Sunday 11 December 2011

The SVP 2011 field trip to Utah; dinosaur footprints in the desert.

Some years ago I attended a day class at Manchester University taught by Peter Falkingham entitled 'Palaeontology - Biomechanics, Tracks and Traces', which looked at dinosaur tracks and the variables involved in track formation, as well as interpretation and biomechanics. We spent a very informative day experimenting with sand trays, looking at the museum's collection of prints and learning how to interpret them and looking at how limb morphology and substrate elasticity affects trackmaking. It was all good stuff. So when my wife Ann-Marie and I decided to attend the 2011 SVP meeting in Las Vegas a certain field trip caught my eye: Tracking Early Dinosaurs Across Southwestern Utah and the Triassic-Jurassic Transition. Dinosaurs? Check. Tracks? Check. Utah? Check. What's not to like?

Skip forward some months later, it's early morning and we're both in full field gear weaving through the somewhat surreal surroundings of slot machines and tables of all-night poker players under the painted sky of the Paris casino, heading for the north entrance near the sports book. Odd groups of incongruous-looking individuals are clustered here and there dressed not for gambling but for the wilderness, and outside we find a row of gleaming SUV's ready to take us out of the city and into the desert to track dinosaurs. We saddle up and off we go, off to track dinosaurs on our first ever SVP field trip.

Leaving Las Vegas. Gathering outside the Paris before heading into the desert.

We had an excellent group of leaders to guide us through our three days exploring tracksites in the desert, and they had done a fair amount of work before we all turned up. They were:

Andrew Milner - St George Dinosaur Discovery Site
Tylor Birthisel - Grand Staircase-Escalante National Monument
Jim Kirkland - Utah Geological Survey
Brent Breithaupt - Bureau of Land Management
Neffra Matthews - National Operations Centre, BLM.
Martin Lockley - Dinosaur Tracks Museum, University of Colorado
Melinda Hurlbut - St George Dinosaur Discovery Site

Part of this prep work were the field guides we were all given when we arrived at the pick-up point, and these were works of scholarship in themselves. As well as in-depth information about the sites we visited, complete with stratigraphic sections, site maps showing trackways, photos etc, there was a guide on the subject of photogrammetry to supplement what we were taught, and the route taken between sites had detailed notes on the various formations and other geological features we could see from the trucks. It was fully referenced and a superb document to have to hand whilst we were travelling, and useful for re-reading and checking information after the trip.

The main track layer in the St George Dinosaur Discovery Centre. Palaeontologists for scale.

Our first stop was the St George Dinosaur Discovery Centre in the city of St George, Utah and which is built over an in-situ multiple trackway located at the top of the Johnson Farm Sandstone Bed in the Whitmore Point Member of the Moenave Formation. The site has been interpreted as being on the western margin of Lake Dixie as the deposits here are predominately shoreline in nature and at this point in the Whitmore Point Member represent transgressions and regressions of the lake (Milner 2011). The museum is small but perfectly formed and is dominated by the huge multiple trackway surface preserved within the building and as well as the in-situ surface many more blocks containing either multiple or single trackways and individual foot impressions are displayed within as well as various body fossils. The site has produced plant fossils, abundant fish remains, tetrapod material and various ichnotaxa including theropod swim tracks. The museum has done and continues to do vital work in the Upper Triassic and Lower Jurassic of Southwest Utah, and has mapped multiple sites in the region. If you're in the area it is well worth spending some time there as the collection is really impressive. Jim Kirkland then took us across the road where we inspected other beds containing fish fossils and what have been interpreted as fish nests in a rippled surface.

Neffra Matthews demonstrates the technique of photogrammetry using a print on the main track layer.

It was at the museum we were also introduced to the technique of photogrammetry, with a detailed explanation by Neffra Matthews on the principals and methodology of this exciting technique of recording fossils in 3D. Most of us don't lug Lidar units with us into the field, but we pretty much all take digital cameras of one sort and another and Neffra demonstrated how we can photograph tracks that can be fed into software to create measurable 3D-models. This has several advantages over other techniques: it's cheap, very portable, it's very accurate, it creates data sets that can be examined in the lab/on a train/on your iPad/pretty much anywhere, plus the information can be easily exchanged via the internet. perhaps most importantly photogrammetry is a non-destructive way of gathering 3D data and rapid prototyping allows the creation of highly accurate physical models suitable for study which are scaleable too.

A well-preserved Eubrontes track seen on the underside of a slab in the museum.

From the museum we headed out into Utah, eventually arriving at Zion National Park and meeting up with the others (after a slight detour around the campsite, where we saw mule deer) at Black Canyon for a look at the section visible there, revealing as it does a sequence from the Petrified Forest Member of the Chinle Formation (Upper Triassic) rising vertically to the spectacular cliffs of the Navajo Sandstone (Early Jurassic). We preceded to drive throughout the park and up past Checkerboard Mesa, a heavily jointed and cross-bedded outcrop of Navajo Sandstone. We passed grazing Bighorn Sheep and headed out of the other side of the park to spend the evening at Thunderbird Lodge, Mount Carmel Junction, east of Zion. An enjoyable meal in the attached restaurant, with good beer and chat followed by an early night in preparation for day two.

The next morning after breakfast we headed in convoy to the Mocassin Mountain tracksite which had been discovered in 2007 by hunters who reported the find to the BLM Kanab Field Office. The site contains multiple layers in the Navajo Sandstone and is in an area frequented by off-highway vehicles (OHV) and the BLM is currently engaged in managing sites like this to preserve the resource for both OHV users, palaeontologists and the public. The site has been vandalised with attempts at casting footprints leaving traces of sealant from what was possibly a pre-constructed form and this activity damages the footprints and information is lost to science because of traces left by the process as well as the removal of grain layers when the cast is removed. This problem reminded me of the appalling destruction of a trackway on the Isle of Wight where some bright spark tried to extract an individual print from a trackway in the Wealden shale; the matrix is far too unstable for this to work and the footprint was heavily vandalised.

Not just Utah: dinosaur footprint destruction in the Wealden of the Isle of Wight.
There is a global issue with the vandalism and theft of trackways.

After a brief introduction by BLM rangers Misty and Alan we set off to inspect the multiple trackways at Mocassin Mountain, which contains multiple trackways from diverse ichnogenera. This site contains a variety of preservation styles and the environment of deposition being dune sets means there are unique morphological characteristics to many of the tracks. With the usual excellent explanations by our leaders we spent some time examining the site before took a group photo and had lunch, then setting off to the nearby Coral Pink Sand Dunes State Park where we viewed the dunes and got happily distracted trying to identify the tracks left by extant organisms in the sand, ably helped by leading ichnologist Tony Martin.

Potter Canyon over the state line in Arizona was our next stop to examine the section there which represents part of the Whitmore Point Member and anther part of the margin of Lake Dixie. We trekked up to the cliff face and got stuck into a bit of prospecting. Jim Kirkland explained the member was deposited on the edge of a large lake (Lake Dixie) and we found ostracods, conchostracans, stromatolites and petrified wood. We then moved on to two localities situated in the Kayenta Formation. The first, the Hamblin Tracksite is due to be destroyed as part of the Southern Parkway Project and efforts are underway to save as much as possible of the website (however in a different location the road is being diverted to preserve the local golf course). The second was an unnamed site with abundant plant remains and a broken trackway surface and as well as gathering plant fossils here one of the crew found a slab with both Grallator tracks and arthropod tracks on the rippled surface.

The evening of the second day was spent back at the museum in St George, where we enjoyed an excellent meal and were guided expertly around the museums collection by Andrew, where we saw coelacanth fossils, exquisite fish specimens and a large phytosaur skull that is still in prep. We also got a close-up look at the smallest Grallator trace in the collection, a wonderful ichnofossil. We retired to a Best Western in St George for a good night's kip.

The smallest Grallator print in the collection. SVP scale bar for scale. How cool is that?

The final day was ushered in with a make-your-own-waffles breakfast, a novelty for those of us visiting from other countries. The train of by now quite dusty field vehicles set off for the Warner Valley to visit an important track site on BLM land. The area is very popular with OHV vehicles and tyre tracks are everywhere . . . however the site has been protected from both OHVs and the weathering of the track surface by water action by a low metal wall to divert the runoff. It's a spectacular locality, looking out across the valley floor towards the hills in the distance with no sign of mankind's hand on the landscape (apart from the car park and a couple of information panels, but let's assume you've got your back to them).

An exceptional Eubrontes track in the Warner Valley. This is the print traced by Martin (see below) and recorded
using photogrammetry (see above).

The trackways are equally impressive and Martin Lockley, Andrew and Tylor gave us a detailed overview of the history and research done at the site as well as pointing out the main features, amongst which were the best Eubrontes tracks we'd seen so far (the maker of Eubrontes tracks is thought to be a Dilophosaurus-sized theropod, Grallator by a smaller theropod dinosaur). We recorded the site using photogrammetry and Martin demonstrated the more traditional technique of tracing which many of the crew then tried out; it's a wonderful way to really study individual prints in detail and consider their morphology.

Dinosaur tracker Martin Lockley traces a Eubrontes print.

A looping 360˙ animation of the same Eubrontes track (see above) from the Warner Valley.
The data was gathered using photogrammetry techniques learnt on the SVP field trip to Utah,
processed in the field on a laptop and animated back here in England.

After that we headed down the road (in our truck Neffra demonstrated how to use the photogrammetric data we collected to reconstruct a footprint in 3D for study later on her laptop - brilliant!) to inspect the Triassic-Jurassic transition, which occurs as an unconformity between the Chinle and the Moenave Formation. Jim Kirkland explained the section to us and the significance of the anhydrite nodules in the Chinle (an increase in arid conditions), and we observed the pebble lag which sits unconformably on top and is present at the base of the Moenave Fm. throughout this part of Utah. Here we a saw a large bird of prey which was possibly a juvenile Bald Eagle.

We then headed off to Fort Pearce for lunch. Fort Pearce was built by Mormons during a period of conflict in the 1880's when the Ute and Navajo objected to their presence. Below the outcrop the fort is perched on lies boulder with petroglyphs etched into the desert varnish and there were more on the valley floor. We heard a very loud boom that could have been mining, or a sonic boom.

A Grallator print on a rippled surface. This print is an impression as viewed from the underside.

Time was pressing so we moved on down the valley to a small canyon where we found tracks and bioturbated surfaces on the underside of in-situ beds on the cliff, and a new and potentially significant Eubrontes print was found, as well as Grallator tracks galore. Our final stop was at the foot of a cliff we subsequently hiked partway up. On our ascent we looked at the lacustrine layers of the Whitmore Point Member with it's abundant fish remains (many in concretions), and then up the trail and into the Kayenta Formation where we studied the limestone fish beds below the distinctive red cliffs of the valley. The view from here was incredible and it was with mixed feelings we hiked back to the trucks below. Our leaders had really brought this area of Utah and Arizona alive and now we understood the fossils, their context and their global importance.

Prospecting in the Kayenta of the Warner Valley. Does it get better than this? I'm not sure it does.

We eventually got back to Vegas in the early evening and after being dropped off and picking up our luggage went to check in. It was an odd feeling walking across the casino floor underneath the painted sky in full field gear, covered in the red dust of the Kayenta with my head spinning with ichnology and the quite incredible landscapes we had seen in the past three days. The contrast between environments couldn't have been greater.

We made it back to the Paris in time for a shower, quick beer and into Concorde A/B to see Jack Horner's address to the meeting, one of the highlights of the SVP 2011. The real highlight was the field trip though, no doubt.

The SVP field trip to Utah at Mocassin Mountain with all leaders, rangers,
Paleo Barbie and other participants present. Scale bars for, er, scale (and photogrammetry).

Thanks once more to the leaders of the field trip, who not only gave us food and tipped us off where to buy beer but also made the whole experience so fascinating and productive; I've only scratched the surface of the content of the trip here and there was so much more to tell than my necessarily simplified account does. In the end apart from the not inconsiderable value of the knowledge gleaned and the new field techniques learnt the great thing was the new friends made as everyone on the trip, leaders and participants alike were wonderful company and it was a joy and honour to spend those three days with such interesting folk. Viva palaeontology!

Tracking Early Jurassic Dinosaurs Across Southwestern Utah and the Triassic-Jurassic Transition. Milner et al. 2011. Nevada State Paleontological Papers No. 1.

Special thanks to Andrew Milner for providing extra information on some of the localities we visited, and Neffra Matthews for providing the photogrammetrical data used in the animation.

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