Earth History GEOL 2110

The Mesozoic EraTectonic and Geologic History

In North America

Major Concepts• The geologic history of North America during the

Mesozoic Era was dominated by two contrasting tectonic processes :On the east, continental rift of Pangea was creating the present-

day Atlantic marginOn the west, compressional tectonics accreted exotic terranes in

the early Mesozoic (Triassic and early Jurassic periods) and then became Andean-type volcanic arc in the mid- to late Mesozoic (Jurassic and Cretaceous periods).

• Sedimentation in the Mesozoic was largely in western NA and was dominantly non-marine with sediment supplied by the erosion of the Appalachians and the emerging Cordilleran Orogen.

• A major transgression in the Cretaceous created a Great Interior Seaway where great accumulation of marine and non-marine sediment were deposited in the Great Plains

Events of the Mesozoic Era

Un-Making PangeaSuperplume

disassembles the Supercontinent

Now PangeaLate Triassic (215Ma)

Late Cretaceous (95Ma)

Continental RiftingRift grabens and aulocogens bounded by normal faults

Mesozoic Rift BasinsNon-marine-type Marine-type

Graded Alluvial Fan Deposits along Graben Fault Scarps

Triassic Red-bed Sedimentation in the West

2013 SEG Field TripPetrified Forest

Painted DesertUpper Triassic Chinle Formation

Petrified WoodReplacement by Silica

Groundwater picks up silica from sediment that is rich in siliceous volcanic ash that is altered to clay (bentonite)

That the wood does not rot, indicates reducing environments with rapid deposition (floodplains, lagoons, ). The petrifaction process preserves the original cellular structure of the wood

Early Jurassic RegressionEolian SS Mark the End of the Absaroka Sequence

Navajo Desert

2013 SEG Field TripCanyon de Chelley

Navajo SandstoneCanyon de Chelley

Navajo Sandstone at Zion NP, Utah

Dinos on the Dunes

Dilophosaurus

Coprolite??Dino-pie

Dilophosaurus Footprints in the Jursassic Kayenta Formation near Tuba City, AZ

Middle Jurassic TransgressionBrings on the Zuni Sequence

Morrison FormationUpper Jurassic Dinosaur Graveyard

Zuni SequenceUnconformity

Absaroka Sequence

Dinosaur National Monument, COnear Green River, UT

Non-marine mudstone, sandstone, siltstone and limestone that is variegated light grey, greenish gray, or red; represents floodplains deposits

TransgressiveRegressive

Zuni Sequence Clastic Wedge Deposit in the Foreland Basin of the Cordilleran Orogen.

Next Lecture

Tectonic History of the North American Cordilleran

Quiz on Chapter 14 (p. 351-381)