Abstract

Circular and tabular (discordant--"dyke" like) dolomite bodies occur mainly in Upper Cenomanian-Turonian limestone and Senonian chalk in the South Judean Desert of Israel. The circular bodies average 40 m in diameter and their density in places reaches 30/km 2 . Tabular bodies, up to 2 m in thickness, are relatively rare. The dolomite in the circular bodies forms a compact subhedral mosaic with straight mutual boundaries and nearly equal 10% enfacial triple point junctions. The tabular bodies consist of a somewhat finer crystalline euhedral mosaic with up to 10% interstitial remnant calcite micrite. Fossil remains are scarce, although in a few places, well preserved apparently dolomitized nannofossils were observed. A hypothetical reefal origin is proposed for the circular dolomite bodies based on paleogeographic considerations, together with their size, shape and limited stratigraphic position. Relatively high values of Zn and Cr occur in pure dolomite samples in both forms. Radial axial zoning possibly typical of high temperature minerals occurs in certain of the dolomite crystals. Worm-like surface morphology on dolomite rhombs may represent remnant unleached high magnesium calcite. These features, together with locally spatially associated coarsely crystalline calcite and barite veins, suggest relatively high temperature dolomitizing solutions. Controls of the dolomitizing solutions were fractures in the chalk resulting in the tabular bodies, and permeability of the reefs.

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