Understanding the kinematic development of basement-involved compressive structures that form at low temperature is dependent, in part, on gaining a better factual understanding of their deformational behavior. Results presented here show that the response of crystalline basement to deformation is incongruous among different structures in Colorado and Wyoming. At Big Thompson anticline and Rattlesnake Mountain anticline, Precambrian basement was not rotated in the anticlinal hinge during Tertiary folding. At both Banner Mountain and at a minor fold on Casper Mountain the basement has been rotated near the anticlinal hinge by as much as 26°. In the steep limb of all four of these monoclinal structures the basement is in fault contact with the stratified cover. At two sites, the Five Springs Creek area of the Bighorn Mountains and Casper Mountain, evidence for greater rotation of basement is clear. Precambrian dikes at Five Springs exhibit rotation of as much as 85° across the Laramide anticlinal hinge. Although the anticline at Casper Mountain shows minor folding, in the footwall a depositional contact on basement is rotated 50° from regional dip. These structures (Big Thompson anticline, Casper Mountain, and Five Springs) show minor fractures in the basement that apparently do not control the kinematics of basement deformation, but do indicate the stress field orientation. Typically σ 1 is nearly horizontal and normal to the fold axis, σ 2 is parallel to the fold axis, and σ 3 is very steep. This is the stress field normally associated with thrust faulting.

Biogenic apatite crystals in living organisms contain relatively high concentrations of carbonate, sodium, and other species, making the crystallite relatively soluble and reactive. During fossilization, apatite composition changes from a metastable carbonate hydroxylapatite to a thermodynamically more stable fluorapatite. Calcium, sodium, carbonate, and hydroxyl are replaced by fluoride, REE, and trace elements during diagenesis. The total REE concentrations in osteological material are generally <20 ppm; in fossil bones, however, the concentrations may be >1000–10,000 ppm. More than 95% of REE in fossil bone is incorporated during diagenesis. The fossilization process occurs within a few thousand years, and thus the chemical composition of the fossils records the composition of early diagenetic fluids. Apatite becomes a “flight recorder” for the environment of early diagenesis and can be used to interpret the condition of the paleoenvironment. REE were analyzed from marine reptile (Mosasauridae) bones collected from five superposed formations (Sharon Springs, Gregory, Crow Creek, DeGrey, and Verendrye) of the Upper Cretaceous Pierre Shale Group at localities along the Missouri River in central South Dakota. Fossil vertebrates from each lithostratigraphic unit sampled of the Pierre Shale Group have different REE signatures. Fossils from the Sharon Springs Formation have distinctive REE signatures that may be further subdivided into three superposed members that correspond with the upper, middle, and lower Sharon Springs Formation. REE signatures are distinctive from each stratigraphic unit; therefore, fossils eroded from their stratigraphic context may be assigned to their proper depositional unit on the basis of REE signature comparisons. Differences in REE compositions of fossil bones among lithostratigraphic subdivisions appear to have resulted from differential mixing of oxygenated and anoxic seawaters. If differences in mixing are interpreted as depth differences, the lower Sharon Springs member was deposited in deep, anoxic water; water depths decreased for the middle and upper Sharon Springs, and the overlying Gregory and Crow Creek units were deposited in even more shallow water. Finally, the overlying DeGrey and Verendrye Formations were deposited in progressively deeper marine waters, but not as deep as for the lower Sharon Springs. These interpretations are generally consistent with those based on faunal diversity and eustatic sea level curves.

Silicic volcanic rocks — dacite, rhyolite, and quartz porphyry — constitute about 35 percent of the Yavapai Supergroup, an older Precambrian sequence in central Arizona. In addition, the series contains about 30 percent pillow and amygdaloidal basalt, 5 percent andesitic rocks, and the remainder is mixed andesitic and silicic-bedded tuffaceous rock. The Yavapai Supergroup is divided into the Ash Creek and Alder Groups, each containing about 20,000 feet of lavas and pyroclastic rocks; no evidence is available to determine the relative ages of the two groups. The pillow basalts, coarsely graded volcanic breccias, and poorly sorted and graded tuffaceous-bedded rocks suggest a marine accumulation in an eugeosyncline. The Yavapai Supergroup is metamorphosed to the greenschist facies. The Ash Creek Group exhibits open folds but is nonfoliated except locally, whereas, the Alder Group is isoclinally folded and dominantly schistose. Twenty-five chemical analyses of the metamorphosed, silicic volcanic rocks reveal varying ratios of sodium and potassium. By comparison with young rhyolitic obsidians, only two rhyolites approach the ratios and total alkali content found in recent obsidians. Five rhyolites contain more sodium and appreciably less potassium, whereas none of the rhyolitic rocks contain more potassium than in young obsidians. High-sodium content is reflected by much albite, and high-potassium content by abundant sericite. Iron-magnesium metasomatism locally has produced much chlorite associated with an increased quartz and decreased albite content. The source of the iron and magnesium may be underlying pillow basalts. Many rhyolitic rocks of Phanerozoic age display variable ratios of Na 2 O and K 2 O caused by hydration of obsidian, hot spring action, and hydrothermal solutions. The redistribution of the alkalis in the Yavapai Supergroup may be caused in part by factors other than regional metamorphism. It is suggested the H 2 O + content, averaging between 5 and 6 percent by volume in these metamorphosed silicic rocks, may be derived in part from interstitial marine water.

Abstract Algal buildups from five stratigraphic intervals in the Pennsylvanian of eastern Kansas, Midcontinent, U.S.A., display three basic fabrics based on their: a) dimension, b) morphology, c) fossil content, d) algal growth forms, and e) nature of framework cavities. Type 1. Constructional mounds composed of cup-shaped in situ algal growth forms are typically small bioherms, either isolated (e.g., Frisbie Limestone Member) or thickened intervals within carbonate banks(e.g., Sniabar Limestone Member), and are basically formed by phylloid green algae. Fossil diversity is very low. Mud and cement fill the abundant small intercup voids within individual mounds. Calcareous sponges, crinoids, and bryozoans, probably cavity dwellers, fill the larger intermound cavities between the smaller mounds. Type 2. Constructional mounds of algae with undulatory growth forms are basically red algae with recognizablethalli characteristics of Archaeolithophyllum, and, only rarely, of phylloid green algae. Buildups of this kind are laterally persistent. Thickening of the banks is generally recognizable at a large scale (ten of meters to kilometers). Smaller, meter-scale bioherms constructed of algae with undulatory growth forms donot occur in the sites studied. Fossil diversity is higher than in type (1) mounds, with calcareous sponges, brachiopods, and bryozoans common throughout the mound, rather than exclusively in cavities between small mounds ofthe type 1 cup-shaped algae. When built by green algae (e.g., parts of the Captain Creek Limestone Member), mounds have a lower diversity than those constructed by red algae (e.g., Spring Hill Limestone Member). Solitary corals, calcareous sponges, and bryozoans occur attached to the walls of the cavities. The abundance of open pores is striking. Type 3. Mounds of accumulated algae with undulatory growth forms are formed by the red algae Archaeolithophyllum missouriense, Archaeolithophyllum lamellosum, and the green alga Eugonophyllum. Depositional relief is not visible on the outcrop, but large-scale variations in bank thickness are notable (e.g., lower part of the Captain Creek Limestone Member). Bryozoans and Thartharella (a probable worm tube) are common. Multiple types of cavities occur, and most are cement-filled. Although the mound types differ in their form, fossil content, and type and distribution of voids, they sharean overall common peloidal clotted matrix that accumulated in specific areas, along with an abundance of gravity-defying peloidal micritic structures in the matrix, and of thin crusts within marine cement that may be relatedto microbial activity. Microbes probably played a crucial role in carbonate precipitation and in lithificationofalgal-dominated buildups.

Abstract Bulk mineable gold deposits in the western United States contain reserves of more than 55 million oz (1,710 metric tons) Au and produce more than 3 million oz (93,300 kg) Au/yr. They can be subdivided into five main deposit types: porphyry-related, sediment-hosted (includes deposits of the Carlin type), metamorphic-hosted, volcanic-hosted , and hot spring gold deposits. Each deposit type can be further divided into several deposit subtypes. Examples of porphyry-related gold deposits are Zortman-Landusky in Montana and the Fortitude and McCoy skarn-hosted gold deposits in Nevada. Major sediment-hosted gold deposits in the western United States occur mainly in Nevada and include the world-class gold deposits located within the Carlin and Getchell trends. Metamorphic deposits include Mother Lode and Mesquite types, located principally in California and Arizona. Volcanic-hosted deposits can be subdivided into three main deposit subtypes: high sulfur deposits such as Summitville, Colorado, and Paradise Peak, Nevada; low sulfur deposits such as Round Mountain, Nevada; and alkalic deposits such as Cripple Creek, Colorado. Hot spring gold deposits are typified by the McLaughlin gold deposit in northern California.