Bunce Elizabeth T.

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Bunce
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Elizabeth T.
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Technical Report

Structure of the western Somali Basin

1967-07 , Bunce, Elizabeth T. , Langseth, Marcus G. , Chase, R. L. , Ewing, W. Maurice

The western Somali Basin in the northwestern Indian Ocean is covered by thick deposits of terrigenous sediments. Seismic reflection profiles show, however, the northern and southern parts to be very different. The northern sections is a deep basin filled with thick uniformly stratified sediments. It is enclosed by the continental margin to the west and north, Chain ridge to the east, and shallow basement structure to the south. A change in depth of basement occurs along an approximately east-west line at latitude 3°30'N very near the southern end of Chain ridge. In the southern portion of the basin the basement is shallow, and, immediately south of latitude 3°30'N, it has high relief. Stratified flat-lying sediments fill the basement depressions, and isolated hills formed of basement material rise above the abyssal plain deposits. Farther to the south the abyssal plain becomes very narrow. Gabbro dredged from the southeast slope of Chain ridge has been dated by the potassium-argon method as 89.6 ± 4.5 m.y., which should be considered a minimum age. The evidence suggests that the entire sediment sequence of the northern basin was deposited subsequent to the formation of the ridge. The thin sediment cover of the southern portion of the basin is probably no older than Tertiary.

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Technical Report

Assessment of seabed seismic systems

1980-04 , Bunce, Elizabeth T.

This project was initiated to accomplish the necessary research and documentation of existing seismic techniques and systems for the study of sediments and sedimentary structures in the oceans. In this respect , it is an 'inventory' of methods and techniques for looking at small-scale features or changes in structures lying from 10 to 1000 m beneath the sea floor. It attempts to assess the vertical and lateral resolution capabilities of existing and technically feasible seismic systems. Some of the questions posed are: how closely can we determine vertical variation such as sediment layer thickness and vertical variation with depth; also lateral coherence or its disruption by such agents as facies changes, thinning or thickening, slumping, faulting; the nature of the basement structure, its areal coherence, velocity structure and associated anomalies?

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Technical Report

Identification of generic study areas for the disposal of low level radioactive waste : western North Atlantic Ocean

1979-07 , Hollister, Charles D. , Bunce, Elizabeth T. , Chandler, Richard S.

There is a growing need to effectively dispose of the low level radioactive waste presently accumulating in the United States. It may be decided to "dump" radioactive contamination products onto the deep sea floor (within 200 miles of the U.S.) in accordance with present IAEA guidelines (see Appendix A) for ocean dumping of low level waste; in the event of such a decision suitable areas must be identified and carefully studied to determine the subsequent influence of the waste on the environment. Using the site suitability criteria mentioned above we have identified two areas of possible use for low level waste disposal, one north of Puerto Rico and one east of Cape Hatteras, as deserving further study. The following report describes the relevant physical and geological characteristics of these two areas that may be important in considering a dumping operation. We have also made some recommendations for confirmatory research. The Hatteras Abyssal Plain, lying close to the 200 mile limit, appears to be a viable region for the focus of future research efforts.

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Technical Report

Narrative of CHAIN cruise #36 : Woods Hole to the Outer Ridge north of Puerto Rico and the Barracuda Fault east of the Lesser Antilles, and back, 4 June - 10 July, 1963

1964-06 , Bunce, Elizabeth T.

This narrative report of CHAIN Cruise 36 includes the chief scientist's journal, a summary track chart, and a log of stations occupied. The cruise was made in two parts : the first, to the Outer Ridge north of Puerto Rico for seismic reflection and refraction work with ATLANTIS II, and the second from the Outer Ridge to the area of the Barracuda Fault east of the Lesser Antilles for bathymetric and gravity surveys and a detailed geophysical study of the area between 16° and 17 °N and 57 ° and 59 °W. The scientific program included echo sounding, continuous seismic reflection profiling, seismic refraction profiles , gravity measurements, dredging, bottom photography, and heat flow measurements.

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Working Paper

Cruise plans for R/V Chain cruise #43 : Indian Ocean expedition

1964-01 , Bunce, Elizabeth T.

The proposed cruise of R/V CHAIN to the Indian Ocean will take place from February to June 1964. Following the Indian Ocean section of the cruise, R/V CHAIN will proceed to the Mediterranean Sea and will do further work in this area. The latter program will be covered in a separate cruise plan. The background and objectives of the scientific program in the Indian Ocean are detailed in the research proposal submitted to the National Science Foundation, found in Appendix A.

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Technical Report

Narrative of Chain cruise #17, phase I : St. George, Bermuda, to Freetown, Sierra Leone, 19 February - 22 March 1961

1964-06 , Voorhis, Arthur D. , Bunce, Elizabeth T.

The journal of a cruise of R/V CHAIN from Bermuda to Freetown, Sierra Leone during February and March, 1961, is the basis of this report. Location of observations are given. The portion of the Mid- Atlantic Ridge lying along the equator was surveyed from 10° to 19°W, and new information concerning the slope and orientation of rift zones was obtained. A detailed bathymetric survey of the Romanche Trench was made. A continuous temperature-depth profile, from the surface to 100 meters, was made along the ship 's track with a thermistor chain. Surface shear was measured with pitotmeters mounted on the chain (surface water velocity relative to the water velocity at the depth of the pitotmeter), to determine the strength and direction of the equatorial undercurrent.

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Technical Report

Abyssal sediment waves in the Amirante Passage, western Indian Ocean

1977-02 , Johnson, David A. , Bunce, Elizabeth T.

The deep western boundary current (DWBC) of the Indian Ocean flows northward along the western margin of the Mascarene Basin, and is funneled through a narrow passage (near 09°S, 52°E) prior to entering the Somali Basin to the north. Recently completed geological and geophysical operations within this passage reveal the presence of fields of well-developed abyssal sediment waves, with amplitudes of 10 to 50 meters and wavelengths of hundreds of meters to ~1 km. The two principal fields of sediment waves are confined to the flanks of the passages, and are restricted to a narrow depth interval (~3950 to 4150 meters). Individual waves appear to be elongated parallel to the passage axis and the presumed flow direction of the DWBC. The waves are relatively transparent to low-frequency echo sounding (3.5 kHz) and seismic profiling (17-70Hz), although weak internal reflectors are present within individual waves. These reflectors are conformable with the overlying sea floor, thereby suggesting neither upslope nor downslope migration of the waves. The sediment comprising the waves is a well-sorted calcareous ooze dominated by fine silt components (principally coccoliths), in marked contrast to the heterogeneous biogenic ooze on the adjacent channel floor. The lithology and local distribution pattern of the waves suggest that they are constructional bedforms associated with the flow of the DWBC, and not slump structures. A deep hydrocast at the sill of the channel indicates a near-bottom layer of Antarctic Bottom Water (Θ <0.9°C) approximately 200 meters thick, whose depth range corresponds with that of the sediment waves. Interpretations of the origin of the sediment waves in terms of the local flow regime will require (1) a more precise description of the physiography and structure of individual sediment waves; and (2) closely-spaced measurements of the nearbottom velocity structure of the DWBC within regions of the passage where sediment waves are apparently forming.

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Technical Report

Narrative of Chain cruise #43 : February - August 1964

1965-02 , Knott, Sydney T. , Bunce, Elizabeth T. , Bowin, Carl O. , Hersey, J. B. , Chase, R. L.

On CHAIN Cruise 43, 15 February to 21 August 1964, geophysical and geological observations were made in the North Atlantic Ocean, the Mediterranean and Red Seas, and the Western part of the Indian Ocean, along the track Woods Hole - Ceuta (Spanish Africa) - La Spezia - Port Said - Aden - Victoria (Seychelles Islands) - Port Louis (Mauritius) - Victoria (Seychelles Islands) - Port Said - Beirut - La Spezia - Monaco - Plymouth (England) - Woods Hole. This report contains (1) a narrative of the cruise, (2) a list of stations, (3) statements of the scientific objectives of the cruise, (4) a summary of the geological and geophysical observations, (5) end-of-cruise reports on equipment and some phases of the research program, and (6) a selection of bottom photographs. WHOI Ref. No. 64-51 contains a detailed navigational plot of the entire cruise, including soundings and the locations of other observations.

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