THE MISSISSIPPIAN-PENNSYLVANIAN MANNING CANYON SHALE, SOLDIER CREEK CANYON, NORTH-CENTRAL, UTAH: A “SHALE” OF MANY ENVIRONMENTS

The Mississippian-Pennsylvanian Manning Canyon Shale is dominantly claystone with interbeds of limestone, sandstone, and siltstone. It has recently garnered renewed interest as a source for hydrocarbons and a potential reservoir for natural gas. The most complete exposed section (1544 ft thick) of Manning Canyon is in Soldier Creek Canyon in the Oquirrh Mountains of north-central Utah. These rocks, particularly the carbonates, show various depositional environments, which can be used to better understand the Manning Canyon regionally and its potential for hydrocarbon generation.

The shale/claystone units are: (1) black to shades of gray, (2) calcareous or non-calcareous, and (3) non-fossiliferous or contain plant and other fossil fragments (brachiopods). These units are often interbedded with thin, non-fossiliferous limestone beds. Palynomorphs indicate a middle to late Chesterian age, and depositional environments include: (1) lower coastal plain, (2) marsh to restricted bay, and (3) open shelf.

The limestone units are calcareous to shaley or silty (quartz) mudstone and vary from thinly laminated to thick bedded or massive; some display cross-bedding while others are bioturbated. Carbonate fabrics include skeletal grainstones through wackestones, and microbial (stromatolitic and thrombolitic) lime mudstones. These carbonates often contain a variety of marine fossils, such as brachipods, bryozoans, crinoids, benthic forams, corals, trilobite carapaces, bivalve molluscs, sponge spicules, and ostracodes, while some units are non-fossiliferous. Non‑skeletal grains consist of intraclasts, coated grains, detrital quartz, and peloids. Depositional environments include: (1) shallow, low to moderate energy subtidal, (2) salinity-restricted platform interior, (3) moderate energy, open marine platform, (4) quiet (below wave and storm base), deep, low-oxygenated water and (5) high‑energy, nearshore terrigenous settings.

Tan-brown-maroon sandstone units consist of fine-grained, subangular to subrounded quartz grains with mild metamorphic overprints. They vary from poor to well sorted, contain clay, and are medium to massive bedded with cross-beds. These units represent an upper shoreface environment.