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An association of organic-rich sediment with phosphorite and glauconite is commonly found in modern coastal upwelling zones. The three lithologies do not always occur together, but where they do, they lie in a characteristic facies pattern, with organic-rich sediment in the center, surrounded by a phosphorite facies which is, in turn, rimmed by a glauconite facies. A fourth lithologic element of upwelling deposits is biosiliceous ooze. Biosiliceous ooze is most commonly composed of diatoms, which evolved in the Cretaceous Period. Radiolarian oozes tend to occur in the deep sea, under divergence zones in the open ocean. Despite the predominance in modern upwelling zones of diatoms, the association of chert, organic-rich rock, phosphorite, and glauconite is common in older ocks as well; the chert in these rocks is radiolarite or spiculite. A possible fifth element of upwelling deposits is calcareous ooze; phosphatized and/or glauconitized and cherty chalks are common in the fossil record, as are organic-rich chalks. The relationship of chalk to upwelling is obscure because in modern upwelling zones, siliceous organisms are far more abundant; calcareous and siliceous phyto-plankton appear to occur almost mutually exclusive of one another. By analogy with the sediments under modern upwelling zones, the presence or absence in rocks of each of the five lithologies--organic-rich rock, phosphorite, glauconite, chert, and chalk--provides clues to the nature of individual upwelling deposits. The presence or absence of each lithology, particularly chert versus chal or the presence or absence of phosphorite, can also provide clues to such parameters as temperature and water mass characteristics.
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