FY93-FY94 ATLANTIC PROGRAM Prepared from Original Proposals and Working Group Reports

Leg 149 is scheduled to core a transect of holes across the ocean-continent transition (OCT) off western Iberia to determine the changes in the physical and petrological nature of the acoustic basement. Four sites that span the OCT have been chosen on basement highs to enable penetration of basement at each site to several hundred meters. It is anticipated that, at most, three of these sites will be drilled during Leg 149. The west Iberia margin is an excellent example of a nonvolcanic rifted or passive continental margin. The OCT in the central Iberia Abyssal Plain segment of the margin has been located by seismic reflection and refraction profiles and by magnetic and gravity modeling. These independent measurements all support a single conceptual model of the crust and upper mantle within the OCT. Leg 149 will test part of this model. Secondary objectives of Leg 149 include examining the depth of the ooze/chalk transition, the history of sediment deformation in the Cenozoic, the post-rift subsidence history of the margin, and the late Cenozoic turbidite succession with a view to testing whether the turbidites are triggered by changes in sea level and hence climatic changes. The objective at a fifth and alternate site, proposed site GAL-1, located west of Galicia Bank, is to determine whether acoustic basement over a reflector called S\ a possible lateral equivalent of the nearby S reflector, consists of continental crustal rocks. This site will be drilled only if the leg objectives can not be achieved at the other four proposed sites.