Induced Polarization—A Tool for Mapping Titanium-Bearing Placers, Hidden Metallic Objects, and Urban Waste on and Beneath the Seafloor

Abstract

Recent experiments with a new marine induced polarization (IP) streamer system show that the system is capable of identifying and mapping placer concentrations of titanium-rich minerals on and beneath the seafloor, as well as facies changes in the substrate beneath sandy shoals. Examination of profile data acquired in the Mississippi Sound and Cape Fear shows that the system can also detect ferrous∕non-ferrous metallic objects buried beneath the seafloor which are not discernible by seismic or other geophysical means. The streamer system was originally designed to detect and map polarizeable titanium-bearing placer deposits to at least [Formula: see text] below the sediment-water interface. Recent data show broad phase-shift (a measure of the IP effect) anomalies from titanium sands along the east side of Cat Island (off the coast of Biloxi, Mississippi), and possibly over the now-submerged portion of the PeeDee river on the Atlantic Continental shelf southwest of Cape Fear (North Carolina-South Carolina border). Interspersed in these data are a number of narrow resistivity and coincident resistivity-IP spikes. Both kinds of anomalies show pronounced drops in the already-low resistivity expected for seawater-saturated unconsolidated sediments, but a number of the anomalies also have coincident phase-shift (induced polarization) excursions. These range from less than 5 to over [Formula: see text] across (half-amplitude measurement), but the IP anomalies can be seen [Formula: see text] laterally from their centers. The sources of these anomalies are apparently man-made objects, buried under a veneer of modern sediments. We speculate that the coincident resistivity-IP spikes are caused by shipwrecks, sunken buoys or parts thereof, or other man-made metallic objects lost and later buried beneath inert, modern sediments. The data imply that this marine IP system should be immediately applicable to finding metallic (ferrous and non-ferrous) unexploded ordnance, as well as buried sub-sea cables and pipelines.