Stories from the Snyder Quarry 2
9:30 pm
Part Two: Bring ‘em Back Intact
As mentioned previously, the main goal of this trip to the Snyder Quarry was to bring back a large block containing an assortment of Triassic fossils: bits and pieces from crocodile-like phytosaurs, heavily armored aetosaurs, and (most tantalizing of all) bones from an early dinosaur. The block had been defined and encased in plaster earlier this spring, when NMMNHS alum Dr. Andy Heckert (now teaching geology at Appalachian State University) brought a group of students to New Mexico for some fieldwork. By all accounts, they did an incredible job expanding the quarry and locating fossils, and the sizeable block they left behind was a fitting testament to their enthusiasm and productivity at the site.
The method of quarrying a big block of fossils like this hasn’t changed much in more than 100 years. Paleontologists define the area containing the fossils by digging a trench around the perimeter. The trench is then dug wider and deeper until the fossils are isolated within a pedestal of rock, which in large blocks can be undercut to form a sort of giant rock mushroom. The fossils atop the pedestal are covered with a layer of wet paper, and the whole pedestal is capped with sheets of burlap soaked in plaster. After the plaster has hardened into a protective jacket, chisels or other wedges are driven underneath to separate the block from the underlying rock, and the whole block can be flipped over onto its face.
Larry Rinehart and Justin Spielmann begin to jacket a smallish pedestal of rock and fossils,
while Volunteer Preparator Jim Moore heads for the burlap.
Flipping a jacket is the diciest part of the whole procedure. If all goes well, the whole block tumbles over neatly, with all its contents intact and snugly nestled within its protective plaster shell. If the flip is not done smoothly, or the plaster is weak or thin, or the rock inside is loose, or the bottom of the pedestal isn’t completely separated from the surrounding rock, then flipping the jacket can cause part or all of its contents to dump, which is never a good thing.
The larger a jacket is, the more difficult it is to flip. A ton of rock isn’t going to turn over quickly or smoothly, and something that heavy is much more likely to tear apart or break away from the thin plaster shell holding it all together. When Andy and his group first attempted to flip the jacket, the plaster started cracking in one corner and the some of the sediment began to shift inside. They set the jacket back down, and made the decision to leave it until a crew could come back, spend some time reinforcing the jacket and hopefully bring it back the the NMMNHS intact.
Which is what we set to work doing after we cleared out the quarry.
We added several more layers of burlap and plaster, paying close attention to the areas where cracking had started. We incorporated two-by-fours into the top of the jacket, that would both reinforce the jacket and act as skids once we turned it over. We drove lengths of tube steel under the block, and tied it all together with chain and ratchet straps, and by Wednesday afternoon we were ready to flip it over.
Luckily for us, Rich Wilke had brought a winch up to the site, which made the flip go much easier. Within a few minutes, Rich, Larry, and Justin had flipped the jacket neatly, and had pulled it up out of the quarry. A nine-image sequence of the flip is shown below the fold:
Larry Rinehart and Justin Spielmann help flip the jacket,
while Curt Haakenson and Robert Hubbard observe.
In quarries where a jacket would need to be dragged or carried for a long distance, burlap and plaster would be added to the underside to seal the fossils within a protective shell. But at the Snyder Quarry, we were able to back our truck right up to the quarry’s edge, so we left the jacket open on the underside (which was now the top), so that the fossils were contained upside-down in a giant plaster bowl. After much pushing, prying, and levering, the jacket was in the back of the truck, ready to transport back to Albuquerque.
Larry prepares to pull the block into the truck with a come-along
Next time: The Art of Ghost Ranch: an O’Keefe-less Overview
We’ve had a few jackets fall apart in the flipping process. Not fun.
Hi Pascal -
Out of curiosity, what sort of fossils have you been digging up?
Matt,
Mostly Jurassic dinosaurs. Allosaurus teeth and the back end of a large (A. ajax size) sauropod. Also a few fish – no mollusks, though, which is my specialty. We do have at least a few bones of Gastonia (or similar thyreophoran) and some small ornithopod long bones as well.