Field School, Day 4 (7/9/03) - West Bijou Creek, private property
On Day #4, we were again in West Bijou Creek. Our goal was to: (1) collect from one quarry; (2) find one new quarry; and (3) prospect for mammal bones of the PU2 of the Puercan age (65.5 - 64.5 mya).
We were immediately rewarded by fossil mammals at he first site we visited. It was named "The Sound of Music" due to its prominent location on top of a hill with some flowers. We found many bone fragments including an entire turtle leg bone and many turtle shell fragments. Note the very different postures in the pictures. At left is the posture of a person looking for fossil bone fragments (on hands & knees). At right is the posture of someone excavating a new fossil leaf locality (upright with pick axe & shovel). Both location were in the D1 sequence of the Denver Basin. The leaf locality was in a cut bank of a gully. We excavated a huge section of overburden to reach the well-preserved leaves. (See the before/after pictures of the excavation in the pictures from Day 4 - link at bottom of page.) In the gully, we found another "present-day" bull snake. Above the gully, we found many ironstone leaves that had weathered to the surface. Leaves in ironstone are nice fossils to look at, but rarely preserve the detailed venation required to make an accurate identification of the species.
The second stop was further to the south and further up in elevation and age. We started our hunt in the more recent D2 sequence of the Denver Basin. The party was divided into two groups: one to hunt for bone fragments on the areas above the creek bed; and the other to hunt for fossil leaf localities by following the lower portions of the creek bed. The bone-hunting group didn't have any success and soon joined the leaf group in the creek bed. A new leaf locality was discovered, called "Smoke Break", which contains well-preserved leaves and appears to be in D2. Further down the creek bed, we discovered what is believed to be the D1/D2 contact with an unconformity (see image at left). The darker layers at the bottom are lignite/coal beds. Sitting directly on top of these are more coarse sandstones and pebbles displaying the cross-bedding of an ancient river. The "Smoke Break" locality could provide important data on leaves just above the D1/D2 contact. It was approximately 3.5 meters above the creek bed, about 2 cm below a rusty (oxidized) layer of sandstones and ironstones. Well-preserved leaves were found there in a fine grained, tan mudstone.
In the evening lecture, Bob Raynolds discussed the paleosol. Pollen from the paleosol is designated as P6. It's believed that an 8 million year gap (unconformity) exists between D1 & D2. The paleosol is considered to be a thermal maximum (or spike) or may be just discolored soils from surface weathering.