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22 November 2019
Because I’m putting together a field course for spring break 2020 to Death Valley California, I was looking through old Death Valley photos this week, from the last time I went to that special place. It was seven years ago! How time flies… This one is in Mosaic Canyon, and was taken by my student Marcelo Arispe, a talented photographer as well as a talented geologist: By the standards of …
21 December 2016
Remember the diamictite I featured here a few weeks ago, from Islay? It was the one that might be a Snowball Earth diamictite. Well, if you follow Snowball Earth science at all, you’ll doubtless be aware that the glaciogenic sediments are characteristically overlain by “cap” carbonates. There’s a stratigraphic successor to the Port Askaig Tillite, too – it’s called the Bonahaven Dolomite. Unlike what you might expect for a cap …
30 November 2016
One fun thing about examining the Port Askaig Tillite in the field is to find odd-shaped exemplars of the unit lying on Islay’s beaches. My favorites were shaped like wands, or antennae, or perhaps the drumsticks freshly detached from a Thanksgiving turkey… a big clast at one end and then a thin septum of the finer-grained matrix to hang on to: Here’s an example: The shape results from differential weathering …
29 November 2016
The Port Askaig Tillite is a Neoproterozoic diamictite on the eastern shore of Islay (Scotland) that may record a “Snowball Earth” glaciation.
16 March 2015
A quick virtual field trip to the Neoproterozoic glaciogenic sedimentary rocks from the central Virginia Blue Ridge province: Can you feel the chill of Snowball Earth?
27 January 2015
The coarser strata of the Neoproterozoic Miette Group in the Canadian Rockies of Alberta record changing water current strength over time, and maybe an iceberg or two.
17 April 2013
Callan and his colleague Jay Kaufman (University of Maryland) go to extraordinary lengths to document an intriguing block of rock in northern Virginia’s Blue Ridge province. Great images and a lot of fun result – but what do these rocks tell us?
11 December 2012
Callan reviews a new book by Doug Macdougall: “Why Geology Matters.”
18 November 2012
My students Alan Pitts, Chris Johnson, Robin Rohrback and I have been busy adding to the Mid-Atlantic Geo-Image Collection. Check out a few of these new GigaPan images: link link link link link link link
29 May 2012
The final meeting of my spring semester Snowball Earth class was a field trip to the University of Maryland, hosted by Snowball guru Jay Kaufman, a specialist in chemostratigraphy using stable isotopes. Here, Jay welcomes the class to his wet lab: Doing chemostratigraphy takes lots of samples. Here’s a drawer full of samples from one of Jay’s many field areas: Then it was time for show and tell. Jay brought …