Two Steps to Triton

Words by L. Whalen
Model by P. Prince

Nothing stays the same very long – and tectonic environments are no exception. Structures from a later event can overprint a previous event. Sorting this all out is both fun and hard work. In this video, Phil recreates two stages of the geologic history of Triton Bay, West Papua (northwest New Guinea).

First, we see convergence forming parallel anticlines. Subsequent extension creates a characteristic rectangular pattern, that when filled in with water matches the local structure.

Ouachita Mountains: Rock Strength in Action

Words by Lisa Whalen

Video/Model: by Phil Prince

Ouachita_Mountains_in_Arkansas
image: wikipedia.org

 

The Ouachita orogeny occurred ~300 million years ago when part of South American collided with the southern part of North America.

Ouachita_Orogeny_geologic_map.png
image: By R.Q. Foote, L.M. Massingill, and R.H. Wells – Petroleum geology and the distribution of conventional crude oil, natural gas, and natural gas liquids, East Texas basin

In this model Phil Prince takes us to the Ouachita Mountains of Arkansas and Oklahoma. Here you will see how the strength of different rock layers coupled with deep erosion can produced the characteristic shape of this range.  Sinuous ridges formed from chert snake around valleys scooped out of shale abutting a broad sandstone plateau.

Valleys and Ridges: Understanding the Geologic Structures in Central Virginia Pt.1

Words by Lisa Whalen

Video by Phil Prince

In this first part of a four part series, Dr. Phil Prince explains why we get the valleys and ridges that are the namesake of the Valley and Ridge province of Virginia.

Valleys and ridges can result from the erosion of anticlines and synclines. Knowing the ages of the rock layers can help determine, which you’re looking at when the topographic profiles have been worn away through time.

When rock strata are folded and produce an anticline, or “positive topography,” if then worn down from the top, older rocks will be exposed in the center. The opposite is true for a syncline.

anticline_and_syncline__structural_geology_intro_by_zesst-d4t1o04
Illustration by Vidimus78

Notice in the cartoon above that the original anticline and syncline are not expressed topographically. Instead two parallel ridges are present where the yellow, and presumably less-erodible strata intersect with the surface.

In this first video we get to see how geologic information overlaid in Google Earth can help illustrate this concept.

Part 2 Coming Soon!

 

Also see the Seneca Rocks field trip series for more information

When Strike-Slip Faults Bend

Text by L. Whalen

Models by P. Prince

 

Strike-slip faults often seem like the least complex faults out of the bunch compared to thrust and normal faults, but it turns out that there’s a lot more to be said (and modeled)!

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Figure from Cunningham and Mann (2007)

 

Strike-slip faults are where the crust is sliding past one another and can form linkages between areas experience convergence or divergence. Where strike-slip faults bend things get interesting as it creates zones of compression (called restraining bends) and tension (called releasing bends).

This video shows the development of a restraining and a releasing bend and then shows a cross-section of the model highlighting the different flower structures (for more information on flower structures see our previous post).

A real world example of where you can find  these structures is the fault system responsible for the Mw 7 earthquake that affected Haiti on January 12th, 2012.

 

haiti-outcrops-1
Zoomed out map of Haiti. For explanation of butterfly outcrop patterns see the video above.
haiti-2
Zoomed in map of Haiti. Note the butterfly pattern in pink.
Seismotectonics of southern Haiti: A new faulting model for the
A) Elevation map of Haiti. B) cross-section showing flower structure located on line A-A’. C) 3-D block diagram showing another view of the structure. Figure from Saint Fleur et al. (2015).