Silence of the cicadas
Signs that summer is almost over despite the continued warm temperatures include the silencing of cicada calls one at a time. A welcome turn of events!
More “crazy-bedding” in the upper Imo
This week was a long one because we worked in two different field areas. On Monday and Tuesday we were back on Tick Creek looking at the last two major eastern drainages. Found good Cane Hill/Imo contacts in each and a fairly consistent
irregular-, channel-bedded sandstone unit with abundant soft-sediment deformation near the top of the Imo. It’s so irregular that I was calling it “crazy-bedded” before long.
“Crazy-bedding” in the upper Imo
Yet more “crazy-bedding” in the upper Imo
There was also a section in the middle of the Cane Hill that was so perfectly cut by its east/west joint that it formed a smooth wall on the north side of the creek. There was a parallel joint face on the south side, but it was not nearly as well exposed.
Danny views joint face “wall” in Cane Hill
Buttresses on Bear Creek
On Tuesday evening we joined Angela Chandler and Lea Nondorf, also of the Survey, on Bear Creek in Marshall to work on several other projects the rest of the week. One ongoing project is to try to resolve edge-matching issues whenever we get a chance. This involves gathering new data in boundary areas between quads that were mapped by different people or who used a different stratigraphy. This week we were also looking for localities in the Imo interval for an upcoming field trip that Angela, Erin Smart and I are leading this spring for the GSA (Geological Society of America) conference in Fayetteville. While looking at various road cuts, we also took new points on an area in the corner of four quads.
Wednesday and part of Thursday we looked at several possible field trip stops in the Imo, none of which seemed particularly suitable for one reason or another. Mostly this is because the Imo doesn’t tend display good outcrops in this area due to its shaley composition and its typically being covered by the flaggy sandstone of the Cane Hill above. We did visit the type section which is in Sulphur Springs Hollow to see if that could be used as a stop, but deemed the area too rugged unless a very small, sturdy group of geologists sign up. A type section is an area where a formation or rock unit is first described and studied in detail. In this case the type section was proposed then summarily abandoned, but there are those working hard to see it reinstated eventually.
Coalified wood prints in Imo sandstone at the type section
Crinoids in red, fossiliferous Imo limestone at the type section
Another project that we are working on for the National Park Service is a compilation of all the quad maps along the Buffalo National River. Our agency and the US Geological Survey have each done about half of the quads in that area. Most of the quads mapped by our agency did not include the higher terrace levels above the river–some as high as 200 feet! This week we were able to get points on a few more of these terraces on the Snowball quad.
Smart Bluff above Arnold Bend on the Buffalo River
Calcite fracture-fillings used as building stones in St. Joe
Quartz crystal encrusted Boone chert used as building stones in St. Joe
We looked in Arnold Bend Thursday afternoon, and differentiated several terrace levels there, then on the way back to town, we stopped at a roadcut on Hwy. 65 that Angela knew about where there are quartz crystals growing in fractured Boone limestone and chert. Danny had stopped at St. Joe on a previous field trip and so directed us there to see the quartz and calcite crystals encrusted on some of the old building stones in town. These stones were no doubt found nearby along the several mineralized fault zones in the area.
Early morning fog on Bear Creek
The next morning there was fog on Bear Creek and we headed up to Jamison Bluff to look for Plattin in the riverbed where it had been mapped previously. This is part of the 6 mile section of the Buffalo between Woolum and Margaret White Bluff that dries up during the summer. All we could find was St. Joe, so that part of the map remains as is.
Jamison Bluff along the Buffalo River
River crossing at Woolum on the Buffalo River
Looking down on Skull Bluff on the Buffalo River
We crossed the Buffalo at Woolum and walked along the top of Skull Bluff to the Nars Cemetery most of which was covered with a terrace deposit (along with almost impenetrable black locust, cedar and briars).
And of course, we couldn’t leave the area without a quick trip to “the Nars” itself for Danny and Lea to see for the first time.
“The Nars”. Buffalo River left, Richland valley right.
“The Nars” is an almost sheer rock wall in the Boone formed as an erosional remnant between the valleys of the Buffalo River and Richland Creek. Quite impressive as usual. After that we had to get back to Little Rock and “the real world”. See you next week.
Tick attacks: severe