Crust of the Earth: A Symposium
Gravity Interpretations from Standard Oceanic and Continental Crustal Sections *
Published:January 01, 1955
From seven continental seismic profiles believed to be the best where gravity and elevation information is also available, and six oceanic seismic stations where gravity data are available, standard continental and sea sections have been determined. Densities of 1.03 for sea water, 2.30 for sediments, and 3.27 for the mantle have been used. The density 2.84 is chosen for crustal rock to make the land and sea columns of equal gravitational attraction from the layer thicknesses determined by these seismic data. The sections obtained are 33 km of crustal rock of density 2.84 overlying the mantle for the standard continental section, and 5 km of sea water, 1 km of sediments, 4½ km of crustal material overlying the mantle for the standard sea column.
Utilizing these standard columns, the Puerto Rico Trench, the great deeps such as the Mindanao Deep, the Gulf Coast geosyncline, and the Bahamas Platform are discussed and their probable structures deduced. It is concluded that the Puerto Rico Trench contains about 6 km of sediments over a standard oceanic crust, that the crustal thickness beneath Puerto Rico is about 25 km, and that the great deeps contain little sediments and probably have been formed by tensional processes. Assuming that the Gulf Coast geosyncline and the Bahamas Platform were formed on an oceanic crust, the base of the Gulf Coast sediments is approximately level at a depth of 12.5 to 15.7 km (41,000 to 51,000 feet) from the shore line to the 100-fathom curve, and the calcareous sediments in the Bahamas are 28.5 km (93,000 feet) thick, with the upper 4.9 km (16,000 feet), observed in the well on Andros Island, laid down in water depths of less than 0.6 km (2000 feet).