{{Short description|Fossiliferous Holocene geologic unit found in Central Alaska}} {{Infobox rockunit | image = | imagesize = 310px | caption = | period = Holocene | age = Holocene <br>{{fossil range|0.001|0.01}}<ref name="Péwé1975a"/><ref name="Péwé1975b"/> | type = Geological formation | prilithology = perennially frozen silt | otherlithology = volcanic ash, forest bed | namedfor = Ready Bullion Creek<ref name="LuttrellOthers1981a">Luttrell, G.W., Hubert, M.., Wright W.B., Jussen, V.M. and Swanson, R.W., 1981. ''Lexicon of geologic names of the United States for 1968-1975''. ''U.S. Geological Survey Bulletin'', 1520, 342 pp.</ref> | namedby = Troy L. Péwé<ref name="LuttrellOthers1981a"/> | region = central Alaska, US, and Yukon Territory Canada. | country = United States of America | coordinates = {{Coord|64|50|37|N|147|43|23|W|region:US-AK|display=inline,title}} | unitof = ''Alaska muck '', '' Alaska silt '' (informal) | subunits = Giddings Forest Bed<ref name="Péwé1989a"/><ref name="PeweOthers1997a"/> | overlies = Goldstream Formation | underlies = ground surface | thickness = {{convert|1 to 5|m|ft|abbr=on}} | extent = Yukon and Tanana river drainage basins, Alaska. | area = | map = | map_caption = }}

The '''Ready Bullion Formation''' is a geologic formation that consists of a {{convert|1-5|m|ft|abbr=on}} thick layer of perennially frozen, medium- to dark-brown, organic-rich, silt. A well preserved forest bed, named the ''Giddings Forest Bed'', occurs at its base. The silt is loess that has been retransported downslope and redeposited by solifluction and other slope processes. The Ready Bullion Formation unconformably overlies the Goldstream Formation and forms the undisturbed surface of historic uplands and valley slopes. Upslope, it laterally grades into the Engineer Loess. The Ready Bullion Formation is the uppermost geologic formation of a {{convert|15-61|m|ft|abbr=on}} thick layer of Late Pliocene to Holocene sediments that blankets the valley walls of the rivers of central Alaska. Vertebrate fossils are scarce within it and consist of only nonextinct taxa. Numerous radiocarbon dates indicate that deposition of the Ready Bullion Formation occurred between 10,500 years ago and present.<ref name="Péwé1975a">Péwé, T.L., 1975. '' Quaternary Geology of Alaska''. ''U.S. Geological Survey Professional Paper'', 835, 245 p.</ref><ref name="Péwé1975b">Péwé, T.L., 1975. ''Quaternary stratigraphic nomenclature in central Alaska''. ''U.S. Geological Survey Professional Paper'', 862, 32 pp.</ref><ref name="Péwé1989a">Péwé, T.L., 1989. ''Quaternary stratigraphy of the Fairbanks area, Alaska''. In Carter, D.L., Hamilton, T.D., and Galloway, J.P., eds., pp. 72-77, ''Late Cenozoic history of the interior basins of Alaska and the Yukon''. ''U.S. Geological Survey Circular'', 1026. Reston, Virginia, 114 pp.</ref>

The Ready Bullion Formation is named for its type location, which is the highwall of a mining cut on Ready Bullion Creek, Alaska. The type section lies within the SW1/4 sec.6, T1S R2W, about {{convert|17|km|mi|abbr=on}} west of Fairbanks, Alaska. this formation is also well exposed in vertical banks on Ready Bullion, Eva, Engineer, Sheep, Fairbanks, and Dome Creeks. It also outcrops in the bluffs and banks in the Fairbanks area; on Wilber, Amy, Lillian, and other creeks in the Livengood area and in placer mining cuts in the Tofty, Circle, and Chicken areas. It also outcrops in placer mines near Dawson, Yukon Territory.<ref name="Péwé1975a"/><ref name="Péwé1975b"/><ref name="Péwé1989a"/>

==Nomenclature== In the late 1800s and early 1900s, geologists<ref name="Dall1868a">Dall, W.H., 1868. ''Explorations in Russian America. (from a letter addressed to J. D. Daya, dated Russian Extension, St. Michaels, R. Am., Aug. 13, 1867)''. ''American Journal of Science '', 2(133), pp.96-99.</ref><ref name="Dawson1894a">Dawson, G.M., 1894. ''Notes on the Occurrence of Mammoth remains in the Yukon District of Canada and in Alaska''. ''Quarterly Journal of the Geological Society'', 50(1-4), pp.1-9.</ref><ref name="Spurr1898a">Spurr, J.E., 1898. ''Geology of the Yukon Gold District, Alaska: By Josian Edward Spurr; with an introductory chapter on the history and condition of the district to 1897 by Harold Beach Goordich''. ''U.S. Geological Survey Annual Report'' 18-III, 328 pp.</ref> recognized that a thick, {{convert|15-61|m|ft|abbr=on}} or more, blanket of, often organic-rich, silty sediment is widely distributed along the Yukon River and its tributaries. They also overlie bedrock and Pliocene gold-bearing fluvial gravels. These massive to weakly bedded silt deposits form conspicuously high bluffs along the banks of streams and rivers. These silty sediments were regarded to be Pliocene and mostly Pleistocene on the basis of its vertebrate fossils and stratigraphy.<ref name="Collier1903a">Collier, A.J., 1903. ''The coal resources of the Yukon, Alaska''. ''U.S. Geological Survey Bulletin'', 218, 71 pp.</ref> In 1898,<ref name="Spurr1898a"/> Spurr applied the name, ''Yukon Silt'', to this same blanket of silty, often either clayey or organic-rich, sediment. In 1892,<ref name="DallOthers1892a">Dall, W.H. and Harris, G.D., 1892. ''Correlation papers: Neocene''. ''Bulletin of the United States Geological Survey'', 84, 349 pp.,</ref> Dall and Harris proposed the name ''Kowak Clays'' for similar fine-grained, Pleistocene, sediments. Along with the Yukon Silt, this term designated the entire thickness of silty sediments blanketing either side of the Yukon River.<ref name="Collier1903a"/>

In the 1940s, various studies<ref name="Rainey1940a">Rainey, F., 1940. ''Archaeological investigation in central Alaska''. ''American Antiquity'', 5(4), pp. 299-308.</ref><ref name="Tuck1940a">Tuck, R., 1940. ''Origin of the muck-silt deposits at Fairbanks, Alaska''. ''Bulletin of the Geological Society of America'', 51(9), pp.1295-1310.</ref><ref name="Hibben1941a">Hibben, F.C., 1941. ''Archaeological Aspects of the Alaska Muck Deposits''. ''New Mexico Anthropologist'', 5(4), pp. 151-157.</ref><ref name="Taber1943a">Taber, S., 1943. ''Perennially frozen ground in Alaska: its origin and history''. ''Bulletin of the Geological Society of America'', 54(10), pp.1433-1548.</ref> were conducted about the archaeology, geocryology, paleontology, and stratigraphy of these silty sediments. In these studies, the terms, ''Yukon Silt'' and ''Kowak Clays'', had disappeared from the published literature. Instead, some of these researchers<ref name="Rainey1940a"/><ref name="Hibben1941a"/> refer informally to these sediments simply as either ''muck'' or ''Alaska muck''. This term ''muck'' was at a that time and is still used by local miners and geologists to refer to typically dark gray to black silt, which contains a considerable quantity of plant remains, lenses of ice, permafrost, and thin beds of peat and volcanic ash that directly overlie gold-bearing fluvial gravels.<ref name="Hibben1941a"/><ref name="Taber1943a"/> Instead of ''muck'' still other researchers use the informal term ''Alaska silts'' for the same sequence of sediments.<ref name="Taber1943a"/>

thumb|upright=1.25|Schematic composite cross section of creek valley near Fairbanks illustrating stratigraphic relations of Goldstream Formation and associated Quaternary deposits.<ref name="Péwé1989a"/> In the summers of 1946, 1947, 1948, 1949, and 1951, Péwé<ref name="Péwé1953a"/> conducted detailed field research concerning the geomorphology and Quaternary Geology of the Fairbanks, Alaska, region within the Tanana River valley and Yukon-Tanana Upland. This research was conducted for the Alaska Terrain and Permafrost Section of the United States Geological Survey in Alaska and a PhD dissertation accepted in 1953. As a part of this study, he subdivided the Alaska muck (Alaska silt) into five informal stratigraphic units. These units are the (1) auriferous gravel, (2) Dawson muck, (3) Fairbanks loess, (4) Goldstream muck, (5) Gold Hill loess, and (5) Engineer muck.<ref name="Péwé1953a">Péwé, T.L., 1953. ''Geomorphology of the Fairbanks area, Alaska''. Palo Alto, California, Stanford University, Ph.D. dissertation, 220 pp.</ref> As the result of years of additional detailed field research for the United States Geological Survey, Péwé formally subdivided the obsolete Alaska muck and Alaska silt terminology into formal geologic formation and defined them according to the rules of stratigraphic nomenclature.<ref name="Péwé1975a"/><ref name="Péwé1975b"/> These geologic formations include the Ready Bullion Formation (Holocene), Engineer Loess (Holocene), Giddings Forest Bed (Holocene), Goldstream Formation (Wisconsin), Eva Formation (forest bed)(Sangamon), Gold Hill Loess (PreSangamon to Pliocene), Dawson Cut Formation (forest bed)(Pliocene), Tanana Formation (Pliocene), Fox Gravel (Pliocene) and Cripple Gravel (Pliocene).<ref name="Péwé1989a">Péwé, T.L., 1989. ''Quaternary stratigraphy of the Fairbanks area, Alaska''. In Carter, D.L., Hamilton, T.D., and Galloway, J.P., eds., pp. 72-77, ''Late Cenozoic history of the interior basins of Alaska and the Yukon''. ''U.S. Geological Survey Circular'', 1026. Reston, Virginia, 114 pp.</ref>

==Description== The Ready Bullion Formation consists of perennially frozen organic-rich silt that contains an abundance of minute carbonized plant fragments, peat lenses, sticks, and logs and rooted stumps. When frozen, it is gray to black and medium- to dark-brown when thawed and oxidized. Locally, especially near junctions with tributary stream and creek, these silts contain beds and lenses of sandy angular gravel that are less than {{convert|1|m|ft|abbr=on}} thick. Ready Bullion Formation is poorly to well stratified and perennially frozen below a depth of {{convert|1|m|ft|abbr=on}}. Unlike the underlying Goldstream Formation, it lacks large foliated ice masses. These silty sediments contain only ice seams and lenses less than {{convert|1|cm|in|abbr=on}} thick and sometimes rare clear-ice masses of recent origin. The Ready Bullion Formation unconformably overlies the Goldstream Formation. This formation is a thin, but widespread, blanket of organic-rich retransported and redeposited loess underlying the creek valley bottoms and lower slopes in central Alaska and the Yukon Territory. It is the parent sediment in which the modern soil is developed.<ref name="Péwé1975a"/><ref name="Péwé1975b"/><ref name="Péwé1989a"/> thumb|upright=1.25| Outcrop and stratigraphy of Quaternary deposits in Eva Mining Cut, Fairbanks, Alaska, region.<ref name="Péwé1975a"/>

'''Giddings Forest Bed''' is the youngest, Holocene, of three laterally persistent Pleistocene forest beds recognized within the Pleistocene deposits underlying the valley walls of the rivers and streams within the Yukon and Tanana river drainages and upland. This forest bed is a regional marker horizon that lies at the base of the Ready Bullion Formation and Engineer Loess.. Unlike the older Eva Forest Bed (Sangamonian Stage) and Dawson Cut Forest Bed (Pre-Sangamonian interglacial). The organic-rich silts of the Giddings Forest Bed contains excellently preserved, frozen leaves, sticks, and logs and rooted stumps. Unlike other forest beds, many of the leaves found in the Giddings Forest Bed are still green and wood is only discolored. The wood of the Eva Forest Bed, which comprises the Eva Formation, is moderately to excellently preserved; not compressed, smashed, or flattened; and wood cell structure is good. In sharp contrast to the Giddings and Eva forest beds, the wood of the Dawson Cut Forest Bed is significantly weathered, smashed, flattened, and iron-stained. Also, the cell structure of its wood is not well preserved. Birch and spruce dominate the Giddings and Eva forest beds. They are rarely found in the Dawson Cut Forest Bed.<ref name="Péwé1989a"/><ref name="PeweOthers1997a"/> The Giddings Forest Bed is named for the late J. Louis Giddings, who first recognized these forest beds in 1938.<ref name="Giddings1938a">Giddings, J.L., 1938. ''Buried Wood from Fairbanks, Alaska''. ''Tree-Ring Bulletin'', 4(4) pp. 3-5.</ref><ref name="Nash2000a">Nash, S.E., 2000. ''James Louis Giddings' archaeological tree-ring dating in the American Arctic: A forgotten legacy''. ''Arctic Anthropology'', 7(1) pp.60-78.</ref> He was a pioneering archaeologist and dendrochronologist in Pleistocene paleoenvironmental studies in Alaska. The type locality of the Giddings Forest Bed is an exposure of ready Bullion Formation located at the mouth of Engineering Creek.<ref name="PeweOthers1997a">Pewe, T.L., Berger, G.W., Westgate, J.A., Brown, P.M., and Leavitt, S.W., 1997. ''Eva Interglaciation Forest Bed, unglaciated east-central Alaska: Global warming 125,000 years ago''. ''Special Paper'', 319. Boulder, Colorado, Geological Society of America, 453 pp. {{ISBN|9780813723198}}</ref> thumb|Gold mining dredge at Cripple Creek, Alaska mining cut circa 1942. On far right, intact and unslumped section exposed in highwall of cut. uppermost, light-colored layer is part of Ready Bullion Formation underlain by dark-colored layer of its Giddings Forest Bed. Light-colored Goldstream Formation resting on thin, dark-colored, and less well exposed layer of Eva Formation (Eva Forest Bed). Between the Eva Forest Bed and bench, on which sheds rest, consists of Gold Hill Loess. Dawson Cut forest Bed at base is concealed beneath accumulated slump sediments. Bench at base of mining cut consists of gold-bearing Pliocene fluvial gravels. As is typical, mining cut that is directly befined and left of gold dredged is badly slumped and jumbled.

==Fossils== Unlike the underlying Goldstream Formation, vertebrate remains in the Ready Bullion Formation are scarce, scattered, and disarticulated. The vertebrate remains, which have been recovered from it, consist only of nonextinct taxa. None of the many extinct Pleistocene forms such as bison, horse, and mammoth present in the underlying Goldstream Formation have been found in it.<ref name="Péwé1989a"/><ref name="Péwé1952a">Péwé, T.L., 1952. ''Geomorphology of the Fairbanks area, Alaska''. Palo Alto, California, Stanford University, Ph.D. dissertation, 220 pp.</ref>

Plant remains, including fresh-looking green leaves, found in the Ready Bullion Formation are abundant and exceedingly well preserved. This formation also contains lenses and pods of peat and Giddings Forest Bed, which contains well-preserved logs, twigs and rooted stumps of birch and spruce.<ref name="Péwé1989a"/><ref name="Taber1943a"/> At one exposure, Giddings described the occurrence of three spruce forest layers with stumps superposed on one another within the Ready Bullion Formation. In this formation, tree remains are much more common than in the underlying Goldstream Formation.<ref name="Péwé1989a"/><ref name="Giddings1938a"/>

==Age== The age of the Ready Bullion Formation in the Fairbanks area is well established by numerous radiocarbon dates made on wood samples from this formation and the contemporaneous Engineer Loess.<ref name="Péwé1975a"/> These radiocarbon dates range from about 3,000 to 10,000 years ago with a majority of them in the range of 5,000-7,000 years ago. For example, a sample of wood (L117H) collected about {{convert|2|m|ft|abbr=on}} below the surface from the Ready Bullion Formation on Eva Creek yielded a radiocarbon date of 3,7500±200 years ago. In addition, a sample of wood (G137S) collected from the base of Engineer Loess at the Eva Creek mining cut yielded a radiocarbon date of 10,500±500 years ago. The radiocarbon dates compiled by Péwé and others<ref name="Péwé1989a"/> demonstrate that deposition of Ready Bullion Formation began shortly after the end of the Pleistocene and it is entirely Holocene in age.

==See also== *List of fossiliferous stratigraphic units in Alaska *Yedoma

==References== {{reflist}}

Category:Paleontology in Alaska Category:Quaternary Alaska Category:Pleistocene Alaska Category:Geologic formations of Alaska