The Mystery of Limestone in Sandstone Layers

How did the pieces of limestone end up inside the sandstone layer?

What are the relative ages of the limestone and sandstone layers?

Answer:

Organic sedimentary rock

When studying an outcrop where the bottom layer is limestone and the layer directly on top of that is sandstone, it raises the intriguing question of how the pieces of limestone became enclosed within the sandstone layer.

Limestone is a sedimentary rock formed from calcium carbonate deposits, often originating from sources such as shells, bones, and corals. On the other hand, sandstone is also a sedimentary rock that is created through the layering of rock particles in horizontal lines. These two types of rocks have different origins and compositions.

In this case, the pieces of limestone found within the sandstone layer likely got there through a process called sedimentation and burial. Over time, as new layers of sediment, including sand, were deposited on top of the existing limestone layer, some small pieces of limestone got incorporated into the growing sandstone layer. These pieces may have been weathered or eroded from the original limestone layer and transported by water before being buried within the sandstone.

Relative dating principles tell us that older rocks are typically found at the bottom of a sequence, while younger rocks are found towards the top. In this outcrop scenario, the sandstone layer containing the pieces of limestone is likely younger than the underlying limestone layer. The sandstone, composed of quartz and feldspar, could be around 416 million years old, while the limestone layer might be approximately 350 million years old.