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The mineralogy of the Cretaceous to Holocene sediments of the Pacific and Atlantic basins has close affinities to present sedimentation patterns. Carbonate sediments dominate equatorial and shallow oceanic areas. Turbidites are common close to continental margins. Siliceous radiolarian and diatomaceous sediments are abundant in zones close to the carbonate compensation depth.
One of the more striking features of the deep sea is the common occurrence of an amorphous metal-oxide basal facies. Many areas of both the Atlantic and Pacific show high iron- and manganese-content sediment facies at, or close to, the contact with basement basalt. This basal facies grades upward into the biogenous and detrital lithogenous overlying sediments. Some areas of the basal facies have high copper and zinc contents, and in other places manganese is prominent. In a few places, this facies is essentially hematitic. The carbonates present in the deep sea include, in addition to calcite and aragonite, dolomite, siderite, rhodochrosite, and ankeritic dolomite. An unusual palygorskite and sepiolite and bentonite associated with dolomite is well developed in the vicinity of the Cap Verde Islands in the eastern Atlantic. Basaltic volcanic glass usually alters to montmorillonite plus a zeolite which is usually phillipsite or clinoptilolite. Erionite has been discovered in the western Pacific for the first time in the deep sea. Biogenous opaline silica dissolves and reprecipitates to form crystobalite cherts. These in turn are recrystallized to form quartz cherts in pre-Cenozoic sediments.
The range of minerals facies available suggests that clay mineral diagenesis is slight but the in situ formation of zeolites and clays from recrystallization of volcanic ash is important.
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