The cliffs of Pennington Bay consist of aeolian limestone deposits formed from dune deposits composed of cemented shell grit and quartz sand. The aeolian limestone formation was deposited as coastal sand dunes.
Sedimentary rocks contain features that show the processes and conditions of deposition. One feature is cross bedding, which is layering within strata and at an angle to the main bedding plane. The direction of motion of the cross-beds can show ancient flow or wind directions (called paleocurrents). The orientation of the cross-beds therefore indicates the direction of the paleocurrents.
In an aeolian environment, cross beds can exhibit inverse grading due to their deposition by grain flows. Winds blow sediment along the ground until they start to accumulate. The side that the accumulation occurs on is called the windward side. As accumulation continues to build, some sediment falls over the end. This side is called the leeward side. As more sediment piles on top the weight causes the underlying sediment to cement together and form cross beds.
Examine the cliff face at the listed coordinates. Focus your examination on flat vertical surfaces. Can you see evidence of layers within the strata. This is cross bedding. Please send your answers for the following earthscience tasks to the cache owner by message or email.
- What is the apparent direction of the cross bedding?
- Does the angle of the cross bedding change?
- Estimate the thickness of the cross bedding layers?
