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Abstract

The Leadville Limestone (Kinderhookian-Osagean) was deposited on a shallow marine shelf impinging on an exposed landmass in the area of the present Front Range and Wet Mountains. The upper Leadville Formation is truncated by an unconformity of regional extent, and karst features related to this unconformity are common within Leadville strata. Along the eastern margin of the Leadville depositional area, the Leadville Formation has been altered to massive dolostone. Seven types of dolomite were recognized. Fine crystalline dolomite is widespread throughout central Colorado and is associated with supratidal facies. Textures indicate pe-necontemporaneous dolomitization in a sabkha setting. Medium and coarse crystalline dolomite make up the bulk of the Leadville Dolomite and are not associated with any specific depositional facies. Dolomitization was largely restricted to the edge of the Mississippian depositional area and was accompauied by the formation of chert nodules. This period of regional dolomitization preceded karst dissolution and brecciation and the creation of caverns. Dolomitization occurred in a sea water-fresh water mixing zone.

Zebra dolomite consists of bands of fine, medium, or coarse dolomite alternating with coarse, white dolomite spar. Zebra dolomite is best developed adjacent to karst channelways, and the zebra spar precipitated into voids created by karst dissolution. Two generations of zebra spar are present: early cloudy zebra spar, which precipitated as isopachous crusts during later stages of karst erosion, and later clear zebra spar, which precipitated from hot brines after burial by Pennsylvanian sediments.

Baroque dolomite formed as breccia matrix in karst caverns. Textures indicate that this dolomite formed by replacement of internal dolomitic cave sediment. Baroqne dolomite precipitation was accompanied by precipitation of base metal sulfides. These features predate stylolite formation and indicate precipitation prior to deep burial. A second episode of base metal deposition occurred after stylolite formation had ceased. This episode was accompanied by replacement of dolomite by calcite and pyrite. The latest dolomite is a cement which occurs in surface exposures and is most likely related to Recent ground-water movement.

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