Photo Uploaded: Jan 03 2010 09:30:38 GMT Taken: 2010:01:01 14:42:55 Manufacturer: Canon Camera: Canon EOS 450D Aperture: F7.1 Shutter: 1/800 sec ISO: 400 Flash: No (Turned off)
Moeraki boulders, New Zealand
The Moeraki Boulders are huge spherical stones that are scattered over the sandy beaches, but they are not like ordinary round boulders that have been shaped by rivers and pounding seas. These boulders are classed as septarian concretions, and were formed in ancient sea floor sediments. They were created by a process similar to the formation of oyster pearls, where layers of material cover a central nucleus or core. For the oyster, this core is an irritating grain of sand. For the boulders, it was a fossil shell, bone fragment, or piece of wood. Lime minerals in the sea accumulated on the core over time, and the concretion grew into perfectly spherical shapes up to three metres in diameter.
The original mudstone seabed has since been uplifted to form coastal cliffs. Erosion of the cliffs has released the three tonne captive boulders, which now lie in a haphazard jumble across the beach. Further erosion in the atmosphere has exposed a network of veins, which gives the boulders the appearance of turtle shells. Similar boulders occur at Shag Point, and the nearby swimming beach of Katiki. In Hawke�s Bay in the North Island, scientists have found that the central core of similar boulders contained perfectly preserved skeletons of turtles, sea snails and extinct reptiles, such as plesiosaurs.