'Columbia University Libraries/Information Services'
Doi
Abstract
The emergence of seismic/sequence stratigraphy since the late 1970s has led to a revolution in stratigraphy and a renewal of interest in the stratigraphic response to eustasy. Two arguments were advanced in support of the eustatic interpretation. One involved widespread seismic evidence for the existence of regional unconformities (sequence boundaries) characterized by apparently abrupt basinward shifts in onlap, which were interpreted to imply relatively rapid falls of sea level with amplitudes of up to several hundred meters. The second was based on the purported global synchroneity of these unconformities, which, if correct, would be difficult to explain by other than a eustatic mechanism. The primary goals of Leg 174A are the following: 1. To date as precisely as possible sequence boundaries of Oligocene—Pleistocene age, and to compare this stratigraphic record with the timing of glacial-eustatic changes inferred from deep-sea d18O variations; 2. To place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; 3. To assess the relationships between depositional facies and sequence architecture; and 4. To provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive continental margins. An additional goal for Leg 174A is technical. The leg represents the first attempt by scientific ocean drilling in almost 30 years to sample a thickly sedimented continental margin in water depths less than 150 m. Two sites (Sites 1071 and 1072) are located on the outer part of the continental shelf in water depths of 88-90 and 98-100 m, respectively. An additional site (Site 1073) is located on the uppermost continental slope, part of the Hudson Apron, in a water depth of 639 m
