Welcome to Weka Pass and some interesting rock formations that you can see as you travel along SH7. The listed co-ordinates brings you to a handily provided parking area and pathway that takes you to the iconic 'Frog Rock' , which is one of a number of distinctive rocky outcrops with unique shape.
Weka Pass, Canterbury
Weka Pass is a gorge located in the northern Canterbury region of New Zealand's South Island between the towns of Waipara and Waikari. The Waipara River cut the Weka Pass by wearing down the soft limestone and mudstone in the area. Erosion has created a number of distinctive limestone formations in the pass, which are known by descriptive names such as Frog Rock and The Seal. The Pass is home to various species of bird, including the weka, kākā, and kiwi, and was also home to the extinct moa.
Māori rock art can be found under a limestone overhang at Waikari, and it is now the prime attraction of the Weka Pass Historic Park. Māori first explored the area approximately a millennium ago and used the limestone overhang for shelter. Early European explorers utilised the overhang for the same purpose.
State Highway 7 runs through the Weka Pass, and so does a railway line. This railway was established in 1882 and although originally intended to be part of the Main North Line from Christchurch to Nelson and Blenheim, the main line ultimately took a coastal route northwards from Waipara and the line through the Weka Pass became part of the Waiau Branch. This branch line operated until 15 January 1978, and the section through the Weka Pass has been saved by a preservation group, the Weka Pass Railway. It is now one of the premier restored/tourist railways in New Zealand.
The limestone in this area goes back to the time when this part of New Zealand was underwater.
Limestone-Forming Environment: Marine
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.
One of these areas is the Bahamas Platform, located in the Atlantic Ocean about 100 miles southeast of southern Florida (see satellite image). There, abundant corals, shellfish, algae, and other organisms produce vast amounts of calcium carbonate skeletal debris that completely blankets the platform. This is producing an extensive limestone deposit.
Varieties of Limestone
There are many different names used for limestone. These names are based upon how the rock formed, its appearance or its composition, and other factors. Here are some of the more commonly used varieties.
Chalk : A soft limestone with a very fine texture that is usually white or light gray in color. It is formed mainly from the calcareous shell remains of microscopic marine organisms such as foraminifers, or the calcareous remains from numerous types of marine algae.
Coquina: A poorly-cemented limestone that is composed mainly of broken shell debris. It often forms on beaches where wave action segregates shell fragments of similar size.
Fossiliferous Limestone: A limestone that contains obvious and abundant fossils. These are normally shell and skeletal fossils of the organisms that produced the limestone.
Lithographic Limestone: A dense limestone with a very fine and very uniform grain size that occurs in thin beds which separate easily to form a very smooth surface. In the late 1700s, a printing process (lithography) was developed to reproduce images by drawing them on the stone with an oil-based ink and then using that stone to press multiple copies of the image.
Oolitic Limestone: A limestone composed mainly of calcium carbonate "oolites", small spheres formed by the concentric precipitation of calcium carbonate on a sand grain or shell fragment.
Travertine: A limestone that forms by evaporative precipitation, often in a cave, to produce formations such as stalactites, stalagmites, and flowstone.
Tufa: A limestone produced by precipitation of calcium-laden waters at a hot spring, lake shore, or other location.
To log this cache you must visit the Waypoint just up from Frog Rock station. ***No need to go near the railway line.***
Please email me the answers to the following questions:
1. At the waypoint describe the colours, texture and weathering that has occurred.
2. Using the above list of limestone types, and your opinion, what type of limestone is prevalent here?
3. Estimate the height of the rock in metres, and what changes would you expect to occur over time?
You don't need permission to log your find, please do so once you've sent your answers by email/Geocaching message.
Please do not post spoiler photos of GZ, and I hope you enjoy your visit.