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20-582: The Puye Formation is a geologic formation exposed east of the Jemez Mountains of northern New Mexico . Radiometric dating constrains its age to between 5 and 2 million years, corresponding to the Pliocene epoch . The Puye Formation is a fanglomerate containing 25 pyroclastic flows , including pumicious ignimbrites and block and ash flows , erupted by vents of the Tschicoma Formation . It

40-446: A facies , stratum , bed , seam , lode etc. Thickness is measured at right angles to the surface of the seam or bed and thus independently of its spatial orientation. The concept of thickness came originally from mining language, where it was used mainly to indicate the workability of seams. It has since become an established term in earth science , for example in geology, for the depth of sedimentary rocks , in hydrogeology for

60-526: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

80-594: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

100-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

120-430: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Thickness (geology) Thickness in geology and mining refers to the distance across a packet of rock , whether it be

140-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

160-633: Is exposed from the mouth of Ancho Canyon in White Rock Canyon north to Santa Clara Peak, and generally underlies the Bandelier Tuff north and east of the city of Los Alamos , covering an area of 518 square kilometers (200 sq mi). It is best exposed in Guaje Canyon and on the southern end of the Puye Escarpment where it is a cliff-forming formation. It is 71 meters (233 ft) thick at

180-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

200-418: Is the lowest part of the formation, some 24 meters (79 ft) thick, which consists of pebbles, cobbles, and small boulders of quartzite and granite with only limited volcanic debris, contrasting with the remainder of the formation. This is separated by a significant unconformity from the underlying Chamita Formation . The Totavi Lentil is raised to formation rank by some investigators. The main body of

220-670: The Rio Grande . The formation is remarkably well preserved for a volcanic fanglomerate, due to its deposition in an active graben associated with Rio Grande Rift . A notable feature of exposures of the formation is the presence of pedestal rocks . The formation is a high-yield aquifer exploited in the Los Alamos area. Use of potassium dichromate in a power plant created an unusually well-characterized source of chromium contamination in this aquifer, which has been studied to understand natural attenuation of such pollutants. The formation

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240-439: The thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of a geologic formation goes back to the beginnings of modern scientific geology. The term

260-622: The Puye Formation consists of fanglomerates in which most of the detritus is volcanic rock of dacitic composition. There are also dacitic tephra beds and some basalt . The formation shows cyclicity on the scale of 5 to 30 meters representing individual eruptive pulses in the northeastern Jemez highlands. Each sequence shows marked facies changes with increased distance from the eruptive center. Deposition ceased with reduction in Tschicoma volcanism and basinwide pedimentation due to downcutting of

280-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

300-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

320-518: The formation to the Santa Fe Group . Because of its diverse lithology , the formation was renamed the Puye Formation by Bailey, Smith, and Ross in 1969 as part of their work establishing the stratigraphy of the Jemez Mountains. Geologic formation A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by

340-546: The tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

360-470: The type section but thickens westward towards the Sierra de los Valles, west of Los Alamos. Drilling has found that the formation is up to 221 meters (725 ft) thick. The formation was deposited between 7 and 4 million years ago, based on radiometric dating of an ash bed in the upper part of the formation and the absence of Bearhead Rhyolite ash (~7 million years old) in the formation. The Totavi Lentil

380-520: Was first named the Puye Gravel by Harold T.U. Smith in his mapping of the Abiquiu quadrangle in 1938. The name was changed to Puye Conglomerate by Roy Griggs in 1964, since the exposures he studied were consolidated enough to stand as cliffs. Griggs also designated a type section and divided the unit into an upper unnamed fanglomerate and a lower Totavi Lentil, named for a nearby settlement. Griggs assigned

400-603: Was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at the surface are fundamental to such fields as structural geology , allowing geologists to infer

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