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Core samples from the West Florida slope contain minor but significant amounts of dolomite in unconsolidated deep-water sediments of Tertiary age. Some of this dolomite appears to be authigenic, and its origin cannot be explained by the well-documented mechanism of dolomitization by contact with brines formed by solar evaporation or igneous activity.
The slope sediments were sampled at water depths ranging from 667 to 4,777 ft, and in test holes penetrating as much as 1,000 ft of sediment, mostly coccolith-foraminiferal ooze and terrigenous clay. Dolomite is most common in Pleistocene, Pliocene, and some Miocene sediments.
Two general groups of dolomite occur: (1) a northern suite of "ideal" composition, silt-size, abraded and ragged, rhombic dolomite crystals; and (2) a southern suite of calcium-rich, sand-size, euhedral, rhombic dolomite crystals that show no evidences of abrasion or corrosion. Sediments containing the northern suite of dolomite crystals have high percentages of terrigenous clay material; associated dolomite appears to be of detrital origin, and transported to the depositional site together with the clay. The calcium-rich dolomite of the southern suite is interpreted as authigenic and probably formed in water depths similar to present depths. From analysis of interstitial waters, this dolomite probably formed from water similar in composition to normal seawater.
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