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UCMP's 2017 Basin & Range field trip, page 2

Thursday, May 25
Richard and I — we were sharing a room — were up around 6:30 since we were supposed to meet the rest of the group downstairs at 7:30. We packed up our stuff and took it out to the vehicle before heading to the lobby. When the group had all gathered (Mackenzie was missing but she would join us a little later), we walked across the street to The Cup for breakfast and coffee. When done, we returned to the hotel, checked out, and went to our vehicles. Peter left us to get his tire patched. Everyone else headed to the Ridley's to get food and ice to last us through the end of the trip. While repacking the coolers, Peter returned and surprised us by turning over two six-packs of Great Basin Brewing's Icky IPA; that's what he had gone out to look for the previous night. What a good guy! From Ridley's, we went to the Shell station across the street to top off our gas tanks and to put air in our traumatized tires. Continuing west on 50, we stopped briefly so people could take photos of the "antler gate" (an arched entry to someone's property that's made entirely of antlers).

Our original plan had been to visit the bristlecone pines in Great Basin National Park and to camp in the Park, but Seth had heard a weather report that called for cold temperatures; fearing that we might be unprepared for cold weather weather (and that the trail would be blocked by snow), he decided to skip the Park and head straight to Utah. We stayed on U.S. Route 6/50 and made a stop at the Border Inn (at the Nevada-Utah border, of course) to fill our water containers. We then entered Utah and Mountain Time (losing an hour). About 34 miles into Utah, we turned north onto Tule Valley Road, an unmarked dirt track that runs roughly north-south along the west side of the House Range. We made one stop to take photos of the dramatic western face of the range, dominated by the cliffs of Notch Peak, before turning east on the Old Route 6 & 50 Road and entering Marjum Canyon.

We stopped near the west end of the canyon, with high cliffs rising on each side, and got out to look at the Cambrian rocks. Seth pointed out large red masses in the rocks on the north side of the canyon. The red masses are infilled caves within the Howell Limestone, recording karsting and a drop in sea level during the Cambrian. On the south side of the road, Seth showed us gray limestones that were micrite (essentially massive carbonate mud), devoid of layering because of heavy bioturbation (mixing of the sediment by animal activity). In some places, orange patterns in the rock provided evidence of infilled burrows, created by arthropods and various worm-like creatures. Chunks of rock that had fallen from higher up on the cliff exhibited a sharp contact between the carbonate mud and an oncolitic rock. Oncoids are layered, spherical structures that form by the growth of cyanobacteria around a nucleus such as a piece of shell.

Continuing up the road, we made a second stop to look at trilobites and other fossils, including algae, in the Wheeler Shale; it too is of Middle Cambrian age but stratigraphically above the Howell Limestone. But first: lunch. During our lunch break, Erik Sperling, an Assistant Professor of Geological Sciences at Stanford and Richard's advisor, drove up. He had flown into Salt Lake City a few hours earlier, rented a car, and somehow managed to find us.

Near the road, small agnostid trilobites, sponge spicules, and unidentifiable organic matter were found in the rocks of the Wheeler. These rocks were deposited in deep water where oxygen concentrations were variable. Higher up the hill the rocks were very laminated, indicating no bioturbation, a sign that oxygen levels were too low for most bottom-dwellers. However,the trilobite Elrathia kingi was quite plentiful. Apparently, it was well-adapted to the low-oxygen conditions. In fact, there are layers in the Wheeler Shales in which Elrathia occurs in dense accumulations, often 1,000 individuals per square meter.

Looking east towards the House Range; Notch Peak stands out prominently. Marjum Pass cuts through the range at the far left.
Orange burrows within a gray Cambrian carbonate mud in Marjum Pass. Our first stop where we observed layers of flash flood deposits
The red areas are infilled caves in the Howell Limestone, north side of Marjum Pass.
Seth discusses the geology on display at the west end of Marjum Canyon. Looking for trilobite fossils in a finely layered, but unbioturbated, section of the Wheeler Formation, east end of Marjum Canyon.
Top: Looking east towards the House Range; Notch Peak stands out prominently. Marjum Pass cuts through the range at the far left. Left middle: Orange burrows within a gray Cambrian carbonate mud in Marjum Pass. Right middle: This rock shows the sharp contact between the heavily bioturbated carbonate mud and the oncolitic mud. Bottom left: The red areas are infilled caves in the Howell Limestone, north side of Marjum Pass. Bottom center: Seth discusses the geology on display at the west end of Marjum Canyon. Center right: A view of one of the Elephant Knees Buttes from the Mud Hills. Photo by Dave Smith. Bottom right: Looking for trilobite fossils in a finely layered, but unbioturbated, section of the Wheeler Formation, east end of Marjum Canyon.

When done with our trilobite hunt, we returned to the vehicles, left Marjum Canyon behind, and stayed on Death Canyon Road before turning southwest onto another dirt track, 3c Road, and took it back to 6/50. We drove west for a bit with the mostly dry Sevier Lake on our left before picking up Tule Valley Road again on the south side of the highway. We drove due south along a very dusty track, then turned west around the southern end of the Barn Hills. Seth steered us to a camping area at the base of Fossil Mountain in the Confusion Range. Only one couple with an RV and a little dog were camping there. The group fanned out to set up their tents while Peter and Emily set about making Peter's jambalaya recipe for dinner. While looking around the camping area, Seth noted that arrowheads have been found here; seconds later Mackenzie bent down and picked one up! The jambalaya took a while to make so we ended up eating in the dark. Seth, Ivo, Franzi and others went off to collect wood for a fire. We sat up and talked to around 11:00. When I went off to find my tent in the darkness, I followed Daniel since his tent was on the same line from the vehicles as mine. The stars this evening were amazing.

Friday, May 26
I got up when it was too light to stay in my tent any longer. After a light breakfast, we prepared to leave camp but found that Seth's Tahoe had a low-tire-pressure warning. The tire looked pretty low, so we left that one and drove off in the other three. Seth led us to a canyon in the House Range. The students split into groups of two or three to describe two-meter sections of the House Limestone. Seth urged the students to pay attention to details, such as ripple marks, burrows, and whether the carbonate rock could be described as a micrite or grainstone (a coarser limestone with grains that are cemented together). Following the exercise, the group discussed the possible depositional environments of the limestone. Based on the existence of ripple marks and fragmented fossils (trilobites, brachiopods, echinoderms), the carbonates were probably deposited in a near-shore, high-energy environment, probably between the fair weather and storm wave bases. Collared lizards, skinks and horned toads were also observed on this outing. On the way back to the cars, we made a side trip to a down-faulted chunk of the House Limestone to take a look at this stratigraphically higher piece. Above the House Limestone is the Fillmore Formation; Seth would have liked for us to look at that too, but the exposures were a bit hard to reach. So we skipped the Fillmore and drove across the valley to look at the Wah Wah Limestone, the next formation in the sequence. We had lunch by the cars before our walk up section, through the Wah Wah and into the Juab Limestone and Kanosh Shale.

Top left: The morning sun illuminates Fossil Mountain, looming above our campsite. The lower half is primarily the Kanosh Shale. Above it are the Lehman Formation, Watson Ranch Quartzite, Crystal Peak Dolomite and the Eureka Quartzite. Bottom left: Peter and Daniel describe their two-meter section of the House Limestone near the canyon mouth. Top right: Mackenzie and Jun describe a two-meter section of the House Limestone in the farthest reaches of the canyon Bottom right: Standing on top of a down-faulted block of the House Limestone, Seth tells us a bit about the overlying Fillmore Formation. From left are Seth, Franzi, Erik, Jun, Cindy and Daniel.

The hillside before us presented a partial cross-section of what was once a thick carbonate platform built up in shallow water on a passive continental margin (i.e., there was no plate boundary in the vicinity). Numerous invertebrate fossils were present in these rocks, all the way to the top of the ridge. More than 60 years ago, geologist Lehi Hintze, who studied these Lower Ordovician rocks extensively, first measured this section and painted his measurements directly on the rocks. The measurements would have been erased by the elements long ago, but geologists periodically repaint them. Seth led us up the slope, following Hintze's trail. We began by looking at the Wah Wah Limestone, a brownish-gray formation of mixed shales, micrites and grainstones. Again the students split into groups to describe two-meter sections. The Wah Wah was probably deposited at a depth similar to that of the House because of the presence of ripple marks, but there was a more diverse biota. In addition to silicified trilobites and echinoderms, there are also sponges with holdfasts, small sponge-microbial mounds, nautiloids, brachiopods, high-spired gastropods, and some graptolites in the shales.

Examining a lower ledge of the Wah Wah Limestone. From here we would continue uphill through the Juab Limestone to the Kanosh Shale. One of the many lizards we encountered on this field trip. The students take advantage of some shade while describing a two-meter section of the Wah Wah Limestone.
Left: Examining a lower ledge of the Wah Wah Limestone. From here we would continue uphill through the Juab Limestone to the Kanosh Shale. Center: One of the many lizards we encountered on this field trip. Right: The students take advantage of some shade while describing a two-meter section of the Wah Wah Limestone. From left are Franzi, Richard, Emily, Mackenzie, Seth, Jun (behind Seth), Ivo, Cindy and Erik.

Above the Wah Wah we moved into the Juab Limestone, generally similar to the Wah Wah, but a more medium to dark gray in color. It contained unsilicified trilobites, brachiopods, crinoid stems, and high-spired gastropods. Although the same major groups are present as in the Wah Wah, Seth pointed out a sharp shift in faunal dominance —whereas the Wah Wah is numerically dominated by trilobites, the Juab is dominated by brachiopods. This ecological shift occurs gradually in many places during the Lower-Middle Ordovician, but in this area it is particularly striking and abrupt.

Looking at fossils in the Juab Limestone. In the background is a nice unconformity between tilted Ordovician beds and overlying Oligocene volcanic rocks. A lone cactus blossom in the Juab Limestone. Examining more fossils in the Juab Limestone.
From a bench in the Juab Limestone, we got this great view to the north. The prominent peak at the left is Fossil Mountain; we're camped just beyond it's eastern shoulder.
Top left: Looking at fossils in the Juab Limestone. In the background is a nice unconformity between tilted Ordovician beds and overlying Oligocene volcanic rocks. Top center: A lone cactus blossom in the Juab Limestone. Top right: Examining more fossils in the Juab Limestone. From left are Mackenzie, Daniel, Peter, Jun (partially hidden), Franzi, Seth, Cindy, Ivo, Richard and Erik. Bottom: From a bench in the Juab Limestone, we got this great view to the north. The prominent peak at the left is Fossil Mountain; we're camped just beyond it's eastern shoulder. Those are the Barn Hills across the valley to the east.

Overlying the Juab Limestone is the Kanosh Shale, which records a local increase in water depth. The Kanosh is composed of a variable mixture of shales and limestones, but we found the shales to be obscured by soil and rubble. The limestones are often very fossiliferous, and in the rock-strewn surface there were abundant brachiopods, gastropods, trilobites, ostracodes, nautiloids, echinoderms, and more.

Top left: Peter in the fossil-rich Kanosh Shale. Top right: Two different kinds of trilobite pygidia (fused segments at the back end) in the Kanosh Shale. Bottom left: Peter, Cindy and Ivo head back to the cars. They're about to cross the obvious boundary between the Kanosh Shale on the left and the lighter Juab Limestone on the right. Bottom right: The sun sets through a gap in the Confusion Range on our last full day of the field trip.

Since it was getting close to 5:00, we climbed back down to the vehicles and returned to camp. It had become quite windy. Seth attempted to fix his bad tire with Fix-a-Flat but it had no visible effect. While he was out doing that, Eric, Richard, Emily and Franzi hiked over to the cliffs northwest of camp to have a look at the upper Kanosh Formation. Seth's spare also turned out to be low on air, so he would have to go into Ely tomorrow to get the tires serviced. Everyone but Seth, Emily, Franzi and Richard would be returning to the Bay Area the next day so Seth would caravan with us as far as Ely.

For dinner, Cindy and Ivo made a big pasta dish with a sauce containing eggplant and olives; I assisted by peeling some garlic. I went out to gather wood for a fire but didn't find much. I'd been told that Seth would want to keep the Expedition that I'd been driving so I removed all my stuff from the back and moved it to my tent. It remained very windy and became overcast — we tried to position the vehicles so that they'd provide some shelter. We all headed to bed before 10:00. Shortly after getting to my tent, it began to drizzle and was still drizzling when I turned out my light.

Saturday, May 27
The plan was to hit the road by 6:00 today so the night before I had asked Daniel to wake me when it was 5:00. I had expected it to be light out at that time, but when Daniel came to wake me, it was still dark. I packed up, brought all my stuff over to the vehicles, and had a very light breakfast.

It wasn't until 6:30 that we finally got underway. Seth, with Richard, Franzi, and Emily, led the way to Ely in the SUV with the nearly-flat tire. It turned out that Seth would not be wanting my Expedition after all, so with Peter and Daniel as passengers, we made to leave camp when — wouldn't you know — our low-tire-pressure warning light came on again. We ignored it. Cindy, Ivo, Mackenzie and Jun were in another SUV. The fourth vehicle would remain at Fossil Mountain since Seth would be needing two vehicles to get his three passengers, all their gear, and all the food bins, coolers, etc. back to Berkeley. At the Border Inn, we found air, so both Seth and I filled our tires. We made it to Ely without incident, meeting up at the Shell station to top off our gas tanks. We said our goodbyes to Seth and the three students remaining with him — they were staying a few days longer to do some field research in the area — and began the long drive back to the Bay Area. We made a few stops for gas and food along the way; I was back at my house in Berkeley by 6:00 PM.

And thus ended the 2017 UCMP field trip! It was not so much about the origins of the Basin & Range itself, but about some of the individual rock formations and what their rocks and fossils tell us about what was going on in terms of changing sea levels, oxygen and carbonates in the oceans, and climate.
 

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