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Posted by / 07-Oct-2017 15:09

Dating sediment cores

Volcanic ash is produced during volcanic eruptions, as can be seen in the billowing ejected material from many volcanos.

Cosmogenic material is the remains of primordial material left over from the creation of the solar system (and perhaps from beyond) and, although very low in abundance, is ubiquitously distributed.

The shells of these organisms are made of either calcium carbonate (Ca CO ).

Although ubiquitous, particularly elevated concentrations of such organisms are most commonly found in biologically productive waters such as the Equatorial Pacific, or the Southern Ocean ringing the continent of Antarctica.

The different combinations of each process' effectiveness result in a commensurate variety of sedimentation rates.

Sediment can accumulate as slowly as 0.1 millimeter (0.04 inch) per 1,000 years (in the middle of the ocean where only wind-blown material is deposited) to as fast as 1 meter (3.25 feet) per year along continental margins .

Because the bottom of the ocean is extremely cold (only 1 to 3 degrees above freezing), the cores are stored in refrigerators onboard the research ship prior to being stored in large refrigerated repositories at shore-based laboratories.

(The larger grains of coarse sand, gravel, and boulders are too large to be transported to the deep sea and therefore are not discussed here.) Physical weathering is caused by mechanical fracturing of rocks, such as that due to the freezing of water in cracks, and results in finer grained, compositionally similar examples of the original rock.More typical deep-sea rates are on the order of several centimeters per 1,000 years.The production of marine sediment is more complex than it may seem.Thus, by examining the amount of dust, as well as its grain size, in the different layers of a sediment core, oceanographers learn how arid the land surface was at a given time, as well as how fast the average wind speeds were.Although such dust is essentially invisible to the human eye, its transport is still an important and long-ranging process.

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Sediment on the seafloor originates from a variety of sources, including biota from the overlying ocean water, eroded material from land transported to the ocean by rivers or wind, ash from volcanoes, and chemical precipitates derived directly from sea water.