The most common theory about how dinosaur footprints were made and preserved as fossils is that the dinosaur stepped in mud along a lake shore leaving a footprint. The mud dried out in the sun and hardened. The next annual flood brought more sediment which buried the hardened footprints in more sediment which eventually hardened.
When mud quickly hardens in the sun the result are mud cracks. As the water is dried out of the mud the overall volume of the mud decreases, resulting in cracks. Mud cracks can also form under water. As sediment builds up underwater the weight of the sediment will squeeze the water out of the lower layers of water. Underwater mud cracks can also form as a result of changes in salinity of the water. In either case this results in mud cracks which can then fossilize. Mud cracks formed underwater have a different pattern than those formed in the sun. And the shape of mud cracks formed in the sun will vary depending on how many times the mud was wet, dried out, and re-cracked.
The dinosaur tracks in our museum come from the Connecticut River Valley in Massachusetts. This setting gives us a unique opportunity to study the relationship of dinosaur tracks and mud cracks. The local conditions were that of a shallow muddy lake shoreline, with frequent water level fluctuations and a high sedimentation rate. The result was rapid, deep, and successive episodes of burial that preserved dinosaur footprints, water ripples, raindrop impressions and mud cracks... but the mud cracks are only seen in certain locations. This should raise the question, why?
Why Mud Cracks There But Not Here?
Our dinosaur tracks come from an area about two miles east of the Connecticut River in Massachusetts. There are no mud cracks found at this location. Notice on the map (use button below) that the river is just a short distance from the Mount Tom range. Dinosaur tracks, along with mud cracks are found between the river and the Mount Tom range. What's the difference?
Let's look at the geology. The Connecticut River Valley is a half-graben. The pivot point is on the west side of the valley at the Mount Tom Range. The east side of the valley sank, dropping thousands of feet. The west edge stayed in place, acting as a hinge point. Several layers of sediment and lava flows (flood basalt) filled the valley as it sank on the east. The sediment is very deep in the east and thin in the west (use the map button above to see a geological diagram).
The evolutionary assumption is that the half-graben formed and filled with sediment over a long period of time, several million years. However, what if it formed in about a year during Noah's Flood. The sediment and lava being deposited quickly. The result would be that the sediment along the western edge, where the layers are thin and mud cracks are found, would be very warm. The heat from the lava flows would have quickly dried the sediment, not the sun. While further away to the east, the lava was buried too deeply and quickly to warm the surface where the dinosaurs were walking. And thus there are no mud cracks found there.
The result would be dinosaur tracks and mud cracks along the western edge, but mud cracks would be rare elsewhere.
What Do Mud Cracks Look Like?
Mud cracks can vary in appearance. You're probably familiar with the ones in the photo at the top of this page. The mud cracks are in different shapes but with fairly straight sides. The above image shows fossils of two other types of mud cracks.
The photo on the left looks like it has lumps all over it. These are small mud cracks that have experienced some erosion. The edges of the cracks are rounded.
The photo on the right is a stone with mud cracks that are random looking.
Raindrop Impressions: How Is It Possible?
The photo above is a picture of a large slab in the Berneski Museum at Amherst College. It is covered with fossil raindrop impressions. They look like small craters all over the surface of the rock.
Try to imagine a situation in which raindop impressions in mud would last long enough to become fossilized. No dinosaur walked on them. No animal walked on them. A very brief shower blew through. It could not have been much of a shower because even a brief rain would create mud mush and wipe away any raindrop impressions that were initially made. This requires mud firm enough to take and hold the impression, and then a situation in which they were quickly, yet gently buried.
This slab was collect in 1863 in Turner's Falls, Massachuestts. That's in the Connecticut River Vally about 33 miles north of where our dinosaur tracks were found. This is a long rift valley that is open to the sea at it's southern end. In addition the patterns in the sediment show that a large amount of sediment came in from the highlands east of the valley. It's easy to visualize parts of this valley, in particular the northern parts, being shielded from direct impact of the rising global flood waters. There would be no direct imapct from tsunamis, or even tides. So the rising and falling water levels would be much gentler, allowing dinosaur foot prints and even raindrop impressions to be preserved instead of washed away.
