LANDFORMS of Chapter 5 – Deserts and Dinosaurs that’s about 350 to 250 m.y.a.. the age of reptiles!

Utah back then from space would have looked like norther Africa today, a study of grays and tans and reds with surprises of bright green along our western boundary and ribbons of green from the very-western mountains east across nearly level plains to the seas east of Utah. Utah then looked arid (in the rain shadow of NV-UT mountain ranges), tropical (Utah drifted north to about 30 degrees north latitude). Utah was exposed land, although the eastern 2/3 was nearly sealevel and flooded by sea level changes. This pattern of Ch05 – Deserts and Dionsaurs, more land than sea, contrasted from Ch04-Broad basins more sea than land. In Ch04-Broad basins E

Utah-back-then’s landforms transformed from Ch04-more sea than land with to mountains on what is now the Colrado Utah border, lazy rivers mostly draining from east to west across coastal plains into flat evaporative basins and shallow seas) into Ch05-more land than sea topography with mountains on the Nevada Utah border, rivers draing east east, and, being in the rain shadow of the NV-UT mountains, remarkable dunes across eastehr Utah, stretching from what is now Wyoming across what is now the Four Corners. The scene was dominated by desert as impressive as today’s Sahara desert with intervening fertile rivering terrain peraps similar to the Nile. Utah-then looked somewhat like northern Africa-now, dry and low relief except for the mountains. All of Utah had gone from below sea level to within a few hundred feet above sea level and mountain terrain on the Nevada border.

Utah then was a contrast of two high terrain west and desert, a study, like northern Africa today of tan and red and bright green. From space it would have looked stark, arid, in the rain shadow of Nevada and very-western Utah’s mountainous terrain. The apparently-unrelenting terrain was near sea level, drained from west to east in contrast to Ch04-Broad basins east to west. The rivers must have been imprssive, lazy and loaded with sediment. Utah back then from space may have resembled the geography of norther Africa from Namibia to Morrocco to Egypt and the Sudan, a study of tans and grays interrupted by brigh green of impressive rivers and coastal plains that connected the higher region of the west with the near sea level region of the east. .

SETTING:

Utah was north of the equator drifting from about 15 degrees north to about 30 degrees north over about 100 million years, from 251 to 145 million years ago (link to Duration Ch05), the early Mesozoic era’s Triassic and Jurassic periods, the age of amphibians and reptiles (link to Ch05:Life then); interpreted from the rock record (link to Ch05-RockRecord). Utah was arid, located in the rain shadow of mountains to the west. Utah was hot, located in the tropics and may have been humid. Utah did not have swamplands such as those (DUP??)

TECTONICS RULES

Cause and Effect. Patterns of landforms result from Earth’s two great process of tectonics and erosion/deposition. Tectonics sets the scene. (Link to Tectonics Ch05-More land than sea) In the previous chapter Ch04-BroadBasins—Utah’s eastward momentum was stalled by the repercussions of ginormous Gondwanland ploughing into what is now SE United States coastal states. By the end of Ch05 more land than sea, Utah was near and below sea level. During Ch05 more land than sea, Pangea, the supercontinent on which Laurasia had been joined (accreted) broke along the what is now the Atlantic ocean. Utah of Chapter 05 reversed relative direction and drifed west. Chapter 3 drift east, Chapter 4 stall, Chapter 5 drift west. IMAGE.

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