Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

L.C. Gerhard


The upper Red River Formation in North Dakota comprises a subtidal/intertidal facies overlain by three evaporitic sequences of four lithologic units each, labeled "P," "R," and "F" in stratigraphic order. Four porosity zones are recognized in the upper Red River: the subtidal/ intertidal facies forms one porosity zone, and each evaporitic sequence contains another. Each unit in a sequence, as well as the sequence itself, is thinner and less widespread than its preceding counterpart. All strata are laterally continuous across the main part of the Williston basin in North Dakota, but, the porosity zones eventually disappear to the east as they approach the basin margin. Porosity within any given zone varies from one part of the basin to another, often within relatively short distances.

The "D" porosity zone consists of two primary lithologic facies: a shallow subtidal burrowed mudstone and skeletal wackestone, and an impermeable, often laminated, black organic skeletal wackestone and packstone deposited in an intertidal or supratidal barred pond environment. Porosity in the subtidal burrowed facies is due to syndepositional dolomitization and later calcite solution and microfracturing. Maximum porosity values related to dolomitization and calcite dissolution occur in the burrowed horizons immediately above the impermeable organic units, which acted as barriers to interstitial fluid movement. Poor development of the organic units near the center of the basin perhaps accounts for sporadic porosity development in that area.

The basal unit of each of the sequences overlying the 11D11 zone consists of open shelf bioturbated skeletal wackestone of characteristically low porosity. Porous, fine-grained, primary supratidal dolomite overlies the subtidal facies, and these units form the 11C," 11B, 11 and "A" porosity zones. A very thin argillaceous marker bed of non-calcareous shale completes each sequence.

Porosity in the supratidal dolomite stems from intercrystalline voids and pinpoint porosity due to solution. Porosity in the upper three zones varies across the basin and is directly related to degree of exposure of the sediment in the supratidal environment, during which dolomitization occurred.

Carroll (246883 kB)

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