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At least 739 records · Page 41Linked to original sources
USGS1918

Stratigraphy of the Hanna Basin, Wyoming

Carbon County, Wyo., has attracted the attention of geologists since the days of the territorial surveys under King, Hayden, and Powell. During this earlier work all the rocks (except the North Park formation) over-lying the uppermost beds of marine origin were grouped in a single formation, for which the name Laramie was proposed.

Wyoming↗
USGS1980

Shorter contributions to stratigraphy and structural geology, 1979

PART A: A system of anticlines lies along the trend of the sinuous course of the Colorado River for a distance of 97 km in the central Grand Canyon. Similar anticlines occur in some perennially wet side canyons. The anticlines are most abundant and well developed along northeast-trending reaches of the main canyon where it is floored by the Cambrian Muav Limestone. Dips of the folded strata are as great as 60?, and the folding locally extends more than 250 m from the river. Low-angle thrust faults in the limbs of the anticlines parallel the river and have formed in response to folding of the comparatively brittle carbonate strata. High-angle reverse kink bands, along which rocks are displaced up toward the river, also parallel the anticlines and have develop2d in response to the upward bulging of the canyon floor. The river anticlines are an unloading phenomenon. They result from lateral squeezing toward the river of saturated shaly parts of the Muav Limestone and underlying Bright Angel Shale. The driving mechanism for the deformation is a stress gradient that results from a difference in lithostatic load between the heavily loaded rocks under the 650-m-high canyon walls and the unloaded canyon floor. Saturation appears to weaken the shaly rocks sufficiently to allow deformation to take place. River anticlines are not present in the eastern Grand Canyon, where the Cambrian rocks also occur at river level. Their absence is explained by a lack of shaly rocks that could flow when saturated. PART B: The current interest in contemporary tectonic processes in the Eastern United States is turning up abundant evidence of crustal movements in late geologic time. Topographic analysis of the highland areas from the southern Blue Ridge to the Adirondack Mountains indicates that most of the landforms owe their origin to erosion of rocks of different resistance rather than to tectonic processes. Most areas of high relief and high altitude have been formed on resistant rocks. The Cambrian and Ordovician belt, containing mostly shale and carbonate rock, on the other hand, forms an extensive lowland from Alabama to the Canadian border and girdles the Adirondack Mountains. Differences in altitude can be explained by the presence of resistant rocks outside the belt; these resistant rocks form local base levels on the streams that drain the belt. A few areas may have undergone local uplift at a higher rate than areas nearby--for example, the Piedmont region northwest of Chesapeake Bay. Most estimates of erosion rates, based on the load transported by streams and of uplift rates, based on removal during a known period of time, are of the same order of magnitude, averaging almost 4x 10^-2 millimeters per year. Rates of uplift, based on study of tilted Pleistocene beaches and repeated geodetic traverses, are at least an order of magnitude higher for comparable areas. Tectonic uplift of the highlands has been slow and involves mostly warping or tilting on a large scale. Erosion rates keep up with or exceed the rate of uplift and have been sufficient to mask evidence of faulting or other differential movements. The high rates of uplift that are inferred on tilted water planes in the glaciated regions or that are measured by differences in repeated geodetic traverses cannot have been sustained for long periods of time. PART C: The Hanson Creek Formation southwest of Eureka, Nev., in the Bellevue Peak Quadrangle is composed of three lithostratigraphic members: (1) a basal dark-gray dolomite, (2) a middle silty thin- to thick-bedded, locally nodular, dark-gray, light-yellow-mottled limestone topped by light-gray dolomite, and (3) an upper dark-gray dolomite, which is herein named the Combs Canyon Dolomite Member. Detailed geologic mapping and accompanying fossil collecting prove that the same lithostratigraphic and biostratigraphic sequence is present in the Mountain Boy Range and 11 km to the south near Wood Cone Peak. Minor differences in

Professional Paper↗
USGS1979

Late Cenozoic deposits, landforms, stratigraphy, and tectonism in Kittitas Valley, Washington

Kittitas Valley, a structurally determined wide segment of the Yakima River valley, is partly filled with the Pliocene Thorp Gravel and with Pleistocene till, outwash, and related sediment that accumulated during three glaciations. The Thorp Gravel, whose age according to fission-track dating is about 3.7 m.y., forms a conspicuous fill terrace locally as high as 130 m. Bodies of drift, all younger than the Thorp Gravel, form nested fill terraces along the Yakima River. The massive moraines, intermediate morphostratigraphic position, and well-developed soil of the Kittitas Drift suggest its correlation with the penultimate northern-hemisphere glaciation of about 0.13 m.y. ago. The Lakedale Drift, which composes a single outwash terrace in Kittitas Valley, evidently correlates with the classical late Wisconsin Glaciation. The newly named Lookout Mountain Ranch Drift, which forms moraines at higher altitudes than and is older than the Kittitas Drift, lacks an attendant valley train. Three faults disrupt the Thorp Gravel but apparently not the Kittitas Drift, and therefore probably are between 0.13 and 3.7 m.y. old. The eastward trend and up-to-the-basin throw of the faults probably reflect reverse faulting due to a regional north-south compression that uparched several east-trending anticlines in central Washington. The southeast trend of the dextrally echelon arrangement of the faults apparently is due to a right-lateral couple across a zone parallel to the Olympic-Wallowa lineament.

Professional Paper↗
USGS1983

Stratigraphy of the Silurian outcrop belt on the east side of the Cincinnati Arch in Kentucky, with revisions in the nomenclature

Silurian rocks form a narrow arcuate outcrop belt about 100 mi long on the east side of the Cincinnati Arch in Kentucky. They range from as much as 300 ft thick in the north to a pinchout edge in the south. The nomenclature of this sequence is revised to reflect mappability and lithologic uniformity on the basis of detailed mapping at a scale of 1:24,000 by the U.S. Geological Survey in cooperation with the Kentucky Geological Survey. The Silurian rocks are divided into two parts: the Crab Orchard Group, raised in rank from Crab Orchard Formation and redefined, in the lower part of the Silurian section, and Bisher Dolomite in the upper part of the section. The Crab Orchard Group is subdivided into the Drowning Creek Formation (new name) at the base of the Silurian, overlain by the Alger Shale (adopted herein) south of Fleming County and by the Estill Shale (elevated to formational rank) north of Bath County. The Brassfield Member (reduced in rank from Brassfield Dolomite or Formation) and the Plum Creek Shale and Oldham Members of the former Crab Orchard Formation are included as members of the Drowning Creek; the Lulbegrud Shale, Waco, and Estill Shale Members of the former Crab Orchard Formation are now included in the Alger. The Drowning Creek Formation, 20 to 50 ft thick, is composed mainly of gray fine to coarse-grained dolomite with shale interbeds. The dolomite beds average several inches thick, with bedding surfaces that are locally smooth but generally irregular and are fossiliferous in many places; fossils include brachiopods, crinoid columnals, horn corals, colonial corals, trilobites, pelecypods, and bryozoans. The shale interbeds average several inches thick, except for its Plum Creek Shale Member which is entirely shale and as much as 12 ft thick, and are most abundant in the upper half of the formation. The members of the Drowning Creek intergrade and are indistinguishable in the northern part of the area. The Alger Shale, as much as 170 feet thick, is predominantly grayish-green clay shale with a thin (0.5-3 ft) dolomite member (the Waco, or its northern equivalent, the Dayton Dolomite Member, reduced in rank from Dayton Limestone) near the base. North of Bath County, the Lulbegrud Shale and Dayton Dolomite Members are reassigned to the underlying Drowning Creek Formation, the Estill Shale Member is elevated to formational status, and the Alger is dropped. The Bisher Dolomite, which overlies the Estill Shale in the northernmost part of the Silurian belt, ranges from 0 to 300 ft in thickness and is composed of medium-to coarse-grained, gray, fossiliferous dolomite. The Silurian section overlies Upper Ordovician rocks in apparent conformity, although faunal studies suggest a minor hiatus, and is overlain by Middle to Upper Devonian rocks in a regional angular unconformity that truncates the entire Silurian section at the southwest end of the outcrop belt, where it is nearest the axis of the Cincinnati Arch. All of the units recognized in the Silurian appear to thicken eastward, away from the axis of the arch and towards the Appalachian basin. This, with the presence of isolated remnants of the Brassfield near the axis, suggest that formation of the arch was initiated in Early Silurian time by subsidence of its eastern flank.

Professional Paper↗
USGS1981

Stratigraphy and structure of the Strawberry Mine roof pendant, central Sierra Nevada, California

The Strawberry mine roof pendant, 90 km northeast of Fresno, Calif., is composed of a sequence of metasedimentary rocks of probable Early Jurassic age and a sequence of metaigneous rocks of middle Cretaceous age. The metasedimentary rocks are a former miogeosynclinal sequence of marl and limestone now metamorphosed to calc-silicate hornfels and marble. A pelecypod found in the calc-silicate hornfels has been tentatively identified as a Mesozoic bivalve, possibly Inoceramus pseudomytiloides of Early Jurassic age. These metasedimentary rocks are similar in lithology, structure, and gross age to the metasedimentary rocks of the Boyden Cave roof pendant and are assigned to the Lower Jurassic Kings sequence. The younger metaigneous rocks are metamorphosed shallow-in trusi ve rocks that range in composi tion from granodiorite to rhyolite. These rocks are similar in composition and age to the metavolcanic rocks of the surrounding Merced Peak quadrangle and nearby Ritter Range, and probably represent necks or dikes that were one source for the meta volcanic rocks. The roof pendant is intruded by several plutons, ranging in composition from dioritic to highly felsic, that constitute part of the granodiorite of Jackass Lakes, also M middle Cretaceous age. The contemporaneous suites of metaigneous, metavolcanic, and plutonic rocks in the region represent a middle Cretaceous period of calc-alkalic volcanism and plutonism in the central Sierra Nevada and are interpreted as part of an Andean-type volcanic-plutonic arc. Three deformations are documented in the roof pendant. The first deformation is reflected only in the metasedimentary rocks and consists of northeast-to east-west-trending folds. Similar structures occur in the Boyden Cave roof pendant and in the Calaveras Formation and represent a Middle Jurassic regional deformation. Evidence of the second deformation occurs in the metasedimentary and metaigneous rocks and consists of folds, faults, minor structures, and regional metamorphism along N. 25? W. trends. Crosscutting of these structures by the contemporaneous granodiorite of Jackass Lakes indicates that this deformation occurred simultaneously with volcanism and plutonism during the middle Cretaceous. The third deformation involved both the roof pendant and adjacent plutonic rocks and consists of folds, faults, schistosities, and regional metamorphism along N. 65? -900 W. trends. Crosscutting of similar structures in other middle Cretaceous plutonic rocks of the Merced Peak quadrangle by undeformed late Cretaceous plutonic rocks indicates a regional deformation of middle to late Cretaceous age. Structures of similar style, orientation, and age occur elsewhere in metavolcanic and plutonic rocks throughout the central Sierra Nevada.

Professional Paper↗
USGS1980

Stratigraphy of mid-Cretaceous formations at drilling sites in Weston and Johnson counties, northeastern Wyoming

The sedimentary rocks of early Late Cretaceous age in Weston County, Wyo., on the east flank of the Powder River Basin, are assigned, in ascending order, to the Belle Fourche Shale, Greenhorn Formation, and Carlile Shale. In Johnson County, on the west flank of the basin, the lower Upper Cretaceous strata are included in the Frontier Formation and the overlying Cody Shale. The Frontier Formation and some of the laterally equivalent strata in the Rocky Mountain region contain major resources of oil and gas. These rocks also include commercial deposits of bentonite. Outcrop sections, borehole logs, and core studies of the lower Upper Cretaceous rocks near Osage, in Weston County, and Kaycee, in Johnson County, supplement comparative studies of the fossils in the formations. Fossils of Cenomanian, Turonian, and Coniacian Age are abundant at these localities and form sequences of species which can be used for the zonation and correlation of strata throughout the region. The Belle Fourche Shale near Osage is about 115 m (meters) thick and consists mainly of noncalcareous shale, which was deposited in offshore-marine environments during Cenomanian time. These strata are overlain by calcareous shale and limestone of the Greenhorn Formation. In this area, the Greenhorn is about 85 m thick and accumulated in offshore, open-marine environments during the Cenomanian and early Turonian. The Carlile Shale overlies the Greenhorn and is composed of, from oldest to youngest, the Pool Creek Member, Turner Sandy Member, and Sage Breaks Member. In boreholes, the Pool Creek Member is about 23 m thick and consists largely of shale. The member was deposited in offshoremarine environments in Turonian time. These rocks are disconformably overlain by the Turner Sandy Member, a sequence about 50 m thick of interstratified shale, siltstone, and sandstone. The Turner accumulated during the Turonian in several shallow-marine environments. Conformably overlying the Turner is the slightly calcareous shale of the Sage Breaks Member, which is about 91 m thick. The Sage Breaks was deposited mostly during Coniacian time in offshore-marine environments. In Johnson County, the Frontier Formation consists of the Belle Fourche Member and the overlying Wall Creek Member, and is overlain by the Sage Breaks Member of the Cody Shale. Near Kaycee, the Belle Fourche Member is about 225 m thick and is composed mostly of interstratified shale, siltstone, and sandstone. These strata are mainly of Cenomanian age and were deposited largely in shallow-marine environments. In this area, the Belle Fourche Member is disconformably overlain by the Wall Creek Member, which is about 30 m thick and grades from interlaminated shale and siltstone at the base of the member to sandstone at the top. The Wall Creek accumulated during Turonian time in shallowmarine environments. These beds are overlain by the Sage Breaks Member of the Cody. Near Kaycee, the Sage Breaks is about 65 m thick and consists mainly of shale which was deposited in offshoremarine environments during Turonian and Coniacian time. Lower Upper Cretaceous formations on the east side of the Powder River Basin can be compared with strata of the same age on the west side of the basin. The Belle Fourche Shale at Osage is represented near Kaycee by most of the Belle Fourche Member of the Frontier. The Greenhorn at Osage contrasts with beds of similar age in the Belle Fourche at Kaycee. An upper part of the Greenhorn Formation, the Pool Creek Member of the Carlile Shale, and the basal beds of the Turner Sandy Member of the Carlile, in Weston County, are represented by a disconformity at the base of the Wall Creek Member of the Frontier in southern Johnson County. A middle part of the Turner in the vicinity of Osage is the same age as the Wall Creek Member near Kaycee. A sequence of beds in the upper part of the Turner and in the overlying Sage Breaks in Weston County is the same age as most of the Sage Breaks M

Professional Paper↗