The Log Springs Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the Jemez, Nacimiento, and

Sandia Mountains The Sandia Mountains (Southern Tiwa: ''Posu gai hoo-oo'', Keres: ''Tsepe,'' Navajo: ''Dził Nááyisí''; Tewa: ''O:ku:p’į'', Northern Tiwa: ''Kep’íanenemą''; Towa: ''Kiutawe'', Zuni: ''Chibiya Yalanne'') are a mountain range located in ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

. Its age is poorly constrained but is thought to be

Namurian The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma (million years ago). It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is ...

(late Mississippian to early Pennsylvanian).

Description

The Log Springs Formation is a sequence of continental

red beds Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain ...

interpreted as reworked

terra rossa Terra rossa (Italian for "red soil") is a well-drained, reddish, clayey to silty soil with neutral pH conditions and is typical of the Mediterranean region. The reddish color of terra rossa is the result of the preferential formation of hematite ...

soils and sediments from nearby highlands filling

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

topography in the underlying Arroyo Penasco Group. Its outcrops are spotty everywhere but near the

type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...

in the southern

Jemez Mountains The Jemez Mountains are a group of mountains in Rio Arriba, Sandoval, and Los Alamos counties, New Mexico, United States. Numerous Puebloan Indian tribes have lived in the Jemez Mountains region since before the Spanish arrived in New Mexico. T ...

, where it is thick, and it does not crop out in the

Sangre de Cristo Mountains ) , country= United States , subdivision1_type= States , subdivision1= , parent= Rocky Mountains , geology= , orogeny= , area_mi2= 17193 , range_coordinates= , length_mi= 242 , length_orientation= north-south , width_mi= 120 , w ...

. The lowermost 3 meters of the formation are hematitic

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

s with numerous 1 to 5 mm

oolite Oolite or oölite (''egg stone'') is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word for egg (ᾠόν). Strictly, oolites consist of ooids of diameter 0.25–2 ...

s or

pisolite A pisolite is a sedimentary rock made of pisoids, which are concretionary grains – typically of calcium carbonate which resemble ooids, but are more than 2 mm in diameter. These grains are approximately spherical and have concentric lay ...

s. The upper part of the formation is an upward coarsening sequence of crossbedded

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals ...

reddish

sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...

. These include abundant

clasts Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

, greenstone, and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

. Though lacking in

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

, the formation is estimated as being

(late Mississippian to early Pennsylvanian) in age based on fossils in underlying and overlying beds. Its clastic beds record the beginnings of

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thick ...

associated with the

Ancestral Rocky Mountains The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through cen ...

. It probably correlates with the

Molas Formation The Molas Formation is a geologic formation that is found in the Four Corners region of the United States. Its age is poorly constrained but is thought to be Namurian (late Mississippian to middle Pennsylvanian). Description The Molas Formati ...

of the

Animas Valley The Animas Valley is a lengthy and narrow, north–south long, valley located in western Hidalgo County, New Mexico in the Bootheel Region; the extreme south of the valley lies in Sonora- Chihuahua, in the extreme northwest of the Chihuahuan De ...

History of investigation

Beds at this stratigraphic position were originally included in the Sandia Formation. However, when Augustus Armstrong determined that the beds were separated from the underlying Mississippian beds by an

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

and were overlain by beds older than the bulk of the Sandia Formation, he recommended separating them into the Log Springs Formation.

Footnotes

References

* * * {{cite journal , last1=Armstrong , first1=Augustus K. , last2=Mamet , first2=Bernard L. , last3=Repetski , first3=John E. , title=Stratigraphy of the Mississippian System, South-Central Colorado and North-Central New Mexico , journal=U.S. Geological Survey Bulletin , date=1992 , volume=1787 , url=https://books.google.com/books?id=hufutQEyDaAC&q=log+springs+formation&pg=PA14 , accessdate=21 May 2019 , doi=10.3133/b1787EE, doi-access=free Carboniferous formations of New Mexico Carboniferous southern paleotropical deposits