- Usage in publication:
-
- Dean Lake chert member
- Modifications:
-
- Original reference
- Dominant lithology:
-
- Chert
- Limestone
- AAPG geologic province:
-
- Montana folded belt
Summary:
Pg. 47 and passim. Dean Lake chert member of Madison limestone. Generally thinnest member of Madison limestone in this area but the most persistent and striking. Outstanding characteristics are great amount of black, blue-black, and dark-gray chert, which occurs as nodules and as intercalated beds between the limestones. In type locality lower 23 feet is blackish-gray limestones interbedded with black-gray and dull tan-gray chert in nodules up to 5 inches diameter. Upper 37 feet massive, blue gray, thick-bedded limestones with crinoid stems and brachiopod fragments, interbedded with beds of very fossiliferous dark chert up to 7 inches thick. Thickness 51 to 74 feet. Underlies Rooney chert member and overlies Saypo limestone member, all in Madison limestone. Age is Mississippian.
Type locality: southeast side of Pentagon Mountain, in SW/4 sec. 14, T. 25 N., R. 14 W., [Pentagon Mountain 7.5-min quadrangle, Flathead Co.], northwestern MT. Named from Dean Lake, a small cirque lake lying at foot of cliffs that form upper part of east side of Pentagon Mountain.
Source: US geologic names lexicon (USGS Bull. 896, p. 578).
- Usage in publication:
-
- Dean Lake chert member
- Modifications:
-
- Not used
- AAPG geologic province:
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- Montana folded belt
- Sweetgrass arch
Summary:
Rocks roughly equivalent to Deiss' Dean Lake chert member of Madison limestone are included in unit MC, basal unit of the Mississippian (Kinderhook) of northwestern Montana.
Source: Publication.
- Usage in publication:
-
- Dean Lake chert
- Modifications:
-
- Revised
- AAPG geologic province:
-
- Montana folded belt
- Sweetgrass arch
Summary:
Pl. 2 (column 38). Dean Lake chert in Hannan limestone. Underlies Rooney chert and overlies Saypo limestone, all in Hannan limestone. Age is Early Mississippian (Kinderhook and Osage).
Source: US geologic names lexicon (USGS Bull. 1200, p. 1058).
- Usage in publication:
-
- Dean Lake chert
- Modifications:
-
- Revised
- AAPG geologic province:
-
- Montana folded belt
Summary:
Pg. 89. Dean Lake chert. Hall (1952, unpub. thesis, [Univ. Wisconsin-Madison, 220 p.]) proposed that Deiss' Dean Lake chert be recognized as a formation. Deiss gave thickness of 60 feet at type section. Hall redefined type section of 105-foot thickness to include about 45 feet of overlying similar beds separated by 11 feet of chert-free limestone. Age is Early Mississippian (Kinderhook).
Source: US geologic names lexicon (USGS Bull. 1200, p. 1058).
- Usage in publication:
-
- Dean Lake Chert Member
- Modifications:
-
- Not used
- AAPG geologic province:
-
- Sweetgrass arch
Summary:
Pg. 2012. Most of Deiss' Dean Lake Chert Member of Madison Limestone is correlative with the middle member of Allan Mountain Limestone (new). Type section of the middle member is [about 20 miles southeast of Dean Lake], in ridge on north side of Gibson Reservoir near the SE/4 sec. 36, T. 22 N., R. 10 W., Patricks Basin 7.5-min quadrangle, [Teton County], northwestern Montana.
Source: Publication.
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).