The local setting of Site 1276 on the Newfoundland rifted margin is shown in Figure F2. Note its location between basement highs to the northwest that are known to be rifted continental crust and crust to the southeast, which is located within the ocean–continent transition zone. The regional U reflection (Fig. F2) that was penetrated at Site 1276 was initially thought simply to record a break-up unconformity (Tucholke et al., l989). However, results at Site 1276 suggest that it may also be related to the regional intrusion of alkaline basalt sills following final continental break-up (Shillington et al., 2006). Seaward of Site 1276, exhumed mantle serpentinite and overlying basaltic flows were recovered within the ocean–continent transition zone at Site 1277 (Shipboard Scientific Party, 2004; Robertson, this volume).
At Site 1276, a single deep hole was drilled at the lower edge of the continental rise and was cored from 800 to 1739 meters below seafloor (mbsf) (Fig. F2). Cored sediments begin with deep-sea sediments of earliest Oligocene age and end with deep-sea sediments of earliest Albian age (Fig. F3). A latest Aptian age was suspected for the oldest sediments, but this has not been confirmed. An excellent, relatively complete sedimentary record (~85%) was obtained for the cored interval. The oldest sediments significantly postdate the crust, which is estimated at ~130 Ma (i.e., end-Hauterivian). Coring terminated within the lower of two sills of alkaline basalt, which intruded at ~105 and ~98 Ma (Hart and Blusztajn, 2006). Intrusion of these sills has influenced the diagenesis of the directly adjacent sediments recovered from Site 1276 (Shipboard Scientific Party, 2004; Pletsch and Cramer, 2006).
In general, sediment recovery documents the evolution of a rifted passive continental margin following regional continental break-up. Deposition first took place on a thermally immature, rapidly subsiding, topographically varied rifted margin on which very rapid sediment accumulation took place at rates up to 105 mm/yr. During this time only a narrow (~100 km) deep-ocean basin separated Site 1276 from the conjugate Iberia margin. This was followed by a more thermally mature phase during which subsidence slowed and sedimentation rates decreased greatly to <7.4 mm/yr. During this time Site 1276 bordered an increasingly wide oceanic basin.
A summary of sediments recovered and their ages is given in Figure F3. The grain-size plot in this figure emphasizes the occurrence of relatively coarse grained sediments that were mainly deposited by turbidity currents (Shipboard Scientific Party, 2004). However, the present paper focuses on the chemical composition and interpretation of the fine-grained sediments, which volumetrically predominate.