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Full-Text Articles in Physical Sciences and Mathematics
Geochemical Evidence For Suppression Of Pelagic Marine Productivity At The Cretaceous/Tertiary Boundary, James C. Zachos, Michael A. Arthur, Walter E. Dean
Geochemical Evidence For Suppression Of Pelagic Marine Productivity At The Cretaceous/Tertiary Boundary, James C. Zachos, Michael A. Arthur, Walter E. Dean
United States Geological Survey: Staff Publications
The normal, biologically productive ocean is characterized by a gradient of the 13C /12C ratio from surface to deep waters. Here we present stable isotope data from planktonic and benthic microfossils across the Cretaceous/Tertiary boundary in the North pacific, which reveal a rapid and complete breakdown in this biologically mediated gradient. The fluxes of barium (a proxy for organic carbon) and CaCO, also decrease significantly at the time of the major marine plankton extinctions. The implied substantial reduction in oceanic primary productivity persisted for ~0.5 Myr before the carbon isotope gradient was gradually re-established. In addition, the …
Cyclostephanos Lacrimis N. Sp. And Cyclostephanos Guatemalae N. Sp.: Two New Centric Diatoms From The Fossil Record Of Guatemala, Edward Theriot, J. Platt Bradbury
Cyclostephanos Lacrimis N. Sp. And Cyclostephanos Guatemalae N. Sp.: Two New Centric Diatoms From The Fossil Record Of Guatemala, Edward Theriot, J. Platt Bradbury
United States Geological Survey: Staff Publications
Two new species of Cyclostephanos are described from Pleistocene diatomites near Lago de Atitlan, Guatemala. In both species, radiating costae continue un- branched to the valve margin and the external expression of the single labiate process is an elongate pore on the mantle beneath a spine. Cyclostephanos lacrimis n. sp. is 7-75 jum in diameter and has no central area strutted processes. Each mantle strutted process is located within a marginal alveolus directly adjacent to a costa; this unique location is usually visible with light microscopy. C. guatemalae n. sp. is smaller (5-23 μm), with a single eccentrically-located strutted process …
State Of Stress And Modern Deformation Of The Northern Basin And Range Province, Mary Lou Zoback
State Of Stress And Modern Deformation Of The Northern Basin And Range Province, Mary Lou Zoback
United States Geological Survey: Staff Publications
Constraints on the current stress regime of the actively extending northern Basin and Range province are provided by deformation data (focal mechanisms and fault slip studies), hydraulic fracturing in situ stress measurements, borehole elongation ("breakouts") analyses, and alignment of young volcanic vents. The integrated data indicate significant variations both in principal stress orientations and magnitudes. An approximately E-W least principal stress direction appears to characterize both the eastern and western margins of the Basin and Range province, whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented NW to N60 °W. …
The Style Of Late Cenozoic Deformation At The Eastern Front Of The California Coast Ranges, Carl M. Wentworth, Mark D. Zoback
The Style Of Late Cenozoic Deformation At The Eastern Front Of The California Coast Ranges, Carl M. Wentworth, Mark D. Zoback
United States Geological Survey: Staff Publications
The 1983 Coalinga earthquake occurred at the eastern boundary of the California Coast Ranges in response to northeast directed thrusting. Such movements over the past 2 Ma have produced Coalinga anticline by folding above the blind eastern tip of the Coalinga thrust zone. The 600-km length of the Coast Ranges boundary shares a common structural setting that involves westward upturn of Cenozoic and Cretaceou strata at the eastern front of the Coast Ranges and a major, southwest facing step in the basement surface beneath the western Great Valley. Like Coalinga anticline, Pliocene and Quaternary folding and faulting along the rest …
The Uranium-Trend Dating Method: Principles And Application For Southern California Marine Terrace Deposits, Daniel R. Muhs, John N. Rosholt, Charles L. Bush
The Uranium-Trend Dating Method: Principles And Application For Southern California Marine Terrace Deposits, Daniel R. Muhs, John N. Rosholt, Charles L. Bush
United States Geological Survey: Staff Publications
Uranium-trend dating is an open-system method for age estimation of Quaternary sediments, using disequilibrium in the 238U–234U–230Th decay series. The technique has been applied to alluvium, colluvium, loess, till, and marine sediments, in this study we tested the U-trend dating method on calcareous marine terrace deposits from the Palos Verdes Hills and San Nicolas Island, California. Independent age estimates indicate that terraces in these areas range from –80 ka to greater than 1.0 Ma. Two low terraces on San Nicolas Island yielded U-trend plots that have a clustered array of points and the ages of …