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22 December 2010
Part 4 of the ongoing series examining the geology of the San Francisco area. In today’s post, Callan visits Kirby Cove in the Marin Headlands, where intensely deformed chert can be found on one end of the cove, pillow basalts on the other, and an “artificial dune” in the middle.
21 December 2010
Episode three in the multi-part series on the geology of San Francisco. This post focuses on the chert layers of the Marin Headlands
19 December 2010
The first in a multi-part series on the geology of San Francisco and the surrounding area.
6 December 2010
The author recounts a field trip in October along the section of Turkey’s North Anatolian Fault that last ruptured in 1944. The rock types on either side of the fault are compared, offset markers are illustrated, and several types of landforms particular to strike-slip faults are shown. The post concludes with an examination of the town of Gerede itself, which is built directly atop the fault.
26 October 2010
Picking up where we left off last time, we were in some partly-serpentenized peridotite, part of the Burham Ophiolite in Turkey’s Tavşanlı Zone, an ancient tectonic suture. Our next stop on the field trip allowed us to visit some diabase dikes: Here’s a close-up of the right contact of the dike with the host peridotite: The field notebook’s long edge is ~18 cm. And here it is again, annotated: Near …
20 October 2010
Before the Tectonic Crossroads conference two weeks ago, I had the good fortune to participate in a Istanbul-to-Ankara geology field examining the Tavşanlı Zone, a tectonic suture zone where a portion of the Tethys Ocean basin closed. This paleo-convergent boundary is marked by a suite of interesting rocks, including blueschists, ophiolites, and eclogites. I’d like to share with you some of the things I saw along the trip. This is …
20 September 2010
Over the summer, I went up to Vermont to visit my friends the Clearys. Joe Cleary is a college friend and a talented luthier. He and his wife Tree and their children Jasper and Juniper have settled in Burlington, a lively town with a lot of cool stuff going on. Joe took time out one morning to show us a superb example of a thrust fault on the shore of …
29 April 2010
Ice… serpentine… halite… What do they all have in common? I’ve discussed mineral “ghosts” here before — really, those are only pseudomorphs, where one mineral’s chemistry becomes unstable due to a change in conditions, and then a new mineral forms in the same space. I’ve also brought up the issue of clasts of minerals which are unstable over the long term (ice). Last night, at the final meeting of the …
25 March 2010
We just looked at the Chilhowee Group, a package of sediments that records the transition for the North American mid-Atlantic from Iapetan rifting through to passive margin sedimentation associated with the Sauk Sea transgression. Well, if we journey a bit further west, we see the sedimentary stack isn’t done telling its story. The saga continues through another two pulses of mountain building. Consider this “unfolded, unfaulted” east-west cross-section cartoon: Part …
4 March 2010
My girlfriend’s mom was in town in January, and we took her down to visit the Capitol Building. The tour had a good bit of history, but definitely missed the opportunity to talk geology. I was particularly struck by the columns in the Hall of Statuary: Close up of one column, with my hand for scale: That’s the Leesburg Conglomerate, a Triassic-aged deposit found in the western part of the …