Gravity Interpretation Along Seismic Refraction Lines Surveyed Near The Canadian Ice Island During 1985

Author : George A. McCalpine
Publisher :
ISBN 13 :
Total Pages : 4 pages
Book Rating : 4.:/5 (936 download)

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Download or read book Report on Gravity Survey written by George A. McCalpine and published by . This book was released on 1972 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: "INTRODUCTION. This report presents the results of the gravity survey performed by Kenting Earth Sciences for Sun Oil Company between June 2, 1971, and June 12, 1971, in an area northwest of Cameron Island, in the Canadian Arctic. A total of 170 new stations, 32 base checks, and 9 repeat stations were occupied on a series of lines 6 kilometers apart and oriented approximately N 20° W - S 20° E. The station spacing along the lines is 2 kilometers. The purpose of the survey in this area was to obtain information on some CIGOL [Canadian Industrial Gas and Oil Ltd.] and surrounding acreage in a position that regionally appeared to be north of the Parry Islands Fold Belt and along the southern flank of the expected thickening into the Sverdrup Basin. METHOD OF SURVEY. The gravity data in this area were obtained using conventional land gravity meters of the Worden type, levelled and read on the surface of the inter-island ice. Positioning was obtained using the Motorola RPS system with transponders set at known triangulation points. Water depths were obtained using an EDO Echo Sounder, which was regularly checked at a position where the water depth had been established by sounding through a hole in the ice with a weighted line. All the equipment was transported from station location to station location by helicopter, where the gravity meter and echo sounder were read on the ice surface, while the Motorola antenna beneath the helicopter received range-range information from the transponder locations. Under good conditions successive locations can be occupied at eight- to fifteen-minute intervals. Base checks at government-established bases or at other locations specifically set for the survey area and tied to the government network were made generally at three- to four-hour intervals. DISCUSSION OF RESULTS. Two maps are included with this report and cover that portion of the Canadian Arctic between lat. 76° and 77° N and long. 104° and 108° W. This map area is designated 79A in the Canadian National Topographic System. Map No. 1 shows bathymetric contours at a 50-foot interval in the area of the detailed survey and at a 100-foot interval over the rest of the map area where control is limited to the widely-spaced government locations. In the area of the detailed survey, the bottom topography is dominated by a westerly-trending high from Cameron Island to about long. 106° 30' W, where it intersects a north-south high which continues off the map to the north. Because of these highs, most of the water depths in the survey area were less than 600 feet, in contrast to the areas of much deeper water in the rest of the map area. Map No. 2 is the Bouguer Gravity Map of the area, based on both the detailed and government-obtained gravity. A density of 2.2 was used for the bottom sediments in making the Bouguer reduction. This value was determined experimentally by studying the gravity-bathymetry relationships, and appears to remove successfully the effects of bottom topography. Individual instances of correlation between questionable gravity values and water depths may result from narrow channeling in the bottom, which could be properly corrected only by some additional terrain-correction calculations, which would require more detailed bathymetric control than is available. The gravity field in this area consists of several large closures separated by a northeast-southwest-trending gradient area which roughly parallels the edge of the Sverdrup Basin. The large closures are of the type generally considered intrabasement or regional and probably do not represent sedimentary deformation. The most significant anomaly disclosed by the survey is shown circled in green on the Bouguer Gravity Map. This anomaly has dimensions of 15 x 10 miles and a gravity relief in excess of 3 milligals. Because of the orientation of its longer axis, it possibly represents a fold parallel to the basin edge. The dashed green lines show gravity effects which correlate fr om line to line but have amplitudes of a milligal or less. Aeromagnetic control in this area shows similar features with magnetic relief of 5 to 20 gammas. These have been tentatively identified as dykes but may also indicate the location of faults. RECOMMENDATIONS. Seismic control would be desirable over the circled anomaly to establish the significance of this type of gravity feature along the southern margin of the Sverdrup Basin" -- ASTIS[online] database.