NAVIGATION:  BACK TO MODULE TWO INTRODUCTION

What is a "Salt Anticline"?

NOTE:  This section is mostly "just for fun".  However, there are a couple very important concepts in this section:  Salt anticlines are important in this module when thinking about (i.e., answering questions about):

1. the formation of sandstone arches in and near Arches National Park - think about how the "doming" or "rising up" salt opens up the sandstone to form "fins" (a stage in arch development)

2. the formation of "Upheaval Dome" controversy - think about the role that doming or bubbling up of salt could possibly cause the form seen at Upheaval Dome.

The Spanish Valley (the valley in which Moab, Utah sits) is a "salt anticline" (see image at right by Ray Wheeler).

Under great pressure, salt can flow like a glacier. Salt of the Paradox Formation was squeezed into a dome in the Moab area, elevating the rocks above it. A "hump" of strata is called an anticline. As the dome gradually rose up, the Colorado cut down through the rising rock to maintain its course.

Cracks formed in the rock over the dome of salt. These are the fissures that allowed formation of fins and arches in Arches National Park and the Slickrock area.

A fault line runs down each side of the Moab valley. These faults join near the entrance to Arches. Perhaps because of water running down along the fault line, salt was dissolved away deep under the rock of Moab. The overlying slab sunk down, creating a "collapsed anticline" that is the Spanish and Moab valley.

Arches National Park (we stop here on our field trip) is sitting on top of a salt bed named the Paradox formation.  It is responsible for the formations at Arches (pedestals, arches, domes, spires, cavities, anticlines, pinnacles, balanced rocks, fins).  The salt bed was covered with residue from the sea that flowed into the Colorado Plateau 300 million years ago (the Pennsylvanian period, Paleozoic era, Phanerozoic eon).  When the sea evaporated and the salt bed was covered with these residues, all that was left was the debris compressed to form rocks.  In some places, this was one mile thick.  The salt bed is very unstable under the pressure of the sandstone.  This made the rock shift and created domes.  The dome sections dropped into cavities.  The Moab Fault is the result of a 2,500 ft displacement and it was a normal fault.  Water washed away the "cement" that was holding the sandstone together creating solitary fins.  The wind washed away the left over debris.  In the winter, water would freeze and expand in the cracks creating a flaking of the rock.  With the pressure of the cold, the fins broke off and the weak and damaged fins collapsed.  The strong survived.  This process took 125 million years.  Faults have caused the displacement of the Moab Fault and the Salt Valley.  Most of the rocks are salmon-colored Entrada Sandstone, which took 20 million years to create, 180 million years ago.  The arches form mostly of this and Navajo Sandstone.  Folds and warps in the layers show the movement of the salt bed and deposits.