The location of this Earthcache is at Blackwattle Bay, just near a lovely bay walk suitable for dogs and bikes (and people of course). The cache is accessible by wheelchair and there is timed street parking available at the different entry points to the path.
Image attribution. By Richard Taylor from Australia (Two bridges) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
For more detailed information about sandstone in the Sydney Basin, see the Mrs Macquarie's Chair Earthcache.
Sandstone is a sedimentary rock, which means it is composed of other material which is cemented together (principally sand). The formation of sandstone involves two stages. First, layers of sand must accumulate, usually from being deposited by water or by wind. Second, once the sand has settled and accumulated, it is compacted by the pressure of the deposits over it.
Over time, as the flow of water or wind continues, cross-beds occur. These are groups of inclined layers of the sandstone strata. The state and inclination of these cross-beds can tell geologists the rough direction of sediment transport at the time of the formulation of the sandstone. Cross-bedding is very a common feature in sedimentary rock types.
The flow of current leads to the formation of dunes within the sediment. With water flows, as the flow continues, sediment is eroded from the upward side of the water flow. Sediment flows over the hump of the dune and then settles on the downward side of the dune. Usually, the slope of upward side of the flow is shallow, whilst the downward side of the flow is relatively more steeper. This gives geologists a good indication of the general direction of the flow at the time.
Image copyright. Own work
Questions.
. At the posted co-ordinates you will find a cutting in the sandstone showing evidence of the different flow rates at which the sandstone has developed in the area. If you observe carefully the area blacked out in the following photo, you will notice there are three major layers exposed.
1. Identify the three layers of bedding in the cutting. What characteristics of the rock demonstrate this cross bedding.
2. Based on your understanding on how cross bedding arises, which way was the middle layer of sandstone flowing (ie. left to right, or right to left).
Answers
You may log the cache once you submit your answers by private message. If I need to clarify your answer, I will send a private message back. If you do not submit your answers within 7 days, don't be offended if your log is deleted. Or course, you can relog it again after sending the answers.....
Feel free to post pictures of the location, but please don't post a picture of the cross-bedding. You might wish to take a picture of the beautiful ANZAC bridge instead.
Sources
University of Pittsburgh
Indiana University
This Earthcache is based on a geology walk produced by the Glebe Society of New South Wales.