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6 January 2012
Friday fold: the Contorted Bed
Callan reviews the geology of the superlatively auriferous Witwatersrand Supergroup of South Africa, and then zooms in on a distinctive marker bed near the base of the sequence. The deformation in this particular banded iron formation (BIF) is an aesthetic wonder, as this suite of images reveal. The layer outcrops in the heart of urban Johannesburg.
5 January 2012
Birds I saw in South Africa
Here’s my species list for the past three weeks: African penguin Cape gannet Bunch of gulls (didn’t bother differentiating them) Bunch of terns (didn’t bother differentiating them) Cape cormorant Reed cormorant White-breasted cormorant Cattle egret Little egret Grey heron Saddle-billed stork Marabou stork White stork Woolly-necked stork Hammerkop Greater flamingo African spoonbill African sacred ibis Hadeda ibis Glossy ibis Egyptian goose Some ducks (didn’t bother differentiating them) Common moorhen Blacksmith …
4 January 2012
Guess hoo’s back?
Scops owl, Kruger National Park, South Africa Hi everyone! I’m back in the States. There will be more photos of wildlife and geology from South Africa to come in the days and weeks ahead, but this little fellow can be an appetizer for you. It was a great trip, but it also feels good to be back at home and back at work!
23 December 2011
Friday fold: a wrinkled mountain in Hermanus
While I was away in South Africa, both Brian Romans of Clastic Detritus and Evelyn Mervine of Georneys posted pictures of folds in quartzite of the Cape Fold Belt in southern South Africa. Well, I’m not going to be left out. Here’s a belated Friday fold for December 23, showing a bunch of sweet folds in a mountain just east of the coastal whale-watching town of Hermanus: Zooming in: And …
12 December 2011
Upcoming plans
A heads-up: I’m leaving Wednesday afternoon for a 3 week trip to South Africa. My wife Lily and I are off on our half-year-delayed honeymoon (to be distinguished from our Canadian Rockies pre-honeymoon last summer mainly by its exorbitant cost and low levels of geology). We will be spending the day in downtown London, England, on Thursday, and then we’ll get to Johannesburg on Friday morning. The plan is to …
17 September 2010
Friday fold: granite dikes, Barberton greenstone belt
Folded & boudinaged granite dikes in tonalitic gneiss, Barberton granite-greenstone belt, South Africa. From Passchier, CW, Myers, JS, and Kroner, A., (1990). FIELD GEOLOGY OF HIGH GRADE GNEISS TERRANES. Very crudely annotated: This is a sweet example of how you can get different structures developing in different orientations relative to the principal stress directions. In this particular part of the Barberton Greenstone Belt, compression (orange arrows) operated from the top …
8 March 2010
Suevite from Vrederfort
One of my students brought this sample in the other day: She said her father collected it in South Africa. It was labeled “suevite.” I learned the term suevite about a year ago, while touring the USGS Chesapeake Bay Impact Crater coring project samples at the USGS Headquarters in Reston, Virginia. Wright Horton taught me that suevite is impact-generated melt that chills with other chunks of the pre-impact rock mixed …
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.