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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 915

Last Page: 915

Title: Mixing-Zone Origin of "Primary" Dolomite Grains from Cretaceous Marine Sandstones of Western Interior Basin: ABSTRACT

Author(s): Stephen P. Cumella

Article Type: Meeting abstract


In a series of papers in the early 1960s, the occurrence of "primary" dolomite grains in Cretaceous sandstones of the Western Interior basin was documented. These grains are usually single crystals, with a rhombic outline that has been modified to varying degrees of roundness by abrasion. The grain size of the dolomite mimics that of other grains in the sandstone. Because these dolomite grains are confined to marine facies, it is unlikely that they are extrabasinal. Also, there is no evidence that the dolomite formed by replacement of other grains. The remaining possibility is that dolomite formed within the basin before significant burial.

Petrographic and stratigraphic evidence from the San Juan basin suggests that primary dolomite was formed in a mixing zone of meteoric water that discharged into shoreface environments. Thick coastal-plain coal sequences and paleoclimatic reconstructions support the existence of a large meteoric flow system in the western part of the Western Interior basin during the Cretaceous. As meteoric water discharged into shoreface sediment, dolomite rhombs were precipitated in the interstices of uncompacted sands. Some of the dolomite thus formed was close enough to the ocean bottom to be later eroded, abraded, and redeposited during storms or transgressions. Dolomite rhombs that were not eroded are similar in appearance to resedimented grains, but show no evidence of abrasion.

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