Kentucky River Fault Zone
Stop #2

Mudcracks

The picture to the left displays lithified mudcracks. At first it might just look like any other rock but a closer inspection will hopfully reveal a series of polygon shaped cracks on the surface of this rock. They are a little difficult to see in a picture but some of the more prominent cracks should be visible.

So now you are probably wondering where these cracks come from. Well they typically form when wet mud contracts as it dries. If you have ever seen a dried up mud puddle you should understand. This is a clue to what this part of the world was like when these rocks formed. It must have been periodically wet and dry, which implies a shallow water environment.

Algal Laminations

In this picture you should notice the very fine layers in the rock. Use the penny as a reference for the thickness of the layers. These are called algal laminations, the name gives some insight into how they formed. Picture in your mind a shallow marine environment with a layer of algae just under the suface of the water. This algae layer acts as a sediment trap; when the sediment covers the original algal layer a new layer of algae forms on top of it. Then the new algal layer traps a new layer of sediment, and so on, and so on. So the algal laminations lend support to the hypothesis that when these rocks formed this was a shallow water environment.

There are large differences between the features that we have observed in the rocks at this stop and the ones we saw at the last stop. One very significant difference is the complete lack of fossils here. Actually this can be explained by what we have already learned. The fact that when these rocks formed this was a shallow water environment, combined with the fact that North America was near the Equator during this time explains the lack of fossils. A warm equatorial environment will lead to high evaporation rates, and if alot of water is being evaporated from a shallow sea the water left behind will become very high in salt. This is because water can evaporate but the salt is left behind.

So if the water is hyper-saline (very salty) most organisms cannot survive, therefore no fossils. Another point is that if there were any critters crawling and digging around when these rocks formed they would have messed up the nice layers. If you refer back to the base map for this trip you will notice that the rocks at stop #2 are older than those at stop #1. Based on the evidence in the two outcrops we can conclude, that sea level in this area must have gotten deeper between the time that the rocks at the two stops were deposited.