Earth Sciences Commons^™

The Fayum Primate Forest Revisited, Thomas M. Bown, Mary Kraus, Scott Wing, John Fleagle, Bruce H. Tiffney, Elwyn Simons, Carl F. Vondra

United States Geological Survey: Staff Publications

In Oligocene times, the Fayum area of northern Egypt was a subtropical to tropical lowland coastal plain with damp soils and seasonal rainfall that supported an abundance and variety of vegetation, including lianes (large vines), tall trees, and possibly mangroves, and a large and varied vertebrate fauna. The Oligocene marine strandline was close by and principal Jebel Qatrani Formation streams were probably brackish several kilometers inland due to tidal incursions. Sediments of the Jebel Qatrani Formation were deposited by several large meandering streams, associated with minor but sometimes extensive flood basin ponds. These rocks provide no evidence for the former …

Aftershocks Of The Coyote Lake, California, Earthquake Of August 6, 1979' A Detailed Study, P. Reasenberg, W. L. Ellsworth

United States Geological Survey: Staff Publications

Aftershock hypocenters and focal mechanism solutions for the Coyote Lake, California, earthquake reveal a geometrically complex fault structure, consisting of multiples lip surfaces. The faulting surface principally consists of two right stepping en echelon, northwest trending, partially overlapping, nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 Parkfield, California, earthquake. The overlap occurs near a prominent bend in the surface trace of the Calaveras fault at San Felipe Lake. Slip during the main rupture, as inferred from the distribution of early aftershocks, appears to have been confined to a 14-km portion of the …

The Distribution Of Natural Fractures And Joints At Depth In Crystalline Rock, Donald A. Seeburger, Mark D. Zoback

United States Geological Survey: Staff Publications

This paper presents the results of studies of the natural fracture distribution encountered in 10 test wells drilled in three areas of the United States. Seven of the wells were drilled to depths of 200-250m, while three were drilled to depths of about 1 km. Using an ultrasonic borehole televiewer, fracture depths, strikes, and dips were determined. Steeply dipping fractures were found throughout each of the wells, and in general, few horizontal fractures were observed. Statistically significant fracture pole concentrations were found for each well which were basically invariant with depth, although some variation of fracture orientation with depth was …

Implications Of An Elastic Analysis Of In Situ Stress Measurements Near The San Andreas Fault, A. Mcgarr, M. D. Zoback, T. C. Hanks

United States Geological Survey: Staff Publications

Twenty-nine measurements of in situ stress obtained with the hydraulic fracturing technique near Palmdale, California, are the basis of an elastic analysis of the state of stress in the Mojave Desert adjacent to the San Andreas fault. The measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km. The elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7.9 MPa/km. Extrapolation yields an average shear stress in the upper 14 km of the …

A Pleistocene Sand Sea On The Alaskan Arctic Coastal Plain, L. David Carter

United States Geological Survey: Staff Publications

A ridge and thermokarst-basin landscape that is strikingly portrayed in Landsat winter imagery consists of large Pleistocene dunes that have been modified by younger eolian activity and thermokarst processes. This is the most extensive area of large stabilized dunes yet reported in the North American Arctic; the landscape is ofparticular interest because it has been proposed as a$rst-order analog for martian fretted terrain. Recognition of the large dunes permits a new interpretation for linear and curvilinear trends visible in Landsat summer imagery.

Late Quaternary Environmental History Of Lake Valencia, Venezuela, J. Platt Bradbury, B. Leyden, M. Salgado-Labouriau, W. M. Lewis Jr., C. Schubert, M. W. Binford, D. G. Frey, D. R. Whitehead, F. H. Weibezahn

United States Geological Survey: Staff Publications

Chemical, paleontological, and mineralogical analyses of a 7.5-meter core from the middle of Lake Valencia, Venezuela, have provided information on the paleoclimatic history of this low-elevation, low-latitude site for the last 13,000 years. The data show that dry climates existed in this region from 13,000 years before present (B.P.) until about 10,000 years B.P. The Lake Valencia Basin was occupied by intermittent saline marshes at that time. About 10,000 years B.P., a permanent lake of fluctuating salinity formed and arboreal plant communities replaced the earlier dominant xeric herbaceous vegetation and marsh plants. By 8500 years B.P., Lake Valencia reached moderate …

Stress Measurements At Depth In The Vicinity Of The San Andreas Fault: Implications For The Magnitude Of Shear Stress At Depth, Mark D. Zoback, Hiroaki Tsukahara, Stephen Hickman

United States Geological Survey: Staff Publications

Using the hydraulic fracturing technique, we have made a systematic series of in situ stress measurements in wells drilled near the San Andreas fault. In an attempt to provide constraints for the magnitude of shear stress on the San Andreas fault at depth we have measured both the variation of stress with distance from the fault in relatively shallow (~230 m) wells and the variation of stress with depth in a ~ 1 km-deep well located 4 km from the fault. The shallow wells are located along profiles roughly perpendicular to the fault in the western Mojave desert near Palmdale …

Actinocyclus Ingens Var. Nodus : A New, Stratigraphically Useful Diatom Of The Circum-North Pacific, Jack G. Baldauf, John A. Barron

United States Geological Survey: Staff Publications

Actinocyclus ingens var, nodus Baldauf, n, var., is a morphologically distinct variety of the Miocene diatom A. ingens Ranray. The last occurrence of this new taxon approximates the top of the lower Middle Miocene Denticula Iauta Zone in the circum-North Pacific. Its first occurrence appears to be in the lower part of the D. fauta zone and possibly lies close to the Lower Miocene-Middle Miocene boundary.

Teleseismic Evidence For A Low-Velocity Body Under The Coso Geothermal Area, P. Reasenberg, W. Ellsworth, A. Walter

United States Geological Survey: Staff Publications

Teleseismic P wave arrivals were recorded by a dense array of seismographs tations located in the Coso geothermal area, California. The resulting pattern of relative residuals reveals an area showing approximately 0.2-s excess travel time that migrates with changing source azimuth, suggesting that the area is the 'delay shadow' produced by a deep, low-velocity body. Inversion of the relative residual data for three-dimensional velocity structure determines the lateral variations in velocity to a depth of 22.5 km beneath the array. An intense low-velocity body, which coincides with the surface expressions of late Pleistocene rhyolitic volcanism, high heat flow, and hydrothermal …

State Of Stress In The Conterminous United States, Mary Lou Zoback, Mark D. Zoback

United States Geological Survey: Staff Publications

Inferring principal stress directions from geologic data, focal mechanisms, and in situ stress measurements, we have prepared a map of principal horizontal stress orientations for the conterminous United States. Stress provinces with linear dimensions which range between 100 and 2000 km were defined on the  basis of the directions and relative magnitude of principal stresses. Within a given province, stress orientations appear quite uniform (usually within the estimated range of accuracy of the different methods used to determine  stress). Available data on the transition in stress direction between the different stress provinces indicate that these transitions can be abrupt, occurring …

Faulting Patterns In North-Central Nevada And Strength Of The Crust, Mary Lou Zoback, Mark D. Zoback

United States Geological Survey: Staff Publications

NNE normal fault trends characterize much of the northern Basin and Range province. These faults make sharp bends to NNW and ENE trends in north- central Nevada in the vicinity of a mid-Miocene rift characterized by a zone of diabase dike swarms, graben-filling flows, and a coinciding aeromagnetic anomaly. Despite a roughly 45 ° change in the least principal stress direction since mid-Miocene time, pre-existing NNW- and ENE-trending faults in the vicinity of the rift accommodated the extension whereas regionally, major crustal blocks were faulted along a NNE trend, approximately perpendicular to the modern least principal stress direction. An assumed …

The Effect Of Dissolution Of Volcanic Glass On The Water Chemistry In A Tuffaceous Aquifer, Rainier Mesa, Nevada, Art F. White, Hans C. Claassen, Larry Benson

United States Geological Survey: Staff Publications

Geochemistry of ground water associated with the Tertiary tuffs within Rainier Mesa, southern Nevada, was investigated to determine the relative importance of glass dissolution in controlling water chemistry. Water samples were obtained both from interstitial pores in core sections and from free-flowing fractures. Cation compositions showed that calcium and magnesium decreased as a function of depth in the mesa, as sodium increased. The maximum effect occurs within alteration zones containing clinoptilolite and montmorillonite, suggesting these minerals effectively remove bivalent cations from the system.

Comparisons are made between compositions of ground waters found within Rainier Mesa that apparently have not reacted …

Uranium Transport In The Walker River Basin, California And Nevada, Larry Benson, D. L. Leach

United States Geological Survey: Staff Publications

During the summer of 1976 waters from tributaries, rivers, springs and wells were sampled in the Walker River Basin. Snow and sediments from selected sites were also sampled. All samples were analyzed for uranium and other elements. The resulting data provide an understanding of the transport of uranium within a closed hydrologic basin as well as providing a basis for the design of geochemical reconnaissance studies for the Basin and Range Province of the Western United States. Spring and tributary data are useful in locating areas containing anomalous concentrations of uranium. However, agricultural practices obscure the presence of known uranium …

Three-Dimensional Crust And Mantle Structure Of Kilauea Volcano, Hawaii, Willam L. Ellsworth, Robert Y. Koyanagi

United States Geological Survey: Staff Publications

Teleseismic P wave arrival times recorded by a dense network of seismograph stations located on Kilauea volcano, Hawaii, are inverted to determine lateral variations in crust and upper mantle structure to a depth of 70 km. The crustal structure is dominated by relatively high velocities within the central summit complex and along the two radial rift zones, compared with the nonrift flank of the volcano. Both the mean crustal velocity contrast between summit and nonrift flank and the distribution of velocities agree well with results from crustal refraction studies. Comparison of the velocity structure with Bouguer gravity anomalies over the …

Review Of The Oligocene Cetacea, Frank C. Whitmore Jr., Albert E. Sanders

United States Geological Survey: Staff Publications

Early in the Oligocene Epoch, Cetacea of the primitive suborder Archaeoceti had already declined sharply from their apparent abundance in Eocene seas. By the beginning of the Miocene, archaeocetes are known to have survived only in the northeast Atlantic and southwest Pacific Oceans. Concurrently with this decline, the first members of the suborders Odontoceti and Mysticeti appeared. They are known from only a few specimens, mostly in upper Oligocene deposits, on both coasts of North America, in Germany, Austria, Italy, the Caucasus, Azerbaijan, Australia, and New Zealand. Two important odontocete genera, Agorophius and Xenorophus, come from beds that are …

The Effect Of Microcrack Dilatancy On The Permeability Of Westerly Granite, Mark D. Zoback, James D. Byerlee

United States Geological Survey: Staff Publications

Permeability and volumetric strain were measured under constant confining pressure and pore pressure as a function of increasing and decreasing differential stress. Permeability was found to increase appreciably during dilatancy. Our results have also shown that permeability and dilatant volume changes are not unique functions of differential stress and that permeability changes with differential stress are not uniquely dependent upon dilatant volume changes. Most significant, however, is that if dilatancy-fluid diffusion occurs in situ, our results indicate that microcrack dilatancy is not a reasonable physical mechanism
to account for such a phenomenon.

The Effect Of Cyclic Differential Stress On Dilatancy In Westerly Granite Under Uniaxial And Triaxial Conditions, Mark D. Zoback, James D. Byerlee

United States Geological Survey: Staff Publications

Laboratory experiments have been performed on samples of Westerly granite in which the differential stress was repeatedly cycled to 85% of the intact sample strength. The experiments have shown that under uniaxial conditions the onset of dilatancy is reduced to fairly low stress; however, under triaxial conditions dilatancy can be an apparently stable process, and the onset of dilatancy is not affected by the repeated cycling. Thus the implication for midcrustal earthquakes is that the onset of dilatancy repeatedly occurs at relatively high stress levels. For example, our results indicate that at typical focal depths of 2.5 and 10 km …

Seismicity Preceding Moderate Earthquakes In California, Robert L. Wesson, William L. Ellsworth

United States Geological Survey: Staff Publications

Regional seismicity data have been examined to determine the nature of seismicity in the years preceding these moderate earthquakes in California: 1952 Kern County (M = 7.7), 1963 Watsonville (M = 5.4), 1964 and 1967 Corralitos (M = 5.0, 5.3), 1966 Parkfield-Cholame (M = 5.1, 5.5), 1968 Borrego Mountain (M = 6.4), 1969 Santa Rosa (M = 5.6, 5.7), and 1971 San Fernando (M = 6.4). In each instance the moderate earthquakes occurred in areas characterized by a relatively high level of small earthquake activity. In most cases the preceding activity in the area immediately surrounding the epicenter was high …

Regional Hydrothermal Alteration Of The Leadville Limestone (Mississippian) Of Central Colorado, L. V. Benson

United States Geological Survey: Staff Publications

Massive metallic-sulfide deposits were implaced in the Leadville Limestone {Mississippian) of Central Colorado less than 70 million years ago. The thermal fluids which precipitated ore at Gilman, Colorado have regionally altered the Leadville Limestone. The sequence of alteration began with the recrystallization of limestone to a dark medium~grained dolomite containing a homogeneous distribution of Fe. This Was followed by partial recrystallization of the medium-grained dolomite to coarse-clear dolomite which contains an inhomogeneous distribution of Fe. The resulting banded rock is known as "zebra rock" . Precipitation of Si0 2 (jasperoid) occurred next. The jaspe=oid formed prior to the deposition of …

Steller's Sea Cow In Pleistocene Interglacial Beach Deposits On Amchitka, Aleutian Isknds, L. M. Gard Jr., G. E. Lewis, Frank C. Whitmore Jr.

United States Geological Survey: Staff Publications

The first discovery of Steller's Sea Cow (Hydrodamalis) in place in Pleistocene deposits has been made in interglacial beach sand and gravel 35 m above present sea level on Amchitka, Aleutian Islands. Uranium series dating of the bone indicates that it is about 135,000 yrs old.

Late Quaternary Eustatic Sea-Level Changes Along The Malibu Coast, Los Angeles County, California, Peter W. Birkeland

United States Geological Survey: Staff Publications

Late Quaternary relative sea-level changes along the Malibu coast can be deciphered by study of geomorphic features and marine and associated stream deposits. Evidence for such changes includes (a) stream downcutting in large valleys during low stands of sea level, (b) stream aggradation in the same valleys during high stands of sea level, and (c) marine shoreline angles whose altitudes coincide with the tops of valley-fill stream deposits. This evidence, and open-system uranium-series dates for shells from the Corral and Dume terrace deposits, provide a time scale for certain sea-level changes. Evidence from other …

Elephant Teeth From The Atlantic Continental Shelf, Frank C. Whitmore Jr., K. O. Emery, H. B. S. Cooke, Donald J. P. Swift

United States Geological Survey: Staff Publications

Teeth of mastodons and mammoths have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, and relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25,000 years.

Panthera Atrox (Mammalia: Felidae) From Central Alaska, Frank C. Whitmore Jr., Helen L. Foster

United States Geological Survey: Staff Publications

A lower jaw of the large Pleistocene cat Panthera atrox (Leidy) was found on an alluvial flat near the mouth of Lost Chicken Creek, about 180 miles northeast of Fairbanks, Alaska. It was probably washed out of carbonaceous silt deposits which, in the adjacent area, have also yielded bones of Equus, Bison, Rangifer, Cervus, and Elephantidae. The Panthera jaw falls within the size range of the series from Rancho La Brea, California, and differs from Rancho La Brea specimens only in a few characteristics. P. atrox appears to have been significantly larger than extinct or …

Miocene Mammals And Central American Seaways, Frank C. Whitmore Jr., Robert H. Stewart

United States Geological Survey: Staff Publications

The fossil mammal faunas of North and South America indicate that the two continents were separated from Paleocene or earlier time until the late Pliocene. Unfortunately our almost complete ignorance of the Tertiary land mammals of Central America, the geology of this large area, makes reconstruction of the Tertiary zoogeography of the region between the continents an exercise involving considerable speculation.

Paleontologic Investigations At Big Bone Lick State Park, Kentucky: A Preliminary Report, C. Bertrand Schultz, Lloyd G. Tanner, Frank C. Whitmore Jr., Louis L. Ray, Ellis C. Crawford

United States Geological Survey: Staff Publications

The Big Bone Lick area in Ketttucky, the first widely known collecting locality for vertebrate fossils in North America is being investigated for further faunal and geologic evidence. Mammal bones, ranging in age from Wisconsin (Tazewell?) to Recent were recovered in 1962 from four different faunal zones in two terrace fills.

Ostracoda Of The Silurian Decker And Manlius Limestones In New Jersey And Eastern New York, Frank M. Swartz, Frank C. Whitmore Jr.

United States Geological Survey: Staff Publications

Descriptions and illustrations are given for 44 ostracode species of the Decker, Rondout and Manlius limestones of the William Nearpass quarries and Dalton Nearpass farm in northwestern New Jersey, and at Austin's Glen and Trilobite Mountain in New York. One brachiopod variety is proposed. The ostracode species are distributed through 11 families and 23 genera. Thirty-two species and one variety are new, and there are eight new genera. Holotype or syntype specimens of 13 of Weller's ostracode species have been restudied and are refigured and redescribed. Stratigraphic sections are described to provide details of the ostracode occurrences, and zonal potentialities …

The Frost-Moved Rubbles Of Jumbo Dome And Their Significance In The Pleistocene Chronology Of Alaska, Clyde Wahrhaftig

United States Geological Survey: Staff Publications

Jumbo Dome, a prominent landmark on the north side of the Alaska Range, is a small body of intrusive andesite surrounded by schist and by poorly consolidated sediments of Tertiary age. Frost-moved rubbles, consisting of coarse andesite blocks, almost completely mantlethe dome and have advanced outward from it across a gently sloping terrain for distances as much as 1 ¼ miles. Several different periods of rubble development are recognized, based on the amount of vegetal covering of the deposits, the preservation of their surface forms, and their degree of erosion by fluvial processes. The rubbles are not now moving and …

Mississippian-Pennsylvanian Boundary Problems In The Rocky Mountain Region, James Steele Williams

United States Geological Survey: Staff Publications

A variety of paleontologic and stratigraphic problems are presented by rocks near the Mississippian- Pennsylvanian boundary in the central and northern Rocky Mountains. Stratigraphic sections of these rocks show diverse interpretations of fundamental concepts of stratigraphy and paleontology. In many places where Upper Mississippian rocks directly underlie Pennsylvanian rocks it is difficult to determine the precise location of the boundary between these units. Formations that straddle the boundary are very useful and satisfactory over large areas. Most geologists use various types of lithologic criteria to distinguish formations, but some appear to rely mainly on faunal data, unconformities, or attempts to …

"Triassic-Jurassic 'Red Beds' Of The Rocky Mountain Region": A Discussion, John B. Reeside Jr.

United States Geological Survey: Staff Publications

The conclusion drawn by Professor E. B. Branson in a recent paper on the "Red Beds" of the Rocky Mountain region that parts of these beds are marine is considered likely. The conclusion that there exists no basis for subdivision of the beds is not accepted, and a division of the Mesozoic part into Lower Triassic, Upper Triassic, and Jurassic units is advocated. The conclusion that no eolian deposits are present likewise is not accepted, and the interpretation of important parts of the Jurassic unit as eolian is advocated. Disagreement is expressed with much of Professor Branson's correlation table, and …

Thomas Chrowder Chamberlin's Contribu-Tions To Glacial Geology, William C. Alden

United States Geological Survey: Staff Publications

So prominent did Thomas Chrowder Chamberlin become in the field of glacial geology that it is a matter of some interest and importance to consider what was the status of the science at the time he turned his attention, as a student and a teacher, to it. So voluminous is the literature of this subject that it is obvious that one cannot in a sketch of this kind give even a general summary of the many books and papers on the subject published in this country, even were it desirable to do so. The intention is to indicate only what …