Stereoscopic-pair projection of aerial photographs in map compilation
No abstract available.
Bulletin of the Geological Society of America↗
SEARCH · Geology Reports
Results for “Geological Bulletin”
Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Origin and development of the Three Forks Basin, Montana
The Three Forks Basin sprawls where the intricately deformed sedimentary and volcanic rocks of the Disturbed Belt along the Rocky Mountain front are faulted against the Precambrian metamorphic rocks that make the core of the Tobacco Root, Madison, Gallatin, and Beartooth ranges. Its eastern edge is linear, controlled by steep faults at the west front of the Bridger Range. All other boundaries are sinuous and show little sign of structural control. Tertiary deposits in the basin , rich in contemporaneous rhyolitic and latitic ash, are about equally of lake, bolson, and stream origin . The western part of the basin is dominated by moderately folded Eocene and lower Oligocene rocks, more than 2000 feet thick. They dip eastward beneath apparently unfolded upper Miocene and Pliocene rocks, more than 1300 feet thick, that also dip gently eastward to the basin edge. Thin but extensive Quaternary deposits lying unconformably on the Tertiary and pre-Tertiary rocks are mainly of rounded terrace and flood-plain gravel, angular fan gravel, and wind-blown silt. The basin began as part of an east-flowing stream system that developed in Late Cretaceous and Paleocene time, concurrently with Laramide folding and thrusting; the faulted contact between metamorphic and sedimentary rocks was especially erodible and became a main drainage way. Recurrent uplift to the west throughout the Tertiary provided gradient and load to the streams; additional load was provided by showers of ash from unknown vents. Relative uplifts of the Bridger Range in Eocene and early Oligocene time, and again in late Miocene and Pliocene time, impeded flow from the basin and led to deposits in channels, flood plains, and lakes. During most of Oligocene and Miocene time, however, the basin was being eroded. By the end of the Tertiary the basin was deeply filled and became part of a regional surface of low relief. Regional northwestward tilting stimulated headward erosion of the Missouri River which then captured the formerly east-draining or closed basin . The Tertiary deposits have been deeply eroded, and the rugged pre- basin surface partly exhumed.
Montana↗
Origin of the Gulf of California
The probable cumulative Late Cretaceous and Cenozoic right-lateral strike-slip displacement along the San Andreas fault in central California is 350 miles. The San Andreas and the allied faults into which it branches southward trend longitudinally into the Gulf of California , and the seismicity of the region indicates that the fault system follows the length of the Gulf and enters the Pacific basin south of Baja California . Crustal structure of most of the Gulf is of oceanic type, so that an origin by structural depression of continental rocks is not possible. Tectonic styles north and south of Los Angeles differ greatly. To the north, the Coast Ranges expose thick Upper Cretaceous and Cenozoic sedimentary rocks that were deposited in local basins and deformed tightly and repeatedly. To the south, in the Peninsular Ranges and Baja California , correlative rocks are thin and show little compressive deformation. The California batholith of mid-Cretaceous age and allied crystalline rocks form the basement of Baja California , southwestern Arizona, and northwestern Sonora and probably extend along the coast of mainland Mexico; the Gulf apparently bisects the crystalline belt longitudinally. These features suggest that Baja California initially lay 300 miles to the southeast, against the continental-margin bulge of Jalisco. The Gulf of California may be a pull-apart feature caused by strike-slip displacement plus up to 100 miles of cross-strike separation of the continental plate, subcontinental materials having welled up into the rift gap. The strike-slip motion has a tensional component across the continental margin south of Los Angeles but a compressional component to the north.
Gulf of California↗
Origin of a salt-water lens in permafrost at Kotzebue, Alaska
Frozen sediments were found to a depth of 238 feet in the drilling of a 325-foot well at Kotzebue , Alaska . Between 79 and 86 feet, however, highly saline water was found in a gravel lens . The writer suggests that the salt water originated by fractionation by freezing. Analyses of this water and of slightly saline water from below the permafrost are given.
Alaska↗
Subaerially carved Arctic seavalley under a modern epicontinental sea
A shallow seavalley , averaging 6 feet in relief, extends from the mouth of Ogotoruk Creek, northwest Alaska, for 15 miles across the floor of the Chukchi Sea to a depth of 135 feet. The seavalley is considered to be a drowned subaerial valley of Pleistocene age, which was excavated on an eustatically emerged epicontinental shelf during periods of glacially depressed sea level.
Bulletin of the Geological Society of America↗
Granitic formations in the east-central Sierra Nevada near Bishop, California
This report establishes lithologic units among the granitic rocks of the east-central Sierra Nevada near Bishop , California . In this area the Sierra Nevada batholith is composed chiefly of quartz-bearing plutonic rocks ranging in composition from quartz diorite to alaskite but includes scattered small masses of darker and older plutonic rocks and remnants of metamorphosed sedimentary and volcanic rocks. The granitic rocks are in discrete plutons, either in sharp contact with one another or separated by thin septa of metamorphic or mafic igneous rock or by late aplitic dikes. The granitic rocks are grouped into lithologic units on the basis of composition, texture, and intrusive relations. The units include six new formations , three informal units made up of the rocks in several plutons, and four informal units that include the rocks in single plutons. The new formations are the Inconsolable Granodiorite, Tinemaha Granodiorite, Wheeler Crest Quartz Monzonite, Round Valley Peak Granodiorite, Lamarck Granodiorite, and Tungsten Hills Quartz Monzonite.
California↗
Patterns and origin of radial dike swarms associated with West Spanish Peak and Dike Mountain, south-central Colorado
West Spanish Peak and Dike Mountain in south-central Colorado are stocks which cut Tertiary sedimentary rocks near the axis of the La Veta syncline, the structural trough of the Raton basin. Associated with these stocks are radial dike swarms . The outline of the West Spanish Peak dike swarm is elliptical. The Dike Mountain swarm is more radial , and its outline is oval. Both systems are elongated normal to the axis of the La Veta syncline. The dikes of the West Spanish Peak swarm are of diverse rock types and represent several separate magmatic phases. Those of the Dike Mountain swarm are facies of syenodiorite and probably represent a single phase of magmatic invasion. The dikes occupy vertical joints that have been generally attributed to radial fissuring during doming of the sedimentary rocks by the emplacement of the stocks. Structural studies, however, indicate that several systems of shear and tension joints resulted from intermittent orogenic stresses of varying direction and magnitude during folding of the syncline before invasion of the magmas, and the writer suggests that selective intrusion into this joint complex accounts for the dike patterns .
Colorado↗
Erosion on miniature pediments in badlands national monument, South Dakota
Measurements of erosion on miniature pediments in Badlands National Monument , South Dakota , show that during almost eight years, the pediments were lowered by sheetwash. The adjacent hillslopes have retreated leaving a belt of newly formed pediment from 6 to 12 cm wide at their bases. The hillslopes are rough and relatively permeable; the miniature pediments are smooth and less permeable. Calculations based on the Manning equation suggest that the velocity of overland flow on the pediments may be of the same magnitude as that on the hillslopes. The decrease in roughness from hillslope to pediment compensates for the decrease in slope angle. The pediments are swept free of debris and are regraded by a more effective utilization of runoff energy.
South Dakota↗
Matureland of northern Chile and its relationship to ore deposits
The old surface that extends over a long north-striking belt in northern Chile probably reached the mature stage of erosion by middle Tertiary time. Low areas are mantled by the piedmont deposits of the pampa, and the higher parts exhibit rock decay, oxidation, leaching, and super-gene enrichment of sulfide mineral deposits as a result of deep weathering. The surface and its deposits are deeply eroded south of the main pampa by the Río Copiapó and its tributaries. Numerous ore deposits in the thick secondary zones have not been eroded, but ore deposits are few in the youthful valleys where the primary zones extend to the surface.
northern Chile↗
Seismic evidence for the thickness of Cenozoic deposits in Mono Basin, California
From gravity and limited seismic data obtained in 1957, Pakiser and others (1960) reported a thickness of Cenozoic deposits in the deepest part of Mono Basin, California, of 5.5 ± 1.5 km. Later, in 1962, from a series of chemical explosions in the westernmost part of Mono Basin and outside the limits of the main depressed structure, the thickness of Cenozoic deposits was estimated to be 1.6 km. In 1966, a series of ten 1-ton chemical explosions was detonated in Mono Lake near the deepest part of the Mono Basin structure for the purpose of studying the relative effectiveness of different types of explosives in generating seismic energy. Seismic waves recorded at distances 25.0 to 92.3 km from the explosions were delayed by 1.43 seconds (referred to a shot on bedrock) as they descended through the low-velocity Cenozoic deposits of Mono Basin. By using the velocities of Cenozoic deposits as determined during the 1957 field season, the thickness of Cenozoic deposits required to account for the 1.43-second delay determined in 1966 has been estimated to be about 5 ± 1 km. The delay of seismic waves emerging in Long Valley was less than expected, indicating that they were propagated into Long Valley mainly through high-velocity rocks. From the rate of deposition of Cenozoic rocks in Mono Basin based on the age and depth of burial of the Bishop Tuff, it was estimated that Mono Basin began to subside in early or middle Pliocene time.
California↗
Comparative hydrogeology: An example of its use
As a start toward needed classifications of hydrogeologic settings, a type of setting is described. The setting includes areas where soluble materials are exposed to considerable recharge from precipitation and where both the topographic relief and permeability are inappreciable. Typical areas of this setting are (1) the Black Belt of the Coastal Plain of Alabama and Mississippi, underlain by chalk of the Selma Group, and (2) a 25-sq-mi area near Harrisburg, Cabarrus County, North Carolina, underlain by gabbro in the Piedmont province. Hydrologic conditions that may be inferred and that are easily discernible from this type of setting include: excessive evapotranspiration, low water-table gradient, water table near land surface, thin soils, ground-water movement being almost inappreciable, and the zone of movement being almost limited to a thin zone that includes the contact between the soil and rock, inappreciable ground-water discharge to streams leading, in turn, to a low base flow in streams, low drainage density, and subsurface water relatively high in dissolved mineral matter. Evaluation of the hydrogeologic setting described leads inductively into the undeveloped field of comparative hydrology, which represents a quick useful means of discerning the significance of processes and principles in particular environments. The setting reveals the significance of solution by subsurface water in developing some plains. Comparative hydrology, using the described setting and typical karst settings as examples, allows an advanced analysis of some pertinent factors.
Alabama, Mississippi, North Carolina↗
Faulting in the Burro Mountain area, California Coast Ranges, and its relation to the Nacimiento fault
The northwest-striking Nacimiento fault, in the southern Coast Ranges of California, has generally been regarded as the boundary between two major structural blocks: the Nacimiento block to the southwest, in which the basement rocks belong to the Franciscan Formation (Upper Jurassic to Upper Cretaceous), and the Salinian block to the northeast, in which the basement rocks are granitic and high-grade metamorphic. It has been found, however, that in the Burro Mountain area of the southern Santa Lucia Range, the “Nacimiento” fault of Jennings (1959) is nearly vertical and is within the Nacimiento block. In this area, the Franciscan Formation crops out northeast of the “Nacimiento” fault through windows in an older, low-angle thrust fault that brings the Asuncion Group of Taliaferro (1943) (Upper Cretaceous) over the Franciscan Formation. The fault boundary between the Nacimiento and the Salinian blocks must therefore lie farther to the northeast, where it may be buried beneath the Asuncion Group and younger strata. This conclusion is supported by Hanna's recent aeromagnetic work (1969).
California↗
Peru-Chile Trench sediments and sea-floor spreading
The hypotheses of sea-floor spreading and plate tectonics require the removal of sediment from oceanic trenches either by crustal underthrusting or by folding against the base of a continental or insular margin. Accordingly, over a period of time the volume of sediment removed by way of spreading must be equal to the difference between the observable volume of undeformed terrigenous deposits in a trench and the volume contributed to it by continental erosion. To assess possible sediment loss from the central Chilean segment (23°–44° S.) of the Peru-Chile Trench, we have compared the volume of terrigenous deposits overlying the land, the continental margin, and filling the trench with that expected from continental denudation. Our data indicate that an episode of sediment removal occurred at the base of the margin and adjacent deep-sea floor in Late Cretaceous and perhaps earlymost Tertiary time and may imply spreading. Nearly 100 × 10 3 km 3 of deposits of Tertiary age, chiefly Eocene to Pliocene, have accumulated on the margin, and perhaps an additional 5 × 10 3 km 3 in the trench. This amount of offshore sediment could be supplied by fairly low rates (3 cm/10 3 yrs) of Tertiary erosion. However, many uncertainties in our denudation-sedimentation budget make it impossible to determine whether or not sediment reaching the base of the margin was removed tectonically in Tertiary time. Between 27° and 44° S., the trench contains nearly 70 × 10 s km 3 of turbidite deposits that we believe accumulated during late Cenozoic periods of glacially lowered sea level. The volume of turbidites in the trench is virtually equal to that expected from continental erosion, which is estimated to have probably been no greater than 5 cm/10 3 yr for the arid region between 27° and 31°, and 50 cm/10 3 yr for the humid and partially glaciated region from 36° to 42°. During this time of rapid erosion and trench filling, magnetic data indicate that convergence of lithospheric plates was taking place below the trench at a rate between 5 and 10 cm/yr. If turbidite deposits were swept from the trench at these rates, then continental denudation must have been exceedingly rapid: 20–40 cm/10 3 yr for the arid zone, and 110–165 cm/10 3 yr for the partially glaciated region. If more conventional estimates of erosion are valid, then either (1) late Cenozoic underthrusting has not taken place (or at a rate much slower than that implied by geophysical data), or (2) underthrusting at the prescribed rates has not involved the removal of a significant volume of sediment from the trench.
Antofagasta↗
New evidence for a Pliocene marine embayment along the lower Colorado River area, California and Arizona
Marine foraminiferal, marine to fresh-water molluscan, and brackish- to fresh-water ostracode faunas occur in a thick section of limestone, silt, and clay of the Bouse Formation along the Colorado River from Parker to Yuma in an area now isolated from the sea. Faunas in the Parker-Blythe-Cibola area are limited in number of species but are remarkably persistent through the formation. The presence of marine Foraminifera, including Globigerina sp., is considered evidence that the area was continuously connected with the ocean. Several thousand feet of similar sediments are found in the subsurface near Yuma and contain faunas which at shallow depths are similar to those to the north, but at greater depths contain bathyal assemblages with an abundance of globigerinids, which indicate a post-Miocene age for the section, and oceanic conditions. It is likely that this marine embayment extended into the Imperial Valley, where the Imperial Formation of probable Pliocene age also contains marine faunas. Evidence presented here strongly indicates a large long-lasting Pliocene marine embayment along the lower Colorado River, connected with the Imperial Valley.
Arizona, California↗
Premetamorphic down-to-basin faulting, folding, and tectonic dewatering, Rangeley area, western Maine
The Rangeley area of western Maine is underlain by a thick sequence of dominantly eugeosynclinal metasedimentary rocks of Ordovician, Silurian, and Devonian age. The dominant structural pattern of these rocks is defined by tight, upright, northeast-trending passive flow folds and by three major normal faults along which younger rocks on the southeast are down-faulted against older rocks on the northwest. Each normal fault, together with a major syncline and a complementary anticline farther southeast, defines a geometrically related fault-fold unit. In best-exposed units, displacement along the faults increases in the direction of plunge of the synclines and of increasing structural relief in the syncline-anticline pairs. A genetic relation between normal faulting and folding is inferred. The dominant fault-fold pattern represents the oldest recognized deformation in the area. Slaty or phyllitic cleavage of this deformation is typically subparallel to the axial surfaces of folds, but locally crosses the faults and the axial surfaces of tight folds at low angles. Metamorphosed clastic dikes along the cleavage suggest that cleavage formation was in part a diagenetic dewatering process. This process probably graded, however, into low-grade metamorphism at depth. It was quickly followed by emplacement of large plutons, local superposed passive slip and flexural slip folding, and by two recognized events of greenschist and amphibolite facies metamorphism. Porphyroblasts of these events have grown across slip cleavages as well as older phyllitic cleavage, and metamorphic zones cross the dominant fault-fold pattern. Deformation, as well as sedimentation, is considered to have been controlled by the ancestral Merrimack synclinorium—a strongly linear two-sided trough that persisted at least from Late Ordovician through Early Devonian time. The fault-fold pattern is inferred to have evolved over a long period of time, as follows: (1) Rapid deposition of 15,000 to 20,000 ft of nearly-impermeable clastic sediments in Late Ordovician and Early Silurian time on the southeast-dipping slope of the sedimentary trough; mass weakened in depth by excess fluid pressure. (2) Continuing sedimentation, down-to-basin creep with associated slump faulting and folding, probably beginning in Middle Silurian time; faults flattened basinward in depth along lower boundary of zone of excess fluid pressure. (3) Horizontal compression developed parallel to slide direction as mass piled against material in the trough; incipient slaty cleavage developed normal to compression, improving vertical permeability. (4) Pore fluids expelled vertically, permitting the slumping mass to compact horizontally, and fold with at least 25 percent shortening. The process culminated in Early Devonian time, during and after deposition of the youngest exposed rocks in the area.
Maine↗
Macusanite occurrence, age, and composition, Macusani, Peru
Macusanite, originally believed to be a type of tektite because of its sculpture, is shown to be related to sillar of the Macusani region, Peru. K-Ar measurements establish identical Pliocene ages (4.2 m.y.) for macusanite and sillar and relate these deposits to the extensive ash flows of the southern Andes. These rocks are unique for glassy rocks in that lithium, boron, and arsenic contents are very high; cesium, rubidium, tellurium, fluorine, and tin are higher than normal; zinc, copper, chromium, and zirconium are lower than normal; and high-alumina minerals such as andalusite are present.
Macusani↗
Late Mesozoic-Cenozoic tectonic aspects of the Atlantic Coastal margin
Data from the middle and northern Atlantic Coastal Plain of the United States and continental slope show that the dominant filling of the Atlantic margin geosyncline occurred in pre-latest Cretaceous time with only thin additions of Cenozoic strata. The influx of significant amounts of detrital material into the offshore areas had largely ceased by latest Cretaceous time, was essentially absent in the early Cenozoic, but increased considerably in the Miocene, indicating a rejuvenation of the Appalachian source area. Basin migration continued throughout the Cenozoic, and the Miocene and Eocene strata are used to illustrate the shifting of the loci of deposition. The distributions of the strata indicate that local to regional tectonic movements are responsible. Comparison with the Gulf Coast geosyncline shows that, although features such as sedimentary thickness, evaporites, and volcanic materials are generally similar between the two margins, major differences in time of filling and regional tectonic movements exist.
New Jersey↗
Fossiliferous boulders in the Woods Hollow Shale, Marathon region, Texas: Discussion
No abstract available.
Texas↗