Figure 1 portrays sediment thickness on the ocean floor in the Northeast Pacific. The very generalized contours show the total thickness of sediments, in kilometers, from the sea floor to the top of basaltic basement.
Except for detailed maps of small areas, sediment thickness maps necessarily must generalize and average local variations in thickness. The abyssal hill topography created during accretion of normal oceanic crust generally has local relief on the order of 100 m over distances of 10 to 20 km, and sediments do not accumulate evenly over this initial relief, even in regions of purely pelagic sedimentation (Fig. 2). In areas of pronounced basement relief— for example, along fracture zones and around seamounts and submarine ridges—local thickness variations can assume extreme values. The contours in Figure 1 are meant to depict typical values; no attempt is made to show small-scale local variations.
Over most of the map area, the thickness depicted is to the top of normal oceanic basaltic crust, but in some areas, strongly reflective chert layers and midplate volcanic rocks mask the oceanic basement on reflection records, and the thickness shown is what is discernible on seismic profiles.
Figures & Tables
This new synthesis includes a section on plate kinematics, documenting the basis for a new interpretation of the magnetic anomaly patterns. It also includes: six chapters on various aspects of tectonics, petrologic characteristics, and hydrothermal processes of active ridges from the Galapagos Rift to the Juan de Fuca Ridge; a section on mid-plate volcanism, including the Hawaii-Emperor chain; five chapters on various aspects of northeastern Pacific sedimentary regimes; and nine chapters on the geology of the Pacific continental margin from the Aleutians to Guatemala, seen from the perspective of marine geology. Three separate oversize plates illustrate the bathymetry of the northeast Pacific; two more on the same base show distribution of sediment samples and types and magnetic anomaly data and tectonic interpretations; and others include a synthesis of the geology and bathymetry of the Hawaiian Islands, details of bathymetry along parts of the East Pacific Rise, and a major seismic profile across the Pacific margin of Guatemala.