ABSTRACT

Miocene calcarenites of Menorca (Spain) exhibit abundant terrigenous dolomite, both as medium-grained polycrystalline rock fragments and as fine-grained individual abraded crystals. Petrographically, this detritus looks both like neighboring Jurassic dolostones and like Triassic Muschelkalk dolostones of the same general area. In order to determine which stratigraphic unit(s) provided this terrigenous dolomite, the iron contents of Triassic and Jurassic dolostones were analyzed, with an electron microprobe, and compared with that of the Miocene terrigenous dolomite. As was expected from their present greater surface exposure, Jurrassic dolostones proved to be the principal source. The trace of probable Triassic dolomite detritus in Miocene samples analyzed is proportionate to the smal area of Triassic exposure relative to that of the Jurassic.

Diagenetic dolomite in Miocene host calcarenites occurs as l) pervasive crystals of fine- to medium-crystalline dolomite and 2) overgrowths on the terrigenous dolomite crystals. These two varieties commonly occur together, but overgrowths occur in some samples in the absence of the pervasive variety, which indicates that "seeding" by terrigenous dolomite promoted diagenetic dolomitization.

Calcitization of Miocene dolomite favored centers of the pervasive variety of dolomite crystals and the inner margins of dolomite overgrowths. These patterns of dedolomite indicate that the two varieties of dolomite are behaviorly correlative, which suggests that they are temporally correlative as well.