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Saddle (baroque) dolomites are characterized by curved crystal faces and sweeping extinction patterns. They are associated with hydrocarbons, sulfates, and base-metal mineralization, and occur as void-filling cements or replacement minerals. Most described saddle dolomites are from carbonates and are interpreted as a diagenetic product that formed under high temperatures during deep burial.
Saddle dolomites are present as nodular, poikilotopic cements in sandstones from a core of the Tuscaloosa Formation in southern Mississippi. The Tuscaloosa, a major oil producer in the area, consists of a series of fluvial/deltaic sands and shales. The sandstone is a fine to medium-grained lithic arenite whose grains are coated with isopachous layers of authigenic chlorite, which petrographic evidence indicates was precipitated at relatively shallow depths. The interrelationships of the chlorite rims and the saddle dolomite cements indicate that some of the dolomites were precipitated before the chlorite rims and that others formed shortly after the chlorite. This suggests that the saddle dolomites grew concurrently with the chlorite during a relatively early, shallow diagenetic event and not during deep burial.
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