Most fossil sites have some unique characteristics that make excavations a challenge. Maybe the bones are fragile and softer than the sediment, or the same color as the sediment. They might be miles from any road, or even underwater. Carmel Church has four features that cause difficulties.
The first, which I mentioned yesterday, is the sheer density of bones; in some areas there are literally no gaps between them. Second, the weathering rates at Carmel Church are spectacular, so that exposed bone sometimes begins to deteriorate in a matter of days. Third, the conglomerate at the base of the bonebed adds a lot of weight, and weakens the clays by providing natural breaks (the clays are actually quite strong). Fourth, the bonebed is underlain by the Eocene Nanjemoy Formation, which is an unconsolidated sand; including it in the jacket adds weight, but no strength.
All of these problems have come together to make this particular jacket a tough one. May efforts yesterday to remove two vertebrae in order to make a gap at the back of the gap were fruitless, as it would take weeks to remove the rest of the bone in those areas.
So, we’re trying a different, dramatic technique; we’re going jacket the exposed bones anyway. Typically, this will break some of the bones that are in the way, especially ribs that run perpendicular to the jacket. By making the jacket first, we can control that breakage, making it much easier to repair the bones when we get them back to the lab. Often, larger bones like vertebrae will separate from each other with minimal breakage using this technique (we’ve done this before).
Today, we made a top jacket on the bones shown above. We’ll probably add some more layers to this tomorrow before trying to turn the jacket, because we want to make sure it’s rigid and that bones can’t easily fall out the bottom.