Overview
The Ready Bullion Formation is a geologic formation that consists of a 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 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. 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 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.
Nomenclature
In the late 1800s and early 1900s, geologists recognized that a thick, 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. In 1898, 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. 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 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.
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 thick. Ready Bullion Formation is poorly to well stratified and perennially frozen below a depth of . Unlike the underlying Goldstream Formation, it lacks large foliated ice masses. These silty sediments contain only ice seams and lenses less than 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. 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.
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. 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. 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.
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. 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 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 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