*Please bring some vinegar with you to complete a brief identification experiment.
*Low tide is the best time to visit this Earth Cache but not essential. You can Click here to check tide times at Port Hedland.
We found this little spot while staying in Port Hedland, we thought the limestone formation here had some interesting elements to it and set out to find some information out about them.
The rocks we are focussing on here today are Costal Limestone which is apart of the Bossut Formation, we couldn’t find a specific age for the formation “not much more than a few million years old’ was the reply from those in the know. We were able to find out it was too young to be part of Canning Basin and is considered to be part of Dampier Sub-basin.
What is Limestone? Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal, and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.
Most limestones form in shallow, calm, warm marine waters. That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can easily extract the needed ingredients from ocean water. When these animals die, their shell and skeletal debris accumulate as a sediment that might be lithified into limestone. Their waste products can also contribute to the sediment mass. Limestones formed from this type of sediment are biological sedimentary rocks. Their biological origin is often revealed in the rock by the presence of fossils.
Some limestones can form by direct precipitation of calcium carbonate from marine or fresh water. Limestones formed this way are chemical sedimentary rocks. They are thought to be less abundant than biological limestones.
Today Earth has many limestone-forming environments. Most of them are found in shallow water areas between 30 degrees north latitude and 30 degrees south latitude. Limestone is forming in the Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, and within the Indonesian archipelago.
Limestone is by definition a rock that contains at least 50% calcium carbonate in the form of calcite by weight. All limestones contain at least a few percent other materials. These can be small particles of quartz, feldspar, clay minerals, pyrite, siderite, and other minerals. It can also contain large nodules of chert, pyrite, or siderite.
Here at Panhole point there are two distinct features that caught our eye.
Solution pits or Panholes as they are also known are depressed, erosional feature found on flat or gently sloping rock. Panholes are the result of long-term weathering and are generally seen on bedrock or very large blocks of rock. These shallow solution basins, or closed depressions, tend to form on bare limestone or silicate rock. They are also found on granitic rock. They are generally characterized by flat bottoms and sometimes by overhanging sides. The initial form may be a closed hollow created by a patch of humus. Diameters are rarely greater than 15 centimeters.
Rootlets are also visible here, as the name suggests they are remnants of plant roots. Over millions of years the tree roots have been replaced by carbonate minerals (limestone). The rootlets have formed as the limestone was weathered or unevenly cemented by calcareous fluids percolating thru the rock/sediment.
To log this Earth Cache we require you to visit GZ and then make your way West towards WP2, make some observations, consider the information given, then message us with the following answers to the best of your ability;
1. To check we have correctly identified the rocks here at Panhole Point we need you to conduct a quick and easy experiment. Using the Vinegar you brought along find a small piece of dry Limestone and pour a small amount of Vinegar on it, what happens?
Bonus points if you can go a step further with this experiment: Take a small piece of Limestone home with you and put it in a small dish. Fill the dish with vinegar to just over the top of the rock. Leave it for a week and tell us what happens.
2. Find a Solution pit, is there any difference in the texture and colour compared to the rock they are based in?
3. When considering the description above would you say the Solution pits here are of average size?
4. Find a Rootlet, what distinguishing features suggest to you it is a rootlet and not a solution pit? ?
5. A photo of course, although this task is optional, I’ll be disappointed not to see photos of this beautiful place!
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 1 week. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted without notice.
Source Roger Hockings, Wikipedia, Geology.com
