Petrified Forest Forest National Park in Arizona has fossilized logs of trees in the Triassic Chinle Petrified Formation. silica required for silicification of the wood was derived from the dissolution of The volcanic ash. rocks of the Painted Desert in Arizona are also from the Triassic Chinle Formation. The TRIASSIC TO JURASSIC 24 National Park in southwestern Utah is known for the cross-bedded sandstones Zion 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 North America during Jurassic, the Appalachians were smaller in size and extent than In they were during Triassic. sediments were deposited east of the Appalachians in the area that is now on Non-marine the continental shelf. western North America, shallow seas flooded the craton, and sandy and shaley In sediments were deposited. 26 FIGURE 13- EVAPORITES IN THE GULF OF MEXICO were deposited during Late Triassic and Jurassic in the Gulf of Mexico area. Evaporites evaporating basin in which seawater from the Atlantic Ocean was concentrated. Great beds of gypsum and salt, more than 1000 m thick, were deposited, indicating an Thick arid climate. of the thick salt beds, called the Louann Salt, formed salt domes in the Gulf of Mexico One area. 27 SALT has a low density and flows plastically when compressed under 1000’s of m of Salt sediment. flows upward through the overlying sediments, forming structures that resemble Salt intrusions, and causing the sediment above them to arch upward into a dome shape. 28 SALT DOMES domes are important economically because oil and natural gas float on water and Salt tend to move upward into the up-arched sediments, where they become trapped. domes are major oil and gas traps. Salt 29 FIGURE 13-9 JURASSIC OF WESTERN NORTH AMERICA the western U.S., the seas transgressed and regressed during Jurassic. In and evaporites were deposited in shallow seas. Limestones 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
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 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
Ch13%20Mesozoic%20Events%20Notes.docx