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Full-Text Articles in Physical Sciences and Mathematics
The Fayum Primate Forest Revisited, Thomas M. Bown, Mary Kraus, Scott Wing, John Fleagle, Bruce H. Tiffney, Elwyn Simons, Carl F. Vondra
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 …
Permeability, Underpressures, And Convection In The Oceanic Crust Near The Costa Rica Rift, Eastern Equatorial Pacific, Roger N. Anderson, Mark D. Zoback
Permeability, Underpressures, And Convection In The Oceanic Crust Near The Costa Rica Rift, Eastern Equatorial Pacific, Roger N. Anderson, Mark D. Zoback
United States Geological Survey: Staff Publications
In situ permeability and pore pressures were measured 200 m deep beneath the top of the oceanic crust at DSDP site 504B. These measurements have relevance for the transition from convective to conductive heat flow on the south flank of the Costa Rica Rift. Conventional 'slug' and constant rate injection tests were made below a hydraulic packer set at various depths in the hole. The packer was first set in a massive flow unit 37 m below the sediment-basement interface. The bulk permeability of the 172.5m of pillow basalts and basaltic flows below the packer was found to be about …
In Situ Study Of The Physical Mechanisms Controlling Induced Seismicity At Monticello Reservoir, South Carolina, Mark D. Zoback, Stephen Hickman
In Situ Study Of The Physical Mechanisms Controlling Induced Seismicity At Monticello Reservoir, South Carolina, Mark D. Zoback, Stephen Hickman
United States Geological Survey: Staff Publications
In two ~1.1-km-deep wells, the magnitudes of the principal in situ stresses, pore pressure, permeability, and the distribution of faults, fractures, and joints were measured directly in the hypocentral zones of earthquakes induced by impoundment of Monticello Reservoir, South Carolina. Analysis of these data suggests that the earthquakes were caused by an increase in subsurface pore pressure sufficiently large to trigger reverse-type fault motion on preexisting fault planes in a zone of relatively large shear stresses near the surface. The measurements indicated (1) near-critical stress differences for reverse-type fault motion at depths less than 200-300 m, (2) possibly increased pore …
Implications Of An Elastic Analysis Of In Situ Stress Measurements Near The San Andreas Fault, A. Mcgarr, M. D. Zoback, T. C. Hanks
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 …
Threshold Friction Velocities And Rupture Moduli For Crusted Desert Soils For The Input Of Soil Particles Into The Air, Dale A. Gillette, John Adams, Daniel R. Muhs, Rolf Kihl
Threshold Friction Velocities And Rupture Moduli For Crusted Desert Soils For The Input Of Soil Particles Into The Air, Dale A. Gillette, John Adams, Daniel R. Muhs, Rolf Kihl
United States Geological Survey: Staff Publications
Desert soils having clay crusts, mostly from the Mojave Desert, were tested for threshold friction velocity (the friction velocity at which soil erosion begins) with an open-bottomed wind tunnel. The soils were also tested for content of clay, water-soluble material, calcium carbonate, organic material, mineralogy of clay and of salts, soil moisture, modulus of rupture, and crust thickness. If no loose material existed on the soil surface, crusts having modulus of rupture greater than 0.7 bar and crust thickness of 0.7 cm to 0.3 cm were effective in protecting against wind erosion. Disturbed clay crusts having modulus of rupture before …
The Distribution Of Natural Fractures And Joints At Depth In Crystalline Rock, Donald A. Seeburger, Mark D. Zoback
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 …
Uranium-Series Age Of The Eel Point Terrace, San Clemente Island, California, D. R. Muhs, B. J. Szabo
Uranium-Series Age Of The Eel Point Terrace, San Clemente Island, California, D. R. Muhs, B. J. Szabo
United States Geological Survey: Staff Publications
Uranium-series analysis of the coral Allopora californica Verrill from the 2nd, 32-m Eel Point terrace on San Clemente Island, California, has yielded an age of 127,000 ± 7,000 yr. The Eel Point terrace is thus correlative with numerous terrace localities on the southern California mainland, with coral reefs on Barbados and New Guinea dated about 120,000 yr, and with substage 5e of the marine oxygen-isotope record. A tectonic uplift rate of about 0.20 m/1,000 yr has been calculated assuming a sea level slightly higher than the present one at the time of terrace formation. Extrapolation of this uplift rate allows …
Aftershocks Of The Coyote Lake, California, Earthquake Of August 6, 1979' A Detailed Study, P. Reasenberg, W. L. Ellsworth
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 …
New Plesiadapiform Primates From The Eocene Of Wyoming And Montana, Kenneth D. Rose, Thomas M. Bown
New Plesiadapiform Primates From The Eocene Of Wyoming And Montana, Kenneth D. Rose, Thomas M. Bown
United States Geological Survey: Staff Publications
Several recently discovered fossil specimens add to our knowledge of plesiadapiform primates.
Diatom Biostratigraphy And Paleoecology Of The Type Section Of The Luisian Stage, Central California, Jack G. Baldauf, John A. Barron
Diatom Biostratigraphy And Paleoecology Of The Type Section Of The Luisian Stage, Central California, Jack G. Baldauf, John A. Barron
United States Geological Survey: Staff Publications
Diatoms from the type section of the Luisian Stage in central California correlate with the lowermost part of the Denticulopsis lauta Zone through the lower part of subzone "a" of the Denticulopsis hustedtii –D. lauta Zone and are early Middle Miocene in age (about 16.0 to 14.0 Ma}. Rocks assigned to the Luisian Stage by benthic foraminifers elsewhere in California exhibit little diachroneity in terms of diatom biostratigraphy; however, detailed studies of boundaries have not been done. Planktic diatoms dominate the assemblages, although an increase in benthic and tychopelagic diatoms in the overlying Hames Member of the Monterey Formation probably …