The prime drilling objectives of Leg 210 were to sample basement and the facies corresponding to the overlying U reflection in the Newfoundland Basin, both of which were deep targets. Additional objectives included investigation of the Cretaceous paleoceanography of the Newfoundland-Iberia rift and the record of how abyssal circulation developed in Paleogene time through this gateway to the sub-Arctic and Arctic seas.
At Site 1276, basement was estimated to be at 2080 meters below seafloor (mbsf) and the depth of U was estimated to be 1866 mbsf. Drilling and coring to these depths presented considerable engineering and operational challenges, both expected and unexpected. We were able to follow our operational plan to case the hole at Site 1276 with both 20- and 16-in casing as planned (Fig. F15 in the "Leg 210 Summary" chapter), but very tight hole conditions prevented us from installing liners to greater depths. Ultimately, these hole conditions also prevented us from logging the hole.
Despite these difficulties, drilling at Site 1276 was an outstanding success. We cored from 800 to 1736.9 mbsf with a remarkable average core recovery of 85%, and we obtained a detailed record of sedimentation from the time that the Newfoundland-Iberia rift was a very narrow ocean basin (latest Aptian[?]-earliest Albian) up to the early Oligocene. This record captures an extensive series of major oceanographic events that affected the expanding North Atlantic Ocean during this time period, and it allowed us to accomplish virtually all of our major paleoceanographic objectives.
Site 1276 bottomed in diabase sills that appear to have been intruded into uppermost Aptian(?)-lower Albian sediments at very shallow subseafloor depths. These sills are estimated to lie only 100-200 m above basement, and it appears completely feasible that future drilling at this site can core to, and into, basement. Two sills were drilled, one at 1613-1623 mbsf and a second from 1719 mbsf to the bottom of the hole at 1737 mbsf (the sill base was not reached or recovered). These sills are diabases that are probably alkaline; they exhibit chilled margins and developed striking hydrothermal metamorphic effects in the enclosing sediments. The upper sill may have formed a seal, preventing the underlying sediments from becoming normally compacted and isolating fluids (including methane) in the section. Preliminary shipboard synthetic-seismogram modeling and velocity-depth analyses indicate that the top of the upper sill is at or near the basinwide U reflection. The sill lies in a unit of extensive uppermost Aptian(?)-lower Albian sedimentary gravity flows (lithologic Subunit 5C), and we interpret the U reflection to be created by a combination of the gravity flows and sills. Seismic signal reflection from the strong impedance contrasts, created by these interbedded igneous and sedimentary rocks, appears to explain the poor seismic signal penetration through U and thus the typically poor seismic definition of underlying basement.
The source of magmatism that created the sills is presently unknown, and such magmatism is certainly unexpected considering the nonvolcanic nature of the conjugate transition zone crust off Iberia. A source (mantle plume?) associated with development of the Newfoundland seamounts ~180 km to the south seems to be unlikely considering the basinwide distribution of the U reflection. However, some kind of regional postrift magmatic effect could help to explain the marked asymmetry of basement depth and roughness between the Newfoundland and Iberia conjugate margins (Fig. F4 in the "Leg 210 Summary" chapter). Shore-based analyses of the Newfoundland Basin reflection data, together with synthetic-seismogram modeling based on the Site 1276 physical property data, age dating, and geochemical analyses, are expected to provide significant insights into this issue.
At Site 1276, we cored a greatly expanded Cretaceous sedimentary sequence, including black shales equivalent to the Hatteras Formation in the western North Atlantic. The black shale sequence extends from the lowermost Albian, or possibly the uppermost Aptian, upward through the Cenomanian/Turonian boundary. It reflects deposition under relatively low oxygen conditions in the deep basin, probably punctuated by intervals of total anoxia. Discrete black organic carbon-rich layers contain either terrestrial or marine carbon, or both, indicating that input from both sources intermittently created reducing conditions at and below the seafloor. The geochemical and sedimentological data indicate a terrigenous input throughout the entire succession.
At Site 1276 we recovered sediments that may include five Oceanic Anoxic Events (OAEs). These are the latest Cenomanian-earliest Turonian(?) OAE 2 ("Bonarelli" event); the mid-Cenomanian event (MCE); and OAE 1b ("Paquier" event), OAE 1c, and OAE 1d in the Albian. In addition, one other, possibly new, Albian event is recognized from its characteristic black color coupled with high total organic carbon (TOC) and related geochemical indicators (see "Oceanic Anoxic Events" in "Geochemistry" and "Biostratigraphy"). Analysis of these sediments will provide a rich data set to examine the paleoceanography of the Cretaceous North Atlantic Ocean as it expanded northward through the Newfoundland-Iberia rift.
Interestingly, similar dark sediments with locally black layers were recovered in parts of the uppermost Cretaceous and Paleocene section. This kind of occurrence has also been observed on the southern Bermuda Rise at Site 387 (Tucholke and Vogt, 1979), suggesting that low-oxygen conditions intermittently affected the North Atlantic at times well after the main episodes of anoxia that are documented in OAEs.
Most upper Turonian and younger sediments are facies characterized by reddish color and brown, green-gray, and other light colors that indicate a well-oxygenated basin, which is in marked contrast to the underlying section with its black shales. This change is well documented farther south in the North Atlantic Basin, where the multicolored sediments form the Plantagenet Formation (Jansa et al., 1979). The paleoceanographic change is thought to be associated with development of longitudinal deep circulation between the North and South Atlantic oceans when these two oceans first became fully connected at abyssal depths near the end of Cenomanian time (Tucholke and Vogt, 1979). Documentation of this oceanographic change off Newfoundland indicates that the widening rift was probably connected to the main North Atlantic Ocean over full ocean depth.
We recovered one of the few nearly complete upper Maastrichtian to lower Danian abyssal sedimentary sections across the Cretaceous/Tertiary (K/T) boundary at Site 1276. Extensive reworking and commonly carbonate free sediments prevent this section from being suitable for analyzing processes of biotic extinction, but the succession of biotic changes is obvious. High sedimentation rates in the lower Paleocene section will facilitate high-resolution study of biotic recovery following the Chicxulub (Yucatan) impact event at the K/T boundary.
The Paleocene/Eocene boundary interval is characterized worldwide by an abrupt warming event referred to as the Paleocene/Eocene Thermal Maximum (PETM), which is recorded by clay-rich precursor beds and followed by a sharp negative 
13C excursion and a benthic foraminiferal extinction event. We cored this sequence at Site 1276. Although the specific boundary clay layer appears to be missing in our cores, a complete succession of the calcareous nannofossil events occurring immediately above the boundary clay layer was recognized and will provide important information on biotic recovery after this event.
Sedimentation patterns in the North and South Atlantic oceans have been profoundly affected by bottom currents since the initiation of strong abyssal circulation in Paleogene time. Determining when this initiation occurred, however, has been problematic because the currents created major unconformities (e.g., Horizon Au in the central North Atlantic Basin) and thus left little lithologic or biostratigraphic record to establish the timing of the event. Current interpretations are that the abyssal circulation developed near the Eocene/Oligocene boundary (Miller and Tucholke, 1983; Davies et al., 2001).
At Site 1276 we cored through a seismic marker that appears to coincide with this Paleogene circulation event. It matches an unconformity between lithologic Units 1 and 2 and a middle Eocene hiatus identified from preliminary biostratigraphy. The hiatus seems to represent a limited length of geologic time compared to other places where the unconformity has been cored, probably because gravity flows were flooding the Newfoundland deepwater margin with abundant sediment at the time. If our preliminary shipboard conclusions about the age of the hiatus are correct, then the age of this major paleoceanographic event may be 4-7 m.y. older than previously supposed. Shore-based analyses are planned to investigate this phenomenon in detail.
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Ms 210IR-103
