Buried paleo-channels on the New Jersey continental margin: channel porosity structures from electromagnetic surveying

We report on a marine electromagnetic (EM) survey across two portions of th e New Jersey continental margin that have been previously shown to contain buried paleo-channels, The EM method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place poros ity constraints on the nature of the channel infill and the contrast in phy sical properties across the channel boundaries. Our data show that a key co ndition for the channels to have an electrical signature is that they incis e an underlying regional unconformity, R, thought to represent a subaeriall y eroded surface, exposed during the late Wisconsinan glaciation. Channels that cut R are seen through increases in apparent porosity. Another seismic ally imaged channel sequence, which lies within the outer-shelf sediment we dge sequence above R, does not have an electrical signature, indicating tha t the sediments above and below the channel boundaries have similar physica l properties. (C) 2000 Elsevier Science B.V. All rights reserved.