Research about Atlantic Ocean, Georges Bank

USGS1982

Stratigraphic reference section for Georges Bank Basin - Depositional model for New England passive margin.

A multichannel seismic reflection profile (U.S. Geological Survey line 19), calibrated with the COST G-1, COST G-2, and Shell Mohican I-100 wells, and seismic-sequence analysis shows that the chronostratigraphic and lithostratigraphic units and depositional history of the Georges Bank basin are similar to those of the Scotian basin. Carbonate rocks of the Iroquois and Abenaki Formations, as much as 16,000 ft (4,800 m) thick, dominated the eastern half of the Georges Bank basin during the Jurassic. As much as 7,500 ft (2,300 m) of the coeval terrigenous clastic deposits of the Mohican, Mohawk, and Mic Mac Formations accumulated updip (westward) in sublittoral, paralic, and nonmarine environments. Siliciclastic deposition, as much as 6,000 ft (1,800 m), dominated the entire basin throughout the Cretaceous and Cenozoic, and it was punctuated briefly by carbonate deposition during the Hauterivian and Paleogene. Tentative correlation between the Georges Bank basin sequences and those of the adjacent, deep North American basin suggests that the deep-sea facies were strongly influenced by depositional events on the shelf. Deposition in both areas has been sensitive to changes in sea level and to paleoclimatic cycles.

Atlantic Ocean, Georges Bank↗

USGS1979

Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean

Velocities were obtained from unreversed, refracted arrivals on analog records from a 48‐channel, 3.6-km hydrophone cable (3.89 km from the airgun array to the last hydrophone array). Approximately 200 records were analyzed along 1500 km of ship track on Georges Bank, northwest Atlantic Ocean, to obtain regional sediment velocity distribution to a depth of 1.4 km below sea level. This technique provides nearly continuous coverage of refraction velocities and vertical velocity gradients. Because of the length of the hydrophone cable and the vertical velocity gradients, the technique is applicable only to the Continental Shelf and the shallower parts of the Continental Slope in water depths less than 300 m. Sediment diagenesis, the influence of overburden pressure on compaction, lithology, density, and porosity are inferred from these data. Velocities of the sediment near the water‐sediment interface range from less than 1500 m/sec on the north edge of Georges Bank to 1830 m/sec for glacial deposits in the northcentral part of the bank. Velocity gradients in the upper 400 m range from 1.0km/sec/km(sec −1 ) on the south edge of the bank to 1.7sec −1 on the north. Minimum gradients of 0.8sec −1 were observed south of Nantucket Island. Velocities and velocity gradients are explained in relation to physical properties of the Cretaceous, Tertiary, and Pleistocene sediments. Isovelocity contours at 100-m/sec intervals are nearly horizontal in the upper 400 m. Isovelocity contours at greater depths show a greater difference from a mean depth because of the greater structural and lithological variation. Bottom densities inferred from the velocities range from 1.7 to 1.9g/cm 3 and porosities range from 48 to 62 percent. The most significant factor controlling velocity distribution on Georges Bank is overburden pressure and resulting compaction. From the velocity data we conclude that Georges Bank has been partially overridden by a continental ice sheet.

Atlantic Ocean, Georges Bank↗