Friday, January 25, 2013

Another gap in the record

Here's another photo of an unconformity you can put your finger on. This one is from the front ranges of the Canadian Rockies. It is a contact between Cambrian and Devonian sediments. On the left, the light grey/buff rocks are Cambrian. This unit is brecciated and trilobite fragments have been found in it. On the right are Devonian rocks. This unit contains stromatoporoids.

Thursday, January 24, 2013

Geology photo: A gap in the record

I took this photo on a GSA pre-meeting field trip in 2010. This is near Red Rocks Amphitheater in Colorado. On the left are the Pennsylvanian-aged red rocks of the Fountain Formation. On the right is Precambrian gneiss. The gap in between represents 1.4 billion years. Cool!

Wednesday, January 23, 2013

On the shoulders of giants

I worked as a research assistant for about six weeks before I moved to Syracuse to start my PhD.  I  worked on a couple of projects, both of which really reinforced that as scientists, our work really is on the shoulders of giants. For those of you who haven't heard this phrase before, it means that our research builds on what has been done by others before us.

One of my projects involved going through old air photos and field books (from the 70s) and comparing what was noted there with the database of existing samples (that information has been transferred into ArcGIS where I'm using it in conjunction with landsat)--figuring out what we have so it can be used to plan future field expeditions to the same regions and so that samples can be pulled for further analysis.

While everyone knows that their field notes need to make sense to themselves days, weeks, or months after returning from the field, we don't always realize that our field notes may be used by someone else forty years later.

I've compiled a list of tips and tricks for making your field notes useful to someone other than yourself, based on what I saw at work:
  • Plain (lined or unlined) paper is easier to read than pre-printed templates that look like forms.
  • Put locations (i.e. lat/long or utm) in the field books for every station you stop at, even if you don't collect a sample there. If someone else in your field party is collecting notes at that location, make a note of it in your field book.
  • If you're marking up air photos or maps and using the same ones for more than one field season/party, colour code them (and include a legend and/or labels). 
  • Be consistent in how you record/label things, and include a key or legend. Review these methods before going into the field each time. Everything recorded in the same field book should use consistent methodologies. These same methods should transfer to maps, air photos etc.
  • Don't repeat sample numbers in the same area. There's nothing worse than coming across an air photo with two station 22's marked on it (they were from two different years, but the years weren't marked on the air photo).
  • Speaking of sample and station numbers, use leading zeros (i.e. 001, 002, 010). It makes it much easier to sort the information once it is transferred to a spreadsheet or database
For some examples of real field notes, check out Accretionary Wedge #47

Tuesday, January 22, 2013

Modern analogues: an a-ha moment

This photo is from my first experiences snorkeling and my first time using an underwater camera. It was in 2006 and I was on vacation (in Fiji) from my job as a geophysicist. While I was in the water I was more focused on seeing this strange (to me) new world and learning how to capture it on film a memory card than thinking about carbonate environments and deposition.

When I looked back at the photos a few years later while I was logging carbonate cores for a class, this one caused an "a-ha" moment. As in, "a-ha, now I understand boundstone."

There are several classification systems for carbonate rocks. As a student, I always found carbonate rocks confusing and complicated and intimidating. I still do, but, now that I've had a the opportunity to snorkel on three different reef systems (the fringing reefs of the Fijian islands, the Belize Barrier Reef and the Great Barrier Reef) it is a bit easier for me to visualize how limestones form.

Boundstone is part of the Dunham classification of carbonate rocks. It's a term for carbonate rocks that are bound at deposition. And in this picture, you can see how that happens. These two speckled butterflyfish (Chaetodon citrinellus) are swimming around coral that is being filled in by sand, shell fragments, and other carbonate detritus. It's being bound in place.

If you want to take it a step further, you could use the Embry and Klovan classification, in which case I think this might be framestone (I hope there are carbonate sedimentologists reading this who can correct me in the comments if I'm wrong).

I am actually fascinated by the whole carbonate classification process. The two dominant classification systems were developed by Dunham and Folk (I met Bob Folk very briefly once, and he was very kind). But their classifications weren't detailed enough for the rocks that Embry and Klovan were looking at, so they expanded the Dunham classification, particularly of boundstone (Embry and Klovan break boundstone up into bafflestone, framestone, and bindstone). I've also been lucky enough to have several conversations with Ashton Embry, and his enthusiasm for geology and knowledge about the Canadian Arctic are amazing.

I think one of the most important things about modern analogues is that they remind us that what we see in the rock record is often formed by processes not instantaneous events. As the space around the coral above is filled in, whether or not it will keep growing up and extending will depend on the relative sea level.

Monday, January 21, 2013

Sedimentation and tectonics, basin initiation and evolution, in ten hundred words

Last week was a busy one for me. It was the first week of classes, but I was also wrapping up an independent study from the previous semester with a presentation to my research group and a paper. Plus I was finalizing an abstract and hosting a visiting prospective grad student.

In the midst of all the craziness, I took time out to try my hand at describing what I do with the Up-Goer Five challenge: describing what I do using only the thousand most common words in the English language. Here's what I came up with:

The places where rocks are stored in the ground are made when big blocks push together or pull away from each other. I study how the blocks move and how all this moving around controls the places where the rocks are stored.

It's short and to the point. Maybe with more time I could have come up with a more creative way to describe studying sedimentation and tectonics as related to sedimentary basin initiation and evolution.

The original call for the geotweep community to try this came from Anne Jefferson over at Highly Allochthonous, and she and co-blogger Chris Rowan did an amazing job organizing the results into a "Ten Hundred Words of Science" tumblr. Check it out, and if you haven't done so already, contribute your own description of what you do!

Monday, January 7, 2013

From my collection (I: Etna scoria)

One of the things I've been putting off doing is cataloging my rock collection before it gets too big and before I forget the details about any of my samples. I'm trying to get into the habit of blogging more often, so I thought I'd combine the two and blog about my collection.

The first sample I'm sharing is one I collected in Sicily in 2005. I was on a day-trip to Sicily from Malta, and one of the stops was at the Rifugio Sapienza on Mount Etna. The map below shows the parking area and ammenities at the Rifugio, with the Silvestri craters running north-south (north is the top) just to the right of center). Click on the link below the map to go to Google Maps where you can zoom out and see exactly where on Mount Etna this is.

Despite being in a national park, we were told to take as much rock as we wanted because they had lots. Still, I was conservative and only brought back what would fit in my pocket.

This scoria (an igneous) is from the Silvestri Craters which formed in 2002. As you can see, there is a change in the size of the holes in the sample. These holes, or vesicles, are from gas bubbles that were trapped in the cooling lava.

 There are a couple of great photos of the 2002 eruption taken from the International space station here and here.  Below are some of my photos of Mount Etna and the Silvestri Craters. I was taken aback by just how much it dominates the landscape of southeast Sicily.

My first view of Mount Etna, approaching from the southeast coast of Sicily

The view from the Greek Theatre at Taormina

People on the horizon for scale.

That's a chain link fence on the bottom right