Moeraki Boulders

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Moeraki Boulders are concretions created by the cementation of the Paleocene mudstone of the Moeraki Formation, from which they have been exhumed by coastal erosion. Moeraki Boulders are concretions that were created by the precipitation of calcite from pore waters within the Moeraki Formation. The spherical shape of these concretions indicates that the source of calcium was mass diffusion and not fluid flow. Studies of the percentage of magnesium and iron contained by and stable isotope composition of the oxygen and carbon comprising the calcite cement and spar comprising the Moeraki Boulders demonstrates that the main body of these concretions started forming in marine mud near the surface of the Paleocene seafloor. The isotopic data are also argued to demonstrate that the reduction of sulfate in saline pore fluids within the mudstone by bacteria caused the precipitation of the calcite forming the Moeraki Boulders. The larger, 2-metre (6-feet) in diameter, Moeraki Boulders are estimated to have taken 4 to 5.5 million years to grow while 10 to 50 metres (30 to 150 feet) of marine mud accumulated on the seafloor above them. After the concretions formed, large cracks, septaria, formed in them. Brown calcite, yellow calcite, and, in rare cases, dolomite and quartz progressively filled these cracks when a drop in sea level allowed fresh groundwater to flow through the mudstone enclosing them.
Local Māori legends explained the boulders as the remains of eel baskets, calabashes, and kumara washed ashore from the wreck of an Arai-te-uru, a large sailing canoe. This legend tells of the rocky shoals that extend seaward from Shag Point as being the petrified hull of this wreck and a nearby rocky promontory as being the body of the canoe's captain.
They are located in New Zealand

leo19 Uploaded by leo19 on Jun 24, 2010. Moeraki Boulders - Desktop Nexus Nature Download free wallpapers and background images: Moeraki Boulders. Desktop Nexus Nature background ID 391295. Moeraki Boulders are concretions created by the cementation of the Paleocene mudstone of the Moeraki Formation, from which they have been exhumed by coastal erosion. Moeraki Boulders are concretions that were created by the precipitation of calcite from pore waters within the Moeraki Formation. The spherical shape of these concretions indicates that the source of calcium was mass diffusion and not fluid flow. Studies of the percentage of magnesium and iron contained by and stable isotope composition of the oxygen and carbon comprising the calcite cement and spar comprising the Moeraki Boulders demonstrates that the main body of these concretions started forming in marine mud near the surface of the Paleocene seafloor. The isotopic data are also argued to demonstrate that the reduction of sulfate in saline pore fluids within the mudstone by bacteria caused the precipitation of the calcite forming the Moeraki Boulders. The larger, 2-metre (6-feet) in diameter, Moeraki Boulders are estimated to have taken 4 to 5.5 million years to grow while 10 to 50 metres (30 to 150 feet) of marine mud accumulated on the seafloor above them. After the concretions formed, large cracks, septaria, formed in them. Brown calcite, yellow calcite, and, in rare cases, dolomite and quartz progressively filled these cracks when a drop in sea level allowed fresh groundwater to flow through the mudstone enclosing them.
Local Māori legends explained the boulders as the remains of eel baskets, calabashes, and kumara washed ashore from the wreck of an Arai-te-uru, a large sailing canoe. This legend tells of the rocky shoals that extend seaward from Shag Point as being the petrified hull of this wreck and a nearby rocky promontory as being the body of the canoe's captain.
They are located in New Zealand Rating: 4.1