Saturday, July 30, 2016

Geo 881: Ball and Pillow

Hey boys and girls! Remember me? I'm that guy who used to talk about rocks all the time! I finally got out last weekend to re-familiarize myself with some of them near Charleston, Oregon, at three state parks: Cape Arago, Shore Acres, and here, Sunset Bay.

The main feature I wanted to illustrate here is called ball-and-pillow structure, and makes up the downward lobate features above the lens cap. This happens when denser sediment is deposited on less dense sediment layers. The denser sediment sinks down into the less dense layers. The underlying sediments often push upward to form flame structures, but in this case, subsequent re-erosion has beveled off the upper layers, creating a disconformity. Above that horizon, you can see more or less laminar bedding, punctuated by imperfections created by burrowing creatures, referred to as bioturbation.

Below the lens cap, and just above the toe of my boot, there's another disconformity where flowing water carved out a small channel then refilled it. I should probably brush up on my sedimentary structures vocabulary, but I refer to these sorts of things as "cut-and-fill structures." There's a lot going on here.

My mindset on this trip was to take photos to show how beautiful the rocks and their colors are, but that certainly doesn't mean I missed the science!

By the way, I'm not going to commit myself  to the one-a-day regime I've done previously, but I figured I'd quit referring to years-worth of days, change the name to "Geo Series," and start the numbering after 880, which was the last of the Geo Series posts I finished, on May 30 of last year.

Photo unmodified. July 21, 2016. FlashEarth location.


Hollis said...

Interesting post, glad you're back at it!

SkinnyDennis said...

Glad you're back, I've been checking every day or so.