November 20, 2011
Finally, the Geology Word of the Week has returned! I took about six weeks off because I was very busy with my wedding and thesis. Six weeks ago, I had announced that the next Geology Word of the Week would be S is for Schist. However, I kept trying (and failing) to write the schist post. Schist is such an important and fun geology word, and I want to take the time to write up the post properly. When the letter “S” rolls around in 26 weeks, I should be finished with my thesis (fingers crossed) and have plenty of time to write up a proper post. So, schist has been moved to the next alphabet. For now, I present… S is for Syncline!
Note: I modified the definitions below after some discussion in the geoblogosphere.
A fold in a sequence of rock layers in which the younger rock layers are found in the center (along the axis) of the fold. Syncline is closely related to the word anticline, which is a fold in a sequence of rock layers in which the older rock layers are found in the center (along the axis) of the fold.
A concave upward (U-shaped) fold in a sequence of rock layers. The lower (and generally younger) rock layers are found at the center (along the axis) of the fold. Synform is closely related to the word antiform, which is a convex upward (upside-down U) fold in which the upper (and generally older) are found at the center (along the axis) of the fold. In the field, many synforms are also synclines. An overturned syncline is called an “antiformal syncline.”
The easiest way to understand synclines and anticlines is to look at a diagram, such as the one below:
Beginner geologists often confuse synclines and anticlines. Remember: A syn makes you grin!
Like many geological structures, synclines and anticlines form at various scales in the field. They can form over vast regions or within a single outcrop or hand sample. Sometimes, small folds are called “synclinal folds” rather than synclines.
Here’s a few more pictures of synclines:
And here’s an anticline:
Finally, I have a question for the geoblogosphere: What is more important for distinguishing anticline vs. syncline: the general shape (right-side-up U or upside-down U) or the age of the rocks? What if there’s been overturn so that folds are forming in a sequence where the younger rocks are the lower layers and the older rocks are the upper layers? Please feel free to discuss this topic in the comments below.
Question answered. But please feel free to continue the discussion below.