonous terrains contribute displaced continental crust (perhaps 70% of total western Mesozoic accretion) and the energy of accretionary collision produces structural effects and regional metamorphism. Passive margin sedimentation accounts for the other part of North American size growth during Mesozoic. 6. Deccan volcanism would have contributed significant amounts of greenhouse gasses (especially CO2) in a relatively short period of time. Such an imbalance in atmospheric gas mixture could have temporarily strongly elevated global temperatures. 7. Obduction involves off-scraping and thrusting of lighter rock, especially sediments, and in some places, pieces of denser seafloor (ophiolites) onto continental crust as a process in tectonic accretion. Subduction involves decent and re-melting of denser seafloor at a convergent boundary. Examples of Triassic obduction are common. Examples of subduction abound: the entire Mesozoic history of the western U.S. is dictated by continual subduction as the Pacific Ocean closes. 8. Chalk is a sedimentary rock composed of microscopic calcareous plankton compressed together. Cretaceous strata are especially rich in chalk deposits. The marine plankton-chalk connection dictates composition and physical properties of the rock. The profusion of coccoliths during Cretaceous is key to chalk’s domination of the marine sediment record of that period. 9. Mesozoic Era lasted approximately 179 million years. Cretaceous Period lasted the longest of the Mesozoic periods, 78 million years. 10. Cordilleran highlands adjacent to the retreating Sundance Sea were the likely sources of clastic sediments comprising the Morrison Formation of the Rocky Mountain region. The Morrison Formation shows evidence of fluvial (river) deposition and includes abundant traces and bones from terrestrial vertebrates, especially dinosaurs. 11. Epicontinental (epeiric) seas were most extensive during Cretaceous and least extensive during Triassic according to Mesozoic paleogeographic maps. 12. When the breakup of Pangaea began about 180 million years ago, the Tethys seaway was located between Gondwanaland and Laurasia on the eastern side of Pangaea. Later, the Tethys occupied the region between Africa-India-Australia (as a southern continent) and Eurasia or Europe (as a northern continent). The Tethys was closed by northward movement of Africa-India-Australia and subduction of Tethys seafloor beneath Eurasia (Europe). The Mediterranean Sea, Adriatic Sea, Aegean Sea, and Black Sea occupy the former position of the Tethys, and thus may be part of the former Tethys. Rocks deposited within the Tethys, which extended from Japan to the western Mediterranean, may be formed in the Alps and Himalayan Mountains. 13. The Late Cretaceous development of a “great embayment” of the Tethys resulted in a connection of the Tethys and the northern Atlantic Ocean. Using the Western Interior Seaway of North America as an example, the distribution of many sea creatures, for example the abundant oysters of that time, could be used as evidence of a connection during that time. 14. c 15. B 16. d 17. b Chapter Activities Student activities for in-depth learning. 1. Some of the best-known and best-preserved early dinosaurs come from a locality in South America at Ischigualasto, Argentina. Look at the University of California, Berkeley, Museum of Paleontology web page on this famous locality and describe the age and types of dinosaur remains that are found here http://www.ucmp.berkeley.edu/mesozoic/triassic/ischigualasto.html. Why do you think that this is such a good place to look for dinosaur bones? 2. The Palisades basalts of the Hudson River area are remarkable volcanic features. Look at the background information on these basalts at http://en.wikipedia.org/wiki/Palisades_Sill and answer these questions. When were the Palisades basalts formed? Where do they lie relative to the Hudson River today? How were they formed? What was going on in the geological history of Pangaea that contributed to the outpouring of basalts that became the Palisades? Chapter 13—Mesozoic Events CHAPTER OVERVIEW The era we call Mesozoic, “Middle Life” (Triassic, Jurassic, and Cretaceous) follows the catastrophic end of Paleozoic. The mass extinctions of Late Palezoic that defined the boundary of those periods meet the “new” challenges and changes on Earth. Those dramatic changes occur in the continental evolution of life forms and the crustal unrest of the continents. The breakup of Pangea is taken as a pivotal point in time and is discussed on a global scale as are the configurations of the continents. A comprehensive view of the accretionary tectonics is discussed along with the other Mesozoic physical processes that affected North America and the rest of the world. LEARNING OBJECTIVES By reading and completing information within this chapter, you should gain an understanding of the following concepts: Explain the breakup of Pangea using stages (steps) in your discussion along with major geographic features. Discuss the conditions that account for the presence of evaporites in the Gulf Coast and how they are related to petroleum traps in overlying Cretaceous and Cenozoic strata. Discuss what is meant by the term accretionary tectonics. Define the accretionary tectonics terms exotic terrane, obduction, and tectonic collage. Describe the major orogenic events that affected western North America during Mesozoic including Sonoma, Nevada, Sevier, and Lamamide. Discuss the epicontinental seas (over the continents) of Jurassic and Cretaceous, and give evidence for their existence. Describe Upper Triassic and Lower Jurassic formations that are exposed in the walls of Zion Canyon in southern Utah. Discuss the geologic history of the Tethys Seaway and the periods of its extent. Describe Gondwana events including those in South America, Africa, and India. CHAPTER OUTLINE The Breakup of Pangea The Mesozoic in Eastern North America Triassic and Jurassic Periods Cretaceous (the “Chalk” Period) The Mesozoic in Western North America Accretionary Tectonics: A Way to Grow Triassic Period: Volcanism, Orogenies, and Arizona’s Petrified Logs Sonoma Orogeny Jurassic Period Orogenies: Nevadan, Sevier, and Laramide Nevadan Orogeny Sevier Orogeny Laramide Orogeny Jurassic Habitats for Marine Reptiles and Dinosaurs The Great Cretaceous Epicontinental Sea Foreland Basin and Economic Resources The Tethys Sea in Europe Gondwana Events South America Africa India Key Terms (pages given in parentheses) accretionary tectonics (392): The growth of a continent by the progressive incorporation of crustal fragments by either obduction or subduction. bentonite (405): Bentonite is composed of clay minerals that are formed by the alteration of volcanic ash. Cretaceous rocks of Wyoming and Colorado include extensive beds of this soft, plastic, light-colored clayey rock. chalk (390): A fine-grained white, soft variety of limestone composed mainly of the microscopic calcareous platelets (coccoliths) of golden-brown algae. The Cretaceous Period takes its name from Creta, the Latin name for chalk. Dakota Group (405): Lower Cretaceous sandstone beds that mark the transgressive phase of the Cretaceous sea. The red, yellow, and brown layers of the Dakota are exposed in many places along the eastern front of the Rocky Mountains, where the inclined beds formed prominent ridges called hogbacks. Deccan Traps (412): The northwestern half of India was flooded with immense quantities of low-viscosity basaltic lava. The now solidified lavas are flood basalts of the Deccan Traps. The outpouring continued from Cretaceous well into Cenozoic. These basalt floods likely record the passage of India across a fixed hot spot in the mantle. exotic terranes (391): Exotic masses of rock of tectonic origin that have been displaced from their origin. foreland basin (403): In terms of plate tectonics, the depositional basin that receives sediments (as well as smaller amounts from the craton). The foreland basin of the western interior of North America was immense. It extended from the Arctic to the Gulf of California, and in some places it was over 1600 kilometers wide. Laramide orogeny (397): In general, those pulses of mountain building that were frequent in late Cretaceous time and were in large part responsible for producing many of the structures of the Rocky Mountains. mélange (396): A sequence of crumpled and altered rock that were affected by compression between converging plates. The Franciscan fold belt of California represents a mélange. Morrison Formation (400): Formation formed when the Sundance Sea regressed, leaving behind a vast, swampy plain across which meandering rivers build floodplains. The Morrison Formation extends across millions of square kilometers of the American West. Enclosed within these floodplain deposits are the bones of more than 70 species of dinosaurs. Nevadan orogeny (395): In general, those pulses of mountain building, intrusion (magmatism), and metamorphism (deformation) that were most frequent during Jurassic and Early Cretaceous along the western part of the Cordilleran Orogenic belt. During Triassic, and increasing in frequency during Jurassic and Cretaceous, graywackes, mudstones, cherts, and volcanics that had been swept into the subduction zone were severely folded, faulted, and metamorphosed. Niobrara Formation (406): Cretaceous carbonate formation including soft, clayey limestones and chalky shales. The Niobrara has yielded the remains of a variety of marine creatures, including enormous numbers of oysters, a large Cretaceous diving bird, marine reptiles, and the large flying reptile Pteranodon. obduction (392): The process whereby one rock mass rides up and over another (the opposite of subduction). rudistid (390): Peculiarly specialized Mesozoic bivalva often having one valve in the shape of a horn coral, covered by the other valve in the form of a lid. salt dome (388): Huge, cylindrical domes that are economically important structures in that they help entrap oil and natural gas. Sevier orogeny (396): A second phase of the tectonic development of the Cordillera which primarily affected shallow-water carbonates and terrigenous clastics deposited over a time span from Middle Jurassic to earliest Cenozoic. During the Sevier Orogeny, strata were sheared from underlying Precambrian rocks and broken along parallel planes of weakness to form multiple, imbricated, low-angle thrust faults. Décollement (“unsticking”) is the term used to describe this kind of structure in which older rocks are thrust on younger in multiple, nearly parallel slabs of crust. Sonoma orogeny (393): Middle Permian orogenic movements, the structural effects of which are most evident in western Nevada. It occurred when an eastward-moving volcanic arc, called the Golconda arc, collided with the Pacific margin of North America (western edge of Nevada). Sonoma terrane (393): Triassic rocks of the far western Cordillena include volcanics and graywackes derived from the island arc. The Sonoma Terrane originated in the Pacific Ocean. Sundance Formation (399): Famous for its fossil content of Jurassic marine reptiles. Sediment in the Sundance Formation and overlying younger Jurassic rock units was derived from the Cordilleran highlands that lay to the west. Sundance Sea (399): A great embayment occurring during the Middle Jurassic. Marine conditions became more widespread. The entire west-central part of the continent was flooded by a wide seaway that extended well into central Utah. Within the Sundance sea were deposited the sand and silts of the Sundance Formation. tectonic collage (392): An analogous region of displaced terranes. Tethys Sea (406): Sea between Eurasia and Africa that began to narrow as a result of compression from the northwardly-moving African plate. CHAPTER 13 Mesozoic Events Peter L. Kresan Photography 2 MESOZOIC ERA ?Mesozoic Era = 251 to 65.5 million years ago. ?Name Mesozoic means "middle life" ?Mesozoic Era consists of three periods: ?Triassic - Oldest. Lasted about 51 million years ?Jurassic - Lasted about 55 million years ?Cretaceous - Youngest. Lasted about 80 million years 3 MESOZOIC ERA ?Mesozoic began after the extinction of Paleozoic organisms. ?Mesozoic rocks contain the remains of organisms that are more advanced than those of Paleozoic, but not as modern as those living today. ?Two new vertebrate classes appeared: birds and mammals. ?Mesozoic lasted approximately 186 million years, and ended with an extinction event in which the dinosaurs met their demise. 4 ?At the beginning of Mesozoic, continents were assembled into a supercontinent, Pangea. ?Pangea formed during Late Paleozoic by the collision and joining of the continents to form a single landmass surrounded by a vast ocean. PANGEA (After C. R. Scotese, et al., 1979, Jour. Geol. 83(3):217–277) 5 PANGEA ?In the equatorial area to the east, between Africa and Europe, and between India and Asia, was an embayment called the Tethys Sea. ?The climate became arid; evaporites (E) were deposited. (After C. R. Scotese, et al., 1979, Jour. Geol. 83(3):217–277) 6 THE BREAKUP OF PANGEA ?Breakup began during Mesozoic and finished during Cenozoic. ?Breakup can be viewed in four stages. ?The northern continents were called Laurasia and the southern continents were called Gondwana. ?As North America and Europe separated, they were called Laurentia and Baltica. 7 THE BREAKUP OCCURRED IN FOUR STAGES: Stage 1: ?Rifting and volcanism along normal faults during Triassic, resulting in the separation of North America (Laurasia) from Gondwanaland. ?Normal faulting in eastern North America, accompanied by the intrusion of dikes and lava flows. ?Atlantic Ocean opened and widened through the extrusion of oceanic basalts. 8 Stage 1 cont.: The continents did not split along the places that marked their previous edges. The old suture (or "seam") between North America and Africa lies in southern Georgia. When Africa pulled away, it left a sliver of the African continent attached to the southeastern U.S. THE BREAKUP OCCURRED IN FOUR STAGES: 9 THE BREAKUP OF PANGEA Stage 2: ?Rifting and separation of Africa, India, and Antarctica. ?Large volumes of basalt were extruded. 10 Stage 3: ?The Atlantic rift extended northward. ?Eurasia moved to the south, partially closing the Tethys Sea. ?South America began to split from Africa by Late Jurassic, and completely separated by Late Cretaceous. ?Australia remained connected with Antarctica. ?India was moving northward toward Asia. ?Greenland began to separate from Europe (Baltica), but remained attached to North America (Laurentia). THE BREAKUP OF PANGEA 11 Stage 4: ?After Mesozoic, the breakup of Pangea continued. ?North America (Laurentia) separated from Eurasia (Baltica) along the North Atlantic rift. ?Antarctica and Australia separated about 45 m.y. ago. The total time for the fragmentation of Pangea was about 150 m.y. THE BREAKUP OF PANGEA 12 TRIASSIC OF EASTERN NORTH AMERICA ?During Triassic in eastern North America, the Appalachian Mountain ranges were much higher than they are today. ?The mountains were eroding at the beginning of Mesozoic. ?Coarse clastic sediments from the mountains filled basins between the mountains during Early and Middle Triassic. ?The Appalachians were reduced by erosion throughout Triassic, Jurassic and Cretaceous. 13 TRIASSIC PALEOGEOGRAPHY 14 FIGURE 13-2 Generalized paleogeographic map for the Triassic Period (250–203 million years ago). TRIASSIC OF EASTERN NORTH AMERICA ?During Late Triassic and Early Jurassic, North America experienced tensional stress and rifting. ?Fault-bounded rift basins developed in eastern North America, extending from Nova Scotia in the north to Georgia in the south. 15 NEWARK SUPERGROUP The fault-bounded basins filled with Upper Triassic and Lower Jurassic sediments eroded from the Appalachians, and basaltic lava flows and diabase intrusions (sills and dikes). These rocks comprise the Newark Supergroup. 16 FIGURE 13-3 Troughlike deposits of Late Triassic rocks in eastern North America. FOUR STAGES OF TRIASSIC HISTORY OF THE CONNECTICUT VALLEY 1.Erosion of mountains 2.Low plain 3.Sediment deposition, lava flows, and intrusions in fault-bounded basin 4.Post-depositional faults 17 NEWARK SEDIMENT DEPOSITION The sediment in the Newark basins was deposited in continental (non-marine) sedimentary environments such as: ?Alluvial fans ?Rivers and floodplains (alluvial) ?Lakes (lacustrine) ?Deserts (aeolian or eolian) 18 NEWARK SEDIMENT DEPOSITION ?The sedimentary rocks are primarily red arkosic sandstone, siltstones, and shales. ?Dinosaur bones and tracks are present locally. ?Some of the lake deposits are black and gray shales with the remains of fish, aquatic reptiles, and freshwater invertebrates. 19 ?The Palisades along the western shore of the Hudson River are created by the exposed diabase sill, about 190 million years old. NEWARK SUPERGROUP – PALISADES SILL 20 TRIASSIC OF WESTERN NORTH AMERICA Several belts of sedimentary deposition were present in western North America during Mesozoic: 1.A western belt of volcanic rocks and graywackes associated with volcanic island arcs 2.An eastern belt of shallow marine sandstones and limestones closer to the mainland 3.And farther eastward, non-marine, continental red beds deposited on the low alluvial plains 21 TRIASSIC PALEOGEOGRAPHY During Middle Triassic, the seas regressed in the U.S. (although they still covered parts of Canada), and the former seafloor was subject to erosion, forming an unconformity. 22 Upper Triassic to Jurassic continental deposits (fluvial, lacustrine, and aeolian) overlie the unconformity. Jurassic Navajo Sandstone Kayenta Formation Wingate Sandstone Triassic Chinle Formation or Group Shinarump Conglomerate Moenkopi Formation TRIASSIC TO JURASSIC 23 FIGURE 13-15 Petrified Forest ?Petrified Forest National Park in Arizona has fossilized logs of trees in the Triassic Chinle Formation. ?The silica required for silicification of the wood was derived from the dissolution of volcanic ash. ?The rocks of the Painted Desert in Arizona are also from the Triassic Chinle Formation. TRIASSIC TO JURASSIC 24 ?Zion National Park in southwestern Utah is known for the cross-bedded sandstones exposed in Zion Canyon. These belong to the Navajo Sandstone. The other units mentioned above are also exposed there. TRIASSIC TO JURASSIC 25 JURASSIC PALEOGEOGRAPHY ?In North America during Jurassic, the Appalachians were smaller in size and extent than they were during Triassic. ?Non-marine sediments were deposited east of the Appalachians in the area that is now on the continental shelf. ?In western North America, shallow seas flooded the craton, and sandy and shaley sediments were deposited. 26 FIGURE 13- EVAPORITES IN THE GULF OF MEXICO ?Evaporites were deposited during Late Triassic and Jurassic in the Gulf of Mexico area. ?Great evaporating basin in which seawater from the Atlantic Ocean was concentrated. ?Thick beds of gypsum and salt, more than 1000 m thick, were deposited, indicating an arid climate. ?One of the thick salt beds, called the Louann Salt, formed salt domes in the Gulf of Mexico area. 27 SALT DOMES ?Salt has a low density and flows plastically when compressed under 1000’s of m of sediment. ?Salt flows upward through the overlying sediments, forming structures that resemble intrusions, and causing the sediment above them to arch upward into a dome shape. 28 SALT DOMES ?Salt domes are important economically because oil and natural gas float on water and tend to move upward into the up-arched sediments, where they become trapped. ?Salt domes are major oil and gas traps. 29 FIGURE 13-9 JURASSIC OF WESTERN NORTH AMERICA ?In the western U.S., the seas transgressed and regressed during Jurassic. ?Limestones and evaporites were deposited in shallow seas. The Navajo Sandstone (Upper Triassic – Lower Jurassic) has large-scale cross-bedding, indicating that it was deposited by the wind, probably in a coastal dune environment. 30 Sundance Sea ?During Middle Jurassic, west-central North America was flooded by a broad seaway, called the Sundance Sea. ?The bones of marine reptiles are found in the sandstones and siltstones of the Sundance Formation, deposited in the Sundance Sea. JURASSIC OF WESTERN NORTH AMERICA 31 FIGURE 13-27 DINOSAURS IN THE MORRISON FORMATION ?After the Sundance Sea regressed, it left behind a vast swampy plain with meandering rivers. ?The deposits of these rivers and floodplains comprise the Jurassic Morrison Formation, which covers a large area in the west. ?The bones of more than 70 species of dinosaurs have been found in the Morrison Formation. 32 CRETACEOUS PALEOGEOGRAPHY ?Cretaceous was a time of high sea level and vast epicontinental seas. ?The most prominent feature in North America during Cretaceous, was the shallow epicontinental sea that flooded much of the western interior of the continent, from the Gulf of Mexico to the Arctic Ocean, as well as the Atlantic and Gulf Coastal Plains. 33 FIGURE 13-12 CRETACEOUS CHALK ?Chalk, a white, fine-grained variety of limestone composed of microscopic shells (called coccoliths) of golden-brown algae, was deposited in many places around the world during Cretaceous. ?The word Cretaceous is derived from the Latin word for chalk, creta. 34 ATLANTIC COASTAL PLAIN ?The Atlantic Coastal Plain began to subside (or sink) early during Cretaceous. ?Marine and deltaic sediments accumulated, gradually building a wedge of sediments that thickened seaward. ?Most Cretaceous sediment in this area was deposited on the present-day continental shelf. 35 ATLANTIC COASTAL PLAIN 36 RUDIST REEFS ?Extensive carbonate reefs grew in the warm tropical seas of Cretaceous. ?A prominent reef-building invertebrate was a bivalve mollusc called a rudist. ?Cretaceous rudist reefs have high porosity and permeability, and are well-known sites of oil and natural gas accumulation. 37 CRETACEOUS OF WESTERN NORTH AMERICA ?In western North America, a range of high mountains formed as a result of orogenies that had begun during Jurassic. ?As the mountains eroded, thick sequences of sediments (up to 15,000 m or 9 mi thick) accumulated in adjacent rapidly subsiding basins. ?The rocks were folded and intruded as a result of continuing tectonic deformation during mid- and Late Cretaceous. 38 CRETACEOUS OF WESTERN NORTH AMERICA ?The sea was east of the mountains, advancing and retreating. The sea flooded the interior lowlands of North America from the Gulf of Mexico to the Arctic in Canada. ?The depositional basin east of the mountains was a foreland basin. 39 FIGURE 13-30 CRETACEOUS FORELAND BASIN 40 FIGURE 13-30 CRETACEOUS COAL ?Coal was deposited in the foreland basin, to the east of the eroding mountain range. ?Cretaceous coal underlies 300,000 km2 of the Rocky Mountain region. ?It is mined for fuel and is valued for its low sulfur content. 41 DAKOTA SANDSTONES ?Transgressive-regressive sedimentary cycles mark the advance and retreat of Cretaceous seas. ?The Dakota Group sandstones were deposited by a transgression, and form hogback ridges along the eastern front of the Rocky Mountains. ?In parts of the Great Plains, the Dakota sandstones are an important source of underground water (aquifer). 42 VOLCANIC ASH AND BENTONITES ?A series of volcanoes in western North America deposited ash over an extensive area. ?The volcanic ash is now altered to a soft clay called bentonite. ?These volcanic ash beds are important because they are useful in correlation and serve as time horizons. 43 NIOBRARA LIMESTONE Cretaceous limestones of the Niobrara Formation deposited in the epicontinental sea contain the remains of marine reptiles, flying reptiles, a diving bird, oysters, and other organisms. 44 MESOZOIC TECTONICS OF WESTERN NORTH AMERICA ?Western North America experienced compressional forces as the continent moved westward, overriding the Pacific plate. ?A subduction zone was present along the western margin of North America. ?Uplift of mountains in the Cordillera was related to sea-floor spreading in the Atlantic. Tectonic activity was greatest in western North America when sea floor spreading was most rapid in the Atlantic. 45 ACCRETIONARY TECTONICS ?As the Pacific plate was subducted under the North American plate, microcontinents, volcanic island arcs, and other exotic terranes carried on the Pacific plate collided with the North American plate and became attached to it. ?The North American continent grew by the accretion of exotic terranes around its edges. ?The growth of a continent by addition of exotic terranes is called accretionary tectonics. 46 MESOZOIC OROGENY IN WESTERN NORTH AMERICA ?Orogenies (or mountain-building events) occurred as the exotic terranes collided with western North America. ?Among these orogenies were the: ???????????????? ????????????????? ???????????????? ?????????????????? 47 SONOMA OROGENY ?The Sonoma orogeny, during Triassic, was the first orogeny in the Cordillera. ?It was caused by the collision of a volcanic arc with western North America. ?Oceanic rocks were obducted (thrust on top of continental rocks). 48 FIGURE 13-14 NEVADAN OROGENY ?Subduction resulted in eastward-shifting phases of deformation, initially affecting the far western Cordillera, and then proceeding eastward to the margin of the craton. This produced the Nevadan orogeny. ?Graywackes, mudstones, cherts, and volcanics were folded, faulted, and metamorphosed, forming a mélange (meaning "a jumble") in the subduction zone. ?This formed the Franciscan fold belt of California. 49 MESOZOIC BATHOLITHS ?Large bodies of magma, derived from melting of rocks in the subduction zone, were intruded into overlying rocks. ?The magma cooled to form enormous granite batholiths. ?This occurred during and after the Nevadan orogeny, during Jurassic and Cretaceous. 50 MESOZOIC BATHOLITHS Examples: ?Sierra Nevada batholith ?Idaho batholith ?Coast Range batholiths ?Baja California batholith 51 SEVIER OROGENY ?A second tectonic phase affected shallow water sedimentary rocks east of the present-day Sierra Nevada mountains. ?Sedimentary rocks were sheared from underlying Precambrian rocks. ?This resulted in the formation of multiple thrust faults stacked upon one another and referred to as imbricate thrusts. ?Thrust faults shortened the crust by more than 100 km (60 mi) in the Nevada-Utah region. 52 IMBRICATE THRUSTS FROM THE SEVIER OROGENY 53 FIGURE 13-23 LARAMIDE OROGENY ?Deformation shifted eastward toward the craton after intrusion of batholiths, and thrust faulting decreased near the end of Cretaceous. ?Domes, basins, monoclines, anticlines, and high angle reverse faults (which become low angle thrust faults at depth) formed during this orogeny. ?Many of the larger faults were reactivated Precambrian faults. 54 ROCKY MOUNTAINS ?The Rocky Mountains formed in New Mexico, Colorado, and Wyoming during the Laramide orogeny. ?The present-day landscape, however, is the result of Cenozoic erosion and uplift. 55 56 •FIGURE 13-2 Generalized paleogeographic map for the Triassic Period. Source:. • FIGURE 13-3 Troughlike deposits of Late Triassic rocks in eastern North America. Source: . •FIGURE 13-15 Geologic column (A). Source: . • FIGURE 13-7 Generalized paleogeographic map for the Jurassic Period. Source: . • FIGURE 13-9 Salt dome. Source: . • FIGURE 13-27 Region inundated by the Middle Jurassic Sundance Sea. Source: . • FIGURE 13-12 Source: . • FIGURE 13-30 Major Cretaceous tectonic features in the western US. Source: Courtesy of Dymek. • FIGURE 13-31 Generalized cross-section, Cretaceous rocks of the back-arc basin, U.S. western interior. Source: King, Philip.; The Evolution of North America. © 1959 Princeton University Press, 1987 renewed PUP, 1977 revised edition, 2005 renewed PUP reprinted by permission of Princeton University Press. • FIGURE 13-14 Part of the western United States during Late Permian/Early Triassic. Source: . • FIGURE 13-23 Sevier-type deformation in western Canada. Source: After Structural Section accompanying map entitled Geology of Jasper National Park, compiled by C. J. Yorath for the Geological Survey of Canada.