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30 July 2015
Stromatolites of the Helena Formation, Grinnell Glacier Cirque, Montana
My favorite place to have lunch in Montana is at the Grinnell Glacier cirque in Glacier National Park. This is the dining room table: You’re looking at a bedding-plane-parallel exposure of Mesoproterozoic stromatolites here. Every few years, I’m lucky enough to hike up there with motivated students and share food atop this unparalleled view into the shallow seas of more than a billion years ago. Stromatolites are sedimentary structures that …
16 March 2015
Mechum River Formation, near Batesville, VA
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?
6 March 2015
Friday fold: Mazatzal Orogeny, Arizona
Reader Mike Pendergrass contributes this Friday’s fold: I found your blog a couple years ago and I share your love of structural geology. I did my Master’s Thesis while at Northern Arizona University in the early 80’s and mapped an area on the Mazatzal Mountains of central Arizona. The Mazatzals in my field area contain metasedimentary rocks that were deformed in the Mazatzal Orogeny (~1.6-1.7 billion years ago). The stratigraphy …
13 February 2015
Friday fold: Ptygmatic Irving Fm., Colorado
Another one from Kim: Kim says: Pygmatic folds in the Precambrian Irving Formation. I think this is 1.7 Ga deformation, late in the Yavapai orogeny, which added various arcs in Colorado to North America. Good place to think about strain ellipses in progressive deformation. Zooming in on the best part, and dialing up the contrast a bit: That’s intense! Seriously strained rocks. What fun!
27 January 2015
Miette Group gritstone showing scours, mudchip rip-ups, cross-bedding, and dropstones
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.
9 January 2015
Friday fold: a surging rippled whale of Grinnell Formation
The Friday fold is asymmetric, overturned, and chock full of primary sedimentary features. Join us in Glacier National Park’s Mesoproterozoic Belt Supergroup.
12 December 2014
Friday fold: Miette slate, Alberta
The Friday fold returns to Canada, looking at Neoproterozoic slate and quartzite at the southern terminus of the Icefields Parkway. Bonus features include ripple marks, graded beds, cross-bedding, cleavage, and boudinage.
1 September 2014
Field work on the Grinnell Formation at Red Rock Canyon, Waterton Lakes National Park, Alberta
Callan’s Rockies field course students document faulting and jointing in Red Rock Canyon, Waterton Lakes National Park, Alberta.
12 July 2014
Stromatolite from near Crypt Lake
Greetings from the field… here’s a scene I contemplated yesterday…
26 March 2014
The Great Unconformity in the Franklin Mountains
Good morning! Let’s take a walk up the east side of the Franklin Mountains, north of El Paso, Texas, to walk across the Great Unconformity. The basement rock exposed here is the Red Bluff Granite, a 1.1 Ga felsic magma that intruded the columnar basalts of the Mundy “Breccia” and the Castner Marble. (It is unknown what substrate the Castner Marble was deposited upon.) This is what the Red Bluff …
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.