We are now one week into fieldwork with undergraduates and the Hell Creek III Research Project. Our camp is pretty large, with 24 people total from UW, UC Berkeley, Montana State and the Museum of the Rockies, undergraduate students (from University of Oregon, University of Michigan, Smith College, and Western Washington University), and many volunteers! Meals are hectic, evening campfires are entertaining, and the fossil-finding thus far is very successful – we’ve found a half dozen dinosaur localities and over one dozen mammal teeth.
You might be wondering what we do all day in the field, if so, read on! In this first field update, we’ll talk about the process of collecting microvertebrates in the field.
Collecting Microvertebrates
Step 1: Surface collecting for microvertebrates
Microvertebrates are small! So small, that to find the really tiny elements (like mammal teeth), we wear knee pads and “cheaters” (magnifying lenses attached to a visor). When we find a fossil, we use an awl to free it from the surrounding sediment, and we put it in a film canister for safe keeping.
Step 2: Find the ‘productive layer’ and collect fossiliferous sediment
After we’ve scoured the outcrop for all the surface fossils we can find, we want to identify exactly where the fossils are coming from in the hill. We trace the surface material to its highest point, and at that level we dig into the hillside and crack open rocks until we find a fossil ‘in situ’ or encased in fresh rock. If we find something, we’ve hit on the ‘productive layer’ and it’s time to collect bags of sediment!
To collect sediment we use geopicks and rock hammers to free in situ rock from the deposit, and a shovel and bag to collect the fossiliferous sediment. Then we pack the material out in frame packs, and we return to camp victorious!
Step 3: Describe the lithology
Identifying rock types and inferring depositional environment remains a big part of what we do during our paleontology fieldwork. Each time we find a productive layer, we describe its rock type and contents in our field notes. Now, after decades of fieldwork, we have a sense for the rock layers most likely to produce fossiliferous material. We’re most often looking for sediments that represent the base of stream channels, because it’s here that materials were dropped from the moving water and fossils, mud balls (‘mud rip-up clasts’), rocks, lignite, and organic material (wood, plants) were deposited. This often produces a ‘dirty’ fossiliferous productive layer, and hopefully it’s highly concentrated with fossils! But we won’t know for sure until we get back to camp.
Step 4: Screenwash collected sediment
We return to camp with bags of sediment, and to reduce the total weight we bring back to Seattle, we first screenwash collected material in the lake. Each day we put our collected sediment into wooden boxes with window screen on the bottom and let these soak overnight in the Fort Peck Reservoir. The gentle wave motion of the lake breaks up hard rocks, and the smaller particles of sand, silt, and clay will fall through the window screen, leaving the larger items (including fossils and larger rock particles) in the boxes. We pull boxes from the water each morning and let them dry during the hot Montana days, bag the sediment each night, and repeat the process with the next material collected.
At the end of this microvertebrate collection process we have a diversity of fossils from different animal groups including mammals, dinosaurs, reptiles, amphibians, and fish! These freshly collected fossils help us reconstruct the paleoenvironment pre- and post- K/Pg extinction.
Want more from the field? Check back for next week’s update and follow our Facebook page to see more photos!