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2014 Spring Break field trip: Kettleman Hills and Death Valley area, page 2
After a difficult night of high winds and blowing sand, Wednesday morning began with a trip to Echo Canyon, just a short drive from the Furnace Creek Visitor Center parking lot. Seth would periodically jump out of his Yukon to check where we were stratigraphically. We looked at rocks of the Wood Canyon Formation with its cool Skolithos pipe rock. Skolithos is a trace fossil consisting of vertical tubes believed to be burrows made by a worm-like organism. In the Early to Middle Cambrian Carrara Formation, we found dendrites (a fern-like pseudofossil) and a trilobite-rich layer contemporaneous with the Marble Mountains' Latham Shale (near Cadiz, California), and below it a layer with oncolites. Oncolites are layered spherical structures formed by cyanobacteria growing around a nucleus and are believed to be indicators of a relatively high-energy, sediment-starved environment. The trilobites found were primarily Olenellids, one of the first groups of trilobites to appear in the fossil record.
Outside the park's southeast boundary, we hiked across an alluvial plain to Bat Mountain to look at Devonian-Mississippian carbonates. The older rocks contained few metazoans stromatoporoids, rugosan and tabulate corals, brachiopods, and crinoids but they started appearing in greater numbers as we went upsection. The early Late Devonian carbonates contained algal mats; high algal production and relative lack of metazoans suggests that these rocks represent a restricted, perhaps lagoonal environment. The Late Devonian section contained abundant dolomite and quartz, the latter originating as sediment derived from continental weathering and accumulating in a shallow-water, high-energy marine environment. The gray Early Mississipian rocks, which record the interval following the Late Devonian Mass Extinction, were full of disarticulated crinoid fragments. Seth had been telling us about mud mounds mound-shaped carbonate buildups and showed us a nice example of one before leading us back to the vehicles.
The next two nights we stayed at the SHEAR Center (Shoshone Education and Research). The facility can only be described as "rustic," but it has a full kitchen, hot showers, and beds, all of which we appreciated.
Thursday morning, Seth got out the white board and outlined how the Neoproterozoic-Cambrian stratigraphy stacked up in the Death Valley area (see stratigraphic column below).
Then it was off to Saratoga Springs at the southernmost point of the park, where we parked at a small parking area near the springs. Seth led us up into the rocky hills just east of the parking area and following the ridge south we moved upsection through the Neoproterozoic, going from the Crystal Springs Formation through a large (~300 million years) stratigraphic gap and into the Beck Spring Formation. The dolomite and limestone of the Crystal Spring Formation contain abundant stromatolites and other microbialites. A diabase (a mafic igneous rock) sill, dating to about 1087 Ma, cuts through this formation. The overlying Beck Spring Formation contains abundant and spectacularly cyclic microbialites and giant ooids (spherical carbonate grains) characteristic of the Neoproterozoic.
Back in the vehicles, we bravely headed north to look for outcrops of the Cryogenian (Late Neopoterozoic) Kingston Peak Formation and Ediacaran Noonday Dolomite. The Kingston Peak contains glacial deposits from at least two Snowball Earth events. The dolomites of the Noonday were deposited during the deglaciation event and contain a host of unusual textural and geochemical features. This and other "cap carbonate" units of similar age are hypothesized to have formed as a result of elevated alkalinity following melting of ice sheets and rapid warming accompanied by intensive chemical weathering of newly exposed silicate rocks.
Near the Dumont Dunes area, we walked through more of the Kingston Peak Formation with Seth pointing out dropstones, isolated rocks found within water-deposited sedimentary rocks that, in this case, are presumed to have fallen from icebergs or floes cast off by glaciers. It was easy to accept this interpretation because the bedding beneath the dropstones was deformed, as if the stones had fallen from above. Then it was on through Tecopa Springs and up to the Old Spanish Trail Highway where Seth brought us to a trilobite locality. This was in that same part of the Carrara Formation that we'd seen in Echo Canyon the day before. The trilobites (and trace fossils) were in a shale, a fine-grained rock formed in a quiet water environment. On the road between Pahrump and Shoshone we stopped to examine an exposure of obsidian, using our headlights to illuminate the outcrop. Obsidian is normally an extrusive volcanic rock that obtains a glass-like quality because of rapid cooling, but this obsidian may have formed near, but below, the surface; it looked more like a coal seam.
We left Shoshone Friday morning and headed to Beatty, Nevada, via Death Valley. Along route 178 Seth and Ash pointed out three classic "turtlebacks" of Death Valley: the Mormon Point, Copper Canyon, and Badwater. These striking domelike structures, which are formed by rapid tectonic unroofing of ancient metamorphic rocks, are called turtlebacks because of their resemblance to turtle shells. After a walk out onto the salt pan at Badwater, the lowest point in North America, we continued on to Beatty. While passing through town, Seth called for a spur-of-the-moment visit to a Middle Ordovician locality in the hills east of town. We climbed dirt roads to reach the site where Seth showed us another mud mound made up of fossiliferous carbonate rocks dominated by algal mats. The silicified fossils within the mound include many of the groups that diversified during the Ordovician radiation of calcareous organisms such as cnidarians, rhombipheran echinoderms, and articulate brachiopods.
After a short delay to repair a flat tire, we headed north on 95, then west on 266/168 to a locality essentially "across the street" from White Mountain Road, and the entrance to the Ancient Bristlecone Pine Forest. Seth's route took us somewhat unexpectedly into CARMA (Combined Array for Research in Millimeter-wave Astronomy), an array of radiotelescopes. The Forest Service road that Seth was looking for was closed off so we were unable to reach the Lower Cambrian trace fossil locality he had in mind.
After camping in Big Pine and starting our final day with a nice breakfast in Bishop, we drove north on 395. Since Big Pine we'd been driving on a thick layer of solidified ash, the Bishop Tuff, ejected during the huge volcanic eruption that resulted in the formation of the Long Valley Caldera in Mono County, south of Mono Lake. Near the south rim of the caldera, we took a short detour to Convict Lake to see Ordovician roof pendants exhibited in the folded rocks west of the lake. The lake itself formed behind terminal and lateral moraines, remnants of an Ice Age glacier. We took another detour east on 120 to take a look at the tufa towers on the south shore of Mono Lake. Carbonates in the water combined with calcium-rich freshwater entering the lake from subaqueous springs to form the limestone towers around the springs. The height of the towers is an indication of former lake levels.
Although it was clear and windy on this side of the mountains, it was obvious that the Sierra Nevadas were being buffeted by storms. In crossing the mountains on 50 West, we did encounter snow, but it was not a problem for our Yukons. It rained off and on all the way back to the Bay Area. And thus ended our Spring Break paleontology field trip for 2014. We're hoping that these trips will become an annual event!
Petterson, R., A.R. Prave, B.P. Wernicke, and A.E. Fallick. 2011. The Neoproterozoic Noonday Formation, Death Valley region, California. Geological Society of America Bulletin 123(7-8):1317-1336.
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