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Structure beneath continental shelf, northeastern Gulf of Mexico
Oceanographic Abstracts
1029
of grain deposition from suspension creating lee-face instability and avalanching tending to create a stable face. Avalanching may be intermittent when periods of grain-stacking separate episodes of sliding; or it may be continuous when grains are in sliding motion at all times over all parts of the lee face, depending on the flow speed over the sand wave and the rate of settling on the lee face in relation to the speed of avalanche descent. Each type of avalanching gives the sand wave a distinctive internal sediment structure and vertical grading. This could prove a useful key to regime variability in cross-stratification studies. ANTOINE JOHN W. and JAMESL. HARDING, 1965. Structure beneath continental shelf, northeastern Gulf of Mexico. Bull. Am. Ass. Petrol. Geol., 49 (2): 157Data from 47 reversed seismic refraction profiles in the northeastern Gulf of Mexico are presented in the form of four east-west and two north-south cross sections. Where possible, correlations are drawn between velocity layers encountered offshore and well data from various oil wells drilled on the Florida mainland. The Peninsular arch of Florida is shown to exhibit a lobe-like extension on its western limb, affecting the attitude of the pre-Cretaceous basement rocks. Under the eastern part of the extreme northeastern Gulf o f Mexico, interpretation of the seismic records is complicated by the presence of strata with lower seismic velocities than the material above. Evidence is presented that these strata lie somewhere near the top o f t h e Upper Cretaceous. The subsurface geology beneath the continental shelf in this area generally parallels that of northern Florida, exhibiting the lateral dual facies relationship of clastic sediments in the west grading to carbonates in the east. Evidence points to the possible existence of scattered reefal deposits in the Upper Cretaceous along the extrapolated axis of the Suwannee strait. ANTOINE JOHN W. and VERNON J. HENRY, JR., 1965. Seismic refraction study of shallow part of the continental shelf off Georgia coast. Bull. Am. Ass. Petrol. Geol., 49 (5) : 601-609. In December, 1962, personnel front Texas A. & M. University's Department of Oceanography and Meteorology and the University of Georgia Marine Institute shot nine reversed seismic refraction profiles over the shallow part of the continental shelf off the Georgia coast. These profiles were located to rnap refracting horizons underlying the submerged coastal plain and to correlate with earlier profiles in deeper water farther east shot in 1955 by groups front Woods Hole Oceanographic Institute and Lamont Geological Observatory. On all nine profiles, four distinct and apparently continuous layers were noted which, based on their depth, attitude, and velocity, are concluded to represent: 1) a layer a few feet beneath the sea bottom, probably Miocene in age; 2) the Oligocene; 3) the early Eocene: and 4) the pre-Cretaceous basement surface. Structural contours on the Oligocene and Eocene refractors indicate the eastern boundary of the Atlantic embayment of Georgia. This feature was open toward the southeast in Oligocene time and toward the south in Eocene time. It is concluded also that the layer originally reported by the Woods Hole Oceanographic Institute to represent the Late Cretaceous is Oligocene or late Eocene in age. ARRHENIUS G., J. MERO and J. KORKISCH, 1964. Origin of oceanic manganese minerals. Science, N. Y., 144 (3615): 170-172. A criterion is suggested for discrimination between ferromanganese oxide minerals, deposited after the introduction o f manganese and associated elements in sea water solution at submarine vulcanism, and minerals which are slowly formed from dilute solution, largely of continental origin. The simultaneous injection of thorium into the ocean by submarine vulcanism is indicated, and its differentiation from continental thorium introduced into the ocean by runoff is discussed. ARTEMENKO N. P., 1963. Damping of oscillations of the magnetic system of BPV-2 current meters. (In Russian). Trudy arkt. nauchnc-issled. Inst., No. 254:40-42 (Abstracted in: Soriet-Bloc Res., Geophys., Astron. Space. 94: 95). Analysis of observations and the result of processing data obtained with BPV-2 and BPV-2p automatic current meters during measurement of sea currents show that when there are high waves the considerable errors in measurement of current direction are caused by oscillations of the magnetic systems and '" yaw " of the instruments. Two types of devices for the damping of the mechanical oscillations of the compass cards of the automatic meters are discussed. The principle of operation of the damping device developed by V. G. Oshmarinova involves a decrease of the oscillations through the magnetic effect of an additional damping indicator with a limited amplitude of oscillations due to the retarding effect of a fluid. It is shown that this design serves as a source of additional deviation errors of a semicircular character. In addition, there are errors, caused by the effect of forces of inertia of the instrument compass card, disturbed by the damping device. In the damping device devised by Yu. K. Alekseyev the system utilizes frictional forces which increase the period of the natural oscillations of the compass card by several times. The shortcoming of the device is that it lowers the sensitivity of the compass card and an increase of its magnetic stagnation, which leads to a considerable measurement error. It is recommended that the damper be filled with a viscous paste, of different viscosity for different latitudes, directly at the work stations, and selection be made of an interval of exposure corresponding to the maximum off-duty factor of the instrument.
1029
of grain deposition from suspension creating lee-face instability and avalanching tending to create a stable face. Avalanching may be intermittent when periods of grain-stacking separate episodes of sliding; or it may be continuous when grains are in sliding motion at all times over all parts of the lee face, depending on the flow speed over the sand wave and the rate of settling on the lee face in relation to the speed of avalanche descent. Each type of avalanching gives the sand wave a distinctive internal sediment structure and vertical grading. This could prove a useful key to regime variability in cross-stratification studies. ANTOINE JOHN W. and JAMESL. HARDING, 1965. Structure beneath continental shelf, northeastern Gulf of Mexico. Bull. Am. Ass. Petrol. Geol., 49 (2): 157Data from 47 reversed seismic refraction profiles in the northeastern Gulf of Mexico are presented in the form of four east-west and two north-south cross sections. Where possible, correlations are drawn between velocity layers encountered offshore and well data from various oil wells drilled on the Florida mainland. The Peninsular arch of Florida is shown to exhibit a lobe-like extension on its western limb, affecting the attitude of the pre-Cretaceous basement rocks. Under the eastern part of the extreme northeastern Gulf o f Mexico, interpretation of the seismic records is complicated by the presence of strata with lower seismic velocities than the material above. Evidence is presented that these strata lie somewhere near the top o f t h e Upper Cretaceous. The subsurface geology beneath the continental shelf in this area generally parallels that of northern Florida, exhibiting the lateral dual facies relationship of clastic sediments in the west grading to carbonates in the east. Evidence points to the possible existence of scattered reefal deposits in the Upper Cretaceous along the extrapolated axis of the Suwannee strait. ANTOINE JOHN W. and VERNON J. HENRY, JR., 1965. Seismic refraction study of shallow part of the continental shelf off Georgia coast. Bull. Am. Ass. Petrol. Geol., 49 (5) : 601-609. In December, 1962, personnel front Texas A. & M. University's Department of Oceanography and Meteorology and the University of Georgia Marine Institute shot nine reversed seismic refraction profiles over the shallow part of the continental shelf off the Georgia coast. These profiles were located to rnap refracting horizons underlying the submerged coastal plain and to correlate with earlier profiles in deeper water farther east shot in 1955 by groups front Woods Hole Oceanographic Institute and Lamont Geological Observatory. On all nine profiles, four distinct and apparently continuous layers were noted which, based on their depth, attitude, and velocity, are concluded to represent: 1) a layer a few feet beneath the sea bottom, probably Miocene in age; 2) the Oligocene; 3) the early Eocene: and 4) the pre-Cretaceous basement surface. Structural contours on the Oligocene and Eocene refractors indicate the eastern boundary of the Atlantic embayment of Georgia. This feature was open toward the southeast in Oligocene time and toward the south in Eocene time. It is concluded also that the layer originally reported by the Woods Hole Oceanographic Institute to represent the Late Cretaceous is Oligocene or late Eocene in age. ARRHENIUS G., J. MERO and J. KORKISCH, 1964. Origin of oceanic manganese minerals. Science, N. Y., 144 (3615): 170-172. A criterion is suggested for discrimination between ferromanganese oxide minerals, deposited after the introduction o f manganese and associated elements in sea water solution at submarine vulcanism, and minerals which are slowly formed from dilute solution, largely of continental origin. The simultaneous injection of thorium into the ocean by submarine vulcanism is indicated, and its differentiation from continental thorium introduced into the ocean by runoff is discussed. ARTEMENKO N. P., 1963. Damping of oscillations of the magnetic system of BPV-2 current meters. (In Russian). Trudy arkt. nauchnc-issled. Inst., No. 254:40-42 (Abstracted in: Soriet-Bloc Res., Geophys., Astron. Space. 94: 95). Analysis of observations and the result of processing data obtained with BPV-2 and BPV-2p automatic current meters during measurement of sea currents show that when there are high waves the considerable errors in measurement of current direction are caused by oscillations of the magnetic systems and '" yaw " of the instruments. Two types of devices for the damping of the mechanical oscillations of the compass cards of the automatic meters are discussed. The principle of operation of the damping device developed by V. G. Oshmarinova involves a decrease of the oscillations through the magnetic effect of an additional damping indicator with a limited amplitude of oscillations due to the retarding effect of a fluid. It is shown that this design serves as a source of additional deviation errors of a semicircular character. In addition, there are errors, caused by the effect of forces of inertia of the instrument compass card, disturbed by the damping device. In the damping device devised by Yu. K. Alekseyev the system utilizes frictional forces which increase the period of the natural oscillations of the compass card by several times. The shortcoming of the device is that it lowers the sensitivity of the compass card and an increase of its magnetic stagnation, which leads to a considerable measurement error. It is recommended that the damper be filled with a viscous paste, of different viscosity for different latitudes, directly at the work stations, and selection be made of an interval of exposure corresponding to the maximum off-duty factor of the instrument.