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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 771

Last Page: 771

Title: Transition from Shelf to Basinal Carbonates in Middle Cambrian Marjum Formation of House Range, Western Utah--Paleoenvironmental Analysis: ABSTRACT

Author(s): Michael J. Brady, Richard B. Koepnick

Article Type: Meeting abstract


Lithofacies of the Marjum Formation in the House Range of west-central Utah indicate that a rather abrupt transition from shallow-shelf to basinal depositional environments persisted in this locality during much of the Middle Cambrian. The beginning of Marjum deposition was marked by the accumulation of deep-water limestones and shales throughout the area, but this pattern soon was disrupted by shoaling and development of shelf conditions in the vicinity of the central and northern House Range. Supratidal to shallow subtidal carbonates formed on the shelf as deposition of slope and basinal sediments continued a few miles south for the remainder of Marjum time.

Algal-laminated and pelletal dolomitic mudstones accumulated in the extensive supratidal and intertidal areas that existed on the shelf. Some stromatolitic units are evenly laminated, whereas others have laminae that are irregular and discontinuous. The pelletal mudstones exhibit fenestral fabrics and contain intraformational conglomerate lenses, commonly including clasts reworked from the stromatolitic units. Wave ripples and desiccation features associated with these lithologies are further evidence of their shoal-water origin and periodic exposure.

Pelleted, intraclastic wackestones and packstones characterize the shallow subtidal environments of the shelf and shelf-slope. Interspersed with the slope sediments are units containing both algal-coated and uncoated intraclasts. The coated grains are on the upper part of the slope and were derived from the shelf edge, whereas the uncoated clasts were largely reworked from slope deposits. In addition, the coated grains have undergone little transport, but the uncoated clasts are well sorted and rounded, and are commonly graded.

Fossiliferous wackestones and laminated mudstones with interbedded shales represent the deeper water toe-of-slope and basinal sediments. The fossiliferous units have been moderately bioturbated, but the finely laminated mudstones, which were deposited well below wave base, are essentially undisturbed. The presence of sponge spicules and presence of small-scale cross laminations and microscopic cut-and-fill structures are typical of these dark, thin-bedded limestones. Depositional slopes in this part of the basin are indicated by penecontemporaneous slump structures and debris lenses deposited by submarine slides.

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