26 February 2013

Using M.A.G.I.C. to zoom in on trace fossils

Posted by Callan Bentley

Yesterday, I worked on my sabbatical project, the Mid-Atlantic Geo-Image Collection (M.A.G.I.C.). Whether I go outside on a given day to shoot GigaPans of local geology depends on multiple factors: (a) How’s the weather? (b) Do I have to watch Baxter? (c) Can I bring Baxter with me? (d) How are the lighting conditions? Yesterday everything lined up: nanny on duty, moderate temps, and high diffuse clouds that permitted a lot of light through. And, most important, I had a target in mind!

For months now, I’ve been meaning to capture a big slab of Massanutten Sandstone that’s exposed near the crest of the Woodstock Tower Road, a forest service road that leads from the Fort Valley through Woodstock Gap (that cuts across Green Mountain, the ridge that separates the Fort Valley from the Little Fort Valley), up and over Three Top Mountain, and down into the Shenandoah Valley to the northwest. Near the crest of the ridge, the beds of Silurian-aged Massanutten Sandstone are almost vertical, and by looking laterally (that is, orthogonal to bedding), you’re in effect “looking down” onto the Silurian seafloor. On one slab, the one I imaged, there are dozens of rope-sized trace fossils. I know very little about ichnology, the study of trace fossils, but my geoblogging colleague Tony Martin does. I thought these might be Arthrophycus, but Tony pointed out yesterday via Twitter that the resolution (of the rock, not the GigaPan) is pretty poor (the substrate is a coarse sandstone rather than something capable of preserving smaller details, like a fine-grained sandstone or a mudrock). My Massanutten traces lack the “ribs” (if that’s the term) that characterize a true Arthrophycus trace. Tony and his colleague Andrew Rindsberg wrote a 2003 paper which has beautiful illustrations of more finely-wrought specimens of that ichnogenus, as well as other curvilinear, bedding-parallel traces. Whatever they are, the sheer surface area of my Massanutten exposure made it worth a little GigaPannery, in my mind, anyhow.

Here’s the process I went through for this sub-project: I drove up to the outcrop (because the weather’s been good this week, the road was open, so I didn’t have to hike). Then I used my branch clippers and bow saw to remove some excess vegetation (mainly small, weedy, dead Ailanthus trees, an invasive species), then I set up the GigaPan robot, and told it to take the picture. Actually, I shot two GigaPans in this session – here’s the second one if you’re interested. I drove back home, then loaded the images into my computer. I had it stitch the GigaPan together, and then I did two things: (1) I uploaded it to the GigaPan website, and (2) I exported it as a TIFF file. I then opened the TIFF in Photoshop, and used my Wacom Cintiq stylus-equipped monitor to manually trace out the trace fossils. Using light blue “ink,” I drew in the traces in a new annotations “layer” (like a transparency) on the image. Then I (3) fused the two layers into one and saved a copy, and (4) deleted the photo and saved a copy showing only the annotations. I then (5, 6) uploaded the two new images to GigaPan’s website.

Once all three were online, I used the Comparative Viewer from Four Chambers Studio to (7) lay the “raw” (original, unannotated) GigaPan on top of the “annotated photo” version, and (8) again with the “annotations-only” version (with no photo).

Here’s a video that examines all three images separately, and then shows you the power of the comparative viewer to compare a “scene from the field” with the “what the professional sees” version (the annotations):


If you want to explore the GigaPans yourself as separate images, then here they are:




If you want to explore them using the comparative viewer (which is definitely the best way to interact with these images), here’s a link for the raw photo overlaid on the annotated photo, and here’s a link for the raw image overlaid on the blue-on-black annotations. Enjoy!

What are your ideas for how we can use this comparative viewer and annotated images for spreading geologic understanding?