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Chalk is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta, meaning chalk. [10] Some deposits of chalk were formed after the Cretaceous. [11] The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period.
The coccolithophores lived in the upper part of the water column. When they died, the microscopic calcium carbonate plates, which formed their shells settled downward through the ocean water and accumulated on the ocean bottom to form a thick layer of calcareous ooze, which eventually became the Chalk Group.
When an earthquake occurs, seismographs near the epicenter are able to record both P and S waves, but those at a greater distance no longer detect the high frequencies of the first S wave. Since shear waves cannot pass through liquids, this phenomenon was original evidence for the now well-established observation that the Earth has a liquid ...
Ripple marks usually form in conditions with flowing water, in the lower part of the Lower Flow Regime. There are two types of ripple marks: Symmetrical ripple marks Often found on beaches, they are created by a two way current, for example the waves on a beach (swash and backwash).
A submarine, undersea, or underwater earthquake is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean. They are the leading cause of tsunamis . The magnitude can be measured scientifically by the use of the moment magnitude scale and the intensity can be assigned using the Mercalli intensity scale .
To map the subduction zone, researchers at sea performed active source seismic imaging, a technique that sends sound to the ocean floor and then processes the echoes that return. The method is ...
Plate tectonics is a scientific theory developed in the 1960s that explains major land form events, such as mountain building, volcanoes, earthquakes, and mid-ocean ridge systems. [26] The idea is that Earth's most outer layer, known as the lithosphere , that is made up of the crust and mantle is divided into extensive plates of rock.
A hole in a 600-mile-long fault line has been discovered at the bottom of the Pacific ocean - and it could be the trigger of a magnitude-9 earthquake on the US coast. Just outside of Oregon ...