Wooster’s Fossil of the Week: A tectonically-deformed Early Cambrian trilobite from southeastern California

April 10th, 2015

Olenellus terminatus whole 585This wonderful trilobite was found last month by Olivia Brown (’15), a student on the Wooster Geology Department’s glorious field trip to the Mojave Desert. Olivia collected it at Emigrant Pass in the Nopah Range of Inyo County, southeastern California. It comes from the Pyramid Shale Member of the Carrara Formation and is uppermost Lower Cambrian. It appears to be the species Olenellus terminatus Palmer, 1998. It is a great specimen because most of the body segments are still in place. At this locality we find mostly the semi-circular cephalon (the head) separated from the rest of the body. The species O. terminatus is so named because it represents the last of its famous lineage of Early Cambrian trilobites. The last time we found such a whole trilobite at this site was in 2011, with Nick Fedorchuk as the paleo star of the day.

This trilobite has been tectonically strained along its main axis, giving it a narrow look it did not possess in life. In fact, these trilobites with their semi-circular cephala make nice indicators of the strain their hosting rocks have experienced.
spines 032515 585This particular kind of trilobite has very distinctive spines, as shown in the close-up above. The long spine on the right comes from the trailing edge of the cephalon and is called a genal spine. The one in the center is a thoracic spine emerging from the third thoracic segment. The primary role of these spines was probably the obvious one: protection from predators. They may also have helped spread the weight of the animal across the substrate if they were walking across soupy mud (much like a snowshoe).

We’ve met this man before in this blog. James Hall (1811–1898) named the genus Olenellus in 1861. He was a legendary geologist, and the most prominent paleontologist of his time. He became the first state paleontologist of New York in 1841, and in 1893 he was appointed the New York state geologist. His most impressive legacy is the large number of fossil taxa he named and described, most in his Palaeontology of New York series. James Hall is in my academic heritage. His advisor was Amos Eaton (1776-1842), an American who learned his geology from Benjamin Silliman (1779-1864) at Yale. One of James Hall’s students was Charles Schuchert (1856-1942), a prominent invertebrate paleontologist. Schuchert had a student named Carl Owen Dunbar (1891-1979). Schuchert and Dunbar were coauthors of a famous geology textbook. Dunbar had a student at Yale named William B.N. Berry (1931-2011), my doctoral advisor. Thus my academic link to old man Hall above.


Adams, R.D. 1995. Sequence-stratigraphy of Early-Middle Cambrian grand cycles in the Carrara Formation, southwest Basin and Range, California and Nevada, p. 277-328. In: Sequence Stratigraphy and Depositional Response to Eustatic, Tectonic and Climatic Forcing. Springer Netherlands.

Cooper, R.A. 1990. Interpretation of tectonically deformed fossils. New Zealand Journal of Geology and Geophysics 33: 321-332.

Hazzard, J.C. 1937. Paleozoic section in the Nopah and Resting Springs Mountains, Inyo County, California. California Journal of Mines and Geology 33: 273-339.

Palmer, A.R. 1998. Terminal Early Cambrian extinction of the Olenellina: Documentation from the Pioche Formation, Nevada. Journal of Paleontology 72: 650–672.

Palmer, A.R. and Halley, R.B. 1979. Physical stratigraphy and trilobite biostratigraphy of the Carrara Formation (Lower and middle Cambrian) in the southern Great Basin. U.S. Geological Survey Professional Paper 1047: 1-131.

Shah, J., Srivastava, D.C., Rastogi, V., Ghosh, R. and Pal, A. 2010. Strain estimation from single forms of distorted fossils—A computer graphics and MATLAB approach. Journal of the Geological Society of India 75: 89-97.

Days Five and Six – Mojave 2015

March 13th, 2015

Day five began at Kelso Dunes - sand, ripples, and Wooster Geologist footprints.

Day five began at Kelso Dunes – sand, ripples, and Wooster Geologist footprints.

Michael for scale.

Michael for scale.

Petroglyphs at Hole in the Wall.

Petroglyphs at Hole in the Wall.

Eric for scale, showing the size of tafoni at Hole in the Wall.

Eric for scale, showing the size of tafoni at Hole in the Wall.

Proof that the Wooster Geologists were at Hole in the Wall.

Proof that the Wooster Geologists were at Hole in the Wall.

And we made a friend at Hole in the Wall.

And we made a friend at Hole in the Wall.

Day five ended with a visit to a lava tube.

Day five ended with a visit to a lava tube.

Day six started with a visit to the Resting Springs Welded Tuff.

Day six started with a visit to the Resting Springs Welded Tuff.

Check out the fault at Resting Springs Pass.

Check out the fault at Resting Springs Pass.

We channeled our inner Dr. Mark Wilson and searched for fossils in the afternoon.

We channeled our inner Dr. Mark Wilson and searched for fossils in the afternoon.

Olivia found this trilobite! Wow!

Olivia found this trilobite! Wow!

We ended the day with date shakes at the China Ranch. Yum!

We ended the day with date shakes at the China Ranch. Yum!

For Our Wooster Family

March 13th, 2015

IMG_0021Here’s a photo of a peaceful sunrise at the Desert Studies Center to let our WOODS friends know that our thoughts are with them.


Days Three and Four – Mojave 2015

March 11th, 2015


Day three was spent examining the sedimentology, structure and paleontology, and a bit of the wildlife biology at Owl Canyon. We even stopped at the Payless Shoestore in nearby Barstow (Dr. Wilson’s hometown).


The wildlife was the desert tortoise.


The first stop the next day was the Granite Mountains.


Students (above) discussed the possibility of magma mixing and the enclaves of mafics.


The group on a large sphere of granite.


The next stop was Amboy Crater – a large basaltic cinder cone with associated lava flows. This is a view of the cone looking from the inside out as Nick secures the perimeter.


Dr. Pollock was in her element on the ridge of basalt.


Dr. Judge explains to the group how during a time of tectonic extension large-scale folding can develop. This was the last stop of the day at Calico Ghost Town.


The tight ptigmatic folds are almost isoclinal – almost.


Using some sticks found on the side of the parking lot – Dr. Judge folds the earths crust at the location along a strike-slip fault, where the fault makes a bend.


Zach Downes was up early taking a photo of the sunrise across Soda Lake – our home playa.

The First Two Days in the Mojave

March 10th, 2015



Nine students and five faculty and staff are part of Desert Geology 2015, a week-long fieldtrip to the Mojave Desert. Here the nine students, joined by Cam Matesich (Wooster ’14) gathered at an overlook of Death Valley (Dante’s View). Cam joined the group on the second day to guide us through various sites and share his experiences working with Park hydrologists as part of GSA’s GEOCORP Program. We are missing desert expert and usual trip leader Dr. Wilson, and Patrice Reeder this year and greatly thank them for getting the trip organized and sending us off on the right foot.


After flying into Las Vegas on the first day the group approaches the red rocks of Red Rock Canyon.


At Red Rocks the group puzzled over the Keystone Thrust Fault that brought gray Paleozoic Limestones on top of the Mesozoic red sandstones.


A winter view of the same Keystone Thrust – photo courtesy of the Red Rock Canyon Visitor Center.


The photographer takes a break.


Day two – The full group at Badwater in Death Valley. Lowest point in the Western Hemisphere.


Cam explains the spring and groundwater flow in Death Valley and how the park monitors and restores the hydrologic landscape in the Park.


The group strikes a pose on the Devils Golf Course – Death Valley.


Along Artists Drive in Death Valley photographers go to work.


Nick strikes a pose on top of a weathered basalt boulder.


Caitlin, the staff hydrologist, explains the hydrology of a large diameter well in a gravel wash.


The faculty at Zabriskie Point in Death Valley. 

Last day in the Mojave Desert for Wooster Geologists … this year

March 15th, 2013

RedRocks031513LAS VEGAS, NEVADA–We left the fine people at the Desert Studies Center in Zzyzx in the morning and drove in an all-too-irregular way through Las Vegas (sorry about that, other drivers!) to the spectacular Red Rocks National Conservation Area northwest of the city. Here we see a Paleozoic section thrust from the west over the white and red rocks of the Aztec Sandstone (Lower Jurassic). The view above is looking directly west from the visitor center. I don’t know all the names of these peaks, but I do recognize Mount Wilson on the left. (I did my dissertation in the Carboniferous rocks exposed in the background, but I don’t think they named the mountain after me.)

Our students, faculty and staff scattered for a couple of hours in this park on yet again a very pleasant day. Many of them climbed the sandstone cliffs, no doubt impressed by the large foresets showing that these sediments were deposited in massive dunes blown in from the east.

RedRocksVisitorCenter031513The redesigned visitor center at Red Rocks is excellent. Above is a view of part of the outside portion that takes advantage of the sun’s angle and cooling breezes. It includes a desert tortoise enclosure where we saw three of these endangered animals. This complex is so attractive and efficient that Yoav Avni took many photographs so that he could show Israeli planners some new ideas for their public displays.

At noon we drove back into Las Vegas and the open jaws of the McCarran Airport Complex. We turned in all four vans with no problems, got our boarding passes for our various destinations, and now are simply waiting in the airport for our flights out. An excellent and enjoyable trip in all respects. Here’s to Jason and Rob at the Desert Studies Center for their friendly and efficient management, to the rangers of the National Park Service for their helpful advice, to the faculty and staff leaders and drivers (so many miles!), and finally to the students who could not have been better ambassadors for Wooster Geology. Their enthusiasm and good humor is what makes these trips so special. We will return!

Exploring the Tecopa region … and finally the trilobites!

March 14th, 2013

SaltSpring031413ZZYZX, CALIFORNIA–This was our last full day of geological adventures in the Mojave Desert for 2013. The weather was even warmer than yesterday, with the temperature in Baker at 4:00 p.m. a delightful 94°F. We began in the usual way from our temporary home at the Desert Studies Center, heading north of Baker again to Shoshone and the Tecopa area. Our first stop was at Salt Creek Spring in the Salt Spring Hills, one of the rare riparian environments in this part of the desert. This place is also notable as the first place gold was found in southern California. This discovery in 1849 began the boom in mining throughout the Mojave Desert.

TafoniMelissa031413One of the interesting geological features we noted was the occurrence of the familiar tafoni, but this time in a deeply eroded outcrop of quartz monzonite (shown above with Melissa Torma). Our companion Yoav Avni believes this may represent a Pleistocene pluvial phase of erosion that has been exhumed in the modern landscape. Tafoni features in granite would seem to require more water than is present today in this system, thus placing these features during a wet interval makes sense.

ShoshoneMuseum031413We next returned to the little settlement of Shoshone, this time visiting the town museum (above). It is well worth touring for its local artifacts, some wildlife displays, and the bones and teeth of the Shoshone Mammoth found in the Tecopa lake sediments.

Archidiskodon_tamenensis031413The mammoth (Archidiskodon tamenensis on the sign) has been very well preserved by the lake clays and silts, especially the diagnostic teeth and jaws. It is an impressive find and an important addition to our knowledge of the ancient Lake Tecopa ecosystem.

OliviaBrownResting Springs031413The Resting Springs Welded Tuff exposed east of Shoshone is one of the most famous roadcuts in the Mojave Desert. Above we see Olivia Brown exploring the glassy black middle of the unit. The colors and hardnesses of the rocks here show degrees of welding from the intense heat developed in this pyroclastic flow. It is technically a devitrified pumice tuff, welded tuff, and vesicular vitrophyre dated by K-Ar methods as 9.5 million years old. The fiamme are fantastic.

JonahDragFold031413In the same outcrop of the Resting Springs Tuff are some impressive faults. Jonah Novek is showing above how he knows this is a normal fault because the drag fold shows downward movement of the hanging wall (the side he is standing on).

TrilobiteCollecting031413At lunchtime we arrived at Emigrant Pass east of Tecopa to collect trilobites from the Cambrian Carrara Formation exposed on the north side of the highway (which happened to be the Old Spanish Trail). After a bit of exploring, our ace field geologist Shelley Judge found the most fossiliferous outcrops. We found hundreds of the fascinating critters, leaving most for future field trips. I like the view above, by the way, because it shows Telescope Peak on the far distant skyline.

TrilobiteWhole031413The best trilobite of the day (and there were many good specimens) was collected by Olivia Brown. It is a rare whole specimen, apparently of the genus Olenellus. You can see all the thoracic segments and spines, as well as the pygidium. The way the cephalon is separated from the thorax may indicate that it is a preserved exuvium (molt). Very nice.

ChinaRanchSign031811aFollowing a geological tradition transferred from Sonoma State University geologists to us via my friend Matthew James, we visited China Ranch south of Tecopa and had date milkshakes. Delicious and refreshingly cool on what turned out to be a very hot day. We also had a good geology lesson with the fanglomerates and ancient lakebeds exposed around the date groves.

TecopaPlaya031413While driving out of Tecopa, we stopped to walk out onto the Lake Tecopa playa, which was covered by a thin crust of salts. From the left are Meagen Pollock, Melissa Torma, Shelley Judge and Olivia Brown. We observed the modern playa sediments juxtaposed with the ancient lake strata exposed as low mounds.

WadeExit031413Last of all was a stop to briefly recognize the Harry Wade exit route out of Death Valley at an historical marker on the highway back to Baker. We came full circle at this point, since we started with Death Valley and now ended looking back into that source of such hardship in 1849.

Our final scientific event of the day was an excellent tour of the night sky by the Laboratory Technician of the Vassar College Environmental Sciences and Geography Department, Rick Jones. The sky is very dark and inviting in this lonely part of the desert.

Enjoying the geology of the Mojave National Preserve

March 13th, 2013

StudentsLavaCave031313ZZYZX, CALIFORNIA–Today the Wooster Geologists explored the Mojave National Preserve. It is a beautiful, spacious, diverse place well maintained and protected by the National Park Service. Our first stop of the morning is shown above. We explored a lava tube in the cinder cones portion of the preserve. We descended into the dark tunnel by the steps above, and then studied the walls and ceiling with our flashlights, as Melissa Torma is doing below.
MelissaCave031313Lava tubes are formed when a lava flow cools on the top and sides, and then the remaining lava flows out, leaving behind the empty shell. In this particular lava tube we could see various level markings the lava left on the walls as it drained away. We also saw spatter and “lavacicles” hanging from the ceiling much like icicles or stalactites in a cave. My favorite part is where we can see from below a granitic boulder that was caught up in the flowing lava.
CambrianLimestoneOutcrop031313South of the lava tube along Kelbaker Road is a small outcrop of Cambrian limestone. We examined these rocks for a short time (above) to sort out their lithologies and the paleoenvironment in which the sediment accumulated. The clues included extensive and diverse horizontal burrow systems (shown below) and numerous oncoids with shelly nuclei.
BurrowsLimestone031313The students determined that the burrows were filled with dolomite from later diagenesis of the sediment, and that the oncoids showed the system was deposited well within the photic zone. We think this rock is a biomicrite formed around the storm wavebase on a shallow carbonate platform.

KelsoDunes031313One of our favorite places is Kelso Dunes. These massive piles of sand are stabilized at their bases but still moving about at their crests. We’ve studied them so many times in the Desert Geology and Sedimentology & Stratigraphy courses that we needed to say little about them. The students raced to the top, noting the diverse sand composition (so much more than just quartz) and eolian structures on the way.

TafoniAnanda031313Ananda Menon is here showing us one of the magnificent tuff beds at the Hole in the Wall locality in the easternmost portion of the Mojave National Preserve. The holes in the wall (is that how the place was named?) are examples of tafoni, a rock weathering pattern. We hiked the Rings Loop Trail examining the tuff units and their diverse clasts, including pumice and charcoal. We also saw good examples of Indian petroglyphs of unknown age.

QtzMonzoniteCimaDome031313While crossing Cima Dome on the way back to Zzyzx, the group visited an outcrop of quartz monzonite which forms at least part of the intrusive body under the uplift. As with most of our outcrops, it was a story of both petrology and structural deformation.

AlienFreshJerky031313Finally, at the end of the day I could not resist taking the Wooster Geologists to the unique store in Baker called “Alien Fresh Jerky“. Half the group loved it, the other seemed offended by the epic cheesiness. At least Melissa Torma and Jonah Novek enjoyed meeting members of the Galactic Peace Patrol parked in front.

Folded rocks, volcanoes, and a little of the Old West

March 12th, 2013

CalicoMemberFolds031213ZZYZX, CALIFORNIA–The spectacular set of folds above are exposed in the lower parking lot of Calico Ghost Town near Barstow, California. This is a famous site that has been visited by hundreds of geologists, but there are still many mysteries about the causes of this deformation and even the correlation of these rocks in the region. The section makes up the Calico Member of the Barstow Formation, which is apparently below the exposed units of the Barstow Formation in Owl Canyon and Rainbow Basin we saw yesterday.
ShelleyCalico031213As a true structural geologist, Shelley Judge is here explaining the folding of these beds with her hands and, later, a sketch on notepaper. “Explaining” is not quite the right word: she wrangles information and observations out of the students first before developing the deformation hypotheses. It is not just about a bit of compression!
StudentsCalico031213After exploring a wadi west of the town, we then spent the rest of the morning in Calico. The students above (from the left, Kyle Burden, Steph Bosch, Sarah Frederick, Olivia Brown and Alex Hiatt) are enjoying the main street of this reconstructed 1880s mining community. There are lots of attractions here, from sarsaparilla in the saloon to a classic old-timey mystery shack. One gentleman, hearing that we were geologists, kindly explained to us how Calico Mountain is an extinct volcano with “sandy dikes” full of metals and remnants of lava flows on its sides. It was fun to see our students grapple with the question: do we correct this nonsense or just smile and avoid the hassle? (I just let it pass because I was hungry for lunch!)
AmboyCrater031213In the afternoon we drove south and east along Interstate 40 and Route 66 (yes, the Route 66) to Amboy Crater (shown above). The day had warmed considerably — my thermometer said it was now 94°F. Nevertheless, the stalwart geology crew walked to this gorgeous cinder cone and climbed to its rim from the inside (shown below). I enjoyed learning about the subtle features of the lava flows that emanated from the cone, including pressure ridges and hexagonal cooling joints. This flows and the cinder cone look amazingly fresh. The lava flows have been dated at between 6000 and 500 years old.

Verbena031213The warm temperatures at Amboy brought out some reptiles, to our delight. We saw at least three desert iguanas and many flowers, including the Sand Verbena (Albronia villosa) shown above. It felt like summer, although we were still in the middle of March. Tomorrow is expected to be even warmer. (Yes!)

Wooster Geologists in ancient lakes

March 11th, 2013

Manix031113ZZYZX, CALIFORNIA–Today Team Mojave studied the remains of ancient lake systems in the dry, dry desert. Early in the morning we drove west from Zzyzx to the Harvard Road exit off Interstate 15 and took a series of sandy roads to Bulwada Ridge on the shoreline of ancient Lake Manix. This Pleistocene, pluvial lake occupied a huge basin east of Barstow, California. Above we see laminated muds deposited in the lake itself. In the foreground are bouldery shoreline sediments. In the background you can see a scarp cut by the modern Mojave River (all underground at this point). Lake Manix was fed by the ancient Mojave River and supported a diverse fauna of fish and invertebrates.

MeagenBeachRidge031113Just to the north of the shoreline are long, twisting gravel bodies. Meagen Pollock is pondering one which has been truncated by modern erosion and now is topped by a beautiful desert pavement. (She found a beautifully polished artifact on one of these surfaces, by the way. It is a scraper with one bifacially-worked edge.) These gravel deposits are ancient beach ridges made by storm waves on Lake Manix.

OwlCanyonGroup031113After our visit to Lake Manix, we traveled to much older lake and river deposits in the Barstow Formation (Upper Miocene) exposed in Owl Canyon near Barstow. Our tradition here is that the students first explore the exposures and then bring back rocks to the picnic area for group analysis and discussion. The students above are clearly happy with all that they learned. (The two distinguished people in the background, by the way, are my parents Gary and Corinne Wilson who came to enjoy the geological fellowship.)


A view from the other side of the table. Photo by Gary Wilson.

DesiccationCracks031113Kyle Burden found this beautiful example of two-stage desiccation cracks, preserved here as molds in the overlying sandstone.

RainbowBasin031113Another Wooster tradition is the group photograph in front of the outstanding syncline in the Barstow Formation exposed in nearby Rainbow Basin.

AftonSide031113Our final stop was in Afton Canyon about 50 miles east of Barstow. This narrow passageway is where Lake Manix drained into Soda and Silver Lakes, apparently more than once in a catastrophic manner. We crossed the mighty Mojave Rover on foot and then walked up this side canyon to check out the flood deposits and the lake deposits high on the skyline. These mark the highest level Lake Manix reached before it overtopped its dam and drained very quickly.

Another stimulating day which ended with a chicken dinner at the Desert Studies Center. Tomorrow we will return to the Barstow region but this time concentrating on structural issues and volcanic and plutonic rocks.


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