Digitised seabed and basement reflections from high-resolution Deep Tow sediment profiler records (1972 Galapagos Spreading Centre cruise South Tow leg 6, SOTW06WT)

In an R/V Thomas Washington survey in 1972, South Tow, leg 6 - SOTW06WT, the Scripps Deep Tow vehicle was deployed over the Galapagos Spreading Centre, covering an area 24 X 50 km including the ridge crest. The vehicle was towed close to the seabed at an altitude of only 130 m on average so that the paper records from the Deep Tow 4 kHz sediment profiler have good vertical resolution. The seabed and basement topography are useful for revealing fault escarpments. Also, if deposition of pelagic sediments is not significantly moderated by bottom currents or other mechanisms, their thickness can potentially be useful to date the underlying basement. Such may be true of the Galapagos Spreading Centre in the Panama Basin which lies close to the equatorial high pelagic productivity belt. Cores show the sediment to be a siliceous-calcareous ooze. The seabed and basement reflections were digitised from A4-sized paper copies of the 4 kHz reflection data, each corresponding to roughly a half-hour duration of the survey. The digitised values were interpolated in survey time to provide coincident values (i.e., two-way seismic time to both reflections at fixed survey time intervals). Two-way times were converted to depths using seismic velocities of 1500 and 1553 m/s for seawater and sediments, respectively. Those interpolated depth values were then merged with navigation (see associated Deep Tow vehicle navigation data set under the "Related Data" links on the right and under the "Related Data Sets" tab on the left) to provide profiles of seabed and basement elevations as well as sediment thickness. Depths to the basement and seabed for each file (corresponding to each A4-sized paper copy) were offset vertically so that the seabed depth coincided in a least-squares sense with the bathymetry column in the associated navigation files. Hence, basement and seabed depths are relative to the ocean surface. These files are in ASCII format and include a header line.