What to take away

My last post on the variety of natural features in Northern New Mexico led me to consider just what geological insights a traveler to our beautiful country could take away with them. It’s easy to be overwhelmed with loads of scenery, lots of facts and examples, and a few really unfamiliar words.

Looking out into the Espanola Basin from the Sangre de Cristo Mountains

Looking out into the Espanola Basin from the Sangre de Cristo Mountains

There are, however,┬ásome basic concepts that a geologist would love to feel you’ve carried home:

  • Northern New Mexico has a spectacular landscape which conceals a rich and eventful geologic history.
  • This history can be pieced together from the rock record, some of which you have just encountered.
  • Geologists attempt to understand the rock record in terms of processes which we can see operating today. This works well for rocks that form at or near the Earth’s surface, less well for rocks that form deep in the crust.
Santa Fe River carrying sand to the Rio Grande

Santa Fe River carrying sand to the Rio Grande

  • Sedimentary and volcanic rocks form at or near the Earth’s surface. On the continents, these rocks form an extensive cover that rests upon an older crystalline basement. The crystalline basement is made up of metamorphic and plutonic rocks that originally formed far below the surface.
Mississippian dolomite resting nonconformably on Precambrian crystalline basement

Paleozoic sedimentary strata resting unconformably on Precambrian crystalline basement

  • Because sedimentary strata and many volcanic lavas and tuffs were originally laid down in horizontal layers, we can infer subsequent crustal movements by their displacements. This includes deformation by flexure, offset by faulting, and elevation above or below sea level.
  • Sedimentary rocks contain the Earth’s archives. They outline areas of uplift and subsidence, record the distribution of ancient environments, and track changes in sea level and climate over the ages. They also preserve the record of life on Earth.
  • Volcanic rocks contain the Earth’s clocks and compasses. They freeze in radioactive elements that act like an hourglass, which we can use to measure the age of the rock. They freeze in magnetic minerals aligned with ancient magnetic fields, which we can use to measure continental drift and plate movements.
  • The metamorphic and plutonic rocks, many of which formed from deeply buried volcanic and sedimentary rocks, contain a blurred, but fascinating, record of conditions and movements deep in the Earth’s crust.
  • The leveling process – weathering and erosion at the Earth’s surface – works swiftly and ceaselessly to wear down the high places and fill in the low ones. Landscapes of great relief and drama like New Mexico’s point to ongoing tectonics and volcanism.
Slot canyon in rhyolite tuff

Slot canyon in rhyolite tuff at Kasha Katuwe Tent Rocks