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McNamara, Missoula Co., Montana, USAi
Regional Level Types
McNamaraFormation
Missoula Co.County
MontanaState
USACountry

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Latitude & Longitude (WGS84): 46° 54' 38'' North , 113° 40' 35'' West
Latitude & Longitude (decimal): 46.91056,-113.67639
GeoHash:G#: c2r4v5z3u
Locality type:Formation
Köppen climate type:Dfb : Warm-summer humid continental climate
Nearest Settlements:
PlacePopulationDistance
Turah306 (2011)14.3km
Piltzville395 (2011)15.2km
Clinton1,052 (2011)16.0km
Bonner-West Riverside1,663 (2011)16.4km
East Missoula2,157 (2011)20.8km


The locality of McNamara is several miles east of the town of Bonner, Missoula County, Montana. The geographic name refers to a historical settlement that has only a few remaining buildings on the north side of the Blackfoot River in the vicinity of the “McNamara Bridge.” Montana Highway 200 (“MT-200") follows the river from Bonner to McNamara Bridge. East of the bridge, MT-200 separates from Blackfoot River, following instead Union Creek that flows over more open terrain. An unpaved road continues in the canyon of Blackfoot River, allowing access to additional outcrops. The west end of McNamara Bridge is indicated by the latitude and longitude values provided for the locality.

The site of McNamara is the type locality of the McNamara Formation, and the formation is exposed along much of this stretch of the Blackfoot River and MT-200. The McNamara Formation is part of the Missoula Group in the Belt Supergroup of Mesoproterozoic age (1,600-1,000 million years). Argillite, siltite (weakly metamorphosed shale and silstone, respectively), and quartz sandstone. This largely detrital interval also contains thin siliceous, phosphoritic, and calcareous layers in the upper part. Karstic features indicate presence of carbonate intervals in the upper part of the Missoula Group, and those may be Cambrian in age. Gabbro and diorite sills, apparently of Mesoproterozoic age, are also exposed in the area. The McNamara Formation is notable for the dark-colored clay chips and nodules of chert that it contains. The chert apparently replaces gypsum/anhydrite that indicates arid
conditions during deposition of the McNamara.

Regions containing this locality

North America PlateTectonic Plate
Rocky Mountains, North AmericaMountain Range

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


8 valid minerals.

Detailed Mineral List:

Anhydrite
Formula: CaSO4
Reference: Norman King Collection
Calcite
Formula: CaCO3
Reference: Norman King: acid test for calcite; thin sections for chalcedony
Dolomite
Formula: CaMg(CO3)2
Reference: Norman King Collection
Goethite
Formula: α-Fe3+O(OH)
Reference: Norman King Collection
Hematite
Formula: Fe2O3
Reference: Norman King Collection
Muscovite
Formula: KAl2(AlSi3O10)(OH)2
Reference: Norman King Collection
Pyrite
Formula: FeS2
Reference: Norman King Collection
Quartz
Formula: SiO2
Reference: Norman King: acid test for calcite; thin sections for chalcedony
Quartz var: Chalcedony
Formula: SiO2
Reference: Norman King: acid test for calcite; thin sections for chalcedony

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
Pyrite2.EB.05aFeS2
Group 4 - Oxides and Hydroxides
Goethite4.00.α-Fe3+O(OH)
Hematite4.CB.05Fe2O3
Quartz4.DA.05SiO2
var: Chalcedony4.DA.05SiO2
Group 5 - Nitrates and Carbonates
Calcite5.AB.05CaCO3
Dolomite5.AB.10CaMg(CO3)2
Group 7 - Sulphates, Chromates, Molybdates and Tungstates
Anhydrite7.AD.30CaSO4
Group 9 - Silicates
Muscovite9.EC.15KAl2(AlSi3O10)(OH)2

List of minerals arranged by Dana 8th Edition classification

Group 2 - SULFIDES
AmBnXp, with (m+n):p = 1:2
Pyrite2.12.1.1FeS2
Group 4 - SIMPLE OXIDES
A2X3
Hematite4.3.1.2Fe2O3
Group 6 - HYDROXIDES AND OXIDES CONTAINING HYDROXYL
XO(OH)
Goethite6.1.1.2α-Fe3+O(OH)
Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Calcite14.1.1.1CaCO3
AB(XO3)2
Dolomite14.2.1.1CaMg(CO3)2
Group 28 - ANHYDROUS ACID AND NORMAL SULFATES
AXO4
Anhydrite28.3.2.1CaSO4
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Muscovite71.2.2a.1KAl2(AlSi3O10)(OH)2
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Quartz75.1.3.1SiO2
Unclassified Minerals, Mixtures, etc.
var: Chalcedony-SiO2

List of minerals for each chemical element

HHydrogen
H MuscoviteKAl2(AlSi3O10)(OH)2
H Goethiteα-Fe3+O(OH)
CCarbon
C DolomiteCaMg(CO3)2
C CalciteCaCO3
OOxygen
O AnhydriteCaSO4
O DolomiteCaMg(CO3)2
O HematiteFe2O3
O MuscoviteKAl2(AlSi3O10)(OH)2
O Goethiteα-Fe3+O(OH)
O CalciteCaCO3
O Quartz (var: Chalcedony)SiO2
O QuartzSiO2
MgMagnesium
Mg DolomiteCaMg(CO3)2
AlAluminium
Al MuscoviteKAl2(AlSi3O10)(OH)2
SiSilicon
Si MuscoviteKAl2(AlSi3O10)(OH)2
Si Quartz (var: Chalcedony)SiO2
Si QuartzSiO2
SSulfur
S AnhydriteCaSO4
S PyriteFeS2
KPotassium
K MuscoviteKAl2(AlSi3O10)(OH)2
CaCalcium
Ca AnhydriteCaSO4
Ca DolomiteCaMg(CO3)2
Ca CalciteCaCO3
FeIron
Fe HematiteFe2O3
Fe Goethiteα-Fe3+O(OH)
Fe PyriteFeS2

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Holocene - Pleistocene
0 - 2.588 Ma



ID: 2070418
Surficial deposits

Age: Pleistocene (0 - 2.588 Ma)

Description: alluvium, fan gravel, terrace gravel, landslide deposits, travertine, till, glacial lake deposits, outwash deposits

Lithology: Sand, gravel

Reference: Zientek, M.L., P.D. Derkey, R.J. Miller, J.D. Causet et al. Spatial Databases for the Geology of the Northern Rocky Mountains - Idaho, Montana, and Washington. U.S. Geological Survey Open-File Report 2005-1235 Version 1.0. [25]

Mesoproterozoic
1000 - 1600 Ma



ID: 3186914
Mesoproterozoic sedimentary and volcanic rocks

Age: Mesoproterozoic (1000 - 1600 Ma)

Stratigraphic Name: Purcell Group

Comments: Omineca Belt

Lithology: Mafic-intermediate volcanic rocks; limestone,shale,argillite,quartzite,dolomite,siltstone; turbidite

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Mesoproterozoic
1000 - 1600 Ma



ID: 2839687
Upper Missoula Group: McNamara, Bonner, and Mount Shields Formations; locally includes lower Libby Formation in northwestern Montana

Age: Mesoproterozoic (1000 - 1600 Ma)

Stratigraphic Name: McNamara Formation; Bonner Quartzite; Mount Shields Formation; Libby Formation

Description: McNamara Formation: Dense green and red siltite and argillite in mudcracked couplets containing diagnostic chert beds and rip-up clasts. Thickness as much as 1,650 m (5,413 ft). Bonner Formation: Pink, cross-bedded, feldspathic, medium- to coarse grained quartzite. Thickness as much as 580 m (1,903 ft). Mount Shields Formation: Upper part: red quartzite, siltite, and argillite in mud-cracked couples and couplets with abundant salt casts. Lower part: light gray, flat-laminated, feldspathic, fine-grained quartzite. Thickness as much as 2,000 m (6,562 ft). In northwestern Montana - Libby Formation:Light to dark gray and greenish gray siltite and argillite with subordinate quartzite in mud-cracked couplets. Thickness as much as 2,300 m (7,546 ft).

Comments: Original map source: Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract betwe

Lithology: Major:{metasiltstone,argillite,quartzite}, Incidental:{chert, salt}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Nelson, W.H., Dobell, J.P. (1961) Geology of the Bonner Quadrangle, Montana. U.S. Geological Survey Bulletin 1111-F, 189-235 (see p. 203).
Berg, R.B. (2006) Geologic Map of the Upper Clark Fork Valley between Bearmouth and Missoula, southwestern Montana. Montana Bureau of Mines and Geology, Open-File Report MBMG 505 (see p. 15).
Lonn, J.D., McDonald, C., Sears, J.W., Smith, L.N. (2010) Geologic Map of the Missoula East 30' x 60' Quadrangle, Western Montana. Montana Bureau of Mines and Geology Open File 593, plates 1 and 2.


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