The whole formation is a 50-million-year-old alluvial plain that was later uplifted by tectonic forces, so such folds would no doubt be everywhere, and slickensides would naturally be abundant and easy to find.
Reading Dave's field trip page again I see that he also explained it, but at the time it went over my head. Your diagram of the cookies really helped me see it.
Splendid! Field Camp map and air photo again. Very nice!
Did IU venture down to the far side of Twin Bridges to the now famous (infamous?) Sandy Hollow/Block Mountain/McCartney Mountain/"Rat's Nest" exposures on the north side of the Big Hole River? There's a several square meter pavement outcrop of slickenside there which has provided the "Eureka" moment for generations of field camp students, including this one back in 1978.
Indiana had a 1-day project at Sandy Hollow, not really mapping per se but to create a comparison correlation diagram between there and the northern Tobacco Roots the students knew well. The Triassic is missing in the TRs, and the marine Jurassic (Ellis Group, Rierdon and Swift) are missing at SH. The Morrison is much thinner at SH. The Kootenai and Colorado Group are vastly thicker at SH. So it is really an exercise in tectonic history; they are supposed to infer the formation of the Foreland Basin from the correlation diagram. They quickly map the anticline, and see the collision structure in the Gastropod Limestone really in just a field trip sense, but the project is a really good one in my view. It's a bit more than 50 miles from the IU station to SH so that puts it at the limit of a day trip for them.
The combined U of Montana/Purdue U field camp of 1978 called it McCartney Mountain and it was our final project. Think we spent 3 days in the field and had another day in class at SW Montana College for drafting. According to our friend Rob Thomas, it's standing room only at SH these days. I recall encountering either IU of YBRA vehicles and students in the Rubies where Sweetwater Road out of Dillon crosses the metamorphics right where the talc mine is today. One of the TAs had rolled an empty Suburban running an errand into Dillon during the middle of the day and that was just below today's mine site. If you haven't been over there since the mine encountered the road, it's worth a look-see. Further SE of the drainage divide, where Sweetwater Rd drops into the Sweetwater Cr canyon before the 90 degree elbow to the NE, it looks like some exposures of Timber Hill basalt draped over some of the Archean metamorphics right by the road. Lots of spectacular geology out there. I need to get in to the Tobacco Roots!
Ah Sacry's. A magical place with so many intriguing complexities! Great article. The Kootenai Fm remains one of my long time favorites!
We see quite a few slickensided serpentine rocks in western Tasmania.
Working on a post on stichtite (from a friend who just visited Tasmania).
Thank you for this, especially the detail about slickensides from folded sedimentary formations.
Last year I collected slickensides from the Chuckanut sedimentary formation near my hometown of Bellingham. At the time, novice geologist that I am, I wonder what the odds were that I had come across rock along some major fault zone -- it seemed like a longshot, even though I was following a field trip guide (https://nwgeology.wordpress.com/the-fieldtrips/the-chuckanut-formation/layers-in-the-chuckanut-a-walk-to-visit-conglomerate-coarse-and-fine-grained-sandstone/) by area geologist and author Dave Tucker and so expected to find it.
The whole formation is a 50-million-year-old alluvial plain that was later uplifted by tectonic forces, so such folds would no doubt be everywhere, and slickensides would naturally be abundant and easy to find.
Reading Dave's field trip page again I see that he also explained it, but at the time it went over my head. Your diagram of the cookies really helped me see it.
Thanks! I'm very glad it was helpful!
Splendid! Field Camp map and air photo again. Very nice!
Did IU venture down to the far side of Twin Bridges to the now famous (infamous?) Sandy Hollow/Block Mountain/McCartney Mountain/"Rat's Nest" exposures on the north side of the Big Hole River? There's a several square meter pavement outcrop of slickenside there which has provided the "Eureka" moment for generations of field camp students, including this one back in 1978.
Indiana had a 1-day project at Sandy Hollow, not really mapping per se but to create a comparison correlation diagram between there and the northern Tobacco Roots the students knew well. The Triassic is missing in the TRs, and the marine Jurassic (Ellis Group, Rierdon and Swift) are missing at SH. The Morrison is much thinner at SH. The Kootenai and Colorado Group are vastly thicker at SH. So it is really an exercise in tectonic history; they are supposed to infer the formation of the Foreland Basin from the correlation diagram. They quickly map the anticline, and see the collision structure in the Gastropod Limestone really in just a field trip sense, but the project is a really good one in my view. It's a bit more than 50 miles from the IU station to SH so that puts it at the limit of a day trip for them.
The combined U of Montana/Purdue U field camp of 1978 called it McCartney Mountain and it was our final project. Think we spent 3 days in the field and had another day in class at SW Montana College for drafting. According to our friend Rob Thomas, it's standing room only at SH these days. I recall encountering either IU of YBRA vehicles and students in the Rubies where Sweetwater Road out of Dillon crosses the metamorphics right where the talc mine is today. One of the TAs had rolled an empty Suburban running an errand into Dillon during the middle of the day and that was just below today's mine site. If you haven't been over there since the mine encountered the road, it's worth a look-see. Further SE of the drainage divide, where Sweetwater Rd drops into the Sweetwater Cr canyon before the 90 degree elbow to the NE, it looks like some exposures of Timber Hill basalt draped over some of the Archean metamorphics right by the road. Lots of spectacular geology out there. I need to get in to the Tobacco Roots!
And I need to spend more time in the Rubies :)