Foraminiferal and sedimentological evidence far uplift of the deep-sea floor, Gorda Rise, northeastern Pacific

Displaced benthic Foraminifera in semiconsolidated clayey sandstone from the Gorda Rise provide evidence for uplift of the deep-sea floor. The sediment was deposited by turbidity currents on the floor of the Escanaba Trough (the axial valley of the Gorda Rise) from a sublittoral source on the continental margin to the east...

A high-resolution sub-bottom profiling system for use in ocean basin

A new high-frequency (3.5-kHz) sub-bottom profiling system is capable of relatively deep penetration into sedimentary deposits, with good resolution of thin reflecting layers. This system has been operated at cruising speeds up to 11 knots and gives up to 0.15 seconds of penetration...

EC00-2540 Field Records for Restricted Use Pesticide Applications and Integrated Crop Management by Private Applicators

Private applicators must record their restricted use pesticide (RUP) applications, as required by the Food, Agriculture, Conservation and Trade (FACT) Act of 1990. The USDA Agricultural Marketing Service administers this activity. In Nebraska, RUP application records must be maintained for three years from the date of application. The certified pesticide applicator should retain these RUP records, but must be able to make them accessible for copying by authorized representatives. This booklet is a suggested guide for preliminary or final RUP application records

Oregon Subduction Zone: Venting, Fauna, and Carbonates

Transects of the submersible Alvin across rock outcrops in the Oregon subduction zone have furnished information on the structural and stratigraphic framework of this accretionary complex. Communities of clams and tube worms, and authigenic carbonate mineral precipitates, are associated with venting sites of cool fluids located on a fault-bend anticline at a water depth of 2036 meters. The distribution of animals and carbonates suggests up-dip migration of fluids from both shallow and deep sources along permeable strata or fault zones within these clastic deposits. Methane is enriched in the water column over one vent site, and carbonate minerals and animal tissues are highly enriched in carbon-12. The animals use methane as an energy and food source in symbiosis with microorganisms. Oxidized methane is also the carbon source for the authigenic carbonates that cement the sediments of the accretionary complex. The animal communities and carbonates observed in the Oregon subduction zone occur in strata as old as 2.0 million years and provide criteria for identifying other localities where modern and ancient accreted deposits have vented methane, hydrocarbons, and other nutrient-bearing fluids

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska

A sequence of ash layers recovered from site 178 of the Deep Sea Drilling Project in the Gulf of Alaska was studied to determine the nature of highly explosive volcanic eruptions associated with the Aleutian Arc and Alaskan Peninsula during the last 8 m.y. The major-element chemistry of 25 distinct ash layers was determined. When the analyses are plotted on conventional major-element variation diagrams, the unusual, highly evolved, calc-alkalic characteristics of the ashes are apparent. Perhaps more significantly, there is a good correlation of certain indices of the degree of chemical evolution of each ash (SiO2 content and Larsen index) with sample age. Both parameters vary cyclically, with maximum values of both indices occurring at present, 2.5, and about 5.0 m.y. ago. The cause of the cyclic activity, as well as discontinuous volcanic activity reported for other areas by other investigators, is not precisely known. However, we suggest that variable rates of subduction provide a viable hypothesis for discontinuous volcanic activity associated with convergent plate boundaries

Structure of the frontal part of the Andean Convergent Margin

A multichannel seismic reflection record across the central Peru margin and trench was improved by processing 24 rather than the 12 channels previously processed and by thorough migrating to reject the strong diffractions that obscured weaker primary reflections. The increased resolution clarifies the structure of the 15‐km‐wide frontal accretionary complex and the adjacent truncated continental framework against which the trench sediment was imbricated. Resolved are individual thrust slices and packets adjacent to the trench axis, subducting sediment‐filled graben in the ocean crust beneath the lower slope, and a Tertiary stratigraphic section of the upper slope Yaquina Basin which is cut by normal faults. The resolution in this multichannel record provides criteria for reinterpreting single‐channel data off Chile with increased confidence. The previously proposed truncation of the South American continent along much of the Peru‐Chile Trench is confirmed and the development of an accretionary complex in front of the truncated continental crust appears to vary with the amount of sediment seen in the trench axis. The Andean margin frontal structure is similar to that off Central America, the Aleutian Trench, and the Japan Trench which suggests common truncation as well as accretion at the front of convergent margins

Coastal upwelling and a history of organic-rich mudstone deposition off Peru

he present-day upwelling circulation off Peru, the regional pattern of organic matter in surface sediments and the stable carbon isotope characteristics of Neogene and Quaternary carbonate lithologies suggest a unique feedback mechanism in continental margin deposition and subsequent alteration after burial. In such a scenario, the high bioproductivity, the position of a poleward flowing undercurrent and the rate of subsidence of margin basins appear to be the principal variables controlling this mechanism. Transfer of organic matter from the sea surface to the sea floor is particularly efficient in the upwelling ecosystem off Peru. Preservation and burial are enhanced by high bulk sedimentation rates along the upper continental slope (between 11°–15°S) at depths where the subsurface current velocities decrease below those normally associated with the poleward flow. Burial and preservation are diminished, however, where shallow water depths promote continuous reworking of the bottom sediments by onshore flows and alongshore water movement (between 6°–10°S). The resulting sedimentary facies are distinctly different from each other in that the former process yields an organic-rich (> 5 wt % Corg) and the latter process yields a calcareous (> 15 wt % CaCo3) mud facies. The bulk sediment accumulation and individual component fluxes are estimated for both portions of the margin situated between 6° and 15°S latitude and lying in < 500 m of water depth. Furthermore, the chemical environment of organic-matter decomposition in the rapidly accumulating carbonate-poor facies is dominated by microbial fermentation and methanogenesis, whereas, the muds containing lesser amounts of organic matter are dominated by microbial sulphate reduction. These differences in facies composition persist throughout the subsequent stages of compaction and diagenesis. Most prominent among these is the formation of ‘organic’ dolomites with distinctly different isotopic signatures and mineral assemblages. The original upwelling facies (i.e., organic-rich muds or calcareous muds), the extent of reworking by subsurface currents, and the subsidence history of the margin basins may be inferred from these sedimentary signatures

Sediment Sources and Dispersal Patterns of Oregon Continental Shelf Sands

Heavy mineral analysis of the rivers of Oregon and northern California has been used to outline four major sources of sediments on the Oregon continental shelf. These sources include the Columbia River Basin, the Oregon Coast Range, the Klamath-Siskiyou Mountains, and terrace deposits along the central Oregon coast. Dispersal patterns of sand-size sediments show that the dominant direction of littoral transport has been to the north at least during the past 18,000 years. Sands were transported 170 miles to the north on the continental shelf during the end of the Late Wisconsin regression and the beginning of the Early Holocene transgression. The observed dispersal patterns of heavy minerals may be indicative of more efficient littoral processes during the last major sea level lowering. Reduction of sand supply to the littoral zone and natural obstacles, such as erosionally resistant headlands, to the littoral transport of sand have apparently limited the northward transport of sand during the past 3,000 years